Cooperative interactions between flagellin and SopE2 in the epithelial interleukin-8 response to Salmonella enterica serovar typhimurium infection.
Flagellin is an important stimulus for epithelial interleukin-8 (IL-8) secretion because of its ability to activate Toll-like receptor 5 (TLR5). SopE2, a Salmonella guanine nucleotide exchange factor (GEF), is also involved in intestinal inflammation. To clarify the proinflammatory mechanisms of these proteins, we examined their effects on IL-8 secretion and intracellular signaling in T84 epithelial cells. A Salmonella strain lacking SopE2 (and its homolog SopE) induced lower levels of IL-8 than the wild type and exhibited reduced activation of mitogen-activated protein kinases (MAPKs). Overexpression of wild-type SopE2 in this strain restored MAPK activation and augmented IL-8 production, whereas a mutant lacking GEF activity failed to increase IL-8 expression. Additional effects on signaling were demonstrated in transient transfection experiments, in which SopE2 enhanced the ability of TRAF6, a signal transducer downstream of TLR5, to activate the NF-kappaB transcription factor in 293 cells. Flagellin was also found to be required for IL-8 induction in T84 cells. In its absence, the ability of SopE2 overexpression to increase IL-8 secretion was impaired. Part of this impairment was related to the decreased motility of the flagellin-deficient strain, but lack of flagellin also affected translocation of SopE2 into the infected cells. Our results indicate that flagellin and SopE2 interact functionally at multiple levels to increase IL-8 secretion by epithelial cells-flagellin facilitating the translocation of SopE2, and SopE2 enhancing signaling pathways activated by flagellin. These observations offer a mechanistic explanation for the involvement of these proteins in the pathogenesis of Salmonella-induced gastroenteritis.
Huang
Fu-Chen
FC
Mucosal Immunology Laboratory, Pediatric Gastroenterology and Nutrition Unit, Massachusetts General Hospital and Harvard Medical School, Charlestown, MA, USA.
Werne
Adam
A
Li
Qian
Q
Galyov
Edouard E
EE
Walker
W Allan
WA
Cherayil
Bobby J
BJ
D001426:Bacterial Proteins / Q000378:metabolism*; D002461:Cell Line, Transformed; D003106:Colon / Q000166:cytology / Q000382:microbiology; D004847:Epithelial Cells / Q000382:microbiology; D005408:Flagellin / Q000378:metabolism*; D005786:Gene Expression Regulation; D020662:Guanine Nucleotide Exchange Factors / Q000378:metabolism*; D006801:Humans; D016209:Interleukin-8 / Q000378:metabolism*; D012486:Salmonella typhimurium / Q000472:pathogenicity*
D001426:Bacterial Proteins; D020662:Guanine Nucleotide Exchange Factors; D016209:Interleukin-8; C436324:SopE2 protein, Salmonella typhimurium; D005408:Flagellin