Regulation of Na/K-ATPase beta 1-subunit gene expression by ouabain and other hypertrophic stimuli in neonatal rat cardiac myocytes

Partial inhibition of Na/K-ATPase by ouabain causes hypertrophic growth and regulates several early and late response genes, including that of Na/K-AT Pase alpha (3) subunit, in cultured neonatal rat cardiac myocytes. The aim of this work was to determine whether ouabain and other hypertrophic stimul i affect Na/K-ATPase beta (1) subunit gene expression. When myocytes were e xposed to non-toxic concentrations of ouabain, ouabain increased beta (1) s ubunit mRNA in a dose- and time-dependent manner. Like the alpha (3) gene, beta (1) mRNA was also regulated by several other well-known hypertrophic s timuli including phenylephrine, a phorbol ester, endothelin-1, and insulin- like growth factor, suggesting involvement of growth signals in regulation of beta (1) expression. Ouabain failed to increase beta (1) subunit mRNA in the presence of actinomycin D. Using a luciferase reporter gene that is di rected by the 5'-flanking region of the beta (1) subunit gene, transient tr ansfection assay showed that ouabain augmented the expression of luciferase . These data support the proposition that ouabain regulates the beta (1) su bunit through a transcriptional mechanism. The effect of ouabain on beta (1 ) subunit induction, like that on alpha (3) repression, was dependent on ex tracellular Ca2+ and on calmodulin. Inhibitions of PKC, Ras, and MEK, howev er, had different quantitive effects on ouabain-induced regulations of beta (1) and alpha (3) subunits. The findings show that partial inhibition of N a/K-ATPase activates multiple signaling pathways that regulate growth-relat ed genes, including those of two subunit isoforms of Na/K-ATPase, in a gene -specific manner.