Regulation of Na,K-ATPase gene expression by thyroid hormone in rat cardiocytes.
Synthesis and activity of the enzymatic equivalent of the sodium pump, Na,K-ATPase, are regulated by thyroid hormone in responsive tissues. The purpose of this study was to determine whether triiodothyronine (T3) regulates the level of the messenger RNA (mRNA) coding for Na,K-ATPase alpha- and beta-subunits in the heart. The expression of Na,K-ATPase mRNAs in in vitro myocardial cells was directly assayed by Northern and slot blot hybridization using Na,K-ATPase alpha- and beta-isoform-specific cDNA probes. Exposure of cultured neonatal rat cardiocytes to 10(-8) M T3 resulted in 1) threefold to fourfold increase in alpha 1- and beta 1-mRNA accumulation, with a maximum elevation at 48 hours, 2) sevenfold increase in alpha 2-mRNA accumulation with a peak elevation at 72 hours, and 3) transient threefold increase in alpha 3-mRNA within the first 24 hours followed by a deinduction thereafter. The increase in alpha 1-mRNA accumulation by T3 occurred over the physiological T3 concentration range with an EC50 of 5 x 10(-10) M. This was associated with a twofold increase in alpha 1-subunit protein accumulation and an increase in Na,K-ATPase transport activity. The half-life of alpha 1-mRNA analyzed by actinomycin D chase was less than 3 hours and was not affected by T3. Transfection experiments with the luciferase reporter gene revealed that thyroid hormone response sequences are located within the 5'-flanking regions of each alpha-isoform gene.(ABSTRACT TRUNCATED AT 250 WORDS)
Kamitani
T
T
Department of Cardiology, Jichi Medical School, Tochigi, Japan.
Ikeda
U
U
Muto
S
S
Kawakami
K
K
Nagano
K
K
Tsuruya
Y
Y
Oguchi
A
A
Yamamoto
K
K
Hara
Y
Y
Kojima
T
T
D000818:Animals; D015152:Blotting, Northern; D002478:Cells, Cultured; D005434:Flow Cytometry; D005453:Fluorescence; D015971:Gene Expression Regulation, Enzymologic; D006321:Heart / Q000187:drug effects; D008156:Luciferases / Q000235:genetics; D009206:Myocardium / Q000166:cytology / Q000201:enzymology*; D012333:RNA, Messenger / Q000235:genetics; D051381:Rats; D017207:Rats, Sprague-Dawley; D000254:Sodium-Potassium-Exchanging ATPase / Q000235:genetics*; D013963:Thyroid Hormones / Q000502:physiology*; D014162:Transfection; D014284:Triiodothyronine / Q000494:pharmacology / Q000502:physiology
D012333:RNA, Messenger; D013963:Thyroid Hormones; D014284:Triiodothyronine; D008156:Luciferases; D000254:Sodium-Potassium-Exchanging ATPase