Vasoactive intestinal peptide stimulates turkey prolactin gene expression by increasing transcription rate and enhancing mRNA stability

This study evaluates the transcriptional and post-transcriptional regulatio n of prolactin (PRL) by vasoactive intestinal peptide (VIP). Pituitary nucl ei from laying (control), incubating (with enhanced VIP secretion), and VIP -immunized laying turkey hens, and from pituitary cells cultured with or wi thout VIP were used in nuclear run-on transcription assays. Cytoplasmic PRL mRNA was analyzed by slot blot hybridization. PRL transcription was greate r in hyperprolactinemic incubating birds (PRL/beta-actin=3.33) than in layi ng birds (PRL/beta-actin=1.83). VIP-immunoneutralized birds had 47% and 51% decreases in PRL transcription and cytoplasmic PRL mRNA, respectively when compared with laying birds. In primary pituitary cell cultures, VIP signif icantly increased the transcription rate of PRL (3.8-fold) and cytoplasmic PRL mRNA (3.2-fold) compared with that of non-VIP-treated pituitary cells. The stability of pre-existing PRL mRNA was measured by Northern blot analys is after addition of actinomycin D. PRL mRNA half-lives were calculated usi ng a two-component model, with a first-long component of 18.0 +/- 1.0 h and a second-short component of 3.7 +/- 0.7 h in non-VIP-treated pituitary cel ls. Both half-lives were significantly increased (53.2 +/- 6.9 and 26.3 +/- 4.3 h) in VIP-treated cells. The present data show that VIP acts to stimul ate PRL expression by up-regulating the transcription rate of PRL and by en hancing PRL mRNA stability.