E2A-BP, A protein binding to E12/E47, inhibits differentiation of myoblasts

The E2A proteins E12 and E47 control cellular growth and differentiation. To identify potential partners that bind E2A proteins in vascular smooth muscle cells, we employed interaction cloning. Using the basic helix-loop-helix domain of E47 to screen for interacting proteins in a human aortic expression library, we isolated several cDNA clones. One clone, termed E2A-BP, was expressed preferentially in aortic smooth muscle cells in adult rats. The E2A-BP message was detected in fetal but not in adult skeletal muscle. Although E2A-BP is a nuclear protein lacking a helix-loop-helix domain, it bound selectively to El 2 and E47 but not MyoD and Id3 in an in vitro binding assay. By gel-shift analysis, E2A-BP inhibited the binding of E47 homodimers and E47-MyoD heterodimers to an E-box probe. In C2C12 myoblasts, overexpression of E2A-BP prevented the expression of muscle specific genes and the formation of myotubes induced by differentiauon medium. In contrast, expression of E2A-BP antisense transcripts in this cell type under conditions in which endogenous message was not expressed accelerated the formation of myotubes. Together these data indicate that, by regulating the function of E2A proteins, E2A-BP may have an important role in promoting cell growth and inhibiting terminal differentiation.