Our previous results have demonstrated that phorbol 12-myristate 13-acetate (TPA) and insulin synergistically stimulate the activity of phosphatidylinositol-3 kinase (PI-3 kinase) and PI-3 kinase plays an important role in both of TPA-induced AP-1 activation and cell transformation in tumour promotion sensitive (P+) JB6 cells. In the present study, we investigated the role of PKC and its isozymes in the synergistic induction of PI-3 kinase by TPA and insulin. Bisindolylmaleimide inhibits TPA-and TPA + insulin-induced PI-3 kinase activity. Pretreatment of cells for 24 h with TPA has significant inhibitory effects on TPA-induced PI-3 kinase activity and abolishes the synergistic effect of TPA and insulin-stimulated PI-3 kinase activity. Furthermore, overexpression of a dominant negative PKCε, but not dominant negative PKCα, blocks the synergistic effect of TPA and insulin-induced PI-3 kinase activity. These results indicate that the potentiation effect of TPA on insulin-induced PI-3 kinase activity is specific through PKCε in JB6 cells.
Bibliographical noteFunding Information:
This work was supported by the Hormel Foundation. We thank Dr. H. H. O. Schmid for critical reading, Dr. Peter Blumberg for generous gifts of dominant negative PKCα and PKCϵ mutants, and Ms. Jeanne Ruble for secretarial assistance.
Copyright 2007 Elsevier B.V., All rights reserved.
- Phorbol ester
- Phosphatidylinositol-3 kinase
- Protein kinase C