Niu Xiaxia, Cui Hongmei, Gu Xinsheng, Wu Ting, Sun Min, Zhou Changlong, Ma Mei
Institute of Toxicology, School of Public Health, Lanzhou University, Lanzhou, China.
College of Basic Medical Sciences, Hubei University of Medicine, Shiyan, China.
Front Oncol. 2022 Mar 16;12:837980. doi: 10.3389/fonc.2022.837980. eCollection 2022.
Low response rate to radiotherapy remains a problem for liver and colorectal cancer patients due to inappropriate DNA damage response in tumors. Here, we report that pregnane X receptor (PXR) contributes to irradiation (IR) resistance by promoting activating transcription factor 3 (ATF3)-mediated ataxia-telangiectasia-mutated protein (ATM) activation. PXR stabilized ATF3 protein by blocking its ubiquitination. PXR-ATF3 interaction is required for regulating ATF3, as one mutant of lysine (K) 42R of ATF3 lost binding with PXR and abolished PXR-reduced ubiquitination of ATF3. On the other hand, threonine (T) 432A of PXR lost binding with ATF3 and further compromised ATM activation. Moreover, the PXR-ATF3 interaction increases ATF3 stabilization through disrupting ATF3-murine double minute 2 (MDM2) interaction and negatively regulating MDM2 protein expression. PXR enhanced MDM2 auto-ubiquitination and shortened its half-life, therefore compromising the MDM2-mediated degradation of ATF3 protein. Structurally, both ATF3 and PXR bind to the RING domain of MDM2, and on the other hand, MDM2 binds with PXR on the DNA-binding domain (DBD), which contains zinc finger sequence. Zinc finger sequence is well known for nuclear receptor peroxisome proliferator-activated receptor-γ (PPARγ) playing E3 ligase activity to degrade nuclear factor κB (NFκB)/p65. However, whether zinc-RING sequence grants E3 ligase activity to PXR remains elusive. Taken together, these results provide a novel mechanism that PXR contributes to IR resistance by promoting ATF3-mediated ATM activation through stabilization of ATF3. Our result suggests that targeting PXR may sensitize liver and colon cancer cells to IR therapy.
由于肿瘤中不适当的DNA损伤反应，肝癌和结直肠癌患者对放疗的低反应率仍然是一个问题。在此，我们报告孕烷X受体（PXR）通过促进激活转录因子3（ATF3）介导的共济失调毛细血管扩张突变蛋白（ATM）激活，导致辐射（IR）抗性。PXR通过阻断其泛素化来稳定ATF3蛋白。PXR与ATF3的相互作用是调节ATF3所必需的，因为ATF3赖氨酸（K）42R的一个突变体失去了与PXR的结合，并消除了PXR降低的ATF3泛素化。另一方面，PXR的苏氨酸（T）432A失去了与ATF3的结合，并进一步损害了ATM激活。此外，PXR-ATF3相互作用通过破坏ATF3-小鼠双微体2（MDM2）相互作用并负调节MDM2蛋白表达来增加ATF3的稳定性。PXR增强了MDM2的自身泛素化并缩短了其半衰期，从而损害了MDM2介导的ATF3蛋白降解。在结构上，ATF3和PXR都与MDM2的RING结构域结合，另一方面，MDM2在含有锌指序列的DNA结合结构域（DBD）上与PXR结合。锌指序列因核受体过氧化物酶体增殖物激活受体-γ（PPARγ）发挥E酶连接酶活性以降解核因子κB（NFκB）/p65而闻名。然而，锌-RING序列是否赋予PXR E3连接酶活性仍不清楚。综上所述，这些结果提供了一种新的机制，即PXR通过稳定ATF3促进ATF3介导的ATM激活，从而导致IR抗性。我们的结果表明，靶向PXR可能使肝癌和结肠癌细胞对IR治疗敏感。
