Regulation of the myoblast-specific expression of the human beta-enolase gene.

The muscle-specific beta-enolase gene is expressed in proliferating adult myoblasts as well as in differentiated myotubes. Through deletion-transfection analysis, we identified a 79-base pair enhancer from the beta-enolase gene that leads to high level expression of a reporter gene in myoblasts, but not in fibroblasts. Following myoblast differentiation into myotubes, the activity of the enhancer declined, indicating that beta-enolase gene expression in myotubes is mediated by other regulators, possibly the myogenic helix-loop-helix family of transcription factors. Electrophoretic mobility shift assays indicated that proteins present in myoblast nuclear extracts specifically bind to the 3' half of the 79-base pair enhancer. This region contains an ets DNA-binding motif which is required not only for high level activity in myoblasts, but also for repressing activity in fibroblasts. Furthermore, the beta-enolase myoblast-specific enhancer shows limited similarity to the myoblast-specific enhancer associated with the human desmin gene, suggesting that gene expression in adult myoblasts may be coordinately regulated.