Thyroid hormone induction of Na(+)-K(+)-ATPase and its mRNAs in a rat liver cell line.
The expression of mRNAs encoding the alpha- and beta-subunits of Na(+)-K(+)-ATPase (Na(+)-K+ pump) was examined in a rat liver cell line, Clone 9, in various thyroidal states. Northern blot analysis of total RNA isolated from cells incubated in hypothyroid serum-containing medium revealed the expression of mRNAs encoding Na(+)-K(+)-ATPase alpha 1-(mRNA alpha 1) and beta- (mRNA beta) subunits; mRNAs encoding the alpha 2- and alpha 3-subunits were undetectable. There was a discrepancy in the abundance of mRNA alpha 1 relative to mRNA beta such that mRNA alpha 1 exceeded the sum of the multiple mRNA beta bands by approximately 35-fold. 3,3',5-Triiodothyronine (T3) produced a coordinate augmentation of mRNA alpha 1 and mRNA beta contents that was demonstrable within 2 h and preceded the stimulation of Na(+)-K(+)-ATPase activity. After incubation of cells with T3 for 48 h, Na(+)-K(+)-ATPase activity was stimulated by 1.32-fold, whereas mRNA alpha 1 and mRNA beta abundances were increased 1.46- and 2.87-fold, respectively. Treatment of cells for 6 h with 10 micrograms/ml cycloheximide, a concentration sufficient to inhibit protein synthesis by 95%, elicited a 3.5- and 5.1-fold increase in mRNA alpha 1 and mRNA beta content, respectively. Cycloheximide abrogated the stimulatory effect of T3 on mRNA beta abundance, whereas the T3-induced increase in mRNA alpha 1 content was not prevented.(ABSTRACT TRUNCATED AT 250 WORDS)
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Department of Biochemistry, Columbia University, College of Physicians and Surgeons, New York, New York 10032.
Ismail-Beigi
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D000818:Animals; D002460:Cell Line; D002999:Clone Cells; D003513:Cycloheximide / Q000494:pharmacology; D007700:Kinetics; D008099:Liver / Q000187:drug effects / Q000201:enzymology*; D014176:Protein Biosynthesis / Q000187:drug effects; D012333:RNA, Messenger / Q000096:biosynthesis / Q000187:drug effects / Q000235:genetics*; D051381:Rats; D000254:Sodium-Potassium-Exchanging ATPase / Q000096:biosynthesis* / Q000235:genetics / Q000378:metabolism; D014158:Transcription, Genetic / Q000187:drug effects; D014284:Triiodothyronine / Q000494:pharmacology*
D012333:RNA, Messenger; D014284:Triiodothyronine; D003513:Cycloheximide; D000254:Sodium-Potassium-Exchanging ATPase