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PubMed1993

G(olf) and Gs in rat basal ganglia: possible involvement of G(olf) in the coupling of dopamine D1 receptor with adenylyl cyclase.

Using specific antibodies and cDNA probes, we have investigated, in rat basal ganglia, the distribution and the regulation of the expression of the alpha subunits of Gs and G(olf), two GTP-binding proteins (G-proteins) that stimulate adenylyl cyclase. We confirmed that G(olf) alpha is highly expressed in caudate-putamen, nucleus accumbens, and olfactory tubercle, whereas Gs alpha is less abundant in these areas than in the other brain regions. Intrastriatal injections of quinolinic acid decreased dramatically the levels of G(olf) alpha protein in the striatum and the substantia nigra, and those of G(olf) alpha mRNA in the striatum. Retrograde lesions of striatonigral neurons with volkensin reduced markedly the levels of D1 dopamine (DA) binding sites, as well as those of G(olf) alpha protein and mRNA in the striatum, without altering D2 binding sites. In contrast, both types of lesions increased the levels of Gs alpha protein in the striatum and substantia nigra. Immunocytochemistry showed the presence of G(olf) alpha protein in striatal medium-sized neurons and in several other neuronal populations. These results demonstrate that striatonigral neurons contain high levels of G(olf) alpha and little, if any, Gs alpha, suggesting that the coupling of D1 receptor to adenylyl cyclase is provided by G(olf) alpha. The levels of G(olf) alpha were five- to sixfold higher in the striatum than in the substantia nigra, indicating a preferential localization of G(olf) alpha in the somatodendritic region of striatonigral neurons and providing a basis for the low efficiency of D1 receptor coupling in the substantia nigra. Six weeks after 6-hydroxydopamine lesions of DA neurons, an increase in G(olf) alpha (+53%) and Gs alpha (+64%) proteins was observed in the striatum. This increase in G(olf) alpha levels may account for the DA-activated adenylyl cyclase supersensitivity, without change in D1 receptors density, that follows destruction of DA neurons. Fine regulation of the levels of G(olf) alpha in physiological or pathological situations may be a critical parameter for the efficiency of DA neurotransmission.

Adenylyl Cyclases↗

PubMed1999

The histopathology of fibrous dysplasia of bone in patients with activating mutations of the Gs alpha gene: site-specific patterns and recurrent histological hallmarks.

Gs alpha mutations and histopathology have been analysed in a series of 13 patients with fibrous dysplasia (FD) of bone, including 12 patients with the McCune-Albright syndrome (MAS) and one patient with monostotic FD. Activating mutations (either R201C or R201H) of the gene encoding the alpha subunit of the stimulatory G protein, Gs, were detected in all cases, including the case of monostotic FD, using a variety of techniques [reverse transcription-polymerase chain reaction (RT-PCR) with allele-specific primers, allele-specific oligonucleotide hybridization, and DNA sequencing]. A spectrum of bone lesions associated with such mutations was identified and it was possible to recognize three primary, but distinct, histological patterns, defined here as Chinese writing type, sclerotic/Pagetoid type, and sclerotic/hypercellular type, which are characteristically associated with the axial/appendicular skeleton, cranial bones, or gnathic bones, respectively. Features of FD histopathology were characterized by confocal fluorescence microscopy, which allowed the definition of osteogenic cell shape changes and 'Sharpey fibre bone' as common denominators of all histological subtypes. Defining characteristics of the different subtypes, two of which diverge from standard descriptions of FD and have never been characterized before, were dependent on the amount and structure of bone tissue within the FD lesion. These data emphasize the non-random (site-specific) variability of FD histopathology in patients carrying activating mutations of the Gs alpha gene and provide additional evidence for the occurrence of Gs alpha mutations in cases of FD other than typical MAS.

Adolescent↗

PubMed2002

S111N mutation in the helical domain of human Gs(alpha) reduces its GDP/GTP exchange rate.

G-protein alpha subunits consist of two domains: a Ras-like domain also called GTPase domain (GTPaseD), structurally homologous to monomeric G-proteins, and a more divergent domain, unique to heterotrimeric G-proteins, called helical domain (HD). G-protein activation, requires the exchange of bound GDP for GTP, and since the guanine nucleotide is buried in a deep cleft between both domains, it has been postulated that activation may involve a conformational change that will allow the opening of this cleft. Therefore, it has been proposed, that interdomain interactions are playing an important role in regulating the nucleotide exchange rate of the alpha subunit. While constructing different Gs(alpha) quimeras, we identified a Gs(alpha) random mutant, which was very inefficient in stimulating adenylyl cyclase activity. The introduced mutation corresponded to the substitution of Ser(111) for Asn (S111N), located in the carboxi terminal end of helix A of the HD, a region neither involved in AC interaction nor in the interdomain interface. In order to characterize this mutant, we expressed it in bacteria, purified it by niquel-agarose chromatography, and studied its nucleotide exchange properties. We demonstrated that the recombinant S111N Gs(alpha) was functional since it was able to undergo the characteristic conformational change upon GTP binding, detected by the acquisition of a trypsin-resistant conformation. When the biochemical properties were determined, the mutant protein exhibited a reduced GDP dissociation kinetics and as a consequence a slower GTPgammaS binding rate that was responsible for a diminished adenylyl cyclase activation when GTPgammaS was used as activator. These data provide new evidence that involves the HD as a regulator of Gs(alpha) function, in this case the alphaA helix, which is not directly involved with the nucleotide binding site nor the interdomain interface.

Adenylyl Cyclases↗

PubMedDate not supplied

Absence of activating mutations in the hot spots of the LH receptor and Gs-alpha genes in Leydig cell tumors.

Leydig-cell tumors are functioning endocrine tumors that produce T autonomously leading to isosexual precocity in boys and virilization in female patients. Molecular abnormalities such as activating mutations of the luteinizing hormone receptor (LHR), a G protein-coupled receptor, and of the Gs-alpha subunit of G protein have recently been described in these tumors. Both mutations cause continuous activation of the cAMP signaling cascade, autonomous production of T and cell proliferation. We searched for activating mutations in exon 11 of the LHR gene and in exons 8 and 9 of the Gs-a gene, which contain all hot spots for those mutations, in 4 Leydig cell tumors obtained from 4 patients (one boy with LH-independent precocious puberty and 3 women with virilization). DNA was extracted from paraffin-embedded neoplastic and non-neoplastic tissues and from peripheral lymphocytes. Hot spot regions of exons 11 of LHR and exons 8 and 9 of Gs-alpha genes were amplified by PCR and the purified PCR products were directly sequenced. No LHR or Gs-alpha gene mutations were found in the 4 tumors studied. Considering the previously reported mutations found in Leydig cell tumors, the absence of activating mutations in the hot spot regions for activating mutations in these tumors indicate molecular heterogeneity among Leydig cell tumors.

Aged↗

PubMed2005

RGS2 interacts with Gs and adenylyl cyclase in living cells.

Regulator of G Protein Signalling (RGS) proteins impede heterotrimeric G protein signalling. RGS2 decreases cAMP production and appears to interact with both adenylyl cyclase (AC) and its stimulatory G protein Gs. We showed previously that Green Fluorescent Protein-tagged RGS2 (GFP-RGS2) localizes to the nucleus in HEK 293 cells and is recruited to the plasma membrane when co-expressed with Gsalpha, or the Gs-coupled beta2-adrenergic receptor (beta2AR). Here, using confocal microscopy we show that co-expression of various AC isoforms (ACI, ACII, ACV, ACVI) also leads to GFP-RGS2 recruitment to the plasma membrane. Bioluminescence Resonance Energy Transfer (BRET) was also used to examine physical interactions between RGS2 and components of the Gs-signalling pathway. A BRET signal was detected between fusion constructs of RGS2-Renilla luciferase (energy donor) and Gsalpha-GFP (energy acceptor) co-expressed in HEK 293 cells. BRET was also observed between GFP-RGS2 and ACII or ACVI fused to Renilla luciferase. Additionally, RGS2 was found to interact with the beta2AR. Purified RGS2 selectively bound to the third intracellular loop of the beta2AR in GST pulldown assays, and a BRET signal was observed between GFP-RGS2 and beta2AR fused to Renilla luciferase when these two proteins were co-expressed together with either ACIV or ACVI. This interaction was below the limit of detection in the absence of co-expressed AC, suggesting that the effector enzyme stabilized or promoted binding between the receptor and the RGS protein inside the cell. Taken together, these results suggest the possibility that RGS2 might bind to a receptor-G protein-effector signalling complex to regulate Gs-dependent cAMP production.

Adenylyl Cyclases↗

PubMed2004

Maintenance of meiotic prophase arrest in vertebrate oocytes by a Gs protein-mediated pathway.

Maintenance of meiotic prophase arrest in fully grown vertebrate oocytes depends on an elevated level of cAMP in the oocyte. To investigate how the cAMP level is regulated, we examined whether the activity of an oocyte G protein of the family that stimulates adenylyl cyclase, Gs, is required to maintain meiotic arrest. Microinjection of a dominant negative form of Gs into Xenopus and mouse oocytes, or microinjection of an antibody that inhibits the Gs G protein into zebrafish oocytes, caused meiosis to resume. Together with previous studies, these results support the conclusion that Gs-regulated generation of cAMP by the oocyte is a common mechanism for maintaining meiotic prophase arrest in vertebrate oocytes.

Animals↗

PubMed1998

Melittin, a metabostatic peptide inhibiting Gs activity.

Some basic amphiphilic peptides are known to directly stimulate heterotrimeric GTP-binding proteins (G proteins). Mastoparan and melittin are known to stimulate Gi activities. Here, we found melittin inhibited guanine nucleotide-dependent adenylyl cyclase activity in synaptic membranes of the rat cerebral cortex. However, in insect cell membranes overexpressing specific heterotrimeric G proteins using baculovirus expression system, melittin showed unique effects different from those by mastoparan on G protein activities. This peptide markedly stimulated Gi1 and G11 activities, whereas it did inhibit Gs activities. Kinetic studies revealed that the inhibition of Gs activity by melittin is attributed to the inhibition of GDP release in exchange for added guanine nucleotides (or the association of guanine nucleotides). Thus, melittin may be the first metabostatic peptide inhibiting G protein (Gs) activity, and both mechanisms through the stimulation of Gi and inhibition of Gs might be involved in the melittin-induced inhibition of adenylyl cyclase.

Adenylyl Cyclases↗

PubMed1996

Identification of a functional Gs protein in Euglena gracilis.

We found a Gs protein coupled to adenylyl cyclase in a free-living protist, Euglena gracilis. This Gs protein of approximately 42 kDa is substrate for cholera toxin and is recognized by an antibody against the C-terminal decapeptide of Gs. Furthermore, this protein is coupled to adenylyl cyclase, as shown by: (a) the activation of the enzyme by GTP-analogues and (b) the effect of cholera toxin on cAMP accumulation in intact cells and the continuous activation of adenylyl cyclase activity in membranes. These data indicate that the Gs-adenylyl cyclase-coupled system is already apparent in the protist kingdom.

Adenosine Diphosphate Ribose↗

PubMed1998

Stimulation of type 1 and type 8 Ca2+/calmodulin-sensitive adenylyl cyclases by the Gs-coupled 5-hydroxytryptamine subtype 5-HT7A receptor.

The neurotransmitter serotonin (5-hydroxytryptamine, 5-HT) plays an important regulatory role in developing and adult nervous systems. With the exception of the 5-HT3 receptor, all of the cloned serotonin receptors belong to the G protein-coupled receptor superfamily. Subtypes 5-HT6 and 5-HT7 couple to stimulation of adenylyl cyclases through Gs and display high affinities for antipsychotic and antidepressant drugs. In the brain, mRNA for 5-HT6 is found at high levels in the hippocampus, striatum, and nucleus accumbens. 5-HT7 mRNA is most abundant in the hippocampus, neocortex, and hypothalamus. To better understand how serotonin might control cAMP levels in the brain, we coexpressed 5-HT6 or 5-HT7A receptors with specific isoforms of adenylyl cyclase in HEK 293 cells. The 5-HT6 receptor functioned as a typical Gs-coupled receptor in that it stimulated AC5, a Gs-sensitive adenylyl cyclase, but not AC1 or AC8, calmodulin (CaM)-stimulated adenylyl cyclases that are not activated by Gs-coupled receptors in vivo. Surprisingly, serotonin activation of 5-HT7A stimulated AC1 and AC8 by increasing intracellular Ca2+. 5-HT also increased intracellular Ca2+ in primary neuron cultures. These data define a novel mechanism for the regulation of intracellular cAMP by serotonin.

Adenylyl Cyclases↗

PubMed1999

Both Gs and Gi proteins are critically involved in isoproterenol-induced cardiomyocyte hypertrophy.

Activation of beta-adrenoreceptors induces cardiomyocyte hypertrophy. In the present study, we examined isoproterenol-evoked intracellular signal transduction pathways leading to activation of extracellular signal-regulated kinases (ERKs) and cardiomyocyte hypertrophy. Inhibitors for cAMP and protein kinase A (PKA) abolished isoproterenol-evoked ERK activation, suggesting that Gs protein is involved in the activation. Inhibition of Gi protein by pertussis toxin, however, also suppressed isoproterenol-induced ERK activation. Overexpression of the Gbetagamma subunit binding domain of the beta-adrenoreceptor kinase 1 and of COOH-terminal Src kinase, which inhibit functions of Gbetagamma and the Src family tyrosine kinases, respectively, also inhibited isoproterenol-induced ERK activation. Overexpression of dominant-negative mutants of Ras and Raf-1 kinase and of the beta-adrenoreceptor mutant that lacks phosphorylation sites by PKA abolished isoproterenol-stimulated ERK activation. The isoproterenol-induced increase in protein synthesis was also suppressed by inhibitors for PKA, Gi, tyrosine kinases, or Ras. These results suggest that isoproterenol induces ERK activation and cardiomyocyte hypertrophy through two different G proteins, Gs and Gi. cAMP-dependent PKA activation through Gs may phosphorylate the beta-adrenoreceptor, leading to coupling of the receptor from Gs to Gi. Activation of Gi activates ERKs through Gbetagamma, Src family tyrosine kinases, Ras, and Raf-1 kinase.

Animals↗

PubMed2004

Live cell imaging of Gs and the beta2-adrenergic receptor demonstrates that both alphas and beta1gamma7 internalize upon stimulation and exhibit similar trafficking patterns that differ from that of the beta2-adrenergic receptor.

To visualize and investigate the regulation of the localization patterns of Gs and an associated receptor during cell signaling, we produced functional fluorescent fusion proteins and imaged them in HEK-293 cells. alphas-CFP, with cyan fluorescent protein (CFP) inserted into an internal loop of alphas, localized to the plasma membrane and exhibited similar receptor-mediated activity to that of alphas. Functional fluorescent beta1gamma7 dimers were produced by fusing an amino-terminal yellow fluorescent protein (YFP) fragment to beta1 (YFP-N-beta1) and a carboxyl-terminal YFP fragment to gamma7 (YFP-C-gamma7). When expressed together, YFP-N-beta1 and YFP-C-gamma7 produced fluorescent signals in the plasma membrane that were not seen when the subunits were expressed separately. Isoproterenol stimulation of cells co-expressing alphas-CFP, YFP-N-beta1/YFP-C-gamma7, and the beta2-adrenergic receptor (beta2AR) resulted in internalization of both fluorescent signals from the plasma membrane. Initially, alphas-CFP and YFP-N-beta1/YFP-C-gamma7 stained the cytoplasm diffusely, and subsequently they co-localized on vesicles that exhibited minimal overlap with beta2AR-labeled vesicles. Moreover, internalization of beta2AR-GFP, but not alphas-CFP or YFP-N-beta1/YFP-C-gamma7, was inhibited by a fluorescent dominant negative dynamin 1 mutant, Dyn1(K44A)-mRFP, indicating that the Gs subunits and beta2AR utilize different internalization mechanisms. Subsequent trafficking of the Gs subunits and beta2AR also differed in that vesicles labeled with the Gs subunits exhibited less overlap with RhoB-labeled endosomes and greater overlap with Rab11-labeled endosomes. Because Rab11 regulates traffic through recycling endosomes, co-localization of alphas and beta1gamma7 on these endosomes may indicate a means of recycling specific alphasbetagamma combinations to the plasma membrane.

Alternative Splicing↗

PubMed2001

Genetic analysis of the Drosophila Gs(alpha) gene.

One of the best understood signal transduction pathways activated by receptors containing seven transmembrane domains involves activation of heterotrimeric G-protein complexes containing Gs(alpha), the subsequent stimulation of adenylyl cyclase, production of cAMP, activation of protein kinase A (PKA), and the phosphorylation of substrates that control a wide variety of cellular responses. Here, we report the identification of "loss-of-function" mutations in the Drosophila Gs(alpha) gene (dgs). Seven mutants have been identified that are either complemented by transgenes representing the wild-type dgs gene or contain nucleotide sequence changes resulting in the production of altered Gs(alpha) protein. Examination of mutant alleles representing loss-of-Gs(alpha) function indicates that the phenotypes generated do not mimic those created by mutational elimination of PKA. These results are consistent with the conclusion reached in previous studies that activation of PKA, at least in these developmental contexts, does not depend on receptor-mediated increases in intracellular cAMP, in contrast to the predictions of models developed primarily on the basis of studies in cultured cells.

Adenylyl Cyclases↗

PubMed1999

Isoprenaline can activate the acetylcholine-induced K+ current in canine atrial myocytes via Gs-derived betagamma subunits.

1. G protein betagamma subunits activate the acetylcholine-induced potassium current IK,ACh. There is no evidence of specificity at the level of the betagamma subunits. Therefore all G protein-coupled receptors in atrial myocytes should be able to activate IK,ACh. Paradoxically, it is often stated that isoprenaline does not activate IK,ACh. Rationales to explain this negative result include insufficient concentrations of Gs in the atrium or restricted access of Gs-derived betagamma subunits to the IK,ACh channel. We took advantage of a non-specific increase in Gs that results after infection with adenovirus. 2. Adenoviral infection unmasked a 1 microM isoprenaline-induced IK,ACh which was prevented by propranolol. Isoprenaline occasionally activated IK,ACh in uninfected and freshly dissociated atrial myocytes but the effect was larger and more consistent in infected myocytes. 3. Pertussis toxin pretreatment (100 ng ml-1 overnight) did not block the effect of isoprenaline. The effect of isoprenaline became persistent if cells were pretreated with cholera toxin (200 ng nl-1). 4. Signal transduction events distal to adenylyl cyclase were not involved in isoprenaline-induced IK,ACh. Forskolin (10 microM) did not activate IK,ACh. Inhibition of adenylyl cyclase with cytoplasmic application of 300 microM 2'-deoxyadenosine 3'-monophosphate did not prevent the activation of IK,ACh by isoprenaline. 5. Cytoplasmic application of a betagamma binding peptide derived from the C terminus of beta-adrenergic receptor kinase 1 (50 microM) prevented the effect of isoprenaline on IK,ACh. The peptide did not prevent the stimulation of the L-type calcium current by isoprenaline. 6. The results indicate that beta-adrenoceptors can activate IK,ACh in atrial myocytes through the release of betagamma subunits from Gs.

Acetylcholine↗

PubMed2005

Gq-mediated activation of c-Jun N-terminal kinase by the gastrin-releasing peptide-preferring bombesin receptor is inhibited upon costimulation of the Gs-coupled dopamine D1 receptor in COS-7 cells.

G protein-coupled receptors (GPCRs) of Gi- or Gq-coupling specificity are effectively linked to activation of the c-Jun N-terminal kinase (JNK) cascade. However, little is known with regard to the regulation of JNK by Gs-coupled receptors. In this report, we used COS-7 cells transfected with the dopamine D1 receptor (D1R) to illustrate the signaling mechanism for Gs-mediated JNK activation. Stimulation of D1R triggered a weak but significant elevation of JNK activity in a time- and dose-dependent manner. This D1R-mediated JNK activation required the participation of Gbetagamma, Src-like kinases, and small GTPases, whereas disruptions of cAMP-, phosphoinositide-3-kinase-, and epidermal growth factor receptor-mediated signaling had no effect. Costimulation of D1R with GPCRs of other coupling specificities resulted in differential activation profiles of JNK. Activation of Gs-coupled D1R weakly potentiated the JNK activation induced by the Gi-coupled opioid receptor-like receptor, but it exhibited a significant inhibitory effect on the kinase activity triggered by the Gq-coupled gastrin-releasing peptide-preferring bombesin receptor (GRPR). Administration of Spadenosine-3',5'-cyclic monophosphorothioate triethylamine (a cAMP analog that mimics the Gs/cAMP signal) also suppressed the JNK activation mediated by Gq-coupled GRPR, as well as the Ca2+-induced kinase activation upon thapsigargin treatment. Moreover, the Ca2+ signal from GRPR synergistically potentiated the D1R-triggered cAMP elevation when the two receptors were stimulated simultaneously. Taken together, our results demonstrated that stimulation of Gs-coupled receptors in COS-7 cells not only enhanced the JNK activity, but also exhibited a "tuning" effect on the kinase activation mediated by GPCRs of other coupling specificities.

Animals↗

PubMed1997

Normal erythrocyte membrane Gs alpha bioactivity in two unrelated patients with acrodysostosis.

Shortening of the tubular bones of the hands and feet with cone shaped epiphyses is known as peripheral dysostosis and is common to several syndromes including acrodysostosis and Albright's hereditary osteodystrophy (AHO). The underlying defect in AHO is known to be a reduction in bioactivity of the alpha subunit of the signal transducing protein, Gs, and heterozygous deactivating mutations have been shown in the Gs alpha gene. Because of additional overlapping clinical and radiological features it has been suggested that acrodysostosis and AHO represent poles of a single diagnostic spectrum. We have measured Gs alpha bioactivity in two unrelated patients with a clinical diagnosis of acrodysostosis and found both to be normal. Mutation analysis of the Gs alpha gene showed no sequence variation in 12 of the 13 exons examined. These results indicate that, at least in a proportion of patients with acrodysostosis, the condition is aetiologically distinct from AHO.

Child, Preschool↗

PubMed1996

Severe dietary magnesium deficiency does not alter levels and function of myocardial Gs alpha and Gi alpha.

Magnesium ions (Mg2+) play a crucial role in the activation and synthesis of guanine nucleotide-binding proteins (G proteins). However, there is no information about the influence of in vivo magnesium deficiency on the function and levels of G proteins. This study was done to investigate whether dietary magnesium deficiency alters function and levels of the two major myocardial G proteins, Gi alpha and Gs alpha. Severe hypomagnesemia and a significant reduction of myocardial magnesium occurred in rats fed a magnesium-deficient diet for 6 wk vs. rats fed a normal-magnesium diet (control). The magnesium-deficient rats developed focal myocardial lesions but their cardiac function was not impaired. Myocardial immunodetectable Gs alpha and Gi alpha levels of magnesium-deficient rats did not differ from control (Gs alpha: 2.39 +/- 0.52 vs. 2.76 +/- 0.72 arbitrary units/microgram protein, P > 0.05; Gi alpha: 1.60 +/- 0.52 vs. 1.89 +/- 0.30 arbitrary units/microgram protein, P > 0.05). Similarly, the function of Gs alpha and Gi alpha estimated by basal and ligand-stimulated adenylyl cyclase activity was not significantly different between the two groups of animals. The results show that dietary-derived magnesium deficiency sufficient to produce severe hypomagnesemia does not produce any significant change in levels or function of myocardial G proteins.

Adenylyl Cyclases↗

PubMed2003

Growth hormone-releasing hormone resistance in pseudohypoparathyroidism type ia: new evidence for imprinting of the Gs alpha gene.

Heterozygous inactivating mutations in the Gs alpha gene cause Albright's hereditary osteodystrophy. Consistent with the observation that only maternally inherited mutations lead to resistance to hormone action [pseudohypoparathyroidism type Ia (PHP Ia)], recent studies provided evidence for a predominant maternal origin of Gs alpha transcripts in endocrine organs, such as thyroid, gonad, and pituitary. The aim of this study was to investigate the presence of pituitary resistance to hypothalamic hormones acting via Gs alpha-coupled receptors in patients with PHP Ia. Six of nine patients showed an impaired GH responsiveness to GHRH plus arginine, consistent with a complete GH deficiency (GH peak from 2.6-8.6 microg/liter, normal > 16.5), and partial (GH peak 13.9 and 13.6 microg/liter) and normal responses were found in two and one patient, respectively. Accordingly, IGF-I levels were below and in the low-normal range in seven and two patients. All patients had a normal cortisol response to 1 microg ACTH test, suggesting a normal corticotroph function that was confirmed by a normal ACTH and cortisol response to CRH test in three patients. In conclusion, we report that in addition to PTH and TSH resistance, patients with PHP Ia display variable degrees of GHRH resistance, consistent with Gs alpha imprinting in human pituitary.

Adrenocorticotropic Hormone↗

PubMed1996

Structural studies of the thyrotropin receptor and Gs alpha in human thyroid cancers: low prevalence of mutations predicts infrequent involvement in malignant transformation.

The genes for either the TSH receptor (TSH-R) or the stimulatory guanine nucleotide-binding protein subunit (Gs alpha) can undergo somatic mutations in thyroid cells, leading to constitutive activation of adenylyl cyclase and the formation of clonal hyperfunctioning thyroid adenomas. Autonomously functioning thyroid adenomas are thought not to be common precursors of thyroid cancer. If this is the case, mutations of the TSH-R or Gs alpha would not be expected to be highly prevalent in thyroid carcinomas. In this paper we report the results of a screen for structural defects in exon 10 of the TSH-R (which includes the whole serpentine structure, but not the extracellular domain) and of Gs alpha in 30 thyroid carcinomas. Five of these were from patients with functioning metastasis, as we hypothesized that if mutations of these genes were to play a role in the progression to malignancy, they would be more likely to manifest in thyroid cancers that retain unusual differentiated function (i.e. capable of synthesizing enough thyroid hormone to render patients euthyroid or hyperthyroid after total thyroidectomy). None of the 30 tumors had activating point mutations of Gs alpha. Only 2 of 30 had somatic mutations of the TSH-R (codon 632: ACC to GCC, Thr to Ala; and ACC to ATC, Thr to Ile, respectively), the latter in a patient with a thyroid hormone-producting follicular carcinoma. These results suggest that events leading to constitutive activation of the adenylate cyclase signal transduction cascade are not a frequent event in the progression toward differentiated thyroid carcinomas.

Base Sequence↗