The involvement of novel protein kinase C isozymes in influencing sensitivity of breast cancer MCF-7 cells to tumor necrosis factor-alpha.
Protein kinase C (PKC) has been implicated in tumor necrosis factor-alpha (TNF) signaling. Structurally and functionally distinct PKC activators and selective inhibitors of PKC were used to investigate the involvement of PKC isozymes in influencing TNF sensitivity in MCF-7 cells. Activators of PKC, such as phorbol-12, 13-dibutyrate (PDBu) (1.0 microM), indolactam V (10 microM), and bryostatin 1 (1.0 microM) decreased the sensitivity of MCF-7 cells to TNF by 5-, 10-, and 1.7-fold, respectively. The PKC-specific inhibitor bisindolylmaleimide II (BIM) (> or = 1 microM) antagonized the effect of PDBu in protecting MCF-7 cells against TNF cytotoxicity. High concentrations of BIM (> or = 10 microM) also significantly enhanced the sensitivity of MCF-7 cells to TNF. In contrast, Gö 6976, a specific inhibitor of cPKCs, did not potentiate TNF sensitivity and failed to reverse the effect of PDBu. In addition, BIM but not Gö 6976 blocked PDBu-mediated down-regulation of TNF receptors. There was no correlation between down-regulation of PKC alpha, -delta, and -epsilon, and protection against TNF cytotoxicity by PKC activators. A 6-hr exposure to 1.0 microM PDBu, 10 microM indolactam V, and 1.0 microM bryostatin 1 caused a 1.8-, 3.5- and 1.2-fold induction, respectively, of nPKC eta in MCF-7 cells. Similar exposure to BIM but not Gö 6976 led to a significant down-regulation of nPKC eta. This novel regulation of PKC eta implicates this isozyme in PDBu-mediated protection of MCF-7 cells against TNF cytotoxicity.
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Department of Pharmacology, University of Pittsburgh School of Medicine, Pennsylvania 15261, USA. anb@prophet.pharm.pitt.edu
D000970:Antineoplastic Agents / Q000494:pharmacology; D001943:Breast Neoplasms / Q000188:drug therapy* / Q000201:enzymology*; D054713:Bryostatins; D002273:Carcinogens / Q000494:pharmacology; D004789:Enzyme Activation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006801:Humans; D007211:Indoles / Q000494:pharmacology; D007527:Isoenzymes / Q000037:antagonists & inhibitors / Q000187:drug effects / Q000502:physiology*; D007769:Lactams / Q000494:pharmacology; D007783:Lactones / Q000494:pharmacology; D018942:Macrolides; D008301:Maleimides / Q000494:pharmacology; D015240:Phorbol 12,13-Dibutyrate / Q000494:pharmacology; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000187:drug effects / Q000502:physiology*; D018124:Receptors, Tumor Necrosis Factor / Q000378:metabolism; D012680:Sensitivity and Specificity; D014407:Tumor Cells, Cultured; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism / Q000494:pharmacology*
D000970:Antineoplastic Agents; D054713:Bryostatins; D002273:Carcinogens; D004791:Enzyme Inhibitors; D007211:Indoles; D007527:Isoenzymes; D007769:Lactams; D007783:Lactones; D018942:Macrolides; D008301:Maleimides; D018124:Receptors, Tumor Necrosis Factor; D014409:Tumor Necrosis Factor-alpha; D015240:Phorbol 12,13-Dibutyrate; C046785:bryostatin 1; C043969:indolactam V; D011493:Protein Kinase C; C088060:bisindolylmaleimide