The E Box Is Essential for Activity of the Cardiac Actin Promoter in Skeletal but Not in Cardiac Muscle

Abstract

The sequence CANNTG (E box) is frequently found in the promoters of muscle-specific genes and binds members of the basic helix-loop-helix (bHLH) family of transcription factors. We compared the need for the E box in the expression of a muscle-specific promoter normally expressed in both cardiac and skeletal muscle. The E box was mutated in a construct of the cardiac α-actin promoter driving the Escherichia coli lacZ gene. The wild-type and mutant constructs were transfected and stably integrated into the genomes of P19 embryonal carcinoma cells. The wild-type promoter was expressed in both cardiac and skeletal myocytes. The promoter lacking an E box was expressed in cardiac but not in skeletal muscle. Neither promoter was active in nonmuscle cells. Thus the E box is not necessary for the cardiac actin promoter activity in P19-derived cardiac muscle but is essential for its activity in skeletal muscle. This result is consistent with our inability to detect cardiac muscle-specific members of the MyoD family of bHLH transcription factors.