Man Ki-Fong, Darweesh Omeed, Hong Jinghui, Thompson Alexandra, O'Connor Charlotte, Bonaldo Chiara, Melkonyan Mark N, Sun Mo, Patel Rajnikant, Ellisen Leif W, Robinson Tim, Song Dong, Koh Siang-Boon
University of Bristol, University Walk, Bristol, UK.
College of Pharmacy, Al-Kitab University, Kirkuk, Iraq.
Oncogene. 2025 May;44(16):1093-1105. doi: 10.1038/s41388-025-03284-5. Epub 2025 Jan 31.
Triple-negative breast cancer (TNBC) is an aggressive and heterogenous breast cancer subtype. RASAL2 is a RAS GTPase-activating protein (GAP) that has been associated with platinum resistance in TNBC, but the underlying mechanism is unknown. Here, we show that RASAL2 is enriched following neoadjuvant chemotherapy in TNBC patients. This enrichment is specific to the tumour compartment compared to adjacent normal tissues, suggesting that RASAL2 upregulation is tumour-selective. Analyses based on 2D/3D cultures and patient-derived xenograft models reveal that RASAL2 confers cross-resistance to common DNA-damaging chemotherapies other than platinum. Mechanistically, we found that apoptotic signalling is significantly downregulated upon RASAL2 expression. This feature is characterised by substantial alterations in the expression of anti-versus pro-apoptotic factors, pointing to heterogeneous mechanisms. In particular, RASAL2 upregulates BCL2 via activation of the oncogenic transcription co-factor YAP. CREB1, a YAP-interacting protein, was identified as the common transcription factor that binds to the promoter regions of RASAL2 and BCL2, driving their collective expression. A subset of RASAL2 colocalises with BCL2 subcellularly. Both proteins decorate mitochondria, where the high levels of mitochondrial RASAL2-induced BCL2 expression render the organelles refractory to apoptosis. Accordingly, mitochondrial outer membrane permeabilisation assay using live mitochondria from RASAL2-high/chemoresistant tumour cells demonstrated attenuated release of death signal, cytochrome c, when exposed to pro-apoptotic factors BAX and tBID. Similarly, these cells were more resilient towards chemotherapy-induced mitochondrial depolarisation. Together, this work reveals a previously undocumented molecular link between RAS GAP and apoptosis regulation, providing a new mechanistic framework for targeting a subset of chemorefractory tumours.
三阴性乳腺癌（TNBC）是一种侵袭性且异质性的乳腺癌亚型。RASAL2是一种RAS GTP酶激活蛋白（GAP），与TNBC中的铂耐药性相关，但其潜在机制尚不清楚。在此，我们表明TNBC患者新辅助化疗后RASAL2表达富集。与相邻正常组织相比，这种富集在肿瘤区域具有特异性，表明RASAL2上调是肿瘤选择性的。基于二维/三维培养和患者来源的异种移植模型的分析表明，RASAL2赋予对除铂之外的常见DNA损伤化疗药物的交叉耐药性。从机制上讲，我们发现RASAL2表达时凋亡信号显著下调。这一特征表现为抗凋亡与促凋亡因子表达的大量改变，提示存在异质性机制。特别是，RASAL2通过激活致癌转录辅因子YAP上调BCL2。CREB1是一种与YAP相互作用的蛋白，被确定为与RASAL2和BCL2启动子区域结合的共同转录因子，驱动它们的共同表达。RASAL2的一个亚群在亚细胞水平上与BCL2共定位。这两种蛋白都定位于线粒体，其中高水平的线粒体RASAL2诱导的BCL2表达使细胞器对凋亡具有抗性。因此，使用来自RASAL2高表达/化疗耐药肿瘤细胞的活线粒体进行的线粒体外膜通透性分析表明，当暴露于促凋亡因子BAX和tBID时，死亡信号细胞色素c的释放减弱。同样，这些细胞对化疗诱导的线粒体去极化更具抵抗力。总之，这项工作揭示了RAS GAP与凋亡调节之间以前未被记录的分子联系，为靶向一部分化疗难治性肿瘤提供了新的机制框架。
