Differential regulation of Na/K-ATPase alpha-subunit isoform gene expressions in cardiac myocytes by ouabain and other hypertrophic stimuli

L. HUANG, P. KOMETIANI AND Z. XIE. Differential Regulation of Na/K-ATPase alpha-subunit Isoform Gene Expressions in Cardiac Myocytes by Ouabain and Other Hypertrophic Stimuli. Journal of Molecular and Cellular Cardiology (1997) 29, 3157-3167. We showed before that partial inhibition of Na/K-ATPase by non-toxic concentrations of ouabain caused hypertrophic growth of neonatal rat cardiac myocytes, and induced several early-and late-response genes that are markers of cardiac hypertrophy. The aim of this study was to determine if the genes of the alpha-subunit isoforms of Na/K-ATPase were among those regulated by ouabain; and if so, to begin the characterization of the pathways regulating these genes. When neonatal myocytes, expressing alpha(1)- and alpha(3)-isoform messages, were exposed to 5-100 mu M ouabain, alpha(1)mRNA was not affected, but alpha(3)mRNA was decreased in a dose- and time-dependent manner. Oubain-induced down-regulation of alpha(3)mRNA was accompanied by a decrease in alpha(3)-protein content in these myocytes. There was a significant correlation between ouabain effects on alpha(3)-repression and skeletal alpha-actin induction; also, ouabain's transcriptional effects on both genes were antagonised by retinoic acid. These findings suggested the association of alpha(3) repression with ouabain-induced hypertrophy. Phenylephrine and a phorbol ester, two hypertrophic stimuli that do not inhibit Na/K-ATPase, also down-regulated alpha(3)mRNA without affecting alpha(1)mRNA, suggesting that alpha(3)-repression is a common feature of the hypertrophic phenotype in these myocytes. Ouabain-induced repression of alpha(3) required the influx of extracellular Ca2+, and was antagonized by inhibitors of protein kinase C, Ca2+-calmodulin kinase, and mitogen-activated protein kinase but not by inhibition of protein kinase A. These data, and prior findings on the mechanisms of hypertrophic effects of phenylephrine and phorbol esters, suggest that transcriptional repression of alpha(3) by ouabain and other hypertrophic stimuli involves a common step regulated by a mitogen-activated protein kinase. (C) 1997 Academic Press Limited.