ATF SITE OF HUMAN RB GENE PROMOTER IS A RESPONSIVE ELEMENT OF MYOGENIC DIFFERENTIATION

RB mRNA increases during terminal differentiation of C2 myoblasts. We demonstrate that RB promoter activity increases about 4-fold during di fferentiation. The increase of RB promoter activity was reduced when a point mutation was designed in the ATF site. In a gel shift assay of the ATF site, two specific bands were observed, One of them, with the lower mobility, disappeared during differentiation. This band reacted with an antibody against ATF-1, We cotransfected an RB promoter-lucife rase plasmid with the TREB36/ATF-1 plasmid, ATF-1 suppressed the activ ity of the wild-type RB promoter but not of that with a point mutation at the ATF site, These results suggest that the ATF site of the RB pr omoter is a responsive element during myogenic differentiation of C2 c ells, We hypothesize that RB promoter activity is stimulated partially due to the dissociation of ATF-1, which suppresses the promoter activ ity through the ATF site in C2 myoblasts.