Listeriolysin O-induced stimulation of mucin exocytosis in polarized intestinal mucin-secreting cells: evidence for toxin recognition of membrane-associated lipids and subsequent toxin internalization through caveolae

Lysteriolysin O (LLO) induces a microtubule-dependent activation of mucin e xocytosis in the human mucin-secreting HT29-MTX, Cholesterol inhibits the L LO-induced mucin exocytosis, whereas the oxidized form of cholesterol had n o inhibitory effect. LLO-induced mucin exocytosis inhibited by cholesterol can be restored by enzymatic treatment with cholesterol oxidase. Inhibition of cholesterol synthesis in HT29-MTX cells results in a decrease in the LL O-induced mucin exocytosis. Other lipids such as gangliosides are able to i nhibit the LLO-induced mucin exocytosis, suggesting that the binding of the toxin occurs at a multiplicity of membrane-associated lipids acting as rec eptors. Incubation of the toxin with lipids such as cholesterol or ganglios ides does not decrease binding of LLO to target membranes. The present work also provides evidence that the LLO-induced mucin exocytosis develops inde pendently of the pore-forming activity of the toxin. Finally, we demonstrat ed that the toxin associates with detergent-insoluble glycolipid microdomai ns (DIGs) containing VIP/21 caveolin, allowing internalization of the toxin and subsequent activation of the mucin exocytosis.