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S Majumder

Publications and source records attributed to S Majumder.

At least 55 records · Page 3Linked to original sources
PubMed1998

Induction of matrix metalloproteinase-9 requires a polymerized actin cytoskeleton in human malignant glioma cells.

Alterations in cytoskeleton and subsequent cell shape changes exert specific effects on the expression of various genes. Our previous results suggested that malignant human gliomas express elevated levels of matrix metalloproteinases compared with normal brain tissue and low grade gliomas. To understand the role of cell shape changes on matrix metalloproteinase expression in human glioma cells, we treated SNB19 cells with cytochalasin-D, an inhibitor of actin polymerization, and colchicine-B, a tubulin inhibitor, in the presence of phorbol 12-myristate 13-acetate. Cytochalasin-D treatment of SNB19 cells resulted in the loss of phorbol 12-myristate 13-acetate-induced matrix metalloproteinase-9 (also known as gelatinase-B) expression and coincided with inhibition of actin polymerization, resulting in cell rounding. Moreover, compared with monolayers, cells grown as spheroids or cell aggregates failed to express matrix metalloproteinase-9 in the presence of phorbol 12-myristate 13-acetate. Matrix metalloproteinase-9 expression was also inhibited by calphostin-C, a protein kinase inhibitor, suggesting the involvement of protein kinase C in matrix metalloproteinase-9 expression. Phorbol 12-myristate 13-acetate-induced invasion of SNB19 cells through Matrigel was inhibited by cytochalasin-D and calphostin-C. These results suggest that the actin polymerization transduces signals that modulate the expression of matrix metalloproteinase-9 expression and the subsequent invasion of human glioma cells.

Actins↗
PubMed1998

The Trypanosoma cruzi immunosuppressive factor (TIF) targets a lymphocyte activation event subsequent to increased intracellular calcium ion concentration and translocation of protein kinase C but previous to cyclin D2 and cdk4 mRNA accumulation.

Many immunosuppressive effects of Trypanosoma cruzi can be reproduced in vitro by a preparation consisting of molecules spontaneously released by this protozoan (termed trypanosomal immunosuppressive factor (TIF)). In this work, we attempted to establish whether TIF-induced inhibition of lymphoproliferation results from preventing lymphocyte activation or impairing a post-activation process. Although [3H]thymidine uptake and expression of CD25 by normal human T lymphocytes stimulated with a phorbol ester were markedly reduced by T. cruzi or TIF, translocation of cytosolic protein kinase C (PKC) to the cell membrane was not affected. Lymphoproliferation induced by ionomycin was also inhibited by T. cruzi or TIF but the typical elevation of intracellular calcium ions [Ca2+]i caused by this calcium ionophore was not altered. The increase in [Ca2+]i induced with anti-CD3 antibody was also unaffected by TIF. TIF did not preclude lymphocytes stimulated with phytohemagglutinin from accumulating normal mRNA levels of NFAT1 (also known as NFATp) and NFATc. NFAT1 and NFATc are components of the NFAT complex that controls transcription of genes coding for several cytokines and whose translocation to the nucleus is dependent upon PKC activation and increased [Ca2+]i. In contrast, the mRNA levels of cyclin D2 and cdk4, which form a holoenzyme complex known to regulate cell progression through the G1 phase, were markedly reduced by TIF. These results indicated that TIF did not inhibit lymphocyte activation leading to early secondary signaling but curtailed a mechanism controlling cell progression through G1 and necessary for reaching S phase.

Animals↗
PubMed1997

Developmental acquisition of enhancer function requires a unique coactivator activity.

Enhancers are believed to stimulate promoters by relieving chromatin-mediated repression. However, injection of plasmid-encoded genes into mouse oocytes and embryos revealed that enhancers failed to stimulate promoters prior to formation of a two-cell embryo, even though the promoter was repressed in the maternal nucleus of both oocytes and one-cell embryos. The absence of enhancer function was not due to the absence of a required sequence-specific enhancer activation protein, because enhancer function was not elicited even when these proteins either were provided by an expression vector (GAL4:VP16) or were present as an endogenous transcription factor (TEF-1) and shown to be active in stimulating promoters. Instead, enhancer function in vivo required a unique coactivator activity in addition to enhancer-specific DNA binding proteins and promoter repression. This coactivator activity first appeared during mouse development in two- to four-cell embryos, concurrent with the major onset of zygotic gene expression. Competition between various enhancers was observed in these embryos, but not competition between enhancers and promoters, and competition between enhancers was absent in one-cell embryos. Moreover, enhancer function in oocytes could be partially restored by pre-injecting mRNA from cells in which enhancers were active, the same mRNA did not affect enhancer function in two- to four-cell embryos.

Animals↗
PubMed1997

Effect of short-term dermal toxicity of fenvalerate on residue, cell architecture and biochemical profiles in broiler chicks.

Effect of fenvalerate on cell architecture, tissue biochemical parameters and its residual concentration was studied in broiler chicks following dermal application at 0.1 and 1% in ethanol once daily for 31 days. It did neither produce loss of body weight nor clinical signs of toxicity. Kidney contained maximal residue followed by heart, fat, liver and brain after 0.1%; and fat contained maximal residue followed by kidney, heart, liver and brain after 1% application. Fenvalerate (0.1%) increased the aspartate aminotransferase (AST) (except brain), alanine aminotransferase (ALT), alkaline phosphatase (AP), acid phosphatase (AcP) (only brain) activities, glycogen level (only liver) in liver, kidney, heart and brain tissues; and 1% increased the AST (except brain), ALT, AcP (except liver and kidney), AP (only heart), glycogen (only liver) and decreased AP (except heart), AcP (only kidney), cholesterol (except liver and heart), and acetylcholinesterase (AChE) (liver and brain) of liver, kidney, heart and brain tissue homogenates respectively. Histopathological examination in general showed aggregation of mononuclear cells in liver, around the kidney tubules and cardiac muscle fibre. In addition, fibrosis in the periportal area of liver, proliferation of ureter and tubular degeneration, and congestion of endocardial vessels were also observed. The intensity of cellular changes was more marked after 1% dermal application.

Animals↗
PubMed1996

Attempts to characterize the mechanisms involved in the growth inhibition of Mycobacterium microti in interferon-gamma or tumor necrosis factor-alpha activated J774A.1 cells.

The growth of Mycobacterium microti was inhibited within J774A.1 macrophage cells activated with either interferon-gamma or tumor necrosis factor-alpha. Activation with interferon-gamma or tumor necrosis factor-alpha alone did not stimulate the production of nitrite in J774A.1 cells. Interferon-gamma but not tumor necrosis factor-alpha increased the production of hydrogen peroxide in a concentration dependent manner but scavengers of reactive oxygen species did not influence the growth inhibiting effect of interferon-gamma within J774A.1 cells. Both interferon-gamma and tumor necrosis factor-alpha enhanced the fusion of M. microti containing phagosomes with lysosomes and the ultimate degradation of bacteria. Our results showed that growth inhibition of M. microti within interferon-gamma or tumor necrosis factor-alpha stimulated J774A.1 cells was independent of reactive oxygen intermediate and reactive nitrogen intermediate production.

Animals↗
PubMed1996

Mechanisms of Trypanosoma cruzi-induced down-regulation of lymphocyte function. Inhibition of transcription and expression of IL-2 receptor gamma (p64IL-2R) and beta (p70IL-2R) chain molecules in activated normal human lymphocytes.

Acute infection with Trypanosoma cruzi, the agent of Chagas' disease, is accompanied by multiple manifestations of immunosuppression, and this parasite has been shown to inhibit T and B lymphocyte functions in vitro through a mechanism involving impaired membrane expression of at least the p55IL-2R (IL-2R alpha) and p70IL-2R (IL-2R beta) components of the multimeric high affinity IL-2R complex. We document in this paper that addition of T. cruzi or a parasite-conditioned medium (trypanosomal immunosuppressive factor (TIF) to cultures of PHA-stimulated normal human blood lymphocytes markedly decreases the cytoplasmic levels of p64IL-2R and p70IL-2R molecules, i.e., the two IL-2R chains that bind IL-2 and participate in signal transduction. These effects highlighted the ability of T. cruzi to curtail biosynthesis of these IL-2R chains and weakened the possibility that decreased membrane IL-2R expression results exclusively from altered chain transportation to the lymphocyte surface. Additional support for impaired lymphocyte production of IL-2R components was derived from northern blot analyses demonstrating TIF-induced decreases in p64IL-2R and p70IL-2R mRNA levels. These reductions are unlikely to be due to conditions affecting mRNA stability, since the rates of decay of both mRNA species were nearly identical in the presence and in the absence of TIF. In addition, nuclear run-on studies revealed that transcription of the p64IL-2R, p70IL-2R, and p55IL-2R genes, but not that of the CD69 gene, was below normal levels in PHA-stimulated lymphocytes incubated with TIF. These results suggest that altered gene transcription is involved in the mechanism by which T. cruzi down-regulates the expression of all the known components of the high affinity IL-2R.

Animals↗
PubMed1996

The disposition kinetics and residues of fenvalerate in tissues following a single dermal application to black Bengal goats.

The disposition kinetics of fenvalerate were studied in goats after dermal application of 100 ml of 0.25% (w/v) solution. The insecticide persisted in the blood for 72 h. The mean (+/- SEM) Vd(area) and apparent t 1/2 (beta) were 9.92 +/- 1.44 L/kg and 17.51 +/- 2.65 h, while the AUC and ClB values were respectively 82.15 +/- 7.40 micrograms h/ml and 0.56 +/- 0.05 L/(kg h). Four days after the dermal application, the highest concentration of fenvalerate residues was found in the adrenal gland, followed by the biceps muscle, omental fat, liver, kidney, lung and cerebrum in that order. Fenvalerate caused hyperglycaemia but had no effect on serum protein and cholesterol levels. Serum acetylcholinesterase activities were increased after 24 h but were below the initial values from 48 to 120 h.

Acetylcholinesterase↗
PubMed1995

Regulation of gene expression at the beginning of mammalian development.

The maternal to zygotic transition can be viewed as a cascade of events that begins when fertilization triggers the zygotic clock that delays early ZGA until formation of a 2-cell embryo. Early ZGA, in turn, appears to be required for expression of late ZGA, and late ZGA is required to form a 4-cell embryo. ZGA in mammals is a time-dependent mechanism rather than a cell cycle-dependent mechanism that delays both transcription and translation of nascent transcripts. Thus, zygotic gene transcripts appear to be handled differently than maternal mRNA, a phenomenon also observed in Xenopus (55). The length of this delay is species-dependent, occurring at the 2-cell stage in mice, the 4-8-cell stage in cows and humans, and the 8-16-cell stage in sheep and rabbits (4). However, concurrent with formation of a 2-cell embryo in the mouse and rabbit (47,56), perhaps in all mammals, a general chromatin-mediated repression of promoter activity appears. Repression factors are inherited by the maternal pronucleus from the oocyte but are absent in the paternal pronucleus and not available until sometime during the transition from a late 1-cell to a 2-cell embryo. This means that paternally inherited genes are exposed to a different environment in fertilized eggs than are maternally inherited genes, a situation that could contribute to genomic imprinting. Chromatin-mediated repression of promoter activity prior to ZGA is similar to what is observed during Xenopus embryogenesis (31,32) and ensures that genes are not expressed until the appropriate time in development when positive acting factors, such as enhancers, can relieve this repression. The ability to use enhancers appears to depend on the acquisition of specific co-activators at the 2-cell stage in mice and perhaps later in other mammals (47,56), concurrent with ZGA. Even then, the mechanism by which enhancers communicate with promoters changes during development (Fig. 2), providing an opportunity for enhancer-mediated stimulating of TATA-less promoters (e.g. housekeeping genes) early during development while eliminating this mechanism later during development.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1995

A unique role for enhancers is revealed during early mouse development.

Transcription and replication of genes in mammalian cells always requires a promoter or replication origin, respectively, but the ability of enhancers to stimulate these regulatory elements and the interactions that mediate this stimulation are developmentally acquired. The primary function of enhancers is to prevent repression, which appears to result from particular components of chromatin structure. Factors responsible for this repression are present in the maternal nucleus of oocytes and its descendant, the maternal pronucleus of mouse 1-cell embryos and in mouse 2-cell embryos, but are absent in the paternal pronucleus. Thus, enhancers are not needed to achieve efficient transcription and replication in paternal pronuclei. However, enhancers, even in the presence of their specific activation protein, are inactive prior to formation of a 2-cell embryo, suggesting that a coactivator essential for enhancer function is not available until zygotic gene expression begins. Furthermore, enhancer stimulation of transcription appears to be mediated through a promoter transcription factor, but this interaction can change as cells undergo differentiation, switching from a TATA-box independent to a TATA-box dependent mode.

Animals↗
PubMed1995

Differential effects of Trypanosoma cruzi on the transcription of the p55IL-2R, c-fos, c-myc and CD69 genes in activated human lymphocytes.

Mitogen-activated lymphocytes co-cultured with either purified Trypanosoma cruzi trypomastigotes or the filtrate of trypomastigote suspensions in culture medium manifest a significant decrease in their capacities to express p55 interleukin-2 receptor molecules (p55IL-2R) on their membrane and proliferate. In this study we found that the cytoplasmic levels of p55IL-2R are also markedly reduced under these conditions. This inhibition appeared to result from altered gene transcription since the levels of p55IL-2R mRNA in phytohaemagglutinin (PHA)-stimulated human peripheral blood mononuclear cells (PBMC) dropped substantially in the presence of parasite suspension filtrate. The rates of decay for p55IL-2R mRNA determined in cultures lacking and containing the parasite filtrate after addition of actinomycin D to inhibit further RNA synthesis were comparable. These results indicated that decreased p55IL-2R mRNA was not due to decreased stability of this mRNA under our conditions and pointed to a transcriptional or pre-transcriptional modification as the likely mechanism by which T. cruzi affects activated lymphocytes. The parasite filtrate did not appear to affect transcription of c-fos or c-myc (known to occur in the very early stages of lymphocyte activation) or that of CD69 (which is concomitant with p55IL-2R transcription). Thus, decreased p55IL-2R gene transcription appears to be a somewhat selective effect of a T. cruzi-derived molecule(s) rather than the consequence of an overall shutdown of gene transcription.

Animals↗
PubMed1995

Trypanosoma cruzi immunosuppressive factor decreases the interleukin-2 mRNA level in cultured normal activated human lymphocytes.

We show here that the marked inhibition of interleukin-2 production seen in hosts acutely infected with Trypanosoma cruzi can be reproduced in vitro by adding a T. cruzi suspension filtrate to cultures of activated human peripheral blood mononuclear cells. This effect was not due to an accelerated decay of interleukin-2 mRNA and appeared to be selective since the levels of other mRNA molecules relevant to lymphocyte activation were not noticeably decreased. The use of normal lymphoid cells in this in vitro system makes it possible to examine the mechanisms used by T. cruzi to induce abnormalities in lymphocyte functions that also occur in infected hosts.

Animals↗
PubMed1995

Jaundice in new born and erythrocyte and plasma antioxidant defence system.

Alteration in the antioxidant defence mechanism of erythrocytes with rise in serum unconjugated bilirubin level in neonates has been observed. The cellular glutathione level was found to be significantly low. The activity of glutathione reductase in erythrocyte increased to combat the cellular loss of reduced glutathione in neonatal jaundice. In plasma fraction the level of glutathione (reduced) was found to be significantly higher with lowering of glutathione reductase level. Glutathione peroxidase was reduced in cellular level whereas an increase was observed in plasma fraction. Gamma glutamyl transpeptidase level was barely detectable in erythrocyte whereas an increase was observed in plasma fraction. In all the cases erythrocyte G-6-PDH activity level was found within normal limits.

Antioxidants↗
PubMed1995

Regulatory effect of the level of free Ca2+ of the host cell on the capacity of Trypanosoma cruzi to invade and multiply intracellularly.

We studied whether modification of the free intracellular Ca2+ level of a mammalian host cell would affect its susceptibility to infection by Trypanosoma cruzi or its capacity to support trypomastigote-->amastigote transformation and amastigote replication. Pretreatment of rat heart myoblasts (RHM) with BAPTA.AM or Quin-2.AM, intracellular Ca2+ chelators, decreased the susceptibility of these cells to infection by untreated trypomastigotes. This was evidenced by a significant drop in both the percentage of infected RHM and the average number of organisms per 100 host cells relative to control values. Similar RHM treatment with the Ca2+ ionophore ionomycin had the opposite effects. The rate of trypomastigote-->amastigote transformation measured in RHM that had been treated with BAPTA.AM, Quin-2.AM, or ionomycin before and after, but not during co-culture with trypomastigotes was not significantly altered. The rate of intracellular amastigote multiplication measured in RHM exposed to the intracellular Ca2+ chelators only after virtually all of the internalized trypomastigotes had transformed into amastigotes was significantly decreased by incubation with BAPTA.AM or Quin-2.AM but was increased by ionomycin. None of the drug treatments affected RHM viability to any significant extent. These results suggest that T. cruzi relies on host cell Ca(2+)-dependent events, utilizes host cell free Ca2+ during invasion, or both, and highlight a requirement for an adequate free Ca2+ level for effective intracellular T. cruzi multiplication but not for trypomastigote-->amastigote transformation.

Aminoquinolines↗
PubMed1994

Effect of interleukin-1 alpha on the growth of Mycobacterium microti within J774A.1 cells.

The effect of mouse recombinant interleukin-1 alpha on the intracellular growth of Mycobacterium microti in a murine macrophage cell line J774A.1 was investigated. Interleukin-1 alpha added after infection to the M. microti-infected macrophage monolayers enhanced the growth of M. microti in a concentration-dependent manner and this growth enhancement was abrogated by neutralization of interleukin-1 alpha with anti-interleukin-1 alpha antibody. Cyclic adenosine monophosphate level in J774A.1 cells was increased by the addition of interleukin-1 alpha. Addition of dibutyryl cyclic adenosine monophosphate to infected J774A.1 cells increased the number of intracellular bacteria in a concentration-dependent manner. These results suggest that interleukin-1 alpha acts as a growth enhancer for intracellular M. microti and the growth enhancing effect of interleukin-1 alpha may be due to enhanced cellular cyclic adenosine monophosphate level.

Animals↗
PubMed1994

Sequence-independent induction of Sp1 transcription factor activity by phosphorothioate oligodeoxynucleotides.

Modified analogues of antisense oligodeoxynucleotides (ODNs), particularly phosphorothioates ([S]ODNs), have been extensively used to inhibit gene expression. The potential sequence specificity of antisense oligomers makes them attractive as molecular drugs for human diseases. The use of antisense [S]ODNs to inhibit gene expression has been complicated by frequent nonspecific effects. In this study we show in diverse cell types that [S]ODNs, independent of their base sequence, mediated the induction of an Sp1 nuclear transcription factor. The [S]ODN-mediated Sp1 induction was rapid and was associated with elevated levels of Sp1 protein. This induction was dependent on NF-kappa B activity, since inhibition of NF-kappa B activity abolished the [S]ODN-induced Sp1 activity. [S]ODN-induced Sp1 activity was seen in mouse spleen cells following in vivo administration. Sp1 activity induced by [S]ODNs required the tyrosine kinase pathway and did not have transactivating potential. These results may help to explain some of the non-specific effects often seen with [S]ODNs.

Animals↗