Mitochondrial H₂O₂ regulates the angiogenic phenotype via PTEN oxidation

Recent studies have demonstrated that the tumor suppressor PTEN (phosphatase and tensin homolog deleted from chromosome 10), the antagonist of the phosphosphoinositol-3-kinase (PI3K) signaling cascade, is susceptible to H₂O₂-dependent oxidative inactivation. This study describes the use of redox-engineered cell lines to identify PTEN as sensitive to oxidative inactivation by mitochondrial H₂O₂. Increases in the steady state production of mitochondrial derived H₂O ₂, as a result of manganese superoxide dismutase (Sod2) overexpression, led to PTEN oxidation that was reversed by the coexpression of the H₂O₂-detoxifying enzyme catalase. The accumulation of an oxidized inactive fraction of PTEN favored the formation of phosphatidylinositol 3,4,5-triphosphate at the plasma membrane, resulting in increased activation of Akt and modulation of its down-stream targets. PTEN oxidation in response to mitochondrial H₂O₂ enhanced PI3K signaling, leading to increased expression of the key regulator of angiogenesis, vascular endothelial growth factor. Overexpression of PTEN prevented the H ₂O₂-dependent increase in vascular endothelial growth factor promoter activity and immunoreactive protein, whereas a mutant PTEN (G129R), lacking phosphatase activity, did not. Furthermore, mitochondrial generation of H₂O₂ by Sod2 promoted endothelial cell sprouting in a three-dimensional in vitro angiogenesis assay that was attenuated by catalase coexpression or the PI3K inhibitor LY2949002. Moreover, Sod2 overexpression resulted in increased in vivo blood vessel formation that was H₂O₂-dependent as assessed by the chicken chorioallantoic membrane assay. Our findings provide the first evidence for the involvement of mitochondrial H₂O₂ in regulating PTEN function and the angiogenic switch, indicating that Sod2 can serve as an alternative physiological source of the potent signaling molecule, H₂O ₂.