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

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Abstract
G8-1, a murine clonal skeletal-muscle cell line, produces a substrate-attached extracellular matrix. To further examine the expression of extracellular-matrix proteins by muscle cells, the collagenous proteins secreted by G8-1 myoblasts were analyzed. 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. 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.