Estrogen regulates the serum level of phosphorylated prolactin in mice

Molecular form identification of anterior pituitary gland-secreted prolactin in chicken

Endocrine changes during bird reproduction are well documented. Prolactin (PRL) exhibits a strong relationship between incubation and broody behavior. The molecular forms of PRL in the anterior pituitary gland during the reproductive cycle have already been previously identified but not those in the secreted form. To identify the molecular forms of secreted PRL during the reproductive cycle, we thus monitored the physiological status and incubation behavior of 10 Silkie hens by a video recording system over 1-2 years. Nine out of ten mature hens exhibited incubation behavior multiple times during the experiment. Ten hens demonstrated two interesting features. In a typical clutch, hens spent 10-15 min in the nest to lay an egg. Once they spent over 1 h in the nest, the nest occupancy increased incrementally. This shift in the nest occupancy occurred 7-10 days before the incubation onset and was highly repeatable. Based on the behavior of the hens, we cultured the anterior pituitary gland during four stages (premature non-laying, laying, trans, and incubation) with physiological PRL-releasing factor, vasoactive intestinal peptide (VIP). Based on our two-dimensional protein analysis, glycosylated PRL (G-PRL) displayed several isoforms with varying isoelectric points (pI), whereas we could detect one primary signal for non-glycosylated PRL (NG-PRL). However, 3-4 NG-PRL isoforms were detected in the anterior pituitary gland. These results suggested that secreted PRL, especially from the trans and incubation stages, contains various isoforms and it is post-translationally glycosylated and phosphorylated.

Estradiol-induced neurogenesis in the female accessory olfactory bulb is required for the learning of the male odor

Odors processed by the main and accessory olfactory bulbs (MOB, AOB) are important for sexual behavior. Interestingly, both structures continue to receive new neurons during adulthood. A role for olfactory neurogenesis in sexual behavior in female mice has recently been shown and gonadal hormones such as estradiol can modulate adult neurogenesis. Therefore, we wanted to determine the role of estradiol in learning the odors of sexual partners and in the adult neurogenesis of female aromatase knockout mice (ArKO), unable to produce estradiol. Female wild-type (WT) and ArKO mice were exposed to male odors during 7 days, and olfactory preferences, cell proliferation, cell survival and functional involvement of newborn neurons were analyzed, using BrdU injections, in combination with a marker of cell activation (Zif268) and neuronal fate (doublecortin, NeuN). Behavioral tasks indicated that both WT and ArKO females were able to discriminate between the odors of two different males, but ArKO mice failed to learn the familiar male odor. Proliferation of newborn cells was reduced in ArKO mice only in the dentate gyrus of the hippocampus. Olfactory exposure decreased cell survival in the AOB in WT females, suggesting a role for estradiol in a structure involved in sexual behavior. Finally, newborn neurons do not seem to be functionally involved in the AOB of ArKO mice compared with WT, when females were exposed to the odor of a familiar male, suggesting that estradiol-induced neurogenesis in the AOB is required for the learning of the male odor in female mice. Aromatase knockout mice (ArKO) presented deficits in olfactory preferences without affecting their olfactory discrimination abilities, and showed no functional involvement of newborn neurons in the accessory olfactory bulb (AOB) in response to the odor of a familiar male. These results suggest that estradiol-induced neurogenesis in the female AOB is required for the learning of the male odor.

From bench to bedside: future potential for the translation of prolactin inhibitors as breast cancer therapeutics

A role for prolactin (PRL) in the pathogenesis of breast cancer has been confirmed at the cellular level in vitro, with multiple transgenic and knockout models in vivo, and within sizable patient populations through epidemiologic analysis. It is the obvious "next step" that these findings are translated into meaningful therapies to block PRL/PRLr function in human breast cancer. Several broad categories of PRL/PRLr antagonists are discussed in their pre-clinical context, including inhibitors of endocrine PRL elaboration, mutant ligand antagonists, ligand chimeras, and inhibitors of PRL-induced signaling and transactivation. The clinical potential for GHr antagonists are also discussed. These varied approaches all have demonstrated as proof-of-principle that PRL/PRLr antagonism can inhibit the in vitro and in vivo growth of breast cancer. Further pre-clinical development is required for most, however, before translation to clinical trials in breast cancer patients can occur.

Paradigm-shifters: phosphorylated prolactin and short prolactin receptors

Since the discovery of physiologically-regulated prolactin (PRL) phosphorylation, one focus of the laboratory has been an examination of the different functions of the unmodified and phosphorylated hormone. In the mammary gland, unmodified PRL promotes growth activities, whereas phosphorylated or pseudophosphorylated PRL antagonizes this while also being a superior agonist for changes that favor differentiation. Phosphorylated PRL also increases expression of the short forms of the PRL receptor. These short forms of the receptor have functions beyond the accepted dominant negative and in mammary epithelial cells are capable of generating an intracellular signal leading to increased tight junction formation and beta-casein expression.

S179D prolactin: antagonistic agony!

The aims of this review are three-fold: first, to collate what is known about the production and activities of phosphorylated prolactin (PRL), the latter largely, but not exclusively, as illustrated through the use of the molecular mimic, S179D PRL; second, to apply this and related knowledge to produce an updated model of prolactin-receptor interactions that may apply to other members of this cytokine super-family; and third, to promote a shift in the current paradigm for the development of clinically important growth antagonists. This third aim explains the title since, based on results with S179D PRL, it is proposed that agents which signal to antagonistic ends may be better therapeutics than pure antagonists-hence antagonistic agony. Since S179D PRL is not a pure antagonist, we have proposed the term selective prolactin receptor modulator (SPeRM) for this and like molecules.