Infection with Moloney murine sarcoma virus inhibits myogenesis and alters the myogenic-associated (2'-5')oligoadenylate synthetase expression and activity.

Infection of rat skeletal muscle cultures on the first or second day in vitro with Moloney murine sarcoma virus (MSV) led to the arrest of myotube formation and to inhibition of both the synthesis of the muscle-specific proteins acetylcholine receptors and creatine kinase and the expression of the myosin light chain-2. Mos-specific RNA transcripts were readily detected at 1 day after infection indicating that viral genes were expressed in infected cells. In parallel, the expression of the cell growth-associated gene--c-myc--in uninfected muscle cultures was drastically reduced with time, while in MSV-infected myoblasts, the amount of c-myc-specific RNA transcripts gradually increased with time after infection. Under these conditions we could demonstrate that the interferon-induced gene (2'-5')oligoadenylate synthetase (2-5A synthetase) was transiently activated in uninfected muscle culture reaching a peak activity on the third day. Infection of myoblasts with murine leukemia virus did not alter the pattern of 2-5 synthetase activity observed in uninfected cells. However, infection with MSV on the second day led to a slight reduction in activity followed by a significant increase on the sixth and seventh day. Similarly, 2-5A synthetase gene expression was down-regulated with time in culture in uninfected myoblasts while re-expressed between the fourth and seventh days in MSV-infected cultures.