Clostridium difficile toxin B differentially affects GPCR-stimulated Ca2+ responses in macrophages: independent roles for Rho and PLA2.
Clostridium difficile toxins cause acute colitis by disrupting the enterocyte barrier and promoting inflammation. ToxB from C. difficile inactivates Rho family GTPases and causes release of cytokines and eicosanoids by macrophages. We studied the effects of ToxB on GPCR signaling in murine RAW264.7 macrophages and found that ToxB elevated Ca(2+) responses to Galphai-linked receptors, including the C5aR, but reduced responses to Galphaq-linked receptors, including the UDP receptors. Other Rho inhibitors also reduced UDP Ca(2+) responses, but they did not affect C5a responses, suggesting that ToxB inhibited UDP responses by inhibiting Rho but enhanced C5a responses by other mechanisms. By using PLCbeta isoform-deficient BMDM, we found that ToxB inhibited Ca(2+) signaling through PLCbeta4 but enhanced signaling through PLCbeta3. Effects of ToxB on GPCR Ca(2+) responses correlated with GPCR use of PLCbeta3 versus PLCbeta4. ToxB inhibited UDP Ca(2+) signaling without reducing InsP3 production or the sensitivity of cellular Ca(2+) stores to exogenous InsP3, suggesting that ToxB impairs UDP signaling at the level of InsP3/Ca(2+)coupling. In contrast, ToxB elevated InsP3 production by C5a, and the enhancement of Ca(2+) signaling by C5a was prevented by inhibition of PLA(2) or 5-LOX but not COX, implicating LTs but not prostanoids in the mechanism. In sum, ToxB has opposing, independently regulated effects on Ca(2+) signaling by different GPCR-linked PLCbeta isoforms in macrophages.
Rebres
Robert A
RA
Alliance for Cellular Signaling at Northern California Institute for Research and Education, VA Medical Center, San Francisco, California, USA. rarebres@yahoo.com.
Moon
Christina
C
Decamp
Dianne
D
Lin
Keng-Mean
KM
Fraser
Iain D
ID
Milne
Stephen B
SB
Roach
Tamara I A
TI
Brown
H Alex
HA
Seaman
William E
WE
D000818:Animals; D001426:Bacterial Proteins / Q000494:pharmacology*; D001427:Bacterial Toxins / Q000494:pharmacology*; D015153:Blotting, Western; D002118:Calcium / Q000378:metabolism*; D002478:Cells, Cultured; D015936:Complement C5a / Q000494:pharmacology; D003599:Cytoskeleton / Q000378:metabolism; D005260:Female; D008264:Macrophages / Q000187:drug effects* / Q000378:metabolism; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010716:Phosphatidylinositols / Q000378:metabolism; D054799:Phospholipase C beta / Q000502:physiology*; D054467:Phospholipases A2 / Q000378:metabolism*; D020033:Protein Isoforms; D015398:Signal Transduction; D014530:Uridine Diphosphate / Q000494:pharmacology; D020741:rho GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism*
D001426:Bacterial Proteins; D001427:Bacterial Toxins; D010716:Phosphatidylinositols; D020033:Protein Isoforms; C031815:toxB protein, Clostridium difficile; D014530:Uridine Diphosphate; D015936:Complement C5a; D019869:Phosphatidylinositol 3-Kinases; D054467:Phospholipases A2; D054799:Phospholipase C beta; D020741:rho GTP-Binding Proteins; D002118:Calcium