ADENOVIRUS E1A INHIBITS CARDIAC MYOCYTE-SPECIFIC GENE-EXPRESSION THROUGH ITS AMINO-TERMINUS

Adenovirus E1A oncoproteins inhibit muscle specific gene expression an d myogenic differentiation by suppressing the transcriptional activati ng functions of basic helix-loop-helix proteins. As one approach to id entifying cardiac-specific gene regulatory proteins, we analyzed the f unctional regions of E1A proteins that are required for muscle gene re pression in cardiac cells, Myocyte-specific promoters, including the a lpha-actins and alpha-myosin heavy chain, were selectively and potentl y inhibited (> 90%) by E1A, while the ubiquitously expressed beta-acti n promoter was only partially (similar to 30%) repressed; endogenous g ene expression was also affected. Distinct E1A protein binding sites m ediated repression of muscle-specific and ubiquitous actin promoters. E1A-mediated inhibition of beta-actin required both an intact binding site for the tumor repressor proteins pRb and p107 and a second E1A do main (residues 15-35). In contrast, cardiac specific promoter repressi on required the E1A amino-terminal residues 2-36. The proximal skeleta l actin promoter (3' to base pair -153) was a target for repression by E1A. Although E1A binding to p300 was not required for inhibition of either promoter, co-expression of p300 partially reversed E1A-mediated transcriptional repression. We conclude that cardiac-specific and gen eral promoter inhibition by E1A occurs by distinct mechanisms and that cardiac-specific gene expression is modulated by cellular factors int eracting with the E1A p300/CBP-binding domain.