V3 VASOPRESSIN RECEPTOR AND CORTICOTROPIC PHENOTYPE IN PITUITARY AND NON PITUITARY-TUMORS

Pituitary corticotropic cells express a specific vasopressin receptor, called V1b or V3, through which vasopressin stimulates corticotropin secretion. We recently cloned a cDNA coding for this receptor and show ed that it belongs to the G protein-coupled receptor family. V3 mRNA i s readily detected by RT-PCR in normal human pituitaries and corticotr opic pituitary adenomas but not in PRL or GH-secreting adenomas, thus demonstrating that, like POMC itself and the CRH receptor, V3 is a mar ker of the corticotropic phenotype. Nuclease protection experiments su ggest that V3 is overexpressed in some corticotropic adenomas, and thu s may play a role in tumor development by activating the phospholipase C-signalling pathway. In addition analysis of its expression in nonpi tuitary neuroendocrine tumors showed a striking association with carci noids of the lung responsible for the ectopic ACTH syndrome.