AUTHOR=Li Muzi , Wang Hui , Liu Jing , Hao Pan , Ma Lei , Liu Qun 

TITLE=The Apoptotic Role of Metacaspase in Toxoplasma gondii

JOURNAL=Frontiers in Microbiology

VOLUME=6

YEAR=2016

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2015.01560

DOI=10.3389/fmicb.2015.01560

ISSN=1664-302X

ABSTRACT=<p><italic>Toxoplasma gondii</italic> is a major opportunistic pathogen that spreads in a range of animal species and human beings. Quite a few characterizations of apoptosis have been identified in <italic>T. gondii</italic> treated with apoptosis inducers, but the molecular mechanisms of the pathway are not clearly understood. Metacaspases are caspase-like cysteine proteases that can be found in plants, fungi, and protozoa in which caspases are absent. Metacaspases are multifunctional proteases involved in apoptosis-like cell death, insoluble protein aggregate clearance, and cell proliferation. To investigate whether <italic>T. gondii</italic> metacaspase (<italic>Tg</italic>MCA) is involved in the apoptosis of the parasites, we generated <italic>Tg</italic>MCA mutant strains. Western blot analysis indicated that the autoproteolytic processing of <italic>Tg</italic>MCA was the same as that for metacaspases of some other species. Indirect immunofluorescence assay (IFA) showed that <italic>Tg</italic>MCA was dispersed throughout the cytoplasm and relocated to the nucleus when the parasites were exposed to the extracellular environment, which indicated the execution of its function in the nucleus. The number of apoptosis parasites was significantly diminished in the <italic>Tg</italic>MCA knockout strain and increased in the <italic>Tg</italic>MCA overexpression strain after treatment with extracellular buffer, as determined by the terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay. The lack of <italic>Tg</italic>MCA did not affect the parasite propagation <italic>in vitro</italic> and virulence <italic>in vivo</italic>, suggesting that it is probably redundant in parasite propagation. But overexpression of <italic>Tg</italic>MCA reduced the intracellular parasites growth <italic>in vitro</italic>. The <italic>Tg</italic>MCA knockout strain showed more viability in extracellular buffer compared to the parental and overexpression lines. In this study, we demonstrated that <italic>Tg</italic>MCA contributes to the apoptosis of <italic>T. gondii</italic>.</p>