Toxin Pores Endocytosed During Plasma Membrane Repair Traffic into the Lumen of MVBs for Degradation

Abstract

Cells permeabilized by the bacterial pore-forming toxin streptolysin O (SLO) reseal their plasma membrane in a Ca2+-dependent manner. Resealing involves Ca2+-dependent exocytosis of lysosomes, release of acid sphingomyelinase and rapid formation of endosomes that carry the transmembrane pores into the cell. The intracellular fate of the toxin-carrying endocytic vesicles, however, is still unknown. Here, we show that SLO pores removed from the plasma membrane by endocytosis are sorted into the lumen of lysosomes, where they are degraded. SLO-permeabilized cells contain elevated numbers of total endosomes, which increase gradually in size while transitioning from endosomes with flat clathrin coats to large multivesicular bodies (MVBs). Under conditions that allow endocytosis and plasma membrane repair, SLO is rapidly ubiquitinated and gradually degraded, in a process sensitive to inhibitors of lysosomal hydrolysis but not of proteasomes. The endosomes induced by SLO permeabilization become increasingly acidified and promote SLO degradation under normal conditions, but not in cells silenced for expression of Vps24, an ESCRT-III complex component required for the release of intraluminal vesicles into MVBs. Thus, cells dispose of SLO transmembrane pores by ubiquitination/ESCRT-dependent sorting into the lumen of late endosomes/lysosomes.

Vaginolysin Drives Epithelial Ultrastructural Responses to Gardnerella vaginalis

“…At lower bacterial densities and toxin concentrations, such as might be encountered during colonization or early stages of infection, host cells can detect PFT activity at the membrane, activate signaling pathways that promote survival, and initiate membrane repair. Lipid metabolism, vesicle trafficking, calcium or potassium signaling, and mitogen-activated protein kinase pathways have all been implicated in such responses (14,15,(35)(36)(37)(38). It was recently recognized that cellular blebbing may represent an additional early defense mechanism for eukaryotic cells (14,16,37,39).…”

“…It was recently recognized that cellular blebbing may represent an additional early defense mechanism for eukaryotic cells (14,16,37,39). Such membrane blebs may promote survival by physically sequestering PFT and/or receptors and may also activate distinct cellular signaling pathways that promote healing of membrane wounds (14,27,35).…”

Role of Pore-Forming Toxins in Bacterial Infectious Diseases

“…Note that during the oligomerization step, some PFTs remain associated with their receptor, whereas others have already disassociated at this point. machinery, targeted to lysosomes for degradation (327). S. aureus alpha-toxin also enters cells via endocytosis, is transported via late endosomes, and then disappears from the cells.…”

Cellular Uptake of Clostridium botulinum C2 Toxin Requires Acid Sphingomyelinase Activity

“…Subsequently, in both cases, ASMase hydrolyzes sphingomyelin (SM) into ceramide (14,15). Ceramide self-associates in plasma membrane microdomains that bud into cells, generating endosomes that induce endocytosis (16). These results indicated that the cleavage of sphingomyelin by secreted ASMase generates ceramide-enriched microdomains in the plasma membrane, promoting endocytosis (14)(15)(16).…”

“…Ceramide self-associates in plasma membrane microdomains that bud into cells, generating endosomes that induce endocytosis (16). These results indicated that the cleavage of sphingomyelin by secreted ASMase generates ceramide-enriched microdomains in the plasma membrane, promoting endocytosis (14)(15)(16). It is as yet unknown whether the activation of ASMase is related to the uptake of C2 toxin in target cells.…”