TY - JOUR T1 - The Involvement of Novel Protein Kinase C Isozymes in Influencing Sensitivity of Breast Cancer MCF-7 Cells to Tumor Necrosis Factor-α JF - Molecular Pharmacology JO - Mol Pharmacol SP - 105 LP - 111 DO - 10.1124/mol.53.1.105 VL - 53 IS - 1 AU - Alakananda Basu Y1 - 1998/01/01 UR - http://molpharm.aspetjournals.org/content/53/1/105.abstract N2 - Protein kinase C (PKC) has been implicated in tumor necrosis factor-α (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 μm), indolactam V (10 μm), and bryostatin 1 (1.0 μm) decreased the sensitivity of MCF-7 cells to TNF by 5-, 10-, and 1.7-fold, respectively. The PKC-specific inhibitor bisindolylmaleimide II (BIM) (≥1 μm) antagonized the effect of PDBu in protecting MCF-7 cells against TNF cytotoxicity. High concentrations of BIM (≥10 μm) 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 PKCα, -δ, and -ε, and protection against TNF cytotoxicity by PKC activators. A 6-hr exposure to 1.0 μm PDBu, 10 μm indolactam V, and 1.0 μm bryostatin 1 caused a 1.8-, 3.5- and 1.2-fold induction, respectively, of nPKCη in MCF-7 cells. Similar exposure to BIM but not Gö 6976 led to a significant down-regulation of nPKCη. This novel regulation of PKCη implicates this isozyme in PDBu-mediated protection of MCF-7 cells against TNF cytotoxicity. ER -