Identification of the functional domain in the transcription factor RTEF-1that mediates alpha(1)-adrenergic signaling in hypertrophied cardiac myocytes

Cardiac myocytes respond to alpha(1)-adrenergic receptor stimulation by a p rogressive hypertrophy accompanied by the activation of many fetal genes, i ncluding skeletal muscle alpha-actin. The skeletal muscle alpha-actin gene is activated by signaling through an MCAT element, the binding site of the transcription enhancer factor-1 (TEF-1) family of transcription factors, Pr eviously, we showed that overexpression of the TEF-1-related factor (RTEF-1 ) increased the alpha(1)-adrenergic response of the skeletal muscle ru-acti n promoter, whereas TEF-1 overexpression did not. Here, we identified the f unctional domains and specific sequences in RTEF-1 that mediate the alpha(1 )-adrenergic response. Chimeric TEF-1 and RTEF-1 expression constructs loca lized the region responsible for the alpha(1)-adrenergic response to the ca rboxyl-terminal domain of RTEF-1, Site-directed mutagenesis was used to ina ctivate eight serine residues of RTEF-1, not present in TEF-1, that are put ative targets of alpha(1)-adrenergic-dependent kinases, Mutation of a singl e serine residue, Ser-322, reduced the alpha(1)-adrenergic activation of RT EF-1 by 70% without affecting protein stability, suggesting that phosphoryl ation at this serine residue accounts for most of the alpha(1)-adrenergic r esponse. Thus, these results demonstrate that RTEF-1 is a direct target of alpha(1)-adrenergic signaling in hypertrophied cardiac myocytes.