The Involvement of Novel Protein Kinase C Isozymes in Influencing Sensitivity of Breast Cancer MCF-7 Cells to Tumor Necrosis Factor-α
- Department of Pharmacology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15261
Abstract
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.
Footnotes
-
Send reprint requests to: Dr. Alakananda Basu, Department of Pharmacology, University of Pittsburgh School of Medicine, E1358 Biomedical Science Tower, Pittsburgh, PA 15261. E-mail:anb{at}prophet.pharm.pitt.edu.
-
This work was supported by National Institutes of Health Grants CA54294 and CA71727.
- Abbreviations:
- TNF
- tumor necrosis factor
- PKC
- protein kinase C
- DAG
- diacylglycerol
- aPKC
- atypical protein kinase C
- cPKC
- conventional protein kinase C
- nPKC
- novel protein kinase C
- NF-κB
- nuclear factor κB
- PDBu
- phorbol-12,13-dibutyrate
- ILV
- indolactam V
- MTT
- 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide
- EGTA
- ethylene glycol bis(β-aminoethyl ether)-N,N,N′,N′-tetraacetic acid
- BIM
- bisindolylmaleimide II
- Me2SO
- dimethyl sulfoxide
- PKA
- cAMP-dependent protein kinase
-
- Received May 9, 1997.
- Accepted October 6, 1997.
- The American Society for Pharmacology and Experimental Therapeutics
