Effects of H₂O₂ on protein tyrosine phosphatase activity in HER14 cells

Oxidative stress has been implicated in protein phosphorylation and dephosphorylation in cells. In our current studies, H₂O₂ was shown to reversibly inhibit protein tyrosine phosphatase (PTPase) activity in HER14 cells. H₂O₂ (150 mM) resulted in 40% inhibition of PTPase activity by 15 min and recovery from inhibition was nearly complete by 60 min. H₂O₂-induced inhibition or recovery of PTPase activity was not affected by cycloheximide, a protein synthesis inhibitor. L-Buthionine-[S,R]-sulfoximine (BSO), an inhibitor of glutathione synthesis, had no effect on H₂O₂-induced inhibition of PTPase activity but retarded the recovery of activity. Epidermal growth factor (EGF) and EGTA, a Ca²⁺ chelator, did not influence H₂O₂-induced inhibition or recovery of PTPase activity. These results suggest that at least 40% of fibroblast PTPase activity can be regulated by cellular redox activity.