Molecular endocrinology最新文献

Reproductive function is coordinated by kisspeptin (Kiss) and GnRH neurons. Phoenixin-20 amide (PNX) is a recently described peptide found to increase GnRH-stimulated LH secretion in the pituitary. However, the effects of PNX in the hypothalamus, the putative signaling pathways, and PNX receptor have yet to be identified. The mHypoA-GnRH/GFP and mHypoA-Kiss/GFP-3 cell lines represent populations of GnRH and Kiss neurons, respectively. PNX increased GnRH and GnRH receptor (GnRH-R) mRNA expression, as well as GnRH secretion, in the mHypoA-GnRH/GFP cell model. In the mHypoA-Kiss/GFP-3 cell line, PNX increased Kiss1 mRNA expression. CCAAT/enhancer-binding protein (C/EBP)-β, octamer transcription factor-1 (Oct-1), and cAMP response element binding protein (CREB) binding sites are localized to the 5' flanking regions of the GnRH, GnRH-R, and Kiss1 genes. PNX decreased C/EBP-β mRNA expression in both cell models and increased Oct-1 mRNA expression in the mHypoA-GnRH/GFP neurons. PNX increased CREB phosphorylation in both cell models and phospho-ERK1/2 in the mHypoA-GnRH/GFP cell model, whereas inhibiting the cAMP/protein kinase A pathway prevented PNX induction of GnRH and Kiss1 mRNA expression. Importantly, we determined that the G protein-coupled receptor, GPR173, was strongly expressed in both GnRH and kisspeptin cell models and small interfering RNA knockdown of GPR173 prevented the PNX-mediated up-regulation of GnRH, GnRH-R, and Kiss1 mRNA expression and the down-regulation of C/EBP-β mRNA expression. PNX also increased GPR173 mRNA expression in the mHypoA-GnRH/GFP cells. Taken together, these studies are the first to implicate that PNX acts through GPR173 to activate the cAMP/protein kinase A pathway through CREB, and potentially C/EBP-β and/or Oct-1 to increase GnRH, GnRH-R, and Kiss1 gene expression, ultimately having a stimulatory effect on reproductive function.

The epigenome undergoes significant remodeling during tissue and organ development, which coincides with a period of exquisite sensitivity to environmental exposures. In the case of endocrine-disrupting compounds (EDCs), exposures can reprogram the epigenome of developing tissues to increase susceptibility to diseases later in life, a process termed "developmental reprogramming." Both DNA methylation and histone modifications have been shown to be vulnerable to disruption by EDC exposures, and several mechanisms have been identified by which EDCs can reprogram the epigenome. These include altered methyl donor availability, loss of imprinting control, changes in dioxygenase activity, altered expression of noncoding RNAs, and activation of cell signaling pathways that can phosphorylate, and alter the activity of, histone methyltransferases. This altered epigenomic programming can persist across the life course, and in some instances generations, to alter gene expression in ways that correlate with increased disease susceptibility. Together, these studies on developmental reprogramming of the epigenome by EDCs are providing new insights into epigenomic plasticity that is vulnerable to disruption by environmental exposures.

Endoplasmic reticulum (ER) stress plays an important role in the pathogenesis of diabetes and the associated β-cell apoptosis. Although microRNAs (miRNAs) have been widely studied in various diseases including diabetes, the role of miRNAs in ER stress and β-cell apoptosis has only started to be elucidated. We recently showed that diabetes increases β-cell miR-204 and have now discovered that miR-204 directly targets the 3'untranslated region of protein kinase R-like ER kinase (PERK), 1 of the 3 ER transmembrane sensors and a key factor of the unfolded protein response (UPR). In addition, by using primary human islets, mouse islets, and INS-1 β-cells, we found that miR-204 decreased PERK expression as well as its downstream factors, activating transcription factor 4 and CCAAT enhancer-binding protein homologous protein, whereas it had no effect on the other 2 ER transmembrane sensors, activating transcription factor 6 and inositol-requiring enzyme-1α. Interestingly, we discovered that miR-204 also inhibited PERK signaling in the context of ER stress, and this exacerbated ER stress-induced β-cell apoptosis. This effect could be mimicked by PERK inhibitors supporting the notion that the miR-204-mediated inhibition of PERK and UPR signaling was conferring these detrimental effects on cell survival. Taken together, we have identified PERK as a novel target of miR-204 and show that miR-204 inhibits PERK signaling and increases ER stress-induced cell death, revealing for the first time a link between this miRNA and UPR.

Nephrogenic syndrome of inappropriate antidiuresis (NSIAD) is a genetic disease first described in 2 unrelated male infants with severe symptomatic hyponatremia. Despite undetectable arginine vasopressin levels, patients have inappropriately concentrated urine resulting in hyponatremia, hypoosmolality, and natriuresis. Here, we describe and functionally characterize a novel vasopressin type 2 receptor (V2R) gain-of-function mutation. An L312S substitution in the seventh transmembrane domain was identified in a boy presenting with water-induced hyponatremic seizures at the age of 5.8 years. We show that, compared with wild-type V2R, the L312S mutation results in the constitutive production of cAMP, indicative of the gain-of-function NSIAD profile. Interestingly, like the previously described F229V and I130N NSIAD-causing mutants, this appears to both occur in the absence of notable constitutive β-arrestin2 recruitment and can be reduced by the inverse agonist Tolvaptan. In addition, to understand the effect of various V2R substitutions on the full receptor "life-cycle," we have used and further developed a bioluminescence resonance energy transfer intracellular localization assay using multiple localization markers validated with confocal microscopy. This allowed us to characterize differences in the constitutive and ligand-induced localization and trafficking profiles of the novel L312S mutation as well as for previously described V2R gain-of-function mutants (NSIAD; R137C and R137L), loss-of-function mutants (nephrogenic diabetes insipidus; R137H, R181C, and M311V), and a putative silent V266A V2R polymorphism. In doing so, we describe differences in trafficking between unique V2R substitutions, even at the same amino acid position, therefore highlighting the value of full and thorough characterization of receptor function beyond simple signaling pathway analysis.

Within the past few decades, the concept of endocrine-disrupting chemicals (EDCs) has risen from a position of total obscurity to become a focus of dialogue, debate, and concern among scientists, physicians, regulators, and the public. The emergence and development of this field of study has not always followed a smooth path, and researchers continue to wrestle with questions about the low-dose effects and nonmonotonic dose responses seen with EDCs, their biological mechanisms of action, the true pervasiveness of these chemicals in our environment and in our bodies, and the extent of their effects on human and wildlife health. This review chronicles the development of the unique, multidisciplinary field of endocrine disruption, highlighting what we have learned about the threat of EDCs and lessons that could be relevant to other fields. It also offers perspectives on the future of the field and opportunities to better protect human health.

Androgen receptor (AR) plays pivotal roles in prostate cancer. Upon androgen stimulation, AR recruits the Protein kinase N1 (PKN1), which phosphorylates histone H3 at threonine 11, with subsequent recruitment of tryptophan, aspartic acid (WD) repeat-containing protein 5 (WDR5) and the su(var)3-9, enhancer of zeste, trithorax/mixed-lineage leukemia (SET1/MLL) histone methyltransferase complex to promote AR target gene activation and prostate cancer cell growth. However, the underlying mechanisms of target gene activation and cell growth subsequent to WDR5 recruitment are not well understood. Here, we demonstrate an epigenetic cross talk between histone modifications and AR target gene regulation. We discovered that K(lysine) acetyltransferase 8 (KAT8), a member of the MOZ, YBF2/SAS2, and TIP 60 protein 1 (MYST) family of histone acetyltransferases that catalyzes histone H4 lysine 16 acetylation, colocalized with WDR5 at AR target genes, resulting in hormone-dependent gene activation in prostate cancer cells. PKN1 or WDR5 knockdown severely inhibited KAT8 association with AR target genes and histone H4 lysine 16 acetylation upon androgen treatment. Knockdown of KAT8 significantly decreased AR target gene expression and prostate cancer cell proliferation. Collectively, these data describe a trans-histone modification pathway involving PKN1/histone H3 threonine 11 phosphorylation followed by WDR5/MLL histone methyltransferase and KAT8/histone acetyltransferase recruitment to effect androgen-dependent gene activation and prostate cancer cell proliferation.

Liver fibrosis is a reversible wound-healing process that is protective in the short term, but prolonged fibrotic responses lead to excessive accumulation of extracellular matrix components that suppresses hepatocyte regeneration, resulting in permanent liver damage. Upon liver damage, nonparenchymal cells including immune cells and hepatic stellate cells (HSCs) have crucial roles in the progression and regression of liver fibrosis. Here, we report differential roles of the glucocorticoid receptor (GR), acting in immune cells and HSCs, in liver fibrosis. In the carbon tetrachloride hepatotoxin-induced fibrosis model, both steroidal and nonsteroidal GR ligands suppressed expression of fibrotic genes and decreased extracellular matrix deposition but also inhibited immune cell infiltration and exacerbated liver injury. These counteracting effects of GR ligands were dissociated in mice with conditional GR knockout in immune cells (GR(LysM)) or HSC (GR(hGFAP)): the impacts of dexamethasone on immune cell infiltration and liver injury were totally blunted in GR(LysM) mice, whereas the suppression of fibrotic gene expression was diminished in GR(hGFAP) mice. The effect of GR activation in HSC was further confirmed in the LX-2 HSC cell line, in which antifibrotic effects were mediated by GR ligand inhibition of Sma and mad-related protein 3 (SMAD3) expression. We conclude that GR has differential roles in immune cells and HSCs to modulate liver injury and liver fibrosis. Specific activation of HSC-GR without alteration of GR activity in immune cells provides a potential therapeutic approach to treatment of hepatic fibrosis.