Developmental and hormonally regulated messenger ribonucleic acid expression of KiSS-1 and its putative receptor, GPR54, in rat hypothalamus and potent luteinizing hormone-releasing activity of KiSS-1 peptide

The gonadotropic axis is centrally controlled by a complex regulatory network of excitatory and inhibitory signals that is activated at puberty. Recently, loss of function mutations of the gene encoding G protein-coupled receptor 54 (GPR54), the putative receptor for the KiSS-1-derived peptide metastin, have been associated with lack of puberty onset and hypogonadotropic hypogonadism. Yet the pattern of expression and functional role of the KiSS-1/GPR54 system in the rat hypothalamus remain unexplored to date. In the present work, expression analyses of KiSS-1 and GPR54 genes were conducted in different physiological and experimental settings, and the effects of central administration of KiSS-1 peptide on LH release were assessed in vivo. Persistent expression of KiSS-1 and GPR54 mRNAs was detected in rat hypothalamus throughout postnatal development, with maximum expression levels at puberty in both male and female rats. Hypothalamic expression of KiSS-1 and GPR54 genes changed throughout the estrous cycle and was significantly increased after gonadectomy, a rise that was prevented by sex steroid replacement both in males and females. Moreover, hypothalamic expression of the KiSS-1 gene was sensitive to neonatal imprinting by estrogen. From a functional standpoint, intracerebroventricular administration of KiSS-1 peptide induced a dramatic increase in serum LH levels in prepubertal male and female rats as well as in adult animals. In conclusion, we provide novel evidence of the developmental and hormonally regulated expression of KiSS-1 and GPR54 mRNAs in rat hypothalamus and the ability of KiSS-1 peptide to potently stimulate LH secretion in vivo. Our current data support the contention that the hypothalamic KiSS-1/GPR54 system is a pivotal factor in central regulation of the gonadotropic axis at puberty and in adulthood.     

Developmental expression of the G protein-coupled receptor 54 and three GnRH mRNAs in the teleost fish cobia

The cDNAs of the G protein-coupled receptor 54 (GPR54) and three prepro-gonadotropin-releasing hormones, GnRH-I (seabream GnRH), GnRH-II (chicken GnRH-II), and GnRH-III (salmon GnRH) were isolated and cloned from the brain of the teleost fish cobia, Rachycentron canadum. The cobia GPR54 cDNA was 95 and 51-56% identical to those of tilapia and mammalian models respectively. The GnRH cDNA sequences of cobia showed strong identities to those of tilapia, Atlantic croaker, red drum, and the seabass and seabream species. The real-time quantitative RT-PCR methods allowed detection of all three GnRH mRNAs on the first day after hatching (DAH). The GnRH-I mRNA levels, which were the lowest among the three GnRHs, increased gradually with two distinct peaks in larvae at 3 and 4 DAH. On the other hand, GnRH-II and GnRH-III mRNAs were significantly higher in larvae at 2 and 6 DAH compared with those on the preceding days. In addition, significant peaks of all the three GnRH mRNAs were observed in the brains of 26-day-old fish. The finding of higher GnRH-I and GnRH-II mRNAs in males than females at 153 DAH may be related to early puberty observed during the first year in laboratory-reared male cobia. Moreover, this study demonstrates for the first time the expression of GPR54 mRNA during larval development in a vertebrate species. The concomitant expression patterns of GPR54 and GnRH mRNAs during different stages of larval and juvenile developments, and during early puberty in male cobia suggest a potential relationship between GPR54 and multiple GnRHs during these stages of development consistent with the role of GPR54 in controlling GnRH release in mammals. The increase in GPR54 and GnRH mRNAs observed during early puberty in cobia is consistent with a similar change reported in pubertal rats. This finding together with the localization of GPR54 mRNAs on GnRH neurons in fish and mammals suggests that the GPR54-GnRH interactions may be conserved in different vertebrate groups.     

Dimerization of the class A G protein-coupled neurotensin receptor NTS1 alters G protein interaction

G protein-coupled receptors (GPCRs) have been found as monomers but also as dimers or higher-order oligomers in cells. The relevance of the monomeric or dimeric receptor state for G protein activation is currently under debate for class A rhodopsin-like GPCRs. Clarification of this issue requires the availability of well defined receptor preparations as monomers or dimers and an assessment of their ligand-binding and G protein-coupling properties. We show by pharmacological and hydrodynamic experiments that purified neurotensin receptor NTS1, a class A GPCR, dimerizes in detergent solution in a concentration-dependent manner, with an apparent affinity in the low nanomolar range. At low receptor concentrations, NTS1 binds the agonist neurotensin with a Hill slope of approximately 1; at higher receptor concentrations, neurotensin binding displays positive cooperativity with a Hill slope of approximately 2. NTS1 monomers activate G alpha q beta(1)gamma(2), whereas receptor dimers catalyze nucleotide exchange with lower affinity. Our results demonstrate that NTS1 dimerization per se is not a prerequisite for G protein activation.     

G protein-coupled receptor oligomerization: implications for G protein activation and cell signaling

The cardiovascular system is richly endowed with G protein-coupled receptors (GPCRs), members of the largest family of plasma membrane-localized receptors. During the last 10 years, it has become increasingly clear that many, if not all, GPCRs function in oligomeric complexes, as either homo- or hetero-oligomers. This review explores the mechanistic implications of GPCR dimerization and/or oligomerization on receptor activation and interactions with G proteins. The effects of GPCR oligomerization on receptor pharmacology, GPCR-mediated signaling, and potential contributions to GPCR crosstalk will be considered in the context of receptors important in the cardiovascular system. Our evolving understanding of the structural and functional consequences of GPCR oligomerization may provide novel and more selective sites for pharmacological tuning of cardiovascular function.     

腺苷酸活化的蛋白激酶通过SP1抑制下丘脑GT1-7神经元KiSS-1基因表达的机制研究

在GT1-7细胞用实时定量PCR检测腺苷酸活化的蛋白激酶(AMPK)对KiSS-1mRNA水平的影响,以报告基因技术检测KiSS-1基因启动子的活性,用Western印迹法检测AMPK对转录因子SP1蛋白表达及其在亚细胞中分布的影响.结果显示,AMPK能降低GT1-7细胞KiSS-1mRNA的表达水平,并能抑制KiSS-1基因的启动子活性;SP1能够增强KiSS-1基因的启动子活性;AMPK能够抑制SP1向细胞核的转位.提示AMPK可能通过抑制转录因子SP1的转位而降低KiSS-1基因的表达.     

Different G protein-coupled receptor kinases govern G protein and beta-arrestin-mediated signaling of V2 vasopressin receptor

Signaling through beta-arrestins is a recently appreciated mechanism used by seven-transmembrane receptors. Because G protein-coupled receptor kinase (GRK) phosphorylation of such receptors is generally a prerequisite for beta-arrestin binding, we studied the roles of different GRKs in promoting beta-arrestin-mediated extracellular signal-regulated kinase (ERK) activation by a typical seven-transmembrane receptor, the Gs-coupled V2 vasopressin receptor. Gs- and beta-arrestin-mediated pathways to ERK activation could be distinguished with H89, an inhibitor of protein kinase A, and beta-arrestin 2 small interfering RNA, respectively. The roles of GRK2, -3, -5, and -6 were assessed by suppressing their expression with specific small interfering RNA sequences. By using this approach, we demonstrated that GRK2 and -3 are responsible for most of the agonist-dependent receptor phosphorylation, desensitization, and recruitment of beta-arrestins. In contrast, GRK5 and -6 mediated much less receptor phosphorylation and beta-arrestin recruitment, but yet appeared exclusively to support beta-arrestin 2-mediated ERK activation. GRK2 suppression actually increased beta-arrestin-stimulated ERK activation. These results suggest that beta-arrestin recruited in response to receptor phosphorylation by different GRKs has distinct functional potentials.     

C-peptide increases the expression of vasopressin-activated calcium-mobilizing receptor gene through a G protein-dependent pathway

OBJECTIVE: Although an increasing number of reports suggest that physiological concentrations of C-peptide protect against the development of diabetic nephropathy, possibly through the modulation of Na-K pump activity, the intracellular pathways controlled by C-peptide are still unrecognized. C-peptide and vasopressin share similar intracellular effects including the activation of calcium influx and endothelial nitric oxide synthase. Both hormones stimulate also the activity of Na-K pump activity. Whether the activity of C-peptide is mediated by the recently identified vasopressin-activated calcium-mobilizing receptor (VACM-1) has never been previously investigated. DESIGN AND METHODS: To clarify this issue, we evaluated the effect of C-peptide on VACM-1 RNA (measured by semiquantitative RT-PCR) and protein expression (measured by immunoblotting) in human skin fibroblasts (where a specific binding of C-peptide was demonstrated) and in human mesangial cells, the cellular target of diabetic nephropathy. RESULTS: C-peptide-induced activation of VACM-1 was demonstrated in fibroblasts from six healthy individuals (0.51+/-0.1 vs 1.48+/-0.4, arbitrary units+/-s.e., P = 0.025). This finding was paralleled by an increased VACM-1 protein expression (5.64+/-1.0 vs 8.47+/-1.2, arbitrary units+/-s.e., P= 0.043). Similar results were confirmed in three independent cultures of human mesangial cells. VACM-1 activation in fibroblasts was insensitive to phosphatidylinositol-3-kinase inhibitor LY294002, but was inhibited by pertussis toxin, suggesting that activation of VACM-1 could be mediated by a G protein-coupled receptor. CONCLUSIONS: This study demonstrates for the first time that C-peptide activates VACM-1, possibly through a G protein-coupled receptor. Further studies are needed to clarify whether VACM-1 is involved in the protective effect of C-peptide against the development of diabetic nephropathy.     

Progestin and G protein-coupled receptor 30 inhibit mitogen-activated protein kinase activity in MCF-7 breast cancer cells

We have previously shown that the G protein-coupled receptor (GPR)30 is critical for progestin-induced growth inhibition. In this study, we addressed signal transduction pathways involved in progestin-mediated signaling. Progestin could not provide any additional growth inhibitory effect to MCF-7 cells treated with specific MAPK kinase inhibitors, PD98059 and U0126. Medroxyprogesteroneacetate (MPA) induced a late (22-23 h) decrease in ERK-1 and -2 activities verified by immunoblotting and kinase assay. The inactivation was abrogated by antiprogestin. Transient expression of GPR30 decreased ERK-1 and -2 activity; and in the cells in which GPR30 expression was decreased by the antisense, ERK activities were increased. The antisense-expressing cells were able to significantly resist the growth-inhibitory effect of the MAPK kinase inhibitors PD98059 and U0126 but not that of other factors tested. Interestingly, the decrease of ERK activity induced by MPA was abrogated by GPR30 antisense. Collectively, these results show that MAPK activity is inhibited by progestin and GPR30 and suggest that progestin-induced ERK inactivation is mediated through GPR30. Coupled with our previous findings, the data imply that up-regulation of GPR30 by progestin leads to ERK-1 and -2 inactivation associated with MPA-induced growth inhibition.     

GPR56, an atypical G protein-coupled receptor, binds tissue transglutaminase, TG2, and inhibits melanoma tumor growth and metastasis

The survival and growth of tumor cells in a foreign environment is considered a rate-limiting step during metastasis. To identify genes that may be essential for this process, we isolated highly metastatic variants from a poorly metastatic human melanoma cell line and performed expression analyses of metastases and primary tumors from these cells. GPR56 is among the genes markedly down-regulated in the metastatic variants. We show that overexpression of GPR56 suppresses tumor growth and metastasis, whereas reduced expression of GPR56 enhances tumor progression. Levels of GPR56 do not correlate with growth rate in vitro, suggesting that GPR56 may mediate growth suppression by interaction with a component in the tumor microenvironment in vivo. We show that GPR56 binds specifically to tissue transglutaminase, TG2, a widespread component of tissue and tumor stroma previously implicated as an inhibitor of tumor progression. We discuss the mechanisms whereby GPR56-TG2 interactions may suppress tumor growth and metastasis.     

The fibrinolytic receptor for urokinase activates the G protein-coupled chemotactic receptor FPRL1/LXA4R

The function of urokinase and its receptor is essential for cell migration in pathological conditions, as shown by the analysis of knockout mice phenotypes. How a protease of a fibrinolytic pathway can induce migration is not understood and no link between this protease and migration-promoting G protein-coupled receptors has been described. We now show that FPRL1/LXA4R, a G protein-coupled receptor for a number of polypeptides and for the endogenous lipoxin A4 (LXA4), is the link between urokinase-type plasminogen activator (uPA) and migration as it directly interacts with an activated, soluble, cleaved form of uPA receptor (uPAR) (D2D3(88-274)) to induce chemotaxis. In this article we show that (i) both uPAR and FPRL1/LXA4R are necessary for the chemotactic activity of uPA whereas FPRL1/LXA4R is sufficient to mediate D2D3(88-274)-induced cell migration. (ii) Inhibition or desensitization of FPRL1/LXA4R by antibodies or specific ligands specifically prevents chemotaxis induced by D2D3(88-274) in THP-1 cells and human peripheral blood monocytes. (iii) Desensitization of FPRL1/LXA4R prevents the activation of tyrosine kinase Hck induced by D2D3(88-274). (iv) D2D3(88-274) directly binds to FPRL1/LXA4R and is competed by two specific FPRL1/LXA4R agonists, the synthetic MMK-1 peptide and a stable analog of LXA4. Thus, a naturally produced cleaved form of uPAR is a unique endogenous chemotactic agonist for FPRL1/LXA4R receptor and its activity can be antagonized by specific ligands. These results provide the first direct link, to our knowledge, between the fibrinolytic machinery and the inflammatory response, demonstrating that uPA-derived peptide fragments can activate a specific chemotactic receptor.     

Targeted disruption of G protein-coupled bile acid receptor 1 (Gpbar1/M-Bar) in mice

G protein-coupled bile acid receptor 1 (Gpbar1/M-Bar) is a novel G protein-coupled receptor for bile acid. Tissue distribution and cell-type specificity of Gpbar1 mRNA suggest a potential role for the receptor in the endocrine system; however, the precise physiological role of Gpbar1 still remains to be elucidated. To investigate the role of Gpbar1 in vivo, the Gpbar1 gene was disrupted in mice. In homozygous mice, total bile acid pool size was significantly decreased by 21-25% compared with that of the wild-type mice, suggesting that Gpbar1 contributes to bile acid homeostasis. In order to assess the impact of Gpbar1 deficiency in bile acid homeostasis more precisely, Gpbar1 homozygous mice were fed a high-fat diet for 2 months. As a result, female Gpbar1 homozygous mice showed significant fat accumulation with body weight gain compared with that of the wild-type mice. These findings were also observed in heterozygous mice to the same extent. Although the precise mechanism for fat accumulation in female Gpbar1 homozygous mice remains to be addressed, these data indicate that Gpbar1 is a potential new player in energy homeostasis. Thus, Gpbar1-deficient mice are useful in elucidating new physiological roles for Gpbar1.     

Cytoplasmic expression of G protein-coupled estrogen receptor 1 correlates with poor postoperative prognosis in non-small cell lung cancer

BackgroundA hormonal role in the development of non-small cell lung cancer (NSCLC) has been well documented, and the classic estrogen receptors (ERs)—ERα and ERβ have been extensively investigated over the past decade. The expression of ERβ was found to be high and display biological activity in NSCLC, but anti-estrogen therapy targeting this receptor has shown limited efficacy for the disease. The third estrogen receptor, G protein-coupled estrogen receptor 1 (GPER1/GPR30), was recently found to be highly expressed in NSCLC. Herein, we aimed to investigate the expression profile of GPER1 and correlate it with clinicopathological factors as well as postoperative prognosis in NSCLC.MethodsWe examined GPER1 and ERβ expression using immunohistochemistry among 183 NSCLC cases, including 132 lung adenocarcinoma (LUAD) with identified epidermal growth factor receptor (EGFR) mutation status and 51 squamous cell carcinoma (SCC) patients. We then conducted correlation analysis between the expression of GPER1 and clinicopathological factors and patients’ postoperative prognosis.ResultsPositive expression of GPER1 was categorized into 2 main classes: nuclei-GPER1 (nGPER1) and concurrent nuclei-and cytoplasm-GPER1 (n/cGPER1), according to its subcellular localization. The LUAD with wild-type EGFR (wt-EGFR) had a higher frequency of n/cGPER1 (50%) but a lower frequency of nGPER1 (31%) when compared with those with mutated EGFR (n/cGPER1: 31%, nGPER1: 41%, respectively). The expression of GPER1, regardless of subcellular localization, was positively correlated with tumor stage and lymph node metastasis. The median recurrence-free survival (mRFS) and overall survival (OS) were significantly worse in participants with n/cGPER1 expression than in those with nGPER1 or without GPER1 expression.ConclusionsThis study revealed that GPER1 is aberrantly highly expressed and presents a unique GPER1 expression profile in NSCLC. The n/cGPER1 expression was significantly associated with EGFR mutation status, tumor stage, lymph node metastasis, and poor postoperative prognosis in NSCLC.     

Directed evolution of a G protein-coupled receptor for expression, stability, and binding selectivity

We outline a powerful method for the directed evolution of integral membrane proteins in the inner membrane of Escherichia coli. For a mammalian G protein-coupled receptor, we arrived at a sequence with an order-of-magnitude increase in functional expression that still retains the biochemical properties of wild type. This mutant also shows enhanced heterologous expression in eukaryotes (12-fold in Pichia pastoris and 3-fold in HEK293T cells) and greater stability when solubilized and purified, indicating that the biophysical properties of the protein had been under the pressure of selection. These improvements arise from multiple small contributions, which would be difficult to assemble by rational design. In a second screen, we rapidly pinpointed a single amino acid substitution in wild type that abolishes antagonist binding while retaining agonist-binding affinity. These approaches may alleviate existing bottlenecks in structural studies of these targets by providing sufficient quantities of stable variants in defined conformational states.     

Adrenomedullin increases the expression of calcitonin-like receptor and receptor activity modifying protein 2 mRNA in human microvascular endothelial cells

Adrenomedullin (AM) is a multifunctional peptide hormone, which plays a significant role in vasodilation and angiogenesis, implicating it in hypertension as well as in carcinogenesis. AM exerts its effects via the calcitonin receptor-like receptor (CRLR, now known as CL) complexed with either receptor activity modifying protein (RAMP) 2 or 3. We have investigated the effect of AM on immortalized human microvascular endothelial cells 1, since endothelial cells are a major source as well as a target of AM actions in vivo. Cells treated with AM showed elevated cAMP in a time (5-45 min)-dependent and dose (10(-6)-10(-14) M)-dependent manner. Pre-treatment with the AM receptor antagonist AM(22-52) partially suppressed the AM-induced increase in cAMP levels. An increase in extracellular signal-regulated kinase 1/2 phosphorylation was observed after 5 min of treatment with 10(-8) M AM. This phosphorylation was specific, since we were able to block the AM-induced effect with 1 microM U0126, a specific mitogen-activated protein/extracellular signal-regulated kinase kinase inhibitor. Using real-time PCR, we were able to show for the first time that AM upregulates peptide and mRNA expression of vascular endothelial growth factor (VEGF). However, AM treatment of cells did not result in increased cell proliferation. Instead, we observed that AM and VEGF induced cell migration, which could be inhibited by the AM(22-52) and anti-VEGF antibody respectively. AM also significantly elevated mRNA levels of CL (after 2 and 24 h treatment) and RAMP2 (after 1 and 24 h treatment). The upregulation of the AM receptor at two time points reflects possibly different cellular responses to short- and long-term exposure to AM.     

金茵利胆灵对豚鼠胆石症及G蛋白偶联胆汁酸受体表达的影响

目的研究金茵利胆灵对豚鼠胆囊容积和成石率与G蛋白偶联胆汁酸受体表达的影响。方法取雌性豚鼠72只,随机分为6组,每组12只,除正常对照组外其余5组给予盐酸林可霉素皮下注射建立胆石症模型。治疗组分为4组给予阿司匹林,金茵利胆灵高、中、低剂量药液灌喂,末次给药后1 h,切除胆囊测量胆囊容积,计算每组动物的胆囊内成石率。将胆囊组织进行HE染色后行显微镜观察,并行免疫组化观察阳性细胞。多组间比较采用单因素方差分析,两组间比较用LSD-t法;计数资料采用χ2检验,两组间比较调整检验水准进行比较;等级资料采用Kruskal-Wallis H检验。结果模型组成石率高于正常对照组,差异有统计学意义(P=0.00);金茵利胆灵高剂量组成石率较其他组降低。模型组胆囊大量中性粒细胞浸润,炎性改变明显;各药物治疗组中金茵高剂量组炎性改变最轻。模型组胆囊容积增加明显,与正常对照组相比差异有统计学意义(P0.01),造模效果较好;金茵利胆灵高剂量组胆囊容积相对最小,金茵利胆灵中剂量组和阿司匹林组胆囊容积相对略小,与模型组相比差异均有统计学意义(P0.01)。模型组胆囊黏膜TGR5阳性表达强,与正常对照组相比差异有统计学意义(P=0.00);金茵利胆灵高剂量组黏膜TGR5阳性表达较弱,与模型组相比差异有统计学意义(P0.01)。结论 TGR5在胆石症豚鼠胆囊黏膜的表达显著增强。金茵利胆灵可以降低胆石症豚鼠胆囊黏膜TGR5阳性表达率,可减轻胆囊炎症,减少胆石形成。     

Fluorescent protein complementation assays: new tools to study G protein-coupled receptor oligomerization and GPCR-mediated signaling

G protein-coupled receptor (GPCR) signaling is mediated by protein–protein interactions at multiple levels. The characterization of the corresponding protein complexes is therefore paramount to the basic understanding of GPCR-mediated signal transduction. The number of documented interactions involving GPCRs is rapidly growing, and appreciating the functional significance of these complexes is clearly the next challenge. New experimental approaches including protein complementation assays (PCAs) have recently been used to examine the composition, plasma membrane targeting, and desensitization of protein complexes involved in GPCR signaling. These methods also hold promise for better understanding of drug-induced effects on GPCR interactions. This review focuses on the application of fluorescent PCAs for the study of GPCR signaling. Potential applications of PCAs in high-content screens are also presented. Non-fluorescent PCA techniques as well as combined assays for the detection of ternary and quaternary protein complexes are briefly discussed.     

Heart failure increases protein expression and enzymatic activity of heme oxygenase-1 in the lung

OBJECTIVE: Heart failure (HF) cell or siderophages are pulmonary macrophages that phagonicytize erythrocytes leaked from the congested capillaries due to HF. Degradation of erythrocytes and hemoglobin increases concentrations of heme in the lung. We hypothesized that the HF-induced increase in the concentration of heme up-regulates the expression and enzymatic activity of heme oxygenase (HO)-1 in the lung. METHODS: Using the aortocaval (AC) fistula model of HF, we examined the following parameters 8-10 weeks after the creation of the fistula: morphological changes in the lung by Prussian blue iron and immunohistochemical staining, HO-1 protein expression and activity in the rat lungs, and concentrations of nitrite/nitrate (NO(x)(-)) and cyclic guanosine 3',5'-monophospate (cGMP) of the lung homogenates. RESULTS: Iron-stained siderophages were observed only in the lungs of rats with AC fistula. Protein level and enzyme activity of HO-1 were significantly enhanced in the lung of HF rats. NO(x)(-) concentrations of the two groups were similar, but cGMP was elevated in the lung of AC fistula rats (0.34+/-0.06 vs. 0.89+/-0.20 pmol/mg protein, P=0.025). Staining of serial sections of the lung tissues demonstrated induction of HO-1 co-localized to iron-stained siderophages. CONCLUSIONS: HF causes increased pulmonary HO-1 expression and activity, which emanates largely from siderophages. Up-regulation of HO-1 may have pulmonary protective in HF.     

β2-Adrenergic receptor regulation by GIT1, a G protein-coupled receptor kinase-associated ADP ribosylation factor GTPase-activating protein

G protein-coupled receptor activation leads to the membrane recruitment and activation of G protein-coupled receptor kinases, which phosphorylate receptors and lead to their inactivation. We have identified a novel G protein-coupled receptor kinase-interacting protein, GIT1, that is a GTPase-activating protein (GAP) for the ADP ribosylation factor (ARF) family of small GTP-binding proteins. Overexpression of GIT1 leads to reduced β₂-adrenergic receptor signaling and increased receptor phosphorylation, which result from reduced receptor internalization and resensitization. These cellular effects of GIT1 require its intact ARF GAP activity and do not reflect regulation of GRK kinase activity. These results suggest an essential role for ARF proteins in regulating β₂-adrenergic receptor endocytosis. Moreover, they provide a mechanism for integration of receptor activation and endocytosis through regulation of ARF protein activation by GRK-mediated recruitment of the GIT1 ARF GAP to the plasma membrane.