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Hypogonadotropic hypogonadism as a presenting feature of late-onset X-linked adrenal hypoplasia congenita.

Mutations in the orphan nuclear receptor DAX-1 cause X-linked adrenal hypoplasia congenita. Affected boys usually present with primary adrenal failure in early infancy or childhood. Impaired sexual development because of hypogonadotropic hypogonadism becomes apparent at the time of puberty. We report adult-onset adrenal hypoplasia congenita in a patient who presented with hypogonadism at 28 yr of age. Although he had no clinical evidence of adrenal dysfunction, compensated primary adrenal failure was diagnosed by biochemical testing. Semen analysis showed azoospermia, and he did not achieve fertility after 8 months of treatment with gonadotropins. A novel Y380D DAX-1 missense mutation, which causes partial loss of function in transient gene expression assays, was found in this patient. This case demonstrates that partial loss-of-function mutations in DAX1 can present with hypogonadotropic hypogonadism and covert adrenal failure in adulthood. Further, an important role for DAX-1 in spermatogenesis in humans is confirmed, supporting findings in the Dax1 (Ahch) knockout mouse.

Adrenal Glands↗

Identification of a mutation in SLC30A2 (ZnT-2) in women with low milk zinc concentration that results in transient neonatal zinc deficiency.

Breast milk normally contains adequate zinc to meet infant requirements up to six months of age; however, transient neonatal zinc deficiency has been documented in exclusively breastfed infants of women with low milk zinc concentration. This condition is not corrected by maternal zinc supplementation, supporting the speculation that it results from an inherited genetic condition. We identified a family in which two exclusively breast-fed infants developed zinc deficiency that was associated with low milk zinc concentration in both women. Sequencing of genomic DNA detected a mis-sense mutation (Ade-->Gua) that substitutes a conserved histidine at amino acid 54 with arginine (H54R) in SLC30A2 (ZnT-2) that is present in both affected subjects and several other siblings. Gene knockdown of SLC30A2 in mammary epithelial cells reduced zinc secretion, illustrating the role of ZnT-2 in zinc secretion from this cell type. Expression of the H54R mutant in human embryonic kidney-293 cells resulted in reduced zinc secretion as a consequence of perinuclear, aggresomal accumulation, whereas co-expression of the H54R mutant and wild-type ZnT-2 did not abrogate increased zinc secretion in cells overexpressing wild-type ZnT-2 alone. Together, these data provide evidence that low milk zinc concentration in some women is a consequence of a genetic disorder resulting from a mutation in SLC30A2 and can result in neonatal zinc deficiency if unrecognized. Further studies are needed to evaluate the incidence and penetrance of this mutation in the human population.

Amino Acid Sequence↗

Antisense p53 oligonucleotides inhibit proliferation and induce chemosensitivity in follicular thyroid cancer cells.

BACKGROUND: The potential of MTp53 knockout by oligodesoxyribonucleotide phosphothioates (ODNs) to affect proliferation, apoptosis and chemosensitivity in undifferentiated thyroid cancer (UTC) cells with a recessive MTp53 mutation was evaluated. MATERIALS AND METHODS: Transient transfections with ODNs complementary to p53 and control ODN (HIV-RT) were carried out in FTC 133 cells. In vitro proliferation was evaluated by cell counting of 10 random fields and by the MTT assay. A single pulse of 100 microg/ml Cytarabine was added to each well and the cells were incubated for an additional day. Chemosensitivity was calculated as the ratio of apoptotic and necrotic cells versus viable cells by flow cytometry (FACS). RESULTS: Transfection of UTC cells with ODN decreased the cell number by up to 70% (p < 0.002). The proliferation rate also decreased up to 35% (p < 0.03), without inducing apoptosis. ODNs rendered FTC cells sensitive to treatment with Cytarabine, inducing apoptosis in 35% of cells, as compared to 17% of cells transfected with the reverse transcriptase gene of HIV (ODN-HIV) and less than 10% of non-transfected cells (p < 0.05). CONCLUSION: Transient MTp53 knockout with ODNs complementary to p53 nucleotide sequences inhibited proliferation and increased chemosensitivity in the UTC cell line FTC133.

Adenocarcinoma, Follicular↗

Comparison of virus transcription during lytic infection of the Oka parental and vaccine strains of Varicella-Zoster virus.

The attenuated Oka vaccine (V-Oka) strain of varicella-zoster virus (VZV) effectively reduces disease produced by primary infection and virus reactivation. V-Oka was developed by propagation of the Oka parental (P-Oka) strain of VZV in guinea pig and human embryo fibroblasts. Complete DNA sequencing of both viruses has revealed 63 sites that differ between P-Oka and V-Oka, 37 of which are located within 21 unique open reading frames (ORFs). Of the ORFs that differ, ORF 62 contains the greatest number (10) of mutated sites. ORF 62 encodes IE 62, the major immediate-early transactivator of virus genes, and is essential for lytic virus replication. To determine whether a disproportionate number of mutations in ORF 62 might account for virus attenuation, we compared the global pattern of V-Oka gene expression to that of P-Oka. Transcription of ORFs 62, 65, 66, and 67 was suppressed, whereas ORF 41 was elevated in V-Oka-infected cells compared to P-Oka-infected cells (P < 0.01; z test). Suppression of ORF 62, 65, and 66 transcription was confirmed by quantitative dot blot and Western blot analyses. Transient-transfection assays to determine whether mutations within V-Oka-derived IE 62 affected its ability to transactivate VZV gene promoters revealed similar IE 62 transactivation of VZV gene 20, 21, 28, 29, 65, and 66 promoters in both P-Oka and V-Oka. Together, our results indicate that mutations in V-Oka IE 62 alone are unlikely to account for vaccine virus attenuation.

Blotting, Western↗

beta-Hexosaminidase isozymes from cells cotransfected with alpha and beta cDNA constructs: analysis of the alpha-subunit missense mutation associated with the adult form of Tay-Sachs disease.

In vitro mutagenesis and transient expression in COS cells has been used to associate a missense mutation with a clinical or biochemical phenotype. Mutations affecting the alpha-subunit of beta-hexosaminidase A (alpha beta) (E.C.3.2.1.52) result in Tay-Sachs disease. Because hexosaminidase A is heterodimeric, analysis of alpha-chain mutations is not straightforward. We examine three approaches utilizing previously identified mutations affecting alpha-chain folding. These involve transfection of (1) the alpha cDNA alone; (2) a beta cDNA construct encoding a beta-subunit substituted at a position homologous to that of the alpha-subunit, and (3) both alpha and beta cDNAs. The latter two procedures amplified residual activity levels over that of patient samples, an effect not previously found with mutations affecting an "active" alpha Arg residue. This effect may help to discriminate between protein-folding and active-site mutations. We conclude that, with proper controls, the latter method of cotransfection can be used to evaluate the effects and perhaps to predict the clinical course of some alpha-chain mutations. Using this technique, we demonstrate that the adult-onset Tay-Sachs mutation, alpha Gly --> Ser269, does not directly affect alpha beta dimerization but exerts an indirect effect on the dimer through destabilizing the folded alpha-subunit at physiological temperatures. Two other alpha mutations linked to more severe phenotypes appear to inhibit the initial folding of the subunit.

Adult↗

The role of p53 in megakaryocyte differentiation and the megakaryocytic leukemias of Down syndrome.

Sequence analysis of the p53 tumor suppressor gene was performed on diagnostic blood and bone marrow samples from nine children with Down syndrome and acute megakaryoblastic leukemia. p53 sequence alterations were not observed in any of seven cases of transient leukemia; however, samples from two of three patients with acute megakaryoblastic leukemia harbored sequence alterations. The acquisition of both mutations (Gly245Val and Arg72Pro) in the transformation from transient leukemia to overt acute megakaryoblastic leukemia suggests a functional role of mutant p53 in the evolution of this disease.

Amino Acid Sequence↗

A synthetic early promoter from a baculovirus: roles of the TATA box and conserved start site CAGT sequence in basal levels of transcription.

Many baculovirus early genes and insect genes transcribed by RNA polymerase II have a conserved transcription start site sequence (CAGT) located downstream of a consensus TATA box. To examine the functions and interactions of these two motifs in initiating accurately positioned basal transcription, a 43-nt synthetic promoter was synthesized from the TATA box and start site sequences of the gp64 early promoter from the Orgyia pseudotsugata multicapsid nuclear polyhedrosis virus (OpMNPV). The synthetic promoter initiated accurately and was also transactivated by the baculovirus transcriptional activator, IE1. To determine the roles of sequences within the 43-nt synthetic promoter, a series of linker-scanning and spacing mutations were analyzed for transcriptional activity, start site selection, and transactivation. Linker-scanning mutations were examined in vivo by transient expression and reporter gene assays. To examine transcription start site selection, promoter constructs were used for in vitro transcription in nuclear extracts from uninfected Spodoptera frugiperda (Sf9) cells. In vivo and in vitro analyses show that the TATA box, and not the start site CAGT, is the primary element controlling start site selection. Substitution of the conserved start site CAGT sequence resulted in a reduction of both reporter gene activity and in vitro transcripts, although transcripts initiated accurately. Data from linker-scanning and spacing mutations indicate that the conserved start site CAGT sequences are not required for accurate initiation but sequences at the start site play an important role in initiation efficiency.

Baculoviridae↗

Yellow fever virus NS2B-NS3 protease: charged-to-alanine mutagenesis and deletion analysis define regions important for protease complex formation and function.

Charged-to-alanine substitutions and deletions within the yellow fever virus NS2B-NS3(181) protease were analyzed for effects on protease function. During cell-free translation of NS2B-3(181) polyproteins, mutations at three charge clusters markedly impaired cis cleavage activity: a single N-terminal cluster in the conserved domain of NS2B (residues ELKK(52-55)) and two in NS3 (ED(21-22), and residue H(47)). These mutations inhibited other protease-dependent cleavages of a transiently expressed nonstructural polyprotein, although differential effects occurred. NS2B and NS3(181) proteins harboring these mutations were impaired in their ability to associate for trans cleavage activity. N-terminal deletions in NS3 also implicated residues ED(21-22) in the association with NS2B. Deletions within NS2B revealed that the conserved domain alone provided minimal cofactor activity, with optimal function requiring both flanking hydrophobic regions. NS2B-3(181)- and NS3(181)-green fluorescent protein fusion proteins were used to determine the intracellular distribution of the protease complex. The former localized in membrane-based vesicular structures, whereas the latter localized poorly. The data suggest that NS2B-NS3 complex formation requires charge interactions involving the N-terminus of the conserved domain of NS2B and 22 N-terminal residues of NS3. A role for the putative transmembrane regions of NS2B in targeting of NS3 to intracellular membranes is also suggested.

Amino Acid Sequence↗

Mutations of the TSH receptor as cause of congenital hyperthyroidism.

4 patients of two families with congenital persistent hyperthyroidism without detectable autoantibodies are reported. The members of the first family affected by hyperthyroidism, i.e. the mother and her two children, showed a germline mutation, a transition of GCC to GTC in the genomic DNA of the TSH receptor, leading to an exchange of alanine by valine at the position 623. The mother was thyroidectomized at two times because of recurrent nodular goiter. The third child of a healthy second family showed a transition of AGC to AAC leading to an exchange of serine by asparagine at the position 505 of the TSH receptor. The mutation of family 1, as a somatic point mutation leading to autonomous thyroid adenoma, has originally been demonstrated to constitutively activate TSH independent cAMP accumulation. The functional tests of the TSH receptor gen mutation, detected in family 2, are ongoing, but an exchange of serine by arginine at the same position has been shown to lead to constitutively active cAMP accumulation. The cases of congenital hyperthyroidism in the first family lead to a reduction of the birth weight and head circumference and to a neonatal but not fetal tachycardia. Bone age of both children was accelerated by one year. In contrast to that, congenital hyperthyroidism of the second family lead to more marked signs of intrauterine hyperthyroidism. The mother observed marked symptoms of fetal and neonatal hyperthyroidism. The bone age at a chronological age of 6 months was 4-6 years and the neonate showed a mild exophthalmus. We conclude, that congenital hyperthyroidism due to constitutively activating TSH receptor mutations has to be considered, if hyperthyroidism is not transient but persistent, and the parameters of autoimmunity are absent. Constitutively active TSH receptor germline mutations lead to different degrees of congenital hyperthyroidism. In contrast to patients with Graves' disease, more aggressive means of treatment like total thyroidectomy and/or radiation seem to be recommendable in cases with severe hyperthyroidism to control the disease.

Base Sequence↗

Alexander-disease mutation of GFAP causes filament disorganization and decreased solubility of GFAP.

Alexander disease is a fatal neurological illness characterized by white-matter degeneration and the formation of astrocytic cytoplasmic inclusions called Rosenthal fibers, which contain the intermediate filament glial fibrillary acidic protein (GFAP), the small heat-shock proteins HSP27 and alphaB-crystallin, and ubiquitin. Many Alexander-disease patients are heterozygous for one of a set of point mutations in the GFAP gene, all of which result in amino acid substitutions. The biological effects of the most common alteration, R239C, were tested by expressing the mutated protein in cultured cells by transient transfection. In primary rat astrocytes and Cos-7 cells, the mutant GFAP was incorporated into filament networks along with the endogenous GFAP and vimentin, respectively. In SW13Vim(-) cells, which have no endogenous cytoplasmic intermediate filaments, wild-type human GFAP frequently formed filamentous bundles, whereas the R239C GFAP formed 'diffuse' and irregular patterns. Filamentous bundles of R239C GFAP were sometimes formed in SW13Vim(-) cells when wild-type GFAP was co-transfected. Although the presence of a suitable coassembly partner (vimentin or GFAP) reduced the potential negative effects of the R239C mutation on GFAP network formation, the mutation affected the stability of GFAP in cells in a dominant fashion. Extraction of transfected SW13Vim(-) cells with Triton-X-100-containing buffers showed that the mutant GFAP was more resistant to solubilization at elevated KCl concentrations. Both wild-type and R239C GFAP assembled into 10 nm filaments with similar morphology in vitro. Thus, although the R239C mutation does not appear to affect filament formation per se, the mutation alters the normal solubility and organization of GFAP networks.

Actin Cytoskeleton↗

Embryonic expression of the divergent Drosophila beta3-tubulin isoform is required for larval behavior.

We have sought to define the developmental and cellular roles played by differential expression of distinct beta-tubulins. Drosophila beta3-tubulin (beta3) is a structurally divergent isoform transiently expressed during midembryogenesis. Severe beta3 mutations cause larval lethality resulting from failed gut function and consequent starvation. However, mutant larvae also display behavioral abnormalities consistent with defective sensory perception. We identified embryonic beta3 expression in several previously undefined sites, including different types of sensory organs. We conclude that abnormalities in foraging behavior and photoresponsiveness exhibited by prelethal mutant larvae reflect defective beta3 function in the embryo during development of chordotonal and other mechanosensory organs and of Bolwig's organ and nerve. We show that microtubule organization in the cap cells of chordotonal organs is altered in mutant larvae. Thus transient zygotic beta3 expression has permanent consequences for the architecture of the cap cell microtubule cytoskeleton in the larval sensilla, even when beta3 is no longer present. Our data provide a link between the microtubule cytoskeleton in embryogenesis and the behavioral phenotype manifested as defective proprioreception at the larval stage.

Animals↗

Identification and inactivation of three group 2 sigma factor genes in Anabaena sp. strain PCC 7120.

Three new Anabaena sp. strain PCC 7120 genes encoding group 2 alternative sigma factors have been cloned and characterized. Insertional inactivation of sigD, sigE, and sigF genes did not affect growth on nitrate under standard laboratory conditions but did transiently impair the abilities of sigD and sigE mutant strains to establish diazotrophic growth. A sigD sigE double mutant, though proficient in growth on nitrate and still able to differentiate into distinct proheterocysts, was unable to grow diazotrophically due to extensive fragmentation of filaments upon nitrogen deprivation. This double mutant could be complemented by wild-type copies of sigD or sigE, indicating some degree of functional redundancy that can partially mask phenotypes of single gene mutants. However, the sigE gene was required for lysogenic development of the temperate cyanophage A-4L. Several other combinations of double mutations, especially sigE sigF, caused a transient defect in establishing diazotrophic growth, manifested as a strong and prolonged bleaching response to nitrogen deprivation. We found no evidence for developmental regulation of the sigma factor genes. luxAB reporter fusions with sigD, sigE, and sigF all showed slightly reduced expression after induction of heterocyst development by nitrogen stepdown. Phylogenetic analysis of cyanobacterial group 2 sigma factor sequences revealed that they fall into several subgroups. Three morphologically and physiologically distant strains, Anabaena sp. strain PCC 7120, Synechococcus sp. strain PCC 7002, and Synechocystis sp. strain PCC 6803 each contain representatives of four subgroups. Unlike unicellular strains, Anabaena sp. strain PCC 7120 has three additional group 2 sigma factors that cluster in subgroup 2.5b, which is perhaps specific for filamentous or heterocystous cyanobacteria.

Anabaena↗

Chromosomal variation and the origin of drug-resistant mutants in mammalian cell lines.

Drug-resistant mutants of somatic cell lines fall into two classes: one seems to correspond to classical gene mutation, the other is characterized, albeit transiently, by karyotypic instability, high reversion frequency, and low plating efficiency. An interpretation of the origin of these drug-resistant mutants is offered on the basis of chromosomal variation, which generates variation of the number of copies of each individual chromosome and, consequently, of gene dosage.

Alleles↗

Mutant elastase in pathogenesis of cyclic and severe congenital neutropenia.

Severe neutropenia is characterized by maturation arrest of myeloid cells at the promyelocyte stage of hematopoiesis. We reported that accelerated apoptosis of bone marrow myeloid progenitor cells was observed in both cyclic (CN) and severe congenital neutropenia (SCN). Short and long-term cultures of bone marrow CD34+ cells revealed reduced production of multipotent progenitors in SCN. In contrast, production of these cells was slightly elevated in CN compared with CD34+ cells from healthy volunteers. Production of myeloid-committed progenitor cells was significantly reduced in both CN and SCN. FACS analysis of CD34+ cells revealed G /G cell cycle arrest in SCN but not in CN.(0) (1) All CN patients and more than 90% of SCN patients have mutation in the neutrophil elastase (NE) gene. Molecular modeling of NE tertiary structure indicates that mutations observed in SCN are primarily located around the glycosylation sites, whereas CN mutations affect predominantly the active site. Transient expression of CN- or SCN-specific mutant NE cDNA results in impaired survival of human myeloid progenitor cells compared with control cells transfected with intact NE cDNA. We hypothesize that abnormal processing and subcellular localization of mutant NE might predetermine the etiology of cyclic or severe congenital neutropenia.

Hematopoiesis↗

Biochemical basis of glucokinase activation and the regulation by glucokinase regulatory protein in naturally occurring mutations.

Glucokinase (GK) has several known polymorphic activating mutations that increase the enzyme activity by enhancing glucose binding affinity and/or by alleviating the inhibition of glucokinase regulatory protein (GKRP), a key regulator of GK activity in the liver. Kinetic studies were undertaken to better understand the effect of these mutations on the enzyme mechanism of GK activation and GKRP regulation and to relate the enzyme properties to the associated clinical phenotype of hypoglycemia. Similar to wild type GK, the transient kinetics of glucose binding for activating mutations follows a general two-step mechanism, the formation of an enzyme-glucose complex followed by an enzyme conformational change. However, the kinetics for each step differed from wild type GK and could be grouped into specific types of kinetic changes. Mutations T65I, Y214C, and A456V accelerate glucose binding to the apoenzyme form, whereas W99R, Y214C, and V455M facilitate enzyme isomerization to the active form. Mutations that significantly enhance the glucose binding to the apoenzyme also disrupt the protein-protein interaction with GKRP to a large extent, suggesting these mutations may adopt a more compact conformation in the apoenzyme favorable for glucose binding. Y214C is the most active mutation (11-fold increase in k(cat)/K(0.5)(h)) and exhibits the most severe clinical effects of hypoglycemia. In contrast, moderate activating mutation A456V nearly abolishes the GKRP inhibition (76-fold increase in K(i)) but causes only mild hypoglycemia. This suggests that the alteration in GK enzyme activity may have a more profound biological impact than the alleviation of GKRP inhibition.

Allosteric Site↗

Biochemical and structural analysis of missense mutations in N-acetylgalactosamine-6-sulfate sulfatase causing mucopolysaccharidosis IVA phenotypes.

Mucopolysaccharidosis IVA (MPS IVA; OMIM#253000), a lysosomal storage disorder caused by a deficiency of N -acetylgalactosamine-6-sulfate sulfatase (GALNS), has variable clinical phenotypes. To date we have identified 65 missense mutations in the GALNS gene from MPS IVA patients, but the correlation between genotype and phenotype has remained unclear. We studied 17 missense mutations using biochemical approaches and 32 missense mutations, using structural analyses. Fifteen missense mutations and two newly engineered active site mutations (C79S, C79T) were characterized by transient expression analysis. Mutant proteins, except for C79S and C79T, were destabilized and detected as insoluble precursor forms while the C79S and C79T mutants were of a soluble mature size. Mutants found in the severe phenotype had no activity. Mutants found in the mild phenotype had a considerable residual activity (1.3-13.3% of wild-type GALNS activity). Sulfatases, including GALNS, are members of a highly conserved gene family sharing an extensive sequence homology. Thus, a tertiary structural model of human GALNS was constructed from the X-ray crystal structure of N -acetylgalacto-samine-4-sulfatase and arylsulfatase A, using homology modeling, and 32 missense mutations were investigated. Consequently, we propose that there are at least three different reasons for the severe phenotype: (i) destruction of the hydrophobic core or modification of the packing; (ii) removal of a salt bridge to destabilize the entire conformation; (iii) modification of the active site. In contrast, mild mutations were mostly located on the surface of the GALNS protein. These studies shed further light on the genotype-phenotype correlation of MPS IVA and structure-function relationship in the sulfatase family.

Amino Acid Sequence↗

Point mutations in the first and third intracellular loops of the glucagon-like peptide-1 receptor alter intracellular signaling.

The glucagon-like peptide-1 receptor (GLP-1R) is a member of the glucagon family of seven transmembrane spanning receptors. To investigate how different portions of the GLP-1R may be important in cAMP and intracellular calcium signaling, single amino acid substitutions in the receptor were made by site directed mutagenesis. Receptor binding, cAMP, and intracellular calcium measurements were made in transfected COS-7 cells. The change of amino acid H180R (His to Arg) in the first intracellular loop caused a decrease in the affinity of binding of GLP-1 from 7 nM in the wild type receptor to 150nM and resulted in a 50% decrease in GLP-1 stimulated cAMP production. In response to 10 nM GLP-1, the receptor's ability to stimulate intracellular calcium was altered from a prolonged to a transient response of the same magnitude. Mutation in the 3rd intracellular loop at position R348G (Arg to Gly) decreased receptor affinity from 7 to 83 nM and nearly abolished cAMP production at all concentrations of GLP-1 tested. The GLP-1 stimulated rise in free intracellular calcium was also diminished and this was reversed when cells were treated with forskolin. These results also indicate that GLP-1R signaling via intracellular calcium is dependent on the receptor's ability to also generate cAMP.

Adenylyl Cyclases↗

Effects of wild-type and mutated p53 and Id proteins on the induction of apoptosis by adenovirus E1A, c-Myc, Bax, and Nip3 in p53 null mouse cerebellum cells.

The sensitivities of apoptosis induced by E1A, c-Myc, Bax, and Nip3 to wild-type (wt) and mutated p53 and Id proteins were analyzed by transient transfection followed by flow cytometry with p53 null mouse cerebellum cell lines W7 and M13 that express wt and mutated p53 in response to dexamethasone, respectively. Apoptosis induced by c-Myc was stimulated weakly by wt p53, strongly by Ids, but suppressed completely by mutated p53 irrespective of coexpression with Ids, while apoptosis induced by E1A was suppressed by mutated p53 but stimulated when coexpressed with Ids. Apoptosis induced by Bax was little affected by wt and mutated p53, but inhibited by Ids, while apoptosis induced by Nip3 was inhibited by both wt and mutated p53 and inhibition was stimulated by Ids. Caspase-1 was activated only by Bax significantly when coexpressed with mutated p53 but not with wt p53. These results indicate that the apoptotic processes elicited by these inducers are different and differently affected by wt and mutated p53 and by Ids.

Adenovirus E1A Proteins↗