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Biomedical subjects

S Ramakrishnan

Publications and source records attributed to S Ramakrishnan.

At least 127 records · Page 7Linked to original sources
PubMed1995

Increased levels of laminin in ascitic fluid of patients with ovarian cancer.

Laminin is a component of the extracellular matrix and is associated with tumor cell metastasis. Present studies show that the ovarian cancer cell lines produce significant amounts of laminin (54-140 ng/ml) in culture. Since ovarian cancer is associated with ascites production, laminin levels were then determined in ascites and serum. The results indicate that the ascites from patients with serous adenocarcinoma of the ovary had higher levels of laminin than the normal peritoneal fluid (P < 0.0001). However, the serum levels of laminin did not differ significantly between the control population and ovarian cancer patients.

Ascitic Fluid↗
PubMed1995

Phenotypic variations and differential migration of NIH:OVCAR-3 ovarian carcinoma cells isolated from athymic mice.

Transplantation of the human ovarian adenocarcinoma cell line, NIH:OVCAR-3 into athymic mice produces two morphologically distinct tumor cell populations (ascites and solid tumors). In the present study, we isolated both tumor cell phenotypes and investigated their relative malignant potential. Since cytoskeletal and morphological changes correlate with metastatic phenotype, expression of the intermediate-filament protein vimentin was compared between ascites and solid tumors. Ascites tumor cells showed a less differentiated epithelial morphology and concurrently expressed higher levels of vimentin. Ascites cells were more efficient in anchorage independent growth when compared with their solid tumor counterpart. Ascites tumor cells were also highly motile compared with the solid tumor cell population (P = 0.006). Migration of ascites tumor cells was further enhanced by type IV collagen, hyaluronic acid, and chondroitin sulfate A. Solid tumor cells removed from the same animal, however, were not significantly affected by these agents. From these studies, we conclude that ovarian cancer cells present in ascites are phenotypic variants which are highly motile compared with solid tumor cells isolated from the same animal. Ascites tumor cells with increased motility may contribute to peritoneal seeding and metastasis.

Adenocarcinoma↗
PubMed1995

Expression of alternate forms of brain opioid 'orphan' receptor mRNA in activated human peripheral blood lymphocytes and lymphocytic cell lines.

We screened a PHA (phytohemagglutinin)-activated human lymphocyte cDNA library for clones with homology to the recently cloned brain opioid receptors. A cDNA clone, AT7-5EU, was isolated which encodes the opioid 'orphan' receptor, a molecule with very high homology to the opioid receptor gene family, but which has not been shown to bind opioids or any other known compounds. The protein coding region of AT7-5EU has complete homology with a reported opioid 'orphan' clone isolated from human brain, but the 5' untranslated regions of AT7-5EU and the human brain clones are divergent, suggesting mechanisms for tissue-specific expression of this receptor. Northern analysis of AT7-5EU mRNA demonstrates the expression of this message in human lymphocytic cell lines of both B-and T-cell lineages. Furthermore, analysis of mRNA from human peripheral blood lymphocytes demonstrates that activation of the lymphocytes with PHA results in at least a 10-fold induction of the AT7-5EU message. These results suggest that the opioid 'orphan' receptor may have an important immunological function in addition to its function in the nervous system.

Base Sequence↗
PubMed1995

Smoking of beedies and cataract: cadmium and vitamin C in the lens and blood.

Estimation of cadmium and vitamin C was performed in the blood and lens of smokers in three age groups up to a maximum age of 58, habituated to smoking a minimum of 10 beedies a day for many years, as well as those of non-smokers in the same age groups. Only nuclear cataracts with or without posterior or anterior subcapsular cataract were chosen. It was found that there was a significant accumulation of cadmium in both the blood and the lens of the smokers. Such an accumulation of cadmium might have a role in cataractogenesis in chronic smokers. In a similar experiment, with smokers and non-smokers of two age groups up to a maximum age of 40, both without cataract, increased levels of cadmium were found in the blood of smokers only, though the extent of accumulation was not as high as in chronic smokers of higher age groups. Vitamin C content of lens was on the lower side of normal in both chronic smokers of beedies in the two age groups and non-smokers with nuclear cataract with or without posterior and anterior subcapsular cataract, and there was no significant change brought about by smoking. Vitamin C levels in blood were towards the lower side of the normal in smokers and non-smokers with and without cataract.

Adult↗
PubMed1995

Expression of biologically active human vascular endothelial growth factor in yeast.

Vascular endothelial growth factor (VEGF) is a glycoprotein consisting of two identical polypeptide chains linked by a disulfide bond. The unique biological activities of VEGF include its potent mitogenic and permeability inducing properties specific for the vascular endothelium. VEGF is implicated in tumor angiogenesis, wound healing, and the stimulation of collateral vessel formation at the site of arterial occlusion. Therefore, in order to produce large quantities of biologically active VEGF, a splice variant (VEGF165) was cloned and expressed in a yeast expression system. The coding region of VEGF165 was isolated from U937 cells by RT-PCR, sequenced and then cloned into the yeast expression vector pHILS1. VEGF165 was secreted into the medium as a dimer. Recombinant VEGF reacted to antibodies raised against the N-terminal and C-terminal synthetic polypeptides of human VEGF. As much as 35-40 mg/L of purified VEGF could be obtained from the yeast expression system. The recombinant protein was biologically active in inducing vascular endothelial cell proliferation in vitro and permeability changes in vivo.

Amino Acid Sequence↗
PubMed1995

Molecular evolutionary analysis of the YWVZ/7B globin gene cluster of the insect Chironomus thummi.

We report the sequence of 8.1 kb of DNA containing the 3' end of one and seven other complete intronless globin genes from the YWVZ/7B locus of the dipteran Chironomus thummi thummi. One of these (ctt-v) appears to be a pseudogene by virtue of a premature termination codon, whereas the others encode apparently functional globin polypeptides. taken together with previously published data, the C. th. thummi YWVZ/7B locus codes for at least 11 globins, five of which differ from one another by no more than two amino acids. In contrast only nine globin genes are found in a comparable genomic clone isolated from C. th. piger. As indicated by sequence alignment, this difference in copy number can be attributed to a loss of one gene (fusion of globin genes 7B8 and 7B10) in the piger lines, coupled with a gain (globin gene 7B9) in the thummi lineage. Comparisons between the thummi and piger sequences showed that YWVZ/7B intergenic regions have maintained a level of 91% similarity since the thummi/piger divergence: most differences are simply due to single base substitutions or insertion/deletion events in either the thummi or the piger DNA, but three instances of partially overlapping deletions were also detected. A phylogenetic analysis of YWVZ/7B gene products was conducted, from which a plausible reconstruction of the evolutionary history of the locus was obtained. In addition, alignment of globin 7B amino acid sequences suggested that globin genes 7B2 and 7B3 (reported at the protein and cDNA level, respectively, but not contained on the C. th. thummi or C. th. piger genomic clones) are possibly chimeric genes. Given the trend toward expansion of the C. thummi globin gene family in general and of the globin 7B subfamily in particular, we propose that increased copy number of these genes has been positively selected as a mechanism to achieve a high Hb concentration in the larval hemolymph.

Amino Acid Sequence↗
PubMed1995

Myoinositol and peroxidation--an in vitro study on human cataractous lens and human erythrocytes.

The effect of myoinositol on in vitro peroxidation induced by hydrogen peroxide in human erythrocytes and human cataractous lenses has been investigated. The lipid peroxidation was monitored as levels of thio barbituric reacting substances (TBARS). Addition of myoinositol decreased the peroxidation effect of hydrogen peroxide in a dose dependent manner. The results suggest a new antioxidant property for inositol.

Cataract↗
PubMed1994

Differential expression of the cell-cell adhesion molecule E-cadherin in ascites and solid human ovarian tumor cells.

Advanced ovarian cancers contain 2 distinct phenotypic populations: (a) free-floating tumor cells in the ascitic fluid and (b) solid tumors. Ascites cells are derived from the solid tumors and spread throughout the peritoneum. Changes in cell-cell and cell-extracellular matrix interactions are thought to be responsible for the origin of ascites cells. Since E-cadherin molecules play a crucial role in the cell-cell interactions in epithelial cells, we investigated the expression of E-cadherin in these 2 phenotypic populations. Paired samples of ascites and solid tumors were obtained from patients. Both primary tumors and tumor cells isolated from an experimental model showed a marked decrease in E-cadherin expression in the ascites cells compared to the respective solid tumors. Semi-quantitative, reverse transcriptase-polymerase chain reaction (RT-PCR) was used to determine the steady-state levels of E-cadherin-specific mRNA. Results indicate that the primary tumors had significantly lower levels of E-cadherin transcript in ascites cells when compared to their solid tumor counterparts. Changes in E-cadherin expression were also reflected in the invasion capacity of tumor cells in vitro. Ascites cells were 4-fold more invasive then solid tumor cells, suggesting that ascites cells are a highly malignant phenotype.

Animals↗
PubMed1994

Recombinant hybrid toxin with dual enzymatic activities. Potential use in preparing highly effective immunotoxins.

Bacterial toxins and ribosomal inhibitory proteins isolated from plants are used to prepare tumor-specific cytotoxic conjugates. The ability of these conjugates to kill tumor cells depends on binding, internalization, translocation to cytoplasm, and translation inhibition. Modulation of any one of these processes can improve cytotoxicity. Since bacterial and plant toxins act at a distinct step in translation, a combination of their activities could be more effective. Therefore, a chimeric protein was prepared by genetically fusing the coding region of the ricin A chain (RTA) and the fragment A of diphtheria toxin (DTA). The hybrid protein (RTA-DTA) expressed in bacteria retained the N-glycosidase activity of the RTA and ADP-ribosylation activity of the DTA. The hybrid toxin was more potent than the ricin A chain (11-fold) and the diphtheria toxin (50-fold) in inhibiting cell-free translation. Immunotoxin made with the hybrid toxin was about 100- and 1000-fold more effective than RTA or DTA conjugate, respectively, in inhibiting tumor cell growth in vitro. These results indicate that the hybrid toxin with dual activities could be useful in preparing potent immunotoxins with better anti-tumor cell activity.

Base Sequence↗
PubMed1994

Vascular permeability factor gene expression in normal and neoplastic human ovaries.

Epithelial ovarian cancer is an aggressive malignancy with a generally poor outcome. To improve survival, novel therapeutic strategies for this disease are needed and require elucidation of the biological events that underlie transformation and tumor growth. Vascular permeability factor (VPF), also known as vascular endothelial growth factor, is a homodimeric glycoprotein that acts on vascular endothelium as a potent permeability-inducing agent and mitogen. The present study demonstrates for the first time the constitutive gene expression of VPF in normal and neoplastic human ovaries. Abundant levels of VPF have been identified by an immunoassay in the ascites of patients with epithelial ovarian cancer (K-T. Yeo et al., Cancer Res., 53: 2912-2918, 1993). We have identified the malignant epithelium as one source of VPF in the ascites. Reverse transcription-polymerase chain reaction has demonstrated the expression of the two secreted isoforms, VPF121 and VPF165, in normal and neoplastic ovaries. Western blotting and an endothelial cell proliferation assay confirmed secretion of a biologically active product. VPF may be an important mediator of ascites formation and tumor metastasis observed in neoplastic conditions of the ovary.

Adult↗
PubMed1994

Mouse fibroblasts defective in thrombin mitogenesis possess functional proteolytically activated receptor for thrombin: requirement for a second signaling pathway.

Thrombin mitogenesis in fibroblasts requires two distinguishable subsets of signals; one generated by proteolytic cleavage, the other by high-affinity cell surface binding. Characterizing two closely related mouse embryo (ME) cell lines with high numbers of thrombin binding sites, we found that one line, B11-A, responds mitogenically to thrombin, epidermal growth factor (EGF), and serum, whereas the B11-B cell line is responsive to EGF and serum, but not to thrombin. The B11-B defect responsible for loss of thrombin responsiveness is not due to differences in the number of high-affinity binding sites, the affinity of thrombin binding to these sites, or to differences in cell surface expression of proteolytically activated receptors for thrombin (PART). The defect is also not associated with an inability of thrombin to activate PART since thrombin stimulates the cleavage-dependent induction of the proto-oncogene c-fos in both B11-A and B11-B cells. Various combinations of thrombin, synthetic thrombin receptor peptide, TRP-14 (SFFLRNPGENTFEL), platelet-derived growth factor (PDGF), and phorbol 12-myristate 13-acetate (PMA) were used to better define the defect in thrombin-mediated mitogenesis in B11-B cells. Direct activation of protein kinase C with PMA in combination with thrombin did not overcome B11-B nonresponsiveness. However, mitogenic responsiveness was regained in B11-B cells by simultaneous addition of PDGF and either thrombin or TRP-14. Therefore, the B11-B defect may involve a set of signals initiated by nonproteolytic thrombin interactions distinct from those initiated by PART, but related to the downstream signals initiated by the tyrosine kinase-associated growth factors, EGF and PDGF.

Amino Acid Sequence↗