Abstract
Clostridium perfringens iota-toxin is a binary actin-ADP-ribosylating toxin composed of the enzymatic component Ia and receptor binding component Ib. Ib binds to a cell surface receptor, forms Ib oligomer in lipid rafts, and associates with Ia. The Ia-Ib complex then internalizes by endocytosis. Here, we showed that acid sphingomyelinase (ASMase) facilitates the cellular uptake of iota-toxin. Inhibitions of ASMase and lysosomal exocytosis by respective blockers depressed cell rounding induced by iota-toxin. The cytotoxicity of the toxin increased in the presence of Ca2+ in extracellular fluids. Ib entered target cells in the presence but not the absence of Ca2+. Ib induced the extracellular release of ASMase in the presence of Ca2+. ASMase siRNA prevented the cell rounding induced by iota-toxin. Furthermore, treatment of the cells with Ib resulted in the production of ceramide in cytoplasmic vesicles. These observations showed that ASMase promotes the internalization of iota-toxin into target cells.
Highlights
Clostridium perfringens iota-toxin belongs to a binary actin-ADP-ribosylating toxin family featuring two individual proteins implicated in enterotoxemia among young domestic livestock [1,2,3,4,5,6].One component of iota-toxin, Ia, ADP-ribosylates monomeric actin, interferes with the actin polymerization within a host cell and disintegrates its cytoskeletal organization [6,7,8]
We investigated the role of Ca2+ in target cell entry of iota-toxin
We previously showed that the binding and oligomerization of Ib to Madin–Darby canine kidney (MDCK) cells was detected in Ca 2+-free buffer, as well as in Ca2+-containing buffer [23], indicating that the binding and oligomer formation of Ib to target cells do not need extracellular Ca2+
Summary
Clostridium perfringens iota-toxin belongs to a binary actin-ADP-ribosylating toxin family featuring two individual proteins implicated in enterotoxemia among young domestic livestock [1,2,3,4,5,6]. One component of iota-toxin, Ia, ADP-ribosylates monomeric actin, interferes with the actin polymerization within a host cell and disintegrates its cytoskeletal organization [6,7,8]. Iota-toxin is endocytosed into target cells and causes cytotoxicity by taking advantage of intracellular transport [3,4,5,6]. Ib is endocytosed, trafficked to early endosomes, and delivered to recycling endosomes and late endosomes. Ib is sorted from late endosomes to lysosomes for breakdown [6,12]
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