Potentiation of MyoD1 activity by 5-aza-2'-deoxycytidine.

A mouse myogenic determination gene, MyoD1, was transfected into the human osteogenic sarcoma cell line TE85. Several stably transfected clones were isolated which, at low frequencies, formed multinucleated cells with the appearance of skeletal myotubes. Southern blot analysis confirmed the integration of multiple copies of the mouse MyoD1 gene, and Northern analysis and immunofluorescence confirmed its expression in the transfectants. Characterization of the transfectants showed that they expressed immunologically detectable myosin, desmin, mRNA for myogenin, and the delta subunit of the acetylcholine receptor. The cells assembled a functional contractile apparatus since they contracted in response to acetylcholine added to the culture medium. The presence of MyoD1 protein did not abrogate the expression of two genes active in bone cells but not in muscle cells. The transfected cells therefore displayed a chimeric phenotype by expressing simultaneously bone and muscle genes. Interestingly, treatment of the MyoD1 transfected cells with 5-aza-2'-deoxycytidine resulted in a substantial increase in the frequency of myogenic conversion. Thus, the methylation inhibitor increased the ability of MyoD1 to function as a trans-acting factor and activate the muscle phenotype.