Huang L, Kometiani P, Xie Z
Department of Pharmacology, Medical College of Ohio, Toledo, Ohio, 43699-0008, USA.
J Mol Cell Cardiol. 1997 Nov;29(11):3157-67. doi: 10.1006/jmcc.1997.0546.
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 alpha1- and alpha3-isoform messages, were exposed to 5-100 micro M ouabain, alpha1 mRNA was not affected, but alpha3 mRNA was decreased in a dose- and time-dependent manner. Ouabain-induced down-regulation of alpha3 mRNA was accompanied by a decrease in alpha3-protein content in these myocytes. There was a significant correlation between ouabain effects on alpha3-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 alpha3 repression with ouabain-induced hypertrophy. Phenylephrine and a phorbol ester, two hypertrophic stimuli that do not inhibit Na/K-ATPase, also down-regulated alpha3 mRNA without affecting alpha1 mRNA, suggesting that alpha3-repression is a common feature of the hypertrophic phenotype in these myocytes. Ouabain-induced repression of alpha3 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 alpha3 by ouabain and other hypertrophic stimuli involves a common step regulated by a mitogen-activated protein kinase.
我们之前表明，无毒浓度的哇巴因对钠钾ATP酶的部分抑制会导致新生大鼠心肌细胞肥大生长，并诱导多种早期和晚期反应基因，这些基因是心肌肥大的标志物。本研究的目的是确定钠钾ATP酶α亚基同工型的基因是否在受哇巴因调控的基因之中；如果是，开始对调控这些基因的途径进行表征。当表达α1和α3同工型信息的新生心肌细胞暴露于5 - 100微摩尔的哇巴因时，α1 mRNA不受影响，但α3 mRNA以剂量和时间依赖性方式减少。哇巴因诱导的α3 mRNA下调伴随着这些心肌细胞中α3蛋白含量的降低。哇巴因对α3抑制和骨骼肌α - 肌动蛋白诱导的作用之间存在显著相关性；此外，维甲酸可拮抗哇巴因对这两个基因的转录作用。这些发现提示α3抑制与哇巴因诱导的肥大有关。去甲肾上腺素和佛波酯这两种不抑制钠钾ATP酶的肥大刺激物，也下调α3 mRNA而不影响α1 mRNA，表明α3抑制是这些心肌细胞肥大表型的一个共同特征。哇巴因诱导的α3抑制需要细胞外Ca2 +的内流，并被蛋白激酶C、Ca2 + - 钙调蛋白激酶和丝裂原活化蛋白激酶的抑制剂拮抗，但不受蛋白激酶A抑制的影响。这些数据以及之前关于去甲肾上腺素和佛波酯肥大作用机制的发现表明，哇巴因和其他肥大刺激物对α3的转录抑制涉及一个由丝裂原活化蛋白激酶调控的共同步骤。
