pyrimidinones and mezerein

Human platelets were depleted of intracellular Ca2+ and then made selectively permeable to external Ca2+ by addition of the ionophore ionomycin. In this cell system a rapid release of arachidonic acid was seen in direct response to added Ca2+ at concentrations corresponding to cytosolic Ca2+ levels measured in thrombin-stimulated platelets. Thrombin and other activators of Ca2+/phospholipid-dependent protein kinase (C-kinase) potentiated the Ca2+-stimulated arachidonic acid release while exerting little or no effect in the absence of added Ca2+. Agents which increase (R59022) or decrease (isoquinolinesulphonylmethylpiperazine) the activation of C-kinase correspondingly enhanced or inhibited, respectively, the potentiation of arachidonic acid release caused by thrombin. These results support the hypothesis that arachidonic acid release in human platelets is regulated by a co-operative action between intracellular Ca2+ and C-kinase.

Topics: 1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine; Arachidonic Acid; Arachidonic Acids; Blood Platelets; Calcium; Diglycerides; Diterpenes; Drug Synergism; Humans; Isoquinolines; Phospholipids; Piperazines; Protein Kinase C; Pyrimidinones; Terpenes; Tetradecanoylphorbol Acetate; Thiazoles; Thrombin

Human myeloid leukemia KG-1 cells are induced to differentiate to macrophage-like cells by tumor-promoting phorbol esters, such as 12-O-tetradecanoylphorbol-13-acetate (TPA). Cells from the cloned subline, KG-1a, unlike the parental line, are resistant to the differentiating effect of TPA. In the present studies, we investigated in these cells protein phosphorylation stimulated by various protein kinase C activators, including 1-oleoyl-2-acetylglycerol in the presence of the diacylglycerol kinase inhibitor R59022, TPA, mezerein, and bryostatin. All the agents stimulated, to a greater extent and with a higher potency, phosphorylation of several proteins in KG-1 cells than in KG-1a cells. On the other hand, these agents markedly stimulated phosphorylation of other proteins in KG-1a cells compared to that in KG-1 cells. The findings indicated that the actions of the diacylglycerol, 1-oleoyl-2-acetylglycerol, and the non-metabolizable activators (TPA, mezerein, and bryostatin) were very similar but not fully equivalent; and that KG-1a cells exhibited altered (increased or decreased) phosphorylation patterns, perhaps related to the TPA resistance characteristic of this subline of cells.

Topics: Bryostatins; Cell Differentiation; Cell Line; Diglycerides; Diterpenes; Drug Resistance; Enzyme Activation; Humans; Lactones; Leukemia, Myeloid, Acute; Macrolides; Phosphorylation; Protein Kinase C; Proteins; Pyrimidinones; Terpenes; Tetradecanoylphorbol Acetate; Thiazoles