PTEN and neoplasm: The oxidation of PTEN forms a disulfide bridge that inactivates its tumor-suppressive catalytic activity;17, 18 Src oxidation increases its autophosphorylation and concomitant activation.19, 20 Indeed, an elevated level of oxidized PTEN and Src in keratinocytes treated with H2O2 and MNNG was detected by PEG-switch assay, further confirmed by Oxyblot (Figure 2d, Supplementary Figures S1B and C).