Biomedical subjects

C Sudhakar

Publications and source records attributed to C Sudhakar.

10 recordsLinked to original sources

PubMed2001

A nuclear protein tyrosine phosphatase induces shortening of G1 phase and increase in c-Myc protein level.

PTP-S2 is a ubiquitously expressed nuclear protein tyrosine phosphatase which shows increased expression upon mitogenic stimulation in a variety of cells in vitro and in vivo. In order to understand the role of this enzyme in cell cycle progression, tetracycline-regulated HeLa clones expressing PTP-S2 were isolated and characterized. Tetracycline-controlled expression of PTP-S2 increased the rate of cell proliferation. An analysis of the distribution of cells in various phases of the cell cycle in an exponentially growing cell population showed that there was a large decrease in the percentage of cells in G1 phase in a PTP-S2-expressing population of cells compared to nonexpressing cells. This decrease in the percentage of cells in G1 was dependent on the level of PTP-S2 expression. There was a corresponding increase in the percentage of cells in G2/M but no significant increase in the percentage of cells in S phase. An analysis of the time course of cell cycle progression after release from double thymidine block showed that the duration of G1 phase was significantly shortened in cells induced to express exogenous PTP-S2. However, the duration of S phase was not significantly altered and the duration of G2 phase was increased to some extent. Induction of PTP-S2 expression was associated with an increase in c-Myc protein levels, although the c-Myc mRNA level was not changed. Our results suggest that overexpression of PTP-S2 promotes progression of cells through G1 to S phase and is associated with increased level of c-Myc protein through a posttranscriptional mechanism.

Animals↗

PubMed2000

QTL: their place in engineering tolerance of rice to salinity.

Secondary salinization and its relationship to irrigation are strong incentives to improve the tolerance of crops to salinity and to drought. Achieving this through the pyramiding of physiological traits (phenotypic selection without knowledge of genotype) is feasible. However, wide application of this approach is limited by the practicalities of assessing not only the parents, but also large numbers of individuals and families in segregating generations. Genotypic information is required in the form of markers for any quantitative trait loci involved (marker-assisted selection) or of direct knowledge of the genes. In the absence of adequate candidate genes for salt tolerance, a quantitative trait locus/marker-assisted selection approach has been used here. Putative markers for ion transport and selectivity, identified from analysis of amplified fragment length polymorphism, had been discovered within a custom-made mapping population of rice. Here it is reported that none of these markers showed any association with similar traits in a closely related population of recombinant inbred lines or in selections of a cultivar. Whilst markers will be of value in using élite lines from the mapping population in backcrossing, this has to be considered alongside the effort required to develop and map any given population. This result cautions against any expectation of a general applicability of markers for physiological traits. It is concluded that direct knowledge of the genes involved is needed. This cannot be achieved at present by positional cloning. The elucidation of candidate genes is required. Here the problem lies not in the analysis of gene expression but in devising protocols in which only those genes of interest are differentially affected by the experimental treatments.

Adaptation, Physiological↗

PubMed2000

Stress responses in two genotypes of mulberry (Morus alba L.) under NaCl salinity.

Changes in biomass yield rates, cell membrane stability (CMS), malondialdehyde (MDA) content and in the levels of physiological stress markers such as proline and glycine betaine in two high yielding genotypes (S1 and ATP, salt tolerant and salt sensitive, respectively) of mulberry under NaCl salinity were studied. Biomass yield rates and CMS were significantly decreased in both the genotypes under stress conditions. Per cent of decrease in biomass yield rate and CMS was relatively less in S1 than in ATP. Salt stress results a significant increase in the accumulation of proline, by 6-fold in S1 and 4-fold in ATP. Glycine betaine content was also increased significantly in stressed plants. However, the per cent increase was more in S1 than in ATP. The level of lipid peroxidation as indicated by MDA formation was greater in ATP than in S1. These results clearly support the better salt tolerant nature of S1 compared to ATP genotype.

Betaine↗

PubMed1999

Induction of p53 dependent apoptosis upon overexpression of a nuclear protein tyrosine phosphatase.

Two ubiquitously expressed protein tyrosine phosphatases, PTP-S2 and PTP-S4 (also known as TC45 and TC48, respectively), are alternately spliced products of the same gene. Overexpression of PTP-S2 by transient transfection induced chromatin condensation and nuclear fragmentation, typical of apoptosis. Expression of PTP-S4 resulted in a much lower number of cells with apoptotic phenotype. PTP-S2 induced apoptosis in MCF7 and A549 human tumor cell lines which are p53 positive but not in HeLa and SW620 cells which are p53 negative. Apoptosis induced by PTP-S2 in MCF7 cells was inhibited by cotransfection with mutant p53 (Arg-273 --> His) but not by wild type p53. PTP-S2 induced apoptosis was inhibited by antiapoptotic protein Bcl2 and certain inhibitors of caspases. These results suggest that the nuclear tyrosine phosphatase PTP-S2 induces p53 dependent, serum starvation independent and caspase mediated apoptosis.

Animals↗

PubMed1998

Exomphalos.

Explore the source record for details and available documents.

Consanguinity↗

PubMed1997

Response of some Calvin cycle enzymes subjected to salinity shock in vitro.

Leaf enzyme extracts of 10 day old seedlings of horsegram were subjected to NaCl or Na2SO4 treatment in vitro. Salinity shock caused decline in the activities of RuBP carboxylase, R-5-P kinase, R-5-P isomerase and NADP-Gly-3-P dehydrogenase. At low concentrations, Na2SO4 did not alter the activities of R-5-P kinase, R-5-P isomerase and NADP-Gly-3-P dehydrogenase. RuBP carboxylase was found to be more sensitive to salt shock than the other enzymes studied. Further, NaCl was more toxic to the enzyme activities as compared to Na2SO4.

Osmotic Pressure↗

PubMed1995

Cell free ascitic fluid prevents loss of cell surface sialic acid from Zajdela Ascitic Hepatoma cells in culture.

In the Zajdela Ascitic Hepatoma (ZAH), a rat tumor, high levels of cell surface sialic acid residues are present which masked the immunogenicity of the cells. We have shown here that cell surface sialic acid level goes down rapidly when ZAH cells are put in culture. The reduction in surface sialic acid levels is due to a decrease in sialic acid residues on the major sialylated glycoprotein, gp 120, as well as a decrease in gp 120 polypeptide. The loss of sialic acid from the cultured cells is reduced if the cells are cultured in the presence of cell free ascitic fluid from ZAH tumor.

Animals↗

PubMed1993

Regulation of expression of beta-galactoside alpha 2,6-sialyltransferase in a rat tumor, Zajdela ascitic hepatoma.

Tumor cell surface sialic acid levels determine a number of important properties governing cellular interactions and cell-cell communication. Towards understanding the mechanism of regulation of sialic acid levels upon cellular transformation, we have studied the regulation of expression of beta-galactoside alpha 2,6-sialyltransferase in a rat tumor, the Zajdela ascitic hepatoma. We demonstrate distinct differences in the regulation of expression of the enzyme in the tumor cells as compared to normal liver cells. The expression of sialyltransferase is regulated both at the transcriptional and post-transcriptional level in a tissue-specific manner.

Animals↗

PubMed1993

Differential expression of thymidine kinase gene in two subpopulations of a rat tumour correlates with their tumorigenic and cell division potential.

We have studied the expression of the thymidine kinase (TK) gene in two kinetically heterogenous populations of a rat tumour cell line--the Zajdela ascitic hepatoma (ZAH). We have demonstrated that the TK gene is differentially expressed in the two cell types. The more tumorigenic and rapidly dividing subpopulation shows higher levels of mRNA and enzyme activity for TK. In addition, we have shown that the tumorigenic cells accumulate the primary unspliced transcript and utilise only part of it for maturation. It is, therefore, likely that ZAH cells regulate their division and possibly tumorigenic potential by regulating the expression of the TK gene.

Animals↗

PubMed1990

Differential amplification and expression of c-myb oncogene in Zajdela ascitic hepatoma.

Organisation and expression of c-myb protooncogene have been studied in a heterogeneous tumour the Zajdela ascitic hepatoma (ZAH). The myb gene is selectively amplified in the more tumorigenic subpopulation of the tumour while the non-lethal subpopulation does not show any change. Analysis of transcripts of the myb gene in tumorigenic versus nontumorigenic cells shows that the level of amplification of the gene does not correspond to the level of its transcription. Results have been discussed in the light of existing evidence regarding the role of c-myb gene expression during cell cycle.

Animals↗