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PubMed1995

Stimulation of Gs and inhibition of Gi protein functions by minimally oxidized LDL.

We have previously shown that treatment of aortic endothelial cells with minimally oxidized LDL (MM-LDL) induces their interaction with monocytes but not neutrophils and that these induced responses are associated with increased cAMP levels. Here we studied the mechanism of by which MM-LDL elevates cAMP levels. Treatment of human aortic endothelial cells with MM-LDL resulted in a saturable dose-dependent increase in cAMP levels. Studies using a combination of pertussis toxin and MM-LDL suggested that part of the cAMP increase was due to the stimulation of Gs complexes. Studies with pertussis toxin-treated membranes in which Gi was completely inhibited were used to directly address the effect of MM-LDL on the Gs pathway. MM-LDL and an oxidized lipid (palmitoyl arachidonyl phosphatidylcholine), the effects of which mimic those of MM-LDL, caused a 40% to 100% increase in cAMP levels in these isolated membranes that was augmented by GTP, thus showing Gs stimulation. These results also show that MM-LDL increases cAMP levels by inhibiting Gi. MM-LDL inhibited ADP ribosylation of Gi by about 30% and completely abolished the ability of serotonin to interact with Gi complexes, whereas direct activation of Gi by mastoparan was not inhibited. This observation suggests that MM-LDL interferes with the interaction of Gi molecules with inhibitory receptors. There was no direct effect of MM-LDL on adenylate cyclase. Overall, these studies show that MM-LDL increases cAMP levels both by stimulating Gi and inhibiting Gi complexes.

Adenylyl Cyclases↗

PubMed1989

One hour of myocardial ischemia decreases the activity of the stimulatory guanine-nucleotide regulatory protein Gs.

The effect of 1 hour of myocardial ischemia on the function of the stimulatory guanine-nucleotide-binding protein Gs was examined. This study follows our recent finding that myocardial ischemia increases the density of beta-adrenoreceptors in a conscious canine model while having the opposite effect on the activity of adenylate cyclase. Coronary artery occlusion was induced in five conscious dogs and verified by measurement of blood flow using the Doppler and microsphere techniques. Alterations in the level and function of Gs were examined in sarcolemmal membranes prepared from ischemic and nonischemic regions of the left ventricle. After 1 hour of coronary artery occlusion, the functional activity of sarcolemmal Gs, as determined by reconstitution with cyc- membranes, decreased by 27 +/- 7% in the ischemic zone. Cholera toxin labeling performed in parallel with the reconstitution studies demonstrated a similar decrease of 28 +/- 7%. This was associated with decreases in basal activity and decreases in adenylate cyclase activity stimulated by GTP, GTP plus isoproterenol, sodium fluoride, and forskolin. Thus, a defect distal to the beta-adrenoreceptor occurs in the transduction of adrenergic signals to the heart as a consequence of 1 hour of ischemia.

Adenylyl Cyclases↗

PubMed1995

Decreased adenylate cyclase activity and expression of Gs alpha in human myocardium after orthotopic cardiac transplantation.

We studied several aspects of guanine nucleotide-stimulated adenylate cyclase function in patients after orthotopic cardiac transplantation. In 28 patients, adenylate cyclase activity was measured in endomyocardial biopsy samples obtained just before and at monthly intervals after cardiac transplantation. In biopsies obtained > or = 6 months after transplantation, basal adenylate cyclase activity was decreased by 67% (n = 12; P < .05), GTP gamma S-stimulated adenylate cyclase activity was decreased by 78% (n = 12; P < .05), Mn+2+forskolin-stimulated adenylate cyclase activity was decreased by 80% (n = 8; P < .05), and Mn+2-stimulated adenylate cyclase activity (a measure of activity of the catalytic subunit of adenylate cyclase) was decreased by 83% (n = 8, P < .05). Western blot analysis demonstrated that 6 months after cardiac transplantation, the level of Gs alpha protein was decreased by 61 +/- 12% (n = 8; P < .001). There was no change in the level of Gi alpha as assessed by pertussis toxin-catalyzed ADP-ribosylation (n = 4; P = NS). With the use of the quantitative polymerase chain reaction, a 50 +/- 10% (n = 6; P < .001) reduction in the steady-state level of Gs alpha mRNA was observed. There was no change in the level of mRNA for Gi-3 alpha. Thus, after orthotopic cardiac transplantation in humans, guanine nucleotide-stimulated adenylate cyclase activity is decreased in parallel with decreased levels of Gs alpha protein and mRNA.

Adenylyl Cyclases↗

PubMed1989

Guanine nucleotide binding regulatory proteins and adenylate cyclase in livers of streptozotocin- and BB/Wor-diabetic rats. Immunodetection of Gs and Gi with antisera prepared against synthetic peptides.

Adenylate cyclase in liver plasma membranes from streptozotocin-diabetic (STZ) or BB/Wor spontaneously diabetic rats showed increased responsiveness to GTP, glucagon, fluoroaluminate, and cholera toxin. Basal or forskolin-stimulated activity was unchanged in STZ rats, but increased in BB/Wor rats. No change in the alpha-subunit of Gi (alpha i) was observed in STZ or BB/Wor rats using pertussis toxin-stimulated [32P]ADP-ribosylation. Immunodetection using antibodies against the COOH-terminal decapeptides of alpha T and alpha i-3 showed no change in alpha i in STZ rats and a slight decrease in BB/Wor rats. Angiotensin II inhibition of hepatic adenylate cyclase was not altered in either diabetic rat. In both models of diabetes, Gs alpha-subunits were increased as measured by cholera toxin-stimulated [32P]-ADP-ribosylation of 43-47.5-kD peptides, reconstitution with membranes from S49 cyc- cells or immunoreactivity using antibodies against the COOH-terminal decapeptide of alpha s. These data indicate that STZ-diabetes increases hepatic Gs but does not change Gi or adenylate cyclase catalytic activity. In contrast, BB/Wor rats show increased hepatic Gs and adenylate cyclase. These changes could explain the increase in hepatic cAMP and related dysfunctions observed in diabetes.

Adenosine Diphosphate Ribose↗

PubMed1999

Influence of treatment schedule and viral challenge dose on the in vivo influenza virus-inhibitory effects of the orally administered neuraminidase inhibitor GS 4104.

Experiments were done to determine how an alteration of the treatment schedule of 5 or 32 mg/kg/day per os (p.o.) doses of GS 4104 [the ethyl ester prodrug of the neuraminidase inhibitor (3R, 4R,5S)-4-acetamido-5-amino-3-(1-ethylpropoxy)-1-cylohexene-1 -carboxylic acid (GS 4071)] would affect influenza A (H1N1) virus infection in mice. Treatments with a low dose, one, two, three or four times daily, were highly inhibitory, unless therapy was terminated relatively early in the infection (days 2-3), in which case efficacy was curtailed. Single administrations at various times relative to virus exposure had essentially no effect. The 32 mg/kg/day dose was significantly inhibitory using all treatment schedules. These data indicated a requirement for the compound to be in the host when lung virus titres were reaching maximal levels and, for minimally effective doses, that at least continued daily therapy was needed to maintain adequate serum levels to achieve an appropriate antiviral effect. Twice daily p.o. treatment for 5 days with 20 mg/kg/day of GS 4104 totally prevented deaths in mice receiving high viral challenge doses that were sufficient to kill placebo-treated controls in less than 5 days. Other parameters of antiviral efficacy (lung consolidation, arterial oxygen saturation, lung virus titres) were also markedly inhibited regardless of viral challenge doses. These data provide further insights into how the maximum therapeutic benefit can be derived from use of this orally effective influenza virus neuraminidase inhibitor.

Amines↗

PubMed1997

Association of alpha S-subunit of the GS protein with microfilaments and microtubules: implication during adrenocorticotropin stimulation in rat adrenal glomerulosa cells.

The aim of the present study was to investigate if and how microfilaments and microtubules could be involved in the early events of ACTH action. In primary cultures of rat glomerulosa cells, a 30-min preincubation with either 10 microM colchicine (a microtubule-disrupting agent) or 10 microM cytochalasin B (a microfilament-disrupting agent) decreased ACTH-induced cAMP production. Moreover, colchicine decreased cAMP production induced by fluoroaluminate (a nonspecific activator of all G proteins), but not of forskolin (which directly activates adenylyl cyclase). These results indicate that microtubules appear to be essential for the GS protein activation. In contrast, cytochalasin B decreased the stimulating effect of both fluoroaluminate and forskolin, indicating that microfilaments may be involved in both GS and adenylyl cyclase activations. Analyses of microfilament- and microtubule-enriched fractions and immunoprecipitation of actin and tubulin indicated that the alpha S-subunit of the GS protein was associated with both structures. Stimulation of cells with ACTH induced a rapid increase (within 1 min) in the levels of microfilaments, microtubules, and alpha S associated with the membrane. In addition, ACTH stimulation of cAMP production was very sensitive to Ca2+, without any stimulation in Ca(2+)-free medium. Under these conditions, actin filaments were short and formed a dense network. These observations suggest that the Ca(2+)-free medium stabilized the actin fibers in such a way that activation by ACTH failed, further documenting the importance of microfilaments in cAMP production.

Actin Cytoskeleton↗

PubMed1994

An unusual presentation of McCune-Albright syndrome confirmed by an activating mutation of the Gs alpha-subunit from a bone lesion.

The McCune-Albright syndrome (MAS) is characterized clinically by polyostotic fibrous dysplasia, café-au-lait skin lesions, sexual precocity, and various other endocrinopathies. Recent investigations suggest an etiological role for embryonic somatic missense mutations that predict the substitution of a His or Cys for Arg at amino acid 201 of the Gs alpha-subunit (Gs alpha). Identification of these mutations in affected tissues is a sensitive assay that may help define a more complete clinical spectrum of the MAS. We investigated a woman who developed fibrous dysplasia 24 yr after premature menstruation. To determine if this was an unusual MAS variant, DNA and RNA were analyzed from affected and unaffected tissues. From samples of affected rib and normal rib DNA was extracted, amplified by polymerase chain reaction, subcloned, and sequenced. RNA was extracted from affected bone, reverse transcribed, amplified by polymerase chain reaction, subcloned, and sequenced. DNA sequence predicting a His for Arg substitution at Gs alpha amino acid 201 was found in 47% of the recombinant plasmids from DNA of affected bone and 17% of the plasmids from DNA of unaffected bone; a significant (P < 0.05) difference in frequency. The His201 substitution was found in 42% of the recombinant plasmids from RNA of affected bone. We conclude that this clinical variant is qualitatively indistinguishable from presentations of the complete MAS.

Adult↗

PubMed1996

Constitutive activation of the Gs alpha protein-adenylate cyclase pathway may not be sufficient to generate toxic thyroid adenomas.

In toxic thyroid adenomas, mutations in the TSH receptor (TSH-R) gene or the gene encoding the alpha-subunit of the stimulatory guanine nucleotide-binding protein (Gs alpha) have been demonstrated to constitutively activate the cAMP cascade, which subsequently stimulates the growth and function of these tumors. However, the widely varying thyroid phenotypes in patients with TSH-R germline mutations, ranging from only slightly enlarged diffuse to multinodular goiters, suggest that additional mechanisms may be effective in the pathogenesis of toxic adenomas. We have investigated the levels of stimulatory and inhibitory G protein alpha-subunits together with basal and TSH-stimulated adenylate cyclase (AC) activity in toxic adenomas with or without activating mutations and in nodular and extranodular tissues of a toxic goiter due to a germline mutation in the TSH-R gene. Augmented expression of Gs alpha protein was detected in all toxic adenomas, independent of the presence of mutations, and in the nodular tissue of the toxic goiter, but not in the nonnodular hyperplastic tissue of the toxic goiter with the mutated TSH-R. Analogously, the expression of the alpha-subunit of the inhibitory G protein (Gi alpha) was also increased in all adenomas and the nodular tissue of the goiter, but, again, not in the hyperplastic goiter tissue. Basal AC activity was high in all tissues with mutations, but was only slightly increased in adenomas without detected mutations. No correlation was detectable between basal or TSH-stimulated AC activity and the levels of Gs alpha and Gi alpha. Our data suggest that mutational activation of the cAMP cascade may not be sufficient to generate toxic nodules and adenomas, but far more complex mechanisms, including alterations of G protein signaling, may be effective in the pathogenesis of these tumors.

Adenoma↗

PubMed1995

Activation of cyclic nucleotide phosphodiesterases in FRTL-5 thyroid cells expressing a constitutively active Gs alpha.

The expression of a constitutively activated Gs alpha protein in the rat thyroid cell line FRTL-5 causes an increase in the hormone-independent adenylyl cyclase activity and promotes TSH-independent growth of the cells. In spite of the constitutive activation of the adenylyl cyclase, the basal cAMP levels in these cells are only marginally increased. To define the role of phosphodiesterases (PDEs) in the genesis of this phenotype, cyclic nucleotide hydrolysis was determined in two cell lines expressing a mutated Gs alpha (Q227L). In these cells, the hydrolysis of both cAMP and cGMP was markedly increased in comparison with normal cells. This increase is the result of the activation of different forms of PDEs. Analysis of the cGMP hydrolysis and Ca++/calmodulin stimulation of the PDE activity indicated that the activity of a Ca++/calmodulin-stimulated PDE is increased in both cell lines. In addition, an increase in high-affinity, rolipram-sensitive cAMP-PDE activity was associated in both cell lines with the appearance of a 67-68 kilodalton (kDa) protein that cross-reacts with two antibodies against cAMP-PDEs. This form had the properties of ratPDE3.2/PDE4D2, a cAMP-PDE that is inducible by TSH in wild type cells. That an increase in cAMP-specific, rolipram-sensitive PDE plays a role in the phenotype induced by Q227L Gs alpha was confirmed by measurements of the mitogenic activity. Incubation with rolipram, which had no effect on wild type cells, caused an increase in cAMP levels and further stimulated TSH-independent proliferation in both cell lines carrying the mutation.(ABSTRACT TRUNCATED AT 250 WORDS)

3',5'-Cyclic-AMP Phosphodiesterases↗

PubMed1992

A pituitary specific point mutation of codon 201 of the Gs alpha gene in a pituitary adenoma of a patient with multiple endocrine neoplasia (MEN) type 1.

The DNA from a pituitary adenoma of a patient with multiple endocrine neoplasia (MEN) type 1 was analyzed to detect a point mutation of the Gs alpha gene (gsp) by the PCR direct-sequencing method. The patient had galactorrhea, amenorrhea and acromegalic features. Hormonal examination revealed high serum levels of PRL and GH. The tumor was histologically diagnosed as a mixed GH cell-PRL cell adenoma in which GH and PRL were produced by different cells. Sequence analysis of the DNAs extracted from paraffin sections of pituitary, parathyroid, and pancreas tumors demonstrated the substitution of thymidine for cytidine in codon 201 of the Gs alpha gene that resulted in replacement of arginine (CGT) with cysteine (TGT) only in the pituitary adenoma, but not in the parathyroid and pancreas tumors. These results suggest that a pituitary specific point mutational activation of the Gs alpha gene may be involved in the development of the pituitary adenoma in this patient.

Adenoma↗

PubMed1979

Effect of selection for high egg production in chickens on shedding of lymphoid leukosis virus and gs antigen into eggs.

Lymphoid leukosis virus (LLV) and group specific (gs) viral antigen were detected less frequently in albumen of eggs from two strains of Single Comb White Leghorns that had been selected for high egg production than in corresponding random-bred control strains, which represented the original base population. In a third selected strain, for which no comparable control strain was available, the frequency with which LLV and gs antigen were detected was similar to the other two selected strains. The greatest contrast was between selected Strain 1 and control Strain 5 in which the percentage of eggs with LLV in albumen was 1.4 and 21.4, respectively, and the percentage with gs antigen was 1.2 and 19.9. These differences between control and selected strains of chickens were not related to genetic cellular resistance to virus infection, because inoculation of chorioallantoic membranes with Rous sarcoma virus of subgroups A and B revealed that the proportion of birds resistant to subgroups A and B viruses was not greater in the selected strains than in the control strains.

Animals↗

PubMed1999

GSH, GSH-related enzymes and GS-X pump in relation to sensitivity of human tumor cell lines to chlorambucil and adriamycin.

Glutathione (GSH) contents and activities of glutathione S-transferase (GST), glutathione reductase (GSH-RD), glutathione peroxidase (GSHpx) and glutathione conjugate export pump (GS-X pump) were determined in eight human tumor cell lines with different sensitivities to adriamycin and chlorambucil. Correlations between sensitivities of the human tumor cells to adriamycin and chlorambucil and the glutathione related factors were analyzed statistically. Sensitivities of the human tumor cells to chlorambucil were found to be correlated to all the glutathione related factors tested (r=0.68-0.88). IC50 values of adriamycin were also positively correlated to GSH contents and activities of GSH-RD, GSHpx and GS-X pump with r values ranging from 0.66 to 0.77 but not to GST activity (r=0.25). Chang liver cells with highest GSH content and highest activities of GST, GSH-RD, GSHpx and GS-X pump were most resistant to both adriamycin and chlorambucil. These data suggested that glutathione related factors may work as an overall detoxification system participating in the detoxification of anticancer drugs such as adriamycin and chlorambucil, and to be involved in cellular resistance to these drugs.

Antineoplastic Agents↗

PubMed1992

Involvement of specific hydrophobic, but not hydrophilic, amino acids in the third intracellular loop of the beta-adrenergic receptor in the activation of Gs.

Mutagenesis and biochemical analysis have indicated that amino acid residues at the amino terminus of the third intracellular loops of guanine nucleotide-binding protein (G protein)-coupled receptors are important in mediating the coupling of the receptors to G proteins. Because the primary sequence of this region is not conserved among all receptors that couple to the same G protein, it has been suggested that some other physicochemical property of this domain may determine G protein activation. To determine the relative contributions of charge distribution and amino acid side chain interactions within this domain of the beta-adrenergic receptor (beta AR) to the activation of the G protein Gs, point mutations were introduced into this region of the beta AR. Replacement of all four of the basic amino acid residues within this region (amino acids 222-236) with serine residues had a negligible effect on the ability of the beta AR to activate Gs. In contrast, replacement of the hydrophobic amino acids within this same region with leucine residues resulted in a mutant receptor that was poorly coupled to Gs. These results suggest that specific hydrophobic interactions within this region of the receptor may play a more significant role than ionic or hydrophilic interactions in mediating G protein activation.

Adenylyl Cyclases↗

PubMed1992

Guanine nucleotides regulate beta-adrenergic activation of Na-H exchange independently of receptor coupling to Gs.

We have previously shown that the beta-adrenergic receptor (beta-AR) stimulates activity of the ubiquitous Na-H exchanger (NHE-1) independently of changes in cAMP accumulation and independently of a cholera toxin-sensitive stimulatory GTP-binding protein (Gs). To further investigate the potential role of a GTP-binding protein in coupling the beta-AR to NHE-1, we have used a recently available nonhydrolyzable GTP analog, "caged" guanosine 5'-O-(3-thiotriphosphate) (GTP gamma S), to study time-dependent effects of GTP on NHE-1 in intact cells. By monitoring intracellular pH (pHi) in cells loaded with the fluorescent pH-sensitive dye, 2,7-biscarboxyethyl-5(6)-carboxyfluorescein, we determined NHE-1 activity in primary cultures of canine enteric endocrine cells, which express an endogenous beta-AR, and in mouse L cells stably transfected with either the wild type hamster beta 2-AR or a mutant construct of the hamster beta 2-AR containing a deletion in amino acid residues 222-229. This D(222-229)beta 2-AR is functionally uncoupled from Gs and adenylylcyclase. In all three cell types, NaF and GTP gamma S induced an increase in activity of the exchanger, determined by assessing the rate of pHi recovery from an acute intracellular acid load (dpHi/dt). This increase in pHi recovery was dependent on extracellular Na+ and sensitive to the amiloride analog ethylisopropylamiloride. GTP gamma S, but not NaF, also increased beta-adrenergic stimulation of resting NHE-1 activity. The alkalinization in response to isoproterenol was reversed by propranolol in the absence, but not the presence, of GTP gamma S and was completely blocked by GDP beta S. The ability of guanine nucleotides to regulate beta-adrenergic activation of NHE-1 in cells expressing the mutant D(222-229)beta 2-AR suggests that functional coupling of the beta-AR to NHE-1 may be mediated by a GTP-binding protein other than Gs.

Amiloride↗

PubMed1992

Inhibition of thyrotropin-induced DNA synthesis in thyroid follicular cells by microinjection of an antibody to the stimulatory G protein of adenylate cyclase, Gs.

Thyrotropin (TSH) is an important regulator of thyroid follicular cells. While its role in the maintenance of differentiated functions is undisputed, its role as a mitogen is less clear. TSH induces DNA synthesis and cell proliferation in some cells, while in others, TSH is mitogenic only in the presence of additional growth factors such as insulin-like growth factor-1. TSH causes elevations in intracellular cAMP and is thought to utilize this second messenger system in its mitogenic action. We studied TSH as a mitogen in Wistar rat thyroid cells (WRT) (Brandi, M. L., Rotella, C. M., Mavilia, C., Franceschelli, F., Tanini, A., and Toccafondi, R. (1987) Mol. Cell. Endocrinol. 54, 91-103) and examined the role of the guanine nucleotide binding protein, Gs, in its mitogenic action. WRT cells synthesized DNA in response to TSH and elevations in cAMP. In addition, TSH caused a rapid stimulation of an indicator gene whose expression is regulated by cAMP response elements. Following microinjection of an inhibitory polyclonal antibody raised against the Gs protein, both TSH-induced changes in gene expression and DNA synthesis were significantly reduced. These results demonstrate that virtually all of the mitogenic action of TSH is transduced through the Gs protein in WRT cells, presumably through the regulation of adenylate cyclase. Whether all or only part of TSH action is mediated by cAMP and the cAMP-dependent protein kinase remains to be determined.

1-Methyl-3-isobutylxanthine↗

PubMed2004

[Study on the targeting effects of M1-GS RNA on K562 cells].

OBJECTIVE: To determine the effects of M1-GS RNA (M1 RNA) on bcr-abl mRNA and oncoprotein after M1 RNA with guide sequence (M1-GS RNA) targeting the oncogene was transfected into K562 cells. METHODS: pAVGS4 (an eukaryocyte expression vector containing M1-GS RNA sequence) and pNAV-1 (as the control) were transfected into K562 cells by X-tremeGENE Q2. Total RNA was extracted at 24, 48, 72 and 96 hours after transfection. Then RT-PCR was done to compare the products at different time point. After collecting pAVGS4-transfected cells and the control cells at 48 and 96 hours after transfection, total protein was extracted and quantified. Change of P210 was determined by Western blot. Colony formation was analyzed at 96 hours after transfection. RESULTS: RT-PCR based on transfected cells at different time point showed that the amount of bcr-abl mRNA began to decrease at 24 hours and reduced to 9.2% and 2.5% respectively at 48 and 72 hours after transfection. Western blot showed that the expression of P210 in the pAVGS4 group reduced to 10.4% of the control at 48 hours and 6.7% of the control at 96 hours after transfection. The inhibition rate of colony formation was 81.3% after K562 cells were transfected by pAVGS4. CONCLUSION: pAVGS4 can efficiently destroy bcr-abl mRNA in K562 cells. The transcript level of bcr-abl mRNA was reduced with the time after transfection. The expression of P210 was decreased significantly at 48 and 96 hours after transfection. K562 cell colony formation was prominently inhibited.

Escherichia coli Proteins↗

PubMed2005

[Cloning and analysis of LMW-GS genes from Triticum aestevum ssp. tibetanum Shao].

The full coding regions (open reading frame,ORF) of LMW-GS genes were amplified from Triticum aestevum ssp. tibetanum Shao accession AS908 by using the primer pairs W1227 and W1228,which were designed according to wheat LMW-GS conservative domains. The amplified DNA fragments were separated and recovered from agrose gel,subsequently ligated into pBluescript SK( +/-)-T vector, and then transformed into E. coil strain DH10B. Three positive clones were screened out and sequenced. Among which, Tibet1 (GenBank accession No:AY299457) and Tibet2 (GenBank accession No: AY299458) are two expressed LMW glutenin genes. Their coding regions are 1 041 bp and 901 bp, and encode two mature proteins with 326 and 281 amino acid residues, respectively. Tibet3 (GenBank accession No:AY299459) is a pseudogene due to that two stop codons are in its coding region. Squence multipule alignment analysis suggested that Tibet1, Tibet2 and Tibet3 have the higher similarity in their structure and quality functions with the known LMW-GS genes with GenBank accession No: AY214450, AJ293099 and AB062871 encoded by Glu-D3, Glu-A 3 and Glu-A3, respectively.

Amino Acid Sequence↗

PubMed1987

Chromosomal assignment of the murine Gi alpha and Gs alpha genes. Implications for the obese mouse.

The G protein family of transmembrane signaling molecules includes Gs and Gi, the stimulatory and inhibitory regulators of adenylate cyclase. These and other characterized G proteins are comprised of beta, gamma, and alpha chains, the latter being the most variable among the proteins and thus serving to distinguish them. Previous results (Begin-Heick, N. (1985) J. Biol. Chem. 260, 6187-6193) suggested that the autosomal recessive mouse mutation obese (ob), which results in an abnormal response of adipose tissue to lipolytic hormones, is due to a defect in the gene coding for the alpha chain of Gi. In order to test this hypothesis we used a cloned cDNA probe representing murine Gi alpha mRNA in conjunction with a panel of Chinese hamster-mouse somatic cell hybrids segregating mouse chromosomes to map the Gi alpha gene in the mouse. In addition, we used a cDNA probe representing the murine Gs alpha gene to a specific mouse chromosome. Our results indicate that the Gi alpha locus maps to mouse chromosome 9, while Gs alpha is localized to region 2E1-2H3 of mouse chromosome 2. Localization of the Gi alpha gene to chromosome 9 excludes this gene as a site of the ob mutation, since the ob locus maps to chromosome 6. Furthermore, our findings indicate that certain members of the murine G protein alpha gene family have dispersed to different chromosomes since diverging from a common ancestral gene.

Animals↗