Yuko Katakami

Synergistic action of protein kinase C and calcium for histamine release from rat peritoneal mast cells

When rat mast cells were stimulated by concanavalin A, phosphatidylinositol turnover was induced. Concurrently, several cytosol proteins were phosphorylated and histamine was released. 1-Oleoyl-2-acetyl-glycerol ( OAG ) and 12-O-tetradecanoylphorbol-13-acetate (TPA), known as direct activators of protein kinase C in intact cells, induced phosphorylation of the same spectrum of proteins. These proteins also served in vitro as preferable substrates for protein kinase C. The simultaneous addition of OAG or TPA and A23187 synergistically enhanced histamine release from mast cells. It is suggestive that protein kinase C activation and Ca2+ mobilization play essential roles for this cellular response.

Effect of 1,25-dihydroxyvitamin D3 on cytokine-induced thymocyte proliferation☆

To clarify the mechanism of the inhibitory effect of 1,25(OH)2D3 on lymphocyte proliferation, the effect of 1,25(OH)2D3 on murine thymocyte proliferation induced by interleukin 1 (IL-1), or 2 (IL-2) was examined. Physiological concentrations of 1,25(OH)2D3 inhibited thymocyte proliferation induced by IL-1 and IL-2 in similar fashion suggesting an inhibition of the response to IL-2 by this hormone. In addition, cortisone-resistant thymocytes (including a majority of medullary thymocytes), which proliferate more vigorously in response to IL-1 than do untreated thymocytes, were more sensitive to 1,25(OH)2D3 inhibition. Therefore, the inhibition of IL-2 production of the mature medullary thymocyte by this hormone was also suggested.

Possible involvement of protein kinase C in interleukin-1 production by mouse peritoneal macrophages

Both lipopolysaccharide (LPS) and phorbol-12,13-dibutyrate (PDBu), a protein kinase C-activating phorbol ester, induced interleukin-1 (IL-1) production in mouse peritoneal macrophages. Prolonged treatment of the cells with PDBu led to the down-regulation and complete disappearance of protein kinase C. In these cells, PDBu did not increase IL-1 production, but LPS still stimulated IL-1 production although the maximum level was slightly reduced. These results suggest that protein kinase C and another unknown signal pathway are involved in LPS-induced IL-1 production.

Cooperative effects of tumor necrosis factor-α and 1,25-dihydroxyvitamin D3 on growth inhibition, differentiation, and c-myc reduction in human promyelocytic leukemia cell line HL-60

The simultaneous addition of recombinant human tumor necrosis factor-alpha (rTNF-alpha) and 1,25-dihydroxyvitamin D3 (1,25-(OH)2D3) synergistically induced growth inhibition and differentiation of the human promyelocytic leukemia cell line HL-60. A significantly greater reduction in c-myc mRNA level was also observed after a 20-h combined treatment with rTNF-alpha and 1,25-(OH)2D3 than was observed following administration of either agent alone. These results suggest that rTNF-alpha and 1,25-(OH)2D3 induce HL-60 cell growth inhibition through different molecular mechanisms, and that their simultaneous administration could provide a new approach to the treatment of cancer.

Inhibitors of IL-2 production and IL-2 receptor expression in human leukemic T-cell line, Jurkat

1-(5-Isoquinolinylsulfonyl)-2-methylpiperazine (H-7), a protein kinase inhibitor, suppressed interleukin 2 (IL-2) production and IL-2 receptor (IL-2R) expression of the human leukemic T-cell line, Jurkat, induced by 12-O-tetradecanoyl-phorbol-13-acetate and phytohemagglutinin-P. This effect was significant at 5 microM H-7 without loss of cell viability. Such activity was not observed with N-(2-guanidinoethyl)-5-isoquinolinesulfonamide (HA 1004), a potent inhibitor of cGMP- and cAMP-dependent kinases, and a weak inhibitor of Ca2+-phospholipid-dependent protein kinase (protein kinase C). These findings suggest that protein kinase C is more closely associated with IL-2 receptor expression and IL-2 production of T cells than cGMP- or cAMP-dependent kinases. In addition, N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide (W-7), a calmodulin inhibitor, suppressed both IL-2 production and IL-2R expression. Cycrosporin A (Cy A), a potent immunosuppressive drug, markedly inhibited IL-2 production of Jurkat cells whereas it did not affect the IL-2R expression. Thus, the mechanism of action of Cy A appears to differ from that of the protein kinase inhibitor, H-7, and the calmodulin inhibitor, W-7.

Effect of prostaglandin E2 on gamma-interferon and 1,25(OH)2D3 vitamin D3-induced c-myc reduction during HL-60 cell differentiation

The effect of prostaglandin E2 (PGE2) on the reduction of c-myc expression during the differentiation of the human leukemic cell line, HL-60, was examined. PGE2, a potent inducer of intracellular cyclic AMP (cAMP) in HL-60 cells, augmented monocyte-associated cell surface antigens induced by human gamma-interferon (IFN-gamma) or 1 alpha,25-dihydroxyvitamin D3 (1,25(OH)2D3) in these cells. The elevation of intracellular cAMP was induced dose-dependently by PGE2, but not by IFN-gamma or 1,25(OH)2D3. Changes were also seen in functional differentiation, such as, the increase of phagocytic capability and superoxide generation. PGE2 also enhanced the reduction of c-myc expression and the down-regulation of transferrin receptor by IFN-gamma or 1,25(OH)2D3, whereas PGE2 alone did not induce these phenotypic changes. These data suggest that IFN-gamma and 1,25(OH)2D3 reduce c-myc expression of HL-60 cells by a mechanism other than the augmentation of intracellular cAMP.

Calcium and Inositol Phospholipid Degradation in Signal Transduction

Signal-induced inositol phospholipid breakdown appears to be a sign for the transmembrane control of cellular functions and proliferation through activation of protein kinase C. This enzyme requires \(C{{a}^{{{{2}^{ + }}}}}\) and phospholipid. Diacylglycerol, which is derived from the phospholipid breakdown, dramatically increases the affinity of protein kinase C for \(C{{a}^{{{{2}^{ + }}}}}\), and thereby renders this enzyme fully active without \(C{{a}^{{{{2}^{ + }}}}}\) mobilization. A series of experiments with exogenous diacylglycerol and are both essential and synergistically effective in eliciting full physiological cellular responses. In many, but not all, tissues such as platelets, mast cells, neutrophils and lymphocytes, stimulation of the receptors that produce cyclic AMP inhibits inositol phospholipid breakdown and blocks the activation of protein kinase C. Tumor-promoting phorbol esters, when intercalated into cell membranes, may substitute for diacylglycerol and permanently activate protein kinase C irrespective of the feedback control by cyclic AMP.