AJP - Cell Physiology, Vol 258, Issue 3 C544-C551, Copyright © 1990 by American Physiological Society
Thyroid hormone induction of Na(+)-K(+)-ATPase and its mRNAs in a rat liver cell line
G. G. Gick and F. Ismail-Beigi
Department of Biochemistry, Columbia University, College of Physicians and Surgeons, New York, New York 10032.
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)
