Overexpression of the Leishmania amazonensis Ca2+-ATPase gene lmaa1 enhances virulence

A gene for a Ca2+-transporting ATPase (lmaa1) from the trypanosomatid parasite Leishmania (mexicana) amazonensis was overexpressed in two clones of L. amazonensis differing in their virulence. RNA and protein expression of the gene was increased in transfectants, as was the infectivity of transfectants versus parental types in both mouse and in vitro macrophage infection experiments. The virulence of the almost avirulent clone was enhanced such that it was more virulent than the parental 'virulent' clone. Growth of the parasites in culture as promastigotes, after isolation from mouse lesions, indicated that transfection led to improved survival of promastigotes during the stationary phase of culture. As it is in this culture phase that infective metacyclic forms develop, the key role of the Lmaa1 protein may be in metacyclogenesis. The protein may be important in the synthesis and trafficking of new proteins through the secretory pathway, as we demonstrate, using a green fluorescent protein hybrid and by immunofluorescence, that the Lmaa1 protein is located in the endoplasmic reticulum in promastigotes and amastigotes of L. amazonensis.