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Biomedical subjects

W F Schwindinger

Publications and source records attributed to W F Schwindinger.

13 recordsLinked to original sources
PubMed1996

Clinical implications of genetic defects in G proteins. The molecular basis of McCune-Albright syndrome and Albright hereditary osteodystrophy.

Inactivating and activating mutations in the gene encoding G alpha s (GNAS1) are known to be the basis for 2 well-described contrasting clinical disorders, Albright hereditary osteodystrophy (AHO) and McCune-Albright syndrome (MAS). AHO is an autosomal dominant disorder due to germline mutations in GNAS1 that decrease expression or function of G alpha s protein. Loss of G alpha s function leads to tissue resistance to multiple hormones whose receptors couple to G alpha s. By contrast, MAS results from postzygotic somatic mutations in GNAS1 that lead to enhanced function of G alpha s protein. Acquisition of the activating mutation early in life leads to a more generalized distribution of the mosaicism and is associated with the classic clinical triad of polyostotic fibrous dysplasia, endocrine hyperfunction, and café au lait skin lesions described in MAS. Acquisition of a similar activating mutation in GNAS1 later in life presumably accounts for the restricted distribution of the gsp oncogene, and is associated with the development of isolated lesions (for example, fibrous dysplasia, pituitary or thyroid tumors) without other manifestations of MAS. Tissues that are affected by loss of G alpha s function in AHO are also affected by gain of G alpha s function in MAS, thus identifying specific tissues in which the second messenger cAMP plays a dominant role in cell growth, proliferation, or function. Further investigations of the functions of G alpha s and other members of the GTPase binding protein family will provide more insight into the pathogenesis and clinical manifestations of human disease.

Adolescent↗
PubMed1995

Urinary cyclic adenosine 3',5'-monophosphate response in McCune-Albright syndrome: clinical evidence for altered renal adenylate cyclase activity.

The recent finding of an activating mutation in the Gs alpha protein, the protein that couples receptors to stimulation of adenylate cyclase, from endocrine and nonendocrine tissues of patients with McCune-Albright syndrome (MAS) suggests that alterations in adenylate cyclase activity may account for the clinical abnormalities in these patients. Many patients with MAS have hypophosphatemia. This may result from the presence of the activating Gs alpha mutation in proximal renal tubules or the elaboration of a phosphaturic factor from fibrous dysplasia. We, therefore, sought to characterize renal cAMP generation and phosphate handling in MAS patients. Intravenous infusion of PTH is a classic clinical test used to evaluate hormonal responsiveness of renal proximal tubule adenylate cyclase and examine PTH-dependent phosphate clearance. We performed PTH infusion in 6 MAS patients, 10 normal subjects, and 6 patients with pseudohypoparathyroidism (PHP). The basal urinary cAMP (UcAMP) level in the MAS group [5.5 +/- 2.6 nmol/dL glomerular filtration (GF)] was elevated (P < 0.05) compared to those in both normal subjects (3.2 +/- 1.2 nmol/dL GF) and patients with PHP (1.9 +/- 0.6 nmol/dL GF). However, PTH-stimulated peak UcAMP (15.0 +/- 7.0 nmol/dL GF) and the peak/basal UcAMP ratio (3.1 +/- 1.7) in MAS were significantly lower than the respective values in normal subjects (30.8 +/- 16.9 nmol/dL GF and 9.3 +/- 2.9; P < 0.05 for both) and were statistically similar to the blunted levels in PHP (respectively, 3.1 +/- 1.5 nmol/dL GF and 2.0 +/- 1.7). By contrast, the PTH-induced phosphaturic response in MAS patients was similar to that in the normal subjects. Our study provides clinical evidence that MAS patients have altered renal adenylate cyclase activity, manifested by an elevated basal UcAMP, but a blunted UcAMP response to PTH stimulation. These observations are presumably due to a mutation in the Gs alpha protein in the renal tubules. Despite the blunted UcAMP excretion, the phosphaturic response to PTH in MAS patients is intact.

Adenylyl Cyclases↗
PubMed1994

A novel Gs alpha mutant in a patient with Albright hereditary osteodystrophy uncouples cell surface receptors from adenylyl cyclase.

Albright hereditary osteodystrophy (AHO) is an autosomal-dominant disorder characterized by decreased expression of Gs alpha and widespread tissue resistance to hormones that activate adenylyl cyclase. We identified a single mutation, R385H, in the Gs alpha gene of a subject with AHO who had evidence for a dysfunctional Gs alpha protein. The R385H substitution is near the carboxyl terminus of the Gs alpha protein and is located five amino acids upstream of the R389P mutation that uncouples Gs alpha from cell surface receptors in the unc clone of S49 murine lymphoma. To test the biological activity of the R385H mutant, we transiently expressed wild type, R385H, and R389P Gs alpha cDNAs in COS-1 cells. Neither of the mutant Gs alpha proteins stimulated adenylyl cyclase in response to l-isoproterenol (1 to 30 microM). By contrast, both mutant Gs alpha proteins showed activation of adenylyl cyclase in response to forskolin (10 microM) and fluoroaluminate (10 mM). We propose that the R385H mutation produces a Gs alpha molecule that is unable to interact with hormone receptors and results in uncoupling of adenylyl cyclase from cell surface receptors. This uncoupling mutation represents a new type of molecular defect that can result in AHO.

1-Methyl-3-isobutylxanthine↗
PubMed1994

Signal-transducing G proteins: basic and clinical implications.

The pivotal role that G proteins play in transmembrane signal transduction is highlighted by the rapidly expanding list of receptors and effector molecules that are coupled through G proteins. G proteins are poised to allow discrimination and diversification of cellular signals into the cytosolic milieu. The utilization of an evolutionarily conserved "GTPase clock" by G proteins, offers insight into the fundamental role these proteins play in biology. Knowledge of the implication of altered expression or function of G proteins in human disease is now emerging. It is not surprising that deficiency or expression of altered forms of these important proteins can lead to global or restricted metabolic disturbances, depending upon the distribution and role of the G protein. Human disorders, including heart failure, alcoholism, endocrine abnormalities, and neoplasia, are now recognized as due in part to altered expression or function of G proteins.

Amino Acid Sequence↗
PubMed1992

Identification of a mutation in the gene encoding the alpha subunit of the stimulatory G protein of adenylyl cyclase in McCune-Albright syndrome.

McCune-Albright syndrome (MAS) is characterized by polyostotic fibrous dysplasia, café-au-lait lesions, and a variety of endocrine disorders, including precocious puberty, hyperthyroidism, hypercortisolism, growth hormone excess, and hyperprolactinemia. The diverse metabolic abnormalities seen in MAS share the involvement of cells that respond to extracellular signals through activation of the hormone-sensitive adenylyl cyclase system (EC 4.6.1.1). Mutations that lead to constitutive activation of Gs alpha, the guanine nucleotide-binding regulatory protein that stimulates adenylyl cyclase activity, have been identified in a subset of human growth hormone-secreting pituitary tumors and human thyroid tumors. We report here the identification of a mutation in the gene encoding Gs alpha in a patient with MAS. Denaturing gradient gel electrophoresis was used to analyze amplified DNA fragments including exon 8 or exon 9 of the Gs alpha gene. In one subject with MAS a G-to-A transition was found in exon 8 of one of the two alleles encoding Gs alpha. This single-base substitution results in the replacement of arginine by histidine at position 201 of the mature Gs alpha protein. Semiquantitative analysis of amplified DNA indicated that the mutant allele was less prevalent than the wild-type allele in peripheral leukocytes and was present in very low levels in skin. These findings support the previous contention that the segmental distribution and variable expression of the cutaneous, skeletal, and endocrine manifestations of MAS reflect an underlying somatic mosaicism. Further, these results suggest that the molecular basis of MAS is a postzygotic mutation in Gs alpha that causes constitutive activation of adenylyl cyclase.

Adenylyl Cyclases↗
PubMed1987

Transcriptional elements of the yeast ribosomal protein gene CYH2.

The sequences responsible for specifying and regulating the transcription of the yeast ribosomal protein gene CYH2 have been studied using deletion analysis. We have identified a region between 235 and 260 nucleotides upstream of the transcription initiation which is necessary for transcription to occur. This region includes sequences which have been identified upstream of most yeast ribosomal protein genes. In the wild type gene the initiation of transcription occurs at several sites spread over about 15 nucleotides. Two TATA regions separated by about 40 nucleotides direct initiation to those sites. Deletion of those two TATA regions reveals a cryptic TATA which directs transcription initiation to specific sites downstream.

Amino Acid Sequence↗
PubMed1985

Saccharomyces cerevisiae coordinates accumulation of yeast ribosomal proteins by modulating mRNA splicing, translational initiation, and protein turnover.

The rate of accumulation of each ribosomal protein is carefully regulated by the yeast cell to provide the equimolar ratio necessary for the assembly of the ribosome. The mechanisms responsible for this regulation have been examined by introducing into the yeast cell extra copies of seven individual ribosomal protein genes carried on autonomously replicating plasmids. In each case studied the plasmid-borne gene was transcribed to the same degree as the genomic gene. Nevertheless, the cell maintained a balanced accumulation of ribosomal proteins, using a variety of methods other than transcription. (i) Several ribosomal proteins were synthesized in substantial excess. However, the excess ribosomal protein was rapidly degraded. (ii) The excess mRNA for two of the ribosomal protein genes was translated inefficiently. We provide evidence that this was due to inefficient initiation of translation. (iii) The transcripts derived from two of the ribosomal protein genes were spliced inefficiently, leading to an accumulation of precursor RNA. We present a model which proposes the autogenous regulation of mRNA splicing as a eucaryotic parallel of the autogenous regulation of mRNA translation in procaryotes. Finally, the accumulation of each ribosomal protein was regulated independently. In no instance did the presence of excess copies of the gene for one ribosomal protein affect the synthesis of another ribosomal protein.

Cloning, Molecular↗
PubMed1984

A comparison of yeast ribosomal protein gene DNA sequences.

The DNA sequences of eight yeast ribosomal protein genes have been compared for the purpose of identifying homologous regions which may be involved in the coordinate regulation of ribosomal protein synthesis. A 12 bp homology was identified in the 5' DNA sequence preceding the structural gene for 6 out of 8 yeast ribosomal protein genes. In each case the homologous sequence was found at a position approximately 300 bp preceding the transcription start of the ribosomal protein gene. This homology was not identified in any non-ribosomal protein gene examined. Additional homologies between ribosomal protein genes were identified in the transcribed regions, including the untranslated 5' and 3' DNA regions flanking the coding regions.

Amino Acid Sequence↗
PubMed1984

DNA sequence analysis on the IBM-PC.

We have developed, for the IBM-PC microcomputer, a menu driven, interactive set of programs which provide the functions routinely used for DNA sequence data analyses.

Amino Acid Sequence↗
PubMed1983

Cycloheximide resistance in yeast: the gene and its protein.

Mutations in the yeast gene CYH2 can lead to resistance to cycloheximide, an inhibitor of eukaryotic protein synthesis. The gene product of CYH2 is ribosomal protein L29, a component of the 60S ribosomal subunit. We have cloned the wild-type and resistance alleles of CYH2 and determined their nucleotide sequence. Transcription of CYH2 appears to initiate and terminate at multiple sites, as judged by S1 nuclease analysis. The gene is transcribed into an RNA molecule of about 1082 nucleotides, containing an intervening sequence of 510 nucleotides. The splice junction of the intron resides within a codon near the 5' end of the gene. In confirmation of peptide analysis by Stocklein et al. (1) we find that resistance to cycloheximide is due to a transversion mutation resulting in the replacement of a glutamine by glutamic acid in position 37 of L29.

Alleles↗
PubMedDate not supplied

Characterization of Albright hereditary osteodystrophy and related disorders.

Albright hereditary osteodystrophy (AHO) is an autosomal dominant disorder with characteristic skeletal and developmental defects and reduced expression or activity of the alpha chain of the G protein that stimulates adenylyl cyclase (Gs alpha). Most patients with AHO exhibit target tissue resistance to multiple hormones whose actions are mediated by cyclic AMP (cAMP) as a second messenger, such as the parathyroid hormone (PTH). This form of the disorder is known as pseudohypoparathyroidism (PHP) type Ia. Patients with PHP type Ia usually have relatives with AHO who do not exhibit hormone resistance despite having the same defect in Gs alpha. This variant, yet unexplained, is known as pseudopseudohypoparathyroidism (PPHP). PHP type Ib is manifested by a limited hormone resistance to PTH and is believed to be caused by defects in the PTH receptor. Patients with PHP type Ic have normal Gs alpha activity and show morphologic defects similar to those in AHO as well as resistance to multiple hormones. PHP type II, a much rarer disease, is probably caused by vitamin D deficiency.

GTP-Binding Proteins↗