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Biomedical subjects

K Das

Publications and source records attributed to K Das.

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

Competitive binding to a charged leucine motif represses transformation by a papillomavirus E6 oncoprotein.

E6 oncoproteins from HPV-16 and bovine papillomavirus type 1 (BPV-1) bind to similar leucine-rich peptides termed charged leucine motifs found on the cellular focal adhesion protein paxillin and the E3 ubiquitin ligase E6AP. BPV-1 E6 (BE6) mutants that do not bind to paxillin are defective at inducing cellular transformation. It is possible, however, that BE6 mutants that do not bind paxillin are defective for transformation for an unrelated reason than the ability to bind to charged leucine motifs. To address the role of BE6 interaction with charged leucine motifs, we fused a BE6-binding charged leucine motif to the amino terminus of BE6, thereby creating an autoinhibitory binding domain. We found that the fusion protein failed to bind to paxillin or transform murine C127 cells. Mutation of the amino terminal binding motif in the fusion protein restored both interaction with paxillin and transformation. This demonstrates that BE6 transformation requires binding to charged leucine motifs on particular cellular proteins and that transformation by papillomavirus oncoproteins can be repressed by competitive interactions with charged leucine motifs.

Amino Acid Sequence↗
PubMed2000

Evaluating contraceptive choice through the method-mix approach. An Indian Council of Medical Research (ICMR) task force study.

The method-mix approach was used to evaluate informed contraceptive choices in the present study. A total of 8,077 potential clients were given a balanced presentation of all available contraceptive methods in the national program, ie, the CuT 200 intrauterine device (IUD), low-dose combined oral pills (OC), condom, and sterilization (female/male) along with a new method, Norplant(R).(1) The majority of women opted for spacing methods; among them, the IUD was preferred by about 60% of clients, followed by condoms (9%), OC (6%), and Norplant (5%). Sterilization, mainly female, was accepted by about 17% of the women making an informed choice. The economic status of couples did not influence the contraceptive choices, as all the methods were offered free of cost in the present study, which is the current practice in the national program. Illiterate women more often accepted sterilization (about 25%) than did literate women (15%). This is because illiterate women had more children; about 30% of illiterate women had three or more children, as opposed to 16.2% of literate women. However, literacy status did not influence the choice of any specific spacing method. The study also revealed that, by encouraging potential clients to make an informed choice, they could override the provider's bias while accepting a particular type of spacing method. This is evident from the observation that Norplant was the first choice of the provider for 35% of the women, whereas only 5% of women preferred and accepted Norplant. The present study stresses an urgent need to promote the practice of informed choices in the national program with a variety of contraceptive options-especially, spacing methods for improving contraceptive prevalence and reproductive health in the country.

Adolescent↗
PubMed2000

The changing epidemiological pattern of hepatitis A in an urban population of India: emergence of a trend similar to the European countries.

The present study was undertaken to determine the seroprevalence of the antibody against hepatitis A virus (IgG anti-HAV) in an urban population sample from Delhi (India) and to assess any change in the epidemiological pattern of HAV infection in this part of the world. A total of 500 healthy subjects were enrolled and divided into groups on the basis of age, sex and per capita income and evaluated for the presence of IgG anti HAV antibodies using a commercially available kit. The mean age of all the subjects was 32.6 +/- 13.2 yr. and the male:female ratio was 1.5:1. The overall prevalence of IgG anti-HAV in all subjects was 71.2% (356/500). The prevalence in subjects >35 years (92.1% [186/202]) was significantly higher than that in subjects <35 years (92.1% [186/202]) was significantly higher than in subjects <35 years (57% [170/298]). No statistically significant difference was observed between male and female subjects (71.4% [217/304] vs. 70.9% [139/196]) or between subjects belonging to middle and low socioeconomic groups (68.9% [135/196] vs. 72.7% [221/304]). These findings when compared with the results that were obtained in 1982, showed a decreasing prevalence of IgG anti-HAV, most significantly in younger age groups (16-35 years). Thus, we may conclude that the seroepidemiology of hepatitis A virus infection in urban population of India seems to be changing with seroprevalence in the younger population approaching a figure similar to that of the more developed European countries.

Adolescent↗
PubMed2000

Role of hepatitis E and other hepatotropic virus in aetiology of sporadic acute viral hepatitis: a hospital based study from urban Delhi.

Major hepatotropic virus continues to be an important cause of acute viral hepatitis (AVH) in developing countries like India. While epidemics of AVH have been well studied few serious sporadic cases from developing countries have been reviewed. We studied prospectively 75 cases of sporadic AVH who reported to our hospital and were evaluated for the presence of various hepatotropic viruses. The seroprevalence of IgG anti-HEV antibodies was studied in the general population as a control. We found 53.3% (40/75) of sporadic AVH cases were due to hepatitis E virus while 11% (8/75) were due to hepatitis B virus. Hepatitis C virus was responsible for 8% (6/75) of the sporadic AVH cases and hepatitis A was found in 5% (4/75) of the cases. No causative agent was found in 23% (17/75) of the sporadic AVH cases. The sporadic AVH cases due to HEV were not clinically or biochemically not different from AVH due to other viruses. We found a high prevalence of IgG anti-HEV in 35.6% (178/500) among the general population of urban Delhi. The study suggested that hepatitis E was the most common cause of sporadic AVH in urban Delhi. High seroprevalence of IgG anti-HEV antibodies in the general population and amongst the sporadic AVH cases suggests that it is unlikely to be protective antibody. IgM anti-HEV positive serology is considered diagnostic of acute hepatitis E infection in India, where hepatitis E is endemic.

Acute Disease↗
PubMed2000

Rupture of a large ophthalmic segment saccular aneurysm associated with closed head injury: case report.

OBJECTIVE AND IMPORTANCE: Although each year approximately 30,000 to 50,000 cases of subarachnoid hemorrhage in the United States are caused by the rupture of intracranial saccular aneurysms, there is little information in the literature documenting the association of aneurysmal rupture with closed head injury. CLINICAL PRESENTATION: A 61-year-old woman presented after a motor vehicle accident with multiple injuries, including a severe closed head injury. Computed tomography revealed a diffuse basal subarachnoid hemorrhage. Angiography revealed the source as a large aneurysm arising from the ophthalmic segment of the left carotid artery. INTERVENTION: After the patient was stabilized for her multiple injuries, she underwent craniotomy and clipping of the aneurysm. She recovered without developing new neurological deficits. CONCLUSION: Although the association of head trauma and aneurysmal subarachnoid hemorrhage is rare, the presence of significant basal subarachnoid blood on a computed tomographic scan should alert the physician to the possibility of a ruptured aneurysm.

Aneurysm, Ruptured↗
PubMed2000

On the accuracy of efficiency of estimating equation approach.

Liang and Zeger (1986, Biometrika 73, 13-22) introduced a generalized estimating equation (GEE) approach based on a working correlation matrix to obtain efficient estimators of regression parameters in the class of generalized linear models for repeated measures data. As demonstrated by Crowder (1995, Biometrika 82, 407-410), because of uncertainty of the definition of the working correlation matrix, the Liang-Zeger approach may, in some cases, lead to a complete breakdown of the estimation of the regression parameters. After taking this comment of Crowder into account, recently Sutradhar and Das (1999, Biometrika 86, 459-465) examined the loss of efficiency of the regression estimators due to misspecification of the correlation structures. But their study was confined to the regression estimation with cluster-level covariates, as in the original paper of Liang and Zeger. In this paper, we study this efficiency loss problem for the generalized regression models with within-cluster covariates by utilizing the approach of Sutradhar and Das (1999).

Biometry↗
PubMed2000

Identification of a second transforming function in bovine papillomavirus type 1 E6 and the role of E6 interactions with paxillin, E6BP, and E6AP.

Papillomavirus E6 oncoproteins transform mammalian cells through interaction with cellular proteins. Bovine papillomavirus type 1 E6 (BE6) interacts with three previously described cellular targets: the E6AP E3 ubiquitin ligase, the calcium-binding protein E6BP (also known as ERC-55), and paxillin, which is a focal adhesion adapter protein. BE6 interacts strongly with each of these proteins in vitro, binding to similar peptide sequences found in E6AP, E6BP, and paxillin. To determine which BE6 interactions are necessary for transformation by BE6, we used a novel selection strategy for temperature-sensitive BE6 mutants in yeast that could discriminate in their interaction between E6AP, E6BP, and paxillin. All BE6 mutants that retained transforming ability retained association with paxillin, while some mutants that were transformation positive failed to interact with E6AP or E6BP. This study demonstrates that oncogene mutants that are temperature sensitive for transformation can be selected in yeast and that the induction of anchorage-independent cell proliferation by BE6 does not require strong association of BE6 with either E6AP or E6BP. Of particular interest is the identification of a BE6 mutant that interacts strongly with the acidic charged leucine motifs of E6AP, E6BP, and paxillin but is devoid of transformation activity, thereby genetically identifying a second essential transformation function in BE6 that is independent of interaction with acidic charged leucine motifs.

Animals↗
PubMed2000

A mutation in human immunodeficiency virus type 1 protease, N88S, that causes in vitro hypersensitivity to amprenavir.

Amprenavir (Agenerase, 141-W94, VX-478) is a human immunodeficiency virus type 1 (HIV-1) protease inhibitor (PRI) recently approved for the treatment of HIV-1 infection in the United States. A major cause of treatment failure is the development of resistance to PRIs. One potential use for amprenavir is as salvage therapy for patients for whom treatment that includes one (or more) of the other four currently approved PRIs-saquinavir, indinavir, ritonavir, and nelfinavir-has failed. We evaluated the cross-resistance to amprenavir of viruses that evolved during treatment with the two most commonly prescribed PRIs, nelfinavir and indinavir. Unexpectedly, a dramatic increase in susceptibility (2.5- to 12. 5-fold) was observed with 20 of 312 (6.4%) patient viruses analyzed. The most pronounced increases in susceptibility were strongly associated with an N88S mutation in protease. All viruses that carried the N88S mutation were hypersensitive to amprenavir. Site-directed mutagenesis studies confirmed the causal role of N88S in determining amprenavir hypersensitivity. The presence of the N88S mutation and associated amprenavir hypersensitivity may be useful in predicting an improved clinical response to amprenavir salvage therapy.

Anti-HIV Agents↗
PubMed2000

Metallothioneins in marine mammals.

Metallothioneins (MTs) have been detected in livers and kidneys of 10 marine mammals species (Pinnipeds and Odontocetes). Characterization of renal MTs of striped dolphin has shown that the protein has two isoforms (MT-1 and MT-2) with a molecular weight estimated around 6,800. MT concentrations also vary widely in marine mammals tissues (from 58 to 1,200 microg x g(-1) ww) underlying the numerous parameters involved: physiological status, pregnancy, age, diet. The participation of this protein in metal detoxification has been investigated since high levels of cadmium (Cd) and mercury (Hg) have been measured in livers and kidneys of marine mammals. It has been suggested that those animals can mitigate at least in part, the toxic effects of Cd and Hg through binding to MTs. The percentage of the cytosolic Cd bound to MTs can reach almost 100%. On the contrary, the percentage of hepatic and renal Hg bound to MT is very low (generally less than 10%) and this metal is mainly associated with selenium (HgSe) under a detoxified form in the insoluble fraction of the tissues. MTs appear to play a minor role in the binding and detoxification of Hg by marine mammals. On the contrary, close and dynamic interactions occur between Cd and MTs. Cytosolic MTs appear as a potential short term way of detoxification of Cd accumulated from diet. Long-term detoxification would imply a sequestration of the metal under a precipitated form (e.g. in lysosomes).

Animals↗
PubMed2000

Effects of acute, moderate ethanol consumption on human platelet aggregation in platelet-rich plasma and whole blood.

BACKGROUND: Platelet-inhibitory effects of alcohol potentially contribute to the reduced risk of coronary heart disease associated with moderate drinking. However, few studies have directly examined the effects of acute consumption of a moderate dose of alcohol on aggregation of platelets from healthy human subjects. In the present study, we examined those effects, with the use of multiple platelet agonists and two aggregation measurement techniques, as part of an ongoing series of studies that evaluate the actions of ethanol on platelet function. METHODS: Human subjects consumed alcohol at a dose equivalent to one drink (0.25 ml/kg) or two drinks (0.5 ml/kg). One hour after ingestion, anticoagulated blood was collected and agonist-induced aggregation of platelets was measured in both whole blood and in platelet-rich plasma. RESULTS: Inhibition of aggregation by ethanol consumption was observed in whole blood (measured as maximum change in impedance) and reached statistical significance (p < 0.05) in the 0.5 ml/kg alcohol group for two collagen concentrations (0.625 and 1.25 microg/ml) as well as for the highest concentration of adenosine diphosphate tested (p < 0.05). Inhibition was 15.4%, 22.6%, and 10.5%, respectively, for these three situations. In platelet-rich plasma, after consumption of 0.5 ml/kg ethanol, aggregation (measured as maximum change in optical density) in response to 1.25 microg/ml collagen was significantly inhibited (p < 0.05); no other significant inhibition was observed at either dose of alcohol in any other cases with platelet-rich plasma. In comparison of male and female subjects, there was a statistically significant difference (p < 0.05) in the degree of inhibition by ethanol consumption (0.5 ml/kg) of whole-blood platelet aggregation induced by collagen, whereby female aggregation was inhibited to a greater extent than male. CONCLUSIONS: This study shows that alcohol, at physiologically relevant doses, below those investigated in most previous human studies, has a dose-dependent inhibitory effect on platelet aggregation. Such an effect could potentially contribute to the beneficial effects of alcohol consumption against coronary artery disease. The inhibitory action is most readily measured with whole-blood platelet aggregometry, with the use of collagen as the agonist. This observation is consistent with the view that alcohol reduces platelet sensitivity to thrombotic stimuli by inhibition of arachidonic acid release and, therefore, subsequent thromboxane synthesis.

Adenosine Diphosphate↗
PubMed2000

Molecular genetic diversity in 5 populations of Madhya Pradesh, India.

This paper presents data on the distribution of 3 amplified fragment length polymorphisms (D1S80, APOB, and YNZ22) in 5 populations of Central India. Using the polymerase chain reaction technique, 3 caste (Brahmin, Khatri, and Dhimer) and 2 tribal (Gond and Baiga) populations were studied for the 3 loci. The allelic variations observed in the caste populations are compatible with those of many Caucasian populations, but the caste populations showed significant overall and interpopulation variability within the region. D1S80 allele *24 varied from 32% (Dhimers) to 42% (Brahmins). Allele *18 was not observed in Baiga tribal populations, but in caste populations it varied from 11% (Dhimers) to 24% (Brahmins). Both tribal populations showed higher frequencies of allele *31 (17%-18%). For APOB, caste populations again showed bimodal distribution of alleles *35 and *37, but in tribal populations higher allele numbers (*47, *49) were also frequent. For YNZ22, extensive variation was observed for all populations studied. Allele *4 was the most common in caste populations, while alleles *2, *7, and *10 were prominent in tribal populations. The level of gene differentiation is not very high for the 3 systems studied in the 5 populations. Overall, allele frequency distribution, heterozygosity, and genetic diversity analysis show that the genetic diversity observed is socially and geographically structured.

Alleles↗
PubMed1999

Predominant expression of the mitochondrial dicarboxylate carrier in white adipose tissue.

We report the identification of a novel mouse protein closely related to the family of mitochondrial uncoupling proteins and the oxoglutarate carrier. The cDNA encodes a protein of 287 amino acids that shares all the hallmark features of the mitochondrial transporter superfamily, including six predicted transmembrane domains. It is nearly identical to the sequence recently reported for the rat mitochondrial dicarboxylate carrier (DIC). We find that murine DIC (mDIC) is expressed at very high levels in mitochondria of white adipocytes and is strongly induced in the course of 3T3-L1 adipogenesis. To determine the consequences of the presence of mDIC on the mitochondrial membrane potential, we transiently expressed mDIC in 293-T cells. Overexpression of mDIC leads to significant mitochondrial hyperpolarization. In addition, exposure to cold down-regulates mDIC levels in vivo. In contrast, free fatty acids lead to an up-regulation of mDIC protein in 3T3-L1 adipocytes. This is the first report demonstrating preferential expression in white adipose tissue of any mitochondrial transporter. However, it remains to be determined which metabolic pathways most critically depend on high level expression of mDIC in the adipocyte.

3T3 Cells↗
PubMed1999

Characterization of the interaction between the Wilson and Menkes disease proteins and the cytoplasmic copper chaperone, HAH1p.

Wilson disease (WD) and Menkes disease (MNK) are inherited disorders of copper metabolism. The genes that mutate to give rise to these disorders encode highly homologous copper transporting ATPases. We use yeast and mammalian two-hybrid systems, along with an in vitro assay to demonstrate a specific, copper-dependent interaction between the six metal-binding domains of the WD and MNK ATPases and the cytoplasmic copper chaperone HAH1. We demonstrate that several metal-binding domains interact independently or in combination with HAH1p, although notably domains five and six of WDp do not. Alteration of either the Met or Thr residue of the HAH1p MTCXXC motif has no observable effect on the copper-dependent interaction, whereas alteration of either of the two Cys residues abolishes the interaction. Mutation of any one of the HAH1p C-terminal Lys residues (Lys(56), Lys(57), or Lys(60)) to Gly does not affect the interaction, although deletion of the 15 C-terminal residues abolishes the interaction. We show that apo-HAH1p can bind in vitro to copper-loaded WDp, suggesting reversibility of copper transfer from HAH1p to WD/MNKp. The in vitro HAH1/WDp interaction is metalospecific; HAH1 preincubated with Cu(2+) or Hg(+) but not with Zn(2+), Cd(2+), Co(2+), Ni(3+), Fe(3+), or Cr(3+) interacted with WDp. Finally, we model the protein-protein interaction and present a theoretical representation of the HAH1p.Cu.WD/MNKp complex.

Adenosine Triphosphatases↗
PubMed1999

Lamivudine (3TC) resistance in HIV-1 reverse transcriptase involves steric hindrance with beta-branched amino acids.

An important component of triple-drug anti-AIDS therapy is 2', 3'-dideoxy-3'-thiacytidine (3TC, lamivudine). Single mutations at residue 184 of the reverse transcriptase (RT) in HIV cause high-level resistance to 3TC and contribute to the failure of anti-AIDS combination therapy. We have determined crystal structures of the 3TC-resistant mutant HIV-1 RT (M184I) in both the presence and absence of a DNA/DNA template-primer. In the absence of a DNA substrate, the wild-type and mutant structures are very similar. However, comparison of crystal structures of M184I mutant and wild-type HIV-1 RT with and without DNA reveals repositioning of the template-primer in the M184I/DNA binary complex and other smaller changes in residues in the dNTP-binding site. On the basis of these structural results, we developed a model that explains the ability of the 3TC-resistant mutant M184I to incorporate dNTPs but not the nucleotide analog 3TCTP. In this model, steric hindrance is expected for NRTIs with beta- or L- ring configurations, as with the enantiomer of 3TC that is used in therapy. Steric conflict between the oxathiolane ring of 3TCTP and the side chain of beta-branched amino acids (Val, Ile, Thr) at position 184 perturbs inhibitor binding, leading to a reduction in incorporation of the analog. The model can also explain the 3TC resistance of analogous hepatitis B polymerase mutants. Repositioning of the template-primer as observed in the binary complex (M184I/DNA) may also occur in the catalytic ternary complex (M184I/DNA/3TCTP) and contribute to 3TC resistance by interfering with the formation of a catalytically competent closed complex.

Allosteric Regulation↗
PubMed1999

The membrane-spanning domains of caveolins-1 and -2 mediate the formation of caveolin hetero-oligomers. Implications for the assembly of caveolae membranes in vivo.

The mammalian caveolin gene family consists of caveolins-1, -2, and -3. The expression of caveolin-3 is muscle-specific. In contrast, caveolins-1 and -2 are co-expressed, and they form a hetero-oligomeric complex in many cell types, with particularly high levels in adipocytes, endothelial cells, and fibroblasts. These caveolin hetero-oligomers are thought to represent the functional assembly units that drive caveolae formation in vivo. Here, we investigate the mechanism by which caveolins-1 and -2 form hetero-oligomers. We reconstituted this reciprocal interaction in vivo and in vitro using a variety of complementary approaches, including the generation of glutathione S-transferase fusion proteins and synthetic peptides. Taken together, our results indicate that the membrane-spanning domains of both caveolins-1 and -2 play a critical role in mediating their ability to interact with each other. This is the first demonstration that these unusual membrane-spanning regions found in the caveolin family play a specific role in protein-protein interactions.

3T3 Cells↗
PubMed1999

Changing characteristics of a colloid cyst of the third ventricle.

We describe extremely unusual radiological characteristics in a colloid cyst of the third ventricle, where the cyst became dense and its size decreased following a cerebrospinal fluid diversion procedure. Such a course of events has been reported in colloid cysts only twice in the literature.

Adolescent↗