Cholera toxin induces tumor necrosis factor alpha production in human monocytes.
Cholera toxin covalently ADP-ribosylates the a subunit of Gs proteins. The modified Gsalpha activates adenylate cyclase and leads to a dramatic increase in intracellular cAMP. The effect of cholera toxin on the production of tumor necrosis factor (TNF-alpha), a critical mediator of toxicity for a number of bacterial and viral infections, has not been examined. Here we show that cholera toxin stimulated human monocytes to secrete TNF-alpha. The subunit A of cholera toxin alone also induced TNF-alpha production, suggesting that TNF-alpha production is mediated through ADP-ribosylation activity of the toxin. Inhibitors of ADP-ribosylation such as 3-aminobenzamide and niacinamide blocked TNF-alpha induction. However, cyclic AMP analogs and adenylate cyclase activator forskolin did not induce TNF-alpha production in monocytes, suggesting that TNF-alpha induction is independent of cAMP. Furthermore, cholera toxin-induced TNF-alpha production was suppressed by protein kinase C inhibitors H7 and sphingosine and by phospholipase C inhibitors U73122 and ET-18-OCH3, suggesting that PLC and PKC mediate TNF-alpha induction. Cholera toxin-mediated induction of TNF-alpha occurs at the transcription level as demonstrated by the time-dependent expression of TNF-alpha mRNA. These results raise the possibility that TNF-alpha may play an important role in cholera toxin-mediated toxicity and demonstrate that cholera toxin activates TNF-alpha production through PLC-dependent and cAMP-independent pathways. The probable mechanisms of signal transduction from cholera toxin to PLC in monocytes will be discussed.
Yan
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Z
Chemistry Department, Georgetown University, Washington, DC 20056, USA. zyan@prius.jnj.com
Yang
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DC
Jett
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D019307:1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine / Q000494:pharmacology; D015124:8-Bromo Cyclic Adenosine Monophosphate / Q000494:pharmacology; D000244:Adenosine Diphosphate / Q000378:metabolism; D001549:Benzamides / Q000494:pharmacology; D002478:Cells, Cultured; D002772:Cholera Toxin / Q000378:metabolism / Q000494:pharmacology*; D000242:Cyclic AMP / Q000378:metabolism; D017868:Cyclic AMP-Dependent Protein Kinases / Q000037:antagonists & inhibitors; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006801:Humans; D007546:Isoquinolines / Q000494:pharmacology; D008214:Lymphocytes / Q000187:drug effects / Q000378:metabolism; D009000:Monocytes / Q000187:drug effects* / Q000378:metabolism*; D009536:Niacinamide / Q000494:pharmacology; D000067856:Poly(ADP-ribose) Polymerase Inhibitors; D011493:Protein Kinase C / Q000037:antagonists & inhibitors; D015398:Signal Transduction; D013110:Sphingosine / Q000494:pharmacology; D013449:Sulfonamides; D014158:Transcription, Genetic; D014409:Tumor Necrosis Factor-alpha / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D010738:Type C Phospholipases / Q000037:antagonists & inhibitors
D001549:Benzamides; D004791:Enzyme Inhibitors; D007546:Isoquinolines; D000067856:Poly(ADP-ribose) Polymerase Inhibitors; D013449:Sulfonamides; D014409:Tumor Necrosis Factor-alpha; D015124:8-Bromo Cyclic Adenosine Monophosphate; D009536:Niacinamide; D000244:Adenosine Diphosphate; D019307:1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine; C025160:3-aminobenzamide; D002772:Cholera Toxin; C043204:N-(2-guanidinoethyl)-5-isoquinolinesulfonamide; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases; D011493:Protein Kinase C; D010738:Type C Phospholipases; D013110:Sphingosine