Adenovirus 5 E1A represses muscle-specific enhancers and inhibits expression of the myogenic regulatory factor genes, MyoD1 and myogenin.

The early region 1A of adenoviruses encodes two multifunctional proteins that have varied effects on viral and host cell transcription. Expression of adenovirus 5 E1A in the mouse myogenic cell line 23A2 inhibits the differentiation of the cells and represses the expression of reporter genes controlled by several muscle-specific regulatory elements. In addition, differentiation-defective 23A2 E1A cells do not express MyoD1 or myogenin, the two myogenic regulatory factors that normally are expressed at high levels in this cell line. We conclude that E1A exerts a negative effect on the differentiation of skeletal muscle cells by interfering with the expression of myogenic regulatory factor genes that are essential for the transcriptional activation of the contractile protein gene set.