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Biomedical subjects

A Shenker

Publications and source records attributed to A Shenker.

At least 19 recordsLinked to original sources
PubMed2001

Drugs used in the treatment of attention-deficit/hyperactivity disorder affect postsynaptic firing rate and oscillation without preferential dopamine autoreceptor action.

BACKGROUND: Current theories propose that low doses of catecholaminergic stimulants reduce symptoms in patients with attention-deficit/hyperactivity disorder by acting on autoreceptors to reduce catecholaminergic transmission; few data are available that directly address this hypothesis. METHODS: We investigated the autoreceptor and postsynaptic receptor actions of systemically administered stimulants on dopaminergic systems in rats with single-unit recording in the substantia nigra pars compacta and globus pallidus, respectively. RESULTS: Dose-response curves for rate indicated that the potencies of the indirect-acting agonists methylphenidate and D-amphetamine at dopaminergic autoreceptors were not greater than at postsynaptic receptors; in fact, D-amphetamine was more potent postsynaptically. In addition to effects on firing rate, spectral/wavelet analyses indicated that these drugs had prominent effects on postsynaptic multisecond oscillations. These oscillations were shifted by stimulants from baseline periods of approximately 30 sec to periods of 5-10 sec. Effects on pattern were found at doses as low as 1.0 mg/kg (methylphenidate) and 0.2 mg/kg (D-amphetamine). At this latter dose, D-amphetamine had little effect presynaptically. CONCLUSIONS: These and prior results demonstrate that there is no autoreceptor-preferring dose range of catecholaminergic stimulants; these drugs at low doses are unlikely to reduce motor activity by this mechanism. Nonetheless, they might affect attentive and cognitive processes by modulating multisecond temporal patterns of central activity.

Animals↗
PubMed2001

Adenovirus-directed expression of functional luteinizing hormone (LH) receptors in undifferentiated rat granulosa cells: evidence for differential signaling through follicle-stimulating hormone and LH receptors.

This study was conducted to determine the feasibility of using replication-defective adenovirus vectors to express receptors for LH. Two vectors were constructed, one that directs the expression of wild-type human LH receptor (LHr; AdRSVLHrwt) and another that directs the expression of the constitutively activated D578H mutant human LH receptor (AdRSVD578HLHr). When infected with AdRSVwtLHr and AdRSVD578HLHr, COS-1 cells expressed LH/hCG-binding sites as reflected by specific binding of [(125)I]hCG. To determine the ability of the vectors to confer LH responsiveness, undifferentiated rat granulosa cells, which possess only FSH receptors, were infected with AdRSVwtLHr and AdRSVD578HLHR: Expression of the constitutively activated D578H LHr increased basal (gonadotropin-independent) estrogen and progesterone production. Expression of the wild-type LHr in granulosa cells did not stimulate basal steroid production, but conferred responsiveness to exogenous LH. For both wild-type LHr and D578HLHr, the absolute levels of steroid production were dependent upon the input of viral titers. Using these vectors, we compared effects of FSH and LH receptor activation in undifferentiated granulosa cells. Stimulation of undifferentiated granulosa cells by FSH and D578HLHr, as well as activation of wild-type LHr with LH resulted in comparable production of progesterone. In contrast, estradiol production in cells stimulated with FSH was greater than that in cells that expressed either D578H receptors or wild-type LHr in the presence of LH. Analysis of messenger RNAs (mRNAs) revealed that activations of FSH and the LH receptors were comparable in the induction of alpha-inhibin and 3betahydroxysteroid dehydrogenase mRNAS: However, activation of FSH receptor led to significantly greater expression of P450 aromatase and LHr mRNAs than did activation of LHR: These results suggest that activation of FSH and LH receptors in granulosa cells may differ with respect to activating intracellular signaling pathways and stimulating gene expression.

8-Bromo Cyclic Adenosine Monophosphate↗
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↗
PubMed1998

Automated high resolution optical mapping using arrayed, fluid-fixed DNA molecules.

New mapping approaches construct ordered restriction maps from fluorescence microscope images of individual, endonuclease-digested DNA molecules. In optical mapping, molecules are elongated and fixed onto derivatized glass surfaces, preserving biochemical accessibility and fragment order after enzymatic digestion. Measurements of relative fluorescence intensity and apparent length determine the sizes of restriction fragments, enabling ordered map construction without electrophoretic analysis. The optical mapping system reported here is based on our physical characterization of an effect using fluid flows developed within tiny, evaporating droplets to elongate and fix DNA molecules onto derivatized surfaces. Such evaporation-driven molecular fixation produces well elongated molecules accessible to restriction endonucleases, and notably, DNA polymerase I. We then developed the robotic means to grid DNA spots in well defined arrays that are digested and analyzed in parallel. To effectively harness this effect for high-throughput genome mapping, we developed: (i) machine vision and automatic image acquisition techniques to work with fixed, digested molecules within gridded samples, and (ii) Bayesian inference approaches that are used to analyze machine vision data, automatically producing high-resolution restriction maps from images of individual DNA molecules. The aggregate significance of this work is the development of an integrated system for mapping small insert clones allowing biochemical data obtained from engineered ensembles of individual molecules to be automatically accumulated and analyzed for map construction. These approaches are sufficiently general for varied biochemical analyses of individual molecules using statistically meaningful population sizes.

Animals↗
PubMed1998

Severe testotoxicosis phenotype associated with Asp578-->Tyr mutation of the lutrophin/choriogonadotrophin receptor gene.

Testotoxicosis is a form of male precocious puberty caused by heterogeneous activating mutations in the gene for the lutrophin/choriogonadotrophin receptor (LHR). A patient with an unusually early and severe presentation of testotoxicosis, including profound Leydig cell hyperplasia, was found to have a sporadic mutation encoding Asp578-->Tyr. The severe testotoxicosis phenotype appears to be related to the strongly activating nature of the Tyr substitution.

Aspartic Acid↗
PubMed1998

An anionic residue at position 564 is important for maintaining the inactive conformation of the human lutropin/choriogonadotropin receptor.

Gonadotropin-independent, male-limited precocious puberty is caused by a variety of mutations in the lutropin/choriogonadotropin receptor (LHR) that produce constitutive receptor activation. Two of these mutations encode replacement of conserved aspartate residues at positions 564 and 578 with glycine. We previously used site-directed mutagenesis to study the functional role of the Asp578 side chain in transmembrane helix 6, and concluded that it is its ability to serve as a properly positioned interhelical hydrogen bond acceptor, rather than its negative charge, that is important for stabilizing the inactive state of the LHR. We now report the effects of substituting seven different amino acids for the Asp564 residue located at the carboxyl terminus of the third intracellular loop. Glycine, alanine, valine, leucine, phenylalanine, and asparagine produced constitutive activation in a COS-7 cell expression system (3-5-fold increase in basal cAMP), but glutamate did not, indicating that a negative charge at position 564 may be important for maintaining the inactive LHR conformation. Characterization of double-mutant receptors showed that certain substitutions at Asp564 and Asp578 have a cumulative effect on basal receptor activity, perhaps because they mimic different aspects of the activation process normally triggered by hormone binding.

Amino Acid Sequence↗
PubMed1997

A model of the lutropin/choriogonadotropin receptor: insights into the structural and functional effects of constitutively activating mutations.

A model of the seven transmembrane helical domain (7-TM) of the human lutropin receptor was constructed from the 2D electron density map of bovine rhodopsin and a set of geometric parameters derived from a published analysis of 204 G-protein coupled receptor sequences. The Self-Consistent Ensemble Optimization method was applied to predict overall side chain packing. The model is consistent with the general helical packing properties expected of transmembrane proteins and suggests possible structural and functional effects of constitutively activating mutations. A tightly packed hydrophobic cluster formed between the intracellular halves of TM5 and TM6, as well as a specific H-bonding network formed between the central regions of TM6 and TM7, is proposed to be critical for stabilizing the inactive form of the receptor. The model suggests that single activating mutations perturb the specific interactions of TM6 with TM5 and TM7, either by disrupting the hydrophobic packing between TM5 and TM6, or by weakening the H-bonds between TM6 and TM7.

Amino Acid Sequence↗
PubMed1997

Fibrous dysplasia of bone in the McCune-Albright syndrome: abnormalities in bone formation.

In addition to café-au-lait pigmentation patterns and hyperendocrinopathies, fibrous dysplasia of bone is a major finding in the McCune-Albright syndrome. Activating missense mutations of the Gs alpha gene leading to overactivity of adenylyl cyclase have been identified in patients with McCune-Albright syndrome, but the mechanism leading to the specific development of fibrous dysplasia in bone has not been elucidated. By means of specific peptide antisera and reverse transcriptase polymerase chain reaction in situ hybridization, we show that expression of Gs alpha and its mRNA is critically up-regulated during maturation of precursor osteogenic cells to normal osteoblast cells and that this pattern of expression is retained in fibrous dysplasia. A functional characterization of fibrous dysplastic tissues revealed that the fibrotic areas consist, in fact, of an excess of cells with phenotypic features of pre-osteogenic cells, whereas the lesional bone formed de novo within fibrotic areas represents the biosynthetic output of mature but abnormal osteoblasts. These cells are noted for peculiar changes in cell shape and interaction with matrix, which were mimicked in vitro by the effects of excess exogenous cAMP on human osteogenic cells. Osteoblasts involved with the de novo deposition of lesional bone in fibrous dysplasia produce a bone matrix enriched in certain anti-adhesion molecules (versican and osteonectin), and poor in the pro-adhesive molecules osteopontin and bone sialoprotein, which is in contrast to the high levels of these two proteins found in normal de novo bone. Our data indicate the need to reinterpret fibrous dysplasia of bone as a disease of cells in the osteogenic lineage, related to the effects of excess cAMP on bone cell function. They further suggest that a critical, physiological, maturation-related regulation of Gs alpha levels makes cells in the osteogenic lineage a natural target for the effects of mutations in the Gs alpha gene and may provide a clue as to why bone itself is affected in this somatic, mutation-dependent disease.

Adolescent↗
PubMed1996

The role of Asp578 in maintaining the inactive conformation of the human lutropin/choriogonadotropin receptor.

A constitutively activating mutation encoding Asp578-->Gly in transmembrane helix 6 of the lutropin/choriogonadotropin receptor (LHR) is the most common cause of gonadotropin-independent, male-limited precocious puberty. This mutant LHR produces a 4.5-fold increase in basal cAMP when expressed in COS-7 cells. To better understand the normal role of Asp578 in the LHR we studied the effect of seven other amino acid substitutions at this position. No agonist binding or response was detected with the Asp578-->Pro mutant. Agonist binding affinity was unaffected by the other substitutions and estimated receptor concentrations ranged from 11 to 184% of wild type. Substitution of Asp578 with Asn, a similarly sized, uncharged residue, did not produce agonist-independent activation. In contrast, replacement with Glu, Ser, or Leu caused 4. 9-5.6-fold stimulation of basal cAMP. Substitution with Tyr (8.5-fold) or Phe (7.5-fold) had a greater activating effect. Only the Tyr, Phe, and Leu mutants showed constitutive activation of the inositol phosphate pathway. Our data suggest that it is the ability of the Asp578 side chain to serve as a properly positioned hydrogen bond acceptor, rather than its negative charge, that is important for stabilizing the inactive state of the LHR. A bulky aromatic side chain at position 578 may further destabilize the inactive receptor conformation.

Animals↗
PubMed1996

Screening of candidate oncogenes in human thyrotroph tumors: absence of activating mutations of the G alpha q, G alpha 11, G alpha s, or thyrotropin-releasing hormone receptor genes.

Activating mutations encoding substitutions at positions Arg201 and Gln227 of the alpha-subunit of the stimulatory G protein. G10 have been found in about 40% of pituitary somatotroph tumors. Although the etiology of thyrotroph adenomas is unknown, their autonomous behavior and blunted response to stimulatory hypothalamic hormone superficially resemble those of somatotroph tumors. We hypothesized that a subset of thyrotroph tumors might be caused by dominant somatic mutations that lead to inappropriate activation of the Gq/phospholipase C beta/Ca2+/protein kinase C. pathway normally triggered by occupancy of the TRH receptor (TRHR). We, therefore, screened samples from nine thyrotroph tumors for the presence of activating mutations of the alpha q, alpha 11, and TRHR genes. Fragments of alpha q and alpha 11 complementary DNA encompassing residues (Arg183 and Gln209) that correspond to Arg201 and Gln227 of alpha q were amplified and sequenced. Temperature gradient gel electrophoresis was used to screen for heterozygous mutations in the TRHR coding sequence as well as for known alpha s mutations. No mutations were detected. We conclude that mutations in these regions of the alpha q, alpha 11, alpha s, and TRHR genes occur infrequently, if at all, in human thyrotroph tumors. Alternative mechanisms underlying thyrotroph tumorigenesis, including changes in the expression levels of G protein alpha-subunits or TRHR, dysregulation of downstream components, inappropriate activation of other stimulatory pathways, or loss of inhibitory inputs, remain to be explored.

Adult↗
PubMed1995

Molecular cloning of human G alpha q cDNA and chromosomal localization of the G alpha q gene (GNAQ) and a processed pseudogene.

G alpha q is the alpha subunit of one of the heterotrimeric GTP-binding proteins that mediates stimulation of phospholipase C beta. We report the isolation and characterization of cDNA clones from a frontal cortex cDNA library encoding human G alpha q. The encoded protein is 359 amino acids long and is identical in all but one amino acid residue to mouse G alpha q. Analysis of human genomic DNA reveals an intronless sequence with strong homology to human G alpha q cDNA. In comparison to G alpha q cDNA, this genomic DNA sequence includes several small deletions and insertions that alter the reading frame, multiple single base changes, and a premature termination codon in the open reading frame, hallmarks of a processed pseudogene. Probes derived from human G alpha q cDNA sequence map to both chromosomes 2 and 9 in high-stringency genomic blot analyses of DNA from a panel of human-rodent hybrid cell lines. PCR primers that selectively amplify the pseudogene sequence generate a product only when DNA containing human chromosome 2 is used as the template, indicating that the authentic G alpha q gene (GNAQ) is located on chromosome 9. Regional localization by FISH analysis places GNAQ at 9q21 and the pseudogene at 2q14.3-q21.

Animals↗
PubMed1995

G protein-coupled receptor structure and function: the impact of disease-causing mutations.

Just as the discovery of 'inborn errors of metabolism' in humans contributed to our basic understanding of normal enzymatic pathways, so can genetic defects in signal transduction help to elucidate the functions normally subserved by different GPCR pathways. Identification and characterization of naturally occurring GPCR mutations not only has inherent value in understanding the molecular basis of disease, but can also accelerate progress in understanding the fundamental mechanisms involved in GPCR synthesis, transport to the membrane, ligand binding, activation and deactivation.

GTP-Binding Proteins↗
PubMed1995

Characterization of heterogeneous mutations causing constitutive activation of the luteinizing hormone receptor in familial male precocious puberty.

Familial male precocious puberty (FMPP) is a gonadotropin-independent disorder that is inherited in an autosomal dominant, male-limited pattern. A heterozygous mutation encoding substitution of Asp578 with Gly in transmembrane helix 6 of the G protein-coupled receptor for luteinizing hormone (LHR) has been found in affected males from nine American FMPP families. Cells expressing the mutant LHR exhibit markedly increased cyclic adenosine monophosphate (cAMP) production in the absence of agonist, suggesting that autonomous Leydig cell activity in FMPP is caused by a constitutively activated LHR. We have now analyzed genomic DNA from affected males from six additional FMPP families. PCR was used to amplify a fragment of the LHR gene encoding amino acid residues 441-594. None of the six new samples contained the Asp578-->Gly mutation, as indicated by absence of digestion with MspI. PCR products were then screened for heterozygous mutations using temperature-gradient gel electrophoresis. DNA fragments from two of the patients migrated abnormally. Direct sequencing of PCR product from one affected German male revealed a heterozygous mutation (ATG-->ATA) encoding Met571-->Ile at the cytoplasmic end of helix 6, the same mutation that has been reported in another European FMPP kindred. Affected males in the second family had a novel Thr577-->Ile mutation (ACC-->ATC). Mutations in different portions of the LHR or in a different gene may be responsible for disease in the other FMPP kindreds. Agonist binding and functional coupling of the mutant receptors to the cAMP and inositol phosphate pathways were studied by transiently expressing them in COS-7 cells. Agonist affinity was unaffected by the mutations.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

Constitutive activation of cyclic AMP but not phosphatidylinositol signaling caused by four mutations in the 6th transmembrane helix of the human thyrotropin receptor.

Four different somatic mutations (F631C, T632I, D633E, and D633Y) in the putative 6th transmembrane helix of the human thyrotropin receptor (TSHR) were recently described in hyperfunctioning thyroid adenomas [Porcellini et al. (1994) J. Clin. Endocrinol. Metab. 79, 657-661]. We transiently expressed these mutant receptors in Cos-7 cells and measured [125I]TSH binding, basal and TSH-stimulated cAMP production, and phosphatidylinositol hydrolysis. The concentration of receptors expressed at the cell surface was lower for the mutants than for the wild type (WT) TSHR. Compared to the WT, all four mutant receptors caused a marked increase in basal cAMP levels, but did not increase basal production of inositol phosphates. This suggests that autonomous thyroid function and adenoma formation may be related to constitutive activation of the cAMP pathway alone. A cluster of conserved residues at the base of the 6th transmembrane helix of the TSHR and other glycoprotein hormone receptors appears important for maintaining an inactive receptor conformation.

Amino Acid Sequence↗