Londhe, A. D.; Rizzo, S.; Rizvi, S. M.; Bergeron, A.; Sagabala, R. S.; Banavali, N. K.; Thevenin, D.; Boivin, B.

Reversible inactivation of protein tyrosine phosphatases by reactive oxygen species (ROS) is essential to the phosphorylation of growth factor receptors. An important outcome of the inactivation of protein tyrosine phosphatase 1B (PTP1B) by ROS involves the conformational change of its phosphotyrosine binding loop which adopts a solvent exposed position in its oxidized form. We previously demonstrated that 14-3-3{zeta} binds to the phosphotyrosine binding loop of the oxidized form of PTP1B. Using a rational approach, we developed a unique protein-protein interaction (PPI) inhibitor peptide derived from the phosphotyrosine binding loop of PTP1B designed to disrupt the interaction between PTP1B and the 14-3-3{zeta}-complex. Exploiting this cell-permeable peptide, we showed decreased association between PTP1B and the 14-3-3{zeta}-complex in cells treated with epidermal growth factor (EGF). We also demonstrated that preventing the association of this 14-3-3{zeta}-complex to PTP1B deterred oxidation and inactivation of PTP1B following EGF receptor (EGFR) activation and generation of ROS. Treating cells with our PPI inhibitor decreased EGFR phosphorylation on PTP1B-specific sites. Furthermore, treating EGFR-driven epidermal cancer cells with our PPI inhibitor also significantly inhibited colony formation and cell viability, consistent with increased activation of PTP1B. These data highlight the ability of PTP1B to down-regulate critical signaling pathways in cancer when activated using peptide drugs such as our protein-protein interaction inhibitor. We anticipate that preventing or destabilizing the reversible oxidation of other members of the protein tyrosine phosphatase superfamily using PPI inhibitors may offer a foundation for a broad therapeutic approach to rectify dysregulated signaling pathways in vivo.