The G-protein family and their interaction with receptors

Drug Delivery Systems in the Development of Novel Strategies for Glioblastoma Treatment

Glioblastoma multiforme (GBM) is a grade IV glioma considered the most fatal cancer of the central nervous system (CNS), with less than a 5% survival rate after five years. The tumor heterogeneity, the high infiltrative behavior of its cells, and the blood-brain barrier (BBB) that limits the access of therapeutic drugs to the brain are the main reasons hampering the current standard treatment efficiency. Following the tumor resection, the infiltrative remaining GBM cells, which are resistant to chemotherapy and radiotherapy, can further invade the surrounding brain parenchyma. Consequently, the development of new strategies to treat parenchyma-infiltrating GBM cells, such as vaccines, nanotherapies, and tumor cells traps including drug delivery systems, is required. For example, the chemoattractant CXCL12, by binding to its CXCR4 receptor, activates signaling pathways that play a critical role in tumor progression and invasion, making it an interesting therapeutic target to properly control the direction of GBM cell migration for treatment proposes. Moreover, the interstitial fluid flow (IFF) is also implicated in increasing the GBM cell migration through the activation of the CXCL12-CXCR4 signaling pathway. However, due to its complex and variable nature, the influence of the IFF on the efficiency of drug delivery systems is not well understood yet. Therefore, this review discusses novel drug delivery strategies to overcome the GBM treatment limitations, focusing on chemokines such as CXCL12 as an innovative approach to reverse the migration of infiltrated GBM. Furthermore, recent developments regarding in vitro 3D culture systems aiming to mimic the dynamic peritumoral environment for the optimization of new drug delivery technologies are highlighted.

Effect of luteinizing hormone/choriogonadotropin receptor (LHCGR) gene on chicken reproductive traits

Luteinizing hormone/choriogonadotropin receptor (LHCGR) gene, potentially related to reproductive traits in chickens, was genotyped by using the Pooled DNA Sequencing, PCR-SSCP and Directing Sequencing techniques. 306 Erlang Mountain chickens form one line (SD03, a line that has been selected for egg quality from a local chicken breed in Sichuan province, China) were genotyped in this study. The associations between LHCGR polymorphisms and six reproductive traits [body weight at first egg (BWAFE), weight of first egg, age at first egg (AFE), number of eggs at 300 days of age (EN), body weight at 300 days of age and egg weight at 300 days of age (EWTA)] were estimated using the one-way analysis of variance method. Results showed that SNP +G4058A and SNP +T4099G of the LHCGR gene were significantly associated with BWFE and AFE. Birds with the AG genotype for the +G4058A SNP exhibited shorter AFE (P < 0.05) and greater EN than those of the GG and AA genotypes, suggesting a balancing selection (overdominance); the effect of allele C in SNP +C3021T and allele C in SNP +T4490C on EN and AFE is additive and may reflect the influence of positive selection. These alleles have promise as genetic markers for future marker-assisted selection.

Synthesis, pharmacological evaluation and QSAR modeling of mono-substituted 4-phenylpiperidines and 4-phenylpiperazines

A series of mono-substituted 4-phenylpiperidines and -piperazines have been synthesized and their effects on the dopaminergic system tested in vivo. The structure activity relationship (SAR) revealed that the position and physicochemical character of the aromatic substituent proved to be critical for the levels of 3,4-dihydroxyphenylacetic acid (DOPAC) in the brain of freely moving rats. In order to investigate how the structural properties of these compounds affect the response, a set of tabulated and calculated physicochemical descriptors were modeled against the in vivo effects using partial least square (PLS) regression. Furthermore, the binding affinities to the dopamine D2 (DA D2) receptor and monoamine oxidase A (MAO A) enzyme were determined for a chosen subset and QSAR models using the same descriptors as in the in vivo model were produced to investigate the mechanisms leading to the observed DOPAC response. These models, in combination with a strong correlation between the levels of striatal DOPAC and the affinities to DA D2 and MAO A, provides a comprehensive understanding of the biological response for compounds in this class.

Systematic in vivo screening of a series of 1-propyl-4-arylpiperidines against dopaminergic and serotonergic properties in rat brain: a scaffold-jumping approach

A series of 1-propyl-4-arylpiperidines were synthesized and their effects on the dopaminergic and serotonergic systems tested in vivo and in vitro. Scaffold jumping among five- and six-membered bicyclic aryl rings attached to the piperidine ring had a marked impact on these effects. Potent and selective dopamine D(2) receptor antagonists were generated from 3-indoles, 3-benzoisoxazoles, 3-benzimidazol-2-one, and 3-benzothiophenes. In contrast, 3-benzofuran was a potent and selective inhibitor of monoamine oxidase (MAO) A. The effects of the synthesized compounds on 3,4-dihydroxyphenylacetic acid (DOPAC) levels correlated very well with their affinity for dopamine D(2) receptors and MAO A. In the 4-arylpiperidine series, the most promising compound for development was the 6-chloro-3-(1-propyl-4-piperidyl)-1H-benzimidazol-2-one (19), which displayed typical dopamine D(2) receptor antagonist properties in vivo but produced only a partial reduction on spontaneous locomotor activity. This indicates that the compound may have a lower propensity to induce parkinsonism in patients.

Synthesis and evaluation of a set of 4-phenylpiperidines and 4-phenylpiperazines as D2 receptor ligands and the discovery of the dopaminergic stabilizer 4-[3-(methylsulfonyl)phenyl]-1-propylpiperidine (huntexil, pridopidine, ACR16)

Modification of the partial dopamine type 2 receptor (D(2)) agonist 3-(1-benzylpiperidin-4-yl)phenol (9a) generated a series of novel functional D(2) antagonists with fast-off kinetic properties. A representative of this series, pridopidine (4-[3-(methylsulfonyl)phenyl]-1-propylpiperidine; ACR16, 12b), bound competitively with low affinity to D(2) in vitro, without displaying properties essential for interaction with D(2) in the inactive state, thereby allowing receptors to rapidly regain responsiveness. In vivo, neurochemical effects of 12b were similar to those of D(2) antagonists, and in a model of locomotor hyperactivity, 12b dose-dependently reduced activity. In contrast to classic D(2) antagonists, 12b increased spontaneous locomotor activity in partly habituated animals. The "agonist-like" kinetic profile of 12b, combined with its lack of intrinsic activity, induces a functional state-dependent D(2) antagonism that can vary with local, real-time dopamine concentration fluctuations around distinct receptor populations. These properties may contribute to its unique "dopaminergic stabilizer" characteristics, differentiating 12b from D(2) antagonists and partial D(2) agonists.

Role of follicle stimulating hormone and epidermal growth factor in the development of porcine preantral follicle in vitro

The aim of the present study was to assess the role of follicle stimulating hormone (FSH), epidermal growth factor (EGF) or a combination of EGF and FSH on the in vitro growth of porcine preantral follicles, estradiol secretion, antrum formation, oocyte maturation and subsequent embryonic development. Porcine preantral follicles were cultured for 3 days in the absence or in the presence of FSH or EGF. Oocytes from these follicles were then matured, fertilized in vitro and embryos were cultured. Estradiol secretion and histological analysis of cultured follicles were also carried out. The results showed that when FSH, or a combination of EGF and FSH, was added to the culture medium, most of preantral follicles grew to antral follicles with high estradiol secretion and the oocytes from these antral follicles could mature, fertilize and develop to the blastocyst stage. Without FSH, or a combination of EGF and FSH, preantral follicles were unable to develop to the antral stage. Histology demonstrated that the resulting follicles were nonantral, estradiol production was reduced and none of their oocytes matured after in vitro maturation. The results indicate the essential role of FSH in promoting in vitro growth of porcine preantral follicle, estradiol secretion, antrum formation, oocyte maturation and subsequent embryonic development. EGF with FSH treatment of porcine preantral follicles improves the quality of oocytes, shown by a higher frequency of embryonic development.

G protein regulation of MAPK networks

G proteins provide signal-coupling mechanisms to heptahelical cell surface receptors and are critically involved in the regulation of different mitogen-activated protein kinase (MAPK) networks. The four classes of G proteins, defined by the G(s), G(i), G(q) and G(12) families, regulate ERK1/2, JNK, p38MAPK, ERK5 and ERK6 modules by different mechanisms. The alpha- as well as betagamma-subunits are involved in the regulation of these MAPK modules in a context-specific manner. While the alpha- and betagamma-subunits primarily regulate the MAPK pathways via their respective effector-mediated signaling pathways, recent studies have unraveled several novel signaling intermediates including receptor tyrosine kinases and small GTPases through which these G-protein subunits positively as well as negatively regulate specific MAPK modules. Multiple mechanisms together with specific scaffold proteins that can link G-protein-coupled receptors or G proteins to distinct MAPK modules contribute to the context-specific and spatio-temporal regulation of mitogen-activated protein signaling networks by G proteins.

Chemical sensing of DNT by engineered olfactory yeast strain

With the increasing threat of environmental toxicants including biological and chemical warfare agents, fabricating innovative biomimetic systems to detect these harmful agents is critically important. With the broad objective of developing such a biosensor, here we report the construction of a Saccharomyces cerevisiae strain containing the primary components of the mammalian olfactory signaling pathway. In this engineered yeast strain, WIF-1alpha, olfactory receptor signaling is coupled to green fluorescent protein expression. Using this 'olfactory yeast', we screened for olfactory receptors that could report the presence of the odorant 2,4-dinitrotoluene, an explosive residue mimic. With this approach, we have identified the novel rat olfactory receptor Olfr226, which is closely related to the mouse olfactory receptors Olfr2 and MOR226-1, as a 2,4-dinitrotoluene-responsive receptor.

Nucleotide receptor signaling in platelets

Upon injury to a vessel wall the exposure of subendothelial collagen results in the activation of platelets. Platelet activation culminates in shape change, aggregation, release of granule contents and generation of lipid mediators. These secreted and generated mediators trigger a positive feedback mechanism potentiating the platelet activation induced by physiological agonists such as collagen and thrombin. Adenine nucleotides, adenosine diphosphate (ADP) and adenosine triphosphate (ATP), released from damaged cells and that are secreted from platelet-dense granules, contribute to the positive feedback mechanism by acting through nucleotide receptors on the platelet surface. ADP acts through two G protein-coupled receptors, the Gq-coupled P2Y1 receptor, and the Gi-coupled P2Y12 receptor. ATP, on the other hand, acts through the ligand-gated channel P2X1. Stimulation of platelets by ADP leads to shape change, aggregation and thromboxane A2 generation. ADP-induced dense granule release depends on generated thromboxane A2. Furthermore, costimulation of both P2Y1 and P2Y12 receptors is required for ADP-induced platelet aggregation. ATP stimulation of P2X1 is involved in platelet shape change and helps to amplify platelet responses mediated by agonists such as collagen. Activation of each of these nucleotide receptors results in unique signal transduction pathways that are important in the regulation of thrombosis and hemostasis.

Mutation of the Follicle-Stimulating Hormone Receptor Gene 5′-Untranslated Region Associated With Female Hypertension

Inactivating mutations in the follicle-stimulating hormone receptor (FSHR) gene have been reported to cause hereditary hypergonadotropic ovarian failure. It has been found recently that the FSHR knockout mouse exhibits hypertension. The aim of the present study was to investigate the association between polymorphisms in the human FSHR gene and essential hypertension (EH) by using single nucleotide polymorphisms (SNPs). We selected 5 SNPs in the gene (rs1394205, rs2055571, rs11692782, rs1007541, and rs2268361) and performed 2 genetic case-control studies in different populations. A confirmative case-control study was performed using 1035 EH patients and 1058 age-matched controls. Transcriptional activities were measured with a luciferase assay system. The first case-control study found that the A allele of rs1394205 was significantly higher in EH females (P=0.010). In addition, in the confirmative case-control study, there was a significant difference for this SNP between female normotensive subjects (44.5%) and EH patients (50.7%) (P=0.043). Multiple logistic regression analysis in female subjects also revealed a significant association of subjects with the A allele of rs1394205 with EH (P=0.033), with the odds ratio calculated as 1.68 (95% CI: 1.04 to 2.73). Transcriptional activity of the A allele was 56+/-8% (mean+/-SD) of that observed for the G-type allele (P=0.001). Serum estradiol levels were significantly lower in patients with the A/A genotype than in patients without the A/A genotype (P=0.004). The SNP in the 5'-untranslated region of the FSHR gene affects levels of transcriptional activity and is a susceptibility mutation of EH in women.

Allosteric activation of the follicle-stimulating hormone (FSH) receptor by selective, nonpeptide agonists

The pituitary glycoprotein hormones, luteinizing hormone and follicle-stimulating hormone (FSH), act through their cognate receptors to initiate a series of coordinated physiological events that results in germ cell maturation. Given the importance of FSH in regulating folliculogenesis and fertility, the development of FSH mimetics has been sought to treat infertility. Currently, purified and recombinant human FSH are the only FSH receptor (FSH-R) agonists available for infertility treatment. By screening unbiased combinatorial chemistry libraries, using a cAMP-responsive luciferase reporter assay, we discovered thiazolidinone agonists (EC50's = 20 microm) of the human FSH-R. Subsequent analog library screening and parallel synthesis optimization resulted in the identification of a potent agonist (EC50 = 2 nm) with full efficacy compared with FSH that was FSH-R-selective and -dependent. The compound mediated progesterone production in Y1 cells transfected with the human FSH-R (EC50 = 980 nm) and estradiol production from primary rat ovarian granulosa cells (EC50 = 10.5 nm). This and related compounds did not compete with FSH for binding to the FSH-R. Use of human FSH/thyroid-stimulating hormone (TSH) receptor chimeras suggested a novel mechanism for receptor activation through a binding site independent of the natural hormone binding site. This study is the first report of a high affinity small molecule agonist that activates a glycoprotein hormone receptor through an allosteric mechanism. The small molecule FSH receptor agonists described here could lead to an oral alternative to the current parenteral FSH treatments used clinically to induce ovarian stimulation for both in vivo and in vitro fertilization therapy.

Neoplastic transformation by the gep oncogene, Galpha12, involves signaling by STAT3

Galpha(12), the alpha-subunit of G12, which has been referred to as the gep oncogene, stimulates mitogenic pathways in different cell types and readily induces neoplastic transformation of fibroblast cell lines. Recently, we have shown that the oncogenic pathway activated by Galpha(12) involves the receptor tyrosine kinase platelet derived growth factor receptor-alpha (PDGFRalpha) and JAK3. In the present study, we demonstrate that the GTPase-deficient activated mutant of Galpha(12) activates signal transducer and activator of transcription 3 (STAT3) via PDGFRalpha as well as JAK3. Here we show that Galpha(12) stimulates the phosphorylation of STAT3 at both Tyrosine-705 and Serine-727 residues. Studies to delineate the mechanism by which Galpha(12) stimulates STAT3 have indicated that the Tyrosine-705-phosphorylation of STAT3 involves the tyrosine kinases, Janus Kinase-3 as well as Src kinase, whereas the Serine-727 phosphorylation of STAT3 occurs via the receptor tyrosine kinase, PDGFRalpha and phosphatidylinositol 3-OH kinase pathway. Our results also indicate that the coexpression of the dominant negative, DNA binding mutant of STAT3 (STAT3DB) inhibits the foci formation as well as anchorage-independent growth of Galpha(12)QL-transfectants, thereby establishing the critical role of STAT3 in Galpha(12)QL-mediated neoplastic cell growth. The results presented here demonstrate, for the first time, the ability of Galpha(12) to recruit multiple receptor-, nonreceptor-, and Ser/Thr kinases to stimulate STAT3-signaling to promote neoplastic transformation.

Glucagon Receptors: Effect of Exercise and Fasting

One paradox of hormonal regulation during exercise is the maintenance of glucose homeostasis after endurance training despite a lower increase in plasma glucagon. One explanation could be that liver sensitivity to glucagon is increased by endurance training. Glucagon exerts its effect through a 62 KDa glycoprotein receptor, member of the G protein-coupled receptor. To determine whether changes with exercise in glucagon sensitivity occurred at the level of the glucagon receptor (GR), binding characteristics of hepatic glucagon receptors were ascertained in rat purified plasma membranes. Saturation kinetics indicated no difference in the dissociation constant or affinity of glucagon receptor, but a significantly higher glucagon receptor binding density in liver in endurance trained compared to untrained animals. Along with endurance training, it appears that fasting also changes GR binding characteristics. In animals fasting 24 hrs, a significant increase in glucagon receptor density was also reported. Although the exact mechanism remains unknown, there is no doubt that the liver can adapt to physiological stress through modulation of GR binding characteristics to enhance the hepatic glucose production responsiveness to glucagon. Key words: glucagon sensitivity, liver, endurance training, rats

Cloning and expression of cDNA for a luciferase from the marine copepod Metridia longa. A novel secreted bioluminescent reporter enzyme

Metridia longa is a marine copepod from which a blue bioluminescence originates as a secretion from epidermal glands in response to various stimuli. We demonstrate that Metridia luciferase is specific for coelenterazine to produce blue light (lambda(max) = 480 nm). Using an expression cDNA library and functional screening, we cloned and sequenced the cDNA encoding the Metridia luciferase. The cDNA is an 897-bp fragment with a 656-bp open reading frame, which encodes a 219-amino acid polypeptide with a molecular weight of 23,885. The polypeptide contains an N-terminal signal peptide of 17 amino acid residues for secretion. On expression of the Metridia luciferase gene in mammalian Chinese hamster ovary cells the luciferase is detected in the culture medium confirming the existence of a naturally occurring signal peptide for secretion in the cloned luciferase. The novel secreted luciferase was tested in a practical assay application in which the activity of A2a and NPY2 G-protein-coupled receptors was detected. These results clearly suggest that the secreted Metridia luciferase is well suited as a reporter for monitoring gene expression and, in particular, for the development of novel ultrahigh throughput screening technologies.

Determining cellular role of G alpha 12

Using the expression strategies described here, we have demonstrated a model system whereby the sequential signaling events involved in cell proliferation and subsequent transformation regulated by G alpha 12 can be investigated. The model system presented here can also be used to study the temporal interrelationships between small GTPases, kinases, and other signaling proteins involved in G alpha 12-signaling pathways. Further analyses using this model system and the strategies presented here should provide valuable clues in defining the signaling network regulated by G alpha 12 in stimulating cell proliferation and oncogenic transformation.

Biological activities of two porcine growth hormone-releasing hormone receptor isoforms

Binding of growth hormone-releasing hormone (GHRH) to two isoforms (G3R and G5R) of the porcine GHRH receptor was studied. Both G3R- and G5R-cDNA were isolated from a porcine anterior pituitary cDNA library and have an identical primary structure from aa 1 to 418 and a different aa sequence from aa 419 to 423. In addition, the G5R isoform contains an extra C-terminal tail of 28 aa. The G3R and G5R mRNAs arise from alternative splicing of a single precursor mRNA for GHRH receptors. A mammalian cell expression vector containing either G3R or G5R cDNA under the regulation of a strong human cytomegalovirus promoter was constructed and used to transfect a human embryonic kidney 293 cell line. Two stable transfectants (293/G3R-4 and 293/G5R-12) were isolated on the basis of high expression of the receptor mRNAs. Both G3R and G5R mRNAs were expressed at similarly high levels in 293/G3R-4 and 293/G5R-12 cells; however, GHRH binding to 293/G3R-4 cells was much greater than that observed for 293/G5R-12 cells. Basal as well as GHRH-stimulated GTPase activity and intracellular cAMP concentration are also significantly greater in 293/G3R-4 cells as compared to 293/G5R-12 cells. We conclude that the modification of GHRH receptor at the C-terminal region hindered GHRH binding to the receptor and thus attenuates its biological activities.

No evidence of somatic activating mutations on gonadotropin receptor genes in sex cord stromal tumors

OBJECTIVE

To search for somatic activating mutations of gonadotropin receptor (FSH-R and LH/chorionic gonadotropin receptor [CG-R]) genes as a cause of sex cord stromal tumors.

DESIGN

Molecular studies in human tissue.

SETTING

University hospital. SPECIMEN(S): Eight granulosa cell tumors collected from paraffin-embedded tissue, eight Leydig cell tumors, and three thecomas collected from fresh-frozen or paraffin-embedded tissue.

INTERVENTION(S)

Tumor samples were used for DNA extraction. The entire exon 11 of the LH/CG-R gene and a hot spot for gonadotropin receptor activating mutations on exon 10 of the FSH-R gene were amplified by polymerase chain reaction. The former was analyzed by denaturing gradient gel electrophoresis and automatic direct sequencing, and the latter by automatic direct sequencing.

MAIN OUTCOME MEASURE(S)

Results of denaturing gradient gel electrophoresis and automatic direct sequencing.

RESULT(S)

No somatic activating mutation was detected in exon 11 of the LH/CG-R gene in eight Leydig cell tumors and three thecomas. In addition, no mutations were detected in eight granulosa cell tumors in the hot spot for activating mutations in exon 10 of the FSH-R gene.

CONCLUSION(S)

Somatic activating mutations of gonadotropin receptors seem to play no relevant role in the development of sex cord stromal tumors.

Molecular architecture and biorecognition processes of the cystine knot protein superfamily: part I. The glycoprotein hormones

In this review article, the reader is introduced to recent advances in our knowledge on a subset of the cystine knot superfamily of homo- and hetero-dimeric proteins, from the perspective of the endocrine glycoprotein hormone family of proteins: follitropin (FSH), Iutropin (LH), thyrotropin. (TSH) and chorionic gonadotropin (CG). Subsequent papers will address the structure-function behaviour of other members of this increasingly significant family of proteins, including various members of the transforming growth factor-beta (TGF-beta) family of proteins, the activins, inhibins, bone morphogenic growth factor, platelet derived growth factor-beta, nerve growth factor and more than 35 other proteins with similar topological features. In the present review article, specific emphasis has been placed on advances with the glycoprotein hormones (GPHs) that have facilitated greater insight into their physiological functions, molecular structures and most importantly the basis of the molecular recognition events that lead to the formation of hetero-dimeric structures as well as their specific and selective recognition by their corresponding receptors and antibodies. Thus, this review article focuses on the structural motifs involved in receptor recognition and the current techniques available to identify these regions, including the role of immunological methodology, peptide fragment design and synthesis and mutagenesis to delineate their structure-function relationships and molecular recognition behaviour.

The inhibitory guanine nucleotide-binding protein Gi2alpha induces and potentiates adipocyte differentiation

The present study further elucidates the involvement of the alpha-subunit of the GTP-binding protein Gi2 in the differentiation of murine 3T3-L1 cells. Control and vector-transfected cells attained a fully differentiated adipocyte phenotype showing ample lipid droplets. Cells expressing wild type (WT)-Gi2alpha or the constitutively active R179E-Gi2alpha, however, became enlarged, less confluent, and produced large amounts of lipids. Differentiation consistently increased the triglyceride (TAG) content in control cells. In both WT-Gi2alpha and R179E-Gi2alpha clones, a marked increase in TAG could be detected even prior to insulin/dexamethasone/isobutyl methylxanthine exposure. The activity of palmitoyl-CoA synthetase (PCS) and glycerophosphate acyltransferase (GPAT) also increased upon differentiation. WT-Gi2alpha and R179E-Gi2alpha overexpression also enhanced PCS and GPAT activities even before differentiation medium was added. The total amount of phospholipids (PL) generally increased upon differentiation; however, pre- and postdifferentiation values were insignificantly different in cells expressing WT-Gi2alpha and R179E-Gi2alpha. Differentiation altered the PL profile with a relative shift from phosphatidylcholine and phosphatidylethanolamine to phosphatidylinositol (PI) in differentiated cells. Finally, differentiation yielded a general increase in the activity of basal PI-phospholipase-C activity. Again, cells expressing WT-Gi2alpha and R179E-Gi2alpha demonstrated elevated enzyme activity and enhanced second messenger accumulation subsequent to differentiation. In summary, cells with the R179E-mutants of Gi2alpha exhibited stimulated lipid turnover and accumulation in both undifferentiated and differentiated cells.

Modulation of Mdm2 expression and p53-induced apoptosis in immortalized human ovarian granulosa cells

The activity of the tumor suppressor gene p53 is implicated in arrest of the cell cycle and the induction of apoptosis. The mdm2 oncogene is transcriptionally activated by p53, and the protein products of this gene can down-modulate biochemical activities and biological effects of p53 in a cell context-dependent manner. We have established highly steroidogenic human granulosa cell lines expressing the Ha-ras oncogene and a temperature sensitive (ts) mutant of p53 (p53val135) to test the involvement of p53-downstream genes in the modulation of apoptosis in these cells. We find that ras-transformed granulosa cells expressing p53val135 undergo apoptosis following a shift from 37 C to 32 C, a temperature at which p53val135 exerts its wild-type activity. Elevating the cellular content of cAMP at 32 C markedly enhances apoptosis. Basic fibroblast growth factor (bFGF) effectively blocks the p53/cAMP-induced apoptosis, but suppresses steroidogenesis. A naturally produced basement membrane-like extracellular matrix (ECM) containing immobilized bFGF exerts a similar antiapoptotic effect, but unlike soluble bFGF, it enhances steroidogenesis in these cells. While cAMP markedly suppresses the p53-induced Mdm2 expression, bFGF and ECM elevate Mdm2 expression 3-5-fold. These effects on Mdm2 expression are most pronounced 2-4 h after the shift to 32 C, before nuclear fragmentation is detected. Cells grown at 32 C in contact with ECM have a more developed actin cytoskeleton both in the absence and presence of cAMP stimulation, compared with cells grown on plastic dishes. We conclude that bFGF and components of the ECM can cross-talk with p53/cAMP-generated signals for apoptosis. These signals may, at least in part, be coordinated by the modulation of Mdm2 expression, which precedes the biochemical events characteristic of apoptosis. The multicomponent ECM also induced differentiation in these ras-transformed cells, while soluble bFGF inhibited differentiation, suggesting that ECM components other than bFGF stimulate differentiation. Organization of the actin cytoskeleton is likely to play an important role in the cross-talk between p53/cAMP- and bFGF/ECM-generated signals. Because the tumor suppressor gene p53 is implicated with apoptosis of primary granulosa cells and the ECM is involved in the prevention of this process, the newly established cell lines can serve as a useful model for apoptosis in highly luteinized granulosa cells.

Thyrotoxicosis in children

Graves' disease is the predominant cause of hyperthyroidism in the pediatric age group. Other disorders must be recognized, however, because adequate management relies on a precise diagnosis. Careful monitoring of the thyroid status is required during this active phase of growth and development.

Different signaling pathways mediate stimulated secretions of endogenous ouabain and aldosterone from bovine adrenocortical cells

Angiotensin II stimulates secretion of corticosteroids and an ouabain-like compound from adrenocortical cells. The angiotensin AT1 and AT2 receptor subtypes have been linked with stimulated secretion of aldosterone and endogenous ouabain, respectively, but the second messenger mechanisms involved in the latter secretion are not known. Accordingly, we investigated the effects of several pharmacological agents that affect signaling pathways on the basal and stimulated secretions of aldosterone and endogenous ouabain from primary cell cultures of bovine adrenocortical cells. The AT2 receptor antagonist, PD 123319, blocked the effects of angiotensin II on secretion of endogenous ouabain but not aldosterone. Treatment of the cells with either dibutyryl cAMP, a membrane permeant analog, or the phorbol ester tetradecanoyl phorbol acetate stimulated aldosterone secretion but had no effect on the secretion of endogenous ouabain. On the other hand, the membrane permeant analog, 8BcGMP, maximally activated secretion of endogenous ouabain whereas incubation of cells with sodium orthovanadate blocked angiotensin II stimulated secretion of endogenous ouabain. Neither 8BcGMP nor sodium orthovanadate affected the basal or stimulated components of aldosterone secretion. These results show that the secretions of aldosterone and endogenous ouabain from bovine adrenocortical cells are mediated by different intracellular signaling mechanisms and provide evidence that the adrenal secretions of these steroids are regulated differently.

Modulation of FSH receptor phosphorylation correlates with hormone-induced coupling to the adenylate cyclase system

The authors have recently demonstrated that an inhibitor of protein phosphorylation, staurosporine (SSP), can dramatically enhance follicle-stimulating hormone (FSH) stimulated cyclic adenosine monophosphate (cAMP) accumulation in rat granulosa cell line (GFSHR-17) overexpressing about 20-fold FSH receptor than primary granulosa cells. Moreover, incubation with SSP can partially release the cells from FSH-induced desensitization. In this work, it was examined whether coupling of FSH receptor to the adenylate cyclase is correlated with the degree of receptor phosphorylation. Immunoprecipitation of FSH receptor after metabolic labeling of the cells with 32P-orthophosphate revealed that preincubation of the cells with SSP resulted in pronounced reduction in FSH receptor phosphorylation compared to control cells, concomitantly with a dramatic increase in FSH-stimulated cAMP accumulation. In contrast, incubation of the cells with saturating dose of FSH, which leads to uncoupling between the receptor and the adenylate cyclase, resulted in enhanced receptor phosphorylation. Moreover, cells preincubated with FSH could be released from desensitization by further incubation with SSP and a significant reduction in FSH receptor phosphorylation. Immunostaining of the cells with FSH receptor antibody reveal a homogenous distribution of the receptor on the surface of SSP-treated cells. Some aggregation of the receptor was evident in control cells that were not treated with SSP. In contrast, massive clustering and capping of the receptor molecules were observed on the surface of FSH-stimulated cells. The current data suggest that phosphorylation-dephosphorylation of the receptor molecules play an important role in the degree of coupling between the receptor and the adenylate cyclase system. Moreover, desensitization to FSH stimulation that is implicated with high degree of receptor phosphorylation may lead to aggregation of the receptor molecules on the cell surface.

Expression of messenger ribonucleic acids of luteinizing hormone and follicle-stimulating hormone receptors in granulosa and theca layers of chicken preovulatory follicles

Expression of luteinizing hormone receptor (LHR) and follicle-stimulating hormone receptor (FSHR) mRNAs was demonstrated in the granulosa and theca layers of the large preovulatory follicles of the chicken ovary by Northern hybridization and reverse transcription-polymerase chain reaction (RT-PCR). Northern hybridization results showed multiple LHR and FSHR mRNA transcripts and the predominant species were 2.3 and 2.5 kb, respectively. The highest abundance of LHR mRNA was found in the granulosa layer of the largest follicle (F1 follicle), while the abundance remained low in the granulosa layers of the third (F3) and fifth largest (F5) follicles. FSH mRNA abundance was the highest in the granulosa layer of F5 follicle, but decreased in the granulosa layers of F3 and F1 follicles. In the theca layers of all the three follicles examined LHR and FSHR mRNAs were extremely low. These results were confirmed by RT-PCR experiment which involved coamplification of LHR or FSHR mRNA and beta-actin mRNA as the internal control. The LHR PCR product was sequenced and indicated 92.2% homology with the corresponding region of the quail LHR cDNA. This study indicated that the marked increase in expression of LHR mRNA in granulosa layer of the F1 follicle might be important for LHR protein synthesis and succeeding bonus progesterone production in F1 follicle destined to ovulation. However, higher expression of FSHR mRNA in the granulosa layer of the less mature follicles may be involved in the differentiation and maturation of granulosa cells in these follicles.

Effect of activating and inactivating mutations of Gs- and Gi2-alpha protein subunits on growth and differentiation of 3T3-L1 preadipocytes

Previous investigations have demonstrated that both Gs- and the Gi-family of GTP-binding proteins are implicated in differentiation of the 3T3-L1 preadipocyte. In order to further analyze the role of Gs alpha vs. Gi2 alpha, which are both involved in adenylate cyclase modulation, we transfected undifferentiated 3T3-L1 cells with two sets of G-protein cDNA: the pZEM vector with either wild type, the activating (i.e., GTP-ase inhibiting) R201C-Gs alpha or the inactivating G226A(H21a)-Gs alpha point mutations, or the pZIPNeoSV(X) retroviral vector constructs containing the Gi2 alpha wild type or the missense mutations R179E-Gi2 alpha, Q205L-Gi2 alpha, and G204A(H21a)-Gi2 alpha. The activating [R201C]Gs alpha-mutant did not significantly affect the differentiation process, i.e., increase in the steady-state levels of G-protein subunits, gross appearance, or insulin-elicited deoxy-glucose uptake into 3T3-L1 adipocytes, despite a marked initial increase in hormone-elicited adenylate cyclase activity. The [H21a]Gs alpha-mutant, on the other hand, enhanced the degree of differentiation slightly, as evidenced by an augmented production of lipid vesicles and insulin-stimulated deoxy-glucose uptake. However, an expected increase in mRNA for hormone-sensitive lipase was not seen. Secondly, it appeared that both activating [R179E]Gi2 alpha or [Q205L]Gi2 alpha mutants reduced cell doubling time in non-confluent 3T3-L1 cell cultures, while [H21a]Gi2 alpha slowed proliferation rate. Furthermore, it seemed that cell proliferation, as evidenced by thymidine incorporation, ceased at a much earlier stage prior to cell confluency when cultures were transfected with the [R179E]Gi2 alpha or [Q205L]Gi2 alpha mutants. Upon differentiation with insulin, dexamethasone, and iBuMeXan, the following cell characteristics emerged: the [R179E]Gi2 alpha and [Q205L]Gi2 alpha mutants consistently enhanced adenylate cyclase activation and cAMP accumulation stimulated by isoproterenol and corticotropin over controls. Deoxy-glucose uptake was also super-activated by the [R179E]Gi2 alpha and [Q205L]Gi2 alpha mutants. Finally, steady-state levels of hormone sensitive lipase mRNA were dramatically increased by [R179E]Gi2 alpha and [Q205L]Gi2 alpha over differentiated controls. The inactivating [H21a]Gi2 alpha-mutant obliterated all signs of preadipocyte differentiation. It is concluded that Gi2 plays a positive and much more important role than Gs in 3T3-L1 preadipocyte differentiation. Cyclic AMP appears to play no role in this process.

Molecular screening for somatic mutations in corticotropic adenomas of dogs with pituitary-dependent hyperadrenocorticism

Pituitary tumorigenesis is now generally regarded as a multistep process of genomic damage leading to uncoupling of interdependent systems that control cell proliferation and differentiation. The alterations include mutations in genes encoding for proteins involved in signal transduction pathways, such as G-proteins and the p21 protein encoded for by the ras genes. Apart from their excessive secretion of ACTH, corticotropic adenomas are characterized by decreased sensitivity to inhibition by glucocorticoids. Therefore, mutations in the glucocorticoid receptor leading to decreased sensitivity to glucocorticoids may contribute to corticotropic tumor formation. In this study, 16 corticotropic adenomas of dogs with pituitary-dependent hyperadrenocorticism were screened for mutations in the Gs alpha, H-, K-, N-ras genes and the coding region of the DNA-binding domain of the glucocorticoid receptor. The cDNA fragment of the Gs alpha gene encompassed codons 159-240. The K-, and N-ras fragments spanned codons 1-71. The H-ras gene was only screened for mutations in codons 12/13 by direct sequencing of the PCR product. The cDNA fragment of the DNA-binding domain of the glucocorticoid receptor encompassed codons 410-500. The Gs alpha, K-ras, N-ras genes and the DNA-binding domain of the glucocorticoid receptor were screened by single-strand conformation polymorphism analysis. No mutations were found in the Gs alpha gene, the ras genes and the DNA-binding domain of the glucocorticoid receptor. It is concluded that mutations in the Gs alpha gene (codons 159-240), the K- and N-ras genes (codons 1-71), the H-ras gene (codons 12/13) and mutations in the DNA-binding domain of the glucocorticoid receptor do not play a role in the tumorigenesis of canine corticotropic adenomas.

The regulation of growth hormone secretion

The regulation of GH secretion involves finely balanced systems with multiple components. As our knowledge of the physiology of GH regulation expands, so does our understanding of the bases for GH diseases. We now can identify several cellular loci that cause GH deficiency or GH excess. In addition, the recent increased understanding of GH physiology has resulted in an increase in potential therapies for growth disorders.

Physiological and biochemical evidence for coordinate increases in muscarinic receptors and Gi during pacing-induced heart failure

BACKGROUND

It is not clear whether the increase in the myocardial guanylyl nucleotide inhibitory protein (Gi), frequently observed in heart failure, is associated with any functional effects.

METHODS AND RESULTS

Eight sham-operated dogs and 10 dogs were studied with pacing-induced heart failure (240 bpm for 4 to 7 weeks), characterized by reduced (P<.05) left ventricular dP/dt (from 2926+/-99 to 1303+/-126 mm Hg/s). The muscarinic agonist acetylcholine (10 micrograms/kg IV) in the presence of ganglionic blockade reduced left ventricular dP/dt more (P<.05) in heart failure (-23+/-2%) than before heart failure (-8+/-2%), despite lesser reductions in arterial pressure. Gi alpha2 was increased by 55% in heart failure. Dose-response curves for carbachol (10-8 to 10-3 mol/L) inhibition of isoproterenol-stimulated adenylyl cyclase demonstrated significantly greater (P<.05) inhibition in heart failure compared with sham-operated dogs. These changes were associated with a coordinate increase in muscarinic receptor density, determined by antagonist binding with 3H-quinuclidinyl benzilate, in heart failure (153+/-6.2 fmol/mg protein) compared with sham-operated dogs (124+/-7.4 fmol/mg protein). Agonist binding with carbachol also revealed an increase in total muscarinic receptors in heart failure without a change in fraction of high- and low-affinity receptors.

CONCLUSIONS

These data, in the aggregate, provide physiological and biochemical evidence to support the concept that the coordinate increases in muscarinic receptor number and Gi levels in heart failure are coupled to increased inhibition of adenylyl cyclase activity and an increased inhibition of myocardial contractility.

The photoactivatable NAD+ analogue [32P]2-azido-NAD+ defines intra- and inter-molecular interactions of the C-terminal domain of the G-protein G alpha t

Recently, we reported the synthesis and use of [32P]2-azido-NAD+ as a probe to study the structural organization of G-proteins. Pertussis toxin was used to 'tether' [32P]2-azido-ADP-ribose of [32P]2-azido-NAD+ to Cys347 of the alpha subunit of the G-protein Gt. Light activation of the azide moiety covalently cross-linked the domain containing Cys347 at the C-terminus of alpha t with neighbouring intra- and inter-molecular domains of holo-transducin. The radiolabel from [32P]2-azido-ADP-ribose was then transferred to the 'acceptor' domain by cleaving the thioglycosidic bond between Cys347 and [32P]2-azido-ADP- ribose with mercuric acetate. ADP-ribosylation followed by photocross-linking of holo-transducin indicated intramolecular interactions of the C-terminal domain with other alpha t domains and intermolecular interactions with holotransducin alpha and gamma subunits. The radiolabelled peptides, which were radiolabelled because of the transfer of the photoactive moiety, were identified by utilizing 2-(2'-nitrophenylsulphenyl)-3-methyl-3'- bromoindolenine ('BNPS-skatole') and CNBr. The results indicate that the C-terminus of alpha t interacts with both N-terminal and C-terminal domains within the alpha t molecular. Mapping the interacting sites between cross-linked alpha dimers and alpha trimers indicates that the C-terminal domain of alpha t is involved in the formation of alpha t homopolymers in solution. In addition, our studies place the beta gamma subunit in close proximity to Cys347 of alpha t, as indicated by the transfer of [32P]2-azido-ADP-ribose from Cys347 to the gamma subunit, which was further localized to the C-terminal half of gamma t. The studies presented here identify the C-terminal intra- and inter-molecular interactions of the alpha subunit of holo-transducin.

Activation of Jun kinase/stress-activated protein kinase by GTPase-deficient mutants of G alpha 12 and G alpha 13

Signal transduction pathways regulated by G12 and G13 heterotrimeric G proteins are largely unknown. Expression of activated, GTPase-deficient mutants of alpha 12 and alpha 13 alter physiological responses such as Na+/H+ exchanger activity, but the effector pathways controlling these responses have not been defined. We have found that the expression of GTPase-deficient mutants of alpha 12 (alpha 12Q229L) or alpha 13 (alpha 13Q226L) leads to robust activation of the Jun kinase/stress-activated protein kinase (JNK/SAPK) pathway. Inducible alpha 12Q229L and alpha 13Q226L expression vectors stably transfected in NIH 3T3 cells demonstrated JNK/SAPK activation but not extracellular response/mitogen-activated protein kinase activation. Transient transfection of alpha 12Q229L and alpha 13Q226L also activated the JNK/SAPK pathway in COS-1 cells. Expression of the GTPase-deficient mutant of alpha q (alpha qQ209L) but not alpha i (alpha iQ205L) or alpha s (alpha sQ227L) was also able to activate the JNK/SAPK pathway. Functional Ras signaling was required for alpha 12Q229L and alpha 13Q226L activation of the JNK/SAPK pathway; expression of competitive inhibitory N17Ras inhibited JNK/SAPK activation in response to both alpha 12Q229L and alpha 13Q226L. The results describe for the first time a Ras-dependent signal transduction pathway involving JNK/SAPK regulated by alpha 12 and alpha 13.

Point mutations of ras and Gs alpha subunit genes in thyroid tumors

We studied 43 thyroid tumors including 5 adenomatous goiters, 7 follicular adenomas, 22 papillary carcinomas, and 9 medullary carcinomas with regard to the presence of point mutations in the genes of Gs alpha subunit (Gs alpha), Gi2 alpha subunit (Gi2 alpha), H-ras, K-ras, and N-ras by a polymerase chain reaction-direct sequencing method. An adenomatous goiter and a follicular adenoma showed double mutations at codon 227 and 231, and 4 papillary carcinomas showed mutation at codon 231 of the Gs alpha gene. An adenomatous goiter, a follicular adenoma, and a papillary carcinoma showed a missense mutation in codon 13 of the K-ras gene. There were no such missense mutations of these G-protein or ras genes in medullary carcinomas. These data indicate that the genetic events involved in the oncogenesis of parafollicular C-cells are different from those of thyroid follicular cells, in which missense mutations of Gs alpha and ras genes seem to play important roles in tumorigenesis.

Subtypes of Guanine-Nucleotide-Binding Regulatory Proteins at the Locus coeruleus Involved in Fentanyl-Induced Muscular Rigidity in the Rat

Previous results from our laboratory have established that the G(o) subtype of guanine nucleotide (GTP)-binding regulatory protein at the locus coeruleus (LC) may participate in the elicitation of muscular rigidity by fentanyl. The present study further examined the involvement of other subtypes of GTP-binding regulatory proteins at the LC in this process, using Sprague-Dawley rats anesthetized with ketamine (120 mg/kg, i.p., with 30 mg/kg/h i.v. infusion supplements) and under mechanical ventilation. Intravenous administration of fentanyl (100 &mgr;g/kg) induced a significant increase in electromyographic signals recorded from the sacrococcygeus dorsi lateralis muscle. Power spectral analysis revealed that this was accomplished by a decrease in the mean power frequency and an increase in the root mean square values of the signals. The above responses were appreciably antagonized by pretreating animals with bilateral microinjection into the LC of pertussis toxin (80 or 160 fmol), N-ethylmaleimide (16 pmol) or 1-(5-isoquinolinesulfonyl)-2-methylpiperazine (100 or 200 fmol); but not by cholera toxin (120 or 240 fmol), forskolin (240 or 480 pmol) or N-ethylmaleimide at a higher dose (32 pmol). These results suggest that, in addition to G(o) protein, fentanyl-induced muscular rigidity may also involve other pertussis toxin-sensitive GTP-binding regulatory proteins, possibly G(i) and G(p) subtypes, in the signal transduction processes following activation of &mgr;-opioid receptors at the LC. Copyright 1995 S. Karger AG, Basel

Analysis of G protein alpha subunit mRNA abundance in preimplantation mouse embryos using a rapid, quantitative RT-PCR approach

We have developed a novel reverse transcription-polymerase chain reaction (RT-PCR)-based approach for systematically quantifying in a single experiment the abundances of many different mRNAs in preimplantation mouse embryos. With this approach, the entire mRNA population from a small number of embryos is amplified while preserving the relative abundance of each mRNA in the cDNA population. The cDNA is analyzed by quantitative hybridization to radiolabeled probes. The approach is very sensitive and provides reliable, quantitative data regarding changes in mRNA abundance. A major advantage of this method is that estimates of mRNA copy number can be obtained and compared between different mRNAs. With this approach, we analyzed the patterns of expression of nine G protein alpha subunit mRNAs (G alpha s, G alpha i, G alpha q, G alpha o, and G alpha 11-15) in oocytes, eggs, and preimplantation embryos from fertilization to the blastocyst stage. Six alpha subunit mRNAs were expressed at significant levels, all of which underwent significant temporal alterations in expression. The mRNAs encoding some alpha subunit types were expressed predominantly in the egg and 1-cell embryo, underwent sharp reductions during the 2-cell stage, and were re-expressed between the 8-cell and blastocyst stages. One alpha subunit mRNA increased in abundance at the early blastocyst stage. The possible significance of these alterations in G protein mRNA abundance to embryonic development is discussed.

Direct effects of vitamin D3 analogues on G-protein mediated signalling systems in rat osteosarcoma cells and rat pituitary adenoma cells

In normal rats treated with 1,25(OH)2D3 or 24,25(OH)2D3, serum Ca2+, ALP, PRL and GH are significantly altered. In order to study the primary effect of vitamin D3 analogues on target organ function, rat UMR 106 osteosarcoma and GH3 pituitary adenoma cells in monolayer culture were exposed accordingly. Surprisingly, prolonged exposure of these cell lines to physiological levels of either 1,25(OH)2D3 or 24,25(OH)2D3 did not significantly affect the secretory parameters (ALP, PRL or GH) tested. However, 1,25(OH)2D3 exposure significantly reduced PTH- and Gpp(NH)p-elicited AC as well as Gpp(NH)p-stimulated PLC activities in the UMR 106 cells. These changes were accompanied by an increase and decrease in the membrane contents of the G-protein subunits G36 beta and Gq/11 alpha, respectively. In contrast, 24,25(OH)2D3 remained without significant biological effect on these signalling systems despite concomitantly augmented levels of G36 beta. TRH- and Gpp(NH)p-elicited PLC activities in the GH3 cells were significantly reduced by 1,25(OH)2D3 with a concurrent reduction in cellular amounts of Gq/11 alpha, however, 24,25(OH)2D3 did not significantly alter any signalling systems nor G-proteins analyzed. It is concluded that the osteoblastic and pituitary cell secretion of ALP, PRL and GH remain unaffected by the presence of 1,25(OH)2D3 and 24,25(OH)2D3, despite distinct alterations in components of G-protein mediated signalling pathways. Hence, other factors like ambient Ca2+ may be responsible for the perturbed secretory patterns of ALP and PRL seen in vitamin D3 treated rats.

The molecular biology of the FSH receptor

The actions of follicle stimulating hormone (FSH) mediated through its receptor are necessary for the proper functioning of mammalian gonads. The FSH receptor is localized on granulosa cells of the ovary and Sertoli cells of the testis. The expression of the FSH receptor (FSHR) in Sertoli cells varies in vivo as a function of the stage of the cycle of the seminiferous epithelium and in culture as a result of the addition of exogenous hormones. The gene for the FSH receptor is large and has been shown to be related in structure to the genes for luteinizing hormone (LH) receptor and thyroid stimulating hormone (TSH) receptor. The promoter region of the gene for FSHR does not contain a TATA box and has multiple transcriptional start sites. Less than 280 bp of the promoter are sufficient in transient transfection assays to direct expression of the chloramphenicol acetyl transferase gene (CAT) in a number of different cell types including non-gonadal cells. However, the promoter does direct the expression of a marker gene only into testis and ovary of transgenic mice.

Cellular distribution of G protein Go alpha in pituitary lactotrophs: effects of dopamine

Membrane-bound GTP-binding (G) proteins mediate signal transduction in a variety of cell systems. The exact mechanisms of G proteins action are still under investigation but they appear to involve effectors located in the plasma membrane as well as in other parts of the cell. With this study, we investigated the cellular and ultrastructural localization of G protein subunits, and particularly of Go alpha, in normal rat anterior pituitaries and in estrone-induced rat adenomatous lactotrophs. We also evaluated the effects of Go alpha cellular redistribution in rat adenomatous lactotrophs following short-term exposure to dopamine (DA). Using the Protein A-gold (PAG) methodology, Go alpha was found to be present in the cysternae of the endoplasmic reticulum of normal pituitary cells and of adenomatous lactotrophs. In the latter, Go alpha could be co-localized with prolactin (PRL). By immunoblots, using specific antisera, significant amounts of Go alpha and Gs42 alpha, together with smaller amounts of Gi alpha, Gs47 alpha and G beta were found to be present in the uncontaminated supernatant fraction of adenomatous lactotrophs. Unexpectedly, exposure of the cells to DA induced a rapid and short-lived decrease in the cytosolic fraction of Go alpha and G beta associated with a decrease of PRL release. Since cytosolic Go alpha can be ADP-ribosylated by pertussis toxin (PT) and is therefore in a heterotrimeric form, our data suggest that the soluble Go protein may play a role during lactotrophs' exposure to an inhibitor of PRL release, perhaps through its relocalization after being internalized with the D2 receptor or by being used for interaction with intracellular and/or membrane-bound effectors.

Characterization of the 5' flanking region of the human follicle-stimulating hormone receptor gene

A genomic clone containing 2.3 kilobases (kb) of the 5' flanking region of the human follicle-stimulating hormone receptor (FSHR) plus the translated region of exon 1 and subsequent sequences of intron A has been isolated and characterized. This portion of the 5' flanking region has neither a TATA nor a CCAAT box and shows features of promoters seen in "housekeeping" genes. Using RNAse protection multiple transcriptional start sites could be identified, the major ones clustered between -114 and -79 bp. Chimeras containing 1486 bp of the 5' flanking region, or deletions thereof, expressed significant chloramphenicol acetyltransferase (CAT) activity when transiently transfected into Chinese hamster ovary (CHO), primary rat Sertoli and human granulosa-lutein cells. Deletion analyses indicated that a proximal promoter can be allocated to the region from -225 to -1 bp.

A comparative study of the role of adenylate cyclase in the release of adrenocorticotropin from the ovine and rat anterior pituitary

The interaction between corticotropin-releasing factor (CRF) and arginine vasopressin (AVP) is important in the regulation of adrenocorticotropin (ACTH) release from the anterior pituitary (AP). CRF exerts its effect on the AP by activating the adenylate cyclase (AC) complex whereas AVP increases the turnover of phosphatidylinositol. In the rat and in man, CRF is the most potent ACTH secretagogue whereas AVP alone is only a weak agonist. Since recent studies in the sheep indicate a reversal of this order of potency, these studies were undertaken to test the hypothesis that a functional alteration of the AC in the ovine corticotrope might limit the ability of CRF to release ACTH from these cells. When rat AP cells were incubated with CRF, a dose-dependent increase in AC activity was observed. This effect was potentiated either by AVP or PMA, although neither agent alone altered AC activity. In contrast, CRF alone, or in combination with AVP or PMA, did not increase AC activity in ovine AP cells. Both cholera toxin (CT) and pertussis toxin (PT) caused a dose-dependent release of ACTH from rat and ovine AP cells, but the amount of ACTH released from the ovine AP cells by both agents was relatively reduced. In the ovine cells, however, AVP acted synergistically with CT or PT to markedly increase the release of ACTH to levels which approached those obtained when the rat AP cells were exposed to CT or PT alone. Forskolin increased AC activity in AP cells of both species, but to a much lower extent in ovine cells than in the rat cells. However, when the ovine cells were exposed to AVP, the AC response to forskolin became similar to the response observed in the rat cells when incubated with forskolin alone. Forskolin also released significantly less ACTH from the ovine AP cells, but AVP also acted synergistically with forskolin to greatly enhance the amount of ACTH released from these cells. Finally, 8-bromo-cyclic AMP produced a similar release of ACTH from both ovine and rat AP cells. We conclude that: (1) the decreased ability of CRF to increase ACTH release from the ovine AP reflects a net decrease in AC activity and cannot be ascribed to an ovine corticotropic resistance to cAMP; (2) the decreased activity of the ovine corticotropic AC complex may in turn reflect functional alterations at the level of both the G proteins and the catalytic subunit; (3) since AVP causes protein kinase C substrate phosphorylation in the ovine AP, AVP may increase AC activity in this tissue by phosphorylating the G proteins and/or the catalytic subunit.

Inhibition of protein phosphatases by okadaic acid and calyculin-A differentially modulates hormonal- and forskolin-stimulated formation of cyclic AMP in AtT-20 corticotrophs: effect of pituitary adenylate activating polypeptide and corticotropin-releasing factor

The effect of phosphatase inhibitors okadaic acid and calyculin-A on cAMP formation and adrenocorticotropic hormone (ACTH) secretion in AtT-20 corticotrophs was investigated. Both okadaic acid and calyculin-A inhibited dose-dependently the accumulation of cAMP in cells stimulated with pituitary adenylate cyclase activating factor (PACAP) and corticotropin-relating hormone (CRF). While in the case of okadaic acid the half-maximum inhibiting concentration was similar for both peptides (IC50 = 4 x 10(-7) M), it appeared that calyculin-A was about one order of magnitude more efficient in inhibiting the effect of PACAP than that of CRF (IC50 = 3.8 x 10(-9) M vs 2.0 x 10(-8) M, respectively). Importantly, the inhibitors blocked the activation by cholera toxin (which acts on Gs-like proteins) of cAMP formation, but failed to alter the effect of forskolin (which bypasses the receptor-G protein complex and activates adenylyl cyclase directly). Treatment of cells with calyculin-A significantly dampened adenylyl cyclase activity in cell membrane fraction, though to a lesser extent than it blocked cAMP formation in the whole cell. Both okadaic acid and calyculin-A inhibited CRF- and PACAP-induced secretion of ACTH. Our data hint that in AtT-20 corticotrophs, inhibition of phosphatases by modulating the state of phosphorylation of the receptor-G proteins complexes for CRF and PACAP, regulates cAMP formation and ACTH secretion.

Changes in type VI adenylyl cyclase isoform expression correlate with a decreased capacity for cAMP generation in the aging ventricle

We investigated the developmental regulation of the beta-adrenergic receptor-Gs-adenylyl cyclase pathway in myocardial membranes from fetal, neonatal, adult, and mature adult rats by measuring the density of the beta-adrenergic receptor and the activities of the stimulatory guanine nucleotide-binding protein Gs and the adenylyl cyclase enzyme. Total beta-adrenergic receptor content (in femtomoles per milligram protein) was greatest in the fetal (124.4 +/- 20.5 fmol/mg) and neonatal (122.3 +/- 16.1 fmol/mg) stages and gradually decreased in the adult (90.9 +/- 8.0 fmol/mg) and mature adult (70.0 +/- 9.6 fmol/mg) stages. An equivalent pattern was seen for adenylyl cyclase activity: the basal activity of the effector enzyme or that measured in the presence of 0.1 mmol/L isoproterenol with 0.1 mmol/L Gpp(NH)p, 10 mmol/L NaF, or 0.05 mmol/L forskolin was greater in the fetus and the neonate than in the adult and the mature adult. These data suggested that decreased stimulation of the catalytic unit by Gs could be the underlying cause of diminished adenylyl cyclase activity with aging. However, quantification of Gs by reconstitution into S49 cyc- membranes (in picomoles cAMP per microgram for 10 minutes) demonstrated no significant decrease during development from fetus (1.55 +/- 0.1 pmol/microgram) to neonate (1.9 +/- 0.5 pmol/microgram) and subsequent aging to adult (2.6 +/- 0.2 pmol/micrograms) and mature adult (1.9 +/- 0.2 pmol/microgram). When Northern blot analysis was used to characterize the relative amounts of mRNA coding for Gs alpha, no significant differences were seen among the developmental stages studied.(ABSTRACT TRUNCATED AT 250 WORDS)

McCune-Albright syndrome

McCune-Albright syndrome (MAS) is characterized by the clinical triad of polyostotic fibrous dysplasia, cafe-au-lait pigmented skin lesions, and multiple endocrinopathies. The molecular basis of MAS is a mutation in G(s)alpha that results in constitutive activation of adenylyl cyclase in affected tissues. This mutation occurs during early embryogenesis, and therefore patients with MAS are mosaic. The identification of activating mutations of Gsa in liver, heart, and gastrointestinal tract of patients with MAS suggests a broader spectrum of clinical disease than previously appreciated.

Establishment of steroidogenic granulosa cell lines expressing follicle stimulating hormone receptors

Follicle stimulating hormone (FSH) plays an important role in the regulation of oogenesis, spermatogenesis and production of steroid hormones. Receptors to FSH, which are uniquely expressed in ovarian granulosa and testicular Sertoli cells, are rapidly lost in tissue culture conditions and upon cell transformation. We have succeeded, by triple transfection of primary rat granulosa cells with SV40 DNA, Ha-ras oncogene and an FSH receptor expression plasmid, to establish stable steroidogenic cell lines expressing FSH receptors. The cell lines respond to rat, ovine and bovine FSH, which stimulate progesterone production at levels comparable to primary granulosa cells obtained from preovulatory follicles. No steroidogenic response is detected upon stimulation with ovine luteinizing hormone or human chorionic gonadotropin. The steroidogenic response is accompanied by de novo appearance of adrenodoxin which serves as a marker for the mitochondrial steroidogenic enzyme system. These cells express approximately 27,000 receptors per cell with a Kd of 100-115 pM. This Kd is close to the value calculated for the native receptor. The ED50 for the steroidogenic response to ovine FSH is 200 pM, suggesting a tight coupling between receptor activation and the steroidogenic response. FSH induces pronounced morphological changes in the established cell lines, which are also characteristic of primary granulosa cells. These FSH responsive cell lines can serve as a useful model for the study of the structure and function of the FSH receptor and the effect of oncogenes on its expression.