title: PKCbeta-dependent activation of RhoA by syndecan-4 during focal adhesion formation.
abstract: Syndecan-4 is a ubiquitously expressed transmembrane heparan sulphate proteoglycan acting in concert with integrins in the formation of focal adhesions and stress fibres. Signalling events studied thus far suggest the formation of a ternary complex between syndecan-4, phosphatidylinositol 4,5-bisphosphate and protein kinase C alpha (PKCalpha). Syndecan-4 clustering at the cell surface has also been associated with RhoA-dependent signalling, but the relationship between PKCalpha and RhoA has not been resolved. Here we present evidence that syndecan-4, PKCalpha and RhoA are in a linear pathway necessary for the formation and maintenance of stress fibres in primary rat embryo fibroblasts. Inhibition of PKCalpha activity through the use of specific pharmacological inhibitors, a dominant-negative construct, or siRNA downregulation of protein levels, attenuated focal adhesion formation and the maintenance of stress fibres. However, these effects could be bypassed through independent activation of RhoA with lysophosphatidic acid, but not by clustering of syndecan-4 with ligand. Furthermore, inhibition of PKCalpha could block the increase in the GTP levels of RhoA induced by clustering of syndecan-4 at the cell surface. All these data point to a mechanism whereby syndecan-4 signals to RhoA in a PKCalpha-dependent manner and PKCalpha directly influences RhoA activity.
authors.affiliation: Division of Biomedical Sciences, Imperial College London, London, SW7 2AZ, UK.
authors.forename: Athanassios
authors.initials: A
authors.lastname: Dovas
authors.forename: Atsuko
authors.initials: A
authors.lastname: Yoneda
authors.forename: John R
authors.initials: JR
authors.lastname: Couchman
mesh_terms: D000818:Animals; D049109:Cell Proliferation / Q000187:drug effects; D002478:Cells, Cultured; D004622:Embryo, Mammalian; D022001:Focal Adhesions / Q000187:drug effects / Q000378:metabolism*; D015870:Gene Expression; D020868:Gene Silencing; D007527:Isoenzymes / Q000378:metabolism; D008246:Lysophospholipids / Q000494:pharmacology; D008562:Membrane Glycoproteins / Q000378:metabolism*; D051571:Protein Kinase C-alpha / Q000037:antagonists & inhibitors / Q000378:metabolism*; D051745:Protein Kinase C-delta / Q000378:metabolism; D051744:Protein Kinase C-epsilon / Q000378:metabolism; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D011509:Proteoglycans / Q000378:metabolism*; D034741:RNA, Small Interfering / Q000378:metabolism; D051381:Rats; D022502:Stress Fibers / Q000187:drug effects / Q000378:metabolism; D053671:Syndecan-4; D020742:rhoA GTP-Binding Protein / Q000378:metabolism*
chemical_list: D007527:Isoenzymes; D008246:Lysophospholipids; D008562:Membrane Glycoproteins; D047428:Protein Kinase Inhibitors; D011509:Proteoglycans; D034741:RNA, Small Interfering; C508307:Sdc4 protein, rat; D053671:Syndecan-4; D051571:Protein Kinase C-alpha; D051745:Protein Kinase C-delta; D051744:Protein Kinase C-epsilon; D020742:rhoA GTP-Binding Protein; C032881:lysophosphatidic acid