PubMed Health⌕ Search

Biomedical subjects

G Adhikary

Publications and source records attributed to G Adhikary.

14 recordsLinked to original sources
PubMed2000

Intracellular pathways linking hypoxia to activation of c-fos and AP-1.

Organisms respond to hypoxia through detection of blood oxygen levels by sensors at peripheral chemoreceptors and by receptors in certain key cells of the body. The pathways over which peripheral chemoreceptor signals are transmitted to respiratory muscles are well established. However, the intracellular pathways that transmit hypoxic stimulus to gene activation are just being identified. Using anti-sense c-fos strategy, we have shown that c-fos is essential for the activation of activator protein-1 transcription factor complex (AP-1) and subsequent stimulation of downstream genes such as tyrosine hydroxylase (TH; Mishra et al. 1998). The purpose of the present study was to identify intracellular pathways that link hypoxia to activation of c-fos. The results of the present study show that hypoxia causes Ca2+ influx through L-type voltage gated Ca2+ channels and that hypoxia-induced c-fos gene expression is Ca2+/calmodulin dependent. We also demonstrate that hypoxia activates the extracellular-regulated kinase (ERK) and p38, but not JNK. Further, phosphorylation of ERK is essential for c-fos activation via SRE cis-element. Further characterization of nuclear signalling pathways provides evidence for the involvement of Src, a non receptor protein tyrosine kinase, and Ras, a small G protein, in the hypoxia-induced c-fos gene expression. These results suggest a possible role for non-receptor protein tyrosine kinases in propagating signals from G-protein coupled receptors to the activation of immediate early genes such as c-fos during hypoxia.

Animals↗
PubMed2000

Dual influence of nitric oxide on gene regulation during hypoxia.

It is being increasingly recognized that nitric oxide (NO) is associated with many physiological processes, including regulation of gene expression. NO shares certain similarities with molecular oxygen (O2). Previous studies have shown that hypoxia up-regulates c-fos, an immediate early gene, and tyrosine hydroxylase (TH), a late response gene that encodes rate limiting enzyme in catecholamine synthesis. Given the similarities between NO and O2, we hypothesized that NO inhibits hypoxia-induced up-regulation of c-fos and TH. Experiments were performed on rat pheochromocytoma (PC12) cells. c-fos and TH mRNA's were analysed by Northern blot and promoter activities by reporter gene assays, respectively. Hypoxia (1% O2 for 6 h) up-regulated c-fos and TH mRNA and increased c-fos promoter activity. Hypoxia-induced c-fos mRNA expression, and promoter activities were significantly potentiated in presence of spermine nitric oxide (SNO), a NO donor. By contrast, SNO significantly inhibited TH mRNA expression and TH promoter activity during hypoxia. Electrophoretic mobility shift-assay showed increased binding of AP-1 and HIF-1 transcription factors to the TH promoter in cells exposed to hypoxia. SNO abolished the binding of AP-1 and HIF-1 to the TH promoter during hypoxia, suggesting that inhibition of hypoxia-induced TH transcription by NO are due to reduced binding of AP-1 and HIF-1 transcription factors. These result demonstrate that NO has both positive and negative influence on gene regulation by hypoxia and suggest that although NO resembles O2 does not always inhibit gene expression during low oxygen.

Animals↗
PubMed1998

Role of c-fos in hypoxia-induced AP-1 cis-element activity and tyrosine hydroxylase gene expression.

Previous studies have demonstrated that hypoxia stimulates expression of the c-fos gene in intact animals and isolated cells. The purpose of the present study was to assess the functional significance of c-fos activation during hypoxia. Using antisense c-fos strategy, we tested the hypothesis that c-fos is essential for activation of activator protein-1 transcription factor complex (AP-1) and subsequent stimulation of down stream genes such as tyrosine hydroxylase (TH) gene during hypoxia. Experiments were performed on rat pheochromocytoma 12 (PC12) cells. AP-1 activity was determined by a reporter gene assay using a luciferase expression vector driven by two copies of an AP-1 cis-element (AP-1-Luc). Cells transfected with AP-1-Luc construct were exposed to normoxia (21% O2) or to varying intensities and/or durations of hypoxia. AP-1 activity increased in response to hypoxia. The magnitude of the response depended on the intensity and duration of the hypoxic stimulus. Increases in AP-1 activity could not be elicited in neuroblastoma cells, indicating that hypoxia-induced increase in AP-1 activity is a cell selective phenomenon. Antisense c-fos abolished hypoxia-induced AP-1 activation in PC12 cells. Hypoxia increased tyrosine hydroxylase-chloramphenicol acetyl transferase activity (TH-CAT), and antisense c-fos and mutations at AP-1 binding sites in TH promoter abolished this effect. These results provide direct evidence that c-fos is essential for functional activation of AP-1 and subsequent activation of delayed response genes such as TH in PC12 cells.

Animals↗
PubMed1996

Na(+)-K(+)-ATPase activity of different regions of rat brain in response to immunization and bone marrow cytokine treatment.

The bone marrow cytokine (Bio-Immuno Modulator, BIM or BM-Fr1) has been suggested to correct immunoincompetence by modulating brain Na(+)-K(+)-ATPase. The brain region affected and mechanism of action of BM-Fr1 are unknown, however. Here we report that immunization of immunocompetent rats indirectly inhibited Na(+)-K(+)-ATPase activity (59%) in the left cerebral lobe (LC) and irrespective of BM-Fr1 treatment, stimulation of the enzyme was observed in the LC at the peak of immune response. BM-Fr1 treatment, which corrected immunoincompetence in malnourished rats, also modulated a different LC Na(+)-K(+)-ATPase profile to that seen in immunocompetent animals. Immunogen and BM-Fr1 seem to exert their influence in brain via a cytosolic inhibitor protein of Na(+)-K(+)-ATPase. Thus we suggest that (1) BM-Fr1 plays an important role in immune homeostatasis by modulating Na(+)-K(+)-ATPase activity of LC and (2) Na(+)-K(+)-ATPase is not the receptor for either immunogen or BM-Fr1.

Adjuvants, Immunologic↗
PubMed1996

Cardiac myotrophin exhibits rel/NF-kappa B interacting activity in vitro.

Myotrophin is a soluble-12 kilodalton protein isolated from hypertrophied spontaneously hypertensive rat and dilated cardiomyopathic human hearts. We have recently cloned the gene coding for myotrophin and expressed it in Escherichia coli. In the present study, the expression of myotrophin gene was analyzed, and at least seven transcripts have been detected in rat heart and in other tissues. We have further analyzed the primary structure of myotrophin protein and identified significant new structural and functional domains. Our analysis revealed that one of the ankyrin repeats of myotrophin is highly homologous specifically to those of myotrophin is highly homologous specifically to those of I kappa B alpha/rel ankyrin repeats. In addition, putative consensus phosphorylation sites for protein kinase C and casein kinase II, which were observed in I kappa B alpha proteins, were identified in myotrophin. To verify the significance of these homologies, kappa B gel shift assays were performed with Jurkat T cell nuclear extract proteins and the recombinant myotrophin. Results of these assays indicate that the recombinant myotrophin has the ability to interact with NF-kappa B/rel proteins as revealed by the formation of ternary protein-DNA complexes. While myotrophin-specific antibodies inhibited the formation of these complexes, rel-specific p50 and p65 antibodies supershifted these complexes. Thus, these results clearly indicate that the myotrophin protein to be a unique rel/NF-kappa B interacting protein.

Amino Acid Sequence↗
PubMed1994

Bacterial expression of human respiratory syncytial viral phosphoprotein P and identification of Ser237 as the site of phosphorylation by cellular casein kinase II.

The phosphoprotein P gene of human respiratory syncytial virus has been cloned and the protein expressed in Escherichia coli. The expressed protein was soluble, unphosphorylated, and constituted approximately 10% of the total bacterial protein. Electrophoretic and antigenic analyses demonstrated the identity of the recombinant protein with viral P protein and P protein synthesized in reticulocyte lysates. Purified recombinant P protein was efficiently phosphorylated in vitro by purified native as well as recombinant casein kinase II (CKII) or by the CKII activity in uninfected cell extracts. Through deletions and site-directed mutagenesis, the site of CKII phosphorylation was mapped to a single serine residue (Ser237) near the C-terminal end of the P protein.

Amino Acid Sequence↗
PubMed1993

An Na+/K(+)-ATPase inhibitor protein from rat brain cytosol.

A protein isolated from rat brain cytosol is found to inhibit Na+/K(+)-ATPase in rat brain and kidney and H+/K(+)-ATPase from toad gastric mucosa, but has no effect on Ca2+,Mg(2+)-ATPase and Ca(2+)-ATPase isolated either from rat testis or goat spermatozoa. The inhibitor has been partially purified by ammonium sulphate precipitation followed by gel-filtration through Sephadex G-100. The inhibitor seems to bind at or close to the ATP binding site of Na+/K(+)-ATPase, such that the binding of the inhibitor to ATPase is reversible and competitive in nature with respect to the substrate. Optimum inhibition is observed at around the phase transition temperature of brain Na+/K(+)-ATPase and the inhibitory activity is only partially dependent on -SH or -NH2 group(s) of the inhibitor protein.

Animals↗
PubMed1992

The in vivo inhibition of transport enzyme activities by chloroquine in different organs of rat is reversible.

The antimalarial drug chloroquine is found to inhibit Na+, K(+)-ATPase, Ca2+, Mg(2+)-ATPase, Ca(2+)-ATPase, pNPPase and acetylcholinesterase activities in different organs of rat in vivo when injected for a certain periods of time. The inhibition seems to be due to the changes in the level of phospholipid, cholesterol and the fatty acid of the lipid and the alteration of the fluidity of the microsomal membranes. However, the enzyme activities return to the normal level in about 2-3 weeks after the discontinuation of the drug suggesting that the drug effect is reversible.

4-Nitrophenylphosphatase↗
PubMed1991

The in vivo inhibition of transport enzyme activities in different organs of rat by chlorpromazine is reversible.

Chlorpromazine, an antipsychotic drug is found to inhibit Na+K(+)-ATPase, Ca(2+)-ATPase and acetylcholinesterase activities in the microsomal membranes of rat in vivo, when the drug is injected for certain periods of time. The inhibition seems to be due to the changes in fatty acid composition of lipid and microviscosity of the membranes. However, once the drug has been withdrawn, the enzyme activities are found to return to the normal level in three to five weeks, suggesting that the drug effect is reversible.

Acetylcholinesterase↗