A Pore-forming Toxin Interacts with a GPI-anchored Protein and Causes Vacuolation of the Endoplasmic Reticulum

Abstract

In this paper, we have investigated the effects of the pore-forming toxin aerolysin, produced by Aeromonas hydrophila, on mammalian cells. Our data indicate that the protoxin binds to an 80-kD glycosyl-phosphatidylinositol (GPI)-anchored protein on BHK cells, and that the bound toxin is associated with specialized plasma membrane domains, described as detergent-insoluble microdomains, or cholesterol-glycolipid “rafts.” We show that the protoxin is then processed to its mature form by host cell proteases. We propose that the preferential association of the toxin with rafts, through binding to GPI-anchored proteins, is likely to increase the local toxin concentration and thereby promote oligomerization, a step that it is a prerequisite for channel formation. We show that channel formation does not lead to disruption of the plasma membrane but to the selective permeabilization to small ions such as potassium, which causes plasma membrane depolarization. Next we studied the consequences of channel formation on the organization and dynamics of intracellular membranes. Strikingly, we found that the toxin causes dramatic vacuolation of the ER, but does not affect other intracellular compartments. Concomitantly we find that the COPI coat is released from biosynthetic membranes and that biosynthetic transport of newly synthesized transmembrane G protein of vesicular stomatitis virus is inhibited. Our data indicate that binding of proaerolysin to GPI-anchored proteins and processing of the toxin lead to oligomerization and channel formation in the plasma membrane, which in turn causes selective disorganization of early biosynthetic membrane dynamics.

Channels formed by subnanomolar concentrations of the toxin aerolysin trigger apoptosis of T lymphomas

“…At least two other channel-forming toxins, Staphylococcus aureus alpha toxin and Actinobacillus actinomycetemcomitans leukotoxin (Chen and Zychlinsky, 1994), also cause apoptosis at low concentrations, and it has been shown recently that, like aerolysin, the outer membrane porin PorB of Neisseria gonorrhoeae causes rapid calcium in¯ux into epithelial cells, which may induce apoptosis by activating cysteine proteases (Muller et al, 1999). It seems reasonable to suppose that the vacuolation of BHK endoplasmic reticulum by aerolysin, which was reported by Abrami et al (1998b), was also a consequence of apoptosis, as was the G-protein activation the same group reported in granulocytes (Krause et al, 1998). Our results are not consistent with their claim that intracellular stores of calcium are released by aerolysin.…”

Distinct Roles for the AAA ATPases NSF and p97 in the Secretory Pathway

“…Such disorganization could result in changes in the ratio, size, and shape of ER cisternae and tubules. Morphologically similar swelling is seen in a few pathological conditions, including intoxication with the pore forming toxin aerolysin (Abrami et al, 1998), prolonged exposure of cells to BFA (Alvarez and Sztul, 1999), and treatment of neurons with tunicamycin (Lin et al, 1999). Further understanding of the events that lead to ER dilation will shed light on how p97 participates in ER homeostasis.…”

Association of Helicobacter pylori Vacuolating Toxin (VacA) with Lipid Rafts

“…Other pore-forming toxins, such as perfringolysin, bind to cholesterol components of lipid rafts (43). It has been proposed that lipid rafts serve as concentrating platforms to promote oligomerization of these toxins on the cell surface, a process that is required for membrane channel formation (57). Two toxins with intracellular enzymatic activity, cholera toxin and tetanus toxin, bind to GM1 and a specific GPI-anchored protein, respectively, which are enriched in lipid raft microdo- mains (43-45, 58, 67).…”

“…Two pore-forming toxins, aerolysin and Clostridium septicum alpha toxin, each bind to GPI-anchored proteins, which are enriched in lipid raft microdomains of the plasma membrane (57,66). Other pore-forming toxins, such as perfringolysin, bind to cholesterol components of lipid rafts (43).…”