Novel Insights into the PKC-dependent Regulation of the Oxidoreductase p66Shc

Dysfunctional mitochondria contribute to the development of many diseases and pathological conditions through the excessive production of reactive oxygen species (ROS), and, where studied, ablation of p66Shc (p66) was beneficial. p66 translocates to the mitochondria and oxidizes cytochrome c to yield H2O2, which in turn initiates cell death. PKC-mediated phosphorylation of serine 36 in p66 has been implicated as a key regulatory step preceding mitochondrial translocation, ROS production, and cell death, and PKC thus may provide a target for therapeutic intervention. We performed a reassessment of PKC regulation of the oxidoreductase activity of p66. Although our experiments did not substantiate Ser(36) phosphorylation by PKC, they instead provided evidence for Ser(139) and Ser(213) as PKC phosphorylation sites regulating the pro-oxidant and pro-apoptotic function of p66. Mutation of another predicted PKC phosphorylation site also located in the phosphotyrosine binding domain, threonine 206, had no phenotype. Intriguingly, p66 with Thr(206) and Ser(213) mutated to glutamic acid showed a gain-of-function phenotype with significantly increased ROS production and cell death induction. Taken together, these data argue for a complex mechanism of PKC-dependent regulation of p66 activation involving Ser(139) and a motif surrounding Ser(213).