Evidence of tyrosine kinase activity in the protozoan parasite Trypanosoma brucei.

Phosphorylation of proteins at tyrosine is an important mechanism for regulating cell growth and proliferation in metazoan organisms. In this report, we have demonstrated that Trypanosoma brucei, a protozoan parasite, possesses a tyrosine kinase that plays a role in regulation of proliferation of this protozoan. Genistein, a tyrosine kinase inhibitor, prevented multiplication of the parasite. An in vitro kinase assay demonstrated the presence of a kinase capable of phosphorylating an exogenous substrate at tyrosine, and genistein was able to reduce trypanosome-mediated phosphorylation of this substrate. An alkali digestion of 32P-labeled trypanosome proteins separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis indicated several proteins phosphorylated at tyrosine. These results indicate that T. brucei has a tyrosine kinase that is involved in proliferation or growth regulation of the parasite and provide further evidence for the possibility of growth factor regulation and signal transduction in trypanosomes.