Interaction of skeletal muscle cells with collagen type IV is mediated by perlecan associated with the cell surface

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Abstract
We have previously shown that the expression of perlecan, a heparan sulfate proteoglycan localized on the myoblast surface, is down‐regulated during terminal differentiation of skeletal muscle myoblasts (Larraín et al. [1997] Exp. Cell Res. 234:405–412). In this study, we have evaluated the biochemical characteristics of perlecan, its association with the myoblast surface, and its involvement in C2C12 myoblast adhesion to different substrates. Perlecan associated with myoblasts was solubilized by Triton X‐100, whereas heparin, high salt, and RGD peptides were unable to solubilize perlecan. Pre‐incubation of myoblasts with [35S]‐Na2SO4, followed by solubilization with Triton X‐100 and immunoprecipitation with antibodies against murine perlecan, demonstrated that this proteoglycan present on the cell surface has a heterogeneous size profile with a Kav value of 0.45, determined by Sepharose CL‐4B chromatography. Myoblasts were found to adhere with decreasing affinities to collagen type IV, type I, laminin, fibronectin, perlecan, and matrigel. We found that cell adhesion to collagen type IV was inhibited by blocking this substrate with exogenous perlecan prior to cell plating, whereas no effect was observed for laminin. Furthermore, adhesion of myoblasts to collagen type IV was inhibited by the perlecan core protein obtained by treatment of perlecan with heparitinase, as well as by pre‐incubation of the cells with antibodies against murine perlecan. These data support the idea that skeletal muscle cells interact with collagen type IV through the perlecan core protein present on the surface of undifferentiated myoblasts. J. Cell. Biochem. 75:665–674, 1999.