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Biomedical subjects

A Ghosh

Publications and source records attributed to A Ghosh.

At least 145 records · Page 8Linked to original sources
PubMed1999

Regulation of CBP-mediated transcription by neuronal calcium signaling.

The transcription factor CREB is involved in mediating many of the long-term effects of activity-dependent plasticity at glutamatergic synapses. Here, we show that activation of NMDA receptors and voltage-sensitive calcium channels leads to CREB-mediated transcription in cortical neurons via a mechanism regulated by CREB-binding protein (CBP). Recruitment of CBP to the promoter is not sufficient for transactivation, but calcium influx can induce CBP-mediated transcription via two distinct transactivation domains. CBP-mediated transcription is stimulus strength-dependent and can be induced by activation of CaM kinase II, CaM kinase IV, and protein kinase A, but not by activation of the Ras-MAP kinase pathway. These observations indicate that CBP can function as a calcium-sensitive transcriptional coactivator that may act as a regulatory switch for glutamate-induced CREB-mediated transcription.

Animals↗
PubMed1999

Synthesis and biological evaluation of a carbocyclic azanoraristeromycin siderophore conjugate.

Synthesis and biological evaluation of a carbocyclic azanoraristeromycin siderophore conjugate 22 is reported. Coupling of previously prepared L-alanyl-4'-azanoraristeromycin 19 with protected tripeptide trihydroxamate 20, followed by hydrogenolytic removal of all protecting groups, provided the first carbocylic azanoraristeromycin siderophore conjugate (22, 8 with iron). Compounds 19 and 22 showed inhibitory activity against tumor cells, and conjugate 22, in particular, displayed significant activity against those viruses (i.e. reo, parainfluenza, vaccinia, cytomegalo) that are known to be inhibited by S-adenosylhomocysteine hydrolase inhibitors.

Adenosine↗
PubMed1999

Three-centre C-H---O hydrogen bonds in the DNA minor groove: analysis of oligonucleotide crystal structures.

AA.TT and GA.TC dinucleotide steps in B-DNA-type oligomeric crystal structures and in protein-bound DNA fragments (solved using data with resolution <2.6 A) show very small variations in their local dinucleotide geometries. A detailed analysis of these crystal structures reveals that in AA.TT and GA.TC steps the electropositive C2-H2 group of adenine is in very close proximity to the keto O atoms of both the pyrimidine bases in the antiparallel strand of the duplex structure, suggesting the possibility of intra-base pair as well as cross-strand inter-base pair C-H---O hydrogen bonds in the DNA minor groove. The C2--H2---O2 hydrogen bonds in the A.T base pairs could be a natural consequence of Watson-Crick pairing. However, the cross-strand interactions between the bases at the 3'-end of the AA.TT and GA.TC steps obviously arise owing to specific local geometry of these steps, since a majority of the H2---O2 distances in both data sets are considerably shorter than their values in the uniform fibre model (3.3 A) and many are even smaller than the sum of the van der Waals radii. The analysis suggests that in addition to already documented features such as the large propeller twist of A.T base pairs and the hydration of the minor groove, these C2-H---O2 cross-strand interactions may also play a role in the narrowing of the minor groove in A-tract regions of DNA and help explain the high structural rigidity and stability observed for poly(dA).poly(dT).

Base Pairing↗
PubMed1999

Purification and characterization of novel toxin produced by Vibrio cholerae O1.

Vibrio cholerae WO7 (serogroup O1) isolated from patients with diarrhea produces an extracellular toxin despite the absence of ctx, zot, and ace genes from its genome. The toxin elongates Chinese hamster ovary cells, produces fluid accumulation in ligated rabbit ileal loops, and agglutinates freshly isolated rabbit erythrocytes. Maximal production of this toxin (WO7 toxin) was seen in AKI medium with the pH adjusted to 8.5 at 37 degrees C under shaking conditions. We purified this toxin to homogeneity by sequential ammonium sulfate precipitation, affinity chromatography using a fetuin-Sepharose CL-4B column, and gel filtration chromatography, which increased the specific activity of the toxin by 1.6 x 10(6)-fold. The toxin is heat labile and sensitive to proteases and has a subunit structure consisting of two subunits with molecular masses of about 58 and 40 kDa as estimated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Agglutination of GM1-coated sheep erythrocytes by toxin suggests that GM1 might be the physiologic receptor for WO7 toxin on the enterocytes. An immunodiffusion test between the antiserum raised against the purified WO7 toxin and the purified toxin gave a well-defined precipitation band. In the immunoblot assay, two bands were observed in the 58- and 40-kDa region. At the same time, antiserum against WO7 toxin failed to show any cross-reactivity with cholera toxin or Escherichia coli heat-labile toxin (LT1) in an immunodiffusion test or immunoblot assay. The enterotoxic activity of WO7 toxin could be inhibited by antiserum against purified WO7 toxin. Our results indicate that WO7 toxin is structurally and functionally distinct from other cholera toxins and that the enterotoxic activities expressed by WO7 toxin appear to contribute to the pathogenesis of disease associated with V. cholerae O1 strains.

Amino Acid Sequence↗
PubMed1999

Serodiagnosis of leishmaniasis with recombinant ORFF antigen.

The serodiagnostic potential of recombinant ORFF protein (rORFF) from Leishmania infantum was assessed by ELISA. Of 49 sera from confirmed cases of visceral leishmaniasis (VL), all were seropositive using 5 ng of rORFF and serum diluted 1:20, while only 38 were positive with 500 ng of soluble antigen (SA) and 44 were positive by a direct agglutination test. There was also a positive correlation between spleen size and level of seropositivity with rORFF or SA. The reciprocal endpoint titer with rORFF was 1,280 for sera from VL patients, but < 20 with sera from malaria, filariasis, and tuberculosis patients, as well as with sera from healthy individuals from endemic and non-endemic areas. Sera from 10 confirmed cutaneous leishmaniasis cases from Turkey were negative or only weakly positive with rORFF although 9 were positive with SA. Thus, rORFF protein appears useful as a sensitive reagent for the differential diagnosis of VL caused by the Leishmania donovani complex.

Animals↗
PubMed1999

Prenatal diagnosis of congenital heart malformations: classification based on abnormalities detected by the four-chamber view.

The aim of the study was to provide logical steps, alternative to the sequential chamber analysis, for diagnosing major congenital heart malformation prenatally. Between 1988 and 1995, of the 14,885 high-risk pregnancies screened at the Departments of Obstetrics and Paediatric Cardiology, University of Hong Kong, 92 fetuses with major congenital heart malformations were detected at 17-36 weeks' gestation (mean=24.6 weeks) by extended fetal echocardiographic screening. These were classified according to obvious abnormalities related to the partition of the heart or ventricular dimensions depicted by the four-chamber view. Subgrouping according to the presence of normal or abnormal ventriculo-arterial connection, with or without outflow tract anomalies, was further attempted. Five groups were identified: (1) septal defects with all four chambers identified (n=62, 67 per cent); (2) intact septation with dilatation of either the right or all four chambers of the heart (n=12, 13 per cent); (3) intact septation with hypoplasia of either one of the ventricles (n=11, 12 per cent); (4) a rudimentary interventricular septum giving an apparent three-chamber heart (n=6, 7 per cent); (5) miscellaneous causes (n=1, 1 per cent). Combined with the information related to the ventricular outflow tracts, the accuracy of arriving at a definitive diagnosis was 97 per cent, when compared with postnatal investigations, surgery and/or autopsies. This simple classification could provide logical steps to arrive at a definitive diagnosis for most major fetal heart malformations.

Dilatation, Pathologic↗
PubMed1999

Molecular mechanisms underlying activity-dependent regulation of BDNF expression.

Activity-dependent changes in synaptic strength, which appear to underlie cortical plasticity, require long-lasting biochemical changes in the postsynaptic neuron. An inductive event common to several forms of synaptic plasticity is an influx of calcium into the postsynaptic cell. Calcium acts as a second messenger to set into motion a cascade of biochemical signaling events that leads to new gene expression. Brain-derived neurotrophic factor (BDNF) is one such calcium-regulated gene that appears to be involved in activity-dependent cortical plasticity. Studies of the mechanism by which calcium influx induces BDNF expression have revealed that the BDNF promoter is regulated by two calcium response elements. One of the elements appears to be regulated by a novel transcription factor, while the other element is regulated by the previously characterized transcription factor CREB. The calcium signal is propagated to the CREB-mediated component of BDNF expression by CaM kinase IV. This signaling pathway, which links calcium influx to the induction of BDNF via CaM kinase IV and CREB, is likely to be centrally involved in mediating long-term activity-dependent plasticity.

Animals↗
PubMed1999

Effect of catecholamines on bursa of fabricius in chicken.

Effect of catecholamines are studied on the bursa of fabricius of chicken. It is found that in epinephrine (E) treated chicken, the lymph follicles are slightly decreased in size. Some amount of nuclear pycnosis is visible in E and norepinephrine (NE) treated chicken. There is no change in the bursa weight and histology in NE treated groups. No deviation is observed in the level of DNA, RNA, total protein and sialic acid content of catecholamine treated birds.

Animals↗
PubMed1998

Patterning of cortical efferent projections by semaphorin-neuropilin interactions.

Cortical neurons communicate with various cortical and subcortical targets by way of stereotyped axon projections through the white matter. Slice overlay experiments indicate that the initial growth of cortical axons toward the white matter is regulated by a diffusible chemorepulsive signal localized near the marginal zone. Semaphorin III is a major component of this diffusible signal, and cortical neurons transduce this signal by way of the neuropilin-1 receptor. These observations indicate that semaphorin-neuropilin interactions play a critical role in the initial patterning of projections in the developing cortex.

Animals↗
PubMed1998

Production and purification of recombinant 2'-5' oligoadenylate synthetase and its mutants using the baculovirus system.

Investigation of the structure-function relationship of the 2'-5' oligoadenylate [2-5 (A)] synthetases has been hampered by the lack of an efficient expression system for a recombinant enzyme. Here, we report that the 9-2 isozyme of murine 2-5 (A) synthetase can be efficiently expressed in insect cells using the baculovirus system. The recombinant protein was purified to apparent homogeneity, and its enzymatic activity was characterized. It had a high specific activity, required double-stranded RNA as a cofactor, and synthesized dimers to hexamers of 2-5 (A). The utility of our expression system was demonstrated by studying the properties of two previously reported mutant proteins. Both of these mutants, when produced in bacteria, are enzymatically inactive, although similarly produced wild-type protein is active. Unexpectedly, when expressed in insect cells, both mutant proteins were enzymatically as active as the wild-type protein. These results suggest that in the eukaryotic expression system described here, the mutant proteins can undergo appropriate modifications or folding that is required for attaining an enzymatically active conformation.

2',5'-Oligoadenylate Synthetase↗
PubMed1998

Heterogeneity in the organization of the CTX genetic element in strains of Vibrio cholerae O139 Bengal isolated from Calcutta, India and Dhaka, Bangladesh and its possible link to the dissimilar incidence of O139 cholera in the two locales.

After a lapse of 33 months, Vibrio cholerae O139, the new serogroup associated with cholera, has re-emerged in Calcutta, India and has become the dominant serogroup causing cholera from September 1996. In neighbouring Bangladesh, V. cholerae O1 biotype El Tor continues to be the dominant cause of cholera with the O139 serogroup accounting for only a small proportion of cases. Comparison of the phenotypic traits of representative O139 strains from Calcutta and Dhaka isolated between December 1996 and April 1997 showed similar phenotypic traits with the exception that Dhaka O139 strains were susceptible to streptomycin whilst Calcutta O139 strains were resistant. The Dhaka and Calcutta O139 strains displayed identical ribotypes but showed remarkable differences in the structure and organization of the CTX genetic element. In the Dhaka O139 strains, two copies of the CTX element were arranged in tandem and this resembled the pattern displayed by the 1992 epidemic strains of O139. The Calcutta O139 strains, in contrast, carried three copies of the CTX genetic element arranged in tandem with the loss of a conserved BglII restriction site in the RS1 element and the appearance of a new HindIII site in the same region. While there may be other factors, it appears that the reorganization of the CTX genetic element in the Calcutta O139 strains may have contributed to the resurgence of this serogroup in Calcutta.

Anti-Bacterial Agents↗
PubMed1998

Identification of a signaling pathway involved in calcium regulation of BDNF expression.

A signaling pathway by which calcium influx regulates the expression of the major activity-dependent transcript of BDNF in cortical neurons has been elucidated. Deletion and mutational analysis of the promoter upstream of exon III reveals that transactivation of the BDNF gene involves two elements 5' to the mRNA start site. The first element, located between 72 and 47 bp upstream of the mRNA start site, is a novel calcium response element and is required for calcium-dependent BDNF expression in both embryonic and postnatal cortical neurons. The second element, located between 40 and 30 bp upstream of the mRNA start site, matches the consensus sequence of a cAMP response element (CRE) and is required for transactivation of the promoter in postnatal but not embryonic neurons. The CRE-dependent component of the response appears to be mediated by CREB since it is part of the complex that binds to this CRE, and since dominant negative mutants of CREB attenuate transactivation of the promoter. A constitutively active mutant of CaM kinase IV, but not of CaM kinase II, leads to activation of the promoter in the absence of extracellular stimuli, and partially occludes calcium-dependent transactivation. The effects of CaM kinase IV on the promoter require an intact CRE. These mechanisms, which implicate CaM kinase IV and CREB in the control of BDNF expression, are likely to be centrally involved in activity-dependent plasticity during development.

Animals↗
PubMed1998

Rapid spread of the new clone of Vibrio cholerae O1 biotype El Tor in cholera endemic areas in India.

Using molecular techniques, we investigated whether the clone of Vibrio cholerae O1 biotype El Tor which appeared in Calcutta, India, in 1994 has spread to other cholera endemic areas in the country. The ribotype of 31 of the 33 strains isolated from different parts of India during 1996 and 1997 was identical to the ribotype displayed by the new clone of V. cholerae O1 which emerged in Calcutta in 1994. Likewise, 12 of the 15 strains examined by pulsed-field gel electrophoresis (PFGE) showed identical profile to that exhibited by the new clone of O1. The restriction fragment length polymorphism (RFLP) of CTX genetic element of these strains also matched with the new clone of O1 which emerged after the outbreak of V. cholerae 0139 in Calcutta. However, two strains (AH042 and AH046) isolated from an outbreak in Ahmedabad (western India) showed different CTX RFLP but had the same ribotype and PFGE profile as the new clone, whereas one strain from Goa (G2) showed distinct ribotype and PFGE profile and the CTX RFLP was identical to the O1 strains which prevailed before the genesis of 0139 in Calcutta. The drug resistance pattern of most of the O1 strains examined in this study, except strain G2, was similar to that of the new clone of V. cholerae O1. None of the strains in this study carried plasmids. Molecular studies clearly show that the new expanded drug resistant clone of V. cholerae O1 has spread to all cholera endemic areas in India and also provide evidence for the evolution of new clones of the O1 serogroup.

Cholera↗