Effects of the disruption of the HSP70-II gene on the growth, morphology, and virulence

The 70-kDa heat shock protein (HSP70) is highly conserved among both prokaryotes and eukaryotes and plays essential roles in diverse cellular functions not only under stress but also under normal conditions. In the protozoan Leishmania infantum, the causative agent of visceral leishmaniasis, HSP70 is encoded by two HSP70 genes. Here, we describe the phenotypic alterations of HSP70-II-deficient (Δhsp70-II) promastigotes. The absence of HSP70-II caused a major alteration in growth as the promastigotes reached stationary phase. In addition, aberrant forms were frequently observed in Δhsp70-II mutant cultures. An accumulation of cells in the G2/M phase in cultures of the Δhsp70-II mutant was determined by flow cytometry. Furthermore, Δhsp70-II promastigotes showed a limited capacity of multiplication within macrophages, even though attachment to and uptake by macrophages did not differ significantly from the wild-type. Moreover, Δhsp70-II was highly attenuated in BALB/c mouse experimental infections. In mutants re-expressing HSP70-II, the growth rate was restored, the normal morphology was recovered, and interactions with macrophages increased. However, promastigotes reexpressing HSP70-II did not recover their virulence. Overall, these data highlight the essential role played by HSP70-II expression in Leishmania virulence, pointing to this gene as a promising target for therapeutic interventions. [Int Microbiol 2008; 11(2):81-89]