Cholera Toxin B Subunit Activates Arachidonic Acid Metabolism

Abstract

Cholera toxin (CT) increases intestinal secretion of water and electrolytes and modulates the mucosal immune response by stimulating cellular synthesis of arachidonic acid (AA) metabolites (e.g., prostaglandin E2), as well as the intracellular second messenger cyclic AMP (cAMP). While much is known about the mechanism of CT stimulation of adenylate cyclase, the toxin’s activation of phospholipase A2, which results in increased hydrolysis of AA from membrane phospholipids, is not well understood. To determine whether CT activation of AA metabolism requires CT’s known enzymatic activity (i.e., ADP-ribosylation of GSα), we used native CT and a mutant CT protein (CT-2*) lacking ADP-ribose transferase activity in combination with S49 wild-type (WT) and S49 cyc− murine Theta (Th)1.2-positive lymphoma cells deficient in GSα. The experimental results showed that native CT stimulated the release of [3H[AA from S49 cyc− cells at a level similar to that for S49 WT cells, indicating that GSα is not essential for this process. Further, levels of cAMP in the CT-treated cyc− cells remained the same as those in the untreated control cells. The ADP-ribosyltransferase-deficient CT-2* protein, which was incapable of increasing synthesis of cAMP, displayed about the same capacity as CT to evoke the release of [3H]AA metabolites from both S49 WT and cyc− cells. We concluded that stimulation of arachidonate metabolism in S49 murine lymphoma cells by native CT does not require enzymatically functional CT, capable of catalyzing the ADP-ribosylation reaction. These results demonstrated for the first time that stimulation of adenylate cyclase by CT and stimulation of AA metabolism by CT are not necessarily coregulated. In addition, the B subunits purified from native CT and CT-2* both simulated the release of [3H]AA from S49 cyc− cells and murine monocyte/macrophage cells (RAW 264.7), suggesting a receptor-mediated cell activation process of potential importance in enhancing immune responses to vaccine components.

Molecular Biology of Escherichia coli Shiga Toxins’ Effects on Mammalian Cells

“…The latter can also be observed after Stx treatment of Burkitt's lymphoma cells [300]. The B subunit of CT accelerates cellular synthesis of arachidonic acid metabolites [341], implying that a signal originating from glycolipid receptors in lipid rafts is responsible for the ceramide increase. Elevated ceramide contents stimulate secretory phospholipase A 2 (sPLA 2 ) [340], transcription and translation of which is induced by Stx1 in primary human glomerular epithelial cells together with the cytosolic PLA 2 (cPLA 2 ) [342].…”

Cholera toxin and Escherichia coli enterotoxin B-subunits inhibit macrophage-mediated antigen processing and presentation: evidence for antigen persistence in non-acidic recycling endosomal compartments

“…In support of this possibility, EtxB and CtxB have been shown to have multiple direct effects on immune cells. These include, for example, alterations in CD4 + T‐cell differentiation, transcription factor activation and apoptosis of CD8 + T cells, isotype switching and activation of B cells, epithelial cell transcytosis and increased arachidonic acid metabolism by macrophages (Francis et al ., 1992; Hirabayashi et al ., 1992; Lycke, 1993; Lencer et al ., 1995b; Li and Fox, 1996; Matousek et al ., 1996; Nashar et al ., 1996b; 1997; Kim et al ., 1998; Matousek et al ., 1998; Truitt et al ., 1998; Peterson et al ., 1999).…”

Post-infection irritable bowel syndrome in the tropical and subtropical regions: Vibrio cholerae is a new cause of this well-known condition

“…These are (a) prostaglandin secretions, (b) activation of the enteric nervous system (ENS), (c) alteration in epithelial barrier function, (d) intestinal inflammatory response, and (e) immunomodulation. A number of studies suggest that prostaglandins (PGE1 and PGE2) and platelet-activating factor (PAF) are involved in the pathogenesis of intestinal secretion caused by CT [35][36][37][38][39]. CT stimulates the epithelial cell phospholipase to produce prostaglandins (PGs).…”