Search PubMed⌕ Search

Biomedical subjects

A Bhattacharyya

Publications and source records attributed to A Bhattacharyya.

At least 19 recordsLinked to original sources
PubMed2001

Lipoarabinomannan from Mycobacterium tuberculosis promotes macrophage survival by phosphorylating Bad through a phosphatidylinositol 3-kinase/Akt pathway.

Efforts in prevention and control of tuberculosis suffer from the lack of detailed knowledge of the mechanisms used by pathogenic mycobacteria for survival within host cell macrophages. The exploitation of host cell signaling pathways to the benefit of the pathogen is a phenomenon that deserves to be looked into in detail. We have tested the hypothesis that lipoarabinomannan (LAM) from the virulent species of Mycobacterium tuberculosis possesses the ability to modulate signaling pathways linked to cell survival. The Bcl-2 family member Bad is a proapoptotic protein. Phosphorylation of Bad promotes cell survival in many cell types. We demonstrate that man-LAM stimulates Bad phosphorylation in a phosphatidylinositol 3-kinase (PI-3K)-dependent pathway in THP-1 cells. Man-LAM activated PI-3K. LAM-stimulated phosphorylation of Bad was abrogated in cells transfected with a dominant-negative mutant of PI-3K (Delta p85), indicating that activation of PI-3K is sufficient to trigger phosphorylation of Bad by LAM. Since phosphorylation of Bad occurred at serine 136, the target of the serine/threonine kinase Akt, the effect of LAM on Akt kinase activity was tested. Man-LAM could activate Akt as evidenced from phosphorylation of Akt at Thr(308) and by the phosphorylation of the exogenous substrate histone 2B. Akt activation was abrogated in cells transfected with Deltap85. The phosphorylation of Bad by man-LAM was abrogated in cells transfected with a kinase-dead mutant of Akt. These results establish that LAM-mediated Bad phosphorylation occurs in a PI-3K/Akt-dependent manner. It is therefore the first demonstration of the ability of a mycobacterial virulence factor to up-regulate a signaling pathway involved in cell survival. This is likely to be one of a number of virulence-associated mechanisms by which bacilli control host cell apoptosis.

Carrier Proteins↗
PubMed2000

Dynamics of compact denatured states of glutaminyl-tRNA synthetase probed by bis-ANS binding kinetics.

Bis-ANS binds to native glutaminyl-tRNA synthetase (GlnRS) with a fast and a slow phase. The rate constant of the slow phase is independent of bis-ANS concentration suggesting a slow conformational change in the pathway of bis-ANS binding. Aging of GlnRS causes a large decrease of the slow phase amplitude with concomitant increase of the fast phase amplitude. Several other large, multi-domain proteins show similar patterns upon aging. The near UV-CD spectra of the native and the aged GlnRS remain similar. Significant changes in far UV-CD, acrylamide quenching and sulfhydryl reactivity, are seen upon aging, suggesting disruptions in native interactions. Refolding of GlnRS from the urea-denatured state rapidly produces a state that is very similar to the equilibrium molten globule state. Bis-ANS binds to the molten globule state with kinetics similar to that of the aged state and unlike that of the native state. This suggests that the slow binding phase of bis-ANS, seen in native proteins, originate from relatively high energy barriers between the native and the more open states. Thus bis-ANS can be used as a powerful probe for large amplitude, low-frequency motions of proteins.

Amino Acyl-tRNA Synthetases↗
PubMed2000

The breast cancer susceptibility gene BRCA1 is required for subnuclear assembly of Rad51 and survival following treatment with the DNA cross-linking agent cisplatin.

Mutations in breast cancer tumor susceptibility genes, BRCA1 and BRCA2, predispose women to early onset breast cancer and other malignancies. The Brca genes are involved in multiple cellular processes in response to DNA damage including checkpoint activation, gene transcription, and DNA repair. Biochemical interaction with the recombinational repair protein Rad51 (Scully, R., Chen, J., Ochs, R. L., Keegan, K., Hoekstra, M., Feunteun, J., and Livingston, D. M. (1997) Cell 90, 425-435), as well as genetic evidence (Moynahan, M. E., Chiu, J. W., Koller, B. H., and Jasin, M. (1999) Mol. Cell 4, 511-518 and Snouwaert, J. N., Gowen, L. C., Latour, A. M., Mohn, A. R., Xiao, A., DiBiase, L., and Koller, B. H. (1999) Oncogene 18, 7900-7907), demonstrates that Brca1 is involved in recombinational repair of DNA double strand breaks. Using isogenic Brca1(+/+) and brca1(-/-) mouse embryonic stem (ES) cell lines, we investigated the role of Brca1 in the cellular response to two different categories of DNA damage: x-ray induced damage and cross-linking damage caused by the chemotherapeutic agent, cisplatinum. Immunoflourescence studies with normal and brca1(-/-) mutant mouse ES cell lines indicate that Brca1 promotes assembly of subnuclear Rad51 foci following both types of DNA damage. These foci are likely to be oligomeric complexes of Rad51 engaged in repair of DNA lesions or in processes that allow cells to tolerate such lesions during DNA replication. Clonogenic assays show that brca1(-/-) mutants are 5-fold more sensitive to cisplatinum compared with wild-type cells. Our studies suggest that Brca1 contributes to damage repair and/or tolerance by promoting assembly of Rad51. This function appears to be shared with Brca2.

Animals↗
PubMed2000

Cell surface Trk receptors mediate NGF-induced survival while internalized receptors regulate NGF-induced differentiation.

Internalization and transport of a ligand-receptor complex are required to initiate cell body responses to target-derived neurotrophin. However, it is not known whether internalized receptors and cell surface receptors initiate the same signaling pathways and biological responses. Here we use a temperature-sensitive mutant of dynamin (G273D) to control the subcellular localization of activated NGF receptors (Trks). We show that dynamin function is required for ligand-dependent endocytosis of Trk receptors. In PC12 cells, nerve growth factor (NGF) stimulation promotes both survival and neuronal differentiation. These distinct biological responses to NGF are controlled by receptors signaling from different locations within the cell. Neuronal differentiation is promoted by catalytically active Trks within endosomes in the cell interior. In contrast, survival responses are initiated by activated receptors at the cell surface where they orchestrate prolonged activation of the kinase Akt. Thus, interactions between Trk receptor tyrosine kinases and intracellular signaling molecules are dictated both by phosphotyrosine motifs within the receptors and by the intracellular location of phosphorylated receptors.

Amino Acid Sequence↗
PubMed2000

Meniscal ossification in spontaneous osteoarthritis in the guinea-pig.

OBJECTIVE: The purpose of this study was to evaluate the ossification state of the meniscus in the guinea-pig stifle joint using micro-computerized tomography. DESIGN: Hind limbs from six (N=12) and 24 (N=11) month-old male Hartley guinea-pigs were removed and the joints were imaged using high resolution micro-computerized tomography. The ossified volume of the medial and lateral menisci from both groups of animals was quantified. RESULTS: Ossification of both the medial and lateral menisci of the both the 6- and 24-month-old animals was observed. In both age groups, the ossified region of the medial meniscus was significantly larger than the lateral meniscus. In addition, there is a significant increase in ossified volume of the medial meniscus between 6 and 24 months of age. CONCLUSIONS: There is a significant amount of ossification of the menisci in the male Hartley guinea-pig, with the medial compartment showing more bone than the lateral. In addition, as the animals age, there is an increase in ossification within the medial compartment. Bone remodeling and cartilage degeneration is evident in the medial compartment within these animals as they age. It is possible that the increased ossification of the medial meniscus could alter the joint biomechanics and, in part, stimulate this medial compartment joint destruction.

Aging↗
PubMed2000

Long-term follow-up of intestinal metaplasia of the gastric cardia.

OBJECTIVE: Recent studies have found a relatively high prevalence of gastric cardia intestinal metaplasia in individuals presenting for elective upper endoscopy. It has been hypothesized that this lesion may be a precursor of gastric cardia cancer. Our objective was to identify the incidence of dysplasia in patients with gastric cardia intestinal metaplasia. METHODS: Twenty-eight patients who had previously been identified with cardia intestinal metaplasia had follow-up examinations performed. None of the patients had dysplasia at the time of diagnosis. All had an examination at 1 yr, and 20 patients had an examination at 3 yr after diagnosis. During follow-up examinations all patients underwent vital staining with methylene blue to help identify areas of intestinal metaplasia in the cardia. Two to four biopsies were taken from blue-stained mucosa. Histological specimens were stained using a combination of hematoxylin and eosin with Alcian blue at pH 2.5. RESULTS: There were 27 men and one woman with a mean age of 69.8 yr (range, 48-83 yr). The mean length of follow-up was 2.5 yr (range, 12-46 months). Only one patient was diagnosed with dysplasia (low-grade) during the study, for an incidence of 1.4% per yr. CONCLUSIONS: The prevalence (0%) and incidence (1.4%/yr) of dysplasia in cardia intestinal metaplasia are low. Although further studies are needed, screening and surveillance for gastric cardia intestinal metaplasia is unlikely to be clinically useful for the prevention of gastric cardia cancer.

Aged↗
PubMed2000

Screening for genetic haemochromatosis in blood samples with raised alanine aminotransferase.

BACKGROUND: In the UK approximately 1 in 140 people are homozygous for the C282Y mutation of the HFE gene and are at risk from iron overload caused by genetic haemochromatosis (GH). Early detection can prevent organ damage secondary to iron deposition and increase life expectancy. AIM: To screen for GH in all blood samples sent to the laboratory for routine liver function tests in which raised serum alanine aminotransferase (ALT) activity was detected. METHODS: ALT was measured in sera sent to the laboratory for routine liver function tests. In those samples found to have raised activity, transferrin saturation and ferritin were measured followed by genetic testing when transferrin saturation was increased. RESULTS: Of the 35 069 serum samples assayed for routine liver function tests, 1490 (4.2%) had raised ALT levels (>50 u/l). Transferrin saturation and serum ferritin concentrations were measured in these patient samples, and in 56 transferrin saturation was >60%. Further blood samples were requested from these patients for genetic testing: 33 samples were obtained. There were nine patients homozygous for the C282Y mutation of the HFE gene and three compound heterozygotes (heterozygous for both C282Y and H63D mutations). CONCLUSIONS: The association of raised ALT activity and transferrin saturation of >60% could provide a simple, cost effective method for detecting individuals with clinical haemochromatosis. Although many patients with GH may have been missed, this study suggests that the clinical penetrance of the disorder may be much lower than is generally supposed and that genetic screening will identify many people who may never develop clinical haemochromatosis.

Adult↗
PubMed1999

Identification of an essential proximal sequence element in the promoter of the telomerase RNA gene of Tetrahymena thermophila.

Telomerase is a ribonucleoprotein reverse transcriptase that synthesizes and maintains telomeric DNA. Studies of telomeres and telomerase are facilitated by the large number of linear DNA molecules found in ciliated protozoa, such as Tetrahymena thermophila. To examine the expression of telomerase, we investigated the transcription of the RNA polymerase III-directed gene encoding the RNA subunit (TER1) of this enzyme. A chimeric gene containing the Glaucoma chattoni TER1 transcribed region flanked by 5' and 3' Tetrahymena regions was used to identify promoter elements following transformation of Tetrahymena cells. Disruption of a conserved proximal sequence element (PSE) located at -55 in the Tetrahymena TER1 5' flanking region eliminated expression of the chimeric gene. In addition, mutation of an A/T-rich element at -25 decreased expression markedly. A gel mobility shift assay and protein-DNA cross-linking identified a PSE-binding polypeptide of 50-60 kDa in Tetrahymena extracts. Gel filtration analysis revealed a native molecular mass of approximately 160 kDa for this binding activity. Our results point to a similar architecture between ciliate telomerase RNA and metazoan U6 small nuclear RNA promoters.

Animals↗
PubMed1999

Rapid nuclear responses to target-derived neurotrophins require retrograde transport of ligand-receptor complex.

Target-derived neurotrophins initiate signals that begin at nerve terminals and cross long distances to reach the cell bodies and regulate gene expression. Neurotrophin receptors, Trks, themselves serve as retrograde signal carriers. However, it is not yet known whether the retrograde propagation of Trk activation reflects movement of Trk receptors from neurites to cell bodies or reflects serial activation of stationary Trk molecules. Here, we show that neurotrophins selectively applied to distal neurites of sensory neurons rapidly induce phosphorylation of the transcription factor cAMP response element-binding protein (CREB) and also cause a slower increase in Fos protein expression. Both nuclear responses require activation of neurotrophin receptors (Trks) at distal nerve endings and retrograde propagation of Trk activation to the nerve cell bodies. Using photobleach and recovery techniques to follow biologically active, green fluorescent protein (GFP)-tagged BDNF receptors (TrkB-GFP) in live cells during retrograde signaling, we show that TrkB-GFP moves rapidly from neurites to the cell bodies. This rapid movement requires ligand binding, Trk kinase activity, and intact axonal microtubules. When they reach the cell bodies, the activated TrkB receptors are in a complex with ligand. Thus, the retrograde propagation of activated TrkB from neurites to cell bodies, although rapid, reflects microtubule-dependent transport of phosphorylated Trk-ligand complexes. Moreover, the relocation of activated Trk receptors from nerve endings to cell bodies is required for nuclear signaling responses. Together, these data support a model of retrograde signaling whereby rapid vesicular transport of ligand-receptor complex from the neurites to the cell bodies mediates the nuclear responses.

Animals↗
PubMed1999

TrkA glycosylation regulates receptor localization and activity.

The human nerve growth factor receptor (TrkA) contains four potential N-glycosylation sites that are highly conserved within the Trk family of neurotrophin receptors, and nine additional sites that are less well conserved. Using a microscale deglycosylation assay, we show here that both conserved and variable N-glycosylation sites are used during maturation of TrkA. Glycosylation at these sites serves two distinct functions. First, glycosylation is necessary to prevent ligand-independent activation of TrkA. Unglycosylated TrkA core protein is phosphorylated even in the absence of ligand stimulation and displays constitutive kinase activity as well as constitutive interaction with the signaling molecules Shc and PLC-gamma. Second, glycosylation is required to localize TrkA to the cell surface, where it can trigger the Ras/Raf/MAP kinase cascade. Using confocal microscopy, we show that unglycosylated active Trk receptors are trapped intracellularly. Furthermore, the unglycosylated active TrkA receptors are unable to activate kinases in the Ras-MAP kinase pathway, MEK and Erk. Consistent with these biochemical observations, unglycosylated TrkA core protein does not promote neuronal differentiation in Trk PC12 cells even at high levels of constitutive catalytic activity.

Animals↗
PubMed1999

Laser and multipolar electrocoagulation ablation of early Barrett's adenocarcinoma: long-term follow-up.

BACKGROUND: Endoscopic ablation of Barrett's esophagus, including associated dysplasia and adenocarcinoma, can be achieved by various techniques, but few long-term results are available. The aim of our study was ablation of intramucosal adenocarcinoma with a combination of Nd:YAG laser plus multipolar electrocoagulation. METHODS: Patients with documented Barrett's esophagus and adenocarcinoma who either had refused surgery or were poor candidates for surgery because of high risk were offered endoscopic therapy. Patients underwent therapy with Nd:YAG laser and multipolar electrocoagulation. They were treated with omeprazole (20 mg twice daily) as maintenance therapy. RESULTS: Six patients were enrolled in the study over a 7-year period. All were men with a mean age of 78.2 years. The mean length of Barrett's esophagus was 6.0 cm (range, 3 to 10 cm). Seventeen Nd:YAG laser (mean, 2.8/patient) and 20 multipolar electrocoagulation (mean, 3.3/patient) sessions were used during the study period. All patients had a complete initial response to therapy. One patient on chronic immunosuppressive medications had recurrence of the tumor after an initial complete response (36-month follow-up). Two patients have no evidence of Barrett's esophagus, and 3 patients have residual intestinal metaplasia on biopsy of an irregular appearing "neo" Z-line. Mean follow-up in this group is 3.4 years (range, 9 to 86 months). CONCLUSIONS: Laser photocoagulation and multipolar electrocoagulation can be successfully and safely used to ablate intramucosal adenocarcinoma in the setting of Barrett's esophagus. Patients remain functional with normal swallowing.

Adenocarcinoma↗
PubMed1999

Durability of new squamous epithelium after endoscopic reversal of Barrett's esophagus.

BACKGROUND: Endoscopic reversal of Barrett's esophagus with multipolar electrocoagulation and high-dose omeprazole has been previously described but long-term results are not available. The aim of this study was to follow patients after endoscopic reversal and to perform a detailed analysis of the "new" squamous mucosa. METHODS: After reversal, patients with Barrett's esophagus were maintained on high-dose omeprazole and underwent interval endoscopy, and large biopsies were obtained of the former Barrett's epithelium. RESULTS: Nine of 11 patients were men; the mean age was 62 years. The mean length of Barrett's mucosa was 4.4 cm; the mean dose of omeprazole used was 49 mg/day. All patients had an initial complete response to treatment-no evidence of Barrett's endoscopically and histologically. Three patients had intestinal metaplasia underlying the new squamous mucosa in the latest follow-up biopsies. In these 3 patients, only 0.4%, 2%, and 8% of the total biopsy area had intestinal metaplasia. All but 4 patients had underlying intestinal metaplasia at variable times during the study period. Patients have been followed for a mean of 36 months (range 19 to 53 months). CONCLUSIONS: New squamous mucosa is durable and resembles normal squamous tissue. Underlying glands of intestinal metaplasia are intermittently found. Because the significance of this residual intestinal metaplasia is unclear, surveillance endoscopy with biopsies of the treated segment is recommended even after reversal therapy.

Aged↗
PubMed1999

Nonresponding schizophrenia: differentiation by neurological soft signs and neuropsychological tests.

Schizophrenia patients have higher scores on neurological soft-signs (NSS) and show greater deficits on a variety of neuropsychological tests than normal control subjects and mixed groups of psychiatric patients. Among chronic schizophrenia patients it is unclear which of these types of deficits most strongly differentiates patients who remain consistently symptomatic in spite of treatment with several conventional neuroleptics (nonresponders) as compared with relapsing chronic schizophrenia patients who improve substantially with treatment (relative responders). In this study, 25 nonresponders and 20 relative responders to conventional neuroleptics were compared on an NSS battery and a limited number of neuropsychological tests, which evaluated deficits influenced by functioning of frontal and nonfrontal brain areas. NSS scores showed the largest difference between relative responders and nonresponders, and statistical analyses suggested that NSS scores were the strongest differentiator between the two groups of chronic schizophrenia patients. Scores differentiating the two groups involved deficits influenced by both frontal and nonfrontal functioning. A predominance of negative symptoms in the current clinical picture was highly correlated with high NSS scores.

Adult↗