Redox Regulation of the Tumor Suppressor PTEN by Hydrogen Peroxide and Tert-Butyl Hydroperoxide.

Organic peroxides and hydroperoxides are skin tumor promoters. Free radical derivatives from these compounds are presumed to be the prominent mediators of tumor promotion. However, the molecular targets of these species are unknown. Phosphatase and tensin homologs deleted on chromosome 10 (PTEN) are tumor suppressors that play important roles in cell growth, proliferation, and cell survival by negative regulation of phosphoinositol-3-kinase/protein kinase B signaling. PTEN is reversibly oxidized in various cells by exogenous and endogenous hydrogen peroxide. Oxidized PTEN is converted back to the reduced form by cellular reducing agents, predominantly by the thioredoxin (Trx) system. Here, the role of -butyl hydroperoxide (-BHP) in redox regulation of PTEN was analyzed by using cell-based and in vitro assays. Exposure to -BHP led to oxidation of recombinant PTEN. In contrast to H₂O₂, PTEN oxidation by -BHP was irreversible in HeLa cells. However, oxidized PTEN was reduced by exogenous Trx system. Taken together, these results indicate that -BHP induces PTEN oxidation and inhibits Trx system, which results in irreversible PTEN oxidation in HeLa cells. Collectively, these results suggest a novel mechanism of -BHP in the promotion of tumorigenesis.