Abstract
The role of the surface membrane Zn-proteinase in protecting the cellular integrity of the macrophage parasite Leishmania mexicana amazonensis from intraphagolysosomal cytolysis was studied. These cells lose their infectivity to host macrophages after prolonged cultivation in axenic growth medium. The virulent and attenuated variants of the parasite cells were cloned. Failure of these attenuated parasite cells to survive inside macrophage phagolysosomes is associated with 20- to 50-fold reduction in the expression of surface gp63 protein. In situ inhibition of gp63 proteinase activity inside Leishmania-infected macrophage phagolysosomes with targeted delivery of an inhibitor of gp63 proteinase activity, 1,10-phenanthroline, selectively eliminated intracellular Leishmania amastigotes, further suggesting the importance of this proteinase in phagolysosomal survival of the parasite. An upstream sequence (US) of the gp63 gene was cloned in front of the bacterial chloramphenicol acetyltransferase (CAT) gene in plasmid pCATbasic. Transfection of L. mexicana amazonensis cells with this recombinant plasmid showed that expression of the CAT gene from this US is 15- to 20-fold higher in virulent clones than in avirulent clones of the parasite. Band shift analysis with the cloned US also showed that binding of protein(s) was 15- to 20-fold higher in virulent cell extract than in avirulent cell extract. Coating of attenuated cells or liposomes with proteolytically active gp63 protects them from degradation inside macrophage phagolysosomes. These results suggest a novel mechanism of survival of this phagolysosomal parasite with the help of its surface Zn-proteinase.