An essential role for the Leishmania major metacaspase in cell cycle progression

Abstract

Metacaspases (MCAs) are distant orthologues of caspases and have been proposed to play a role in programmed cell death in yeast and plants, but little is known about their function in parasitic protozoa. The MCA gene of Leishmania major (LmjMCA) is expressed in actively replicating amastigotes and procyclic promastigotes, but at a lower level in metacyclic promastigotes. LmjMCA has a punctate distribution throughout the cell in interphase cells, but becomes concentrated in the kinetoplast (mitochondrial DNA) at the time of the organelle's segregation. LmjMCA also translocates to the nucleus during mitosis, where it associates with the mitotic spindle. Overexpression of LmjMCA in promastigotes leads to a severe growth retardation and changes in ploidy, due to defects in kinetoplast segregation and nuclear division and an impairment of cytokinesis. LmjMCA null mutants could not be generated and following genetic manipulation to express LmjMCA from an episome, the only mutants that were viable were those expressing LmjMCA at physiological levels. Together these data suggest that in L. major active LmjMCA is essential for the correct segregation of the nucleus and kinetoplast, functions that could be independent of programmed cell death, and that the amount of LmjMCA is crucial. The absence of MCAs from mammals makes the enzyme a potential drug target against protozoan parasites.

Antagonic activities of Trypanosoma cruzi metacaspases affect the balance between cell proliferation, death and differentiation

“…12 Nevertheless, RNA interference of the three MCAs together resulted in a rapid arrest of growth with a delay in kinetoplast segregation and a cytokinesis block. In addition, Ambit et al 13 showed that limited levels of LmjMCA are essential for normal cell proliferation. As T. cruzi lacks components necessary for the RNA interference pathway, 33 and knockout strategies are restricted to non-essential single copy genes, we decided to study metacaspase overexpression in the different life-cycle stages with an inducible vector.…”

“…5 Their substrate specificity is for basic residues at P1 position, making them unable to cleave caspase substrates. 6 Evidences suggest that metacaspases modulate cell death, [7][8][9][10][11] cell cycle progression [12][13][14] and protein aggregation, 15 but there is still controversy about their functions and their relation with caspases. [16][17][18] The fact that metacaspases are not present in humans and fulfil important roles in trypanosomatids make them attractive drug targets, and a first series of inhibitors with trypanocidal activity has been developed recently.…”

Inhibition of active nuclear transport is an intrinsic trigger of programmed cell death in trypanosomatids

“…Furthermore, the L. major metacaspase seems to have an essential function in cell-cycle progression rather than in PCD. 28 And, in T. brucei, metacaspases appear to be associated with RAB11-positive endosomes, 15 and not to intervene in apoptosis. Still, intriguingly, some reports have described 'caspase-like' activities in these protozoa.…”

Miltefosine induces metacaspase and PARP genes expression in Leishmania infantum

“…Also they implicated L. major active metacaspase has effective role in the separation of the nucleus and the kinetoplast, function that could be independent of PCD. 26 In this study, PARP and metacaspase gene expression increased simultaneously. This evolution could repair cell DNA damage.…”

“…In mammalians, caspases do not only function in PCD, but they also have functions in cell proliferation and differentiation. 11 Ambit et al 26 found that LmjMCA is expressed in actively replicating amastigotes and procyclic promastigotes, but at a lower level in metacyclic promastigotes. Over expression of LmjMCA in promastigotes leads to severe growth retardation.…”