Inflammatory Bowel Diseases Group, Mater Research Institute - University of Queensland, Translational Research Institute, Woolloongabba, Queensland; Inflammatory Disease Biology and Therapeutics Group, Mater Research Institute - University of Queensland, Translational Research Institute, Woolloongabba, Queensland.
Inflammatory Bowel Diseases Group, Mater Research Institute - University of Queensland, Translational Research Institute, Woolloongabba, Queensland.
Cell Mol Gastroenterol Hepatol. 2021;11(1):33-53. doi: 10.1016/j.jcmgh.2020.05.012. Epub 2020 Jun 1.
BACKGROUND & AIMS: Chronic bowel inflammation increases the risk of colon cancer; colitis-associated cancer (CAC). Thiopurine treatments are associated with a reduction in dysplasia and CAC in inflammatory bowel disease (IBD). Abnormal Wnt/β-catenin signalling is characteristic of >90% of colorectal cancers. Immunosuppression by thiopurines is via Rac1 GTPase, which also affects Wnt/β-catenin signalling. Autophagy is implicated in colonic tumors, and topical delivery of the thiopurine thioguanine (TG) is known to alleviate colitis and augment autophagy. This study investigated the effects of TG in a murine model of CAC and potential mechanisms.
Colonic dysplasia was induced by exposure to azoxymethane (AOM) and dextran sodium sulfate (DSS) in wild-type (WT) mice and mice harboring intestinal epithelial cell-specific deletion of autophagy related 7 gene (Atg7). TG or vehicle was administered intrarectally, and the effect on tumor burden and β-catenin activity was assessed. The mechanisms of action of TG were investigated in vitro and in vivo.
TG ameliorated DSS colitis in wild-type but not Atg7 mice, demonstrating that anti-inflammatory effects of locally delivered TG are autophagy-dependent. However, TG inhibited CAC in both wild-type and Atg7 mice. This was associated with decreased β-catenin activation/nuclear translocation demonstrating that TG's inhibition of tumorigenesis occurred independently of anti-inflammatory and pro-autophagic actions. These results were confirmed in cell lines, and the dependency on Rac1 GTPase was demonstrated by siRNA knockdown and overexpression of constitutively active Rac1.
Our findings provide evidence for a new mechanism that could be exploited to improve CAC chemoprophylactic approaches.
慢性肠道炎症会增加结肠癌（CAC）的风险。在炎症性肠病（IBD）中，硫唑嘌呤治疗与异型增生和 CAC 减少有关。异常的 Wnt/β-连环蛋白信号是 >90%结直肠癌的特征。硫唑嘌呤的免疫抑制作用是通过 Rac1 GTPase 实现的，Rac1 GTPase 也会影响 Wnt/β-连环蛋白信号。自噬与结肠肿瘤有关，已知硫唑嘌呤的噻唑嘌呤（TG）局部给药可缓解结肠炎并增强自噬。本研究旨在探讨 TG 在 CAC 小鼠模型中的作用及其潜在机制。
在野生型（WT）和肠上皮细胞特异性缺失自噬相关基因 7（Atg7）的小鼠中，通过暴露于氧化偶氮甲烷（AOM）和葡聚糖硫酸钠（DSS）诱导结肠异型增生。通过直肠内给予 TG 或载体，评估其对肿瘤负担和β-连环蛋白活性的影响。在体外和体内研究了 TG 的作用机制。
TG 改善了 WT 但不改善 Atg7 小鼠的 DSS 结肠炎，表明局部给予 TG 的抗炎作用依赖于自噬。然而，TG 抑制了 WT 和 Atg7 小鼠的 CAC。这与β-连环蛋白激活/核易位减少有关，表明 TG 抑制肿瘤发生发生独立于抗炎和促进自噬作用。这些结果在细胞系中得到了证实，并且通过 siRNA 敲低和组成性激活 Rac1 的过表达证实了对 Rac1 GTPase 的依赖性。
我们的研究结果提供了新的机制证据，这可能被利用来改善 CAC 的化学预防方法。
