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Biomedical subjects

P Karmakar

Publications and source records attributed to P Karmakar.

17 recordsLinked to original sources
PubMed2006

Li ion scattering from Au nanoclusters on TiO2(110).

The neutralization of low energy 7Li+ scattered from Au nanoclusters deposited on TiO2(110) was measured with time-of-flight spectroscopy as a function of cluster size, emission angle, and ion energy. The neutralization shows maxima for cluster diameters approximately 3 nm, and again for thick Au films. The data are compared to previous experiments with Na projectiles. Possible explanations of the observed effects are discussed.

Journal Article↗
PubMed2001

Induction of apoptosis by Phenothiazine derivatives in V79 cells.

Phenothiazine derivatives chlorpromazine (cpz) and trifluoperazine (tfp) were found to induce apoptosis, abnormal cell cycle and expression of p53 in Chinese hamster lung fibroblast V79 cells. Both the drugs can induce apoptosis when cells are treated with drug at a concentration of 10 microg/ml within 4 h, as detected by propidium iodide staining and DNA fragmentation analysis. Flow cytometric analysis revealed that the apoptotic response is mediated by a loss of G(1) population of cells. In Western blot analysis, p21 is induced and p53 is accompanied by additional bands. Also indirect immunolabeling of single cells revealed that p21 is accumulated from cytoplasm into nucleus after the drug treatment and the intensities of p53 increased. Our findings demonstrate for the first time that phenothiazine derivatives, in addition to their cytotoxic effects, could induce apoptosis, an observation that has important clinical implications.

Animals↗
PubMed2001

Werner syndrome protein interacts with human flap endonuclease 1 and stimulates its cleavage activity.

Werner syndrome (WS) is a human premature aging disorder characterized by chromosomal instability. The cellular defects of WS presumably reflect compromised or aberrant function of a DNA metabolic pathway that under normal circumstances confers stability to the genome. We report a novel interaction of the WRN gene product with the human 5' flap endonuclease/5'-3' exonuclease (FEN-1), a DNA structure-specific nuclease implicated in DNA replication, recombination and repair. WS protein (WRN) dramatically stimulates the rate of FEN-1 cleavage of a 5' flap DNA substrate. The WRN-FEN-1 functional interaction is independent of WRN catalytic function and mediated by a 144 amino acid domain of WRN that shares homology with RecQ DNA helicases. A physical interaction between WRN and FEN-1 is demonstrated by their co-immunoprecipitation from HeLa cell lysate and affinity pull-down experiments using a recombinant C-terminal fragment of WRN. The underlying defect of WS is discussed in light of the evidence for the interaction between WRN and FEN-1.

Adenosine Triphosphatases↗
PubMed2001

p53 Modulates the exonuclease activity of Werner syndrome protein.

Werner syndrome (WS) is characterized by the early onset of symptoms of premature aging, cancer, and genomic instability. The molecular basis of the defects is not understood but presumably relates to the DNA helicase and exonuclease activities of the protein encoded by the WRN gene that is mutated in the disease. The attenuation of p53-mediated apoptosis in WS cells and reported physical interaction between WRN and the tumor suppressor p53 suggest that p53 and WRN functionally interact in a pathway necessary for the normal cellular response. In this study, we have demonstrated that p53 inhibits the exonuclease activity of the purified full-length recombinant WRN protein. p53 did not have an effect on a truncated amino-terminal WRN fragment that retains exonuclease activity but lacks the physical interaction domain for p53 located in the carboxyl terminus. Two naturally occurring p53 mutants found in human cancer displayed a reduced ability to inhibit WRN exonuclease activity. In cells arrested in S phase with hydroxyurea, WRN exits the nucleolus and colocalizes with p53 in the nucleoplasm. The regulation of WRN function by p53 is likely to play an important role in the maintenance of genomic integrity and prevention of cancer and other clinical symptoms associated with WS.

Adenosine Triphosphatases↗
PubMed2001

A functional interaction of Ku with Werner exonuclease facilitates digestion of damaged DNA.

Werner syndrome (WS) is a premature aging disorder where the affected individuals appear much older than their chronological age. The single gene that is defective in WS encodes a protein (WRN) that has ATPase, helicase and 3'-->5' exonuclease activities. Our laboratory has recently uncovered a physical and functional interaction between WRN and the Ku heterodimer complex that functions in double-strand break repair and V(D)J recombination. Importantly, Ku specifically stimulates the exonuclease activity of WRN. We now report that Ku enables the Werner exonuclease to digest through regions of DNA containing 8-oxoadenine and 8-oxoguanine modifications, lesions that have previously been shown to block the exonuclease activity of WRN alone. These results indicate that Ku significantly alters the exonuclease function of WRN and suggest that the two proteins function concomitantly in a DNA damage processing pathway. In support of this notion we also observed co-localization of WRN and Ku, particularly after DNA damaging treatments.

Adenine↗
PubMed2001

Sequential assembly of the nucleotide excision repair factors in vivo.

Here, we describe the assembly of the nucleotide excision repair (NER) complex in normal and repair-deficient (xeroderma pigmentosum) human cells, employing a novel technique of local UV irradiation combined with fluorescent antibody labeling. The damage recognition complex XPC-hHR23B appears to be essential for the recruitment of all subsequent NER factors in the preincision complex, including transcription repair factor TFIIH. XPA associates relatively late, is required for anchoring of ERCC1-XPF, and may be essential for activation of the endonuclease activity of XPG. These findings identify XPC as the earliest known NER factor in the reaction mechanism, give insight into the order of subsequent NER components, provide evidence for a dual role of XPA, and support a concept of sequential assembly of repair proteins at the site of the damage rather than a preassembled repairosome.

Cell Line↗
PubMed2001

Analysis of repair and PCNA complex formation induced by ionizing radiation in human fibroblast cell lines.

Proliferating cell nuclear antigen (PCNA), an auxiliary factor for DNA polymerase delta and epsilon, is involved in both DNA replication and repair. Previous studies in vitro have demonstrated the requirement of PCNA in the resynthesis step of nucleotide excision repair (NER) and base excision repair (BER). Using a native chromatin template isolated under near physiological conditions, we have analysed the involvement of PCNA in the BER pathway in different NER defective human cell lines. The repair sites and PCNA were visualized by indirect immunolabelling followed by fluorescence microscopy. The results indicate that exposure to X-rays triggers the induction of PCNA in all the three human fibroblast cell lines studied, namely normal, xeroderma pigmentosum group A (XP-A) and Cockayne syndrome group B (CS-B). In all the cell lines, induction of PCNA and repair patches occurred in a dose- and time-dependent fashion. Induction of repair patches in NER-deficient XP-A cells suggests that the X-ray-induced lesions are largely repaired via the BER pathway involving PCNA as one of the key components of this pathway. X-ray-induced repair synthesis was greatly inhibited by treatment of cells with DNA polymerase inhibitors aphidicolin and cytosine arabinoside. Interestingly, inhibition of repair resynthesis did not affect the intensity of PCNA staining in X-irradiated cells indicating that the PCNA may be required for the BER pathway at a step preceding the resynthesis step.

Cell Line↗
PubMed2001

Fragile X syndrome in Calcutta, India.

Fragile-X-linked mental retardation usually results from amplification of the CGG repeat in the 5' untranslated region of the FMR1 gene. To assess the extent of variation of the CGG repeat in the population from the eastern region of India we studied 98 mentally retarded individuals living in and around Calcutta and identified 21 distinct alleles ranging in size from 8 to 44 CGG repeats. A repeat size of 28 was the most frequent; this value is different from the most frequent repeat size found in other studies, indicating a racial or ethnic variation. Patients with the clinical features of the syndrome have been found to carry expanded CGG repeats. Thus, it can be inferred that the expansion of CGG repeats may be a frequent cause of the syndrome in our population.

Adolescent↗
PubMed2000

Werner syndrome protein: biochemical properties and functional interactions.

Werner syndrome is a premature aging syndrome displaying numerous signs and symptoms found in normal aging. The disease is associated with a mutation in the WRN gene. We have purified the Werner protein (WRN) and studied its biochemical activities and its protein interactions. WRN is a helicase and an exonuclease and also has an associated ATPase activity. WRN interacts physically and functionally with replication protein A (RPA), which stimulates its helicase activity. We have studied the WRN exonuclease activity and found that it can be blocked by certain DNA lesions and not by others. Thus, while WRN does not bind to DNA damage, it may have properties that allow it to sense the presence of damage in DNA. More recently we have found other protein interactions that involve physical and functional interactions with WRN, which could suggest a role for WRN in DNA repair.

Antigens, Nuclear↗
PubMed2000

Characteristics of UV-induced repair patches relative to the nuclear skeleton in human fibroblasts.

We have tried to characterize the nucleotide excision repair (NER) events associated with the nuclear skeleton in both repair-proficient and repair-deficient human cell lines following UV irradiation. The repair patches were labelled with biotin-16-dUTP and the repair sites were visualized by fluorescence microscopy using fluorescence-conjugated antibodies to biotin. The intensities of repair labelling measured for the three human cell lines of normal, xeroderma pigmentosum group C (XP-C) and Cockayne syndrome group B (CS-B) are in good agreement with their known repair capabilities. Digestion of nuclei with DNase I markedly solubilized the repair patches in normal (3-fold reduction after 1 h post-UV incubation) and transcription-coupled repair (TCR)-defective Cockayne syndrome cells (6-fold reduction after 1 h post-UV incubation). The intensity of repair labelling remained the same in TCR-proficient XP-C cells after DNase I digestion, indicating that the repair events mediated by the TCR pathway are tightly associated with the nuclear skeleton. Treatment with ammonium sulphate after DNase I digestion further reduced the intensity of repair patches in both normal and Cockayne syndrome cells, but not in XP-C cells. The tight association of repair patches generated by the TCR pathway with the nucleoskeleton in XP-C cells reinforces the concept of functional compartmentalization of the nucleus, where NER is highly heterogeneous.

Cell Nucleus↗
PubMed2000

Real-time projection MR angiography: feasibility study.

Intraarterial injections of small doses of gadopentetate dimeglumine were combined with a fast spoiled-gradient-echo magnetic resonance (MR) sequence to obtain real-time projection angiographic images of the rabbit aorta and canine coronary arteries. Arterial filling and washout, as well as venous and perfusion phases, were clearly displayed, demonstrating that arterial fluoroscopy in which an MR technique is used is feasible.

Adult↗
PubMed1997

Recent epidemiological status of malaria in Calcutta Municipal Corporation area, West Bengal.

In Calcutta, Plasmodium falciparum cases and death due to malaria show remarkably increasing trend since 1990. The incidence of P. falciparum malaria has increased more than eleven folds in 1996 in comparison to 1990, with 0, 0, 0, 3, 7, 52 and 17 deaths in 1990, 1991, 1992, 1993, 1994, 1995 and 1996 respectively. Situation is more serious than what it is projected in official records as annual blood examination rate (ABER) in Calcutta Municipal area is poor, varying from 1.5 to 3.9 in 1993 and 1996 respectively. This is further evident from the fact that in a study area in 19 months (January 1995 to July 1996) the slide positivity rate (SPR) was 47.94% on an average 28.72% suffer from P. falciparum infection (as low as 0.5% in June 1996 and as high as 71.5% in November 1996). For the first time resistance of P. falciparum to chloroquine has been noted at RII and RIII level. The response of the same parasite strain to sulfa-pyrimethamine combination drug is very much promising. Fresh infection is occurring in all the months of the year and the favourable period is from July to November 1995 that is corroborating with Container index and Breteau index related to the vector mosquito Anopheles. Susceptibility status of An. stephensi indicates that the mosquito species has acquired resistance to DDT, BHC, propoxure and malathion but is still susceptible to fenthion and deltamethrin.

Animals↗
PubMed1990

Micro in vitro assessment of Plasmodium falciparum sensitivity to chloroquine and mefloquine in Gujarat.

Micro in vitro tests conducted in 1987 in Surat district of Gujarat on sensitivity status of P. falciparum to chloroquine and mefloquine revealed that the parasite has developed resistance to chloroquine upto 32 pmol. The ED 99 in Hazira, Gothan and Umra areas of the district was found to be 17.3, 18.5 and 8.7 pmol/well for chloroquine and for mefloquine it was 14.5, 4.8 and 6.8 pmol/well respectively. Monitoring of P. falciparum resistance is indicated under National Malaria Eradication Programme.

Animals↗
PubMed1990

Status of Plasmodium falciparum resistance to chloroquine in Gujarat, Rajasthan and Maharashtra states of India.

An extended study from 1978-88 revealed that in the western states of India i.e., Rajasthan, Gujarat and Maharashtra; P. falciparum resistance to chloroquine has a scattered pattern in its distribution. However in Gujarat, R-III level of resistance is established in southern districts showing four fold increase from 1.79% in 1985 to 8.2% in 1988. In this area use of some alternate drug is indicated.

Animals↗