Dose-dependent differential effect of hemin on protein synthesis and cell proliferation inLeishmania donovani promastigotes culturedin vitro

Leishmania donovani requires an exogenous source of heme for growth and transformation. Inin vitro culture of the free-living promastigotes, exogenously added hemin enhances cell proliferation. In this investigation, the question of the function of heme with particular reference to protein synthesis and cell proliferation has been addressed. The results ofin vitro cell culture experiments demonstrated that hemin (10 μM) alone is suitable for supporting optimum level of protein synthesis, and thereby cell proliferation of promastigotes to an extent that it can replace fetal bovine serum. However,in situ labelling experiments along with Western blots revealed that high concentration of hemin (50 μM) reduced the level of protein synthesis in general and of β-tubulin in particular with a concomitant induction of hsp90, and induced consequent morphological changes that are observed duringin situ transformation of promastigotes in mammalian macrophages. These results therefore suggest that sudden exposure to high concentration of heme in mammalian macrophages may be one of the key factors that trigger promastigote to amastigote transformation inL. donovani. Furthermore, hemin with its dual characteristic could be used as a tool to understand molecular mechanism of cell proliferation and transformation in these parasites.