The regulation of human corticotrophin-releasing hormone gene expression in the placenta

Corticotrophin-releasing hormone (CRH) is a 41 amino acid neuropeptide that is expressed in the hypothalamus and the human placenta. Placental CRH production has been linked to the determination of gestational length in the human. Although encoded by a single copy gene, CRH expression in the placenta is regulated differently to the hypothalamus. Glucocorticoids stimulate CRH promoter activity in the placenta but inhibit it's activity in the hypothalamus, via mechanisms involving different regions of the CRH promoter. We discuss how various stimuli alter CRH promoter activity and why these responses are unique to the placenta.     

The regulation of human corticotrophin-releasing hormone gene expression in the placenta.

Corticotrophin-releasing hormone (CRH) is a 41 amino acid neuropeptide that is expressed in the hypothalamus and the human placenta. Placental CRH production has been linked to the determination of gestational length in the human. Although encoded by a single copy gene, CRH expression in the placenta is regulated differently to the hypothalamus. Glucocorticoids stimulate CRH promoter activity in the placenta but inhibit it's activity in the hypothalamus, via mechanisms involving different regions of the CRH promoter. We discuss how various stimuli alter CRH promoter activity and why these responses are unique to the placenta.     

Mitogen-activated protein kinase in human eggs.

Mitogen-activated protein (MAP) kinase in human eggs has been investigated by using immunoblotting with both anti-Active MAPK and anti-ERK2 antibodies. The results showed that the main form of MAP kinase was p42ERK2. It was in a dephosphorylated form in oocytes at the germinal vesicle stage, but fully phosphorylated in unfertilised mature eggs. MAP kinase phosphorylation was significantly decreased when pronuclei were formed after intracytoplasmic sperm injection. Neither MAP kinase expression nor activity was detected in morphologically degenerated eggs. Although MAP kinase still existed in early embryos arrested at the 8-cell or morula stages, little, if any, activity could be detected. These data suggest that MAP kinase may play an important role in the cell cycle regulation of human eggs, as in other mammalian species.     

Differential processing of corticotrophin-releasing hormone by the human placenta and hypothalamus

The molecular forms of corticotrophin-releasing hormone (CRH) in human placentae and hypothalami were investigated by gel permeation chromatography of water extracts. Hypothalamic extracts produced one peak of immunoreactivity which coeluted with human CRH at Kd = 0.53. Placental extracts, however, had in addition to that peak, two other peaks eluting earlier at the void and at Kd = 0.35-0.38. Tryptic digestion of the middle peak produced immunoreactivity which coeluted with the standard. Larger forms were also found in plasma of women in the third trimester of pregnancy and during labour but not in eluates from superfused placental fragments which had only CRH41-sized material. These data indicate that tissue-specific post-translational processing occurs for CRH, and suggests that the link between synthesis and secretion is more immediate in the placenta than hypothalamus.     

Mitogen-activated protein kinase activation by stimulation with thyrotropin-releasing hormone in rat pituitary GH3 cells.

We examined whether mitogen-activated protein (MAP) kinase is activated by thyrotropin-releasing hormone (TRH) in GH3 cells, and whether MAP kinase activation is involved in secretion of prolactin from these cells. Protein kinase inhibitors--such as PD098059, calphostin C, and genistein--and removal of extracellular Ca2+ inhibited MAP kinase activation by TRH. A cAMP analogue activated MAP kinase in these cells. Effects of cAMP on MAP kinase activation were inhibited by PD098059. TRH-induced prolactin secretion was not inhibited by levels of PD098059 sufficient to i activation but was inhibited by wortmannin (1 microM) and KN93. Treatment of GH3 cells with either TRH or cAMP significantly inhibited DNA synthesis and induced morphological changes. The effects stimulated by TRH were reversed by PD098059 treatment, but the same effects stimulated by cAMP were not. Treatment of GH3 cells with TRH for 48 h significantly increased the prolactin content in GH3 cells and decreased growth hormone content. The increase in prolactin was completely abolished by PD098059, but the decrease in growth hormone was not. These results suggest that TRH-induced MAP kinase activation is involved in prolactin synthesis and differentiation of GH3 cells, but not in prolactin secretion.     

Mitogen-activated protein kinase activation and regulation in the pressure-loaded fetal ovine heart

The mitogen-activated protein (MAP) kinase signaling pathways help to mediate the hypertrophic response of the pressure-loaded adult heart, although their importance in fetal myocardium is less known. The goal of this study was to determine the role the MAP kinase signaling pathways play in regulating the response of the fetal heart to a pressure load. Aortic (Ao) and pulmonary artery (PA) bands were placed in 132-day fetal sheep for 7 days. Protein levels of the total and active (phosphorylated) terminal MAP kinases extracellular signal-regulated kinase (ERK/P-ERK), c-Jun NH(2)-terminal kinase (JNK/P-JNK), and p38/P-p38 and the MAP kinase phosphatases MKP-1, MKP-2, and MKP-3 were made in the right and left ventricular (RV and LV) free walls. In both Ao- and PA-banded animals, total heart weight normalized to body weight was significantly increased, largely due to an increase in RV free wall mass in the Ao-banded animals and an increase in septal mass in the PA-banded fetuses. Total protein levels of the three terminal kinases and of P-ERK and P-JNK remained stable in both groups of banded animals. However, P-p38 was significantly increased in RV and LV of Ao- and PA-banded fetuses. Whereas MKP-1 and MKP-2 protein levels were unchanged following Ao- and PA-banding, MKP-3 protein levels were significantly increased in the RV of the PA-banded animals. These findings indicate that the MAP kinase signaling pathways are active in the fetal heart and help to modulate the response of prenatal myocardium to a pressure load.     

Mitogen-activated protein kinase (MAP kinase) activation in Xenopus oocytes: Roles of MPF and protein synthesis

Mitogen-activated protein kinase (MAP kinase) is a serine/threonine kinase whose enzymatic activity is thought to play a crucial role in mitogenic signal transduction and also in the progesterone-induced meiotic maturation of Xenopus oocytes. We have purified MAP kinase from Xenopus oocytes and have shown that the protein is present in metaphase ll oocytes under two different forms: an inactive 41-kD protein able to autoactivate and to autophosphorylate in vitro, and an active 42-kD kinase resolved into two tyrosine phosphorylated isoforms on 2D gels. During meiotic maturation, MAP kinase becomes tyrosine phosphorylated and activated following the activation of the M-phase promoting factor (MPF), a complex between the p34^cdc2 kinase and cyclin B. In vivo, MAP kinase activity displays a different stability in metaphase l and in metaphase II: protein synthesis is required to maintain MAP kinase activity in metaphase I but not in metaphase II oocytes. Injection of either MPF or cyclin B into prophase oocytes promotes tyrosine phosphorylation of MAP kinase, indicating that its activation is a downstream event of MPF activation. In contrast, injection of okadaic acid, which induces in vivo MPF activation, promotes only a very weak tyrosine phosphorylation of MAP kinase, suggesting that effectors other than MPF are required for the MAP kinase activation. Moreover, in the absence of protein synthesis, cyclin B and MPF are unable to promote in vivo activation of MAP kinase, indicating that this activation requires the synthesis of new protein(s). © 1993 Wiley-Liss, Inc.     

Mitogen-activated protein kinase cascades in plant signaling

Mitogen-activated protein kinase (MAPK) cascades are key signaling modules downstream of receptors/sensors that perceive either endogenously produced stimuli such as peptide ligands and damage-associated molecular patterns (DAMPs) or exogenously originated stimuli such as pathogen/microbe-associated molecular patterns (P/MAMPs), pathogen-derived effectors, and environmental factors. In this review, we provide a historic view of plant MAPK research and summarize recent advances in the establishment of MAPK cascades as essential components in plant immunity, response to environmental stresses, and normal growth and development. Each tier of the MAPK cascades is encoded by a small gene family, and multiple members can function redundantly in an MAPK cascade. Yet, they carry out a diverse array of biological functions in plants. How the signaling specificity is achieved has become an interesting topic of MAPK research. Future investigations into the molecular mechanism(s) underlying the regulation of MAPK activation including the activation kinetics and magnitude in response to a stimulus, the spatiotemporal expression patterns of all the components in the signaling pathway, and functional characterization of novel MAPK substrates are central to our understanding of MAPK functions and signaling specificity in plants.     

Irisin induces trophoblast differentiation via AMPK activation in the human placenta

Irisin, an adipokine, regulates differentiation and phenotype in various cell types including myocytes, adipocytes, and osteoblasts. Circulating irisin concentration increases throughout human pregnancy. In pregnancy disorders such as preeclampsia and gestational diabetes mellitus, circulating irisin levels are reduced compared to healthy controls. To date, there are no data on the role and molecular function of irisin in the human placenta or its contribution to pathophysiology. Aberrant trophoblast differentiation is involved in the pathophysiology of preeclampsia. The current study aimed to assess the molecular effects of irisin on trophoblast differentiation and function. First-trimester placental explants were cultured and treated with low (10 nM) and high (50 nM) physiological doses of irisin. Treatment with irisin dose-dependently increased both in vitro placental outgrowth (on Matrigel™) and trophoblast cell-cell fusion. Adenosine monophosphate-activated protein kinase (AMPK) signaling, an important regulator of cellular energy homeostasis that is involved in trophoblast differentiation and pathology, was subsequently investigated. Here, irisin exposure induced placental AMPK activation. To determine the effects of irisin on trophoblast differentiation, two trophoblast-like cell lines, HTR-8/SVneo and BeWo, were treated with irisin and/or a specific AMPK inhibitor (Compound C). Irisin-induced AMPK phosphorylation in HTR-8/SVneo cells. Additionally, as part of the differentiation process, integrin switching from α6 to α1 occurred as well as increased invasiveness. Overall, irisin promoted differentiation in villous and extravillous cell-based models via AMPK pathway activation. These findings provide evidence that exposure to irisin promotes differentiation and improves trophoblast functions in the human placenta that are affected in abnormal placentation.     

Induction and regulation of human interleukin 2 gene expression: significance of protein kinase C activation

Phytohemagglutinin (PHA) and a tumor-promoting phorbol ester, 12-O-tetradecanoylphorbol-13-acetate (TPA) act synergistically to induce interleukin 2 (IL2) mRNA in human lymphocytes in vitro. The induction was inhibited by a potent inhibitor of protein kinase C (C-kinase), 1-(5-isoquinolinylsulfonyl)-2-methylpiperazine (H-7) at less than 10 microM. H-7 inhibited C-kinase activity itself in lymphocytes at the same range of the concentration but did not interfere with the translocation of C-kinase from the cytosol to the membrane fraction of the lymphocytes induced by TPA. H-7 is also known to inhibit cAMP-dependent protein kinase (A-kinase) and cGMP-dependent protein kinase (G-kinase). However, the lymphocytes cultured with dibutyryl cAMP or dibutyryl cGMP could not be activated to produce IL2 mRNA. These results show that activation of C-kinase but not A-kinase and G-kinase is necessary in signal transduction for IL2 gene expression. Prostaglandin E2, which is known to elevate intracellular cAMP level, also inhibited IL2 mRNA induction in the lymphocytes stimulated with PHA and TPA. Addition of alpha-methylornithine and methylglyoxal bis (guanyl hydrazone), which inhibit polyamine synthesis, did not affect the induction of IL2 mRNA in the lymphocytes stimulated with PHA and TPA, indicating that polyamine synthesis is not necessary for IL2 mRNA induction.     

Mitogen-activated protein kinase p38 mediates regulation of chondrocyte differentiation by parathyroid hormone

Parathyroid hormone (PTH) and its related peptide regulate endochondral ossification by inhibiting chondrocyte differentiation toward hypertrophy. However, the intracellular pathway for transducing PTH/PTH-related peptide signals in chondrocytes remains unclear. Here, we show that this pathway is mediated by mitogen-activated protein kinase (MAPK) p38. Incubation of hypertrophic chondrocytes with PTH (1-34) induces an inhibition of p38 kinase activity in a time- and dose-dependent manner. Inhibition of protein kinase C prevents PTH-induced p38 MAPK inhibition, whereas inhibition of protein kinase A has no effect. Thus, protein kinase C, but not protein kinase A, is required for the inhibition of p38 MAPK by PTH. Treatment of hypertrophic chondrocytes by PTH or by p38 MAPK inhibitor SB203580 up-regulates Bcl-2, suggesting that Bcl-2 lies downstream of p38 MAPK in the PTH signaling pathway. Inhibition of p38 MAPK in hypertrophic chondrocytes by either PTH, SB303580, or both together leads to a decrease of hypertrophic marker type X collagen mRNA and an increase of the expression of prehypertrophic marker cartilage matrix protein. Therefore, inhibition of p38 converts a hypertrophic cell phenotype to a prehypertrophic one, thereby preventing precocious chondrocyte hypertrophy. Taken together, these data suggest a major role for p38 MAPK in transmitting PTH signals to regulate chondrocyte differentiation.