Cloning and expression of a unique short form of the porcine prolactin receptor.

Abstract

Prolactin (PRL) is required not only for maintenance of gestation in pigs but also for mammary gland development and subsequent lactogenesis. The actions of PRL are modulated by both long and short isoforms of the PRL receptor (PRLR), where short isoforms can interfere with the essential signaling function of the long isoform. Using 3' RACE we have isolated a unique splice variant of the porcine PRLR (pPRLR) that contains a short intracellular domain of 38 aa that is encoded by splicing from exon 9 to a novel exon 11 located 17.5 kb downstream of exon 10 on chromosome 16. The short pPRLR was detected as a 42 kDa protein in membranes from porcine mammary glands. Functional analyses indicated that the short pPRLR functions as a dominant negative against the differentiative function of the long pPRLR and does not transduce a signal to the rat β-casein promoter. Differential abundance of long pPRLR and short pPRLR mRNA was established in a range of porcine tissues. The binding affinity of the short pPRLR for pPRL was lower (K(d) = 3.7 nM) than the affinity of the long pPRLR (K(d) = 1.6 nM) despite a fourfold higher level of binding sites for the short pPRLR. Our data raise the possibility that the short pPRLR in pigs may function independently from the long pPRLR, where the splicing strategy used to generate the short pPRLR likely evolved under different selection pressures to those acting on the long pPRLR.