Protein kinase Cε activates protein kinase B/Akt via DNA-PK to protect against tumor necrosis factor-α-induced cell death

We have previously shown that protein kinase C epsilon(PKC epsilon) protects breast cancer cells from tumor necrosis factor-alpha (TNF)-induced cell death. In the present study, we have investigated if the antiapoptotic function of PKC epsilon is mediated via Akt and the mechanism by which PKC epsilon regulates Akt activity. TNF caused a transient increase in Akt phosphorylation at Ser(473) in MCF-7 cells. Overexpression of PKC epsilon in MCF-7 cells increased TNF-induced Akt phosphorylation at Ser(473) resulting in its activation. Knockdown of PKC epsilon by small interfering RNA (siRNA) decreased TNF-induced Akt phosphorylation/activation and increased cell death. Introduction of constitutively active Akt protected breast cancer MCF-7 cells from TNF-mediated cell death and partially restored cell survival in PKC epsilon-depleted cells. Depletion of Akt in MCF-7 cells abolished the antiapoptotic effect of PKC epsilon on TNF-mediated cell death. Akt was constitutively associated with PKC epsilon and DNA-dependent protein kinase (DNA-PK), and this association was increased by TNF treatment. Overexpression of PKC epsilon enhanced the interaction between Akt and DNA-PK. Knockdown of DNA-PK by siRNA inhibited TNF-induced Akt phosphorylation and the antiapoptotic effect of Akt and PKC epsilon. These results suggest that PKC epsilon activates Akt via DNA-PK to mediate its antiapoptotic function. Furthermore, we report for the first time that DNA-PK can regulate receptor-initiated apoptosis via Akt.