SYNTHESIS AND SECRETION OF A 38-KDA GLYCOPOLYPEPTIDE COINCIDES WITH L6 MYOBLAST FUSION

Rat L6 myoblastic cell line fused rapidly after two day cultivation in a medium containing horse serum and insulin. We analyzed whether the induction of plasma membrane or secreted proteins occurred simultaneou sly with ongoing fusion. Thus the cells were metabolically labeled wit h [S-35]methionine followed by biotinylation of the cell surface prote ins. Detergent-solubilized proteins derivatized with biotin were isola ted with streptavidin-agarose and subjected to SDS polyacrylamide gel electrophoresis. This analysis did not show fusion-associated inductio n of any surface proteins. However, analysis of the microsomal fractio n revealed a fusion-associated 38-kDa glycopolypeptide.This polypeptid e appeared simultaneously with the formation of the multinucleated cel ls and then declined with decreasing fusion activity. Pulse-chase labe ling experiments showed that the 38-kDa component was secreted into th e medium. These results indicate that a secreted protein component is induced during the fusion of L6 myoblasts.