Trypanosoma brucei and Trypanosoma cruzi: life cycle-regulated protein tyrosine phosphatase activity

Recent evidence that Trypanosoma brucei synthesizes stage-regulated phosphotyrosine containing proteins and protein kinases stimulated us to assay bloodstream and insect stages of Trypanosoma cruzi and both pleomorphic and monomorphic clones of T. brucei for tyrosine phosphatase activity. Bloodstream and procyclic insect stages of T. brucei contained a 55-kDa protein that cross-reacted with monoclonal antibodies directed against the human placental tyrosine phosphatase PTP1B. Protein lysates of all life cycle stages of both trypanosomes dephosphorylated a nonspecific substrate, pNPP, and the specific substrate Tyr(P)Raytide. Dephosphorylation of Tyr(P)Raytide was effectively inhibited only by sodium vanadate, a specific phosphotyrosine phosphatase inhibitor, but pNPP activity was also inhibited by sodium fluoride (NaF) in lysates of T. brucei and by NaF and sodium tartrate in lysates of T. cruzi, suggesting that their respective lysates also contained serine/threonine and acid phosphatase activities. Fractionation studies revealed that most of this activity was in the cytosol. Stage regulation of tyrosine phosphatase activity in T. cruzi was strongly suggested by differences in the optimal pH for tyrosine phosphatase activity (7.0 for amastigotes and epimastigotes; 5.0 for trypomastigotes). We conclude that both species of trypanosomes synthesize tyrosine phosphatases and propose that identification and characterization of the enzymes responsible for this phosphatase activity could provide information about trypanosomal virulence or the regulation of trypanosomal growth and differentiation.