PROLACTIN RECEPTOR HETEROGENEITY IN BOVINE FETAL AND MATERNAL TISSUES

Study of diverse PRL actions at a variety of fetal and maternal target s during pregnancy is complicated by receptor heterogeneity and multip le ligands circulating at this time. In the present studies, we have e xamined PRL receptors at a variety of potential targets by reverse tra nscription-PCR and Western analysis. Bovine tissues contain two differ ent transcripts for the PRL receptor; the one that encodes a short for m includes an additional 39 bases at a position identical to the devia tion from the long form found in rodents and sheep. Western analyses o f PRL receptors in microsomal fractions from various maternal and feta l tissues revealed considerable size heterogeneity. Collectively, the larger immunoreactive moieties (apparent M-r 100 kDa or greater) and t he smaller species (4755 kDa) correlated well with the relative abunda nce of the transcripts for the different forms of the receptor and var ied considerably among tissues. N-Glycosylation was shown to be the ma jor, but not the only, modification of both receptor forms when transi ently transfected into COS-7 and END-6.2 cells. Much of the short form could be reduced to the mobility predicted from the complementary DNA by culture with tunicamycin; this was not true of the long form, sugg esting modifications specific for its cytoplasmic domain. Differences in the pattern of immunoreactive species in the COS-7 and END-6.2 cell s are consistent with cell-specific modifications. The ability of thes e receptor forms to mediate a transcriptional response to PRL and its placental relative, placental lactogen, was evaluated with a PRL respo nse element inserted upstream from a thymidine kinase promoter/reporte r gene construct transiently transfected into CHO-K1 cells. Both hormo nes were able to stimulate reporter gene expression through the long f orm, but not the short form, of the receptor. These studies will facil itate examination of tissue-specific actions of PRL and related hormon es during pregnancy.