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S Kartha

Publications and source records attributed to S Kartha.

28 records · Page 2Linked to original sources
PubMed1988

Kidney epithelial cells express c-sis protooncogene and secrete PDGF-like protein.

Nontransformed monkey kidney cells (BSC-1 line), used as a model for renal epithelium, were assayed for release of platelet-derived growth factor (PDGF)-like proteins. BSC-1 cells continuously released a mitogenic activity for fibroblasts and a chemoattractant activity for smooth muscle cells, each of which was inhibited 80-90% by an antibody to human PDGF. A cDNA probe for the PDGF B-chain gene (c-sis), but not for the A-chain gene, hybridized to mRNA obtained from growing and quiescent cells. c-sis gene expression and PDGF-like protein secretion were studied in the presence of known growth-regulatory molecules. A secreted BSC-1 cell protein identical to transforming growth factor beta 2 inhibited DNA synthesis in growing cultures and induced marked accumulation of c-sis mRNA without a corresponding increase in the release of PDGF-like activity. Adenosine diphosphate stimulated DNA synthesis in quiescent cultures and enhanced both c-sis expression and release of PDGF-like activity. However, growing and quiescent cells did not express the PDGF receptor gene or exhibit a mitogenic response to authentic PDGF. Thus the PDGF-like protein released by these kidney epithelial cells could contribute to growth control by a paracrine mechanism.

Animals↗
PubMed1988

Kinetics of a novel cytosolic protein during the onset of renal epithelial cell growth.

Exposure of monkey kidney epithelial cells (BSC-1 line) to medium with a reduced K concentration (3.2 mM) stimulated growth and transiently activated glyceraldehyde-3-phosphate dehydrogenase (G3PD). The increase in enzyme activity was mediated by a cytosolic modifier protein that was purified using affinity and size-exclusion chromatography, and anion-exchange high-performance liquid chromatography. The apparent molecular mass of the protein was 62 kDa. A monospecific antibody to the protein was prepared from rabbit antiserum and used as an immunoprobe. Immunocytochemical staining and Western blotting revealed that the protein was a normal constituent of the cytosol and that it accumulated in cells exposed to low-K medium. A quantitative enzyme-linked immunosorbent assay showed that the amount of modifier protein increased progressively for up to 2 h in cells exposed to low-K medium, and then returned to the control value, a kinetic profile similar to that observed for G3PD activity. These results indicate that the modifier protein is a constituent of renal epithelial cells and accumulates transiently in the cytosol where it could regulate G3PD activity during the onset of growth induced by the low-K mitogenic signal.

Animals↗
PubMed1987

ADP activates protooncogene expression in renal epithelial cells.

Purine nucleotides, particularly adenosine diphosphate (ADP), are the most potent mitogens known for monkey kidney epithelial cells of the BSC-1 line. To explore the molecular mechanisms by which ADP exerts its mitogenic effect, we tested the hypothesis that stimulation of DNA synthesis in these renal cells is mediated by activation of protooncogenes. Transcripts of the c-Ha-ras protooncogene were identified in quiescent, high density cells. Addition of ADP to the culture medium stimulated protooncogene expression fourfold. Maximal expression of c-ras was observed by 12 h after exposure to ADP, and preceded the initiation of DNA synthesis. Expression of the c-myc protooncogene was not detected in unstimulated cells, but accumulated maximally after 1 h of exposure to ADP. As with ADP-stimulated expression of the c-ras protooncogene, transcripts of the transferrin receptor gene reached a maximal value at 12 h, whereas the abundance of gamma-actin mRNA was not altered for up to 24 h. The results indicate that exogenous ADP stimulates protooncogene expression before initiation of DNA synthesis in renal epithelial cells in culture. These findings suggest that some physiological effects of this adenine nucleotide could be mediated by proteins specified by protooncogenes.

Actins↗
PubMed1985

Aggregation-deficient embryonal carcinoma cells: defects in peanut agglutinin (PNA) receptors.

The components involved in cell adhesion were studied using the H6 line of embryonal carcinoma cells. H6 cells are especially suitable for studies on cell interactions, since genetic mutants can be selected, and various processes of cell adhesion can be controlled by regulating the calcium concentration in the medium. Three aggregation-defective variants of H6 were isolated, all of which showed reduced binding of the lectin, peanut agglutinin (PNA). Quantitation of PNA receptors on the cell surface by immunoprecipitation of iodinated surface proteins indicated that these receptors were reduced on the variants by one-half to one-quarter. The separation of immunoprecipitated PNA receptors on sodium-dodecyl-sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) demonstrated that one type of receptor, with an apparent molecular weight of 94 kilodaltons, was reduced. Parental and variant cells bind similar quantities of concanavalin A and soybean agglutinin, suggesting that there is no generalized effect on major glycoproteins. Thus, the defect in aggregation and the defect in the 94-kilodalton protein may be correlated, and this glycoprotein may have a role in the mediation of H6 cell-cell adhesion.

Animals↗
PubMed1985

Purine nucleotides stimulate DNA synthesis in kidney epithelial cells in culture.

Adenine nucleotides infused into animals with acute renal failure appear to enhance recovery of kidney function and structure. To determine whether these compounds could act by a direct effect on renal cell metabolism, their capacity to stimulate DNA synthesis was evaluated in cultures of monkey kidney epithelial cells (BSC-1 line). AMP and ADP enhanced DNA synthesis by threefold more than was previously observed with other mitogens for these cells. Guanosine and inosine and their nucleotides and adenosine and ATP were also mitogenic but to a lesser extent, whereas pyrimidine derivatives were ineffective. In the presence of AMP, autoradiography of [3H]thymidine-labeled cells indicated that a greater number of cells entered the S phase of the cell cycle, and assessment of cell number revealed increased multiplication. The mitogenic effect of adenine nucleotides was not reproduced by agents that raise the cellular content of cAMP and was serum independent. Adenine nucleotides did not alter DNA synthesis when added to cultures of mouse fibroblasts. These results indicate that provision of exogenous purine nucleosides and nucleotides stimulate DNA synthesis in renal epithelial cells in culture.

Adenine Nucleotides↗
PubMed1984

Junction formation in aggregated embryonal carcinoma cells.

Under the action of supplemental calcium, H6 mouse embryonal carcinoma cell aggregates undergo compaction, a morphological phenomenon similar to mouse embryonic compaction. Formation of various types of cell junctions, especially gap junctions, is associated with compaction of the embryo and we sought to analyze the pattern of junction formation during aggregation and compaction of H6 cells. At 24 hr of aggregation, gap junctions were abundant in both uncompacted and compacted aggregates but quantitative analysis of freeze fracture replicas of these junctions showed a 20-fold increase in the size of the largest gap junctions in compacted aggregates. Such a difference in size could even be detected at 12 hr of aggregation. Tight junctions were not normally formed in 12 hr aggregates but initial stages of tight junction formation could be noticed in 12 hr compacted aggregates. More definitive tight junctions and desmosomes were evident only after 48 hr of aggregation. Thus we have observed that both uncompacted and compacted aggregates can form gap junctions at similar frequencies, suggesting that cell flattening, which contributes to the compacted morphology, is not a requisite for gap junctions. Likewise, generation of the compacted morphology seems to be independent of gap junction formation. This supports the idea that compaction in embryonal carcinoma cells results from calcium-induced cell flattening, probably through the mobilization of cytoskeletal elements. Calcium-dependent features of H6 cell aggregation and compaction enables the independent analysis of separate steps in compaction.

Animals↗
PubMed1983

Calcium-induced compaction and its inhibition in embryonal carcinoma cell aggregates.

H6 embryonal carcinoma cells form aggregates of cells in culture medium which contains 2 mM calcium. These aggregates are described as uncompacted, indicating that the individual cells of the aggregate are spherical and are in limited contact with each other. In contrast, compaction of the aggregate, induced by increasing the calcium concentration, results in a tight mass of cells flattened against one another and connected by intercellular junctions. At least 85-97% of the aggregates undergo compaction in 7 mM calcium and are subsequently decompacted if removed to 2 mM calcium. Since calcium ionophore A23187 does not induce compaction, extracellular rather than intracellular calcium seems to be the limiting factor. We have demonstrated that this calcium-induced morphogenetic change is sensitive to inhibition by agents which also prevent the calcium-dependent compaction of the 8-cell mouse embryo. The cytoskeletal-binding drugs tetracaine HCl, colcemid, vinblastine, colchicine, and cytochalasin B each inhibit compaction of H6 aggregates. Interference at surface molecule sites by exposure to the lectins wheat germ agglutinin or concanavalin A or by interruption of glycosylation with exposure to tunicamycin, or by reaction with anti-H6 Fab or anti-F9, also prevent compaction. Since the mouse embryo and embryonal carcinoma cells share certain processes which are involved in initiating and maintaining compaction, these processes and their subsequent roles in differentiation may be examined using embryonal carcinoma cell aggregates.

Animals↗
PubMedDate not supplied

A novel early growth response gene rapidly induced by fibroblast, epithelial cell and lymphocyte mitogens.

Mitogens evoke many alterations in gene expression in eukaryotic cells. Genes which are activated rapidly and transiently, that are evolutionarily conserved and whose induction is shared by diverse cell types when exposed to different growth stimuli are likely to be of critical importance in transducing mitogenic signals and regulating cellular proliferation. c-myc and c-fos are the only known genes fulfilling these criteria. We report on the molecular cloning of a novel early growth response (egr) gene which also satisfies these conditions. In response to serum, its 3.7 kb mRNA is induced dramatically in mouse fibroblasts reaching a peak level at about 30 minutes that is ten times higher than the maximal value attained by c-fos mRNA. This transcript is induced by the tumor promoter 12-O-tetradecanoyl-phorbol-13-acetate and is "superinduced" by serum and cycloheximide together. Importantly, the gene is highly induced by different mitogens in a wide array of cell types: insulin stimulated rat hepatoma cells, adenosine diphosphate treated monkey kidney epithelial cells, and phytohemagglutinin stimulated human peripheral blood lymphocytes. Given the many properties that this gene shares with c-myc and c-fos, it may play a key role in the control of cell growth and perhaps in oncogenesis.

Animals↗