Regulation of Na/K-ATPase β1-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-ATPase alpha (3) subunit, in cultured neonatal rat cardiac myocytes. The aim of this work was to determine whether ouabain and other hypertrophic stimuli affect Na/K-ATPase beta (1) subunit gene expression. When myocytes were exposed to non-toxic concentrations of ouabain, ouabain increased beta (1) subunit 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 stimuli 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 directed by the 5'-flanking region of the beta (1) subunit gene, transient transfection assay showed that ouabain augmented the expression of luciferase. These data support the proposition that ouabain regulates the beta (1) subunit through a transcriptional mechanism. The effect of ouabain on beta (1) subunit induction, like that on alpha (3) repression, was dependent on extracellular Ca2+ and on calmodulin. Inhibitions of PKC, Ras, and MEK, however, had different quantitive effects on ouabain-induced regulations of beta (1) and alpha (3) subunits. The findings show that partial inhibition of Na/K-ATPase activates multiple signaling pathways that regulate growth-related genes, including those of two subunit isoforms of Na/K-ATPase, in a gene-specific manner.