Roswell Park Cancer Institute, Buffalo, NY 14263, USA.
Proc Natl Acad Sci U S A. 2013 May 14;110(20):E1857-66. doi: 10.1073/pnas.1222805110. Epub 2013 Apr 29.
Vertebrate Toll-like receptor 5 (TLR5) recognizes bacterial flagellin proteins and activates innate immune responses to motile bacteria. In addition, activation of TLR5 signaling can inhibit growth of TLR5-expressing tumors and protect normal tissues from radiation and ischemia-reperfusion injuries. To understand the mechanisms behind these phenomena at the organismal level, we assessed nuclear factor kappa B (NF-κB) activation (indicative of TLR5 signaling) in tissues and cells of mice treated with CBLB502, a pharmacologically optimized flagellin derivative. This identified the liver and gastrointestinal tract as primary CBLB502 target organs. In particular, liver hepatocytes were the main cell type directly and specifically responding to systemic administration of CBLB502 but not to that of the TLR4 agonist LPS. To assess CBLB502 impact on other pathways, we created multireporter mice with hepatocytes transduced in vivo with reporters for 46 inducible transcription factor families and found that along with NF-κB, CBLB502 strongly activated STAT3-, phenobarbital-responsive enhancer module (PREM), and activator protein 1 (AP-1-) -driven pathways. Livers of CBLB502-treated mice displayed induction of numerous immunomodulatory factors and massive recruitment of various types of immune cells. This led to inhibition of growth of liver metastases of multiple tumors regardless of their TLR5 status. The changed liver microenvironment was not, however, hepatotoxic, because CBLB502 induced resistance to Fas-mediated apoptosis in normal liver cells. Temporary occlusion of liver blood circulation prevented CBLB502 from protecting hematopoietic progenitors in lethally irradiated mice, indicating involvement of a factor secreted by responding liver cells. These results define the liver as the key mediator of TLR5-dependent effects in vivo and suggest clinical applications for TLR5 agonists as hepatoprotective and antimetastatic agents.
脊椎动物 Toll 样受体 5（TLR5）识别细菌鞭毛蛋白并激活对运动细菌的先天免疫反应。此外，TLR5 信号的激活可以抑制 TLR5 表达肿瘤的生长，并保护正常组织免受辐射和缺血再灌注损伤。为了在机体水平上理解这些现象背后的机制，我们评估了用 CBLB502 处理的小鼠组织和细胞中的核因子 kappa B（NF-κB）激活（表明 TLR5 信号），CBLB502 是一种药理学优化的鞭毛蛋白衍生物。这确定了肝脏和胃肠道是 CBLB502 的主要靶器官。特别是，肝实质细胞是对 CBLB502 全身给药直接和特异性反应的主要细胞类型，但对 TLR4 激动剂 LPS 则没有反应。为了评估 CBLB502 对其他途径的影响，我们用体内转导的报告基因创建了多报告基因小鼠，这些报告基因可用于 46 种诱导转录因子家族，发现除了 NF-κB 之外，CBLB502 还强烈激活 STAT3、苯巴比妥反应增强子模块（PREM）和激活蛋白 1（AP-1）驱动的途径。CBLB502 处理的小鼠肝脏显示出大量免疫调节因子的诱导和各种类型免疫细胞的大量募集。这导致抑制了多种肿瘤的肝转移生长，而与 TLR5 状态无关。然而，改变的肝脏微环境没有毒性，因为 CBLB502 诱导正常肝细胞对 Fas 介导的细胞凋亡产生抗性。暂时阻断肝脏血液循环可防止 CBLB502 保护致死性辐射小鼠中的造血祖细胞，表明涉及由反应性肝细胞分泌的因子。这些结果将肝脏定义为 TLR5 依赖性体内效应的关键介导者，并表明 TLR5 激动剂作为肝保护和抗转移剂的临床应用。
