Submitted on February 23, 2007
Accepted on August 30, 2007
Toll-like receptor (TLR) 2 induced through TLR4 signaling initiated by Helicobacter pylori cooperatively amplifies iNOS induction in gastric epithelial cells
Kaname Uno1, Katsuaki Kato2*, Tomoaki Atsumi3, Takehito Suzuki1, Jun Yoshitake1, Hidetoshi Morita4, Shuichi Ohara3, Yashige Kotake5, Tooru Shimosegawa3, and Tetsuhiko Yoshimura1
1 Research Project of Biofunctional Reactive Species, Yamagata Promotional Organization for Industrial Technology, Yamagata, Yamagata, Japan
2 Cancer Detection Center, Miyagi Cancer Society, Sendai, Miyagi, Japan
3 Division of Gastroenterology, Tohoku University Graduate School of Medicine, Sendai, Miyagi, Japan
4 Azabu University School of Veterinary Medicine, Sagamihara, Kanagawa, Japan
5 Free Radical Biology and Aging Research Program, Oklahoma Medical Research Foundation, Oklahoma City, Oklahoma, United States
* To whom correspondence should be addressed. E-mail: kkato{at}cat-v.ne.jp.
Cell-surface Toll-like receptors (TLRs) initiate innate immune responses, such as inducible nitric oxide synthase (iNOS) induction, to microorganisms' surface pathogens. TLR2 and TLR4 play important roles in gastric mucosa infected with Helicobacter pylori (H.pylori), which contains lipopolysaccharide (LPS) as a pathogen. The present study investigates their physiological roles in the innate immune response of gastric epithelial cells to H.pylori-LPS. Changes in expression of iNOS, TLR2 and TLR4 as well as downstream activation of mitogen-activated protein kinases (MAPKs) and nuclear factor kappa B (NF
B) were analyzed in normal mouse gastric mucosal GSM06 cells following stimulation with H.pylori-LPS and interferon (IFN)-
. Specific inhibitors for MAPKs and NFB and small interfering RNA (siRNA) for TLR2 or TLR4 were employed. Immunohistochemistry of TLR2 was examined in human gastric mucosa. H.pylori-LPS stimulation induced TLR2 in GSM06 cells, but TLR4 was unchanged. TLR2 induction resulted from TLR4 signaling that propagated through extracellular signal-related kinase (ERK) and NFB activation, as corroborated by the decline in TLR4 expression upon siRNA treatment and pretreatment with inhibitors. The induction of iNOS and the associated NO production in response to H.pylori-LPS stimulation were inhibited by declines in not only TLR4 but also TLR2. Increased expression of TLR2 was identified in H.pylori-infected human gastric mucosa. TLR4 signaling initiated by H.pylori-LPS and propagated via ERK and NFB activation induced TLR2 expression in gastric epithelial cells. Induced TLR2 cooperated with TLR4 to amplify iNOS induction. This positive correlation may constitute a mechanism for stimulating the innate immune response against various bacterial pathogens, including H.pylori-LPS.
