Extracellular-matrix synthesis by skeletal muscle in culture. Major secreted collagenous proteins of clonal myoblasts

We have previously shown that G8-1, a murine clonal skeletal-muscle cell line, produces a substrate-attached extracellular matrix [Beach, Burton, Hendricks & Festoff (1982) J. Biol. Chem. 257, 11437-11442]. To examine further the expression of extracellular-matrix proteins by muscle cells, we have analysed the collagenous proteins secreted by G8-1 myoblasts. We have found that collagens and/or procollagens, corresponding to genetic types I, III and IV (and possibly V), are produced and secreted by G8-1 myoblasts. The major secreted collagenous polypeptides were identified as alpha 1 type I and its precursors by using pulse-chase studies, pepsin and collagenase digestions and CNBr fragmentation. The presence of lesser amounts of the other collagens was determined by immunoprecipitation. These results demonstrate that clonal skeletal-muscle cells, in the absence of fibroblasts and an exogenous collagen substrate, are able to synthesize and secrete several extracellular-matrix collagenous proteins in proportions similar to those which are commonly found in muscle tissue and mixed cultures of muscle cells and fibroblasts.