G protein-coupled receptors as targets for prolactin actions

Impact of Macroprolactinemia on Cardiometabolic Effects of Atorvastatin in Women With Hypercholesterolemia

Premenopausal women with macroprolactinemia are characterized by increased cardiometabolic risk. No previous study has investigated the impact of any lipid-lowering agent on circulating levels of cardiometabolic risk factors in patients with elevated macroprolactin content. We studied 2 groups of women matched for age, body mass index, plasma lipids, and blood pressure: 12 women with macroprolactinemia and 14 women with prolactin levels within the reference range. Because of coexistent isolated hypercholesterolemia, all subjects were then treated with atorvastatin (20 mg daily). Glucose homeostasis markers, plasma lipids, as well as circulating levels of uric acid, high-sensitivity C-reactive protein (hsCRP), fibrinogen, homocysteine, and 25-hydroxyvitamin D were measured before entering the study and 6 months later. The treatment arms differed in baseline values of hsCRP and 25-hydroxyvitamin D, as well as in insulin sensitivity. Atorvastatin decreased total and low-density lipoprotein cholesterol levels stronger in women without than in women with macroprolactinemia. In normoprolactinemic women, atorvastatin decreased circulating levels of uric acid, hsCRP, fibrinogen, homocysteine, and increased concentrations of 25-hydroxyvitamin D, whereas in women with macroprolactinemia the drug decreased levels of hsCRP and homocysteine, as well as impaired insulin sensitivity. Both study groups differed in post-treatment insulin sensitivity and post-treatment values of prolactin before polyethylene glycol precipitation, macroprolactin, total cholesterol, low-density lipoprotein cholesterol, glycated hemoglobin, uric acid, hsCRP, fibrinogen, homocysteine, and 25-hydroxyvitamin D. In conclusion, the obtained results suggest that macroprolactinemia may attenuate cardiometabolic effects of atorvastatin.

AG and UAG induce β-casein expression via activation of ERK1/2 and AKT pathways

The ghrelin peptides were found to circulate in two major forms: acylated ghrelin (AG) and unacylated ghrelin (UAG). Previous studies showed that AG regulates β-casein (CSN2) expression in mammary epithelial cells. However, little is known about the mechanisms by which AG regulates CSN2 gene and protein expression. Evidence suggests that UAG has biological activity through GHSR1a-independent mechanisms. Here, we investigated the possible GHSR1a-mediated effect of UAG on the expression of CSN2 in primary bovine mammary epithelial cells (pbMECs) isolated from lactating cow. We found that both AG and UAG increase the expression of CSN2 in a dose-dependent manner in pbMECs in comparison with the control group. Increased expression of CSN2 was blocked by [D-Lys3]-GHRP-6 (an antagonist of the GHSR1a) and NF449 (a Gs-α subunit inhibitor) in pbMECs. In addition, both AG and UAG activated AKT/protein kinase B (AKT) and extracellular signal-regulated kinase 1/2 (ERK1/2) pathways, whereas [D-Lys3]-GHRP-6 and NF449 inhibited the phosphorylation of AKT and ERK1/2 in pbMECs respectively. Blockade of ERK1/2 and AKT signaling pathways prevented the expression of CSN2 induced by AG or UAG. Finally, we found that both AG and UAG cause cell proliferation through identical signaling pathways. Taken together, these results demonstrate that both AG and UAG act on ERK1/2 and AKT signaling pathways to facilitate the expression of CSN2 in a GHSR1a-dependent manner.

Testosterone and prolactin regulation of metabolic genes and citrate metabolism of prostate epithelial cells

The control and alteration of key regulatory enzymes is a determinant of the reactions and pathways of intermediary metabolism in mammalian cells. An important mechanism in the metabolic control is the hormonal regulation of the genes associated with the transcription and the biosynthesis of these key enzymes. The secretory epithelial cells of the prostate gland of humans and other animals possess a unique citrate-related metabolic pathway regulated by testosterone and prolactin. This specialized hormone-regulated metabolic activity is responsible for the major prostate function of the production and secretion of extraordinarily high levels of citrate. The key regulatory enzymes directly associated with citrate production in the prostate cells are mitochondrial aspartate aminotransferase, pyruvate dehydrogenase, and mitochondrial aconitase. Testosterone and prolactin are involved in the regulation of the corresponding genes associated with these enzymes (which we refer to as "metabolic genes"). The regulatory regions of these genes contain the necessary response elements that confer the ability of both hormones to control gene transcription. In this report, we describe the role of protein kinase c (PKC) as the signaling pathway for the prolactin regulation of the metabolic genes in prostate cells. Testosterone and prolactin regulation of these metabolic genes (which are constitutively expressed in all mammalian cells) is specific for these citrate-producing cells. We hope that this review will provide a strong basis for future studies regarding the hormonal regulation of citrate-related intermediary metabolism. Most importantly, altered citrate metabolism is a persistent distinguishing characteristic (decreased citrate production) of prostate cancer (PCa) and also (increased citrate production) of benign prostatic hyperplasia (BPH). An understanding of the role of hormonal regulation of metabolism is essential to understanding the pathogenesis of prostate disease. The relationships described for the regulation of prostate cell metabolism provides insight into the mechanisms of hormonal regulation of mammalian cells in general.