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Biomedical subjects

S Khan

Publications and source records attributed to S Khan.

At least 127 records · Page 7Linked to original sources
PubMed2001

Structural plasticity of the proteasome and its function in antigen processing.

The proteasome is the main provider of peptide ligands for major histocompatibility complex class I molecules. During an immune response to pathogens, the proinflammatory cytokine interferon (IFN)-gamma and tumor necrosis factor (TNF)-alpha are released, which induce the proteasome subunits LMP2, LMP7, and MECL-1. These replace the constitutively expressed active site subunits of the proteasome (delta, MB1, and Z) leading to a marked change in the cleavage preference of the proteasome and the production of T-cell epitopes. Proteasome activity is further changed by the IFN-gamma-mediated induction of the proteasome regulator PA28alpha/beta and the downregulation of PA28gamma. Why such an extensive exchange of proteasome active site subunits and regulators occurs is still poorly understood. In this article we discuss recent insights in the structural consequences of proteasome reorganization and their effects on epitope generation and shaping of the cytotoxic immune response. Moreover, we review the latest data on how the ubiquitin pathway targets protein antigens for peptide processing and discuss the potential of proteasome inhibitors for the modulation of antigen presentation.

Amino Acid Sequence↗
PubMed2001

Relationship of p53 expression with clinicopathological variables and disease outcome: a prospective study on 315 consecutive breast carcinoma patients.

Breast cancer is an increasingly important cause of illness and death among women. In recent years several novel prognostic determinants of breast cancer have been identified which includes p53. Alterations of p53 are one of the most common abnormalities detected in primary breast cancer. In this study alteration of p53 in primary carcinoma breast was correlated with other pathological variables and disease outcome. In this prospective study the expression of p53 oncoprotein was analyzed immunohistochemically on 315 patient's tumour specimens of infiltrating ductal carcinoma of breast from 1992 to 1997. These patients also had axillary lymph nodes sampling. Both univariate and multivariate statistical analysis was performed to analyze results including disease outcome. Overexpression of p53 was observed in 55.23% tumours. Axillary lymph node metastasis had significant correlation with positivity of p53 (p<0.05). A significant number of p53 patients developed local recurrence and distant metastases to brain, liver, lung and bone (p< 0.05). At a median follow-up of 48 months (4 years) in p53 positive patients, the median overall survival (OS) was 3.0 years and disease free survival (DFS) was 2.5 years. p53 negative tumour patients showed a better survival. In this group the median OS was 3.8 years and the DFS was 3.3 years. The above findings have reinforced the view that p53 immunohistochemical detection is of help in detecting a subgroup of breast carcinoma patients who are at high risk. This may also be of particular relevance in decisions regarding adjuvant chemotherapy to these patients.

Antineoplastic Agents↗
PubMed2000

Mutations in yeast ARV1 alter intracellular sterol distribution and are complemented by human ARV1.

Intracellular cholesterol redistribution between membranes and its subsequent esterification are critical aspects of lipid homeostasis that prevent free sterol toxicity. To identify genes that mediate sterol trafficking, we screened for yeast mutants that were inviable in the absence of sterol esterification. Mutations in the novel gene, ARV1, render cells dependent on sterol esterification for growth, nystatin-sensitive, temperature-sensitive, and anaerobically inviable. Cells lacking Arv1p display altered intracellular sterol distribution and are defective in sterol uptake, consistent with a role for Arv1p in trafficking sterol into the plasma membrane. Human ARV1, a predicted sequence ortholog of yeast ARV1, complements the defects associated with deletion of the yeast gene. The genes are predicted to encode transmembrane proteins with potential zinc-binding motifs. We propose that ARV1 is a novel mediator of eukaryotic sterol homeostasis.

Acyltransferases↗
PubMed2000

Sequence and analysis of chromosome 1 of the plant Arabidopsis thaliana.

The genome of the flowering plant Arabidopsis thaliana has five chromosomes. Here we report the sequence of the largest, chromosome 1, in two contigs of around 14.2 and 14.6 megabases. The contigs extend from the telomeres to the centromeric borders, regions rich in transposons, retrotransposons and repetitive elements such as the 180-base-pair repeat. The chromosome represents 25% of the genome and contains about 6,850 open reading frames, 236 transfer RNAs (tRNAs) and 12 small nuclear RNAs. There are two clusters of tRNA genes at different places on the chromosome. One consists of 27 tRNA(Pro) genes and the other contains 27 tandem repeats of tRNA(Tyr)-tRNA(Tyr)-tRNA(Ser) genes. Chromosome 1 contains about 300 gene families with clustered duplications. There are also many repeat elements, representing 8% of the sequence.

Arabidopsis↗
PubMed2000

Substance P modulation of striatal dopamine outflow is determined by M(1) and M(2) muscarinic receptors in male wistar rats.

Substance P (SP) stimulates striatal dopamine outflow through a cholinergic muscarinic link. SP-induced increase in acetylcholine (Ach) is concentration-dependent, whereas the stimulation of dopamine outflow is seen only over a limited concentration range. M(1) and M(2) receptor stimulation has opposite effects on dopamine outflow. We postulated that the effect of SP on dopamine outflow depends on the M(1)/M(2) balance. We show that Ach (10-2500 microM) stimulates dopamine outflow in striatal slices in a biphasic manner, similar to SP (0.01-100 nM). An inactive SP concentration (10 nM) which was higher than the active concentration range, became active in the presence of the M(2) antagonist methoctramine (100 microM). Conversely, the effect of 1 nM SP was reversed by the M(1) antagonist pirenzepine (1 microM). Our observations show that SP modulation of dopamine outflow is determined by a balance between M(1) and M(2) receptors.

Acetylcholine↗
PubMed2000

Childhood absence epilepsy in 8q24: refinement of candidate region and construction of physical map.

Childhood absence epilepsy (CAE), one of the common idiopathic generalized epilepsies, accounts for 8 to 15% of all childhood epilepsies. Inherited as an autosomal dominant trait, frequent absence attacks start in early or midchildhood and disappear by 30 years of age or may persist through life. Recently, we mapped the locus for CAE persisting with tonic-clonic seizures to chromosome 8q24 (ECA1) by genetic linkage analysis. As a further step in the identification of the ECA1 gene, we constructed a bacterial artificial chromosome- and yeast artificial chromosome-based physical map for the 8q24 region, spanning about 3 Mb between D8S1710 and D8S523. Accurately ordered STS markers within the physical map aided in the analysis of haplotypes and recombinations and reduced the ECA1 region to 1.5 Mb flanked by D8S554 and D8S502. Pairwise analysis in six families confirmed linkage with a pooled lod score of 4.10 (&theta; = 0) at D8S534. The sequence-ready physical map as well as the narrowed candidate region described here should contribute to the identification of the ECA1 gene.

Base Sequence↗
PubMed2000

An automated method of sample preparation of biofluids using pierceable caps to eliminate the uncapping of the sample tubes during sample transfer.

Biological samples are normally collected and stored frozen in capped tubes until analysis. To obtain aliquots of biological samples for analysis, the sample tubes have to be thawed, uncapped, samples removed and then recapped for further storage. In this paper, we report an automated method of sample transfer devised to eliminate the uncapping and recapping process. This sampling method was incorporated into an automated liquid-liquid extraction procedure of plasma samples. Using a robotic system, the plasma samples were transferred directly from pierceable capped tubes into microtubes contained in a 96-position block. The aliquoted samples were extracted with methyl-tert-butyl ether in the same microtubes. The supernatant organic layers were transferred to a 96-well collection plate and evaporated to dryness. The dried extracts were reconstituted and injected from the same plate for analysis by liquid chromatography with tandem mass spectrometry.

Blood Chemical Analysis↗
PubMed2000

Antimicrobial actions of the NADPH phagocyte oxidase and inducible nitric oxide synthase in experimental salmonellosis. II. Effects on microbial proliferation and host survival in vivo.

The roles of the NADPH phagocyte oxidase (phox) and inducible nitric oxide synthase (iNOS) in host resistance to virulent Salmonella typhimurium were investigated in gp91phox(-/)-, iNOS(-/)-, and congenic wild-type mice. Although both gp91phox(-/)- and iNOS(-/)- mice demonstrated increased susceptibility to infection with S. typhimurium compared with wild-type mice, the kinetics of bacterial replication were dramatically different in the gp91phox(-/)- and iNOS(-/)- mouse strains. Greater bacterial numbers were present in the spleens and livers of gp91phox(-/)- mice compared with C57BL/6 controls as early as day 1 of infection, and all of the gp91phox(-/)- mice succumbed to infection within 5 d. In contrast, an increased bacterial burden was detected within reticuloendothelial organs of iNOS(-/)- mice only beyond the first week of infection. Influx of inflammatory CD11b(+) cells, granuloma formation, and serum interferon gamma levels were unimpaired in iNOS(-/)- mice, but the iNOS-deficient granulomas were unable to limit bacterial replication. The NADPH phagocye oxidase and iNOS are both required for host resistance to wild-type Salmonella, but appear to operate principally at different stages of infection.

Animals↗
PubMed2000

Rapid purification of protein complexes from mammalian cells.

The evaluation of the protein binding partner(s) of biologically important proteins is currently an area of intense research, especially since the development of the yeast two-hybrid assay. However, not all protein-protein interactions uncovered by this assay are biologically relevant and another confirmatory assay must be performed. Ideally, this assay should be rapid, versatile and performed under conditions which mimic the 'normal' physiological state as closely as possible. Towards this goal, we have constructed two eukaryotic expression vectors that facilitate the purification of a protein of interest, along with any associated proteins, from mammalian cells. These vectors incorporate the following features: (i) a tetracycline-responsive promoter so that the level of protein production can be regulated; (ii) an N-terminal glutathione S-transferase tag or a triple repeat of the HA1 epitope, to facilitate purification of the protein either by glutathione affinity chromatography or immunoprecipitation, respectively, followed by a multiple cloning site; (iii) the gene for the enhanced green fluorescent protein (for detection of the presence of the fusion protein and subcellular localization); (iv) a puromycin marker for the selection of stable transformants; (v) a truncated EBNA protein and oriP sequence for episomal replication of the vector. These latter two features permit expansion of small cultures of transfected cells under puromycin selection, thereby increasing the amount of tagged protein that can be purified. We show that these vectors can be used to direct the doxycycline-inducible expression of tagged proteins and to recover tagged CIP1-p21 protein complexes from HeLa cells. Furthermore, we show that these tagged p21-purified complexes contain both cyclin A and Cdk2, which are known to interact with p21, but not beta-actin.

Animals↗
PubMed2000

Cooperativity of Staphylococcal aureus enterotoxin B superantigen, major histocompatibility complex class II, and CD80 for immunotherapy of advanced spontaneous metastases in a clinically relevant postoperative mouse breast cancer model.

One of the leading causes of death for women is metastatic breast cancer. Because most animal tumors do not accurately model clinical metastatic disease, the development of effective therapies has progressed slowly. In this study, we establish the poorly immunogenic mouse 4T1 mammary carcinoma as a postsurgical animal model. 4T1 growth characteristics parallel highly invasive human metastatic mammary carcinoma and, at the time of surgery, the extent of disease is comparable with human stage IV breast cancer. Progress in understanding the immune response has led to innovative immune-based anticancer therapies. Here, we test in this postsurgical model, a novel cell-based vaccine, combining MHC class II, CD80(B7.1), and SEB superantigen. Effective treatment of tumor-bearing mice with this immunotherapy requires expression of all three molecules. Mean survival time is extended from 5-7.5 weeks for control-treated mice to 6-10.5 weeks for therapy-treated mice. Increased survival is accompanied by a maximum of 100-fold decrease in clonogenic lung metastases. These therapeutic effects are particularly noteworthy because: (a) the postoperative model demonstrates that early metastases responsible for morbidity are established by 2 weeks after tumor inoculation with 7 x 10(3) parental 4T1 cells into the mammary gland; (b) the immunotherapy is started 4 weeks after tumor inoculation when the mice contain extensive, pre-established, disseminated metastases; and (c) CD4+ and CD8+ T cells are required for the effect.

Animals↗
PubMed2000

Overproduced Salmonella typhimurium flagellar motor switch complexes.

Three Salmonella typhimurium flagellar motor proteins, FliG, FliM and FliN, are required for the switching of rotation sense. The proteins have been localized to the cytoplasmic module of the flagellar base. Structures, which were morphologically indistinguishable from the native transmembrane MS-ring and cytoplasmic C-ring basal body modules, formed in Escherichia coli upon plasmid-encoded synthesis of these proteins together with FliF. The structures localized to the cell membrane and contained all three motor proteins, as determined by immuno-electron microscopy. This result supports the deduction, based on earlier biochemical analysis, that the C-ring is composed entirely of these proteins and, therefore, functions as a dedicated motor component. In addition, it demonstrates that the morphologically correct assembly of the C-ring onto the MS-ring proceeds independently of other structural components of these modules.

Bacterial Proteins↗
PubMed2000

Postmenopausal hormone therapy increases risk for venous thromboembolic disease. The Heart and Estrogen/progestin Replacement Study.

BACKGROUND: Oral contraceptive use increases risk for venous thromboembolism, but data on the effect of postmenopausal hormone therapy are limited. OBJECTIVE: To determine the effect of therapy with estrogen plus progestin on risk for venous thromboembolic events in postmenopausal women. DESIGN: Randomized, double-blind, placebo-controlled trial. SETTING: 20 clinical centers in the United States. PARTICIPANTS: 2763 postmenopausal women younger than 80 years of age (mean age, 67 years) who had coronary heart disease but no previous venous thromboembolism and had not had a hysterectomy. INTERVENTION: Conjugated equine estrogens, 0.625 mg, plus medroxyprogesterone acetate, 2.5 mg, in one tablet (n = 1380) or placebo that was identical in appearance (n = 1383). MEASUREMENTS: Documented deep venous thrombosis or pulmonary embolism. RESULTS: During an average of 4.1 years of follow-up, 34 women in the hormone therapy group and 13 in the placebo group experienced venous thromboembolic events (relative hazard, 2.7 [95% CI, 1.4 to 5.0] [P = 0.003]; excess risk, 3.9 per 1000 woman-years [CI, 1.4 to 6.4 per 1000 woman-years]; number needed to treat for harm, 256 [CI, 157 to 692]). In multivariate analysis, the risk for venous thromboembolism was increased among women who had lower-extremity fractures (relative hazard, 18.1 [CI, 5.4 to 60.4]) or cancer (relative hazard, 3.9 [CI, 1.6 to 9.4]) and for 90 days after inpatient surgery (relative hazard, 4.9 [CI, 2.4 to 9.8]) or nonsurgical hospitalization (relative hazard, 5.7 [CI, 3.0 to 10.8]). Risk was decreased with aspirin (relative hazard, 0.5 [CI, 0.2 to 0.8]) or statin use (relative hazard, 0.5 [CI, 0.2 to 0.9]). CONCLUSIONS: Postmenopausal therapy with estrogen plus progestin increases risk for venous thromboembolism in women with coronary heart disease. This risk should be considered when the risks and benefits of therapy are being weighed.

Aged↗
PubMed2000

Activation of the human estrogen receptor by the antiestrogens ICI 182,780 and tamoxifen in yeast genetic systems: implications for their mechanism of action.

The antiestrogens tamoxifen and ICI 182,780 have been portrayed as competitive antagonists of the estrogen binding site of the alpha-form of the human estrogen receptor (ER). However, in functional studies, neither compound has consistently been able to block estradiol-induced transcription. In this report, three yeast genetic systems were used to investigate the effects of tamoxifen and ICI 182,780 on ER dimerization, transcriptional activation, and the interaction of the receptor with a coactivator, RIP140. Tamoxifen and ICI 182,780 were able to induce ER dimerization and ER-dependent transcription, albeit at up to 15,000-fold higher concentrations than that of estradiol. In the presence of RIP140, the transcription response maximum was increased up to 30-fold for estradiol and both antiestrogens. Whole yeast cell [(3)H]estradiol binding studies demonstrated that tamoxifen could displace the estradiol from the ER, whereas ICI 182,780 treatment resulted in a 4-fold increase in [(3)H]estradiol binding to the receptor. No antagonism of estradiol was observed with tamoxifen or ICI 182,780 in any of the yeast models employed. We have concluded that the antiestrogen activity of compounds like tamoxifen and ICI 182,780 is not caused by their ability to competitively antagonize estradiol binding to the hormone binding site, but possibly by their ability to induce ER-dependent transcription, which in mammalian systems would result in receptor down-regulation. Compounds such as tamoxifen act through the hormone binding site, whereas ICI 182,780 may cause receptor activation through an allosteric binding site.

Binding Sites↗
PubMed2000

Distinct versus redundant properties among members of the INK4 family of cyclin-dependent kinase inhibitors.

p16(INK4a), p15(INK4b), p18(INK4c) and p19(INK4d) comprise a family of cyclin-dependent kinase inhibitors and tumor suppressors. We report that the INK4 proteins share the ability to arrest cells in G1, and interact with CDK4 or CDK6 with similar avidity. In contrast, only p18 and particularly p19 are phosphorylated in vivo, and each of the human INK4 proteins shows unique expression patterns dependent on cell and tissue type, and differentiation stage. Thus, the INK4 proteins harbor redundant as well as non-overlapping properties, suggesting distinct regulatory modes, and diverse roles for the individual INK4 family members in cell cycle control, cellular differentiation, and multistep oncogenesis.

Binding, Competitive↗
PubMed2000

OFD II, OFD VI, and Joubert syndrome manifestations in 2 sibs.

We present 2 sibs with manifestations of oral-facial-digital syndromes (OFD) and Joubert syndrome. The index patient was the 5th child of healthy nonconsanguineous Turkish parents. At birth this female patient had large hydrocephalus, hypertelorism, deep-set eyes, nystagmus, broad mouth, thick oral frenula, cleft palate, hamartomas of the tongue, postaxial polydactyly of fingers, normal toes, and hypotonia. Cranial MRI showed hydrocephalus and Dandy-Walker malformation. The child had no psychomotor development, was unable to swallow and had severe seizures. She died at 2 months of recurrent apneic episodes. At birth the brother of the index patient showed prominent forehead, broad, deep nasal bridge, cleft palate, multiple hamartomas of the tongue, irregular alveolar ridges, retrognathia, bilateral postaxial polydactyly of the hands and feet, and broad halluces. He had an abnormal breathing pattern with phases of tachypnea and apnea. Cranial MRI showed hydrocephalus, hypoplasia of the cerebellar vermis, Dandy-Walker malformation, and hypomyelination of the corpus callosum. Renal ultrasonography demonstrated multiple small cysts. Ocular fixation was absent and he had a mild nystagmus.

Abnormalities, Multiple↗
PubMed2000

Risk of cryptogenic fibrosing alveolitis in metal workers.

We report increased proportional mortality from cryptogenic fibrosing alveolitis in the workforce of a major UK engineering company. Measures of metal exposure from unbiased historical occupational records showed that among employees who have worked with metal, the risk of death from or with cryptogenic fibrosing alveolitis increased in relation to the duration of metal-working.

Aged↗