Novel insights into the PKCβ-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. PKCβ-mediated phosphorylation of serine 36 in p66 has been implicated as a key regulatory step preceding mitochondrial translocation, ROS production, and cell death, and PKCβ thus may provide a target for therapeutic intervention. We performed a reassessment of PKCβ regulation of the oxidoreductase activity of p66. Although our experiments did not substantiate Ser³⁶ phosphorylation by PKCβ, they instead provided evidence for Ser¹³⁹ and Ser²¹³ as PKCβ phosphorylation sites regulating the pro-oxidant and pro-apoptotic function of p66. Mutation of another predicted PKCβ phosphorylation site also located in the phosphotyrosine binding domain, threonine 206, had no phenotype. Intriguingly, p66 with Thr²⁰⁶ and Ser²¹³ 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 PKCβ-dependent regulation of p66 activation involving Ser¹³⁹ and a motif surrounding Ser²¹³.