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Biomedical subjects

G R Guy

Publications and source records attributed to G R Guy.

64 records · Page 4Linked to original sources
PubMed1985

A combination of calcium ionophore and 12-O-tetradecanoyl-phorbol-13-acetate (TPA) stimulates the growth of purified resting B cells.

In this study we investigated whether the calcium ionophores A23187 and ionomycin can act synergistically with the phorbol ester 12-O-tetradecanoyl-phorbol-13-acetate (TPA) to stimulate the growth of resting B lymphocytes purified from human tonsil cells. Ionomycin, A23187, and TPA added separately to cultures at doses of 0.4-1.6 micrograms/ml, 0.2-0.8 micrograms/ml, and 0.05-0.25 ng/ml respectively, did not induce DNA synthesis in resting B lymphocytes. In contrast, calcium ionophores at concentrations of 0.4-1.6 micrograms/ml ionomycin and 0.2-0.8 micrograms/ml A23187, in the presence of 0.05-4 ng/ml TPA, induced marked DNA synthesis and B-cell proliferation, as shown by analyses of incorporation of [3H]thymidine, growth kinetics, and the percentage of cells in the S and G2 + M phases of the cell cycle. These results show that the synergistic effects of calcium ionophores and TPA can bypass the requirement for antigen and exogenous growth factors in B-cell activation. These observations are similar to those obtained from studies of T lymphocytes by other workers.

B-Lymphocytes↗
PubMed1983

Effects of a tumor promoter on phospholipid metabolism in HeLa cells.

The tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA) caused a marked stimulation of inorganic [32P]orthophosphate incorporation into HeLa-cell phosphatidylcholine (PC), phosphatidylethanolamine (PE), and lysophosphatidylethanolamine. The increased incorporation of inorganic [32P]orthophosphate into PE and lysophosphatidylethanolamine in the presence of TPA was not associated with an increase in PE synthesis as detected by the incorporation of [3H]serine or [3H]ethanolamine. The PC-specific exchange protein from beef liver was used to insert PC labeled with [3H]choline, inorganic [32P]orthophosphate, or [14C]arachidonic acid plus [3H]palmitic acid into the outer monolayer of intact HeLa cell membranes. Radioactivity from the latter two compounds was rapidly incorporated into PE and lysophosphatidylethanolamine; the incorporation was stimulated by TPA. It was concluded that TPA stimulated the formation of PE by base exchange between ethanolamine and PC.

HeLa Cells↗
PubMed1982

The purification and some properties of a stereospecific D-asparaginase from an extremely thermophilic bacterium, Thermus aquaticus.

A specific D-asparaginase was isolated and crystallized from Thermus aquaticus strain T351. It is present in larger amounts than the L-asparaginase. The enzyme has a molecular weight of 60 000, an isoelectric point of 4.8 and a Km of 2 mM. It has 6 disulphide bonds/molecule, and a histidine residue at the active site. It is inhibited by keto acids and by high salt concentrations.

Asparaginase↗
PubMed1982

Resistance of A-431 epidermoid carcinoma cells to early membrane changes induced by tumour promoters.

The A-431 human epidermoid carcinoma cell line was resistant to 12-O-tetradecanoylphorbol-13-acetate (TPA) inhibition of epidermal growth factor binding, enhanced incorporation of [3H]choline into phospholipids and uptake of 86Rb an [3H]2-deoxyglucose. The cells were also resistant to TPA-stimulated release of radioactive choline derivatives and arachidonic acid from cells prelabelled with [3H]choline or [14C]arachidonic acid, respectively. The A-431 cells did not metabolise [3H]TPA. Despite their TPA-unresponsiveness, A-431 cells contained specific, high affinity binding sites for [3H]phorbol-12,13-dibutyrate with characteristics similar to other cultured cell lines.

Arachidonic Acid↗
PubMed1982

Tumor promoter stimulation of phosphatidylcholine turnover in HeLa cells.

Incubation of HeLa cells for 24 hr with [3H]choline resulted in extensive labeling of the phosphorylcholine and phosphatidylcholine pools. 12-O-Tetradecanoylphorbol-13-acetate (TPA), other phorbol ester tumor promoters, and mezerein stimulated the release of [3H]choline and [3H]phosphorylcholine from such prelabeled cells. The release was accompanied by decreased radioactivity in the phosphorylcholine pool, raising the possibility that the released materials were derived by leakage from this pool. However, TPA did not induce the release of radioactivity from cells containing a prelabeled nucleotide pool. Similarly, the TPA-stimulated release of radioactivity from prelabeled cells closely paralleled the label present in the phospholipid pool rather than the phosphocholine pool. Consequently, it is suggested that the primary source of the released material is phosphatidylcholine acting as a substrate for a phospholipase C enzyme. TPA also simulated the incorporation of [3H]choline into phospholipids, but a time-course study indicated that phospholipase C activation preceded this event. This was supported by the observation that incorporation of [3H]choline was also stimulated by exogenously added phospholipase C.

Choline↗
PubMed1981

Tumor promoter inhibition of intercellular communication between cultured mammalian cells.

Cocultures were established of a cell line deficient in hypoxanthine-guanine phosphoribosyltransferase (PG-19; HPRT-) and a mouse epidermal cell line (HEL-37; HPRT+). The cocultures were incubated in a medium containing hypoxanthine, aminopterin and thymidine (HAT). HPRT- cells die in HAT medium unless rescued by metabolic cooperation with HPRT+ cells. The extent of cell death was measured by the release of radioactivity from PG-19 cells previously labelled with [3H]thymidine, and expressed as the lytic index. The lytic index was significantly increased (decreased metabolic cooperation) by tumor-promoting phorbol esters but not by non-promoting esters. The enhanced lytic index was obtained when promoters were incubated with cocultures for 10 h in a total incubation time of 48 h.

Animals↗
PubMedDate not supplied

Analysis of cellular phosphoproteins by two-dimensional gel electrophoresis: applications for cell signaling in normal and cancer cells.

Two-dimensional (2-D) gel electrophoresis has been used to map proteins from various cell types in an effort to eventually link such maps to the sequencing of the entire human genome. While this analysis indicates the cellular disposition and expression of proteins, another application of 2-D gels, the analysis of phosphoproteins, can provide much information as to the assembly and "wiring" of the signal transduction circuits within cells which appear to be enervated by phosphate exchange. The preparation and separation of 32P-labeled proteins is described, as well as various analytical methods, including: the variety of gel systems available for specialist types of analyses, comparing 33P- and 32P-labeling of proteins, imaging techniques, phosphoamino analysis, phosphopeptide separation, identifying the amino acid groups that are phosphorylated, and the identification of phosphoproteins on 2-D gels by immunoprecipitation, corunning of purified proteins, comparative mapping and microsequencing, and by Western blotting. Examples (in brackets) are given of applications in which 2-D phosphogels can be applied, which offer advantages over other techniques. These include: (i) identifying in vivo substrates for kinases (protein kinase C activated by phorbol myristate acetate), (ii) investigating cytokine signaling pathways (tumor necrosis factor and interleukin-1), (iii) investigating the effects of drugs on signaling pathways (okadaic acid, menadione and cyclooxygenase inhibitors), (iv) characterization of specific phosphoproteins (heat-shock protein Hsp27 and stathmin), (v) comparing normal and transformed cells (MRC-5 human lung fibroblasts and their SV-40-transformed counterparts, MRC-5 SV1 cells), (vi) purifying phosphoproteins, (vii) investigating the relationship of protein phosphorylation to stages in the cell cycle (stathmin), (viii) investigating protein/protein interactions, (ix) mapping in vitro kinase substrates (protein kinase C, protein kinase A, and mitogen activated protein kinase activated protein kinase 2), and (x) locating and identifying cellular phosphatases (Hsp27 phosphatase). It is possible that the mapping of phosphoproteins can be linked to other 2-D gel databases and that information derived from these can be used in the future to better understand the signaling mechanisms of normal and cancerous cells.

Amino Acid Sequence↗