ucn-1028-c and Burkitt-Lymphoma

Induction of the p40/46 and p69/71 isoforms of the 2',5'-oligoadenylate (2-5A) synthetase by interferon-alpha (IFN-alpha) is variable among six different Burkitt lymphoma cell lines with Ramos cells expressing among the highest levels of these enzymes. Inhibitors of protein kinase C (PKC) block induction of mRNAs encoding both isoforms; however, induction of the p69/71 isoform is more sensitive to these inhibitors. Down-regulation of PKC by prolonged treatment with 12-O-tetradecanoylphorbol-13-acetate (TPA) also blocks induction of 2-5A synthetase mRNAs and decreases both constitutive and IFN-alpha-induced enzymatic activity. Cotreatment of cells with TPA and IFN-alpha increases induction of 2-5A synthetase mRNAs above that seen in cells treated with IFN-alpha alone. IFN-alpha does not directly activate PKC-alpha or PKC-delta, the two most abundant PKC isoforms present in Ramos cells, suggesting that PKC activation by another signaling pathway is necessary for maximal induction of 2-5A synthetases by IFN-alpha.

Topics: 2',5'-Oligoadenylate Synthetase; Alkaloids; Benzophenanthridines; Burkitt Lymphoma; Enzyme Activation; Enzyme Induction; Enzyme Inhibitors; Gene Expression Regulation, Enzymologic; Humans; Interferon-alpha; Isoenzymes; Naphthalenes; Phenanthridines; Protein Kinase C; RNA, Messenger; Signal Transduction; Tetradecanoylphorbol Acetate; Tumor Cells, Cultured

In addition to a role for de novo protein synthesis in apoptosis we have previously shown that activation of a protein phosphatase or loss of activity of a kinase is also important in radiation-induced apoptosis in human cells [Baxter, and Lavin (1992): J Immunol 148:149-1954]. We show here that some inhibitors of protein kinases exacerbate radiation-induced apoptosis in the human cell line BM13674. The specific protein kinase A inhibitor isoquinoline sulfonamide (20 microM) gave rise to significantly increased levels of apoptosis at 2-6 h postirradiation compared to values after radiation exposure only. The same concentration of isoquinolinesulfonamide, which was effective in increasing apoptosis, reduced activity markedly. A 66% inhibition of cyclic AMP-dependent protein kinase A activity occurred in unirradiated cells at this concentration of H89 and activity was reduced to 58% in irradiated cells. Calphostin C, a specific inhibitor of protein kinase C, at a concentration of 0.1 microM, which caused 68% inhibition of enzyme activity in irradiated cells, failed to enhance the level of radiation-induced apoptosis. Other kinase inhibitors did not lead to an additional increase in apoptosis over and above that observed after irradiation. The results obtained here provide further support for an important role for modification of existing proteins during radiation-induced apoptosis.

Topics: 1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine; Apoptosis; Burkitt Lymphoma; Cyclic AMP-Dependent Protein Kinases; Enzyme Inhibitors; Humans; Isoquinolines; Naphthalenes; Piperazines; Polycyclic Compounds; Protein Kinase C; Protein Kinase Inhibitors; Protein Kinases; Sulfonamides; Tumor Cells, Cultured