Divergent transcriptional enhancer factor-1 regulates the cardiac troponin T promoter

MCAT elements are essential for cardiac gene expression during development. Avian transcriptional enhancer factor- 1 ( TEF- 1) proteins are muscle- enriched and contribute to MCAT binding activities. However, direct activation of MCAT- driven promoters by TEF- 1-related proteins has not been uniformly achieved. Divergent TEF ( DTEF)- 1 is a unique member of the TEF- 1 multigene family with abundant transcripts in the heart but not in skeletal muscle. Herein we show that DTEF- 1 proteins are highly expressed in the heart. Protein expression is activated at very early stages of chick embryogenesis ( Hamburger- Hamilton stage 4, 16 - 18 h), after which DTEF- 1 becomes abundant in the sinus venosus and is expressed in the trabeculated ventricular myocardium and ventricular outflow tracts. By chromatin immunoprecipitation, DTEF- 1 interacts with the cardiac troponin T ( cTnT) promoter in vivo. DTEF- 1 also interacts with MEF-2 by coimmunoprecipitation and independently or cooperatively ( with MEF- 2) trans- activates the cTnT promoter. DTEF- 1 isoforms do not activate the cTnT promoter in fibroblasts or skeletal muscle. DTEF- 1 expression occurs very early in chick embryogenesis ( 16 - 18 h), preceding sarcomeric protein expression, and it activates cardiac promoters. As such, DTEF- 1 may be an early marker of the myocardial phenotype. DTEF- 1 trans- activates the cTnT promoter in a tissue- specific fashion independent of AT- rich, MEF- 2, or GATA sites. The observed spatial pattern suggests decreasing levels of expression from the cardiac inlet to the ventricular outflow tracts, which may mark a cardiogenic or differentiation pathway that parallels the direction of flow through the developing chick heart.