幽門螺旋桿菌在胃上皮細胞引發第二型環氧化酶表現之機轉~RhoA/ROCK和PI3K/Akt之作用探討~

Abstract

幽門螺旋桿菌屬格蘭氏陰性微耗氧菌，與慢性胃炎、消化性潰瘍及胃癌的發生有關。流行病學研究顯示，胃癌、幽門螺旋桿菌與第二型環氧化酶具高度關連性，而本實驗室先前之研究亦發現，胃癌病人分離出之幽門螺旋桿菌誘發胃上皮細胞表現較多第二型環氧化酶，而H. pylori活化COX-2之promoter需 κB、NF-IL6與CRE這些cis-elements之參與，且TLR2/9、PI-PLC/PKC/c-Src或MAPKs參與其訊息傳遞路徑。因此本論文進一步釐清H. pylori誘發COX-2表現之機制。我們發現，H. pylori可活化PI3K/Akt及RhoA/ROCK，並發現它們參與H. pylori誘發之COX-2表現。PI3K與ROCK之抑制劑可阻斷幽門螺旋桿菌誘發之COX-2表現及promoter活性， ROCK抑制劑可降低H. pylori活化之IKK和RSK-1，使IκBα免於分解，並降低核內之p65含量與活性。除了NF-κB外，H. pylori亦增加C/EBPβ和C/EBPδ結合至COX-2 promoter之NF-IL6 site，PI3K和ROCK亦參與此過程之調控，雖然它們不調控H. pylori引發之C/EBPβ Thr235磷酸化， RhoA/ROCK可能參與H. pylori誘發之C/EBPδ表現。本論文首次指出H. pylori可經由RhoA/ROCK路徑調控COX-2之表現，主要作用在NF-κB和NF-IL6 sites，ROCK經由活化IKK，增加p65之Ser536磷酸化，而調控NF-κB之活性；也增加C/EBPδ mRNA之表現量，而增加NF-IL6之活性。

Helicobacter pylori (H. pylori) is a Gram-negative microaerophilic bacterium that causes chronic gastritis, peptic ulcer, and gastric carcinoma. Epidemiological studies have shown the correlation between gastric cancer, H. pylori and COX-2. Our previous studies have shown that TLR2/TLR9 and PI-PLC/PKC/c-Src or MAPKs were involved in the H. pylori-induced COX-2 expression in AGS gastric epithelial cells. Since the κB、NF-IL6 and CRE sites were critical for H. pylori-induced COX-2 promoter activity, we further elucidated the mechanisms underlying the H. pylori-induced COX-2 expression. In this study, we demonstrated that RhoA/ROCK and PI3K/Akt were activated after H. pylori infection and participated in the H. pylori-induced COX-2 expression. Both pharmacological inhibitors of PI3K (LY294002) and ROCK (Y27632) could attenuate H. pylori-induced COX-2 expression and promoter activity. Y27632 inhibited the H. pylori-induced IKK and RSK-1 activity, IκBα degradation and nuclear p65 activity. By DAPA and ChIP, we demonstrated the in vitro and in vivo bindings of C/EBPβ and C/EBPδ to the COX-2 promoter induced by H. pylori. The binding processes were regulated by PI3K and ROCK, although they were irrelevant to H. pylori-induced C/EBPβ Thr235 phophorylation. Furthermore, H. pylori could induce C/EBPδ mRNA expression via RhoA/ROCK pathway. In summary, we are the first to report that RhoA/ROCK regulated the H. pylori-induced COX-2 expression via NF-κB and NF-IL6 sites. ROCK not only stimulated NF-κB by augmenting the phosphorylation of IKK and p65, but also activated NF-IL6 by increasing the C/EBPδ mRNA expression.