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Biomedical subjects

K S Saini

Publications and source records attributed to K S Saini.

13 recordsLinked to original sources
PubMed1998

Biochemical and molecular mechanisms regulating apoptosis.

In eukaryotes, the regulation of tissue cell numbers is a critical homeostatic objective that is achieved through tight control of apoptosis, mitosis and differentiation. While much is known about the genetic regulation of cell growth and differentiation, the molecular basis of apoptosis is less well understood. Genes involved in both cell proliferation and apoptosis reflect the role of some stimuli in both of these processes, the cell response depending on the overall cellular milieu. Recent research has given fascinating insights into the complex genetic and molecular mechanisms regulating apoptosis. A picture is emerging of the initiation in certain cells, after an apoptotic trigger, of sequential gene expression and specific signal transduction cascades that guide cells along the cell death pathway. Changes in gene expression precede the better known biochemical and morphological changes of apoptosis. It seems possible that, as a result of increased understanding of the cellular events preceding cell death, apoptosis may become more amenable to manipulation by appropriate drug- and gene-based therapies.

Animals↗
PubMed1996

Introduction and expression of the bacterial glyoxylate cycle genes in transgenic mice.

The glyoxylate cycle, catalysed by two unique enzymes: isocitrate lyase (ICL; EC 4.1.3.1) and malate synthase (MS; EC 4.1.3.2), is necessary for the net conversion of acetate into glucose. This metabolic pathway operates in microorganisms, higher plants and nematodes. Two bacterial genes, encoding ICL and MS, were modified in order to introduce them into the mouse germ line. The ovine metallothionein-Ia (MT-Ia) promoter-ace B gene-ovine growth hormone (GH) gene (3' GH sequence) construct was fused to the ovine, MT-Ia promoter-ace A gene-ovine GH gene (3' GH sequence). Therefore, in this single DNA sequence, both ace A and ace B are under independent MT-Ia promoter control and can be induced by zinc. Transgenic mice were generated by pronuclear microinjection of the ace B-ace A gene construct. We now report the establishment of four mouse lines carying these two transgenes. Studies on the progeny of these lines indicate that one line (No. 91) is expressing both genes at the mRNA and enzyme levels in the liver and intestine, whereas another line (No. 66) has a much lower expression. Both enzyme activities were detected in the liver and intestine at levels up to 25% of those measured in fully derepressed Escherichia coli cells.

Animals↗
PubMed1996

Streptozotocin at low doses induces apoptosis and at high doses causes necrosis in a murine pancreatic beta cell line, INS-1.

The ability of beta cells to endure assaults by various environmental agents, including toxins and viruses, may be relevant to the development of diabetes. We have examined the mode of cell death caused by streptozotocin (STZ) in a murine pancreatic beta cell line, INS-1. Apoptosis was identified by detection of initial endonuclease-mediated DNA strand breaks by DNA gel electrophoresis. Apoptosis and necrosis were distinguished morphologically by light and electron microscopy. Higher rates of apoptosis, as compared to necrosis, were observed when cells were exposed to 15 mM STZ for 1 hr followed by a 24 hrs recovery period. Higher doses of STZ (30 mM) caused the cells to undergo necrosis (22%) as well as apoptosis (17%). These results suggest that the cytotoxic effect of STZ, at low doses, on beta cells involves the activation of the apoptotic pathway, whereas, at high doses, the mode of beta cell death is predominantly necrosis.

Animals↗
PubMed1992

Elevated expression of pp60c-src in low grade human bladder carcinoma.

The results presented in this report demonstrate that the tyrosine-specific protein kinase activity of pp60c-src is elevated over that recorded in normal bladder mucosa in a subset of human bladder carcinomas. Increased kinase activity was observed mainly in low grade bladder lesions and was associated, at least in part, with elevated levels of pp60c-src expression. Extension of this analysis to a panel of human bladder carcinoma cell lines confirmed previous observations of low pp60c-src kinase activity in three lines established from high grade (GIII) bladder tumors and revealed increased kinase activity in three alternative bladder lines derived from GI or GII tumors. Use of an anti-phosphotyrosine antibody in Western blot analysis revealed the presence of novel phosphotyrosyl cellular substrates in human bladder cell lines and tumors displaying elevated pp60c-src kinase activity. These observations suggest an association for the src protooncogene in urothelial cell differentiation events.

Blotting, Western↗
PubMed1992

Differences in messenger RNA expression of carcinoembryonic antigen in surgical specimens of colorectal carcinoma.

Carcinoembryonic antigen (CEA) is the most widely used tumor marker for colorectal cancer. Plasma CEA levels have been variably associated with prognosis. Since plasma CEA level is multifactorial, CEA gene expression in tumors may provide one precise mechanism to evaluate its functional role. This study evaluated CEA expression at the messenger RNA (mRNA) level in 22 human colorectal carcinomas and their adjacent normal mucosae by Northern blot hybridization using a 32P-labeled CEA probe (a loop-domain specific cDNA, LV7). Both tumor and normal mucosa displayed three mRNA species of 4.0, 3.6, and 3.0 kb in length. The expression of 3.6-kb mRNA which encodes for CEA was dominant and it was correlated with another 4.0-kb CEA mRNA expression. The expression of 3.0-kb mRNA which encodes for nonspecific cross-reacting antigen was weak and not detectable in 8 of 22 colon tumors and 12 of 22 normal colon mucosae. In only one tumor, a 4.5-kb mRNA (which might encode for a new family member of CEA) was expressed. A two- to fourfold higher expression of CEA mRNA (3.6 kb) was observed in 11 of 22 colorectal tumors (2 of 9 proximal colon tumors and 9 of 14 rectosigmoid tumors) when compared with morphologically normal adjacent mucosae. Preoperative plasma CEA levels and Dukes' staging had no correlation with this CEA mRNA expression. CEA mRNA did not appear to correlate with metastasis because its expression in the primary colon cancers with metastases (Dukes' stage D tumor) was not always increased. These data also imply that factors other than mRNA expression in tumor might be important in regulating plasma CEA levels.

Aged↗
PubMed1991

Glycerol 3-phosphate dehydrogenase gene expression in cultured 3T3-L1 adipocytes: regulation by insulin, dexamethasone and dibutyryl cAMP at the level of mRNA abundance, transcription and mRNA stability.

In fully differentiated 3T3-L1 adipocytes, glycerol 3-phosphate dehydrogenase (G3PDH:Sn-glycerol 3-phosphate:NAD+ 2-oxidoreductase, EC 1.1.1.8) is subject to regulation by hormones and dibutyryl cAMP. An increase by insulin (4-fold) and decrease by dexamethasone (by 50%) and dibutyryl cAMP (by 70%) was observed for G3PDH mRNA abundance as analyzed by Northern blot hybridization. In addition, incubation of adipocytes with dibutyryl cAMP resulted in 3-fold increase in G3PDH gene transcription as measured by nuclear transcript elongation assay. The effects of these modulators on the control of G3PDH mRNA stability were also investigated. The G3PDH mRNA has a half-life of about 125 min. Dibutyryl cAMP caused an increase in G3PDH mRNA degradation by greater than 2-fold (t1/2 = 55 min) whereas insulin had an opposite effect (t1/2 = 240 min) and dexamethasone was without any effect on G3PDH mRNA stability. Taken together, our results directly demonstrate that in fully differentiated 3T3-L1 adipocytes the regulation of G3PDH gene expression by dibutyryl cAMP and insulin is exerted by alterations in transcription as well as mRNA stability.

3T3 Cells↗
PubMed1990

Molecular events regulating messenger RNA stability in eukaryotes.

The regulation of mRNA turnover plays a major role in the overall control of gene expression. Transcriptional control of eukaryotic gene regulation by external and/or internal stimuli has received considerable attention and the purpose of this review is to highlight recent work elucidating the mechanisms underlying the steady-state levels of mRNAs in the cytoplasm. Protection of mRNA from the action of nucleases as it passes from the nucleus to the ribosomes for translation is achieved, at least in part, by its union with mRNA binding proteins and the presence of poly(A) tail. The half-life of a message represents a balance between the transcriptional activity and intracellular degradative processes. These properties can be modulated by the presence of specific nucleotide sequences in a mRNA along with cis- and trans-acting elements and accompanied by post-translational feed back mechanisms. Presently, various regulatory mechanisms involved in the mRNA decay process are ill-defined. The work described here illustrates the complexity of this emerging field of study and outlines its contribution to our understanding of gene regulation in eukaryotes.

Animals↗
PubMed1985

Purification and characterization of goblet-cell mucin of high Mr from the small intestine of sheep.

Crude soluble mucus from sheep small intestine was freed of nearly all the nucleic acid contaminants by precipitation with protamine sulphate and treatment with nucleases. After removal of non-covalently bound proteins by equilibrium density-gradient centrifugation in CsCl, a high-Mr glycoprotein was isolated by repeated h.p.l.c. from the partially purified mucin. The high degree of purity of the high-Mr mucin was borne out by (a) the observation of a single boundary on analytical ultracentrifugation in the presence of 5M-guanidinium chloride and (b) the observation of apparent monodispersity on sedimentation-equilibrium analysis. The Mr of the highly purified mucin, determined by sedimentation equilibrium, was 5.0 (+/- 0.1) X 10(6) and was concentration-independent. Finally, only goblet cells and the mucus blanket lining the intestinal epithelial cells were immunofluorescent when guinea-pig anti-(highly purified mucin) serum was used in an indirect immunofluorescence assay. The above antiserum reacted with apparently equal strength with goblet cells and with free mucin in abomasum, caecum and colon. The chemical composition of the glycoprotein was 66% carbohydrate and 34% protein, 45% of the latter being composed of valine and threonine. The glycoprotein migrated anodally on immunoelectrophoresis and contained 7.1% (w/w) sulphate. Neutral hexoses accounted for nearly half of the total carbohydrate content, followed by galactosamine and glucosamine. Whereas fucose and sialic acid were present in only small amounts, uronic acid was not detectable in the highly purified mucus glycoprotein.

Amino Acids↗