Kirtane A, Ismail-Beigi N, Ismail-Beigi F
Department of Medicine, College of Physicians and Surgeons, Columbia University, New York, New York 10032.
J Membr Biol. 1994 Jan;137(1):9-15. doi: 10.1007/BF00234994.
The role of enhanced Na+ entry in the induction of Na,K-ATPase subunit mRNAs by serum was investigated in a "nontransformed" rat liver cell line, Clone 9. Exposure of cells to 10% calf serum resulted in a 1.5-fold increase in the rate of Na+ entry associated with a transient rise in cell Na+ content (twofold at 15 min) and a sustained 1.15-fold rise in cell K+ content. After 6 hr of exposure to serum mRNA alpha 1 and mRNA beta 1 content increased by 1.8- and 2.6-fold, respectively. In nuclear run-on assays, serum stimulated the transcription of the alpha 1 gene approximately 1.9-fold while the transcription rate of the beta 1 gene remained unchanged. In cells incubated in Na(+)-free medium where NaCl was replaced by choline chloride, the induction of mRNA alpha 1 by serum was fully preserved, whereas the increase in mRNA beta 1 was prevented. An unexpected finding was that incubation of cells in Na(+)-free medium alone for 6 hr increased mRNA alpha 1 but not mRNA beta 1 content. These results indicate that Na,K-ATPase subunit mRNAs are differentially induced by serum, and that the induction of mRNA alpha 1, in contrast to that of mRNA beta 1, is transcriptionally mediated and does not require the presence of Na+ in the extracellular medium.
在一种“未转化”的大鼠肝细胞系Clone 9中，研究了增强的钠离子内流在血清诱导钠钾ATP酶亚基mRNA中的作用。将细胞暴露于10%小牛血清中，导致钠离子内流速率增加1.5倍，同时细胞内钠离子含量短暂升高（15分钟时为两倍），细胞内钾离子含量持续升高1.15倍。暴露于血清6小时后，α1 mRNA和β1 mRNA含量分别增加了1.8倍和2.6倍。在核转录分析中，血清刺激α1基因的转录约1.9倍，而β1基因的转录速率保持不变。在无钠培养基（用氯化胆碱代替氯化钠）中培养的细胞中，血清对α1 mRNA的诱导作用完全保留，而β1 mRNA的增加则受到抑制。一个意外的发现是，仅在无钠培养基中培养细胞6小时会增加α1 mRNA但不会增加β1 mRNA的含量。这些结果表明，血清对钠钾ATP酶亚基mRNA的诱导存在差异，与β1 mRNA不同，α1 mRNA的诱导是由转录介导的，并且不需要细胞外培养基中存在钠离子。
