INSULIN-LIKE GROWTH-FACTOR-I INDUCES PHOSPHORYLATION IN LEISHMANIA (LEISHMANIA) MEXICANA PROMASTIGOTES AND AMASTIGOTES

Protein phosphorylation controls major steps of proliferation and diff erentiation in eukaryotic cells, However there are few studies done in protozoa particularly when being triggered by external stimuli. In th is paper we have examined the tyrosine-and serine/threonine-phosphoryl ated proteins in both promastigote and amastigote-like farms of Leishm ania (Leishmania) mexicana stimulated with insulin-like growth factor (IGF)-I. Stimulation with IGF-I induces major tyrosine phosphorylation of a 185-kDa protein in promastigotes and 60- and 40-kDa proteins in amastigotes. Analysis of total phosphorylation revealed additional set s of phosphorylated proteins: a 110-kDa protein band in promastigotes and two other proteins of 120 and 95 kDa in the amastigote-like farms. To further analyze the IGF-I-mediated response we compared it with th e phosphorylation pattern obtained with a known inducer of protein kin ase C, phorbol myristate acetate. This analysis showed overlapping pho sphorylation of most of the proteins but mainly of the 185- and 110-kD a proteins in the promastigotes and the 95-, 60- and 40-kDa proteins i n the amastigote-like forms. We thus conclude that there are phosphory lation-dependent pathways in Leishmania parasites induced by IGF-I tha t are stage-specific.