Effects of regulatory domains of specific isoforms of protein kinase C on growth control and apoptosis in MCF-7 breast cancer cells.
Protein kinase C (PKC) is a multigene family consisting of at least 11 isoforms that play key roles in growth control and tumorigenesis. To understand the roles of specific isoforms of PKC in breast cancer, we generated derivatives of the human breast cancer cell line MCF-7 that stably overexpress dominant negative mutants (REG) of PKC-alpha, -epsilon, or -zeta, which encode only the regulatory domains of the respective isoforms. When stimulated to re-enter the cell cycle after serum starvation, the MCF-7/PKC-alpha-REG cell line exhibited enhanced cell-cycle progression in comparison to the control cell line. These cells also showed increased sensitivity to growth inhibition and induction of apoptosis in response to various cytotoxic stimuli, including serum starvation, tamoxifen, and gamma-radiation. Western blot analysis indicated that the MCF-7/PKC-alpha-REG cell line displayed marked decreases in the levels of the cyclin-dependent kinase inhibitor p21CIP1 and the anti-apoptotic protein bcl-2. Similar, but less striking, effects were seen in the MCF-7/PKC-epsilon-REG cell line, and the MCF-7/PKC-zeta-REG cell line showed minimal changes, when compared to the control cells. Taken together, these results suggest that the endogenous PKC-alpha in MCF-7 cells plays a critical role in regulating cell-cycle control and apoptosis, in part through upregulating the expression of p21CIP1 and bcl-2. Therefore, inhibitors of PKC-alpha may potentiate the activity of cytotoxic agents in the therapy of breast cancer.
Soh
Jae-Won
JW
Herbert Irving Comprehensive Cancer Center and Department of Medicine, College of Physicians & Surgeons, Columbia University, New York, NY 10032, USA. jk190@columbia.edu
Lee
Yun-Sil
YS
Weinstein
I Bernard
IB
D018931:Antineoplastic Agents, Hormonal / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects; D015153:Blotting, Western; D001943:Breast Neoplasms / Q000201:enzymology*; D002453:Cell Cycle / Q000187:drug effects; D045744:Cell Line, Tumor / Q000187:drug effects / Q000201:enzymology; D005260:Female; D005434:Flow Cytometry; D006801:Humans; D007527:Isoenzymes; D011493:Protein Kinase C / Q000096:biosynthesis*; D013629:Tamoxifen / Q000494:pharmacology
D018931:Antineoplastic Agents, Hormonal; D007527:Isoenzymes; D013629:Tamoxifen; D011493:Protein Kinase C