Na,K-ATPase mRNA beta 1 expression in rat myocardium--effect of thyroid status.
The abundance of Na,K-ATPase and its alpha and beta subunit mRNAs is upregulated in cardiac and other target tissue by thyroid hormone (T3). Multiple Na,K-ATPase mRNA beta 1 species encoding an identical beta 1 polypeptide are expressed in the heart. The different mRNA beta 1 species result from utilization of two transcription start-sites in the first exon and multiple (five) poly(A) signals in the terminal exon of the beta 1 gene. In the present study we identify the mRNA beta 1 species that are expressed in rat ventricular myocardium under basal conditions, and determine whether they are differentially regulated by T3. mRNA beta 1 species were identified by 3'-RACE followed by DNA sequencing, and by Northern blotting using probes derived from different regions of rat cDNA beta 1. Five mRNA beta 1 species are expressed in rat heart: mRNA beta 1 species that are initiated at the first transcription start-site and end at the first, second and fifth poly(A) sites (resulting in mRNAs of 1630, 1810, and 2780 nucleotides), and mRNA beta 1 species initiated at the second transcription start-site and ending at the second and fifth poly(A) sites (resulting in mRNAs of 1500 and 2490 nucleotides); in order of increasing length, the five mRNAs constitute 0.04, 0.15, 0.38, 0.11 and 0.32 of total mRNA beta 1 content. In hypothyroid rats (induced by addition of propyl-thiouracil to the drinking water for 3 weeks), total mRNA beta 1 content decreased to 0.18 euthyroid levels, which was associated with a disproportionate 7.5-fold decrease in the abundance of the longest transcript (P < 0.05); transcripts initiating at the first transcription start-site and ending at the second poly(A) signal in hypothyroid hearts were 0.26 euthyroid levels (P < 0.05). Hyperthyroidism induced by injection of normal rats with three doses of 100 micrograms T3/100 g body weight every 48 h resulted in an overall approximately 2-fold increase in mRNA beta 1 content with no change in the fractional contribution of any of the mRNA beta 1 species. The results indicate a complex heterogeneity in the expression of mRNA beta 1 in myocardium.
Shao
Y
Y
Department of Medicine, Case Western Reserve University, Cleveland, OH 44106-4951, USA.
Pressley
T A
TA
Ismail-Beigi
F
F
D000818:Animals; D001483:Base Sequence; D015152:Blotting, Northern; D005786:Gene Expression Regulation / Q000235:genetics*; D006980:Hyperthyroidism / Q000378:metabolism; D007037:Hypothyroidism / Q000378:metabolism; D008297:Male; D008969:Molecular Sequence Data; D009206:Myocardium / Q000378:metabolism*; D011441:Propylthiouracil / Q000494:pharmacology; D012333:RNA, Messenger / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D016415:Sequence Alignment; D000254:Sodium-Potassium-Exchanging ATPase / Q000235:genetics*; D013961:Thyroid Gland / Q000378:metabolism; D014158:Transcription, Genetic / Q000235:genetics; D014284:Triiodothyronine / Q000378:metabolism*
D012333:RNA, Messenger; D014284:Triiodothyronine; D011441:Propylthiouracil; D000254:Sodium-Potassium-Exchanging ATPase