Regulation of myogenic terminal differentiation by the hairy-related transcription factor CHF2

We have recently cloned a novel basic helix-loop-helix factor, CHF2, that f unctions as a transcriptional repressor. To address its role in the regulat ion of myogenic terminal differentiation, we analyzed its expression patter n during C2C12 mouse myotube formation. In undifferentiated myoblasts, CHF2 is expressed at high levels. After induction of myotube formation in low s erum, CHF2 expression is barely detectable at 3 days after induction, Myoge nin expression, in contrast, peaks at 3 days. In transiently transfected 10 T1/2 embryonic fibroblasts, CHF2 inhibited MyoD-dependent activation of the myogenin promoter in a dose-dependent fashion. Electrophoretic mobility sh ift analysis indicated that CHF2 inhibits the binding of the MyoD.E47 heter odimer to the E-box binding site. CHF2 also inhibited myogenic conversion o f 10T1/2 cells by MyoD, as measured by skeletal myosin heavy chain protein expression. Coimmunoprecipitation analysis indicated that CHF2 forms a prot ein complex with MyoD. Mutational analysis of CHF2 indicated that the repre ssion activity for both transcription and myogenic conversion mapped to a h ydrophobic carboxyl-terminal region and did not require either the basic he lix-loop-helix or YRPW motifs, Our data indicate that CHF2 functions as a t ranscriptional repressor of myogenesis by formation of an inactive heterodi meric complex with MyoD and likely plays an important role in muscle develo pment.