Department of Microbiology, Faculty of Pharmaceutical Sciences, Tokushima Bunri University, Tokushima 770-8514, Yamashiro, Japan.
Toxins (Basel). 2021 Oct 12;13(10):721. doi: 10.3390/toxins13100721.
Iota-toxin from type E is a binary toxin composed of two independent proteins: actin-ADP-ribosylating enzyme component, iota-a (Ia), and binding component, iota-b (Ib). Ib binds to target cell receptors and mediates the internalization of Ia into the cytoplasm. Extracellular lysosomal enzyme acid sphingomyelinase (ASMase) was previously shown to facilitate the internalization of iota-toxin. In this study, we investigated how lysosomal cathepsin promotes the internalization of iota-toxin into target cells. Cysteine protease inhibitor E64 prevented the cytotoxicity caused by iota-toxin, but aspartate protease inhibitor pepstatin-A and serine protease inhibitor AEBSF did not. Knockdown of lysosomal cysteine protease cathepsins B and L decreased the toxin-induced cytotoxicity. E64 suppressed the Ib-induced ASMase activity in extracellular fluid, showing that the proteases play a role in ASMase activation. These results indicate that cathepsin B and L facilitate entry of iota-toxin via activation of ASMase.
E 型志贺毒素是一种由两个独立的蛋白质组成的二聚体毒素：肌动蛋白 ADP-核糖基转移酶成分，iota-a（Ia），和结合成分，iota-b（Ib）。Ib 与靶细胞受体结合，并介导 Ia 进入细胞质。先前的研究表明，细胞外溶酶体酶酸性鞘磷脂酶（ASMase）促进志贺毒素的内化。在这项研究中，我们研究了溶酶体组织蛋白酶如何促进志贺毒素进入靶细胞。半胱氨酸蛋白酶抑制剂 E64 可预防志贺毒素引起的细胞毒性，但天冬氨酸蛋白酶抑制剂 pepstatin-A 和丝氨酸蛋白酶抑制剂 AEBSF 则不能。溶酶体半胱氨酸蛋白酶组织蛋白酶 B 和 L 的敲低降低了毒素诱导的细胞毒性。E64 抑制 Ib 在细胞外液中诱导的 ASMase 活性，表明蛋白酶在 ASMase 激活中发挥作用。这些结果表明，组织蛋白酶 B 和 L 通过激活 ASMase 促进志贺毒素的进入。
