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Isolation and Characterization of the Promoter Region of the Rat Vasopressin V1b Receptor Gene

Regulation of pituitary vasopressin V1b receptors plays a critical role in regulating pituitary adrenocorticotropic hormone (ACTH) secretion during adaptation to stress. The objective of this study was to isolate the promoter regulatory region of the V1b receptor gene to better understand the molecular mechanisms involved in V1b receptor regulation. Screening of a rat genomic library using probes directed to the coding region and to the 5′UTR of the rat V1b receptor resulted in the isolation of several clones containing the 5′upstream regions of the V1b receptor cDNA. Sequencing of an 11.2 Kb fragment revealed 8.2 Kb upsteam of the reported cDNA sequence, which contains a putative promoter regulatory region. The 3′ end of the clone contained 1472 base pairs corresponding to the recognized cDNA sequence, followed by 1506 bp of unknown sequence located at the end of the sixth transmembrane domain, probably corresponding to an intron, characteristic of these family of receptors. An additional 161 bp intron was found in the 5′UTR, similar to that described in the rat oxytocin receptor gene. 5′RACE and RNase protection analysis mapped two major putative transcription start points at −830 and −861 bp from the starting methionine. Analysis of the putative promoter region showed no indication of a proximal TATA box, but the presence of a CACA box, a GAGA box, several AP‐1 and AP‐2 sites and a cluster of Sp1 sites upstream of the AP‐2 sites. A luciferase construct containing a 2.1‐kb of putative promoter, and part of the 5′UTR including the first intron, showed promoter activity when transfected into COS‐7, CHO and PC12 cell lines but not in AtT‐20 cells. A similar construct without the intron and distal 5′UTR sequence has no promoter activity in the same cell lines. In summary, the V1b receptor gene contains at least 3 exons and 2 introns. The 5′flanking sequence contains several potential sites for transcriptional regulation, and induced luciferace activity only in constructs containing intron 1, suggesting that the latter is important for receptor gene activation. The data provide bases for future analysis of the regulatory elements controlling V1b receptor transcription.