Arhets P, Olivo J C, Gounon P, Sansonetti P, Guillén N
Unité de Pathogénie Microbienne Moléculaire, Institut National de la Santé et de la Recherche Médicale U389, 75724 Paris Cédex 15, France.
Mol Biol Cell. 1998 Jun;9(6):1537-47. doi: 10.1091/mbc.9.6.1537.
Several changes in cell morphology take place during the capping of surface receptors in Entamoeba histolytica. The amoebae develop the uroid, an appendage formed by membrane invaginations, which accumulates ligand-receptor complexes resulting from the capping process. Membrane shedding is particularly active in the uroid region and leads to the elimination of accumulated ligands. This appendage has been postulated to participate in parasitic defense mechanisms against the host immune response, because it eliminates complement and specific antibodies bound to the amoeba surface. The involvement of myosin II in the capping process of surface receptors has been suggested by experiments showing that drugs that affect myosin II heavy-chain phosphorylation prevent this activity. To understand the role of this mechanoenzyme in surface receptor capping, a myosin II dominant negative strain was constructed. This mutant is the first genetically engineered cytoskeleton-deficient strain of E. histolytica. It was obtained by overexpressing the light meromyosin domain, which is essential for myosin II filament formation. E. histolytica overexpressing light meromyosin domain displayed a myosin II null phenotype characterized by abnormal movement, failure to form the uroid, and failure to undergo the capping process after treatment with concanavalin A. In addition, the amoebic cytotoxic capacities of the transfectants on human colon cells was dramatically reduced, indicating a role for cytoskeleton in parasite pathogenicity.
在溶组织内阿米巴表面受体封帽过程中，细胞形态会发生几种变化。变形虫会形成尾状结构，这是一种由膜内陷形成的附属物，它会积累封帽过程产生的配体 - 受体复合物。膜脱落在尾状结构区域特别活跃，并导致积累的配体被清除。据推测，这种附属物参与了针对宿主免疫反应的寄生防御机制，因为它能清除与变形虫表面结合的补体和特异性抗体。实验表明，影响肌球蛋白II重链磷酸化的药物会阻止表面受体的封帽活性，这提示了肌球蛋白II参与了表面受体的封帽过程。为了了解这种机械酶在表面受体封帽中的作用，构建了一种肌球蛋白II显性负性菌株。该突变体是第一株经过基因工程改造的溶组织内阿米巴细胞骨架缺陷菌株。它是通过过表达轻酶解肌球蛋白结构域获得的，该结构域对肌球蛋白II丝的形成至关重要。过表达轻酶解肌球蛋白结构域的溶组织内阿米巴表现出肌球蛋白II缺失表型，其特征为运动异常、无法形成尾状结构以及在用伴刀豆球蛋白A处理后无法进行封帽过程。此外，转染子对人结肠细胞的阿米巴细胞毒性能力显著降低，表明细胞骨架在寄生虫致病性中发挥作用。
