Department of Gastrointestinal Surgery, Guangxi Medical University Cancer Hospital, Guangxi Medical University, Nanning, Guangxi, P.R. China.
Guangxi Key Laboratory of Basic and Translational Research of Colorectal Cancer, Nanning, Guangxi, P.R. China.
Cancer Med. 2024 Nov;13(21):e70397. doi: 10.1002/cam4.70397.
Isobutyric acid (IBA), a short-chain fatty acid, has been unequivocally demonstrated to exert significant influence on the progression of colorectal cancer (CRC). Nevertheless, a comprehensive understanding of its intricate regulatory mechanisms remains elusive.
Employing advanced techniques such as western blot, RT-qPCR, and flow cytometry, we systematically investigated the impact of IBA on the expression of PD-L1 in CRC cells. Concurrently, employing RNA silencing technology and small-molecule inhibitors, we delved into the molecular intricacies underlying the regulatory axis of IBA involving ROCK1/c-Myc/PD-L1. Furthermore, through flow cytometry analysis, we examined the alterations in the tumor immune microenvironment following anti-PD-L1 antibody therapy in a murine tumor model treated with IBA.
Elevated levels of IBA were found to robustly activate PD-L1 expression in CRC cells both in vitro and in vivo, concomitantly reshaping the tumor immune microenvironment. Subsequent mechanistic investigations unveiled that IBA, through its interaction and activation of ROCK1, promotes the activation of c-Myc, thereby enhancing the transcription of PD-L1. Silencing of ROCK1 and application of ROCK1 inhibitors effectively reversed the regulatory effects of IBA on PD-L1. Additionally, IBA inhibited the activity of infiltrating CD8 T cells, resulting in diminished antitumor immunity and attenuating the sensitivity to anti-PD-L1 therapy.
Our study elucidates a novel mechanism by which IBA inhibits the sensitivity of CRC to anti-PD-L1 antibody therapy. Emphasizing IBA and its downstream pathways as potential therapeutic targets for immune therapy resistance mechanisms, our findings provide a novel theoretical foundation for overcoming immune therapy resistance.
异丁酸（IBA）是一种短链脂肪酸，已明确证明其对结直肠癌（CRC）的进展有重大影响。然而，其复杂的调控机制仍不清楚。
我们采用 Western blot、RT-qPCR 和流式细胞术等先进技术，系统研究了 IBA 对 CRC 细胞中 PD-L1 表达的影响。同时，我们利用 RNA 沉默技术和小分子抑制剂，深入研究了 IBA 涉及 ROCK1/c-Myc/PD-L1 的调控轴的分子机制。此外，通过流式细胞术分析，我们研究了在 IBA 处理的荷瘤小鼠模型中，抗 PD-L1 抗体治疗后肿瘤免疫微环境的变化。
我们发现，IBA 可在体外和体内均能强烈激活 CRC 细胞中的 PD-L1 表达，同时重塑肿瘤免疫微环境。随后的机制研究表明，IBA 通过与 ROCK1 的相互作用和激活，促进 c-Myc 的激活，从而增强 PD-L1 的转录。沉默 ROCK1 和应用 ROCK1 抑制剂可有效逆转 IBA 对 PD-L1 的调控作用。此外，IBA 抑制浸润 CD8 T 细胞的活性，导致抗肿瘤免疫减弱，降低对抗 PD-L1 治疗的敏感性。
我们的研究阐明了 IBA 抑制 CRC 对抗 PD-L1 抗体治疗敏感性的新机制。强调 IBA 及其下游途径作为免疫治疗耐药机制的潜在治疗靶点，我们的发现为克服免疫治疗耐药提供了新的理论基础。
