Protein kinase C delta overexpression enhances radiation sensitivity via extracellular regulated protein kinase 1/2 activation, abolishing the radiation-induced G(2)-M arrest

Abstract

Protein kinase C (PKC) has been widely implicated in regulation of cell growth/cell cycle progression and apoptosis. However, the role of PKCS in radiosensitivity and cell cycle regulation remains unclear. Overexpression of PKCdelta increased Ca2+- independent PKC activity without altering other PKC isoforms (PKCalpha, -beta1, -epsilon, and -zeta), and extracellular regulated protein kinase (ERK) 1/2 activity was also increased in PKCdelta-specific manner. A clonogenic survival assay showed that PKCdelta-overexpressed cells had more radiosensitivity and pronounced induction of apoptosis than control cells. Flow cytometric analysis revealed that PKCdelta made the cells escape from radiation-induced G(2)-M arrest. Moreover, p53 and p21(Waf) induction by radiation were higher in PKCdelta-overexpressed cells than control cells, and PKCdelta-mediated apoptosis was reduced, when radiation-induced ERK1/2 activity was inhibited by PD98059. Furthermore, PKCdelta antisense and rottlerin, PKC inhibitor-abrogated PKCS-mediated radiosensitivity and reduced ERK1/2 activity to the control vector level. These results demonstrated that PKCS overexpression enhanced radiation-induced apoptosis and radiosensitivity via ERK1/2 activation, thereby abolishing the radiation-induced G(2)-M arrest and finally apoptosis.