EXPRESSION OF THE PROTOONCOGENE C-JUN IS MAINTAINED DURING MYOGENIC DIFFERENTIATION IN RAT L6 MYOBLASTS

Skeletal myoblasts undergo terminal differentiation when maintained un der low-mitogen conditions. We have examined the expression of c-jun, one of the growth-factor-inducible immediate-early genes, during myoge nic differentiation of L6 myoblasts. The steady-state levels of c-jun mRNA, c-Jun polypeptide, and activator protein 1 binding activity were not markedly altered in L6 cells undergoing myogenic differentiation. Although expression of c-jun is induced by serum mitogens in fibrobla sts and other cell fines, addition of high serum to proliferating myob lasts resulted in the activation of another immediate early gene junB, but not c-jun mRNA expression. These results indicate that regulation of c-jun may differ from that of other immediate early genes in L6 ce lls. Manipulation of myogenesis by exposing L6 cells to dimethyl sulfo xide also suggested that expression of myogenin and muscle differentia tion could occur in the presence of high levels of c-Jun. Furthermore, expression of c-jun from Moloney murine leukaemia viral long-terminal repeat in transfected L6 cells confirmed that constitutive expression of c-jun does not interfere with myogenesis in L6 myoblasts. Therefor e, regulation of c-jun expression in rat L6 cells differs from that in the mouse C2 cell line.