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S Sircar

Publications and source records attributed to S Sircar.

At least 19 recordsLinked to original sources
PubMed2000

The effect of mutant peptide cofactors on adenovirus protease activity and virus infection.

Adenoviruses encode a cysteine protease, adenain, required for uncoating and virion maturation. Adenain activity is regulated by an 11-amino-acid peptide cofactor thiol-bonded distal to the active site. Structural and experimental data suggest that the peptide might stabilize adenain in an optimal conformation for enzyme activity by bridging two noncontiguous regions of the molecule. The sequence requirements for this mechanism were examined both in vitro and ex vivo by means of mutant peptides and databank analysis. The results of in vitro experiments suggested that activation is not an all or nothing mechanism. With the exception of the smallest peptide, the mutant peptides bound to adenain, activated it, and competed with the wild-type peptide, but all of this occurred with reduced efficiency. When added to the medium of infected cells, most of the peptides inhibited infectious virus production to varying degrees in a dose-dependent manner and in accordance with their in vitro activity on adenain. We interpret this inhibition to be due to unscheduled adenain activation. Examination of the activation peptide sequences from 19 adenovirus serotypes revealed a limited number of conserved sequence features. These features were in agreement with the experimental data. We conclude that binding and activation of adenain by pVIc may be reversible and this reversibility may be an integral aspect of the in vivo regulation of enzyme activity in the course of virus assembly. The peptide cofactor binding domain is therefore a potential target for the development of anti-adenoviral agents.

Adenoviruses, Human↗
PubMed2000

Adenovirus endopeptidase hydrolyses human squamous cell carcinoma antigens in vitro but not ex vivo.

The serpins SCCA1 and SCCA2 are highly expressed in the epithelium of the conducting airways, a common site of infection by group C adenoviruses, such as human adenovirus type 2 (Ad2). Based on the common location we examined a possible interaction between them. In vitro experiments with recombinant proteins showed that SCCA1 inhibited the viral protease in a dose-dependent manner. Both serpins were cleaved in a manner consistent with hydrolysis within their reactive site loop, without the formation of an SDS-resistant complex, as in the case of papain. Infection of SCCA1-expressing cells did not result in the cleavage of SCCA1, nor was the yield of infectious virus affected as compared to SCCA1-negative parental cells. This may be due to differential localization, the serpin being cytoplasmic and viral protease being nuclear. Surprisingly, however, virus infection, which tends to inhibit host protein synthesis, caused a significant increase in SCCA1 expression well into the late phase of infection.

Adenocarcinoma↗
PubMed2000

Cytohistological study of urinary bladder neoplasms.

Eighty patients presenting with painless hematuria and 24 patients of transitional cell carcinoma bladder coming for follow up were included in this study to assess the role of exfoliative (voided urine) and lavage (saline lavage) cytology in initial diagnosis and follow up of the patient with carcinoma bladder. Freshly voided urine samples and saline lavage bladder washing samples were collected. A thorough cystoscopic examination was done and biopsy was taken from any apparent growth. Cytological smears were stained with hematoxylene and eosin and PAP's stain, histology sections were stained with hematoxylene and eosin. A statistically significant correlation (p < 0.001) was observed between the increasing grade of malignancy and cytopositivity. A good association was observed between histology and two methods of cytology (p < 0.01). The sensitivity, specificity and overall diagnostic accuracy of lavage cytology was more as compared to exfoliative cytology (71.05%, 56.0%, 78.85% Vs 47.37%, 41.18% and 61.54%). Cystopositivity was more with single large sessile tumour as compared to multiple small pedunculated tumours. Cytohistological discrepancy was observed in patients of transitional cell carcinoma with recurrence. It is concluded that cytology may act as a good adjuvant to histology in picking up early flat lesions and/or follow up of patients with transitional cell carcinoma.

Carcinoma, Transitional Cell↗
PubMed1998

Adenovirus endopeptidase and papain are inhibited by the same agents.

Adenoviruses encode a cysteine protease (AVP) which carries out highly specific cleavages on at least seven viral proteins and two cellular proteins. Virus infectivity is dependent on this function. The three-dimensional positions of the amino acids involved in catalysis display a striking similarity to those of papain, suggesting a similar catalytic mechanism. This similarity has prompted us to compare the effect of papain inhibitors on the two enzymes. AVP and papain activity was tested on a fluorescent peptide substrate as well as on metabolically labeled adenovirus (Ad2) precursor proteins. Hep2 cells infected with Ad2 were exposed to inhibitors and assayed for, (a) infectious virus, (b) in situ Ad2 protease activity, (c) physical particle production and their polypeptide composition. We found that in both substrate systems AVP was sensitive to the papain inhibitors benzamidoacetonitrile, acetamidoacetonitrile and N-methoxyphenylalanine glycylnitrile, and that the degree of sensitivity was influenced by the substrate. Unlike papain, AVP was relatively insensitive to E64. In ex vivo tests, Hep2 cells infected with Ad2 were exposed to inhibitors and assayed for, (a) infectious virus, (b) in situ Ad2 protease activity, (c) physical particle production and their polypeptide composition. A 4-fold reduction in virus titer was obtained when the inhibitors were added between 17 and 25 h after infection. Processing of precursor proteins was also inhibited yet the production of physical particles was only reduced 2-fold. These experiments show that papain inhibitors are also capable of inhibiting the adenovirus protease both in vitro and ex vivo, thus forging a possible link between structural similarity and functionality.

Acetonitriles↗
PubMed1998

Choice of cooking oils--myths and realities.

In contrast to earlier epidemiologic studies showing a low prevalence of atherosclerotic heart disease (AHD) and type-2 dependent diabetes mellitus (Type-2 DM) in the Indian subcontinent, over the recent years, there has been an alarming increase in the prevalence of these diseases in Indians--both abroad and at home, attributable to increased dietary fat intake. Replacing the traditional cooking fats condemned to be atherogenic, with refined vegetable oils promoted as "heart-friendly" because of their polyunsaturated fatty acid (PUFA) content, unfortunately, has not been able to curtail this trend. Current data on dietary fats indicate that it is not just the presence of PUFA but the type of PUFA that is important--a high PUFA n-6 content and high n-6/n-3 ratio in dietary fats being atherogenic and diabetogenic. The newer "heart-friendly" oils like sunflower or safflower oils possess this undesirable PUFA content and there are numerous research data now available to indicate that the sole use or excess intake of these newer vegetable oils are actually detrimental to health and switching to a combination of different types of fats including the traditional cooking fats like ghee, coconut oil and mustard oil would actually reduce the risk of dyslipidaemias, AHD and Type-2 DM.

Cooking↗
PubMed1997

ANA-negative SLE presenting with nephritis and oculomotor palsy--a case report.

Most large series of patients with systemic lupus erythematosus (SLE) have revealed a very small group of patients who are persistently antinuclear antibody (ANA) negative with prominent dermatologic involvement but infrequent neurological and renal involvement. We present a very unusual case report of a young female with ANA-negative SLE presenting with lupus nephritis and oculomotor palsy without any dermatologic manifestations.

Adolescent↗
PubMed1996

New stimulation ligand of the adenovirus 2 protease.

The catalytic activity of the adenovirus cysteine peptidase is increased by a specific 11-amino-acid peptide adduct (GVQSLKRRRCF, referred to as pVIc). To identify additional peptides which might bind and alter the activity of the protease, a cysteine-constrained random peptide phage library was screened. Of 29 different phages which were isolated, 7 contained the consensus sequence VEGGS. Despite a superficial similarity to the substrate cleavage site of the protease, the peptide was not digested by the enzyme. VEGGS and pVIc altered protease activity similarly without sharing sequence similarity. To similar degrees, pVIc and VEGGS (a) stimulated the activity of the recombinant protease, (b) had no effect on viral protease, (c) increased the fluorescence emission of tryptophan residues in the protease, suggesting a conformational change, and (d) inhibited wt virus infection, but rescued ts1 infection at the nonpermissive temperature. The experiments also suggest that once the protease has been stimulated by one peptide, the other peptide has no further activity on the recombinant adenovirus cysteine protease, suggesting that the two peptides bring about the same change on the protease via different binding sites.

Adenoviruses, Human↗
PubMed1996

Inhibition of adenovirus infection with protease inhibitors.

The effect of a series of cysteine and serine protease inhibitors was tested on the growth of human adenovirus type 2 in tissue culture. In accordance with the nature of the adenovirus protease, only the cysteine protease inhibitors were effective in significantly reducing the production of infectious virus. Addition of the inhibitors to the medium 18 h after infection gave IC50 of 30, 40 and 80 nM with N-ethylmaleimide, leupeptin and E64c, respectively. Several lines of evidence suggest that inhibition of infectious virus formation operated through the inhibition of the viral protease rather than cellular toxicity: (a) the yield of physical particles declined only 4-5-fold, while that of infectious virus declined 3-7 orders of magnitude, (b) these particles contained unprocessed precursor proteins and (c) pulse-chase experiments showed that the inhibitors prevented the efficient processing of viral precursor proteins. We conclude that the cysteine protease inhibitors efficiently depress the formation of infectious adenovirus by inhibiting the viral protease.

Adenoviruses, Human↗
PubMed1996

Epidemiology and clinical presentation of abdominal tuberculosis--a retrospective study.

The epidemiology and clinical presentation of abdominal tuberculosis were studied retrospectively in 298 adult cases admitted in Safdarjang Hospital, New Delhi over a 3-year period. These constituted 17% of the total number of admissions for tuberculosis. Age at presentation was variable with maximum cases in 21 to 40-year age group (58% of cases) with a mean age of 32.7 years. There was a slight female preponderance (57%). Sixty-three per cent were residing in urban areas. Pain abdomen, ascites and subacute intestinal obstruction were the commonest modes of presentation (34%, 30%, 28% respectively). Other clinical features included fever (21%), altered bowel habits (19%), weight loss (8%) and lump abdomen (6%). Acute intestinal obstruction and lower gastro-intestinal bleeding were uncommon (5% and 4% respectively). Co-existent pulmonary tuberculosis was seen in 16% cases. Histological evidence was available in 41% cases. Majority improved with conservative management with only 21% requiring surgical intervention. Mortality recorded was 11%.

Abdomen↗
PubMed1995

Proline 137 is critical for adenovirus protease encapsidation and activation but not enzyme activity.

Infection with the adenovirus type 2 ts1 mutant at the nonpermissive temperature resulted in the production of noninfectious virions. This has been ascribed to the P137L mutation in the virus-encoded cysteine protease which causes a defect in protease activity. Here we have examined the ts1 defect in detail as a means of learning more about the viral protease. The ts1 protease accumulated in the nucleus normally and was found associated with incomplete particles as was the case with wt. This enzyme was active in both wt and ts1 incomplete particles produced at 39 degrees (ts1-39 TCs), provided they were dissociated with 4 M urea. While the wt protease was packaged into complete particles, the ts1-39 particles were totally devoid of protease. This defect was nearly completely corrected by addition of the 11-residue activating peptide PVIc (GVQSLKRRRCF) to the medium late in infection. Rescue of ts1 occurred via restoration of enzyme activity and packaging of the ts1 enzyme into complete virions. Recombinant ts1 enzyme was not temperature sensitive. The P137L mutation responsible for the ts1 defect appeared therefore to be an in vivo phenotype involving apparently linked events of protease packaging and activation mediated by the PVI protein.

Adenoviridae↗
PubMed1992

Adenovirus transformation revertant resistant to retransformation by E1 but not by SV40-T and HPV16-E7 oncogenes.

We have previously described a revertant cell line which expresses a dominant tumor suppressor phenotype to E1 but not to heterologous oncogenes such as c-myc, N-ras, or polyoma middle t (Sircar et al. (1988) Oncogene 3, 725-728). DNA tumor virus oncogenes have been suggested to transform cells via the common mechanism of sequestering the Rb-105 antioncoprotein. This paradigm would predict that our revertant cell line, which is resistant to retransformation by E1a, should also be resistant to the other members of the Rb-105 binding family of oncogenes. To test this hypothesis we transfected the revertant cell line with plasmids bearing SV40-T or the HPV16-E7 oncogenes. Because transformation was obtained by both oncogenes at efficiencies similar to the transformation of a related revertant cell line, the results suggest that the resistance phenotype is specific to E1a. This specificity was further confirmed by cell fusion experiments.

Adenoviridae↗
PubMed1991

Suppression of adrenocortical function in female mice by lindane (gamma-HCH).

Lindane (gamma-HCH) given to adult female mice orally at various doses and over varying periods adversely affected adrenocortical function. Adrenal weights decreased and both fasciculata and reticularis zones markedly regressed. Histopathological lesions were also noted and plasma and glandular glucocorticoid contents were significantly reduced. Simultaneously an increase in cholesterol and a decrease in ascorbic acid content of the adrenal glands were noticed. The adrenotoxic effect of this chlorinated insecticide possibly results from depressed corticoid production in situ and/or suppressed activity of enzyme(s) that catalyze the peripheral transformation of steroids.

Administration, Oral↗
PubMed1991

Dominant suppression of adenovirus mediated transformation and insufficiency of p105Rb binding as a condition for oncogenic transformation.

An adenovirus-specific transformation resistant cell line (G2) expressing biologically active E1a proteins and originally isolated as a revertant from Ad2-transformed rat cells (F4), was shown to form stable Rb-E1a and 300K-E1a complexes in immunoprecipitation experiments. Consistent with the transformation resistant phenotype, cell hybrids between G2 and F4 were all nontumorigenic. Retrovirus insertion mutagenesis resulted in tumorigenic cell lines and identified a common locus responsible for the E1a-specific dominant tumor suppressor phenotype of G2 cells.

Adenoviruses, Human↗
PubMed1990

Effect of lindane on mitochondrial side-chain cleavage of cholesterol in mice.

Cholesterol side-chain cleavage of mitochondria, the key rate limiting step in steroid biosynthesis in ovarian tissues, was studied in female Swiss mice fed lindane (gamma-hexachlorocyclohexane) at various doses and over varying periods. The insecticide adversely affected cholesterol side-chain cleavage of the ovary as judged by decreased conversion of this sterol to pregnenolone and subsequently to progesterone in a dose-dependent manner. The formation of pregnenolone was maximally inhibited (75% inhibition) at the highest intake of insecticide with simultaneous inhibition of its conversion to progesterone. At all doses, the rate of inhibition of pregnenolone formation was comparatively higher than its conversion to progesterone. The significant inhibition of cholesterol side-chain cleavage by lindane and resultant decrease in the rate of steroidogenesis in the ovary would account for the observed gonadal hormone deficiency and related reproductive disorders in the lindane-fed mice.

Administration, Oral↗
PubMed1990

Tumor necrosis factor mediated cytolysis requires the adenovirus E1a protein but not the transformed phenotype.

Adenovirus transformed cells are susceptible to lysis by human recombinant tumor necrosis factor (TNF). This susceptibility correlates with the presence of E1a in these cells. A flat revertant cell line which expresses a biologically functional E1a but not the transformed phenotype was nevertheless susceptible to TNF. However, flat revertants retransformed by 5-azacytidine, without concomitant reactivation of E1a, were resistant to TNF-alpha. This result suggests TNF susceptibility is not transformation but E1a dependent. To study the mechanism of cytolysis in these cell lines, we examined the possibility that changes in the transcription of E1a were brought about by TNF, as it was reported in the case of a c-myc transformed cell line. The results showed that TNF did not affect either E1a or c-myc transcription in our cells during the development of the cytotoxic response.

Adenoviridae↗
PubMed1990

Drug-induced revertants of adenovirus-transformed cells: retransformation by 5-azacytidine without reactivation of E1a.

We have isolated drug-resistant variants from adenovirus-transformed rat cells that had concomitantly lost their transformed phenotype. Our aim was to determine the reason for reversion, to attempt retransformation with 5-azacytidine (5-AzaC) and to study the mechanism of retransformation. Of the three cell lines studied, one (G4F) had lost the integrated E1a genes, whereas the other two (G2a and G5) failed to synthesize E1a RNA or proteins. Incubation of these cell lines with 3 microM-5-AzaC for 2 days, followed by passaging in the absence of drug, gave rise to transformed foci in all of the cell lines. The efficiency of transformation was typical of each cell line. Surprisingly, retransformation was not accompanied by the reappearance of detectable levels of E1a gene activity in the G2aAza and G5Aza cell lines. In search of a mechanistic explanation for the loss of gene activity in the revertants and its reappearance in the retransformants, we examined the state of methylation of the E1a gene region in these cells. Neither the E1a promoter nor its upstream region was methylated in the revertants or the 5-AzaC retransformants. These results suggest that E1a transcription was suppressed by mechanisms other than DNA methylation and that 5-AzaC could retransform these cells without lifting the E1a-suppressed state.

Adenovirus Early Proteins↗