Adrenergic regulation of the skeletal alpha-actin gene promoter during myocardial cell hypertrophy.
The skeletal alpha-actin gene is expressed in fetal rat heart and is induced during norepinephrine (NE)-stimulated hypertrophy in cultures of neonatal rat cardiac myocytes. Here we report that NE positively regulates the human skeletal alpha-actin gene promoter in transiently transfected neonatal rat cardiac myocytes. NE increased expression from the full-length promoter by 2.4-fold. A DNA region required for NE responsiveness but not for tissue-specific expression was located between base pair -2000 and base pair -1300. Distinct regions required for cardiac myocyte expression were located between -1300 to -710 and -153 to -87. None of these elements separately conferred tissue specificity or adrenergic responsiveness on a heterologous promoter, although the intact promoter from -2000 to -36 conferred both when cloned in its correct position and orientation. Additional elements in the basal promoter (-87 to +187) were required for maximal NE responsiveness. The NE induction was mediated by the beta-adrenergic receptor in high-density cultures (3-4 x 10(6) cells per 60-mm dish), as was induction of hypertrophy, contractility, and endogenous skeletal alpha-actin gene expression. The beta-adrenergic agonist isoproterenol was as potent as NE in inducing expression. Furthermore, beta-adrenergic antagonists inhibited the effects on skeletal alpha-actin gene expression but alpha 1-adrenergic antagonists did not. The alpha 1-adrenergic system was intact in these high-density cultures, since the effects of NE on the expression of another contractile protein gene, alpha-myosin heavy chain, were blocked by alpha 1- but not by beta-adrenergic antagonists. In these high-density cultures, cell contact and intermyocardiocyte bridging were prevalent. When cardiac myocytes were plated at a low density, minimizing cell contact, NE induction of skeletal alpha-actin gene expression and hypertrophy was mediated by the alpha 1-adrenoceptor. Factors related to cell communication may influence the pathways mediating NE-regulated gene transcription during cardiac myocyte hypertrophy.
Bishopric
N H
NH
Department of Veterans Affairs Medical Center III-C, San Francisco, CA 94121.
Kedes
L
L
D000199:Actins / Q000235:genetics*; D000818:Animals; D000831:Animals, Newborn; D006332:Cardiomegaly / Q000378:metabolism; D002455:Cell Division / Q000187:drug effects; D002478:Cells, Cultured; D006321:Heart / Q000187:drug effects*; D006801:Humans; D009206:Myocardium / Q000166:cytology / Q000378:metabolism*; D009638:Norepinephrine / Q000494:pharmacology*; D011401:Promoter Regions, Genetic / Q000187:drug effects*; D051381:Rats; D014162:Transfection
D000199:Actins; D009638:Norepinephrine