title: Alpha-actinin interactions with syndecan-4 are integral to fibroblast-matrix adhesion and regulate cytoskeletal architecture.
abstract: All cells of the musculoskeletal system possess transmembrane syndecan proteoglycans, notably syndecan-4. In fibroblasts it regulates integrin-mediated adhesion to the extracellular matrix. Syndecan-4 null mice have a complex wound repair phenotype while their fibroblasts have reduced focal adhesions and matrix contraction abilities. Signalling through syndecan-4 core protein to the actin cytoskeleton involves protein kinase Cα and Rho family G proteins but also direct interactions with α-actinin. The contribution of the latter interaction to cell-matrix adhesion is not defined but investigated here since manipulation of Rho GTPase and its downstream targets could not restore a wild type microfilament organisation to syndecan-4 null cells. Microarray and protein analysis revealed no significant alterations in mRNA or protein levels for actin- or α-actinin associated proteins when wild type and syndecan-4 knockout fibroblasts were compared. The binding site for syndecan-4 cytoplasmic domain was identified as spectrin repeat 4 of α-actinin while further experiments confirmed the importance of this interaction in stabilising cell-matrix junctions. However, α-actinin is also present in adherens junctions, these organelles not being disrupted in the absence of syndecan-4. Indeed, co-culture of wild type and knockout cells led to adherens junction-associated stress fibre formation in cells lacking syndecan-4, supporting the hypothesis that the proteoglycan regulates cell-matrix adhesion and its associated microfilament bundles at a post-translational level. These data provide an additional dimension to syndecan function related to tension at the cell-matrix interface, wound healing and potentially fibrosis.
authors.affiliation: Department of Biomedical Sciences, University of Copenhagen, Denmark.
authors.forename: E
authors.initials: E
authors.lastname: Okina
authors.forename: A
authors.initials: A
authors.lastname: Grossi
authors.forename: S
authors.initials: S
authors.lastname: Gopal
authors.forename: H A B
authors.initials: HA
authors.lastname: Multhaupt
authors.forename: J R
authors.initials: JR
authors.lastname: Couchman
mesh_terms: D000185:Actinin / Q000737:chemistry / Q000378:metabolism*; D000818:Animals; D001696:Biomechanical Phenomena; D002448:Cell Adhesion; D002478:Cells, Cultured; D005109:Extracellular Matrix / Q000378:metabolism*; D005347:Fibroblasts / Q000378:metabolism / Q000502:physiology*; D022001:Focal Adhesions / Q000378:metabolism*; D051379:Mice; D018345:Mice, Knockout; D008958:Models, Molecular; D011485:Protein Binding; D054730:Protein Interaction Domains and Motifs; D055503:Protein Multimerization; D021381:Protein Transport; D022502:Stress Fibers / Q000378:metabolism / Q000648:ultrastructure*; D053671:Syndecan-4 / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D020741:rho GTP-Binding Proteins / Q000378:metabolism
chemical_list: C508306:Sdc4 protein, mouse; D053671:Syndecan-4; D000185:Actinin; D020741:rho GTP-Binding Proteins