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• W2000461686 abstract "The role of non-Smad proteins in the regulation of transforming growth factor-β (TGFβ) signaling is an emerging line of active investigation. Here, we characterize the role of KLF14, as a TGFβ-inducible, non-Smad protein that silences the TGFβ receptor II (TGFβRII) promoter. Together with endocytosis, transcriptional silencing is a critical mechanism for down-regulating TGFβ receptors at the cell surface. However, the mechanisms underlying transcriptional repression of these receptors remain poorly understood. KLF14 has been chosen from a comprehensive screen of 24 members of the Sp/KLF family due to its TGFβ inducibility, its ability to regulate the TGFβRII promoter, and the fact that this protein had yet to be functionally characterized. We find that KLF14 represses the TGFβRII, a function that is augmented by TGFβ treatment. Mapping of the TGFβRII promoter, in combination with site-directed mutagenesis, electromobility shift, and chromatin immunoprecipitation assays, have identified distinct GC-rich sequences used by KLF14 to regulate this promoter. Mechanistically, KLF14 represses the TGFβRII promoter via a co-repressor complex containing mSin3A and HDAC2. Furthermore, the TGFβ pathway activation leads to recruitment of a KLF14-mSin3A-HDAC2 repressor complex to the TGFβRII promoter, as well as the remodeling of chromatin to increase histone marks that associate with transcriptional silencing. Thus, these results describe a novel negative-feedback mechanism by which TGFβRII activation at the cell surface induces the expression of KLF14 to ultimately silence the TGFβRII and further expand the network of non-Smad transcription factors that participate in the TGFβ pathway. The role of non-Smad proteins in the regulation of transforming growth factor-β (TGFβ) signaling is an emerging line of active investigation. Here, we characterize the role of KLF14, as a TGFβ-inducible, non-Smad protein that silences the TGFβ receptor II (TGFβRII) promoter. Together with endocytosis, transcriptional silencing is a critical mechanism for down-regulating TGFβ receptors at the cell surface. However, the mechanisms underlying transcriptional repression of these receptors remain poorly understood. KLF14 has been chosen from a comprehensive screen of 24 members of the Sp/KLF family due to its TGFβ inducibility, its ability to regulate the TGFβRII promoter, and the fact that this protein had yet to be functionally characterized. We find that KLF14 represses the TGFβRII, a function that is augmented by TGFβ treatment. Mapping of the TGFβRII promoter, in combination with site-directed mutagenesis, electromobility shift, and chromatin immunoprecipitation assays, have identified distinct GC-rich sequences used by KLF14 to regulate this promoter. Mechanistically, KLF14 represses the TGFβRII promoter via a co-repressor complex containing mSin3A and HDAC2. Furthermore, the TGFβ pathway activation leads to recruitment of a KLF14-mSin3A-HDAC2 repressor complex to the TGFβRII promoter, as well as the remodeling of chromatin to increase histone marks that associate with transcriptional silencing. Thus, these results describe a novel negative-feedback mechanism by which TGFβRII activation at the cell surface induces the expression of KLF14 to ultimately silence the TGFβRII and further expand the network of non-Smad transcription factors that participate in the TGFβ pathway. The family of cytokines composed of TGFβ, 4The abbreviations used are: TGFβ, transforming growth factor-β; TGFβRII, TGFβ receptor type II; CMV, cytomegalovirus; RT, reverse transcription; GAPDH, glyceraldehyde-3-phosphate dehydrogenase; B2M, β2-microglobulin; TUBB2, β2-Tubulin; HPRT1, hypoxanthine phosphoribosyltransferase 1; GST, glutathione S-transferase; HDAC, histone deacetylase; WT, wild type; KLF14, Krüppel-like factor 14; ChIP, chromatin immunoprecipitation. bone morphogenetic proteins, activins, inhibins, connective tissue growth factors (CCN family), along with their corresponding signaling molecules, are master regulators of normal homeostasis and development (1Zavadil J. Bottinger E. Oncogene. 2005; 24: 5764-5774Crossref PubMed Scopus (1358) Google Scholar, 2Truty M. Urrutia R. Pancreatology. 2007; 7: 423-435Crossref PubMed Scopus (122) Google Scholar, 3Raftery L. Sutherland D. Dev. Biol. 1999; 210: 251-268Crossref PubMed Scopus (275) Google Scholar, 4Moustakas A. Heldin C. J. Cell Sci. 2005; 118: 3573-3584Crossref PubMed Scopus (884) Google Scholar, 5Miyazono K. Maeda S. Imamura T. Cytokine & Growth Factor Rev. Bone Morph. Prot. 2005; 16: 251-263Crossref PubMed Scopus (700) Google Scholar, 6Massague J. Gomis R. FEBS Lett. 2006; 580 (Istanbul Special Issue): 2811-2820Crossref PubMed Scopus (629) Google Scholar, 7Knight P. Glister C. Reproduction. 2006; 132: 191-206Crossref PubMed Scopus (884) Google Scholar, 8Itman C. Mendis S. Barakat B. Loveland K. Reproduction. 2006; 132: 233-246Crossref PubMed Scopus (148) Google Scholar, 9Ellenrieder V. Fernandez Zapico M. Urrutia R. Curr. Opin. Gastroenterol. 2001; 17: 434-440Crossref PubMed Scopus (12) Google Scholar, 10Bachman K. Park B. Curr. Opin. Oncol. 2005; 17: 49-54Crossref PubMed Scopus (159) Google Scholar). Consequently, alterations in these pathways lead to severe malformations and diseases, including cancer. TGFβ is the best characterized pathway within this family of cytokines. Recent studies reveal, for instance, the existence of two types of membrane-to-nucleus TGFβ signaling mechanisms, namely the Smad-dependent and non-Smad protein-mediated cascades, although evidence of cross-talk between these two cascades is also emerging (4Moustakas A. Heldin C. J. Cell Sci. 2005; 118: 3573-3584Crossref PubMed Scopus (884) Google Scholar, 9Ellenrieder V. Fernandez Zapico M. Urrutia R. Curr. Opin. Gastroenterol. 2001; 17: 434-440Crossref PubMed Scopus (12) Google Scholar). Therefore, even though our understanding of the complexity underlying TGFβ signaling continues to grow, classification into these two types of mechanisms has helped to organize the nascent theoretical framework for advancing this field of research by the integration of new findings into easily understandable paradigms. The canonical Smad-mediated TGFβ pathway is activated by binding of TGFβ1, -2, and/or -3 cytokines to the TGFβRII, which then dimerizes with and activates the TGFβ receptor I through serine phosphorylation of the regulatory GS-domain. The Type I receptor, in turn, phosphorylates receptor-bound Smad (Smad2/3) at the C-terminal SXS motif, releasing them from retention in the cytoplasm and allowing their translocation into the nucleus. Smad4 acts as a common partner of activated Smads to help execute their function. In this manner, TGFβ signaling is transduced through the cytoplasm into the nucleus to form complexes with distinct transcriptional regulators for specific gene promoters. The role of non-Smad protein-mediated pathways in the regulation of TGFβ signaling is also an active line of investigation. For instance, the Sp/KLF family of proteins is emerging as important non-Smad protein-mediated pathway cascades and, under certain circumstances, a cross-talk regulator with Smads to achieve distinct cellular functions. Sp1 is the founding member this expanding group of Sp/KLF proteins. The structure of these proteins is defined by the presence of three highly conserved and homologous C-terminal Cys2His2 zinc finger domains, which are responsible for DNA binding, and a variable N-terminal domain, which is responsible for transcriptional regulation (11Lomberk G. Urrutia R. Biochem. J. 2005; 392: 1-11Crossref PubMed Scopus (159) Google Scholar, 12Black A.R. Black J.D. Azizkhan-Clifford J. J. Cell Physiol. 2001; 188: 143-160Crossref PubMed Scopus (877) Google Scholar, 13Turner J. Crossley M. Trends Biochem. Sci. 1999; 24: 236-240Abstract Full Text Full Text PDF PubMed Scopus (264) Google Scholar). However, the identification and characterization of this family of proteins has revealed that many bind to GC-rich target sequences similar, if not identical to, the “Sp1 sites” through which they can either activate or repress gene expression (11Lomberk G. Urrutia R. Biochem. J. 2005; 392: 1-11Crossref PubMed Scopus (159) Google Scholar, 12Black A.R. Black J.D. Azizkhan-Clifford J. J. Cell Physiol. 2001; 188: 143-160Crossref PubMed Scopus (877) Google Scholar, 13Turner J. Crossley M. Trends Biochem. Sci. 1999; 24: 236-240Abstract Full Text Full Text PDF PubMed Scopus (264) Google Scholar). Therefore, the discovery of repressors within this Sp/KLF family of transcriptional regulators has challenged the early paradigm that Sp1 activates all GC-rich sites. As a result, these Sp/KLF transcriptional repressors provide a novel mechanism for silencing a large number of genes that are already known to be activated by Sp1, particularly in response to TGFβ. TGFβRII has been previously shown to be activated by Sp1 (14Bae H.W. Geiser A.G. Kim D.H. Chung M.T. Burmester J.K. Sporn M.B. Roberts A.B. Kim S.J. J. Biol. Chem. 1995; 270: 29460-29468Abstract Full Text Full Text PDF PubMed Scopus (115) Google Scholar). However, since these elegant studies were done, 24 Sp/KLF transcription factors have been discovered with some members acting as activators while others as repressors via the same type of GC-rich cis regulatory sequences used by Sp1. Thus, some Sp/KLF transcription factors are excellent candidates that may play a role in silencing of TGFβRII. Indeed, fortunately, in the current study, we describe, for the first time, the functional characterization of KLF14 as a novel non-Smad regulatory protein of the TGFβ pathway. Our results outline a novel, biochemically significant role for KLF14 in the silencing of the TGFβRII via Sp/KLF sites. This pathway provides a well characterized example of how Sp/KLF proteins are emerging as important non-Smad proteins that can directly regulate TGFβ signaling by regulating the expression of key molecules from this pathway. Cell Culture-Tissue culture reagents were purchased from commercial sources (Invitrogen). The human pancreatic epithelial cancer cell lines, PANC-1, ASPC-1, Capan-1, Capan-2, BxPC-3, L3.6, MiaPaCa-2, and CFPAC-1, were obtained from American Type Culture Collection and maintained according to the supplier’s suggestions. All cells were grown at 37 °C in a humidified incubator under 5% CO2. Plasmid Construction-Standard molecular biology techniques were used to clone KLF4, KLF5, KLF7, KLF9, KLF11, KLF14, and KLF15 into the pcDNA3.1/His (Invitrogen) and pCMVtag2 (Stratagene) vectors for expression as His-tagged or FLAG-tagged proteins, respectively, as well as the truncated (263 bp) TGFβRII promoter into the pGL3-Lux vector (Promega). The p3TP-Lux reporter plasmid containing TGFβ-responsive elements was kindly provided by Dr. Anita Roberts (National Institutes of Health) as a positive control for TGFβ1 stimulation experiments (data not shown). Full-length TGFβRII reporter was kindly provided by Dr. David Danielpour (Case Western). Semi-quantitative RT-PCR-Total RNA was extracted from cells according to the manufacturer’s instructions using an RNeasy Kit (Qiagen), and 5 μg was used for cDNA synthesis using oligo(dT) primer using the SuperScript™ III First-Strand Synthesis System for RT-PCR (Invitrogen) per the manufacturer’s protocol. RT-PCR was performed using LA TaqDNA Polymerase with a GC Buffers kit (Takara) per the manufacturer protocols. Semiquantitative RT-PCR analysis was performed with the primer sets provided in supplemental Table S1. Each experiment was done in triplicate. Amplification of four human housekeeping genes, GAPDH (Unigene Hs.544577), β2-microglobulin (B2M, Hs.709313), β2-Tubulin (TUBB2, Hs.300701), and hypoxanthine phosphoribosyltransferase 1 (HPRT1, Hs.412707) was used for all samples as an internal control. Densitometric values were obtained and normalized to the average of the housekeeping cDNAs for each individual sample using Scion Image Beta 4.02 software (Scion Corp.). To represent the TGFβ inducibility of individual KLF transcripts, each TGFβ-treated sample was compared with an untreated control that was originally plated and ultimately collected at the same time to minimize compounding factors, which can often influence gene expression (i.e. cell cycle stage, cell density, potential unknown paracrine, and/or autocrine stimuli). At each time point, values were determined by first normalizing the TGFβ-treated sample (T, treated) to the average of the four aforementioned housekeeping genes in the same sample (TC, treated housekeeping gene control). This resultant value was divided by the corresponding untreated sample (UT, untreated) normalized in the same manner (UTC, untreated housekeeping gene control), to express the fold of TGFβ induction ([T/TC]/[UT/UTC] = fold TGFβ-induction). Another housekeeping gene, β-actin (ACTB, Hs.520640), was not used in our analyses, because it showed significant differences with TGFβ treatment over control values (data not shown). Western Blot-Total protein extracts were prepared by lysing cells in radioimmune precipitation assay buffer supplemented with Complete protease inhibitor mixture (Roche Applied Science). Cellular lysates were subjected to 10% SDS-PAGE and then separated proteins are transferred to polyvinylidene difluoride membranes (Millipore). Membranes were incubated overnight at 4 °C in blocking solution (Tris-buffered saline solution containing 5% nonfat dried milk and 0.1% Tween 20). Subsequently, membranes were incubated with specified primary antibodies overnight at 4 °C. Immune complexes were visualized by enhanced chemiluminescence (Pierce) and exposed to x-ray film. An antibody against β2-actin (Sigma) was used as loading control. Transcriptional Reporter Assays-Cells were transfected with specified reporter constructs along with expression constructs and/or empty vector using electroporation (2 × 106 cells/0.4-cm microcuvette, 360 V, and 10 ms) and subsequently serum-starved overnight. Transfection was performed with equimolar concentrations of DNA, and expression was quantified with Western blotting directed against epitope-tagged proteins as described. Cells were stimulated with TGFβ1 (R&D Systems) as specified and assayed at various specified time points. At 24 or 48 h after transfection and treatment as noted, cells were lysed, and luciferase measurements were performed using a 20/20 luminometer (Turner Designs) according to manufacturer’s suggestions (Promega). Data were normalized as relative light units and normalized to the protein concentration as the mean ± S.D. All experiments were performed in triplicate at least three independent times. Immunoprecipitation-Cells were transfected with FLAG-tagged constructs. At 24 h post-transfection, cells were washed and lysed in lysis buffer (150 mm NaCl, 0.5% Nonidet P-40, 50 mm Tris-HCl, pH 7.5, 20 mm MgCl2) supplemented with Complete protease inhibitor tablets (Roche Applied Science) for 30 min at 4 °C. Immunoprecipitations were performed using anti-FLAG M2 agarose-conjugated antibodies (Sigma) for 2 h at 4 °C. To detect interaction with endogenous co-repressors, immunocomplexes were collected by centrifugation, washed with lysis buffer, and analyzed by Western blot as described above using anti-mSin3a and HDAC2 antibodies (Santa Cruz Biotechnology). Chromatin Immunoprecipitation-ChIP assays were performed using the EZ-ChIP kit. The following primer set for the 263-bp TGFβRII promoter was used for PCR: 5′-GCA GAT GTT CTG ATC TAC TA-3′ (forward); 5′-AGC TGG GCA GGA CCT CTC TC-3′ (reverse) using TaKaRa LA Taq according to the manufacturer’s protocol (Mirus). Site-directed Mutagenesis-Site-directed mutagenesis was performed with QuikChange® II site-directed mutagenesis kits per the manufacturer’s protocol (Stratagene). All constructs were sequenced by the Mayo Clinic Molecular Biology Core Facility. GST Fusion-The KLF14 cDNA fragment encoding amino acids 191–323 corresponding to the DNA-binding zinc finger region was cloned into the GST fusion vector pGEX 5X-1 (Amersham Biosciences) using standard techniques. GST fusion protein expression was induced in BL21 cells (Stratagene) by the addition of 1 mm isopropyl-d-thiogalactopyranoside and incubation for 2 h. Cells were lysed and subsequently purified by using glutathione-Sepharose 4B affinity chromatography as previously described (15Zhang J.S. Moncrieffe M.C. Kaczynski J. Ellenrieder V. Prendergast F.G. Urrutia R. Mol. Cell Biol. 2001; 21: 5041-5049Crossref PubMed Scopus (153) Google Scholar). Electromobility Shift Assay-Gel shift assays were performed as previously described (16Cook T. Gebelein B. Mesa K. Mladek A. Urrutia R. J. Biol. Chem. 1998; 273: 25929-25936Abstract Full Text Full Text PDF PubMed Scopus (160) Google Scholar). Briefly, 1.75 pmol of double-stranded oligonucleotides were end-labeled with [γ-32P]ATP using 10 units of T4 polynucleotide kinase and appropriate buffer (700 mm Tris-HCl, pH 7.6, 100 mm MgCl2, 50 mm dithiothreitol) according to the manufacturer’s instructions (Promega). The reaction was incubated at 37 °C for 10 min and halted with addition of TE plus EDTA (0.5 m EDTA, 1 m Tris, pH 8.0, H2O). Protein lysates included 0.5 μg of purified GST-KLF14/ZF fusion protein and in some experiments rhSP1 (Promega) at the indicated dilutions. A 5× ZnCl2 buffer was used in this reaction (100 mm Hepes, pH 7.5, 250 mm KCl, 25 mm MgCl2, 50 μm ZnCl2, 30% glycerol, 1 mg/ml bovine serum albumin, 250 μg/ml poly(dI-dC), H2O) for 10 min at room temperature. The γ-32P-labeled oligonucleotides were added for 20 min. In some cases, an excess of cold probe, at the indicated dilutions, was added concomitant with the addition of radiolabeled probe in addition to anti-Sp1 polyclonal rabbit antibody purchased from commercial sources (Millipore). The mixtures were electrophoresed in a 4% nondenaturing polyacrylamide gel in a Hoeffer midi-gel using 0.5× Tris borate-EDTA for ∼4 h at 160 V. Gels were then transferred to blotting paper (Whatman 3MM), covered in plastic wrap, and vacuum dried for 1.5 h at 65 °C. Dried gels were then analyzed using a Storm Scanner 860 PhosphorImager (Amersham Biosciences). Sp1 consensus and Sp1 mutant double-stranded oligonucleotides were obtained from commercial sources (Santa Cruz Biotechnology) with the following sequences: Sp1 consensus, 5′-ATT CGA TCG GGG CGG GGC GAG C-3′ (forward); 5′-GCT CGC CCC GCC CCG ATC GAA T-3′ (reverse) and Sp1 mutant, 5′-ATT CGA TCG GTT CGG GGC GAG C-3′ (forward); 5′-GCT CGC CCC GAA CCG ATC GAA T-3′ (reverse). A Yet Undefined Sp/KLF Repressor Protein Plays a Role in Silencing of the Type II TGFβ-receptor Promoter-Previous studies have described the regulation of the TGFβRII by TGFβ ligands, primarily showing a bimodal response consisting of an Sp1-dependent up-regulation (14Bae H.W. Geiser A.G. Kim D.H. Chung M.T. Burmester J.K. Sporn M.B. Roberts A.B. Kim S.J. J. Biol. Chem. 1995; 270: 29460-29468Abstract Full Text Full Text PDF PubMed Scopus (115) Google Scholar, 17Venkatasubbarao K. Ammanamanchi S. Brattain M.G. Mimari D. Freeman J.W. Cancer Res. 2001; 61: 6239-6247PubMed Google Scholar) and a subsequent down-regulation of receptor transcript levels upon this stimulation (18Woodward T.L. Dumont N. O'Connor-McCourt M. Turner J.D. Philip A. J. Cell Physiol. 1995; 165: 339-348Crossref PubMed Scopus (34) Google Scholar, 19Nishikawa Y. Wang M. Carr B.I. J. Cell Physiol. 1998; 176: 612-623Crossref PubMed Scopus (34) Google Scholar, 20Gazit D. Ebner R. Kahn A.J. Derynck R. Mol. Endocrinol. 1993; 7: 189-198Crossref PubMed Scopus (88) Google Scholar). Interestingly, although the activation of TGFβRII promoter, in particular by Sp1, has received precise attention, how this receptor is repressed remains poorly understood. Consequently, the major goal of the current study has been to characterize the role of a specific family of non-Smad proteins (Sp/KLF transcription factors), which may functionally explain the down-regulation TGFβRII through GC-rich Sp1-like sequences. Our studies began with examination of the transcriptional activity of the TGFβRII gene promoter in PANC1 epithelial cells, a widely used model for studying TGFβ signaling. We have performed an initial series of reporter assays using full-length TGFβRII and the previously described, TGFβ-sensitive, 263-bp core promoter, which is located 5′ of the transcriptional start site (14Bae H.W. Geiser A.G. Kim D.H. Chung M.T. Burmester J.K. Sporn M.B. Roberts A.B. Kim S.J. J. Biol. Chem. 1995; 270: 29460-29468Abstract Full Text Full Text PDF PubMed Scopus (115) Google Scholar). Treatment of PANC1 cells with exogenous TGFβ1 leads to a marked reduction in activity of the full-length TGFβRII reporter when compared with untreated control cells (Fig. 1A). This silencing effect is recapitulated in the 263-bp TGFβRII core promoter, suggesting that both the previously described activation pathway (14Bae H.W. Geiser A.G. Kim D.H. Chung M.T. Burmester J.K. Sporn M.B. Roberts A.B. Kim S.J. J. Biol. Chem. 1995; 270: 29460-29468Abstract Full Text Full Text PDF PubMed Scopus (115) Google Scholar) and the negative transcriptional regulatory mechanism characterized further here (Fig. 1A), are operational at this core promoter level. Using bioinformatics analyses (TRANSFAC Public), we have identified five putative Sp/KLF binding sites within this TGFβ-sensitive, 263-bp core promoter region (Fig. 1B). Four of these sites (#1–4) have been previously identified, although an additional site (#5) has not been previously reported (14Bae H.W. Geiser A.G. Kim D.H. Chung M.T. Burmester J.K. Sporn M.B. Roberts A.B. Kim S.J. J. Biol. Chem. 1995; 270: 29460-29468Abstract Full Text Full Text PDF PubMed Scopus (115) Google Scholar, 21Jennings R. Alsarraj M. Wright K.L. Munoz-Antonia T. Oncogene. 2001; 20: 6899-6909Crossref PubMed Scopus (21) Google Scholar). Some of these previously identified sites have been shown to be activated by Sp1. However, whether novel Sp/KLF silencer proteins can also bind to this sequence to reverse the activation by Sp1 remained unknown. Therefore, this analysis has led us to the hypothesis that a yet undefined Sp/KLF repressor protein plays a role in the silencing of this promoter. Novel TGFβ-inducible Non-Smad, Sp/KLF Proteins Are Identified as Candidate Regulators of the Type II TGFβ-receptor- To test our hypothesis, we have developed a four-tier screening approach. This approach includes first, testing which of the 24 known Sp/KLF proteins are expressed in TGFβ-sensitive epithelial cells and, thus, can be considered initial candidates to target the TGFβRII promoter. Our experimental cell model, PANC1, a human epithelial cell line, is an optimal model for our studies, because they have adequate expression of TGFβRII mRNA and display growth inhibition to exogenous TGFβ1 stimulation (22Schneider D. Kleeff J. Berberat P.O. Zhu Z. Korc M. Friess H. Buchler M.W. Biochim. Biophys. Acta. 2002; 1588: 1-6Crossref PubMed Scopus (57) Google Scholar). In addition, as shown in Fig. 2A, each of the 24 known Sp/KLF transcription factors are consistently expressed in these cells, which made it ideal for performing a comprehensive screen. Second, we determine whether any Sp/KLF genes are TGFβ-inducible with a kinetic that is consistent with playing a role in the down-regulation of the TGFβRII. Third, by utilizing transfection studies combined with reporter assays, we test the potential of distinct members of this family to repress TGFβRII promoter activity and then, by electromobility shift assays, determine which sites on the promoter are utilized by our candidate KLF protein. Finally, we examine whether the repressor that is isolated according to these criteria binds to the endogenous TGFβRII gene and can remodel chromatin on this target, suggesting the bona fide target status of the candidate KLF protein. Thus, by applying this comprehensive screening, our study has been robust in evaluating the KLF protein family in the TGFβ response and regulation of the TGFβRII. The genomic axiom that functionally related genes follow a similar pattern of expression suggested that, hypothetically, the protein that represses the TGFβRII may be expressed in a similar manner after TGFβ treatment, in particular, during the repression response to this cytokine. Consequently, we have evaluated which, if any, of these Sp/KLF members are inducible by TGFβ1 treatment. Thus, using RNA from PANC1 cells either untreated or treated with TGFβ1, we have performed RT-PCR at various time points (Fig. 2B). As a positive control for TGFβ-mediated transcriptional induction, we monitor the expression of p21, a known TGFβ-inducible gene within the pathway. Of the 24 known Sp/KLF transcription factors, we have identified 7 that were markedly induced with exogenous TGFβ1 treatment, suggesting that these could be potential candidate transcriptional repressors of the TGFβRII promoter (Fig. 2B). These results are not only consistent with our previous work, which identified KLF11 as a TGFβ-inducible gene (16Cook T. Gebelein B. Mesa K. Mladek A. Urrutia R. J. Biol. Chem. 1998; 273: 25929-25936Abstract Full Text Full Text PDF PubMed Scopus (160) Google Scholar, 23Subramaniam M. Harris S.A. Oursler M.J. Rasmussen K. Riggs B.L. Spelsberg T.C. Nucleic Acids Res. 1995; 23: 4907-4912Crossref PubMed Scopus (220) Google Scholar), but, more importantly, it characterizes previously unidentified KLF targets for this cascade, namely KLF4, -5, -7, -9, -14, and -15. Thus, based upon their expression patterns, these seven genes are good candidates to further investigate their regulation of the TGFβRII promoter. Subsequently, we have tested the transcriptional activity of these candidates on the TGFβRII promoter using reporter assays by co-transfecting the 263-bp core TGFβRII promoter-luciferase construct with cDNAs encoding each of the seven TGFβ-inducible KLF candidates. Out of these, five candidates induced a marked decrease in TGFβRII promoter activity, namely KLF4, -7, -11, -14, and -15 (Fig. 3A). KLF5 did not affect TGFβRII promoter activity above control levels, whereas KLF9 appeared to slightly activate this promoter, therefore these two proteins were not continued in subsequent experiments due to our objective of identifying TGFβRII repressors. To confirm whether this observed repression of TGFβRII promoter regulation is consistent with TGFβ pathway activation, these five proteins were further tested in PANC1 cells treated with exogenous TGFβ1 treatment. Interestingly, upon treatment, these KLF proteins were capable of further repressing TGFβRII promoter activity, with the largest repression achieved by KLF14 (Fig. 3B). These data also indicate that a second TGFβ-dependent mechanism, directly (signal-induced KLF expression or post-translational modifications) or indirectly (induction of another transcription factor), cooperates with KLF proteins to additionally repress this gene. Upon increasing concentrations of KLF14 cDNA in transfection studies, we found a concentration-dependent repression of the core TGFβRII promoter (Fig. 3C). Together, these results strongly identify KLF14 as a good candidate to be a regulator of TGFβRII promoter activity and expression. KLF14, a Novel Non-Smad Protein, Regulates the Type II TGFβ-receptor-The gene encoding KLF14 has been previously identified by our group and named BTEB5 due to its sequence similarities to members of this subfamily of KLF silencing proteins. 5Reported by J. Kaczynski and R. Urrutia to NCBI, 2002. Although, recently, genetic studies have reported the genomic structure, intronless nature, and potential imprinted status of this gene (24Parker-Katiraee L. Carson A.R. Yamada T. Arnaud P. Feil R. Abu-Amero S.N. Moore G.E. Kaneda M. Perry G.H. Stone A.C. Lee C. Meguro-Horike M. Sasaki H. Kobayashi K. Nakabayashi K. Scherer S.W. PLoS Genet. 2007; 3: 665-678Crossref Scopus (69) Google Scholar), a functional characterization of this protein at the cellular and biochemical level has never been performed. Because our data indicate that KLF14 appears to be a potent regulator of the TGFβRII in promoter assays combined with this existing gap in knowledge on this KLF family member and its targets, the choice to further investigate the role of this particular KLF in TGFβRII regulation would significantly expand the current knowledge on the functional properties of members of this family. Noteworthy, we have validated these in vitro reporter results in vivo by assessing whether this protein has a regulatory effect on endogenous TGFβRII levels in PANC1 cells. Initial correlative experiments demonstrate that the levels of TGFβRII mRNA levels decrease at a time in which the amount of KLF14 increases (repression phase of the bimodal expression pattern of TGFβRII in response to TGFβ), raising the possibility that KLF14 is induced to subsequently down-regulate the TGFβRII (Fig. 4A). To mechanistically support this correlation, we have performed RT-PCR on cells overexpressing KLF14 to determine TGFβRII levels in comparison to mock transfected cells in the presence or absence of exogenous TGFβ1 stimulation (Fig. 4B). KLF14 overexpression alone is sufficient to decrease TGFβRII mRNA, interestingly to the same extent as TGFβ1 stimulation alone. Furthermore, subsequent TGFβ1 treatment in cells transfected with KLF14 leads to further down-regulation of TGFβRII transcripts. Because KLF14 is a TGFβ-inducible gene, the further decrease in TGFβRII mRNA levels observed upon TGFβ1 treatment likely results from the induction of endogenous Sp/KLF transcription factors by this cytokine. These results suggest that TGFβ down-regulates TGFβRII transcripts through KLF14 expression with subsequent negative regulation of promoter activity. Next, we have tested whether the effect of KLF14 on TGFβRII expression interfered with TGFβ-induced signals that target downstream genes, su" @default.
• W2000461686 created "2016-06-24" @default.
• W2000461686 creator A5013280795 @default.
• W2000461686 creator A5029404091 @default.
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• W2000461686 creator A5072437086 @default.
• W2000461686 date "2009-03-01" @default.
• W2000461686 modified "2023-10-16" @default.
• W2000461686 title "Silencing of the Transforming Growth Factor-β (TGFβ) Receptor II by Krüppel-like Factor 14 Underscores the Importance of a Negative Feedback Mechanism in TGFβ Signaling" @default.
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