Papers by Tapas Kumar Sengupta
Dalton Transactions, 2013
Three Cu II complexes of bis-pyrazole based ligands have been synthesized and structurally charac... more Three Cu II complexes of bis-pyrazole based ligands have been synthesized and structurally characterized by X-ray crystallography. One of the ligand (L2) contains a methionine ester conjugated to a bis-pyrazole carboxylate through an amide linkage. The binding constant for complexes 1-3 with CT DNA are of the order of 10 4 M -1 . The crystal structure suggests that the axial Cu-O bonds (ca. 2.31(4) Å) are relatively labile and hence during the redox cycle with ascorbic acid and oxygen one or both the axial Cu-O bonds might open to promote copper oxygen reaction and generate ROS. The chemical nuclease activity of complexes 1-3 in dark, show complete relaxation of supercoiled DNA at 100 μM concentration in presence of ascorbic acid (H 2 A). The mechanistic investigation suggests that the complexes 1 and 2 show involvement of peroxo species whereas 3 shows involvement of both singlet oxygen and peroxo species in DNA cleavage. The singlet oxygen formation in dark is otherwise unfavourable but the presence of methionine as pendant arm in L2 might activate the generation of singlet oxygen from the metal generated peroxo species. The results of DNA cleavage studies suggest that methionine based copper(II) complexes can promote dual pathway for DNA cleavage. Probing the cytotoxic activity of these complexes on MCF-7, human breast cancer cell line shows that 3 is the most effective one with an IC 50 of 70(2) μM.
Royal Society Open Science, Nov 1, 2016
Interspecific competition in bacteria governs colony growth dynamics and pattern formation. Here,... more Interspecific competition in bacteria governs colony growth dynamics and pattern formation. Here, we demonstrate an interesting phenomenon of interspecific competition between Bacillus cereus MSM-S1 and Pseudomonas sp. MSM-M1, where secretion of an inhibitor by Pseudomonas sp. is used as a strategy for survival. Although B. cereus grows faster than Pseudomonas sp., in the presence of Pseudomonas sp. the population of B. cereus reduces significantly, whereas Pseudomonas sp. do not show any marked alteration in their population growth. Appearance of a zone of inhibition between growing colonies of two species on nutrient agar prevents the expanding front of the MSM-S1 colony from accessing and depleting nutrients in the region occupied by MSM-M1, thereby aiding the survival of the slower growing MSM-M1 colonies. To support our experimental results, we present simulations, based on a chemotactic model of colony growth dynamics. We demonstrate that the chemical(s) secreted by Pseudomonas sp. is responsible for the observed inhibition of growth and spatial pattern of the B. cereus MSM-S1 colony. Our experimental results are in excellent agreement with the numerical results and confirm that secreted inhibitors enable Pseudomonas sp. to survive and coexist in the presence of faster growing B. cereus, in a common niche.
Role of Histone Methyltransferases during Regeneration of Hydra
Hydra, a freshwater polyp of the phylum Cnidaria, has an immense ability to regenerate lost body ... more Hydra, a freshwater polyp of the phylum Cnidaria, has an immense ability to regenerate lost body parts by reorganizing the available tissue without involving cellular proliferation by a process known as morphallaxis. Evoking gene regulatory networks at precise time points is essential to achieve this feat. Epigenetic regulators presumably play the key role in fine-tuning these transcriptional changes by modulating the chromatin topography. However, the role of epigenetic modifiers in shaping the regeneration process in Hydra remains an open question. In this study, we attempted to characterize a number of histone methyltransferases from Hydra and investigated their role during regeneration. Preliminary screening performed using specific pharmacological inhibitors indicated a role of SETD8, an enzyme responsible for deposition of H4K20me1, during Hydra regeneration. Our work demonstrates a significant delay in the tentacle bud emergence and impairment of foot regeneration upon treati...
Drug-induced destabilization of bcl-2 mRNA: a new approach for inducing apoptosis in tumor cells
Current opinion in investigational drugs (London, England : 2000), 2004
Recent evidence suggests that the 3' untranslated region (3' UTR) of some mRNAs is a mole... more Recent evidence suggests that the 3' untranslated region (3' UTR) of some mRNAs is a molecular hotspot for pathology. The 3' UTR of bcl-2 mRNA contains several AU-rich elements (AREs) that promote mRNA destabilization. Recent studies have demonstrated that the protein, nucleolin, binds to an ARE in bcl-2 mRNA, thereby protecting this mRNA from nuclease degradation. All-trans retinoic acid, taxol and okadiac acid induce downregulation or inactivation of nucleolin, which destabilizes bcl-2 mRNA and triggers apoptosis. The ARE instability elements in bcl-2 mRNA are potential therapeutic targets for inducing apoptosis and overcoming drug resistance in cancer cells.
SPIE Proceedings, 2013
Internet Lecture bioNaP (www.iiserkol.ac.in/~nghosh) Saratov Fall Meeting, 2012 Internet Lecture ... more Internet Lecture bioNaP (www.iiserkol.ac.in/~nghosh) Saratov Fall Meeting, 2012 Internet Lecture 1 / 17 Challenges New approaches Need of polarimetry Fractal patterns in bacterial colonies Mueller matrix polarimetry Results Concluding remarks bioNaP (www.iiserkol.ac.in/~nghosh) Saratov Fall Meeting, 2012 Internet Lecture 2 / 17
Molecular Pharmacology, 2005
All-trans retinoic acid (ATRA) induces differentiation of promyelocytic leukemia cells, but the m... more All-trans retinoic acid (ATRA) induces differentiation of promyelocytic leukemia cells, but the mechanisms by which cellular differentiation leads to apoptosis are not well understood. Studies were done to address the question whether ATRA-induced apoptosis is a consequence of destabilization of bcl-2 mRNA and decreased cellular levels of the anti-apoptotic protein, bcl-2. ATRA induced differentiation of HL-60 cells along the granulocytic pathway within 48 hr. The halflives of bcl-2 mRNA in HL-60 cells incubated with ATRA for 48 hr or 72 hr were reduced to 39 % and 7 % of the corresponding untreated control values, respectively. Cellular differentiation was accompanied by downregulation of the cytoplasmic levels of nucleolin, a bcl-2 mRNA stabilizing protein. Binding of a bcl-2 mRNA instability element (ARE-1) to nucleolin in S100 extracts from ATRA-treated cells was decreased to 15 % of control within 72 hr. The decay of 5' capped, polyadenylated bcl-2 mRNA transcripts containing ARE-1 was more rapid in S100 extracts from ATRA-treated cells compared to untreated cells. However, when recombinant nucleolin was added to extracts of ATRA-treated cells, the rate of bcl-2 mRNA decay was similar to the rate in extracts of untreated cells . These results provide evidence that ATRA-induced apoptosis is a consequence of cellular differentiation, which leads to nucleolin downregulation and bcl-2 mRNA instability.
Molecular Cancer Research, 2009
Overexpression of the proto-oncogene bcl-2 promotes abnormal cell survival by inhibiting apoptosi... more Overexpression of the proto-oncogene bcl-2 promotes abnormal cell survival by inhibiting apoptosis. Expression of bcl-2 is determined, in part, by regulatory mechanisms that control the stability of bcl-2 mRNA. Elements in the 3′-untranslated region of bcl-2 mRNA have been shown to play a role in regulating the stability of the message. Previously, it was found that the RNA binding proteins nucleolin and Ebp1 have a role in stabilizing bcl-2 mRNA in HL60 cells. Here, we have identified HuR as a component of bcl-2 messenger ribonucleoprotein (mRNP) complexes. RNA coimmunoprecipitation assays showed that HuR binds to bcl-2 mRNA in vivo. We also observed an RNA-dependent coprecipitation of HuR and nucleolin, suggesting that the two proteins are present in common mRNP complexes. Moreover, nucleolin and HuR bind concurrently to bcl-2 AU-rich element (ARE) RNA in vitro, suggesting separate binding sites for these proteins on bcl-2 mRNA. Knockdown of HuR in A431 cells leads to down-regulat...
Journal of Medical Microbiology, 1995
Vibrio cholerae 0139 organisms isolated from different parts of India and from Bangladesh were ch... more Vibrio cholerae 0139 organisms isolated from different parts of India and from Bangladesh were characterised with respect to their haemagglutination (HA) activity, plasmid content, cholera toxin (CT) production, cell surface protein and lipopolysaccharide (LPS) profiles, and antigenic properties. Of 28 V. cholerae 0139 isolates tested, 14 (50 YO) were shown to agglutinate chicken erythrocytes; the HA activity was sensitive to D-mannose 0.1 %. In parallel experiments, 12 (92.3%) of 13 V. cholerae 0 1 (El Tor) and 12 (75%) of 16 non-0 1, non-0 139 strains agglutinated chicken erythrocytes. Plasmid analysis of 32 0 139 isolates showed that 12 (37.5%) carried one or more plasmids of 35-8-2.6 MDa. Plasmids were not detected in any of the V. cholerae 0 1 strains, although plasmids were demonstrable in 35% of the non-01, non-0139 strains tested. V. cholerae 0139 isolates showed an ability to produce CT that depended on media composition and other cultural conditions. A comparison of envelope and outer-membrane protein profiles between 0 1 and 0 139 isolates failed to show any significant differences. LPS analysis of 0139 isolates revealed that these organisms were devoid of long " 0 " side-chain polysaccharides. Some of the non-0 1, non-0139 strains also showed similar LPS profiles whereas others showed the presence of long repetitive " 0 " side-chain polysaccharides similar to those seen in 0 1 organisms. An antiserum raised against V. cholerae 0 1 strain 0395 did not show any significant reactivity towards 0139 and non-01, non-0139 strains although it reacted with other 0 1 strains. Furthermore, the anti-01 serum induced marked protection against challenge with an 0 1 strain but not with an 0 139 strain in passive protection experiments. All these results indicate that, despite sharing some common properties with V. cholerae 01, the 0139 isolates posses certain characteristics that make them distinct from their 0 1 counterparts.
FEMS Microbiology Letters, 1998
A diarrheogenic strain of non-O1/non-O139 Vibrio cholerae (10325) belonging to serogroup O34 was ... more A diarrheogenic strain of non-O1/non-O139 Vibrio cholerae (10325) belonging to serogroup O34 was earlier shown to express a new type of pilus composed of a 20-kDa subunit protein. Amino-terminal sequence data (determined up to 20 amino acid residues) of this protein showed it to be different from the subunit proteins of other known types of pili of V. cholerae. On the other hand, it showed complete homology with the corresponding sequence of a 22-kDa outer membrane protein (OmpW) of V. cholerae. Expression of 10325 pili was favored in AKI rather than in NB medium and at 30³C rather than at 37³C. Further, cultural conditions favoring pilus expression also enhanced autoagglutination and adherence properties of strain 10325. An antiserum to the 20-kDa protein induced passive protection against challenge with the parent organism 10325, but not against V. cholerae O1 strains. Such protection was shown to be mediated by inhibition of intestinal colonization in vivo.
FEMS Microbiology Letters, 1993
A clinical isolate of non-01 V. cholerae (10325) was shown to exhibit higher haemagglutination an... more A clinical isolate of non-01 V. cholerae (10325) was shown to exhibit higher haemagglutination and intestinal adherence activities in vitro when grown in enriched media, such as trypticase soy broth (TSB) as compared to those of cells grown in a synthetic Tris-buffered or 'T'-medium. A comparison of their cell-surface protein and lipopolysaccharide profiles suggested the involvement of a 20-kDa protein in the cellular adherence process. An antiserum, raised specifically against the 20-kDa protein, recognised pilus structures on the surface of TSB grown cells, Further studies showed that the pilus was morphologically as well as antigenically distinct from toxin coregulated pilus (TCP) or other types of pili expressed by both 01 and non-01 organisms. Inhibition data established the involvement of the 20-kDa protein in haemagglutination as well as intestinal tissue adherence activities of the parent organism.
FEMS Microbiology Letters, 1994
Vibrio cholerae belonging to the recently described serogroup 0139, which are responsible for the... more Vibrio cholerae belonging to the recently described serogroup 0139, which are responsible for the current cholera epidemics in India and Bangladesh, were shown to express pilus-like structures partially cross-reacting with the toxin-coregulated pilus of V. cholerae strain (0395) belonging to the 01 serogroup and classical biotype. The 0139 pili were composed of 20 kDa subunit proteins which were antigenically related to the 20 kDa pilus protein of another diarrhoeagenic non-01 V. cholerae strain (serogroup 034) isolated earlier. The pili described in this study were found to be involved in the intestinal colonization process and, therefore, may contribute towards the virulence of the 0139 epidemic isolates.
Journal of Biological Chemistry, 2010
The antiapoptotic Bcl-2 protein is overexpressed in a variety of cancers, particularly leukemias.... more The antiapoptotic Bcl-2 protein is overexpressed in a variety of cancers, particularly leukemias. In some cell types this is the result of enhanced stability of bcl-2 mRNA, which is controlled by elements in its 3-untranslated region. Nucleolin is one of the proteins that binds to bcl-2 mRNA, thereby increasing its halflife. Here, we examined the site on the bcl-2 3-untranslated region that is bound by nucleolin as well as the protein binding domains important for bcl-2 mRNA recognition. RNase footprinting and RNA fragment binding assays demonstrated that nucleolin binds to a 40-nucleotide region at the 5 end of the 136-nucleotide bcl-2 AU-rich element (ARE bcl-2 ). The first two RNA binding domains of nucleolin were sufficient for high affinity binding to ARE bcl-2 . In RNA decay assays, ARE bcl-2 transcripts were protected from exosomal decay by the addition of nucleolin. AUF1 has been shown to recruit the exosome to mRNAs. When MV-4-11 cell extracts were immunodepleted of AUF1, the rate of decay of ARE bcl-2 transcripts was reduced, indicating that nucleolin and AUF1 have opposing roles in bcl-2 mRNA turnover. When the function of nucleolin in MV-4-11 cells was impaired by treatment with the nucleolin-targeting aptamer AS1411, association of AUF1 with bcl-2 mRNA was increased. This suggests that the degradation of bcl-2 mRNA induced by AS1411 results from both interference with nucleolin protection of bcl-2 mRNA and recruitment of the exosome by AUF1. Based on our findings, we propose a model that illustrates the opposing roles of nucleolin and AUF1 in regulating bcl-2 mRNA stability.
Nucleic Acids Research, 2001
The RegA proteins from the bacteriophage T4 and RB69 are translational repressors that control th... more The RegA proteins from the bacteriophage T4 and RB69 are translational repressors that control the expression of multiple phage mRNAs. RegA proteins from the two phages share 78% sequence identity; however, in vivo expression studies have suggested that the RB69 RegA protein binds target RNAs with a higher affinity than T4 RegA protein. To study the RNA binding properties of T4 and RB69 RegA proteins more directly, the binding sites of RB69 RegA protein on synthetic RNAs corresponding to the translation initiation region of two RB69 target genes were mapped by RNase protection assays. These assays revealed that RB69 RegA protein protects nucleotides-9 to-3 (relative to the start codon) on RB69 gene 44, which contains the sequence GAAAAUU. On RB69 gene 45, the protected site (nucleotides-8 to-3) contains a similar purine-rich sequence: GAAAUA. Interestingly, T4 RegA protein protected the same nucleotides on these RNAs. To examine the specificity of RNA binding, quantitative RNA gel shift assays were performed with synthetic RNAs corresponding to recognition elements (REs) in three T4 and three RB69 mRNAs. Comparative gel shift assays demonstrated that RB69 RegA protein has an ∼7-fold higher affinity for T4 gene 44 RE RNA than T4 RegA protein. RB69 RegA protein also binds RB69 gene 44 RE RNA with a 4-fold higher affinity than T4 RegA protein. On the other hand, T4 RegA exhibited a higher affinity than RB69 RegA protein for RB69 gene 45 RE RNA. With respect to their affinities for cognate RNAs, both RegA proteins exhibited the following hierarchy of affinities: gene 44 > gene 45 > regA. Interestingly, T4 RegA exhibited the highest affinity towards RB69 gene 45 RE RNA, whereas RB69 RegA protein had the highest affinity for T4 gene 44 RE RNA. The helixloop groove RNA binding motif of T4 RegA protein is fully conserved in RB69 RegA protein. However, homology modeling of the structure of RB69 RegA protein reveals that the divergent residues are clustered in two areas of the surface, and that there are two large areas of high conservation near the helix-loop groove, which may also play a role in RNA binding.
Journal of Biological Chemistry, 1999
The T4 translational repressor RegA protein folds into two structural domains, as revealed by the... more The T4 translational repressor RegA protein folds into two structural domains, as revealed by the crystal structure (Kang, C.-H.,
Journal of Biological Chemistry, 2003
bcl-2 mRNA contains an AU-rich element (ARE) that functions in regulating bcl-2 stability. Our ea... more bcl-2 mRNA contains an AU-rich element (ARE) that functions in regulating bcl-2 stability. Our earlier studies indicated that taxol-or okadaic acid-induced bcl-2 mRNA destabilization in HL-60 cells is associated with decreased binding of transacting factors to the ARE. To identify factors that play a role in the regulation of bcl-2 mRNA stability, bcl-2 ARE-binding proteins were purified from HL-60 cells. Three polypeptides of 100, 70, and 32 kDa were isolated from a bcl-2 ARE affinity matrix. Matrix-assisted laser desorption ionization mass spectroscopy analysis identified these proteins as full-length nucleolin and proteolytic fragments of nucleolin. RNA gel shifts assays indicated that recombinant nucleolin (residues 284-707) binds specifically to bcl-2 ARE RNA. In addition, recombinant nucleolin decreases the rate of decay of mRNA in HL-60 cell extracts in an ARE-dependent manner. Taxol or okadaic acid treatment of HL-60 cells results in proteolysis of nucleolin in a similar time frame as drug-induced bcl-2 mRNA down-regulation. These findings suggest that nucleolin functions as a bcl-2-stabilizing factor and that taxol and okadaic acid treatment induces apoptosis in HL-60 cells through a process that involves down-regulation of nucleolin and destabilization of bcl-2 mRNA.
FEMS Microbiology Letters, 1992
An antiserum was raised against the outer membrane (OM) preparation of a Vibrio cholerae 01 strai... more An antiserum was raised against the outer membrane (OM) preparation of a Vibrio cholerae 01 strain (Classical, Ogawa) and rendered specific for the outer membrane proteins (OMPs) by absorption with its lipopotysaccharide (LPS). The anti-OMP serum showed reactivity against OM preparations of other 01 and non-01 V. cholerae strains in enzyme-linked immunosorbent assay. The antiserum also induced significant protection against V. cholerae challenge in the suckling mouse model. This protection was found to be independent of biotype, serotype as well as serovar of the challenge organism and was demonstrable even at subagglutinating dilutions of antiserum. The Fab (IgG) fragment, prepared from the anti-OMP serum, also induced passive protection in similar experiments, Further studies demonstrated that the anti-OMP serum as well as its Fab (IgG) fragment markedly inhibited the intestinal colonization of a highly colonizing V.
Blood, 2006
B-cell chronic lymphocytic leukemia (CLL) is characterized by the accumulation of clonal B cells ... more B-cell chronic lymphocytic leukemia (CLL) is characterized by the accumulation of clonal B cells that are resistant to apoptosis as a result of bcl2 oncogene overexpression. Studies were done to determine the mechanism for the up-regulation of bcl-2 protein observed in CD19+ CLL cells compared with CD19+ B cells from healthy volunteers. The 11-fold higher level of bcl-2 protein in CLL cells was positively correlated with a 26-fold elevation in the cytosolic level of nucleolin, a bcl2 mRNA–stabilizing protein. Measurements of the bcl2 heterogeneous nuclear/bcl2 mRNA (hnRNA)/mRNA ratios and the rates of bcl2 mRNA decay in cell extracts indicated that the 3-fold higher steady-state level of bcl2 mRNA in CLL cells was the result of increased bcl2 mRNA stability. Nucleolin was present throughout the nucleus and cytoplasm of CLL cells, whereas in normal B cells nucleolin was only detected in the nucleus. The addition of recombinant human nucleolin to extracts of normal B cells markedly sl...
Biochemical Journal, 2006
The 3′-UTR (untranslated region) of bcl-2 mRNA contains an ARE (AU-rich element) that potentially... more The 3′-UTR (untranslated region) of bcl-2 mRNA contains an ARE (AU-rich element) that potentially regulates the stability of bcl-2 mRNA in a cell specific fashion. Previous studies have demonstrated that multiple proteins interact with bcl-2 mRNA in HL-60 (human leukaemia-60) cells, potentially contributing to the overexpression of Bcl-2 protein. Treatment of HL-60 cells with taxol or okadaic acid has been shown to induce destabilization of bcl-2 mRNA, which was associated with decreased binding of trans-acting factors to bcl-2 mRNA. Nucleolin has been identified as one of the bcl-2 mRNA-binding proteins [Sengupta, Bandyopadhyay, Fernandes and Spicer (2004) J. Biol. Chem. 279, 10855–10863]. In an effort to identify additional bcl-2 mRNA-binding proteins, two polypeptides of approx. 45 kDa and 60 kDa were isolated from HL-60 cells by AREbcl-2 (transcripts that contain bcl-2 AREs) RNA affinity chromatography. These proteins were identified as the human proliferation associated protein...
Biochemical Journal, 2008
OSM (oncostatin M) is a pleiotropic cytokine belonging to the IL (interleukin) 6 family that modu... more OSM (oncostatin M) is a pleiotropic cytokine belonging to the IL (interleukin) 6 family that modulates the growth of some cancer cell lines. We have found that PMA treatment of human U937 lymphoma cells increased the steady-state levels of OSM mRNA. Furthermore, the half-life of OSM mRNA was increased from 2.3 to 6.2 h. Measurement of mRNA/hnRNA (heterogeneous nuclear RNA) ratios in PMA-treated cells suggests further that the increase in OSM mRNA is due to enhanced mRNA stability. Consistent with this, synthetic OSM mRNA transcripts decayed faster in extracts of untreated U937 cells than in extracts of PMA-treated cells. The 3′-untranslated region of OSM mRNA contains a putative ARE (AU-rich element) that may play a role in mRNA stabilization. Addition of the OSM ARE motif to the 3′-end of β-globin mRNA increased its decay rate in vitro. Decay assays with β-globin–AREOSM and β-globin transcripts indicate that PMA induces mRNA stabilization in an ARE-dependent manner. PMA also induce...
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Papers by Tapas Kumar Sengupta