Wellcome Trust Centre for Molecular Parasitology, Institute of Infection, Immunity and Inflammation, College of Medical, Veterinary and Life Sciences, University of Glasgow, Glasgow G12 8TA, UK.
Cell Death Dis. 2012 Sep 6;3(9):e385. doi: 10.1038/cddis.2012.113.
Metacaspases (MCAs) are caspase family cysteine peptidases that have been implicated in cell death processes in plants, fungi and protozoa. MCAs have also been suggested to be involved in cell cycle control, differentiation and clearance of aggregates; they are virulence factors. Dissecting the function of MCAs has been complicated by the presence in many organisms of multiple MCA genes or limitations on genetic manipulation. We describe here the creation of a MCA gene-deletion mutant (Δmca) in the protozoan parasite Leishmania mexicana, which has allowed us to dissect the role of the parasite's single MCA gene in cell growth and cell death. Δmca parasites are viable as promastigotes, and differentiate normally to the amastigote form both in in vitro macrophages infection and in mice. Δmca promastigotes respond to cell death inducers such as the drug miltefosine and H(2)O(2) similarly to wild-type (WT) promastigotes, suggesting that MCAs do not have a caspase-like role in execution of L. mexicana cell death. Δmca amastigotes replicated significantly faster than WT amastigotes in macrophages and in mice, but not as axenic culture in vitro. We propose that the Leishmania MCA acts as a negative regulator of amastigote proliferation, thereby acting to balance cell growth and cell death.
类半胱天冬酶（MCAs）是一种半胱氨酸肽酶家族的胱天蛋白酶，在植物、真菌和原生动物的细胞死亡过程中被牵连。MCAs 也被认为参与细胞周期控制、分化和聚集物清除；它们是毒力因子。由于许多生物体中存在多个 MCA 基因或遗传操作的限制，因此解析 MCA 的功能变得复杂。我们在这里描述了在原生动物寄生虫利什曼原虫中创建 MCA 基因缺失突变体（Δmca），这使我们能够剖析寄生虫的单个 MCA 基因在细胞生长和细胞死亡中的作用。Δmca 寄生虫作为前鞭毛体是可行的，并且在体外巨噬细胞感染和小鼠中正常分化为无鞭毛体形式。Δmca 前鞭毛体对细胞死亡诱导剂（如 miltefosine 药物和 H2O2）的反应与野生型（WT）前鞭毛体相似，表明 MCAs 在执行利什曼原虫细胞死亡中没有半胱天冬酶样作用。Δmca 无鞭毛体在巨噬细胞和小鼠中的复制速度明显快于 WT 无鞭毛体，但在体外无细胞培养中则不然。我们提出，利什曼 MCA 作为无鞭毛体增殖的负调节剂发挥作用，从而平衡细胞生长和细胞死亡。
