Nasirudeen A M A, Tan Kevin S W
Laboratory of Molecular and Cellular Parasitology, Department of Microbiology, Faculty of Medicine, National University of Singapore, Singapore.
Eur J Cell Biol. 2004 Sep;83(9):477-82. doi: 10.1078/0171-9335-00411.
Blastocystis hominis undergo apoptosis after treatment with a cytotoxic monoclonal antibody (MAb), 1D5, by mechanisms that are not fully understood, although our previous study demonstrated that caspase-3-like protease activity is involved. To elucidate the mechanism of MAb 1D5-induced apoptosis, we inhibited Blastocystis caspase-3-like protease to investigate if there would be a concomitant decrease in in situ DNA fragmentation. However, MAb 1D5-induced apoptosis, evidenced by DNA fragmentation, was not completely blocked by pretreating with specific caspase-3 inhibitor, Ac-DEVD-CHO, indicating that caspase-independent apoptotic pathways might also be involved. Our results also revealed that the treatment with MAb 1D5 resulted in the loss of mitochondrial membrane potential (deltapsim), independent of Ac-DEVD-CHO pretreatment. In conclusion, this study demonstrates that MAb 1D5-induced apoptosis in B. hominis is not wholly dependent on caspase-3-like protease activity and is associated with mitochondrial dysregulation. This is the first report showing evidence for complex apoptotic pathways in a unicellular parasite.
人芽囊原虫在用细胞毒性单克隆抗体（MAb）1D5处理后会发生凋亡，其机制尚未完全明确，尽管我们之前的研究表明其涉及类半胱天冬酶-3蛋白酶活性。为阐明单克隆抗体1D5诱导凋亡的机制，我们抑制人芽囊原虫的类半胱天冬酶-3蛋白酶，以研究原位DNA片段化是否会随之减少。然而，由DNA片段化证明的单克隆抗体1D5诱导的凋亡并未因用特异性半胱天冬酶-3抑制剂Ac-DEVD-CHO预处理而完全被阻断，这表明非半胱天冬酶依赖性凋亡途径可能也参与其中。我们的结果还显示，用单克隆抗体1D5处理会导致线粒体膜电位（Δψm）丧失，且与Ac-DEVD-CHO预处理无关。总之，本研究表明单克隆抗体1D5诱导人芽囊原虫凋亡并不完全依赖类半胱天冬酶-3蛋白酶活性，且与线粒体功能失调有关。这是首份显示单细胞寄生虫中存在复杂凋亡途径证据的报告。
