Phorbol 12-Myristate 13-Acetate Induces Protein Kinase Cη-specific Proliferative Response in Astrocytic Tumor Cells

doi:10.1074/jbc.M003203200

Phorbol 12-Myristate 13-Acetate Induces Protein Kinase Cη-specific Proliferative Response in Astrocytic Tumor Cells*

From the Departments of ^‡Pathology (Neuropathology),^¶Biomedical Engineering, and ^‖Pharmacology, University of Virginia, Charlottesville, Virginia 22908

Abstract

Protein kinase C (PKC) activation has been implicated in cellular proliferation in neoplastic astrocytes. The roles for specific PKC isozymes in regulating this glial response, however, are not well understood. The aim of this study was to characterize the expression of PKC isozymes and the role of PKC-η expression in regulating cellular proliferation in two well characterized astrocytic tumor cell lines (U-1242 MG and U-251 MG) with different properties of growth in cell culture. Both cell lines expressed an array of conventional (α, βI, βII, and γ) and novel (θ and ε) PKC isozymes that can be activated by phorbol myristate acetate (PMA). Another novel PKC isozyme, PKC-η, was only expressed by U-251 MG cells. In contrast, PKC-δ was readily detected in U-1242 MG cells but was present only at low levels in U-251 MG cells. PMA (100 nm) treatment for 24 h increased cell proliferation by over 2-fold in the U-251 MG cells, whereas it decreased the mitogenic response in the U-1242 MG cells by over 90%. When PKC-η was stably transfected into U-1242 MG cells, PMA increased cell proliferation by 2.2-fold, similar to the response of U-251 MG cells. The cell proliferation induced by PMA in both the U-251 MG and U-1242-PKC-η cells was blocked by the PKC inhibitor bisindolylmaleimide (0.5 μm) and the MEK inhibitor, PD 98059 (50 μm). Transient transfection of wild type U-251 with PKC-η antisense oligonucleotide (1 μm) also blocked the PMA-induced increase in [³H]thymidine incorporation. The data demonstrate that two glioblastoma lines, with functionally distinct proliferative responses to PMA, express different novel PKC isozymes and that the differential expression of PKC-η plays a determining role in the different proliferative capacity.

Footnotes

↵* This work was supported by Grants NS35122 (to I. M. H.) from NINDS, National Institutes of Health and GM31184 (to J. J. S.) from HHS, National Institutes of Health.The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
↵§ To whom correspondence should be addressed: Dept. of Pathology (Neuropathology), University of Virginia, Charlottesville, VA 22908. Tel.: 804-924-9175; Fax: 804-924-9177; E-mail: imh5c@virginia.edu.
Published, JBC Papers in Press, May 9, 2000, DOI 10.1074/jbc.M003203200
Abbreviations:

PKC

protein kinase C

MAP

mitogen-activated protein

PMA

phorbol myristate acetate

ERK

extracellular signal-regulated kinase

BIM

bisindolylmaleimide

MEK

mitogen-activated kinase effector kinase

α-MEM

minimal essential medium-α modification

CMV

cytomegalovirus

ODN

oligo(deoxy)nucleotide

PAGE

polyacrylamide gel electrophoresis

EGF

epidermal growth factor
- Received April 13, 2000.
The American Society for Biochemistry and Molecular Biology, Inc.