The regulation of mammary prolactin receptor metabolism by a retroviral envelope protein

Abstract

In a previous study, infection with the mouse mammary tumor virus (MMTV) was shown to increase the sensitivity of the mammary epithelium toward prolactin (PRL); furthermore, this effect could be mimicked by the binding of the MMTV envelope protein (gp52) to its cell receptor. The present work has investigated the possibility that gp52-induced changes in the PRL receptor (PRLR) were responsible for this phenomenon. In vitro, gp52 doubled the PRLR concentration in the plasmalemma of mammary epithelium without affecting the affinity. The origins of these PRLRs were twofold: first, gp52 stimulated PRLR mRNA nearly fivefold, suggesting that some of the receptors were newly synthesized. Second, there was a redistribution of PRLRs within the mammary cell: PRLRs were shifted from an internal pool to the plasma membrane. This relocation was very rapid, occurring within 30 min. There did not appear to be any contribution from alterations in PRLR degradation, since the half-life of PRLR was not affected by gp52. In summary, the MMTV increases the PRL sensitivity of mouse mammary epithelium by elevating PRLRs through both enhanced synthesis and recruitment from microsomes.

Rapid hormonal regulation of N-acetylglucosamine transferase I

“…Previous studies have shown that long-term upregulation is a result of increased transcription of the receptor gene (Bolander et al 1997); however, there is also a rapid component that is independent of gene expression. This acute phase is caused by a redistribution of prolactin receptors from a substantial intracellular reservoir to the cell surface.…”

Effects of Pup Separation on Stress Response in Postpartum Female Rats

“…The hyperprolactinemia that occurs during lactation is due to the neural stimulus of suckling and inhibitory regulation of dopaminergic neurons [ 12 , 47 ], an acutely regulated process. The half-life for mRNA is approximately three hours [ 48 ], therefore, one hour of pup separation was not enough time for CNS PRL-R mRNA levels to return to the pre-pregnancy state. After 24 h or eight days of separation, however, PRL-R mRNA levels were reduced and then returned to the pre-pregnancy state eight days after lactation was terminated.…”