REGULATION OF CYCLINS AND P34(CDC2) EXPRESSION DURING TERMINAL DIFFERENTIATION OF C2C12 MYOCYTES

Little is known about the expression of cell cycle regulatory genes up on terminal differentiation of skeletal muscle cells. In this report, we demonstrate that the expressions of cyclin A, cyclin D1 and p34(cdc 2) are downregulated upon C2C12 myocytes differentiation and are not i nducible in differentiated myotubes. SV40 large T antigen can induce c ell cycle entry of myotubes through its induction of these genes' expr essions and pRB phosphorylation as well as its suppression of Rb expre ssion. These results provide the first direct evidence that the irreve rsible downregulation of cyclins and cyclin-dependent kinases is one m echanism for the permanent cell cycle withdrawal of myotubes. (C) 1995 Academic Press, Inc.