title: Syndecan-4 regulates ATF-2 transcriptional activity in a Rac1-dependent manner.
abstract: Syndecan-4 is a transmembrane heparan sulfate proteoglycan that co-operates with integrins during cell-matrix interactions for the assembly of focal adhesions and actin stress fibers and in the phosphorylation of focal adhesion kinase (FAK) on Tyr397. These cellular events are regulated by the small GTPase Rho, and in the absence of syndecan-4 ligation, cellular levels of GTP-bound Rho are decreased implicating syndecan-4 in the regulation of the small GTPases. In the present study we report that, compared with wild type cells, fibronectin-adherent syndecan-4-null fibroblasts showed enhanced lamellipodia and increased Rac1 activity that could be down-regulated by re-expression of syndecan-4 in the mutant cells. Consistent with the role for Rac1 in activating p38 and JNK signaling, syndecan-4-null cells display higher levels of active p38 MAPK and JNK that were abolished by the expression of a dominant-negative RacN17 mutant. Since p38 and JNK regulate gene expression by phosphorylating and activating transcription factors, we compared both the phosphorylation state and the transcriptional activity of the ATF-2 transcription factor, as a direct p38 and JNK target in syndecan-4-null and wild type cells. In the absence of syndecan-4, both ATF-2 phosphorylation and transcriptional activity were significantly more elevated compared with wild type cells, and both activities were decreased either by the re-expression of syndecan-4 or by the expression of RacN17. Our results reveal a novel function for syndecan-4 in modulating nuclear transcriptional activity and indicate an underlying mechanism that acts at the level of Rac1-p38/JNK signaling.
authors.affiliation: Cutaneous Biology Research Center, Massachusetts General Hospital, Harvard Medical School, Charlestown, Massachusetts 02129, USA.
authors.forename: Stefania
authors.initials: S
authors.lastname: Saoncella
authors.forename: Enzo
authors.initials: E
authors.lastname: Calautti
authors.forename: Wendy
authors.initials: W
authors.lastname: Neveu
authors.forename: Paul F
authors.initials: PF
authors.lastname: Goetinck
mesh_terms: D051698:Activating Transcription Factor 2; D000256:Adenoviridae / Q000235:genetics; D000818:Animals; D002467:Cell Nucleus / Q000378:metabolism; D017362:Cyclic AMP Response Element-Binding Protein / Q000378:metabolism*; D004247:DNA / Q000378:metabolism; D005347:Fibroblasts / Q000378:metabolism; D005353:Fibronectins / Q000378:metabolism; D022001:Focal Adhesions; D005786:Gene Expression Regulation; D049452:Green Fluorescent Proteins / Q000378:metabolism; D006801:Humans; D048031:JNK Mitogen-Activated Protein Kinases / Q000378:metabolism; D008156:Luciferases / Q000378:metabolism; D048670:MAP Kinase Kinase 4; D008562:Membrane Glycoproteins / Q000378:metabolism / Q000502:physiology*; D051379:Mice; D020929:Mitogen-Activated Protein Kinase Kinases / Q000378:metabolism; D010766:Phosphorylation; D011509:Proteoglycans / Q000378:metabolism / Q000502:physiology*; D015398:Signal Transduction; D053671:Syndecan-4; D014157:Transcription Factors / Q000378:metabolism*; D014158:Transcription, Genetic; D015533:Transcriptional Activation; D014443:Tyrosine / Q000737:chemistry; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism; D020830:rac1 GTP-Binding Protein / Q000378:metabolism*
chemical_list: C497105:ATF2 protein, human; D051698:Activating Transcription Factor 2; C497106:Atf2 protein, mouse; D017362:Cyclic AMP Response Element-Binding Protein; D005353:Fibronectins; D008562:Membrane Glycoproteins; D011509:Proteoglycans; C508304:SDC4 protein, human; C508306:Sdc4 protein, mouse; D053671:Syndecan-4; D014157:Transcription Factors; D049452:Green Fluorescent Proteins; D014443:Tyrosine; D004247:DNA; D008156:Luciferases; D048031:JNK Mitogen-Activated Protein Kinases; D048051:p38 Mitogen-Activated Protein Kinases; D048670:MAP Kinase Kinase 4; D020929:Mitogen-Activated Protein Kinase Kinases; D020830:rac1 GTP-Binding Protein