bluuebunny/crossref_metadata_2025 huggingface dataset:
Mechanisms and Physiological Significance of the Cholinergic Control of Pancreatic β-Cell Function
Authors: Gilon Patrick , Henquin Jean-Claude
Published: January 2014

Acetylcholine (ACh), the major parasympathetic neurotransmitter, is released by intrapancreatic nerve endings during the preabsorptive and absorptive phases of feeding. In β-cells, ACh binds to muscarinic M3 receptors and exerts complex effects, which culminate in an increase of glucose (nutrient)-induced insulin secretion. Activation of PLC generates diacylglycerol. Activation of PLA2 produces arachidonic acid and lysophosphatidylcholine. These phospholipid-derived messengers, particularly diacylglycerol, activate PKC, thereby increasing the efficiency of free cytosolic Ca2+ concentration ([Ca2+]c) on exocytosis of insulin granules. IP3, also produced by PLC, causes a rapid elevation of [Ca2+]c by mobilizing Ca2+ from the endoplasmic reticulum; the resulting fall in Ca2+ in the organelle produces a small capacitative Ca2+ entry. ACh also depolarizes the plasma membrane of β-cells by a Na+- dependent mechanism. When the plasma membrane is already depolarized by secretagogues such as glucose, this additional depolarization induces a sustained increase in [Ca2+]c. Surprisingly, ACh can also inhibit voltage-dependent Ca2+ channels and stimulate Ca2+ efflux when [Ca2+]c is elevated. However, under physiological conditions, the net effect of ACh on [Ca2+]c is always positive. The insulinotropic effect of ACh results from two mechanisms: one involves a rise in [Ca2+]c and the other involves a marked, PKC-mediated increase in the efficiency of Ca2+ on exocytosis. The paper also discusses the mechanisms explaining the glucose dependence of the effects of ACh on insulin release.
Expression of p27Kip1 in Osteoblast-Like Cells during Differentiation with Parathyroid Hormone*
Authors: Onishi Takehisa , Hruska Keith
Published: January 2014

PTH is a major systemic regulator of bone metabolism and plays an important role in both bone formation and resorption. PTH either inhibits or stimulates osteoblastic cell proliferation depending on the model that is studied. We analyzed the cell cycle of the UMR-106 cell line, a relatively differentiated osteoblastic osteogenic sarcoma line in which PTH is known to inhibit proliferation but the mechanism of action is unknown. PTH decreased the proportion of cells in S phase and increased the number of G1 phase cells. We examined the effect of PTH on the regulators of the G1 phase cyclin-dependent kinases and found that PTH increased p27Kip1, but not p21Cip1, levels. This effect was mimicked by 8-bromo-cAMP, but not by phorbol 12-myristate 13-acetate. The protein kinase A inhibitor KT5720 abolished the effect of PTH on the increase in p27Kip1 expression. PTH increased CDK2-associated p27Kip1 without affecting the levels of CDK2. CDK2 activity was down-regulated by both PTH and 8-bromo-cAMP treatment. These data suggest that PTH blocks entry of cells into S phase and inhibits cell proliferation as the consequence of an increase in p27Kip1, which is mediated through the protein kinase A pathway. The inhibition of G1 cyclin-dependent kinases by p27Kip1 could cause a reduction of phosphorylation of key substrates and inactivation of transcription factors essential for entry into S phase. The inhibition of cell cycle progression through PKA-mediated p27Kip1 induction might play an important role in PTH-induced differentiation of osteoblasts.
Orthovanadate Stimulates Cyclic Guanosine Monophosphate-Inhibited Cyclic Adenosine Monophosphate Phosphodiesterase Activity in Isolated Rat Fat Pads through Activation of Particulate Myelin Basic Protein Kinase by Protein Tyrosine Kinase
Authors: Ueki Hiroshi , Mitsugi Shuichi , Kawashima Yoshihito , Motoyashiki Toshio , Morita Tetsuo
Published: January 2014

Involvement of protein kinases in the stimulation of cGMP-inhibited cAMP phosphodiesterase (PDE) activity by orthovanadate (vanadate) was studied. When the fat pads were incubated with 2 mm vanadate or 10 nm insulin, the stimulation of myelin basic protein kinase (MBPK) activity in the particulate by vanadate reached a maximum at 60 min. In contrast, insulin showed a transient increase at 20 min. A 60-min incubation of the fat pads with vanadate stimulated all activities of protein tyrosine kinase (PTK), MBPK, and PDE in the particulate, in a similar dose-dependent manner. Amiloride, a PTK inhibitor, inhibited the stimulations of three enzymes by vanadate in a similar concentration range. Enzyme fractions, which were separated from the solubilized particulate, were subjected to the immunoblot analysis. A fraction of MBPK was identified to contain a major protein of mol wt (44K) and a minor one (42K), both of which are immunoreactive with a mitogen-activated protein kinase (MAPK) antibody. The partially purified PDE activity was stimulated by the addition of the partially purified MBPK. The further stimulation was observed with the PTK-activated MBPK. These results suggest that vanadate stimulates in part the PDE activity through the activation of the particulate MBPK, probably MAPKs, by PTK sensitive to vanadate.
The Formation of Thyrotropin Receptor (TSHR) Antibodies in a Graves’ Animal Model Requires the N-Terminal Segment of the TSHR Extracellular Domain
Authors: Kikuoka Shuichi , Shimojo Naoki , Yamaguchi Ken-Ichi , Watanabe Yukihiko , Hoshioka Akira , Hirai Aizan , Saito Yasushi , Tahara Kazuo , Kohn Leonard D. , Maruyama Naoki , Kohno Yoichi , Niimi Hiroo
Published: January 2014

Immunization of AKR/N mice with murine fibroblasts, transfected with the TSH receptor (TSHR) and a murine major histocompatibility complex class II molecule having the same H-2k haplotype (but not either alone), induces immune thyroid disease with the humoral and histological features of human Graves’, including the presence of two different TSHR antibodies (TSHRAbs): stimulating TSHRAbs, which cause hyperthyroidism; and TSH-binding-inhibiting immunoglobulins. The primary functional epitope for both types of antibodies in Graves’ patients is on the N-terminal portion of the extracellular domain of the TSHR, residues 25 to 165; most require residues 90–165 to express TSHRAb activity, as evidenced in studies using chimeras of the TSHR and lutropin-choriogonadotropin receptor (LH-CGR). To evaluate the role of this region of the TSHR in the formation of Graves’ TSHRAbs, we immunized AKR/N mice with fibroblasts transfected with three human TSHR chimeras with residues 9–165 (Mc1+2), 90–165 (Mc2), or 261–370 (Mc4) substituted by equivalent residues of the rat LH-CGR. Mice immunized with the Mc1+2 and Mc2 chimeras, with the N-terminal portion of the extracellular domain of the TSHR substituted by LH-CGR residues, did not develop TSHRAbs. Mice immunized with the Mc4 chimera, having a major portion of the C-terminal portion of the extracellular domain of the TSHR replaced by comparable LH-CGR residues, can develop TSHRAbs. The results suggest that the N-terminal segment of the TSHR extracellular domain is not only a critical functional epitope for Graves’ TSHRAbs, but it is important also in their formation in a mouse model of Graves’ disease.
5-Lipoxygenase Metabolites Inhibit Bone Formation in Vitro
Authors: Traianedes Kathy , Dallas Mark R. , Garrett I. Ross , Mundy Gregory R. , Bonewald Lynda F.
Published: January 2014

The leukotrienes and peptido-leukotrienes are 5-lipoxygenase (5-LO) metabolites of arachidonic acid that appear to have unique effects on bone, distinct from those of the prostaglandins. Application of exogenous leukotrienes in vitro and in vivo results in increased osteoclast formation and bone resorption. While 5-LO metabolites of arachidonic acid clearly stimulate osteoclastic bone resorption, little is known concerning their effects on osteoblastic bone formation. We examined the effects of the 5-LO metabolites 5-HETE, the leukotriene LTB4 and, as representative of the peptido-leukotrienes, LTD4 on the formation of mineralized nodules of fetal rat calvarial cells in the presence of dexamethasone and recombinant human bone morphogenetic protein-2 (rhBMP-2). We also examined the effects of these 5-LO metabolites on alkaline phosphatase activity and cell proliferation in these cultures and the effects of 5-HETE and LTB4 on cultured explants of neonatal murine calvariae. We found that the bone-forming capacity of osteoblasts was impaired when cells were cultured in the presence of 5-LO metabolites. These data indicate that metabolites of the 5-LO pathway are negative regulators of bone formation. The continued presence of these metabolites in the bone environment might account, in part, for the bone loss associated with chronic inflammatory conditions.
Effects of Growth Hormone Secretagogues on Prolactin Release in Anesthetized Dwarf (dw/dw) Rats*
Authors: Carmignac Danielle F. , Bennett Pamela A. , Robinson Iain C. A. F.
Published: January 2014

In addition to stimulating GH release, GH secretagogues such as GH-releasing peptide-6 (GHRP-6) stimulate small amounts of ACTH and PRL release. Although the effects on ACTH have recently been studied, there is little information about the effects of GHRP-6 on PRL. We have now studied GHRP-6-induced GH and PRL release and their regulation by estrogen (E2) in anesthetized male and female rats and in GH-deficient dwarf (dw/dw) rats that maintain high pituitary PRL stores and show elevated hypothalamic GH secretagogue receptor expression. Whereas GHRP-6 (0.1–2.5 μg, iv) did not induce PRL release in normal male or female rats, significant PRL responses were observed in dw/dw females. These responses were abolished by ovariectomy and could be strongly induced in male dw/dw rats by E2 treatment. These effects could be dissociated from GHRP-6-induced GH release in the same animals, but not from PRL release induced by TRH, which was also abolished by ovariectomy and induced in males by E2 treatment. However, the effects of GHRP-6 on PRL were unlikely to be mediated by TRH because in the same animals, TSH levels were unaffected by GHRP-6 whereas they were increased by TRH. The increased PRL response could reflect an increase in GH secretagogue receptor expression that was observed in the arcuate and ventromedial nuclei of E2-treated rats. Our results suggest that the minimal PRL-releasing activity of GHRP-6 in normal rats becomes prominent in GH-deficient female dw/dw rats and is probably exerted directly at the pituitary; these GHRP-6 actions may be modulated by E2 at both hypothalamic and pituitary sites.
Cyclical Alternative Exon Splicing of Transcription Factor Cyclic Adenosine Monophosphate Response Element-Binding Protein (CREB) Messenger Ribonucleic Acid during Rat Spermatogenesis*
Authors: Daniel Philip B. , Habener Joel F.
Published: January 2014

During spermatogenesis, the levels of cAMP in seminiferous tubules undergo stage-dependent cyclical fluctuations. We show that changes in cAMP levels are accompanied by alternative exon splicing of the RNA encoding the cAMP-responsive transcription factor CREB (cAMP response element-binding protein), expressed in both the Sertoli and germ cells. Exons Y and W are expressed exclusively in the testis, and they introduce stop codons into the normal protein coding frame of CREB. The splicing in of W was shown earlier to activate the internal translation of two alternative products of the CREB messenger RNA (mRNA) containing the DNA-binding domain (I-CREBs). The I-CREBs act as potent inhibitors of activator isoforms of CREB. The functions of the alternatively spliced exon Y are unknown. To investigate whether the splicing of exons W and Y is regulated during spermatogenesis, seminiferous tubules, isolated from adult rats, were dissected into segments representing different stages of the spermatogenic cycle and were analyzed by RT-PCR. The analyses of pooled-tubule segments revealed stage-dependent splicing of both exons W and Y in the CREB transcripts. Single tubules were dissected into smaller segments for greater staging accuracy and were analyzed by RT-PCR for CREB mRNAs containing either exons W or Y, as well as for FSH receptor mRNA. This analysis confirmed that a marked, cycle-dependent variation in CREB mRNA levels was occurring. Maximal splicing of exons W and Y occurs independently at different stages of the spermatogenic cycle, stages II-VI and IX, respectively. The distinct spermatogenic cycle-dependent regulation of the splicing of exons W and Y provides further evidence in support of a functional relevance for CREB-W and Y mRNA isoforms in spermatogenesis.
Nitric Oxide Plays an Important Role in the Diurnal Change of Tuberoinfundibular Dopaminergic Neuronal Activity and Prolactin Secretion in Ovariectomized, Estrogen/Progesterone-Treated Rats**This study was supported, in part, by Grants NSC86–2314-B010-M10 and NSC87–2314-B010–016 (to J.-T.P) from the National Science Council of the Republic of China.
Authors: YEN Shih-Hui , Pan Jenn-Tser
Published: January 2014

A significant diurnal change of tuberoinfundibular dopaminergic (TIDA) neuronal activity coincident with the estrogen (E2)-induced afternoon PRL surge has been reported in ovariectomized, E2-primed (OVX+E2) rats. Systemic injection of a nitric oxide (NO) synthase (NOS) inhibitor, NG-nitro-l-arginine (l-NA, 50 mg/kg, ip at 1000 and 1200 h), significantly blocked the diurnal changes of TIDA neuronal activity and PRL secretion at 1500 and 1700 h in OVX+E2 rats. Coadministration of l-arginine (300 mg/kg, ip) with l-NA completely prevented the effects of l-NA. Total nitrite/nitrate levels in the serum of l-NA- and l-NA+l-arginine-treated rats substantiated the effects of l-NA and l-arginine on NO production. Pretreatment of antisense oligodeoxynucleotide (ODN; 1μ g/3 μl; intracerebroventricularly at 48, 24, and 7 h before sacrifice) against the messenger RNA (mRNA) of constitutive NOS, i.e. neuronal NOS or endothelial NOS, was also effective in preventing the diurnal changes of TIDA neuronal activity and PRL surge at 1500 h. The same treatment of antisense ODN against the mRNA of inducible NOS, i.e. macrophage NOS, had no effect.

Progesterone (P4) has been reported to advance and augment the diurnal changes of TIDA neuronal activity and the afternoon PRL surge, by 1 h, in both proestrous and OVX+E2 rats. We further showed that l-NA dose dependently (50 but not 5 mg/kg, ip at 1000 and 1200 h) blocked the effect of P4 on TIDA neurons and serum PRL at 1300 h, which effect could be negated by simultaneous administration of l-arginine (300 mg/kg, ip). Pretreatment with antisense ODNs against the mRNA of neuronal NOS or endothelial NOS, but not macrophage NOS, was also effective in preventing the P4’s effect on TIDA neuronal activity and PRL secretion at 1300 h. In summary, NO may play a physiological role in the E2- and P4-regulated diurnal changes of TIDA neuronal activity and PRL secretion.
Chronic Exposure to High Glucose Concentrations Increases Proglucagon Messenger Ribonucleic Acid Levels and Glucagon Release from InR1G9 Cells1
Authors: Dumonteil Eric , Ritz-Laser Beate , Magnan Chistophe , Grigorescu Iléana , Ktorza Alain , Philippe Jacques
Published: January 2014

α cell function is impaired in diabetes. In diabetics, plasma levels of glucagon are high despite persistently elevated glucose levels and may even rise paradoxically in response to a glucose load; high plasma glucagon levels are accompanied by increased proglucagon gene expression. We have investigated the effects of high glucose concentrations on InR1G9 cells, a glucagon-producing cell line. We show here that chronically elevated glucose concentrations increase glucagon release by 2.5- to 4-fold, glucagon cell content by 2.5- to 3-fold, and proglucagon messenger RNA levels by 4- to 8-fold, whereas changes for 24 h have no effect on proglucagon messenger RNA levels. Persistently elevated glucose affects proglucagon gene expression at the level of transcription and insulin is capable of preventing this effect. We conclude that chronically elevated glucose may be an important factor in the α cell dysfunction that occurs in diabetes and thus that glucose may not only affect the β cell but also the α cell.
Pituitary and Testicular Function in Growth Hormone Receptor Gene Knockout Mice
*
Authors: Chandrashekar Varadaraj , Bartke Andrzej , Coschigano Karen T. , Kopchick John J.
Published: January 2014

The role of GH in the control of pituitary and testicular function is poorly understood. GH receptor gene knockout (GHR-KO) mice were recently produced. As these mice are good experimental animals to assess the influence of the effects of GH and insulin-like growth factor-I (IGF-I), the present studies were undertaken. Young adult male GHR-KO mice and their normal siblings were tested for fertility and subsequently injected (ip) with saline or GnRH (1 ng/g BW) in saline. Fifteen minutes later, blood was obtained via heart puncture. Plasma IGF-I, PRL, LH, and testosterone concentrations were measured by RIAs. In addition, the testicular testosterone response to LH treatment was evaluated in vitro. The results indicate that the absence of GH receptors (GHRs) was associated with an increase (P < 0.005) in plasma PRL levels, and circulating IGF-I was not detectable. Although the basal plasma LH levels were similar in GHR-KO mice relative to those in their normal siblings, the circulating LH response to GnRH treatment was significantly (P < 0.001) attenuated. Plasma testosterone levels were unaffected by disruption of the GHR gene. However, basal (P < 0.01) and LH-stimulated (P < 0.001) testosterone release from the isolated testes of GHR-KO mice were decreased. The rate of fertility in GHR-KO male mice was also reduced. These results indicate that the lack of GHRs (with GH resistance and lack of IGF-I secretion) induces hyperprolactinemia and alters the effect of GnRH on LH secretion as well as testicular function. Thus, GH and IGF-I influence pituitary and gonadal functions in male mice.
Pesticides Interfere with the Nongenomic Action of a Progestogen on Meiotic Maturation by Binding to its Plasma Membrane Receptor on Fish Oocytes
Authors: Das Shampa , Thomas Peter
Published: January 2014

Although many environmental contaminants disrupt endocrine function by binding to nuclear steroid receptors, it is not known whether they are capable of binding to steroid membrane receptors and interfering with nongenomic actions of steroids. The binding of several organochlorine pesticides to the plasma membrane receptor for the maturation-inducing steroid, 17,20β,21-trihydroxy-4-pregnen-3-one (20β-S), in the ovaries of spotted seatrout (Cynoscion nebulosus) was investigated in in vitro competition assays. Kepone and o,p′-DDD were competitive inhibitors of 20β-S binding and caused concentration-dependent displacement of [3H]-20β-S from its receptor site over the range of 10−4 to 10−6 or 10−7 M, whereas several other pesticides had lower affinities for the receptor. Interference with the nongenomic actions of 20β-S on final meiotic maturation of spotted seatrout oocytes (final oocyte maturation, FOM) was examined in an in vitro bioassay. A concentration-dependent inhibition of FOM in response to 20β-S was observed after 5 min and 12 h exposure to the same range of Kepone and o,p′-DDD concentrations (10−4 to 10−6 or 10−7 M). The close correspondence between competitive binding of the two pesticides to the 20β-S membrane receptor and their inhibition of 20β-S induced FOM suggests a mechanism of endocrine disruption mediated by binding to a steroid membrane receptor and antagonism of a nongenomic steroid action.
Glucagon-Like Peptide 1 Elevates Cytosolic Calcium in Pancreaticβ -Cells Independently of Protein Kinase A1
Authors: Bode Hans-Peter , Moormann Birgit , Dabew Regina , Göke Burkhard
Published: January 2014

Glucagon-like peptide 1 (7–36)amide (GLP-1) is an insulinotropic intestinal peptide hormone with a potential role as antidiabetogenic therapeutic agent. It mediates a potentiation of glucose-induced insulin secretion, by activation of adenylate cyclase and subsequent elevation of cytosolic free calcium,[ Ca2+]cyt. We investigated the role of protein kinase A (PKA) in GLP-1 signal transduction, using isolated mouse islets as well as the differentiated β-cell line INS-1. Two specific inhibitors of PKA, (Rp)-adenosine cyclic 3′,5′-phosporothioate (Rp-cAMPS, up to 3 mm) and KT5720 (up to 10 μm), did not inhibit the GLP-1-induced[ Ca2+]cyt elevation. Another PKA inhibitor, H-89, reduced the [Ca2+]cyt elevation only when applied at high concentrations (10–40 μm), higher than sufficient for PKA inhibition in many cell types. Furthermore, at these concentrations, H-89 also inhibited presumably PKA-independent processes such as glucose-induced [Ca2+]cyt elevations and intracellular calcium storage. This suggests a PKA-independent action of H-89. Similarly to H-89, the potent but unselective protein kinase inhibitor staurosporine inhibited the GLP-1-induced [Ca2+]cyt elevation only at high concentrations, at which it also inhibited glucose-induced [Ca2+]cyt elevations. The same observations as with GLP-1 were made when adenylate cyclase was stimulated with forskolin, for selective examination of signal transduction downstream of receptor and G protein. Our results suggest that the GLP-1-induced[ Ca2+]cyt elevation is mediated independently of PKA and thus belongs to the yet-little-characterized ensemble of effects that are mediated by binding of cAMP to other target proteins.
Insulin-Like Growth Factor (IGF)-Binding Protein-Related Protein-1: An Autocrine/Paracrine Factor That Inhibits Skeletal Myoblast Differentiation but Permits Proliferation in Response to IGF1
Authors: Haugk Kathleen L. , Wilson Heather-Marie P. , Swisshelm Karen , Quinn LeBris S.
Published: January 2014

Skeletal myogenic cells respond to the insulin-like growth factors (IGF-I and IGF-II) by differentiating or proliferating, which are mutually exclusive pathways. What determines which of these responses to IGF skeletal myoblast undergo is unclear. IGF-binding protein-related protein 1 (IGFBP-rP1) is a secreted protein with close homology to the IGF-binding proteins (IGFBPs) in the N-terminal region. IGFBP-rP1, previously called mac25 and IGFBP-7, is highly expressed in C2 skeletal myoblasts during the proliferative phase, but is down-regulated during myoblast differentiation. To determine the role of IGFBP-rP1 in myogenesis, IGFBP-rP1 was overexpressed in C2 myoblasts using a retroviral vector. Western blots indicated that the resulting C2-rP1 myoblasts secreted approximately 27-fold higher levels of IGFBP-rP1 than control C2-LX myoblasts that were transduced with a control vector (LXSN). Compared with C2-LX myoblasts, the differentiation responses of C2-rP1 myoblasts to IGF-I, IGF-II, insulin, and des(1–3)IGF-I were significantly reduced (P < 0.05). However, proliferation responses of C2-rP1 and C2-LX myoblasts to these same factors were not significantly different. Exposure of control C2-LX myoblasts to factors secreted by C2-rP1 myoblasts using a transwell coculture system reduced C2-LX myoblast differentiation significantly (P < 0.05). Experiments with the mitogen-activated protein kinase (MAPK) kinase inhibitor PD098059 suggested that IGFBP-rP1 inhibits a MAPK-dependent differentiation pathway. In confirmation of this idea, levels of phosphorylated extracellular signal-regulated kinase-2 (a MAPK) were reduced in C2-rP1 myoblasts compared with those in C2-LX myoblasts. These findings indicate that IGFBP-rP1 may function as an autocrine/paracrine factor that specifies the proliferative response to the IGFs in myogenesis.
Expression of Enzymes Synthesizing (Aldehyde Dehydrogenase 1 and Retinaldehyde Dehydrogenase 2) and Metabolizing (Cyp26) Retinoic Acid in the Mouse Female Reproductive System*
Authors: Vermot Julien , Fraulob Valérie , Dollé Pascal , Niederreither Karen
Published: January 2014

Vitamin A is required for female reproduction. Rodent uterine cells are able to synthesize retinoic acid (RA), the active vitamin A derivative, and express RA receptors. Here, we report that two RA-synthesizing enzymes [aldehyde dehydrogenase 1 (Aldh1) and retinaldehyde dehydrogenase 2 (Raldh2)] and a cytochrome P450 (Cyp26) that metabolizes vitamin A and RA into more polar metabolites exhibit dynamic expression patterns in the mouse uterus, both during the ovarian cycle and during early pregnancy. Aldh1 expression is up-regulated during diestrus and proestrus in the uterine glands, whereas Raldh2 is highly induced in the endometrial stroma in metestrus. Cyp26 expression, which is not detectable during the normal ovarian cycle, is strongly induced in the uterine luminal epithelium, 24 h after human CG hormonal administration. Raldh2 stromal expression also strongly responds to gonadotropin (PMSG and human CG) induction. Furthermore, Raldh2 expression can be hormonally induced in stromal cells of the vagina and cervix. All three enzymes exhibit differential expression profiles during early pregnancy. Aldh1 glandular expression is sharply induced at 2.5 gestational days, whereas Raldh2 stromal expression increases more steadily until the implantation phase. Cyp26 epithelial expression is strongly induced between 3.5–4.5 gestational days, i.e. when the developing blastocysts colonize the uterine lumen. These data suggest a need for precise regulation of RA synthesis and/or metabolism, in both cycling and pregnant uterus.
Characterization of Two Fly LGR (Leucine-Rich Repeat-Containing, G Protein-Coupled Receptor) Proteins Homologous to Vertebrate Glycoprotein Hormone Receptors: Constitutive Activation of Wild-Type Fly LGR1 But Not LGR2 in Transfected Mammalian Cells**This study was supported by NIH Grant HD-23273. The GenBank submission number for fly LGR2 is AF274591.
Authors: Nishi Shinya , Hsu Sheau Yu , Zell Karen , Hsueh Aaron J. W.
Published: January 2014

The receptors for lutropin (LH), FSH, and TSH belong to the large G protein-coupled receptor (GPCR) superfamily and are unique in having a large N-terminal extracellular (ecto-) domain important for interactions with the large glycoprotein hormone ligands. Recent studies indicated the evolution of a large family of the leucine-rich repeat-containing, G protein-coupled receptors (LGRs) with at least seven members in mammals. Based on the sequences of mammalian glycoprotein hormone receptors, we have identified a new LGR in Drosophila melanogaster and named it as fly LGR2 to distinguish it from the previously reported fly LH/FSH/TSH receptor (renamed as fly LGR1). Genomic analysis indicated the presence of 10 exons in fly LGR2 as compared with 16 exons in fly LGR1. The deduced fly LGR2 complementary DNA (cDNA) showed 43 and 64% similarity to the fly LGR1 in the ectodomain and transmembrane region, respectively. Comparison of 12 LGRs from diverse species indicated that these proteins can be divided into three subfamilies and fly LGR1 and LGR2 belong to different subfamilies. Potential signaling mechanisms were tested in human 293T cells overexpressing the fly receptors. Of interest, fly LGR1, but not LGR2, showed constitutive activity as reflected by elevated basal cAMP production in transfected cells. The basal activity of fly LGR1 was further augmented following point mutations of key residues in the intracellular loop 3 or transmembrane VI, similar to those found in patients with familial male precocious puberty. The present study reports the cloning of fly LGR2 and indicates that the G protein-coupling mechanism is conserved in fly LGR1 as compared with the mammalian glycoprotein hormone receptors. The characterization of fly receptors with features similar to mammalian glycoprotein hormone receptors allows a better understanding of the evolution of this unique group of GPCRs and future elucidation of their ligand signaling mechanisms.
Expression of Cyclin-Dependent Kinase Inhibitors in Epiphyseal Chondrocytes Induced to Terminally Differentiate with Thyroid Hormone
Authors: Ballock R. Tracy , Zhou Xiaolan , Mink Lynn M. , Chen Daniel H. C. , Mita Barry C. , Stewart Matthew C.
Published: January 2014

A growing body of evidence suggests that systemic hormones and peptide growth factors may exert their effects on cell growth and differentiation in part through regulation of the cell division cycle. We hypothesized that thyroid hormone regulates terminal differentiation of growth plate chondrocytes in part through controlling cell cycle progression at the G1/S restriction point. Our results support this hypothesis by demonstrating that treatment of epiphyseal chondrocytes with thyroid hormone under chemically defined conditions results in the arrest of DNA synthesis and the onset of terminal differentiation, indicating that thyroid hormone is one factor capable of regulating the transition between cell growth and differentiation in these cells. This terminal differentiation process is associated with induction of the cyclin/cyclin-dependent kinase inhibitors p21cip-1, waf-1 and p27kip1, suggesting that thyroid hormone may regulate terminal differentiation in part by arresting cell cycle progression through induction of cyclin-dependent kinase inhibitors.
Local Integration of Glutamate Signaling in the Hypothalamic Paraventricular Region: Regulation of Glucocorticoid Stress Reponses
Authors: Ziegler Dana R. , Herman James P.
Published: January 2014

The present study is a test of the hypothesis that endogenous glutamatergic input to the hypothalamic paraventricular nucleus (PVN) is involved in stress-induced activation of the hypothalamic-pituitary-adrenocortical (HPA) axis. We examined whether corticosterone (CORT) responses to restraint stress could be attenuated by bilateral 50nl microinjections of kynurenic acid (KYN, ionotropic glutamate receptor antagonist) into the medial PVN of conscious rats. Immediately following microinjection, rats were subjected to 30 min restraint, and stress-induced plasma CORT was measured at 30, 60, 120, and 180 min following the onset of restraint. KYN (50 pmol) significantly reduced cumulative CORT responses to acute restraint stress by 24%. In contrast, microinjections centered dorsal to the PVN increased CORT responses by 31%, suggestive of a disinhibition of local PVN-inhibitory input. KYN injections immediately anterior, ventral, or posterior to the PVN had no effect, suggesting an absence of potential diffusion artifacts. These results provide evidence that endogenous glutamate in the PVN and surrounding peri-PVN region plays a physiologically significant role in both generating and limiting glucocorticoid stress responses in awake rats.
Galanin-Like Peptide (GALP) Is a Target for Regulation by Leptin in the Hypothalamus of the Rat
Authors: Juréus Anders , Cunningham Matthew J. , McClain Molly E. , Clifton Donald K. , Steiner Robert A.
Published: January 2014

Galanin-like peptide (GALP), which was recently isolated from the porcine hypothalamus, shares sequence homology with galanin and binds with high affinity to galanin receptors. To study the distribution and regulation of GALP-expressing cells in the brain, we cloned a 120 base-pair cDNA fragment of rat GALP and produced an antisense riboprobe. In situ hybridization for GALP mRNA was then performed on tissue sections throughout the forebrain of adult ovariectomized female rats. We found GALP mRNA-containing cells in the arcuate nucleus (Arc), caudal dorsomedial nucleus, median eminence and the pituitary. Because GALP mRNA in the Arc appeared to overlap with the known distribution of leptin receptor mRNA, we tested the hypothesis that GALP expression is regulated by leptin. Using in situ hybridization, we compared the number of GALP mRNA-containing cells among groups of rats that were fed ad lib or fasted for 48 h and treated with either leptin or vehicle. Fasting reduced the number of identifiable cells containing GALP mRNA in the Arc, whereas the treatment of fasted animals with leptin produced a 4-fold increase in the number of cells expressing GALP message. The presence of GALP mRNA in the hypothalamus and pituitary and its regulation by leptin suggests that GALP may have important neuroendocrine functions, including the physiological regulation of feeding, metabolism, and reproduction.
Intracellular Regeneration of Glucocorticoids by
11β-Hydroxysteroid Dehydrogenase (11β-HSD)-1 Plays a Key
Role in Regulation of the Hypothalamic-Pituitary-Adrenal Axis: Analysis
of 11β-HSD-1-Deficient Mice**The Wellcome Trust supported this work through a program grant (to J.J.M. and J.R.S.) and a Career Development Fellowship (to M.C.H.).
Authors: Harris Hayley J. , Kotelevtsev Yuri , Mullins John J. , Seckl Jonathan R. , Holmes Megan C.
Published: January 2014

11β-Hydroxysteroid dehydrogenases (11β-HSDs) catalyze interconversion of active corticosterone and inert 11-dehydrocorticosterone, thus regulating glucocorticoid access to intracellular receptors in vivo. 11β-HSD type 1 is a reductase, locally regenerating active glucocorticoids. To explore the role of this isozyme in the brain, we examined hypothalamic-pituitary-adrenal axis (HPA) regulation in mice homozygous for a targeted disruption of the 11β-HSD-1 gene. 11β-HSD-1-deficient mice showed elevated plasma corticosterone and ACTH levels at the diurnal nadir, with a prolonged corticosterone peak, suggesting abnormal HPA control and enhanced circadian HPA drive. Despite elevated corticosterone levels, several hippocampal and hypothalamic glucocorticoid-sensitive messenger RNAs were normally expressed in 11β-HSD-1-deficient mice, implying reduced effective glucocorticoid activity within neurons. 11β-HSD-1-deficient mice showed exaggerated ACTH and corticosterone responses to restraint stress, with a delayed fall after stress, suggesting diminished glucocorticoid feedback. Indeed, 11β-HSD-1-deficient mice were less sensitive to exogenous cortisol suppression of HPA activation. Thus 11β-HSD-1 amplifies glucocorticoid feedback on the HPA axis and is an important regulator of neuronal glucocorticoid exposure under both basal and stress conditions in vivo.
Inhibition of Ret Oncogene Activity by the Protein Tyrosine Phosphatase SHP1
Authors: Hennige Anita M. , Lammers Reiner , Höppner Wolfgang , Arlt Dorit , Strack Volker , Teichmann Reinhard , Machicao Fausto , Ullrich Axel , Häring Hans-Ulrich , Kellerer Monika
Published: January 2014

Germline mutations in the Ret protooncogene give rise to the inherited endocrine cancer syndromes MEN types 2A and 2B and familiar medullary thyroid carcinoma. Although it is well accepted that the constitutive active tyrosine kinase of Ret oncogenes ultimately leads to malignant transformation, it is not clear whether a decrease in the autophosphorylation of oncogenic Ret forms can affect the mitogenic and transforming activities of Ret. Potential modulators of the tyrosine kinase activity of Ret could be tyrosine phosphatases that are expressed in human thyroid tissue. Therefore, we investigated the impact of the tyrosine phosphatases SHP1 and SHP2 on the intrinsic tyrosine kinase activity and oncogenic potency of Ret with a 9-bp duplication in the cysteine-rich domain (codons 634–636), which was described in a patient with MEN type 2A recently. SHP1 and SHP2 were stably overexpressed in NIH3T3 fibroblasts together with Ret-9bp. Coexpression of SHP1 with Ret-9bp reduced the autophosphorylation of Ret-9bp by 19 ± 7% (P = 0.01, n = 4), whereas no effect was seen with SHP2. Furthermore, Ret-9bp could be coimmunoprecipitated with SHP1 but not with SHP2 antibodies. Suppression of the Ret-9bp tyrosine kinase activity by SHP1 caused a decrease in activation of Erk2 (extracellular signal-regulated kinase) and abolished PKB/Akt (protein kinase B) phosphorylation. In addition, diminished Ret-9bp autophosphorylation led to reduced phosphorylation of the transcription factor jun-D. Finally, the inhibitory effect on Ret-9bp signaling resulted in a 40–60% reduction of[ 3H]thymidine incorporation and in reduced ability of NIH3T3 cells to form colonies in soft agar. In conclusion, the data suggest that SHP1 caused a moderate reduction of Ret autophosphorylation, which led to a strong suppression of the Ret oncogene activity.
Early Expression of Pituitary Adenylate Cyclase-Activating Polypeptide and Activation of its Receptor in Chick Neuroblasts*
Authors: Erhardt Nola M. , Fradinger Erica A. , Cervini Laura A. , Rivier Jean E. , Sherwood Nancy M.
Published: January 2014

To investigate the involvement of pituitary adenylate cyclase- activating polypeptide (PACAP) and GH-releasing factor (GRF) during early chick brain development, we established neuroblast- enriched primary cell cultures derived from embryonic day 3.5 chick brain. We measured increases in cAMP generated by several species-specific forms of the peptides. Dose-dependent increases up to 5-fold of control values were measured in response to physiological concentrations of human/salmon, chicken, and tunicate PACAP27. Responses to PACAP38 were more variable, ranging from 5-fold for human PACAP38 to 4-fold for chicken PACAP38, to no significant response for salmon PACAP38, compared with control values. The responses to PACAP38 may reflect a greater difference in peptide structure compared with PACAP27 among species. Increases in cAMP generated by human, chicken, and salmon/carp GRF were not statistically significant, whereas increases in response to lower-range doses of tunicate GRF27-like peptide were significant, but small. We also used immunocytochemistry and Western blot to show synthesis of the PACAP38 peptide. RT-PCR was used to demonstrate that messenger RNAs for PACAP and GRF and a PACAP-specific receptor were present in the cells. This is a first report suggesting an autocrine/paracrine system for PACAP in early chick brain development, based on the presence of the ligand, messages for the ligand and receptor, and activation of the receptor in neuroblast-enriched cultures.
Maternal Undernutrition during Early to Midgestation Programs Tissue-Specific Alterations in the Expression of the Glucocorticoid Receptor, 11β-Hydroxysteroid Dehydrogenase Isoforms, and Type 1 Angiotensin II Receptor in Neonatal Sheep*
Authors: Whorwood C. B. , Firth K. M. , Budge H. , Symonds M. E.
Published: January 2014

We have investigated the effects of maternal nutrient restriction in the sheep during the period of rapid placental growth (i.e. 28–77 days gestation; term = 147 days) on feto-placental growth and expression of the glucocorticoid receptor (GR), types 1 and 2 11β-hydroxysteroid dehydrogenase (11βHSD1, 11βHSD2), and types 1 and 2 angiotensin II receptor (AT1, AT2) in fetal and neonatal offspring. Ewes (n = 63) of similar age, body weight, and body composition were randomly allocated to a nutrient-restricted (NR) group in which they consumed 3.2 MJ/day metabolizable energy (ME; equivalent to 50% of predicted requirements) or to a control group in which they consumed 6.7 MJ/day ME (equivalent to 110% of predicted requirements). After 77 days gestation, ewes from both dietary groups consumed close to 100% of ME requirements up to term. Newborn offspring of NR ewes were of similar body weight, but had increased crown-rump length, greater placental weight, and increased placental/body weight ratio (P < 0.01) compared with controls. Their kidneys were heavier (P < 0.05), but shorter in length, with increased ratios of transverse width to length (P < 0.001).

GR messenger RNA (mRNA) expression in neonatal offspring from NR ewes was increased in adrenal, kidney, liver, lung, and perirenal adipose tissue (P < 0.01). Conversely, 11βHSD1 mRNA expression was unaffected, except in perirenal adipose tissue, where it was higher in lambs born to NR ewes (P < 0.01). 11βHSD2 mRNA expression was decreased in adrenals and kidney (P < 0.001). Maternal NR also resulted in significantly increased AT1 expression in those tissues in which expression of GR was increased and/or 11βHSD2 was decreased, i.e. adrenals, kidney, liver, and lung. AT2 expression was unaffected by maternal NR. Although 11βHSD2 mRNA was undetectable in term placenta, it was abundant in midgestation placenta and was lower after maternal NR (P < 0.001). There was close agreement between levels of 11βHSD enzyme (i.e. 11β-dehydrogenase and 11-oxoreductase) activities and abundance of 11βHSD1 mRNA and 11βHSD2 mRNA expression.

The persistence of tissue-specific increases in the expression of GR, 11βHSD1 and AT1 and decreases in the expression of 11βHSD2 in adrenals and kidney in newborn offspring in response to a defined period of maternal nutrient restriction during early to midgestation suggests that gene expression has been programmed by nutrient availability to the fetus before birth. These data suggest key potential mechanisms by which maternal nutrition prenatally programs physiological pathways, such as the renin-angiotensin system, in the offspring that may lead to raised blood pressure and other cardiovascular disease risk factors in later life.
Reciprocal Control of Expression of mRNAs for Osteoclast Differentiation Factor and OPG in Osteogenic Stromal Cells by Genistein: Evidence for the Involvement of Topoisomerase II in Osteoclastogenesis
Authors: Yamagishi Takumi , Otsuka Eri , Hagiwara Hiromi
Published: January 2014

Osteoclast-like cells, in cocultures with mouse spleen cells and clonal osteogenic stromal ST2 cells, are formed from spleen cells with monocyte/macrophage lineage in response to a combination of osteoclast differentiation factor (RANKL) and OPG, a decoy receptor for RANKL, produced by ST2 cells in response to 1α,25-dihydroxyvitamin D3. Treatment of ST2 cells with the natural isoflavonoid genistein for 6 h before coculture with spleen cells inhibited the formation of tartrate-resistant acid phosphatase-positive osteoclast-like cells. When we measured levels of RANKL mRNA in ST2 cells, we found that genistein decreased the level of this mRNA. By contrast, the level of OPG mRNA was enhanced by genistein. Genistein is a specific inhibitor of topoisomerase II (topo II) and an inhibitor of protein tyrosine kinase, as well as being a potent phytoestrogen. To characterize the mode of action of genistein, we examined the effects of an inactive form of genistein (daidzein), 17β-estradiol, inhibitors of topo II, and inhibitors of tyrosine kinases on the formation of tartrate-resistant acid phosphatase-positive osteoclast-like cells. Among the compounds tested, two inhibitors of topo II, amsacrine and etoposide, attenuated the formation of osteoclast-like cells via reciprocal regulation of the expression of mRNAs for RANKL and OPG in ST2 cells, acting similarly to genistein. Our findings indicate that genistein might inhibit the formation of osteoclast-like cells via inhibition of the activity of topo II, suggesting the novel possibility that topo II might play an important role in osteoclastogenesis.
Calcitonin Induces IL-6 Production via Both PKA and PKC Pathways in the Pituitary Folliculo-Stellate Cell Line
Authors: Kiriyama Yoshimitsu , Tsuchiya Hiroyuki , Murakami Takeshi , Satoh Kumi , Tokumitsu Yukiko
Published: January 2014

It has been demonstrated that calcitonin-binding sites are present in a variety of tissue types, including in the pituitary gland. Interleukin-6 (IL-6) is also produced in the pituitary and it regulates the secretion of various hormones. In this study, we examined the expression of the calcitonin receptor and the mechanism of IL-6 production induced by calcitonin in the pituitary folliculo-stellate cell line (TtT/GF). The mRNA of calcitonin receptor subtype C1a, but not that of C1b, was detected by RT-PCR in TtT/GF cells and in the normal mouse pituitary. Calcitonin increased cAMP accumulation and IL-6 production in a concentration-dependent manner in TtT/GF cells. As calcitonin activates the PKA and PKC pathways, we investigated the contributions of PKA and PKC to IL-6 production. IL-6 production was only slightly increased by either 8-bromo-cAMP (1 mm) or phorbol 12-myristate 13-acetate (100 nm) alone. However, IL-6 was synergistically induced in the presence of both 8-bromo-cAMP (1 mm) and phorbol 12myristate 13-acetate (100 nm). Furthermore, calcitonin-induced IL-6 production was completely suppressed by H-89 (PKA inhibitor) or GF109203X (PKC inhibitor), indicating that the activation of both PKA and PKC is necessary for calcitonin-induced IL-6 production. On the other hand, pertussis toxin (Gi/Go signaling inhibitor) treatment achieved an approximately 9-fold increase in calcitonin-induced IL-6 production. These results show that calcitonin-stimulated IL-6 production is mediated via both PKA- and PKC-signaling pathways, whereas calcitonin also suppresses IL-6 production by activating Gi/Go proteins in folliculo-stellate cells.
Interaction Between Dax-1 and Steroidogenic Factor-1 in Vivo: Increased Adrenal Responsiveness to ACTH in the Absence of Dax-1
Authors: Babu Poda Suresh , Bavers David L. , Beuschlein Felix , Shah Sonalee , Jeffs Baxter , Jameson J. Larry , Hammer Gary D.
Published: January 2014

Two nuclear receptors, dosage-sensitive sex reversal adrenal hypoplasia congenita, critical region on the X chromosome gene-1 (Dax-1) and steroidogenic factor-1 (SF-1), are required for adrenal development and function. In vitro assays suggest that Dax-1 represses SF-1 mediated transcription. In this study, we generated SF-1+/−: Dax-1−/Y mice to examine the role of Dax-1 in SF-1-dependent steroidogenesis in vivo. While the SF-1 expression was impaired in SF-1+/− mice, there was no change in Dax-1 expression in SF-1+/− mice and no change in SF-1 expression in Dax-1−/Y mice. SF-1+/− mice had small adrenal glands with adrenal hypoplasia and cellular hypertrophy. The loss of Dax-1 in SF-1+/−: Dax-1−/Y mice reversed the decreased adrenal weight and histological abnormalities observed in SF-1+/− mice. SF-1+/− mice had elevated ACTH and the lowest corticosterone following restraint stress. In contrast, Dax-1−/Y mice had elevated corticosterone and decreased ACTH. Adrenal responsiveness (ACTH/corticosterone) was highest in Dax-1−/Y mice, intermediate in WT and SF-1+/−: Dax-1−/Y mice, and lowest in SF-1+/− mice. In accordance with these findings, ACTH stimulation testing resulted in the highest levels of corticosterone in the Dax-1−/Y mice. Protein levels of P450c21 and the ACTH receptor were increased in Dax-1−/Y mice and intermediate in SF-1+/−: Dax-1−/Y mice following chronic food deprivation. These results are consistent with a model in which Dax-1 functions to inhibit SF-1-mediated steroidogenesis in vivo.