FRINK Linked Data Fragments server

Matches in SemOpenAlex for { <https://semopenalex.org/work/W2022232747> ?p ?o ?g. }

• W2022232747 endingPage "16472" @default.
• W2022232747 startingPage "16466" @default.
• W2022232747 abstract "IB1/JIP-1 is a scaffold protein that interacts with upstream components of the c-Jun N-terminal kinase (JNK) signaling pathway. IB1 is expressed at high levels in pancreatic β cells and may therefore exert a tight control on signaling events mediated by JNK in these cells. Activation of JNK by interleukin 1 (IL-1β) or by the upstream JNK constitutive activator ΔMEKK1 promoted apoptosis in two pancreatic β cell lines and decreased IB1 content by 50–60%. To study the functional consequences of the reduced IB1 content in β cell lines, we used an insulin-secreting cell line expressing an inducible IB1 antisense RNA that lead to a 38% IB1 decrease. Reducing IB1 levels in these cells increased phosphorylation of c-Jun and increased the apoptotic rate in presence of IL-1β. Nitric oxide production was not stimulated by expression of the IB1 antisense RNA. Complementary experiments indicated that overexpression of IB1 in insulin-producing cells prevented JNK-mediated activation of the transcription factors c-Jun, ATF2, and Elk1 and decreased IL-1β- and ΔMEKK1-induced apoptosis. These data indicate that IB1 plays an anti-apoptotic function in insulin-producing cells probably by controlling the activity of the JNK signaling pathway. IB1/JIP-1 is a scaffold protein that interacts with upstream components of the c-Jun N-terminal kinase (JNK) signaling pathway. IB1 is expressed at high levels in pancreatic β cells and may therefore exert a tight control on signaling events mediated by JNK in these cells. Activation of JNK by interleukin 1 (IL-1β) or by the upstream JNK constitutive activator ΔMEKK1 promoted apoptosis in two pancreatic β cell lines and decreased IB1 content by 50–60%. To study the functional consequences of the reduced IB1 content in β cell lines, we used an insulin-secreting cell line expressing an inducible IB1 antisense RNA that lead to a 38% IB1 decrease. Reducing IB1 levels in these cells increased phosphorylation of c-Jun and increased the apoptotic rate in presence of IL-1β. Nitric oxide production was not stimulated by expression of the IB1 antisense RNA. Complementary experiments indicated that overexpression of IB1 in insulin-producing cells prevented JNK-mediated activation of the transcription factors c-Jun, ATF2, and Elk1 and decreased IL-1β- and ΔMEKK1-induced apoptosis. These data indicate that IB1 plays an anti-apoptotic function in insulin-producing cells probably by controlling the activity of the JNK signaling pathway. c-Jun N-terminal kinase interleukin inducible nitric-oxide synthase mitogen-activated protein MAP kinase/extracellular signal-regulated kinase kinase kinase 1 JNK binding domain green fluorescent protein glutathioneS-transferase tumor necrosis factor interferon IB1/JIP-1 are recently characterized mammalian scaffold proteins involved in the regulation of the JNK1 signaling pathway (1.Bonny C. Nicod P. Waeber G. J. Biol. Chem. 1998; 273: 1843-1846Abstract Full Text Full Text PDF PubMed Scopus (137) Google Scholar, 2.Dickens M. Rogers J.S. Cavanagh J. Raitano A. Xia Z. Halpern J.R. Greenberg M.E. Sawyers C.L. Davis R.J. Science. 1997; 277: 693-696Crossref PubMed Scopus (624) Google Scholar, 3.Whitmarsh A.J. Cavanagh J. Tournier C. Yasuda J. Davis R.J. Science. 1998; 281: 1671-1674Crossref PubMed Scopus (583) Google Scholar). These two isoforms bind to and associate in a single transduction complex three kinases, MLK3, MKK7, and JNK, which together constitute an ordered unit of sequential signaling molecules transducing a variety of stress signals (2.Dickens M. Rogers J.S. Cavanagh J. Raitano A. Xia Z. Halpern J.R. Greenberg M.E. Sawyers C.L. Davis R.J. Science. 1997; 277: 693-696Crossref PubMed Scopus (624) Google Scholar, 3.Whitmarsh A.J. Cavanagh J. Tournier C. Yasuda J. Davis R.J. Science. 1998; 281: 1671-1674Crossref PubMed Scopus (583) Google Scholar). To date, five different isoforms of the protein have been cloned, which are mainly N-terminal splice variants that arise from expression of one single gene on human chromosome 11p11.2-p12 (1.Bonny C. Nicod P. Waeber G. J. Biol. Chem. 1998; 273: 1843-1846Abstract Full Text Full Text PDF PubMed Scopus (137) Google Scholar, 4.Mooser V. Maillard A. Bonny C. Steinmann M. Shaw P. Yarnall D.P. Burns D.K. Schorderet D.F. Nicod P. Waeber G. Genomics. 1999; 55: 202-208Crossref PubMed Scopus (28) Google Scholar, 5.Kim I.J. Lee K.W. Park B.Y. Lee J.K. Park J. Choi I.Y. Eom S.J. Chang T.S. Kim M.J. Yeom Y.I. Chang S.K. Lee Y.D. Choi E.J. Han P.L. J. Neurochem. 1999; 72: 1335-1343Crossref PubMed Scopus (48) Google Scholar). A S59N mutation close to the JNK binding domain of IB1 has recently been associated with a late onset type 2 diabetes (6.Waeber G. Delplanque J. Bonny C. Mooser V. Steinmann M. Widmann C. Maillard A. Miklossy J. Dina C. Hani E.H. Vionnet N. Nicod P. Boutin P. Froguel P. Nat. Genet. 2000; 24: 291-295Crossref PubMed Scopus (157) Google Scholar). Functionally, this mutation led to an increased susceptibility of JNK-mediated apoptosis in different cell systems, implying a presumably important functional role of IB1 in controlling the cell response to proapoptotic stimuli (6.Waeber G. Delplanque J. Bonny C. Mooser V. Steinmann M. Widmann C. Maillard A. Miklossy J. Dina C. Hani E.H. Vionnet N. Nicod P. Boutin P. Froguel P. Nat. Genet. 2000; 24: 291-295Crossref PubMed Scopus (157) Google Scholar).Interleukin 1 (IL-1β), which activates JNK essentially through the MKK7 pathway in several cells and tissues (7.Cuenda A. Dorow D.S. Biochem. J. 1998; 333: 11-15Crossref PubMed Scopus (56) Google Scholar, 8.Finch A. Holland P. Cooper J. Saklatvala J. Kracht M. FEBS Lett. 1997; 418: 144-148Crossref PubMed Scopus (38) Google Scholar, 9.Lawler S. Cuenda A. Goedert M. Cohen P. FEBS Lett. 1997; 414: 153-158Crossref PubMed Scopus (45) Google Scholar, 10.Whitmarsh A.J. Shore P. Sharrocks A.D. Davis R.J. Science. 1995; 269: 403-407Crossref PubMed Scopus (877) Google Scholar), is believed to play a key role in the process of selective β cell destruction observed in type 1 diabetes. Chronic exposure of pancreatic islets or of β-derived cell lines to IL-1β had been shown to lead to the selective death of the β cells, whereas non-β cells such as glucagon-producing cells appeared more resistant to the action of the cytokine (reviewed in Refs. 11.Mauricio D. Mandrup-Poulsen T. Diabetes. 1998; 47: 1537-1543Crossref PubMed Scopus (148) Google Scholar, 12.Mandrup-Poulsen T. Diabetologia. 1996; 39: 1005-1029Crossref PubMed Scopus (514) Google Scholar, 13.Nerup J. Mandrup-Poulsen T. Helqvist S. Andersen H.U. Pociot F. Reimers J.I. Cuartero B.G. Karlsen A.E. Bjerre U. Lorenzen T. Diabetologia. 1994; 37 Suppl. 2: 82-89Crossref Scopus (181) Google Scholar, 14.Mandrup-Poulsen T. Zumsteg U. Reimers J. Pociot F. Morch L. Helqvist S. Dinarello C.A. Nerup J. Cytokine. 1993; 5: 185-191Crossref PubMed Scopus (90) Google Scholar, 15.Rabinovitch A. Suarez-Pinzon W.L. Biochem. Pharmacol. 1998; 55: 1139-1149Crossref PubMed Scopus (421) Google Scholar). The molecular basis for the preferential killing of pancreatic β versus α cells by IL-1β is not fully understood. One important player in this phenomenon is the inducible nitric-oxide synthase gene iNOS, which is specifically expressed in the β cells upon IL-1β treatment (16.Heitmeier M.R. Scarim A.L. Corbett J.A. J. Biol. Chem. 1997; 272: 13697-13704Abstract Full Text Full Text PDF PubMed Scopus (142) Google Scholar, 17.Larsen C.M. Wadt K.A. Juhl L.F. Andersen H.U. Karlsen A.E. Su M.S. Seedorf K. Shapiro L. Dinarello C.A. Mandrup-Poulsen T. J. Biol. Chem. 1998; 273: 15294-15300Abstract Full Text Full Text PDF PubMed Scopus (160) Google Scholar, 18.Reimers J.I. Bjerre U. Mandrup-Poulsen T. Nerup J. Cytokine. 1994; 6: 512-520Crossref PubMed Scopus (62) Google Scholar, 19.Reimers J.I. Andersen H.U. Mauricio D. Pociot F. Karlsen A.E. Petersen J.S. Mandrup-Poulsen T. Nerup J. Diabetes. 1996; 45: 771-778Crossref PubMed Google Scholar, 20.Cetkovic-Cvrlje M. Eizirik D.L. Cytokine. 1994; 6: 399-406Crossref PubMed Scopus (171) Google Scholar). A number of reports have indeed clearly shown that β cell apoptosis is NO-dependent (see for example two recent reports (21.Thomas H.E. Darwiche R. Corbett J.A. Kay T.W. J. Immunol. 1999; 163: 1562-1569PubMed Google Scholar, 22.Grey S.T. Arvelo M.B. Hasenkamp W. Bach F.H. Ferran C. J. Exp. Med. 1999; 190: 1135-1146Crossref PubMed Scopus (179) Google Scholar)). In line with this, pancreatic islets from iNOS KO mice show a better resistance to IL-1β cytotoxicity (23.Flodstrom M. Tyrberg B. Eizirik D.L. Sandler S. Diabetes. 1999; 48: 706-713Crossref PubMed Scopus (144) Google Scholar).This NO-dependent killing of β cells has been, however, challenged by several reports pointing to the existence of NO-independent death signaling pathways (24.Delaney C.A. Pavlovic D. Hoorens A. Pipeleers D.G. Eizirik D.L. Endocrinology. 1997; 138: 2610-2614Crossref PubMed Scopus (275) Google Scholar, 25.Suarez-Pinzon W.L. Strynadka K. Rabinovitch A. Endocrinology. 1996; 137: 5290-5296Crossref PubMed Scopus (55) Google Scholar). For example, there is no direct correlation between expression of iNOS and sensitivity to IL-1β between β cells at different stages of differentiation (26.Nielsen K. Karlsen A.E. Deckert M. Madsen O.D. Serup P. Mandrup-Poulsen T. Nerup J. Diabetes. 1999; 48: 2324-2332Crossref PubMed Scopus (62) Google Scholar). Importantly, the iNOS inhibitor l-NMMA does not prevent IL-1β-induced β cell death in rat or human islets (24.Delaney C.A. Pavlovic D. Hoorens A. Pipeleers D.G. Eizirik D.L. Endocrinology. 1997; 138: 2610-2614Crossref PubMed Scopus (275) Google Scholar, 25.Suarez-Pinzon W.L. Strynadka K. Rabinovitch A. Endocrinology. 1996; 137: 5290-5296Crossref PubMed Scopus (55) Google Scholar). It is also possible to block NO synthesis by blocking the extracellular signal-regulated kinase and p38 MAP kinase pathways, however, without any positive effect on cell survival (17.Larsen C.M. Wadt K.A. Juhl L.F. Andersen H.U. Karlsen A.E. Su M.S. Seedorf K. Shapiro L. Dinarello C.A. Mandrup-Poulsen T. J. Biol. Chem. 1998; 273: 15294-15300Abstract Full Text Full Text PDF PubMed Scopus (160) Google Scholar).To better understand the molecular mechanisms that specifically sensitize β cells to IL-1β-induced death, we recently used two different subclones of the pluripotent pancreatic endocrine stem cell clone (MSL). The MSL AN697C1 subclone gave rise to two derived cell lines, namely the glucagon-secreting AN-glu, and after stable transfection with the transcription factor pancreatic duodenal homeobox factor-1, the insulin secreting AN-ins (27.Serup P. Jensen J. Andersen F.G. Jorgensen M.C. Blume N. Holst J.J. Madsen O.D. Proc. Natl. Acad. Sci. U. S. A. 1996; 93: 9015-9020Crossref PubMed Scopus (130) Google Scholar). Despite having similar rates of NO synthesis, we found that the AN-ins cells were more susceptible to apoptosis elicited by IL-1β. The AN-ins cells show a markedly increased activation of JNK in response to IL-1β, thus providing a molecular basis for the observed difference in their IL-1β sensitivity. In these cell systems, we demonstrated that the two MAP kinases p38 and the extracellular signal-regulated kinase were fully dispensable to promote the apoptotic response. In contrast, JNK activation is essential as blocking JNK with the use of the JNK binding domain (JBD) of JIP-1/IB1 (2.Dickens M. Rogers J.S. Cavanagh J. Raitano A. Xia Z. Halpern J.R. Greenberg M.E. Sawyers C.L. Davis R.J. Science. 1997; 277: 693-696Crossref PubMed Scopus (624) Google Scholar) prevented apoptosis by more than 90%. 2A. Ammendrup, A. Oberson, K. Nielsen, N. Andersen, P. Serup, O. Madsen, T. Mandrup-Poulsen, and C. Bonny, submitted for publication. 2A. Ammendrup, A. Oberson, K. Nielsen, N. Andersen, P. Serup, O. Madsen, T. Mandrup-Poulsen, and C. Bonny, submitted for publication. Not only did JBD prevent apoptosis, but also a significant fraction of cells exposed to the cytokine were able to retain their ability to divide in culture.2Taken together, these data indicate that activation of the JNK pathway certainly plays an important role in IL-1β-mediated apoptosis. Because IL-1β is known to activate JNK through MKK7 in different cell lines and tissues (7.Cuenda A. Dorow D.S. Biochem. J. 1998; 333: 11-15Crossref PubMed Scopus (56) Google Scholar, 8.Finch A. Holland P. Cooper J. Saklatvala J. Kracht M. FEBS Lett. 1997; 418: 144-148Crossref PubMed Scopus (38) Google Scholar, 9.Lawler S. Cuenda A. Goedert M. Cohen P. FEBS Lett. 1997; 414: 153-158Crossref PubMed Scopus (45) Google Scholar, 10.Whitmarsh A.J. Shore P. Sharrocks A.D. Davis R.J. Science. 1995; 269: 403-407Crossref PubMed Scopus (877) Google Scholar) and because both kinases interact with the scaffold protein IB1, these data suggest that the control of the MKK7-JNK signaling pathway by IB1 may interfere with the response of cells activated by IL-1β. In this report, we specifically examined the role of IB1 in IL-1β-induced apoptosis in pancreatic β cell lines.DISCUSSIONWe showed herein that stress events decrease IB1 levels in insulin-producing cells. Our results using a cell line expressing IB1 antisense RNA indicate that this single event sensitizes cells to IL-1β-induced apoptosis without an increase in NO synthesis. Because IL-1β is recognized as one of the key mediators of pancreatic β cell apoptosis in type 1 diabetes, we propose that the high amount of IB1 normally present in insulin-producing cells is a critical parameter that preserves cells from cytokine-induced destruction (Fig.8).The absence of increased NO production in response to IL-1β in the INS-1 AS7 relative to INS-1 CTR1 cells indicates that activation of other pathways is responsible for the higher apoptotic rate of this cell line. This does not preclude NO as a necessary mediator of apoptosis in this cell system. Indeed, INS-1 cells have been shown to be protected from the deleterious effects of IL-β by the iNOS inhibitor l-NMMA (39.Hohmeier H.E. Thigpen A. Tran V.V. Davis R. Newgard C.B. J. Clin. Invest. 1998; 101: 1811-1820Crossref PubMed Scopus (146) Google Scholar). Rather, these and previous data indicate that NO is not the only player mediating β cell apoptosis and that independent activation of JNK is also required.2In this sense, endogenous regulators of JNK may play a specific role in the development of β cell apoptosis.Our results indicate that IB1 plays an important role in limiting the effects of JNK signaling on the fate of insulin-producing cells. Three lines of evidences support this conclusion. First, decreasing IB1 levels with an antisense RNA sensitizes the INS AS7 cells to IL-1β-induced apoptosis (Fig. 5). This effect is likely to result from an increased ability of JNK to phosphorylate its substrates including c-Jun (Fig. 7). Second, overexpression of IB1 protects pancreatic β cell lines against the two proapoptotic stimuli IL-1β and ΔMEKK1 (Fig. 2). This effect correlates with the ability of IB1 to block JNK-mediated activation of c-Jun and ATF2 (Fig. 4,A and B). Third, we found a correlation in INS-1 cells between the decrease in IB1 levels and the proapoptotic potential of the three cytokines IL-1β, TNF-α, and IFN-γ alone or in combination (Fig. 1 B).IB1/JIP-1 binds three kinases, MLK3, MKK7, and JNK, which together constitute an ordered three-partite signaling module leading to activation of JNK. We described IB1 as being localized in both the nucleus and cytoplasm of pancreatic β cells (1.Bonny C. Nicod P. Waeber G. J. Biol. Chem. 1998; 273: 1843-1846Abstract Full Text Full Text PDF PubMed Scopus (137) Google Scholar). Because IB1 is expressed at very high levels in pancreatic β cells compared with most other cell types, the high amount of IB1 in pancreatic β cells may exert a very stringent control on JNK signaling. High levels of IB1 may be expected to have negative effects on the ability of the JNK cascade to transmit signaling (2.Dickens M. Rogers J.S. Cavanagh J. Raitano A. Xia Z. Halpern J.R. Greenberg M.E. Sawyers C.L. Davis R.J. Science. 1997; 277: 693-696Crossref PubMed Scopus (624) Google Scholar, 3.Whitmarsh A.J. Cavanagh J. Tournier C. Yasuda J. Davis R.J. Science. 1998; 281: 1671-1674Crossref PubMed Scopus (583) Google Scholar, 5.Kim I.J. Lee K.W. Park B.Y. Lee J.K. Park J. Choi I.Y. Eom S.J. Chang T.S. Kim M.J. Yeom Y.I. Chang S.K. Lee Y.D. Choi E.J. Han P.L. J. Neurochem. 1999; 72: 1335-1343Crossref PubMed Scopus (48) Google Scholar), and in β cells, this may be accounted for by two distinct mechanisms. First, high amounts of IB1 may have a “dispersive” effect by favoring the formation of incomplete, nonproductive signaling complexes (i.e. complexes lacking either one of the three kinases that normally transmit signaling) (2.Dickens M. Rogers J.S. Cavanagh J. Raitano A. Xia Z. Halpern J.R. Greenberg M.E. Sawyers C.L. Davis R.J. Science. 1997; 277: 693-696Crossref PubMed Scopus (624) Google Scholar, 3.Whitmarsh A.J. Cavanagh J. Tournier C. Yasuda J. Davis R.J. Science. 1998; 281: 1671-1674Crossref PubMed Scopus (583) Google Scholar). This situation occurs in experimental conditions like the transfection studies used in this study and as a result leads to uncoupling of JNK from its upstream activators MKK7 and MLK3. This leads to inefficient JNK activation that translates into low c-Jun, ATF2, or Elk1 phosphorylation (5.Kim I.J. Lee K.W. Park B.Y. Lee J.K. Park J. Choi I.Y. Eom S.J. Chang T.S. Kim M.J. Yeom Y.I. Chang S.K. Lee Y.D. Choi E.J. Han P.L. J. Neurochem. 1999; 72: 1335-1343Crossref PubMed Scopus (48) Google Scholar). Second, IB1 may have a “competitive” effect in the nucleus acting against the binding of c-Jun and ATF2 to JNK. This hypothesis is supported by the observation that IB1/JIP-1 binds ∼100-fold more tightly to the same domain of JNK than does c-Jun or ATF2 (2.Dickens M. Rogers J.S. Cavanagh J. Raitano A. Xia Z. Halpern J.R. Greenberg M.E. Sawyers C.L. Davis R.J. Science. 1997; 277: 693-696Crossref PubMed Scopus (624) Google Scholar). In conditions where most of the JNKs available in a cell would be bound to IB1, c-Jun and ATF2 would be efficiently prevented to interact with and to be activated by JNK. As a consequence, high amounts of IB1 may “route” JNK signaling toward factors, such as Elk1 that do not use a “JNK binding domain” similar to that of c-Jun, ATF2, or IB1 to become substrate of JNK (40.Gupta S. Barrett T. Whitmarsh A.J. Cavanagh J. Sluss H.K. Derijard B. Davis R.J. EMBO J. 1996; 15: 2760-2770Crossref PubMed Scopus (1173) Google Scholar,41.Yang S.H. Whitmarsh A.J. Davis R.J. Sharrocks A.D. EMBO J. 1998; 17: 1740-1749Crossref PubMed Scopus (266) Google Scholar).Our data indicate that the near absence of c-Jun and ATF2 activation at late time points (3–6 h of IL-1β, Fig. 3 A) in whole cell lysates occurs despite a robust activation of JNK (Fig. 3 B). There is thus dissociation between JNK activation and c-Jun and ATF2 phosphorylation in these cells. Transient transfection experiments employing ΔMEKK1 indicate that only Elk1 is strongly activated by JNK, in contrast to c-Jun and ATF2 (Fig. 4 B). In control experiments performed with HeLa and Swiss 3T3 cells (which express only minute amounts of IB1), activation of the three factors reached similar high levels.3 Therefore in pancreatic β cells, JNK signaling appears to be “routed” preferentially toward Elk1 activation, and our data indicate that IB1 may play a role in this process (Figs. 4 B and 7). The selective activation of Elk1 in detriment to c-Jun and ATF2 is presumably not sufficient to induce apoptosis (42.Xia Z. Dickens M. Raingeaud J. Davis R.J. Greenberg M.E. Science. 1995; 270: 1326-1331Crossref PubMed Scopus (5027) Google Scholar). If the model holds true, the observed IB1 decrease following JNK stimulation is therefore likely to represent an important control step to allow for the apoptotic response to develop (Fig. 8). The mechanisms by which the stability of IB1 is regulated by JNK is not known yet, but we may speculate that it involves a phosphorylation-dependent ubiquitination process, as observed with other JNK targets (34.Fuchs S.Y. Xie B. Adler V. Fried V.A. Davis R.J. Ronai Z. J. Biol. Chem. 1997; 272: 32163-32168Abstract Full Text Full Text PDF PubMed Scopus (126) Google Scholar, 35.Fuchs S.Y. Dolan L. Davis R.J. Ronai Z. Oncogene. 1996; 13: 1531-1535PubMed Google Scholar).The critical role of IL-1β as mediator of pancreatic β cell death in type 1 diabetes is well recognized (12.Mandrup-Poulsen T. Diabetologia. 1996; 39: 1005-1029Crossref PubMed Scopus (514) Google Scholar, 14.Mandrup-Poulsen T. Zumsteg U. Reimers J. Pociot F. Morch L. Helqvist S. Dinarello C.A. Nerup J. Cytokine. 1993; 5: 185-191Crossref PubMed Scopus (90) Google Scholar). Our data have demonstrated the essential role that activation of the JNK pathway plays in IL-1β-induced β cell apoptosis.2 The intracellular events that transmit IL-1β signaling involve the sequential activation of the two kinases MKK7 and JNK (7.Cuenda A. Dorow D.S. Biochem. J. 1998; 333: 11-15Crossref PubMed Scopus (56) Google Scholar, 8.Finch A. Holland P. Cooper J. Saklatvala J. Kracht M. FEBS Lett. 1997; 418: 144-148Crossref PubMed Scopus (38) Google Scholar, 9.Lawler S. Cuenda A. Goedert M. Cohen P. FEBS Lett. 1997; 414: 153-158Crossref PubMed Scopus (45) Google Scholar). These kinases are held together in a multiple protein complex by the scaffold protein IB1. Here, we have established that high expression of this scaffold protein in pancreatic β cells limits the output of JNK signaling toward apoptosis induced by IL-1β. As this protective effect may be attenuated following the observed decrease of IB1 in IL-1β-treated cells, our results may lead to therapeutic strategies aimed at preserving IB1 function in pancreatic β cells. IB1/JIP-1 are recently characterized mammalian scaffold proteins involved in the regulation of the JNK1 signaling pathway (1.Bonny C. Nicod P. Waeber G. J. Biol. Chem. 1998; 273: 1843-1846Abstract Full Text Full Text PDF PubMed Scopus (137) Google Scholar, 2.Dickens M. Rogers J.S. Cavanagh J. Raitano A. Xia Z. Halpern J.R. Greenberg M.E. Sawyers C.L. Davis R.J. Science. 1997; 277: 693-696Crossref PubMed Scopus (624) Google Scholar, 3.Whitmarsh A.J. Cavanagh J. Tournier C. Yasuda J. Davis R.J. Science. 1998; 281: 1671-1674Crossref PubMed Scopus (583) Google Scholar). These two isoforms bind to and associate in a single transduction complex three kinases, MLK3, MKK7, and JNK, which together constitute an ordered unit of sequential signaling molecules transducing a variety of stress signals (2.Dickens M. Rogers J.S. Cavanagh J. Raitano A. Xia Z. Halpern J.R. Greenberg M.E. Sawyers C.L. Davis R.J. Science. 1997; 277: 693-696Crossref PubMed Scopus (624) Google Scholar, 3.Whitmarsh A.J. Cavanagh J. Tournier C. Yasuda J. Davis R.J. Science. 1998; 281: 1671-1674Crossref PubMed Scopus (583) Google Scholar). To date, five different isoforms of the protein have been cloned, which are mainly N-terminal splice variants that arise from expression of one single gene on human chromosome 11p11.2-p12 (1.Bonny C. Nicod P. Waeber G. J. Biol. Chem. 1998; 273: 1843-1846Abstract Full Text Full Text PDF PubMed Scopus (137) Google Scholar, 4.Mooser V. Maillard A. Bonny C. Steinmann M. Shaw P. Yarnall D.P. Burns D.K. Schorderet D.F. Nicod P. Waeber G. Genomics. 1999; 55: 202-208Crossref PubMed Scopus (28) Google Scholar, 5.Kim I.J. Lee K.W. Park B.Y. Lee J.K. Park J. Choi I.Y. Eom S.J. Chang T.S. Kim M.J. Yeom Y.I. Chang S.K. Lee Y.D. Choi E.J. Han P.L. J. Neurochem. 1999; 72: 1335-1343Crossref PubMed Scopus (48) Google Scholar). A S59N mutation close to the JNK binding domain of IB1 has recently been associated with a late onset type 2 diabetes (6.Waeber G. Delplanque J. Bonny C. Mooser V. Steinmann M. Widmann C. Maillard A. Miklossy J. Dina C. Hani E.H. Vionnet N. Nicod P. Boutin P. Froguel P. Nat. Genet. 2000; 24: 291-295Crossref PubMed Scopus (157) Google Scholar). Functionally, this mutation led to an increased susceptibility of JNK-mediated apoptosis in different cell systems, implying a presumably important functional role of IB1 in controlling the cell response to proapoptotic stimuli (6.Waeber G. Delplanque J. Bonny C. Mooser V. Steinmann M. Widmann C. Maillard A. Miklossy J. Dina C. Hani E.H. Vionnet N. Nicod P. Boutin P. Froguel P. Nat. Genet. 2000; 24: 291-295Crossref PubMed Scopus (157) Google Scholar). Interleukin 1 (IL-1β), which activates JNK essentially through the MKK7 pathway in several cells and tissues (7.Cuenda A. Dorow D.S. Biochem. J. 1998; 333: 11-15Crossref PubMed Scopus (56) Google Scholar, 8.Finch A. Holland P. Cooper J. Saklatvala J. Kracht M. FEBS Lett. 1997; 418: 144-148Crossref PubMed Scopus (38) Google Scholar, 9.Lawler S. Cuenda A. Goedert M. Cohen P. FEBS Lett. 1997; 414: 153-158Crossref PubMed Scopus (45) Google Scholar, 10.Whitmarsh A.J. Shore P. Sharrocks A.D. Davis R.J. Science. 1995; 269: 403-407Crossref PubMed Scopus (877) Google Scholar), is believed to play a key role in the process of selective β cell destruction observed in type 1 diabetes. Chronic exposure of pancreatic islets or of β-derived cell lines to IL-1β had been shown to lead to the selective death of the β cells, whereas non-β cells such as glucagon-producing cells appeared more resistant to the action of the cytokine (reviewed in Refs. 11.Mauricio D. Mandrup-Poulsen T. Diabetes. 1998; 47: 1537-1543Crossref PubMed Scopus (148) Google Scholar, 12.Mandrup-Poulsen T. Diabetologia. 1996; 39: 1005-1029Crossref PubMed Scopus (514) Google Scholar, 13.Nerup J. Mandrup-Poulsen T. Helqvist S. Andersen H.U. Pociot F. Reimers J.I. Cuartero B.G. Karlsen A.E. Bjerre U. Lorenzen T. Diabetologia. 1994; 37 Suppl. 2: 82-89Crossref Scopus (181) Google Scholar, 14.Mandrup-Poulsen T. Zumsteg U. Reimers J. Pociot F. Morch L. Helqvist S. Dinarello C.A. Nerup J. Cytokine. 1993; 5: 185-191Crossref PubMed Scopus (90) Google Scholar, 15.Rabinovitch A. Suarez-Pinzon W.L. Biochem. Pharmacol. 1998; 55: 1139-1149Crossref PubMed Scopus (421) Google Scholar). The molecular basis for the preferential killing of pancreatic β versus α cells by IL-1β is not fully understood. One important player in this phenomenon is the inducible nitric-oxide synthase gene iNOS, which is specifically expressed in the β cells upon IL-1β treatment (16.Heitmeier M.R. Scarim A.L. Corbett J.A. J. Biol. Chem. 1997; 272: 13697-13704Abstract Full Text Full Text PDF PubMed Scopus (142) Google Scholar, 17.Larsen C.M. Wadt K.A. Juhl L.F. Andersen H.U. Karlsen A.E. Su M.S. Seedorf K. Shapiro L. Dinarello C.A. Mandrup-Poulsen T. J. Biol. Chem. 1998; 273: 15294-15300Abstract Full Text Full Text PDF PubMed Scopus (160) Google Scholar, 18.Reimers J.I. Bjerre U. Mandrup-Poulsen T. Nerup J. Cytokine. 1994; 6: 512-520Crossref PubMed Scopus (62) Google Scholar, 19.Reimers J.I. Andersen H.U. Mauricio D. Pociot F. Karlsen A.E. Petersen J.S. Mandrup-Poulsen T. Nerup J. Diabetes. 1996; 45: 771-778Crossref PubMed Google Scholar, 20.Cetkovic-Cvrlje M. Eizirik D.L. Cytokine. 1994; 6: 399-406Crossref PubMed Scopus (171) Google Scholar). A number of reports have indeed clearly shown that β cell apoptosis is NO-dependent (see for example two recent reports (21.Thomas H.E. Darwiche R. Corbett J.A. Kay T.W. J. Immunol. 1999; 163: 1562-1569PubMed Google Scholar, 22.Grey S.T. Arvelo M.B. Hasenkamp W. Bach F.H. Ferran C. J. Exp. Med. 1999; 190: 1135-1146Crossref PubMed Scopus (179) Google Scholar)). In line with this, pancreatic islets from iNOS KO mice show a better resistance to IL-1β cytotoxicity (23.Flodstrom M. Tyrberg B. Eizirik D.L. Sandler S. Diabetes. 1999; 48: 706-713Crossref PubMed Scopus (144) Google Scholar). This NO-dependent killing of β cells has been, however, challenged by several reports pointing to the existence of NO-independent death signaling pathways (24.Delaney C.A. Pavlovic D. Hoorens A. Pipeleers D.G. Eizirik D.L. Endocrinology. 1997; 138: 2610-2614Crossref PubMed Scopus (275) Google Scholar, 25.Suarez-Pinzon W.L. Strynadka K. Rabinovitch A. Endocrinology. 1996; 137: 5290-5296Crossref PubMed Scopus (55) Google Scholar). For example, there is no direct correlation between expression of iNOS and sensitivity to IL-1β between β cells at different stages of differentiation (26.Nielsen K. Karlsen A.E. Deckert M. Madsen O.D. Serup P. Mandrup-Poulsen T. Nerup J. Diabetes. 1999; 48: 2324-2332Crossref PubMed Scopus (62) Google Scholar). Importantly, the iNOS inhibitor l-NMMA does not prevent IL-1β-induced β cell death in rat or human islets (24.Delaney C.A. Pavlovic D. Hoorens A. Pipeleers D.G. Eizirik D.L. Endocrinology. 1997; 138: 2610-2614Crossref PubMed Scopus (275) Google Scholar, 25.Suarez-Pinzon W.L. Strynadka K. Rabinovitch A. Endocrinology. 1996; 137: 5290-5296Crossref PubMed Scopus (55) Google Scholar). It is also possible to block NO synthesis by blocking the extracellular signal-regulated kinase and p38 MAP kinase pathways, however, without any positive effect on cell survival (17.Larsen C.M. Wadt K.A. Juhl L.F. Andersen H.U. Karlsen A.E. Su M.S. Seedorf K. Shapiro L. Dinarello C.A. Mandrup-Poulsen T. J. Biol. Chem. 1998; 273: 15294-15300Abstract Full Text Full Text PDF PubMed Scopus (160) Google Scholar). To better understand the molecular mechanisms that specifically sensitize β cells to IL-1β-induced death, we recently used two different subclones of the pluripotent pancreatic endocrine stem cell clone (MSL). The MSL AN697C1 subclone gave rise to two derived cell lines, namely the glucagon-secreting AN-glu, and after stable transfection with the transcription factor pancreatic duodenal homeobox factor-1, the insulin secreting AN-ins (27.Serup P. Jensen J. Andersen F.G. Jorgensen M.C. Blume N. Holst J.J. Madsen O.D. Proc. Natl. Acad. Sci. U. S. A. 1996; 93: 9015-9020Crossref PubMed Scopus (130) Google Scholar). Despite having similar rates of NO synthesis, we found that the AN-ins cells were more susceptible to apoptosis elicited by IL-1β. The AN-ins cells show a markedly increased activation of JNK in response to IL-1β, thus providing a molecular basis for the observed difference in their IL-1β sensitivity. In these cell systems, we demonstrated that the two MAP kinases p38 and the extracellular signal-regulated kinase were fully dispensable to promote the apoptotic response. In contrast, JNK activation is essential as blocking JNK with the use of the JNK binding domain (JBD) of JIP-1/IB1 (2.Dickens M. Rogers J.S. Cavanagh J. Raitano A. Xia Z. Halpern J.R. Greenberg M.E. Sawyers C.L. Davis R.J. Science. 1997; 277: 693-696Crossref PubMed Scopus (624) Google Scholar) prevented apoptosis by more than 90%. 2A. Ammendrup, A. Oberson, K. Nielsen, N. Andersen, P. Serup, O. Madsen, T. Mandrup-Poulsen, and C. Bonny, submitted for publication. 2A. Ammendrup, A. Oberson, K. Nielsen, N. Andersen, P. Serup, O. Madsen, T. Mandrup-Poulsen, and C. Bonny, submitted for publication. Not only did JBD prevent apoptosis, but also a significant fraction of cells exposed to the cytokine were able to retain their ability to divide in culture.2 Taken together, these data indicate that activation of the JNK pathway certainly plays an important role in IL-1β-mediated apoptosis. Because IL-1β is known to activate JNK through MKK7 in different cell lines and tissues (7.Cuenda A. Dorow D.S. Biochem. J. 1998; 333: 11-15Crossref PubMed Scopus (56) Google Scholar, 8.Finch A. Holland P. Cooper J. Saklatvala J. Kracht M. FEBS Lett. 1997; 418: 144-148Crossref PubMed Scopus (38) Google Scholar, 9.Lawler S. Cuenda A. Goedert M. Cohen P. FEBS Lett. 1997; 414: 153-158Crossref PubMed Scopus (45) Google Scholar, 10.Whitmarsh A.J. Shore P. Sharrocks A.D. Davis R.J. Science. 1995; 269: 403-407Crossref PubMed Scopus (877) Google Scholar) and because both kinases interact with the scaffold protein IB1, these data suggest that the control of the MKK7-JNK signaling pathway by IB1 may interfere with the response of cells activated by IL-1β. In this report, we specifically examined the role of IB1 in IL-1β-induced apoptosis in pancreatic β cell lines. DISCUSSIONWe showed herein that stress events decrease IB1 levels in insulin-producing cells. Our results using a cell line expressing IB1 antisense RNA indicate that this single event sensitizes cells to IL-1β-induced apoptosis without an increase in NO synthesis. Because IL-1β is recognized as one of the key mediators of pancreatic β cell apoptosis in type 1 diabetes, we propose that the high amount of IB1 normally present in insulin-producing cells is a critical parameter that preserves cells from cytokine-induced destruction (Fig.8).The absence of increased NO production in response to IL-1β in the INS-1 AS7 relative to INS-1 CTR1 cells indicates that activation of other pathways is responsible for the higher apoptotic rate of this cell line. This does not preclude NO as a necessary mediator of apoptosis in this cell system. Indeed, INS-1 cells have been shown to be protected from the deleterious effects of IL-β by the iNOS inhibitor l-NMMA (39.Hohmeier H.E. Thigpen A. Tran V.V. Davis R. Newgard C.B. J. Clin. Invest. 1998; 101: 1811-1820Crossref PubMed Scopus (146) Google Scholar). Rather, these and previous data indicate that NO is not the only player mediating β cell apoptosis and that independent activation of JNK is also required.2In this sense, endogenous regulators of JNK may play a specific role in the development of β cell apoptosis.Our results indicate that IB1 plays an important role in limiting the effects of JNK signaling on the fate of insulin-producing cells. Three lines of evidences support this conclusion. First, decreasing IB1 levels with an antisense RNA sensitizes the INS AS7 cells to IL-1β-induced apoptosis (Fig. 5). This effect is likely to result from an increased ability of JNK to phosphorylate its substrates including c-Jun (Fig. 7). Second, overexpression of IB1 protects pancreatic β cell lines against the two proapoptotic stimuli IL-1β and ΔMEKK1 (Fig. 2). This effect correlates with the ability of IB1 to block JNK-mediated activation of c-Jun and ATF2 (Fig. 4,A and B). Third, we found a correlation in INS-1 cells between the decrease in IB1 levels and the proapoptotic potential of the three cytokines IL-1β, TNF-α, and IFN-γ alone or in combination (Fig. 1 B).IB1/JIP-1 binds three kinases, MLK3, MKK7, and JNK, which together constitute an ordered three-partite signaling module leading to activation of JNK. We described IB1 as being localized in both the nucleus and cytoplasm of pancreatic β cells (1.Bonny C. Nicod P. Waeber G. J. Biol. Chem. 1998; 273: 1843-1846Abstract Full Text Full Text PDF PubMed Scopus (137) Google Scholar). Because IB1 is expressed at very high levels in pancreatic β cells compared with most other cell types, the high amount of IB1 in pancreatic β cells may exert a very stringent control on JNK signaling. High levels of IB1 may be expected to have negative effects on the ability of the JNK cascade to transmit signaling (2.Dickens M. Rogers J.S. Cavanagh J. Raitano A. Xia Z. Halpern J.R. Greenberg M.E. Sawyers C.L. Davis R.J. Science. 1997; 277: 693-696Crossref PubMed Scopus (624) Google Scholar, 3.Whitmarsh A.J. Cavanagh J. Tournier C. Yasuda J. Davis R.J. Science. 1998; 281: 1671-1674Crossref PubMed Scopus (583) Google Scholar, 5.Kim I.J. Lee K.W. Park B.Y. Lee J.K. Park J. Choi I.Y. Eom S.J. Chang T.S. Kim M.J. Yeom Y.I. Chang S.K. Lee Y.D. Choi E.J. Han P.L. J. Neurochem. 1999; 72: 1335-1343Crossref PubMed Scopus (48) Google Scholar), and in β cells, this may be accounted for by two distinct mechanisms. First, high amounts of IB1 may have a “dispersive” effect by favoring the formation of incomplete, nonproductive signaling complexes (i.e. complexes lacking either one of the three kinases that normally transmit signaling) (2.Dickens M. Rogers J.S. Cavanagh J. Raitano A. Xia Z. Halpern J.R. Greenberg M.E. Sawyers C.L. Davis R.J. Science. 1997; 277: 693-696Crossref PubMed Scopus (624) Google Scholar, 3.Whitmarsh A.J. Cavanagh J. Tournier C. Yasuda J. Davis R.J. Science. 1998; 281: 1671-1674Crossref PubMed Scopus (583) Google Scholar). This situation occurs in experimental conditions like the transfection studies used in this study and as a result leads to uncoupling of JNK from its upstream activators MKK7 and MLK3. This leads to inefficient JNK activation that translates into low c-Jun, ATF2, or Elk1 phosphorylation (5.Kim I.J. Lee K.W. Park B.Y. Lee J.K. Park J. Choi I.Y. Eom S.J. Chang T.S. Kim M.J. Yeom Y.I. Chang S.K. Lee Y.D. Choi E.J. Han P.L. J. Neurochem. 1999; 72: 1335-1343Crossref PubMed Scopus (48) Google Scholar). Second, IB1 may have a “competitive” effect in the nucleus acting against the binding of c-Jun and ATF2 to JNK. This hypothesis is supported by the observation that IB1/JIP-1 binds ∼100-fold more tightly to the same domain of JNK than does c-Jun or ATF2 (2.Dickens M. Rogers J.S. Cavanagh J. Raitano A. Xia Z. Halpern J.R. Greenberg M.E. Sawyers C.L. Davis R.J. Science. 1997; 277: 693-696Crossref PubMed Scopus (624) Google Scholar). In conditions where most of the JNKs available in a cell would be bound to IB1, c-Jun and ATF2 would be efficiently prevented to interact with and to be activated by JNK. As a consequence, high amounts of IB1 may “route” JNK signaling toward factors, such as Elk1 that do not use a “JNK binding domain” similar to that of c-Jun, ATF2, or IB1 to become substrate of JNK (40.Gupta S. Barrett T. Whitmarsh A.J. Cavanagh J. Sluss H.K. Derijard B. Davis R.J. EMBO J. 1996; 15: 2760-2770Crossref PubMed Scopus (1173) Google Scholar,41.Yang S.H. Whitmarsh A.J. Davis R.J. Sharrocks A.D. EMBO J. 1998; 17: 1740-1749Crossref PubMed Scopus (266) Google Scholar).Our data indicate that the near absence of c-Jun and ATF2 activation at late time points (3–6 h of IL-1β, Fig. 3 A) in whole cell lysates occurs despite a robust activation of JNK (Fig. 3 B). There is thus dissociation between JNK activation and c-Jun and ATF2 phosphorylation in these cells. Transient transfection experiments employing ΔMEKK1 indicate that only Elk1 is strongly activated by JNK, in contrast to c-Jun and ATF2 (Fig. 4 B). In control experiments performed with HeLa and Swiss 3T3 cells (which express only minute amounts of IB1), activation of the three factors reached similar high levels.3 Therefore in pancreatic β cells, JNK signaling appears to be “routed” preferentially toward Elk1 activation, and our data indicate that IB1 may play a role in this process (Figs. 4 B and 7). The selective activation of Elk1 in detriment to c-Jun and ATF2 is presumably not sufficient to induce apoptosis (42.Xia Z. Dickens M. Raingeaud J. Davis R.J. Greenberg M.E. Science. 1995; 270: 1326-1331Crossref PubMed Scopus (5027) Google Scholar). If the model holds true, the observed IB1 decrease following JNK stimulation is therefore likely to represent an important control step to allow for the apoptotic response to develop (Fig. 8). The mechanisms by which the stability of IB1 is regulated by JNK is not known yet, but we may speculate that it involves a phosphorylation-dependent ubiquitination process, as observed with other JNK targets (34.Fuchs S.Y. Xie B. Adler V. Fried V.A. Davis R.J. Ronai Z. J. Biol. Chem. 1997; 272: 32163-32168Abstract Full Text Full Text PDF PubMed Scopus (126) Google Scholar, 35.Fuchs S.Y. Dolan L. Davis R.J. Ronai Z. Oncogene. 1996; 13: 1531-1535PubMed Google Scholar).The critical role of IL-1β as mediator of pancreatic β cell death in type 1 diabetes is well recognized (12.Mandrup-Poulsen T. Diabetologia. 1996; 39: 1005-1029Crossref PubMed Scopus (514) Google Scholar, 14.Mandrup-Poulsen T. Zumsteg U. Reimers J. Pociot F. Morch L. Helqvist S. Dinarello C.A. Nerup J. Cytokine. 1993; 5: 185-191Crossref PubMed Scopus (90) Google Scholar). Our data have demonstrated the essential role that activation of the JNK pathway plays in IL-1β-induced β cell apoptosis.2 The intracellular events that transmit IL-1β signaling involve the sequential activation of the two kinases MKK7 and JNK (7.Cuenda A. Dorow D.S. Biochem. J. 1998; 333: 11-15Crossref PubMed Scopus (56) Google Scholar, 8.Finch A. Holland P. Cooper J. Saklatvala J. Kracht M. FEBS Lett. 1997; 418: 144-148Crossref PubMed Scopus (38) Google Scholar, 9.Lawler S. Cuenda A. Goedert M. Cohen P. FEBS Lett. 1997; 414: 153-158Crossref PubMed Scopus (45) Google Scholar). These kinases are held together in a multiple protein complex by the scaffold protein IB1. Here, we have established that high expression of this scaffold protein in pancreatic β cells limits the output of JNK signaling toward apoptosis induced by IL-1β. As this protective effect may be attenuated following the observed decrease of IB1 in IL-1β-treated cells, our results may lead to therapeutic strategies aimed at preserving IB1 function in pancreatic β cells. We showed herein that stress events decrease IB1 levels in insulin-producing cells. Our results using a cell line expressing IB1 antisense RNA indicate that this single event sensitizes cells to IL-1β-induced apoptosis without an increase in NO synthesis. Because IL-1β is recognized as one of the key mediators of pancreatic β cell apoptosis in type 1 diabetes, we propose that the high amount of IB1 normally present in insulin-producing cells is a critical parameter that preserves cells from cytokine-induced destruction (Fig.8). The absence of increased NO production in response to IL-1β in the INS-1 AS7 relative to INS-1 CTR1 cells indicates that activation of other pathways is responsible for the higher apoptotic rate of this cell line. This does not preclude NO as a necessary mediator of apoptosis in this cell system. Indeed, INS-1 cells have been shown to be protected from the deleterious effects of IL-β by the iNOS inhibitor l-NMMA (39.Hohmeier H.E. Thigpen A. Tran V.V. Davis R. Newgard C.B. J. Clin. Invest. 1998; 101: 1811-1820Crossref PubMed Scopus (146) Google Scholar). Rather, these and previous data indicate that NO is not the only player mediating β cell apoptosis and that independent activation of JNK is also required.2In this sense, endogenous regulators of JNK may play a specific role in the development of β cell apoptosis. Our results indicate that IB1 plays an important role in limiting the effects of JNK signaling on the fate of insulin-producing cells. Three lines of evidences support this conclusion. First, decreasing IB1 levels with an antisense RNA sensitizes the INS AS7 cells to IL-1β-induced apoptosis (Fig. 5). This effect is likely to result from an increased ability of JNK to phosphorylate its substrates including c-Jun (Fig. 7). Second, overexpression of IB1 protects pancreatic β cell lines against the two proapoptotic stimuli IL-1β and ΔMEKK1 (Fig. 2). This effect correlates with the ability of IB1 to block JNK-mediated activation of c-Jun and ATF2 (Fig. 4,A and B). Third, we found a correlation in INS-1 cells between the decrease in IB1 levels and the proapoptotic potential of the three cytokines IL-1β, TNF-α, and IFN-γ alone or in combination (Fig. 1 B). IB1/JIP-1 binds three kinases, MLK3, MKK7, and JNK, which together constitute an ordered three-partite signaling module leading to activation of JNK. We described IB1 as being localized in both the nucleus and cytoplasm of pancreatic β cells (1.Bonny C. Nicod P. Waeber G. J. Biol. Chem. 1998; 273: 1843-1846Abstract Full Text Full Text PDF PubMed Scopus (137) Google Scholar). Because IB1 is expressed at very high levels in pancreatic β cells compared with most other cell types, the high amount of IB1 in pancreatic β cells may exert a very stringent control on JNK signaling. High levels of IB1 may be expected to have negative effects on the ability of the JNK cascade to transmit signaling (2.Dickens M. Rogers J.S. Cavanagh J. Raitano A. Xia Z. Halpern J.R. Greenberg M.E. Sawyers C.L. Davis R.J. Science. 1997; 277: 693-696Crossref PubMed Scopus (624) Google Scholar, 3.Whitmarsh A.J. Cavanagh J. Tournier C. Yasuda J. Davis R.J. Science. 1998; 281: 1671-1674Crossref PubMed Scopus (583) Google Scholar, 5.Kim I.J. Lee K.W. Park B.Y. Lee J.K. Park J. Choi I.Y. Eom S.J. Chang T.S. Kim M.J. Yeom Y.I. Chang S.K. Lee Y.D. Choi E.J. Han P.L. J. Neurochem. 1999; 72: 1335-1343Crossref PubMed Scopus (48) Google Scholar), and in β cells, this may be accounted for by two distinct mechanisms. First, high amounts of IB1 may have a “dispersive” effect by favoring the formation of incomplete, nonproductive signaling complexes (i.e. complexes lacking either one of the three kinases that normally transmit signaling) (2.Dickens M. Rogers J.S. Cavanagh J. Raitano A. Xia Z. Halpern J.R. Greenberg M.E. Sawyers C.L. Davis R.J. Science. 1997; 277: 693-696Crossref PubMed Scopus (624) Google Scholar, 3.Whitmarsh A.J. Cavanagh J. Tournier C. Yasuda J. Davis R.J. Science. 1998; 281: 1671-1674Crossref PubMed Scopus (583) Google Scholar). This situation occurs in experimental conditions like the transfection studies used in this study and as a result leads to uncoupling of JNK from its upstream activators MKK7 and MLK3. This leads to inefficient JNK activation that translates into low c-Jun, ATF2, or Elk1 phosphorylation (5.Kim I.J. Lee K.W. Park B.Y. Lee J.K. Park J. Choi I.Y. Eom S.J. Chang T.S. Kim M.J. Yeom Y.I. Chang S.K. Lee Y.D. Choi E.J. Han P.L. J. Neurochem. 1999; 72: 1335-1343Crossref PubMed Scopus (48) Google Scholar). Second, IB1 may have a “competitive” effect in the nucleus acting against the binding of c-Jun and ATF2 to JNK. This hypothesis is supported by the observation that IB1/JIP-1 binds ∼100-fold more tightly to the same domain of JNK than does c-Jun or ATF2 (2.Dickens M. Rogers J.S. Cavanagh J. Raitano A. Xia Z. Halpern J.R. Greenberg M.E. Sawyers C.L. Davis R.J. Science. 1997; 277: 693-696Crossref PubMed Scopus (624) Google Scholar). In conditions where most of the JNKs available in a cell would be bound to IB1, c-Jun and ATF2 would be efficiently prevented to interact with and to be activated by JNK. As a consequence, high amounts of IB1 may “route” JNK signaling toward factors, such as Elk1 that do not use a “JNK binding domain” similar to that of c-Jun, ATF2, or IB1 to become substrate of JNK (40.Gupta S. Barrett T. Whitmarsh A.J. Cavanagh J. Sluss H.K. Derijard B. Davis R.J. EMBO J. 1996; 15: 2760-2770Crossref PubMed Scopus (1173) Google Scholar,41.Yang S.H. Whitmarsh A.J. Davis R.J. Sharrocks A.D. EMBO J. 1998; 17: 1740-1749Crossref PubMed Scopus (266) Google Scholar). Our data indicate that the near absence of c-Jun and ATF2 activation at late time points (3–6 h of IL-1β, Fig. 3 A) in whole cell lysates occurs despite a robust activation of JNK (Fig. 3 B). There is thus dissociation between JNK activation and c-Jun and ATF2 phosphorylation in these cells. Transient transfection experiments employing ΔMEKK1 indicate that only Elk1 is strongly activated by JNK, in contrast to c-Jun and ATF2 (Fig. 4 B). In control experiments performed with HeLa and Swiss 3T3 cells (which express only minute amounts of IB1), activation of the three factors reached similar high levels.3 Therefore in pancreatic β cells, JNK signaling appears to be “routed” preferentially toward Elk1 activation, and our data indicate that IB1 may play a role in this process (Figs. 4 B and 7). The selective activation of Elk1 in detriment to c-Jun and ATF2 is presumably not sufficient to induce apoptosis (42.Xia Z. Dickens M. Raingeaud J. Davis R.J. Greenberg M.E. Science. 1995; 270: 1326-1331Crossref PubMed Scopus (5027) Google Scholar). If the model holds true, the observed IB1 decrease following JNK stimulation is therefore likely to represent an important control step to allow for the apoptotic response to develop (Fig. 8). The mechanisms by which the stability of IB1 is regulated by JNK is not known yet, but we may speculate that it involves a phosphorylation-dependent ubiquitination process, as observed with other JNK targets (34.Fuchs S.Y. Xie B. Adler V. Fried V.A. Davis R.J. Ronai Z. J. Biol. Chem. 1997; 272: 32163-32168Abstract Full Text Full Text PDF PubMed Scopus (126) Google Scholar, 35.Fuchs S.Y. Dolan L. Davis R.J. Ronai Z. Oncogene. 1996; 13: 1531-1535PubMed Google Scholar). The critical role of IL-1β as mediator of pancreatic β cell death in type 1 diabetes is well recognized (12.Mandrup-Poulsen T. Diabetologia. 1996; 39: 1005-1029Crossref PubMed Scopus (514) Google Scholar, 14.Mandrup-Poulsen T. Zumsteg U. Reimers J. Pociot F. Morch L. Helqvist S. Dinarello C.A. Nerup J. Cytokine. 1993; 5: 185-191Crossref PubMed Scopus (90) Google Scholar). Our data have demonstrated the essential role that activation of the JNK pathway plays in IL-1β-induced β cell apoptosis.2 The intracellular events that transmit IL-1β signaling involve the sequential activation of the two kinases MKK7 and JNK (7.Cuenda A. Dorow D.S. Biochem. J. 1998; 333: 11-15Crossref PubMed Scopus (56) Google Scholar, 8.Finch A. Holland P. Cooper J. Saklatvala J. Kracht M. FEBS Lett. 1997; 418: 144-148Crossref PubMed Scopus (38) Google Scholar, 9.Lawler S. Cuenda A. Goedert M. Cohen P. FEBS Lett. 1997; 414: 153-158Crossref PubMed Scopus (45) Google Scholar). These kinases are held together in a multiple protein complex by the scaffold protein IB1. Here, we have established that high expression of this scaffold protein in pancreatic β cells limits the output of JNK signaling toward apoptosis induced by IL-1β. As this protective effect may be attenuated following the observed decrease of IB1 in IL-1β-treated cells, our results may lead to therapeutic strategies aimed at preserving IB1 function in pancreatic β cells. We are grateful to Christian Widmann for the generous gift of the ΔMEKK1 expressing plasmid and for helpful discussions." @default.
• W2022232747 created "2016-06-24" @default.
• W2022232747 creator A5002023781 @default.
• W2022232747 creator A5003912657 @default.
• W2022232747 creator A5009716617 @default.
• W2022232747 creator A5047797878 @default.
• W2022232747 creator A5050307056 @default.
• W2022232747 creator A5084753559 @default.
• W2022232747 date "2000-06-01" @default.
• W2022232747 modified "2023-10-10" @default.
• W2022232747 title "IB1 Reduces Cytokine-induced Apoptosis of Insulin-secreting Cells" @default.
• W2022232747 cites W1570066979 @default.
• W2022232747 cites W1572174728 @default.
• W2022232747 cites W1964669410 @default.
• W2022232747 cites W1967218150 @default.
• W2022232747 cites W1970958250 @default.
• W2022232747 cites W1976385326 @default.
• W2022232747 cites W1980824229 @default.
• W2022232747 cites W1984903682 @default.
• W2022232747 cites W1993424948 @default.
• W2022232747 cites W1999734356 @default.
• W2022232747 cites W2002282120 @default.
• W2022232747 cites W2006217609 @default.
• W2022232747 cites W2013471091 @default.
• W2022232747 cites W2020890845 @default.
• W2022232747 cites W2022762164 @default.
• W2022232747 cites W2024901243 @default.
• W2022232747 cites W2026284192 @default.
• W2022232747 cites W2031475525 @default.
• W2022232747 cites W2032590374 @default.
• W2022232747 cites W2034712114 @default.
• W2022232747 cites W2037295277 @default.
• W2022232747 cites W2038030189 @default.
• W2022232747 cites W2038545492 @default.
• W2022232747 cites W2038862314 @default.
• W2022232747 cites W2047154536 @default.
• W2022232747 cites W2047604959 @default.
• W2022232747 cites W2054276465 @default.
• W2022232747 cites W2058857909 @default.
• W2022232747 cites W2060478296 @default.
• W2022232747 cites W2063720970 @default.
• W2022232747 cites W2089465684 @default.
• W2022232747 cites W2092762008 @default.
• W2022232747 cites W2098719212 @default.
• W2022232747 cites W2103487277 @default.
• W2022232747 cites W2118457425 @default.
• W2022232747 cites W2127857033 @default.
• W2022232747 cites W2158179799 @default.
• W2022232747 cites W2159947323 @default.
• W2022232747 cites W2161993072 @default.
• W2022232747 cites W7135663 @default.
• W2022232747 doi "https://doi.org/10.1074/jbc.m908297199" @default.
• W2022232747 hasPubMedId "https://pubmed.ncbi.nlm.nih.gov/10748095" @default.
• W2022232747 hasPublicationYear "2000" @default.
• W2022232747 type Work @default.
• W2022232747 sameAs 2022232747 @default.
• W2022232747 citedByCount "118" @default.
• W2022232747 countsByYear W20222327472012 @default.
• W2022232747 countsByYear W20222327472013 @default.
• W2022232747 countsByYear W20222327472014 @default.
• W2022232747 countsByYear W20222327472015 @default.
• W2022232747 countsByYear W20222327472016 @default.
• W2022232747 countsByYear W20222327472017 @default.
• W2022232747 countsByYear W20222327472019 @default.
• W2022232747 countsByYear W20222327472022 @default.
• W2022232747 countsByYear W20222327472023 @default.
• W2022232747 crossrefType "journal-article" @default.
• W2022232747 hasAuthorship W2022232747A5002023781 @default.
• W2022232747 hasAuthorship W2022232747A5003912657 @default.
• W2022232747 hasAuthorship W2022232747A5009716617 @default.
• W2022232747 hasAuthorship W2022232747A5047797878 @default.
• W2022232747 hasAuthorship W2022232747A5050307056 @default.
• W2022232747 hasAuthorship W2022232747A5084753559 @default.
• W2022232747 hasBestOaLocation W20222327471 @default.
• W2022232747 hasConcept C134018914 @default.
• W2022232747 hasConcept C185592680 @default.
• W2022232747 hasConcept C190283241 @default.
• W2022232747 hasConcept C203014093 @default.
• W2022232747 hasConcept C2778690821 @default.
• W2022232747 hasConcept C2779306644 @default.
• W2022232747 hasConcept C502942594 @default.
• W2022232747 hasConcept C55493867 @default.
• W2022232747 hasConcept C86803240 @default.
• W2022232747 hasConcept C95444343 @default.
• W2022232747 hasConceptScore W2022232747C134018914 @default.
• W2022232747 hasConceptScore W2022232747C185592680 @default.
• W2022232747 hasConceptScore W2022232747C190283241 @default.
• W2022232747 hasConceptScore W2022232747C203014093 @default.
• W2022232747 hasConceptScore W2022232747C2778690821 @default.
• W2022232747 hasConceptScore W2022232747C2779306644 @default.
• W2022232747 hasConceptScore W2022232747C502942594 @default.
• W2022232747 hasConceptScore W2022232747C55493867 @default.
• W2022232747 hasConceptScore W2022232747C86803240 @default.
• W2022232747 hasConceptScore W2022232747C95444343 @default.
• W2022232747 hasIssue "22" @default.
• W2022232747 hasLocation W20222327471 @default.
• W2022232747 hasOpenAccess W2022232747 @default.
• W2022232747 hasPrimaryLocation W20222327471 @default.

• next