Phorbol Esters Induce Death in MCF-7 Breast Cancer Cells with Altered Expression of Protein Kinase C Isoforms

Role for p53-independent Induction of gadd45 in Initiating Death

Vente, James E. de
Kukoly, Cynthia A.
Bryant, Winifred O.
Posekany, Karla J.
Chen, Jianming
Fletcher, Donald J.
Parker, Peter J.
Pettit, George J.
Lozano, Guillermina
Cook, Paul P.
Ways, D. Kirk

*Departments of Medicine, **Anatomy/Cell Biology, and ***Microbiology/Immunology, East Carolina University School of Medicine, Greenville, North Carolina 27858; ****Imperial Cancer Research Fund, Protein Phosphorylation Laboratory, London, United Kingdom WC2A 3PX; *****Cancer Research Institute, Arizona State University, Tempe, Arizona 85287; and ******Department of Molecular Genetics, M. D. Anderson Cancer Center, University of Texas, Houston, Texas 77030
This work was presented in abstract form at the 76th Annual Meeting of the Endocrine Society in Anaheim, CA, on 18 June 1994.
Address correspondence to D. Kirk Ways, M.D., Ph.D., East Carolina University School of Medicine, Department of Medicine, Greenville. NC 27858. Phone: 919-816-2567; FAX: 919-816-3096.
Revised for publication 30 March 1995 and accepted in revised form 20 June 1995.

Journal of Clinical Investigation 96(4):p 1874-1886, October 1995.

Protein kinase C (PKC) modulates growth, differentiation, and apoptosis in a cell-specific fashion. Overexpression of PKC-alpha in MCF-7 breast cancer cells (MCF-7-PKC-alpha cell) leads to expression of a more transformed phenotype. The response of MCF-7 and MCF-7-PKC-alpha cells to phorbol esters (TPA) was examined. TPA-treated MCF-7 cells demonstrated a modest cytostatic response associated with a G₁ arrest that was accompanied by Cip1 expression and retinoblastoma hypophosphorylation. While p53 was detected in MCF-7 cells, evidence for TPA-induced stimulation of p53 transcriptional activity was not evident. In contrast, TPA treatment induced death of MCF-7-PKC-alpha cells. Bryostatin 1, another PKC activator, exerted modest cytostatic effects on MCF-7 cells while producing a cytotoxic response at low doses in MCF-7-PKC-alpha cells that waned at higher concentrations. TPA-treated MCF-7-PKC-alpha cells accumulated in G₂/M, did not express p53, displayed decreased Cip1 expression, and demonstrated a reduction in retinoblastoma hypophosphorylation. TPA-treated MCF-7-PKC-alpha cells expressed gadd45 which occurred before the onset of apoptosis. Thus, alterations in the PKC pathway can modulate the decision of a breast cancer cell to undergo death or differentiation. In addition, these data show that PKC activation can induce expression of gadd45 in a p53-independent fashion. (J. Clin. Invest. 1995. 96:1874-1886.) Key words: protein kinase C centered dot phorbol esters centered dot breast cancer centered dot apoptosis centered dot p53