Characterization of the RDC1 gene which encodes the canine omolog of a proposed human VIP receptor Expression does not correlate with an increase in VIP binding sites

Abstract
We have isolated a portion of the canine gene encoding the orphan receptor RDC1 [1]. The complete coding sequence is contained in a single exon, and an intron divides the 5′ untranslated region of RDC1 mRNA. The RDC1 protein is 94% homologous to the gene product of GPRN1, which has been proposed to serve as a VIP receptor when expressed in CHO‐K1 and COS‐7 cells (Sreedharan, S.P. et al. (1991) Proc. Natl. Acad. Sci. USA 88, 4986–4990). Northern analysis indicates that CHO‐K1 cells endogenously express a 2.1 kb RDC1 mRNA. However, while CHO‐K1 cells possess detectable low affinity [125I]VIP binding sites, VIP binding is not altered in membranes of CHO‐K1 cells expressing varying amounts of the RDC1 gene construct. Further, endogenous VIP binding is not increased by transient expression of RDC1 in COS‐7 cells. Taken together, the data suggest that RDC1 is not a canine homolog of the proposed VIP receptor.