Phorbal 12-myristate 13-acetate induces protein kinase C eta-specific proliferative response in astrocytic tumor cells

Protein kinase C (PKC) activation has been implicated in cellular prolifera tion in neoplastic astrocytes, The roles for specific PKC isozymes in regul ating this glial response, however, are not well understood. The aim of thi s study was to characterize the expression of PKC isozymes and the role of PKC-eta expression in regulating cellular proliferation in two well charact erized 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 (alpha, beta I, beta II, and gamma) and novel (theta and epsi lon) PKC isozymes that can be activated by phorbol myristate acetate (PMA), Another novel PKC isozyme, PKC-eta, was only expressed by U-251 MG cells. In contrast, PKC-delta was readily detected in U-1242 MG cells but was pres ent only at low levels in U-251 MG cells. PMA (100 nM) treatment for 24 h i ncreased cell proliferation by over 2-fold in the U-251 MG cells, whereas i t decreased the mitogenic response in the U-1242 MG cells by over 90%. When PKC-eta was stably transfected into U-1242 MG cells, PMA increased cell pr oliferation by 2.2-fold, similar to the response of U-251 MG cells. The cel l proliferation induced by PMA in both the U-251 MG and U-1242-PKC-eta cell s was blocked by the PKC inhibitor bisindolylmaleimide (0.5 mu M) and the M EK inhibitor, PD 98059 (50 mu M). Transient transfection of wild type U-251 with PKC-eta antisense oligonucleotide (1 mu M) also blocked the PMA-induc ed increase in [H-3]thymidine incorporation. The data demonstrate that two glioblastoma lines, with functionally distinct proliferative responses to P MA, express different novel PKC isozymes and that the differential expressi on of PKC-eta plays a determining role in the different proliferative capac ity.