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Biomedical subjects

X Yuan

Publications and source records attributed to X Yuan.

At least 73 records · Page 4Linked to original sources
PubMed2000

[Neurofibromatosis type 2].

OBJECTIVE: To investigate the clinical characteristics and management strategies of bilateral acoustic neuromas. METHODS: The data of 7 patients with bilateral acoustic neuromas collected between 1990 to 1998 were retrospectively analyzed. RESULTS: Altogether 122 patients with acoustic tumors were treated from 1990 to 1998, in which 7 cases (5.8%, 6 male and 1 female) had bilateral acoustic neuromas. The age at onset of symptoms ranged from 13 to 60 years (average 29.1 years). Progressive hearing loss and tinnitus were the initial symptoms in 4 cases. Either strabismus, ptosis, headache or dysequilibrium was presented in 4 cases. Six cases complicated tumors in the central nervous system and/or other sites. Five cases had cafe au lait spots. One case had posterior subcapsular lenticular opacity. Four cases fell into severe (Wishart) type and 2 into mild (Gardner) type. The tumors were unilaterally removed in 4 patients through the retrolabyrinthine approach (1 case) or the retrosigmoid approach (3 cases). In these 4 patients, one died of central respiratory failure after the operation; two had contralateral tumor removal through retrosigmoid approach 3 weeks after the first surgery. One of the patients died of encephaledema after the surgery. No hearing impairment and facial nerve paralysis occurred in one case operated on through the retrolabyrinthine approach, whereas in those through retrosigmoid approach, 4 ears had hearing loss and 3 sides had facial nerve paralysis. CONCLUSION: The clinical characteristics and treatment strategies for bilateral acoustic neuromas are different from those of unilateral acoustic neuroma. Individualization of management is a prerequisite for the success of the treatment. To avoid injury to the VII and VIII cranial nerves, monitoring the nerve functions during the surgery is important.

Adolescent↗
PubMed1999

Structure-activity relationships of biphenyl tetrazoles as metallo-beta-lactamase inhibitors.

Resistance to carbapenem antibiotics in gram-negative bacteria is due, in part, to expression of a wide spectrum metallo-beta-lactamase, which renders the drug inactive. Biphenyl tetrazoles containing 3-n-butyl-1-phenylpyrazole-5-carboxylates or the corresponding 5-ethyl esters were found to inhibit metallo-beta-lactamases as well as renal dehydropeptidase I to a lesser extent.

Bacteroides fragilis↗
PubMed1999

Voltage-activated K+ channels and membrane depolarization regulate accumulation of the cyclin-dependent kinase inhibitors p27(Kip1) and p21(CIP1) in glial progenitor cells.

Neural cell development is regulated by membrane ion channel activity. We have previously demonstrated that cell membrane depolarization with veratridine or blockage of K+ channels with tetraethylammonium (TEA) inhibit oligodendrocyte progenitor (OP) proliferation and differentiation (); however the molecular events involved are largely unknown. Here we show that forskolin (FSK) and its derivative dideoxyforskolin (DFSK) block K+ channels in OPs and inhibit cell proliferation. The antiproliferative effects of TEA, FSK, DFSK, and veratridine were attributable to OP cell cycle arrest in G1 phase. In fact, (1) cyclin D accumulation in synchronized OP cells was not affected by K+ channel blockers or veratridine; (2) these agents prevented OP cell proliferation only if present during G1 phase; and (3) G1 blockers, such as rapamycin and deferoxamine, mimicked the anti-proliferative effects of K+ channel blockers. DFSK also prevented OP differentiation, whereas FSK had no effect. Blockage of K+ channels and membrane depolarization also caused accumulation of the cyclin-dependent kinase inhibitors p27(Kip1) and p21(CIP1) in OP cells. The antiproliferative effects of K+ channel blockers and veratridine were still present in OP cells isolated from INK4a-/- mice, lacking the cyclin-dependent kinase inhibitors p16(INK4a) and p19(ARF). Our results demonstrate that blockage of K+ channels and cell depolarization induce G1 arrest in the OP cell cycle through a mechanism that may involve p27(Kip1) and p21(CIP1) and further support the conclusion that OP cell cycle arrest and differentiation are two uncoupled events.

8-Bromo Cyclic Adenosine Monophosphate↗
PubMed1999

Seismic Evidence for a Detached Indian Lithospheric Mantle Beneath Tibet.

P-to-S converted teleseismic waves recorded by temporary broadband networks across Tibet show a north-dipping interface that begins 50 kilometers north of the Zangbo suture at the depth of the Moho (80 kilometers) and extends to a depth of 200 kilometers beneath the Bangong suture. Under northern Tibet a segmented south-dipping structure was imaged. These observations suggest a different form of detachment of the Indian and Asian lithospheric mantles caused by differences in their composition and buoyancy.

Journal Article↗
PubMed1999

Defective calcium binding to fibrillin-1: consequence of an N2144S change for fibrillin-1 structure and function.

Fibrillin-1 is a major structural component of 10-12 nm connective tissue microfibrils and has a modular organisation that includes 43 calcium binding epidermal growth factor-like (cbEGF) domains and seven transforming growth factor beta-binding protein-like (TB) domains. Mutations in the fibrillin-1 (FBN1) gene cause the Marfan syndrome (MFS) and related connective tissue disorders. We have previously investigated an N2144S change, identified in a MFS patient, which removes one of the key calcium binding ligands within cbEGF domain 32. In this study the structural consequences of the N2144S amino acid change for the folding and calcium binding properties of mutant and wild-type TB6-cbEGF32 and cbEGF32-33 domain pairs have been analysed by nuclear magnetic resonance. The presence of an N2144S substitution does not alter the native fold of either the TB6 domain, or cbEGF domains 32 and 33. Comparison of calcium dissociation constants measured for the wild-type and mutant pairs shows that: (i) the affinity of cbEGF32 is weakly enhanced by N-terminal linkage of TB6 relative to cbEGF32 in isolation; (ii) the affinity of cbEGF32 is approximately ninefold decreased by the N2144S substitution in the TB-cbEGF pair; and (iii) reduced affinity of cbEGF32 does not result in lower affinity of cbEGF33 for calcium. Together, these data suggest that the TB6-cbEGF32 linkage is flexible and the structural effect of the mutation is localised to the interdomain linkage. We have also investigated the effect of defective calcium binding to cbEGF32 on fibrillin-1 produced by N2144S MFS fibroblasts. 35S-pulse-chase analysis shows that the N2144S substitution does not detectably affect fibrillin-1 biosynthesis, rate of secretion or processing. Deposition of reducible fibrillin-1 into the extracellular matrix was also unaffected. The implications of these results for the assembly and properties of the microfibril are discussed.

Actin Cytoskeleton↗
PubMed1999

Implantable polymers for tirapazamine treatments of experimental intracranial malignant glioma.

Malignant gliomas remain refractory to intensive radiotherapy and cellular hypoxia enhances clinical radioresistance. Under hypoxic conditions, the benzotriazine di-N-oxide (3-amino-1,2,4-benzotriazine 1,4-dioxide) (tirapazamine) is reduced to yield a free-radical intermediate that results in DNA damage and cellular death. For extracranial xenografts, tirapazamine treatments have shown promise. We therefore incorporated tirapazamine into the synthetic, biodegradable polymer, measured the release, and tested the efficacy both alone and in combination with external beam radiotherapy in the treatment of experimental intracranial human malignant glioma xenografts. The [(poly(bis(p-carboxyphenoxy)-propane) (PCPP):sebacic acid (SA) (PCPP:SA ratio 20:80)] polymer was synthesized. The PCPP:SA polymer and solid tirapazamine were combined to yield proportions of 20% or 30% (wt/wt). Polymer discs (3 x 2 mm) (10 mg) were incubated (PBS, 37 degrees C), and the proportion of the drug released vs. time was recorded. Male nu/nu nude mice were anesthetized and received intracranial injections of 2 x 10(5) U251 human malignant glioma cells. For single intraperitoneal (i.p.) drug and/or external radiation treatments, groups of mice had i.p. 0.3 mmol/kg tirapazamine, 5 Gy cranial irradiation, or combined treatments on day 8 after inoculation. For fractionated drug and radiation treatments, mice had i.p. 0.15 mmol/kg tirapazamine, 5 Gy radiation, or combined treatments on days 8 and 9 after inoculation. For intracranial (i.c.) polymer treatments, mice had craniectomies and intracranial placement of polymer discs at the site of cellular inoculation. The maximally tolerated percentage loading of tirapazamine in the polymer.disc was determined. On day 7 after inoculation, groups of mice had i.c. empty or 3% tirapazamine alone or combined with radiation (5 Gy x 2 doses) or combined with i.p. drug (0.15 mmol/kg x 2 doses on days 8 and 9). Survival was recorded. Polymers showed controlled, protracted in vitro release for over 100 days. The 5 Gy x 1 treatment resulted in improved survival; 28.5 +/- 3.7 days (P = 0.01 vs. controls), while the single i.p. 0.3 mmol/kg tirapazamine treatment, 17.5 +/- 1.9 days (P = NS) and combined treatments; 21.5 +/- 5.0 days (P = NS) were not different. The fractionated treatments: 5 Gy x 2, i.p. 0.15 mmol/kg tirapazamine x 2 and the combined treatments resulted in improved survival: 44.5 +/- 3.9 (P < 0.001), 24.5 +/- 2.3 (P = 0.05) and 50.0 +/- 6.0 (P < 0.001), respectively. Survival after intracranial empty polymer was 16.5 +/- 3.0 days and increased to 31.0 +/- 3.0 (P = 0.003) days when combined with the 5 Gy x 2 treatment. The survival after the polymer bearing 3% tirapazamine alone vs. combined with radiation was not different. The combined 3% tirapazamine polymer, i.p. tirapazamine, and radiation treatments resulted in both early deaths and the highest long-term survivorship. The basis for potential toxicity is discussed. We conclude that implantable biodegradable polymers provide controlled intracranial release for treatment of experimental glioma. For treatment of malignant gliomas, the combination of continuous polymer-mediated delivery and fractionated systemic delivery of tirapazamine with external beam radiotherapy warrants further exploration.

Absorbable Implants↗
PubMed1999

Association of polymorphisms in the beta2-adrenergic receptor gene with obesity, hypertriglyceridaemia, and diabetes mellitus.

To assess the role of polymorphisms in the beta2-adrenergic receptor gene in the development of obesity and obesity-related metabolic disorders, we analysed Arg16Gly, Gln27Glu, and Thr164Ile polymorphisms in 400 non-obese subjects (body mass index < 27 kg/m2) and 108 obese subjects (body mass index> or =27 kg/m2). The Gln27Glu substitution was twice as common in obese subjects as in non-obese subjects (0.14 vs 0.07, p = 0.001, odds ratio 2.14, 95 % confidence interval 1.35-3.41). The frequency of the Glu27 allele was also higher in patients with Type II (non-insulin-dependent) diabetes mellitus than nondiabetic subjects (0.14 vs 0.07, p = 0.001, odds ratio 2.13, 95% confidence interval 1.34-3.41). Analysis of variance of multiple variables showed an association between 2-h post-load glucose concentrations and body mass index but not with the Glu27 variant, suggesting that the association with diabetes could be secondary to obesity. Obese subjects carrying the variant allele had higher concentrations of serum triglyceride than obese subjects homozygous for the wild type allele (2.68+/-1.90 vs 1.18+/-1.15 mmol/l, p = 0.02). Conversely, the frequency of Gly16 homozygotes was lower in obese women when compared with non-obese women (11% vs 28%, p = 0.01, odds ratio 0.30, 95% confidence interval 0.12-0.75), although the association was not present in male subjects. Thr164Ile substitution was not detected in the subjects of this study. These observations suggest that the amino-terminal polymorphisms of the beta2-adrenergic receptor gene could be involved in the molecular pathogenesis of obesity and hypertriglyceridaemia, and thereby the development of Type II diabetes mellitus.

Amino Acid Substitution↗
PubMed1999

Analysis of trinucleotide-repeat combination polymorphism at the rad gene in patients with type 2 diabetes mellitus.

A combined (GTT)n (ATT)n trinucleotide-repeat polymorphism designated as RAD1 has been identified at intron 2 of the rad gene on chromosome 16q. An association between the total length of the RAD1 locus and type 2 diabetes has been shown in white American subjects, but not in Finns. We genotyped 115 Japanese patients with type 2 diabetes and 114 nondiabetic control subjects at the RAD1 locus by the direct sequencing method, and found 16 RAD1 alleles composed of various combinations of GTTs and ATTs. Allele 14 consisting of four GTTs and seven ATTs accounted for the majority in both control subjects and diabetic patients, suggesting that RAD1 polymorphism is not a major genetic component for susceptibility to common forms of diabetes in the Japanese. There was no significant association between total repeat length and diabetes. However, the frequency of minor alleles containing five GTTs or three GTTs was significantly higher in diabetic patients versus nondiabetic subjects (4.8% v 0.9%, P = .012). Thus, genetic variability at the rad gene in linkage disequilibrium with RAD1 could be associated with a predisposition to type 2 diabetes in the Japanese population.

Adult↗
PubMed1999

Adenovirus-mediated wild-type p53 expression induces apoptosis and suppresses tumorigenesis of experimental intracranial human malignant glioma.

Adenoviral-mediated gene transfer for the treatment of experimental intrinsic malignant brain neoplasms holds promise. The role, however, of intracellular, adenoviral-mediated p53 expression to inhibit growth of experimental human intracranial malignant gliomas remains largely unexplored. Using the AdCMV.p53 vector we measured the in vitro expression of p53 and the resultant effect upon U251 human malignant glioma cellular proliferation. We further measured the survival of nude mice after intracranial injection of the infected vs. control U251 cells. The growth of the infected U251 cells was inhibited when compared to both the uninfected cells and cells infected with the control vector (AdCMV.Null). Agarose gel electrophoresis confirmed the AdCMV.p53-dependent cellular apoptosis. Nude mice having intracranial injections of the U251 cells infected with the control (AdCMV.Null) vector showed diminished survival. In contrast, mice having intracranial injections of the cells infected with the AdCMV.p53 vector showed 100% survivorship measured 100 days after treatment. Gene therapy via the AdCMV.p53 viral vector holds promise for the clinical treatment of human malignant gliomas.

Adenoviridae↗
PubMed1999

Presence of telomeric G-strand tails in the telomerase catalytic subunit TERT knockout mice.

BACKGROUND: Telomerase consists of two essential subunits, the template RNA (TR; telomerase RNA) and the catalytic subunit TERT (telomerase reverse transcriptase). Knockout mice with a mTR (mouse TR) deletion have been described and well characterized. However, mice with a mTERT (mouse TERT) deletion have not been reported. RESULTS: mTERT-knockout mice have been constructed. The first generation mTERT -/- mice were fertile, and did not show any noticeable macroscopic or microscopic phenotypic change. All tissue cells derived from mTERT -/- mice that were examined lacked telomerase activity, indicating that mTERT is the only gene encoding the telomerase catalytic subunit. Pulse field gel electrophoresis (PFGE) and nondenaturing in-gel hybridization analyses showed that mouse telomeric DNA has G-strand 5'-overhangs, as demonstrated for human and yeast cells. This telomeric single-stranded G-tail was also observed in MEF (mouse embryonic fibroblast) and liver cells derived from mTERT -/- mice. CONCLUSIONS: mTERT-knockout mice show phenotypes that are apparently normal at least during the early generations. This observation is similar to that obtained with the mTR-knockout mice. The presence of the telomeric G-strand tails in mTERT -/- mice suggests that these telomeric 5'-overhangs are produced by telomerase-independent mechanisms, as has been proposed for yeast and human.

Amino Acid Sequence↗
PubMed1999

Association of an (A-C)n dinucleotide repeat polymorphic marker at the 5'-region of the aldose reductase gene with retinopathy but not with nephropathy or neuropathy in Japanese patients with Type 2 diabetes mellitus.

AIMS: Recently an (A-C)n dinucleotide repeat polymorphic marker in the 5'-region of the ALR2 gene encoding aldose reductase was found to be associated with diabetic retinopathy in the Chinese population in Hong Kong, and with nephropathy and neuropathy in the British Caucasian population. The present study assessed the association between the polymorphism and microvascular complications in Japanese patients with Type 2 diabetes mellitus. METHODS: DNA from 87 Japanese patients with Type 2 diabetes mellitus and 90 control subjects with normal glucose tolerance were typed for the polymorphic marker by polymerase chain reaction and direct sequencing. RESULTS: Six alleles, namely Z-12, Z-6, Z-4, Z-2, Z, and Z+2 were identified. There was no significant difference in allele distribution between diabetic patients and controls. The Z-2 allele frequency was significantly higher in subjects with diabetic retinopathy than those without retinopathy (0.35 vs. 0.20, P=0.039), suggesting that aldose reductase is involved in the development of diabetic retinopathy. In contrast, the microsatellite marker was not associated with diabetic nephropathy, peripheral or autonomic neuropathy. The discrepancy may be partly attributable to the low frequency of Z+2 allele in the Japanese subjects. CONCLUSIONS: The (A-C)n dinucleotide repeat polymorphism may be a useful genetic marker to screen for patients at high risk of retinopathy.

Adult↗
PubMed1999

Synthetic, implantable, biodegradable polymers for controlled release of radiosensitizers.

INTRODUCTION: Synthetic, implantable, biodegradable polymers offer the sustained local release of disparate therapeutic agents for the treatment of human malignant brain tumors. The role of polymeric devices for the local delivery of radiosensitizers remains unexplored, however. We therefore quantified the release of the representative radiosensitizers IUdR (5-iodo-2'-deoxyuridine), tirapazamine (3-amino-1,2,4-benzotriazine-1,4-dioxide) and etanidazole [N-(2-hydroxyethyl)-2-nitro-1-imidazole-1-acetamide] from the [(poly(bis(p-carboxyphenoxy)-propane) (PCPP):sebacic acid (SA) (PCPP:SA ratio 20:80)] polymer. METHODS: For measurements of controlled release, triplicate polymer discs were incubated for known intervals in 2 ml 0.1 phosphate-buffered saline, pH 7.4, 37 degrees C. Using a predefined schedule, the supernatant fractions were systematically removed and replaced with fresh solution. The supernatant fractions were measured. The cumulative percentage of the loaded drug that appeared in these serial supernatant fractions was plotted vs. time. The percentage of the drug that was loaded into each polymer and that was released vs. time was fit to the power function of the form y = (a) x tb, where y is the cumulative released agent, a and b are constants and t is time (days). RESULTS: The IUdR was released over an interval of approximately one week, while the release of the tirapazimine persisted for over 100 days. The etanidazole was released most rapidly, over a period of hours. Modeling of release showed that regardless of percentage loading of the drug, the monoexponential function showed high correlation of the fit of the plot of the release vs. time. CONCLUSIONS: These results suggest that the hydrophilicity and percentage loading of the drug predominantly determine the rate of release. Based upon these results, IUdR and tirapazamine warrant preclinical testing for radiosensitization of human malignant brain tumors via the synthetic, implantable, biodegradable polymeric devices.

Biocompatible Materials↗
PubMed1999

Synthetic, implantable polymers for IUdR radiosensitization of experimental human malignant glioma.

BACKGROUND: Recently, polymeric controlled delivery of chemotherapy has been shown to improve survival of patients with malignant glioma. We tested the delivery of IUdR via polymers for radiosensitization of experimental intracranial human malignant glioma. To assess efficacy, we measured the in vitro release, the in vivo delivery of IUdR and the resultant radiosensitization of experimental human U251 glioblastoma xenografts. METHODS: In vitro: To measure release, increasing (10%, 30%, 50%) proportions of IUdR in synthetic [(poly(bis(p-carboxyphenoxy)-propane) (PCPP):sebacic acid (SA) polymer discs were serially incubated in buffered saline and the supernatant fractions were assayed. In vivo: To compare local vs. systemic delivery, mice bearing flank xenografts had intratumoral or contralateral flank IUdR polymer (50% loading) treatments. Mice bearing intracranial (i.c.) xenografts had i.c. vs. flank IUdR polymer treatments. Four or 8 days after implantation of polymers, mice were sacrificed and the percentage tumor cells that were labeled with IUdR was measured using quantitative microscopic immunohistochemistry. For comparisons of radiosensitization, mice bearing i.c. xenografts had i.c. vs. flank IUdR polymers and cranial fractionated external beam irradiation (2 Gy BID x 4 days). RESULTS: In vitro: Increasing percentage loadings of IUdR resulted in higher percentages of release: 43.7 +/- 0.1, 70.0 +/- 0.2, and 90.2 +/- 0.2 (p < 0.001 ANOVA) for the 10, 30, and 50% loadings, respectively. In vivo: For the flank tumors, both the ipsilateral and contralateral IUdR polymers resulted in similarly high percentages labeling of the tumors vs. time. For the ipsilateral IUdR polymers, the percentages of tumor cellular labeling after 4 vs. 8 days were 45.8 +/- 7.0 vs. 40.6 +/- 3.9 (p = NS. For the contralateral polymer implants, the percentages tumor cellular labeling were 43.9 +/- 10.1 vs. 35.9 +/- 5.2 (p = NS) measured 4 vs. 8 days after implantation. For the i.c. tumors treated with extracranial IUdR polymers, the percentages of tumor cellular labeling were low: 13.9 +/- 8.8 and 11.2 +/- 5.7 measured 4 and 8 days after implantation. For the i.c. tumors having the i.c. IUdR polymers, however, the percentages labeling were comparatively much higher: 34.3 +/- 4.9 and 35.3 +/- 4.0 on days 4 and 8, respectively. For the i.c. tumors, examination of the percentage cellular labeling vs. distance from the implanted IUdR polymer showed labeling was highest closest to the polymer disc. Radiosensitization: For mice bearing i.c. tumors and receiving flank vs. intracranial IUdR polymer treatments, the survival after external beam irradiation was significantly higher for the intracranial treatments: 49 + 8.9 vs. 80 + 4.1 (p = 0.03) days, respectively. CONCLUSIONS: Implantable biodegradable polymers provide the local, controlled release of IUdR and result in the high, local delivery of IUdR to experimental intracranial human malignant glioma. The local delivery and labeling result in improved survival following radiotherapy. This technique holds promise for the local delivery of IUdR for radiosensitization of human brain tumors.

Animals↗
PubMed1999

Cloning, sequencing, and localization of bovine estrogen receptor-beta within the ovarian follicle.

The potential role of estrogen receptor-beta (ERbeta) in normal ovarian folliculogenesis and in reproductive disorders such as ovarian follicular cysts has not been well defined. Therefore, we were interested in cloning, sequencing, and localizing ERbeta mRNA and protein within the bovine ovary. Bovine ERbeta (bERbeta) was amplified by reverse transcription-polymerase chain reaction (RT-PCR), then cloned and sequenced. Results showed that the open reading frame of bERbeta cDNA spanned 1584 nucleotides encoding a protein of 527 amino acids. The N-terminal region of bERbeta was found to be 80% homologous to human and mouse ERbeta and 79% homologous to rat ERbeta. Bovine ERbeta DNA-binding domain was 100% homologous to human, mouse, and rat ERbeta sequences. The C-terminal/ligand-binding domain of bERbeta was 89% homologous to human, 86% homologous to mouse, and 88% homologous to rat ERbeta. Human and bovine ERbeta amino acid sequences are similar in that their coding region extended farther 5' than initially reported for the published rat ERbeta sequence. Using in situ hybridization and immunohistochemistry, ERbeta mRNA and protein, respectively, were demonstrated to be present in granulosa cells of antral follicles in various stages of follicular growth. These findings suggest a role for bERbeta in ovarian follicular growth and maturation.

Amino Acid Sequence↗
PubMed1999

Cell culture of sporadic hepatitis E virus in China.

The isolation and identification of the 87A strain of epidemic hepatitis E virus (HEV) by means of cell culturing have been described previously. This paper reports the successful isolation of a sporadic HEV strain (G93-2) in human lung carcinoma cell (A549) cultures. The etiology, molecular and biological properties, and serological relationship of this new strain to other, epidemic HEV strains are described. The propagation of both sporadic and epidemic HEV strains in a cell culture system will facilitate vaccine research.

Acids↗
PubMed1999

A glucan synthase FKS1 homolog in cryptococcus neoformans is single copy and encodes an essential function.

Cryptococcal meningitis is a fungal infection, caused by Cryptococcus neoformans, which is prevalent in immunocompromised patient populations. Treatment failures of this disease are emerging in the clinic, usually associated with long-term treatment with existing antifungal agents. The fungal cell wall is an attractive target for drug therapy because the syntheses of cell wall glucan and chitin are processes that are absent in mammalian cells. Echinocandins comprise a class of lipopeptide compounds known to inhibit 1,3-beta-glucan synthesis, and at least two compounds belonging to this class are currently in clinical trials as therapy for life-threatening fungal infections. Studies of Saccharomyces cerevisiae and Candida albicans mutants identify the membrane-spanning subunit of glucan synthase, encoded by the FKS genes, as the molecular target of echinocandins. In vitro, the echinocandins show potent antifungal activity against Candida and Aspergillus species but are much less potent against C. neoformans. In order to examine why C. neoformans cells are less susceptible to echinocandin treatment, we have cloned a homolog of S. cerevisiae FKS1 from C. neoformans. We have developed a generalized method to evaluate the essentiality of genes in Cryptococcus and applied it to the FKS1 gene. The method relies on homologous integrative transformation with a plasmid that can integrate in two orientations, only one of which will disrupt the target gene function. The results of this analysis suggest that the C. neoformans FKS1 gene is essential for viability. The C. neoformans FKS1 sequence is closely related to the FKS1 sequences from other fungal species and appears to be single copy in C. neoformans. Furthermore, amino acid residues known to be critical for echinocandin susceptibility in Saccharomyces are conserved in the C. neoformans FKS1 sequence.

Amino Acid Sequence↗
PubMed1999

Polymorphism in the 5'-leader cistron of the beta2-adrenergic receptor gene associated with obesity and type 2 diabetes.

We screened the 5'-untranslated region of the beta2-adrenergic receptor gene from 40 obese subjects by the PCR-direct sequencing technique. Two polymorphic sites were identified; a T-->C substitution at -47 and a T-->C substitution at -20. We further analyzed the association of the polymorphisms with obesity in 574 subjects by PCR and restriction digestion. The substitution at -47 was in tight linkage disequilibrium with that at -20. The polymorphisms were also in linkage disequilibrium with codon 16 and codon 27 polymorphisms. Subjects carrying the -47C/-20C allele had greater body mass index (25.5+/-4.5 vs. 24.4+/-4.1 kg/m2, p=0.007) and higher serum triglyceride levels (166+/-160 vs. 139+/-95 mg/dl, p=0.015) than -47T/-20T homozygotes. The variant allele frequency was significantly higher in obese subjects than in non-obese subjects (0.18 vs. 0.11, p=0.0026). Furthermore, an increased frequency of the variant allele was shown in diabetic patients compared with non-diabetic subjects (0.19 vs. 0.11, p=0.0005). The association may be attributable to the greater proportion of diabetic patients in the obese group. The exchange at -47 may alter the expression level of the beta2-adrenergic receptor gene, because the nucleotide substitution at -47 results in a Cys-->Arg exchange at the C terminal of the leader peptide. The -47C/-20C allele may be associated with genetic predisposition to obesity and obesity-related metabolic disorders.

Body Mass Index↗