Ruemmele F M, Russo P, Beaulieu J, Dionne S, Levy E, Lentze M J, Seidman E G
Mucosal Immunology Laboratory, Division of Gastroenterology and Nutrition, Department of Pediatrics, Ste. Justine Hospital, University of Montreal, Montreal, Canada.
J Cell Physiol. 1999 Oct;181(1):45-54. doi: 10.1002/(SICI)1097-4652(199910)181:1<45::AID-JCP5>3.0.CO;2-Q.
FAS-FAS ligand interaction has been implicated in increased enterocyte apoptosis seen in immune-mediated bowel injury. However, scant information exists on the role of FAS in physiological enterocyte turnover. In the present study, the regulation of enterocyte FAS and FAS ligand expression by cytokines and its functional role in human intestinal epithelial cell apoptosis and proliferation were analyzed with two different models: a nontransformed human intestinal epithelial cell line (HIEC) and normal colonic explant cultures. HIEC constitutively expressed FAS, as analyzed by flow cytometry. However, stimulation with agonistic anti-FAS antibody (1-500 ng/ml) did not induce HIEC apoptosis. In contrast, in the presence of tumor necrosis factor alpha (TNFalpha) and/or interferon gamma (IFNgamma), HIEC became highly susceptible to FAS-induced apoptosis. The sensitizing effect to FAS-induced apoptosis was mediated via TNFalpha- and IFNgamma-induced upregulation of FAS expression (maximally 348%). Receptor studies showed that the effect of TNFalpha on FAS was mediated via the p55 TNF receptor. In colonic organ cultures, IFNgamma and TNFalpha also enhanced colonocyte FAS expression, resulting in a markedly increased apoptotic response to stimulation of this receptor, as shown by in situ terminal deosyuridine triphosphate nick-end staining. Neither FAS ligand expression nor its induction by cytokines was observed in HIEC or colonic explants. Proliferation studies showed that FAS is not implicated in regulating HIEC growth. These findings suggest that, despite the fact that normal human enterocytes express FAS, costimulatory factors, such as TNFalpha or IFNgamma, abundantly secreted under inflammatory conditions, are necessary to sensitize intestinal epithelial cells to FAS-induced apoptosis by upregulating this receptor.
FAS与FAS配体的相互作用与免疫介导性肠损伤中肠上皮细胞凋亡增加有关。然而，关于FAS在生理性肠上皮细胞更新中的作用，现有信息很少。在本研究中，我们使用两种不同模型分析了细胞因子对肠上皮细胞FAS和FAS配体表达的调节及其在人肠上皮细胞凋亡和增殖中的功能作用：一种未转化的人肠上皮细胞系（HIEC）和正常结肠外植体培养物。通过流式细胞术分析，HIEC组成性表达FAS。然而，用激动性抗FAS抗体（1 - 500 ng/ml）刺激并未诱导HIEC凋亡。相反，在存在肿瘤坏死因子α（TNFα）和/或干扰素γ（IFNγ）的情况下，HIEC对FAS诱导的凋亡变得高度敏感。对FAS诱导凋亡的致敏作用是通过TNFα和IFNγ诱导的FAS表达上调（最大上调348%）介导的。受体研究表明，TNFα对FAS的作用是通过p55 TNF受体介导的。在结肠器官培养物中，IFNγ和TNFα也增强了结肠细胞FAS表达，导致对该受体刺激的凋亡反应明显增加，原位末端脱氧尿苷三磷酸缺口末端标记法显示了这一点。在HIEC或结肠外植体中未观察到FAS配体表达及其由细胞因子诱导的情况。增殖研究表明，FAS与调节HIEC生长无关。这些发现表明，尽管正常人肠上皮细胞表达FAS，但在炎症条件下大量分泌的共刺激因子，如TNFα或IFNγ，通过上调该受体使肠上皮细胞对FAS诱导的凋亡敏感是必要的。
