TOPBP1

引言肿瘤细胞通常被认为线粒体呼吸有缺陷，但人类非小细胞肺癌(NSCLC)肿瘤组织相对于邻近的良性肺有增强的葡萄糖氧化。2024年2月6日，中国医学科学院/北京协和医学院周光飙、王桂珍及刘雨桃共同通讯在Cell Discovery (IF 34)在线发表题为“CIP2A induces PKM2 tetramer formation and oxidative phosphorylation in non-small cell lung cancer”的研究论文，该研究表明癌蛋白蛋白磷酸酶2A (CIP2A)抑制糖酵解并促进非小细胞肺癌细胞的氧化代谢。CIP2A结合到丙酮酸激酶M2 (PKM2)并诱导PKM2四聚体的形成，丝氨酸287作为PKM2二聚体-四聚体转换所必需的新磷酸化位点。CIP2A将PKM2重定向到线粒体，通过在苏氨酸69位点磷酸化Bcl2，导致Bcl2的上调。临床发现肿瘤组织中CIP2A水平与磷酸化PKM2 S287水平呈正相关。以CIP2A为靶点的化合物与糖酵解抑制剂协同抑制细胞体外和体内增殖。这些结果表明CIP2A通过促进四聚体PKM2的形成来促进氧化磷酸化，并且靶向CIP2A和糖酵解在非小细胞肺癌中具有治疗潜力。癌细胞表现出Warburg效应(有氧糖酵解)，通常被认为线粒体呼吸有缺陷。然而，最近的证据表明，癌细胞也保留线粒体呼吸，这使得细胞增殖。通过术中13C-葡萄糖在体内输注，人类非小细胞肺癌(NSCLC)肿瘤相对于邻近良性肺具有增强的葡萄糖氧化。与此一致的是，小鼠肺癌肿瘤的生长需要电子传递链氧化泛醇，而癌细胞中缺乏线粒体复合物III会损害肿瘤的生长。与正常肺组织相比，KRAS驱动的小鼠肺肿瘤增加了葡萄糖对三羧酸(TCA)循环的贡献，而丙酮酸的线粒体代谢对于体内肿瘤的形成至关重要。在细胞水平上，肺腺癌细胞线粒体复合体I和复合体II呼吸活性显著增加；胆管癌干细胞(CSCs)具有更有效的呼吸表型，并依赖线粒体氧化代谢来维持干细胞，而胰腺癌CSCs依赖于氧化磷酸化(OXPHOS)，代谢可塑性非常有限。在三阴性乳腺癌中，一些癌蛋白，如C-JUN，可以抑制糖酵解途径，而MYC和MCL1通过增加OXPHOS和活性氧的产生，共同维持CSC对化疗的耐药性。然而，氧化代谢在癌细胞中的作用和机制仍有待阐明。蛋白磷酸酶2A (PP2A)是一种丝氨酸/苏氨酸磷酸酶，由催化C亚基、结构α亚基和调节/可变B亚基12组成，它的能力被PP2A的癌症抑制剂(CIP2A)抑制，CIP2A是一种多功能癌蛋白，以前被称为KIAA1524或p9013-15。CIP2A与100多种蛋白质相互作用，并参与许多信号通路。CIP2A结合并阻止c-Myc的蛋白水解降解，并与DNA拓扑异构酶II结合蛋白1 (TopBP1)相互作用，以维护染色体稳定性，并使粉碎的染色体在有丝分裂进入时聚集。CIP2A调节细胞周期进程，促进恶性转化，并使癌细胞耐药。CIP2A在70%以上的实体或血液恶性肿瘤中过表达，并与患者预后不良相关。小鼠CIP2A缺乏可导致对DMBA诱导的基底样乳腺癌形成的抗性，抑制CIP2A可诱导细胞周期阻滞，促进细胞凋亡或细胞衰老，并在体外和体内显示出治疗效果。因此，CIP2A在癌变过程中发挥着重要的作用，更多地研究其生物学功能可能有助于开发CIP2A抑制剂来治疗癌症。CIP2A诱导PKM2构象变化和生物学功能的示意图（Credit: Cell Discovery）一些报道表明CIP2A与代谢重编程有关。在慢性髓性白血病细胞系K562中，CIP2A可增强线粒体呼吸功能。在人视网膜色素上皮RPE1细胞中，CIP2A的缺失使代谢转向糖酵解途径，增加糖酵解相关基因的表达，并下调TCA周期相关基因。然而，CIP2A在代谢重编程中的作用机制及其与代谢酶的潜在相互作用有待进一步研究。该研究检测了CIP2A在代谢重编程中的作用和作用机制，发现CIP2A通过诱导PKM2寡聚化促进NSCLC细胞的氧化代谢，其中S287是决定二聚体转换的关键氨基酸。CIP2A通过PKM2介导的Bcl2苏氨酸磷酸化上调Bcl2 (T)。体外和体内实验表明，CIP2A抑制剂联合糖酵解抑制剂对NSCLC细胞的抑制作用增强。该研究揭示了CIP2A在调节PKM2寡聚化中的新功能，并为非小细胞肺癌的治疗提供了潜力。原文链接https://www-nature-com.libproxy1.nus.edu.sg/articles/s41421-023-00633-0责编|探索君排版|探索君文章来源|“iNature”End往期精选围观一文读透细胞死亡(Cell Death) | 24年Cell重磅综述（长文收藏版）热文Science最新发布：全世界最前沿的125个科学问题热文Nature | 2024年值得关注的七项技术热文Nature | 自身免疫性疾病能被治愈吗？科学家们终于看到了希望热文Nature | 癌症与神经系统的致命舞蹈

肺癌已成为最致命的恶性肿瘤，每天死亡人数超过350人。临床研究表明，约70%的患者需要放疗(RT)，约77%的肺癌患者接受了放疗。尽管放疗的疗效显著提高，但放射耐药是复发的关键驱动因素。例如，癌细胞在持续暴露于电离辐射(IR)中产生耐药性。因此，需要了解肺癌细胞如何产生辐射抗性并逃避辐射的致命影响。图片来源：https://pubmed-ncbi-nlm-nih-gov.libproxy1.nus.edu.sg/38169561/近日，来自中国医学科学院和北京协和医学院的研究者们在Theranostics杂志上发表了题为“NRF2 promotes radiation resistance by cooperating with TOPBP1 to activate the ATR-CHK1 signaling pathway”的文章，该研究通过与RPA32和TOPBP1合作激活ATR-CHK1信号通路，探索NRF2在促进辐射抗性中的新作用。此外，本研究的发现不仅为肺癌细胞耐辐射的分子机制提供了新的见解，而且验证了NRF2作为放射治疗的潜在靶点。放射抵抗是制约放射治疗应用的主要因素。电离辐射(IR)杀死癌细胞主要是通过引起DNA损伤，特别是双链断裂(DSBs)。耐辐射癌细胞已经发展出强大的DNA损伤修复能力，以在红外环境中生存。核因子-红细胞2相关因子- 2 (NRF2)与放射线抗性相关。研究者之前报道了NRF2作为ATR激活剂在dsb反应中的新功能。然而，NRF2调控DNA损伤修复和辐射抗性的机制尚不清楚。研究者利用TCGA数据库和组织芯片分析NRF2与肺癌患者预后的相关性。构建放射耐药肺癌细胞，通过体内和体外实验探讨NRF2在放射耐药中的作用。利用免疫沉淀、免疫荧光和提取染色质部分来探讨其潜在的机制。在本研究中，TCGA数据库和临床肺癌样本显示NRF2高表达与肺癌患者预后不良相关。研究者建立了高水平表达NRF2的放射耐药肺癌细胞，其抗氧化和DNA修复能力增强。此外，研究者发现NRF2可以独立于其抗氧化功能参与DNA损伤反应。在机制上，研究者证明了NRF2促进了复制蛋白a32 (RPA32)的磷酸化，并且DNA拓扑异构酶2结合蛋白1 (TOPBP1)以NRF2依赖的方式被募集到DSB位点。NRF2易位到DSB位点，促进RPA32的磷酸化，并通过招募TOPBP1到DNA损伤位点激活ATR/CHK1通路。图片来源：https://pubmed-ncbi-nlm-nih-gov.libproxy1.nus.edu.sg/38169561/综上所述，研究者证明NRF2的高核表达与肺癌患者的不良预后相关，并促进了放射耐药的发展。在对IR或CPT的反应中，NRF2易位到DSB位点，促进RPA32的磷酸化，并通过将TOPBP1招募到DNA损伤位点激活ATR/CHK1通路。本研究提示NRF2可能是改善肺癌放疗的一个有希望的靶点。参考文献：Xiaohui Sun et al. NRF2 promotes radiation resistance by cooperating with TOPBP1 to activate the ATR-CHK1 signaling pathway. Theranostics. 2024 Jan 1;14(2):681-698. doi: 10.7150/thno.88899.本文仅用于学术分享，转载请注明出处。若有侵权，请联系微信：bioonSir 删除或修改！

A small molecule that indirectly targets the tough-to-drug MYC gene was effective against two different types of breast cancer in mice, including an aggressive form with a high degree of MYC expression. A small molecule that indirectly targets the tough-to-drug MYC gene appears to work against breast and ovarian cancers in mice.  In an article published Oct. 25 in the Proceedings of the National Academy of Sciences, researchers from Baylor College of Medicine presented data showing that their drug 5D4, a new class of therapy called a TopBP1 inhibitor, could stop the growth of breast and ovarian tumors in mouse models. It worked even better when combined with the PARP 1/2 inhibitor talazoparib, marketed by Pfizer as Talzenna. “It’s very exciting to have found a TopBP1 inhibitor that really stops cancer growth in cells and in animal models in the lab,” Fang-Tsyr Lin, M.D., Ph.D., first and co-corresponding author, said in a press release. The new findings stem from more than a decade of research on TopBP1, a protein that the researchers previously described as a “convergent point” of several pathways involved in cancer development. They include one that promotes the expression of MYC, the protein products of which have been found to be deregulated in more than half of cancers in humans. MYC overexpression has been linked with worse outcomes in breast, blood, lung and other types of cancer, but inhibiting it directly has proven challenging. The Baylor team knew from earlier experiments by other researchers that inhibiting TopBP1 had the effect of boosting expression of another gene, MIZ1, and that, downstream, MIZ1 expression limits MYC’s ability to perpetuate cancer. “Thus, enhancement of MIZ1 activity can attenuate the [cancer-causing] activity of MYC and may be exploited as a therapeutic strategy,” the scientists reasoned in their paper. Given that suppressing TopBP1 frees up MIZ1, “targeting [TopBP1] may … result in the anti-MYC effect.” Before they could see whether this worked in practice, the researchers needed to find a drug that could target exactly the right spot of the protein expressed by the TopBP1 gene. Testing thousands of compounds through a type of analysis called a molecular docking screen and further optimizing the hits gave them 5D4. After validating the small molecule’s anti-TopBP1, anti-MYC and anti-cancer activity in cell studies, the researchers moved to testing 5D4 in mice. They injected ovarian cancer and breast cancer cells into two separate groups of animals, then dosed them with either 5D4 or a control solution every three days, giving three doses total. At the end of the period, they found that the drug reduced tumor growth in both of the models compared to controls. This was also the case for a second, more aggressive model of breast cancer with a high level of MYC overexpression. Next, based on mechanistic and cell study evidence that suggested a TopBP1 inhibitor would have synergistic activity with PARP inhibitors, the researchers tried dosing talazoparib together with 5D4 in two separate mouse models of breast cancer, including one that had a mutation that made it resistant to PARP inhibitors. The results showed that cancer growth was inhibited with the combination to a greater degree than 5D4 alone and that tumors that were resistant to talazoparib were still responsive to 5D4. The mice didn’t develop apparent side effects to the drugs in any of the experiments. One limitation to the study is that the mouse model used was immunocompromised, so it’s unclear how an intact immune response might affect treatment. However, based on the mechanism of PARP inhibitors, there’s reason to believe the combination approach might be even better in that instance, researchers pointed out, a possibility that they believe warrants further study. The researchers plan to prepare 5D4 for use in humans, to optimize its anti-tumor effect in combination with other drugs and to reduce the potential for toxicities, Lin said in the press release.