PKCε-mediated ERK1/2 activation involved in radiation-induced cell death in NIH3T3 cells

Protein kinase C (PKC) isoforms play distinct roles in cellular functions. We have previously shown that ionizing radiation activates PKC isoforms (alpha, delta, epsilon, and zeta), however, isoform-specific sensitivities to radiation and its exact mechanisms in radiation mediated signal transduction are not fully understood. In this study, we showed that overexpression of PKC isoforms (alpha, delta, epsilon, and zeta) increased radiation-induced cell death in NIH3T3 cells and PKCepsilon overexpression was predominantly responsible. In addition, PKCepsilon overexpression increased ERK1/2 activation without altering other MAP-kinases such as p38 MAPK or JNK Co-transfection of dominant negative PKCepsilon (PKCepsilon-KR) blocked both PKCepsilon-mediated ERK1/2 activation and radiation-induced cell death, while catalytically active PKCepsilon construction augmented these phenomena. When the PKCepsilon overexpressed cells were pretreated with PD98059, MEK inhibitor, radiation-induced cell death was inhibited. Co-transfection of the cells with a mutant of ERK1 or -2 (ERK1-KR or ERK2-KR) also blocked these phenomena, and co-transfection with dominant negative Ras or Raf cDNA revealed that PKCepsilon-mediated ERK1/2 activation was Ras-Raf-dependent. In conclusion, PKCepsilon-mediated ERK1/2 activation was responsible for the radiation-induced cell death. (C) 2002 Elsevier Science B.V. All rights reserved.