Involvement of upstream open reading frames in regulation of rat V1b vasopressin
receptor expression.
Nomura, Atsushi, Yasumasa Iwasaki, Masayuki Saito, Yoshiaki Aoki, Etsuko Yamamori,
Nobuaki Ozaki, Kazushige Tachikawa, Noriko Mutsuga, Minako Morishita, Masanori
Yoshida, Masato Asai, Yutaka Oiso, and Hidehiko Saito.
1First Department of Internal Medicine and 2Department of Clinical Laboratory
Medicine, Nagoya University School of Medicine and Hospital, Nagoya
466«hyphen»8560; and 3Molecular Medicine Research Laboratories, Yamanouchi
Institute for Drug Discovery Research, Tsukuba 305«hyphen»0841, Japan
APStracts 8:0025E, 2001.
The V1b vasopressin receptor, expressed mainly in the corticotroph of the anterior
pituitary, mediates the stimulatory effect of vasopressin on ACTH release. To clarify the
regulation of receptor expression, we cloned, sequenced (up to ~5 kb from the translation
start site), and characterized the 5'-flanking region of the rat V1b receptor gene. We
identified the transcription start site by amplification of cDNA ends and found a new
intron within the 5'-untranslated region (5'-UTR) by comparing the sequence with that of
cDNA. We then confirmed that the obtained promoter indeed has transcriptional activity
by use of the luciferase reporter in AtT-20 mouse corticotroph cells. Interestingly, there
were five short upstream open reading frames (uORFs) located within the 5'-UTR that
were found to suppress V1b expression. Subsequent mutational analyses showed that the
two downstream uORFs have an inhibitory effect on expression in both homologous and
heterologous contexts. Furthermore, the inhibition did not accompany a parallel decrease
in mRNA, suggesting that the suppressive effect occurs at a level downstream of
transcription. Taken together, our data strongly suggest that the expression of the V1b
receptor is regulated at the posttranscriptional as well as transcriptional level through
uORFs within the 5'-UTR region of the mRNA. Whether the uORF-mediated regulation
of V1b expression is functionally linked to any intracellular and/or extracellular factor(s)
awaits further research.
Received 8 June 2000; accepted in final form 22 January 2001
APS Manuscript Number E250-0.
Article publication pending Am J Physiol Endocrinol Metab
ISSN 1080-4757 Copyright 2001 The American Physiological Society.
Published in APStracts on 27 February 2001