BACKGROUND Ferroptosis is a novel mode of non-apoptotic cell death induced by build-up of toxic lipid peroxides (lipid-ROS) in an iron dependent manner. Cancer-associated fibroblasts (CAFs) support tumor progression and drug resistance by secreting various bioactive substances, including exosomes. Yet, the role of CAFs in regulating lipid metabolism as well as ferroptosis of cancer cells is still unexplored and remains enigmatic. METHODS Ferroptosis-related genes in gastric cancer (GC) were screened by using mass spectrum; exosomes were isolated by ultra-centrifugation and CAF secreted miRNAs were determined by RT-qPCR. Erastin was used to induce ferroptosis, and ferroptosis levels were evaluated by measuring lipid-ROS, cell viability and mitochondrial membrane potential. RESULTS Here, we provide clinical evidence to show that arachidonate lipoxygenase 15 (ALOX15) is closely related with lipid-ROS production in gastric cancer, and that exosome-miR-522 serves as a potential inhibitor of ALOX15. By using primary stromal cells and cancer cells, we prove that exosome-miR-522 is mainly derived from CAFs in tumor microenvironment. Moreover, heterogeneous nuclear ribonucleoprotein A1 (hnRNPA1) was found to mediate miR-522 packing into exosomes, and ubiquitin-specific protease 7 (USP7) stabilizes hnRNPA1 through de-ubiquitination. Importantly, cisplatin and paclitaxel promote miR-522 secretion from CAFs by activating USP7/hnRNPA1 axis, leading to ALOX15 suppression and decreased lipid-ROS accumulation in cancer cells, and ultimately result in decreased chemo-sensitivity. CONCLUSIONS The present study demonstrates that CAFs secrete exosomal miR-522 to inhibit ferroptosis in cancer cells by targeting ALOX15 and blocking lipid-ROS accumulation. The intercellular pathway, comprising USP7, hnRNPA1, exo-miR-522 and ALOX15, reveals new mechanism of acquired chemo-resistance in GC.

中文翻译：

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CAF 分泌的 miR-522 抑制铁死亡并促进胃癌的获得性化疗耐药。

背景铁死亡是一种新的非凋亡细胞死亡模式，由有毒脂质过氧化物（脂质-ROS）以铁依赖性方式积聚诱导。癌症相关成纤维细胞（CAF）通过分泌包括外泌体在内的各种生物活性物质来支持肿瘤进展和耐药性。然而，CAF 在调节脂质代谢以及癌细胞铁死亡中的作用仍未被探索，并且仍然是个谜。方法采用质谱技术筛选胃癌（GC）中铁死亡相关基因；通过超速离心分离外泌体，并通过 RT-qPCR 测定 CAF 分泌的 miRNA。Erastin 用于诱导铁死亡，并通过测量脂质-ROS、细胞活力和线粒体膜电位来评估铁死亡水平。结果在这里，我们提供的临床证据表明，花生四烯酸脂氧合酶 15 (ALOX15) 与胃癌中脂质-ROS 的产生密切相关，并且外泌体-miR-522 是 ALOX15 的潜在抑制剂。通过使用原代基质细胞和癌细胞，我们证明外泌体-miR-522主要来源于肿瘤微环境中的CAF。此外，发现异质核核糖核蛋白 A1 (hnRNPA1) 介导 miR-522 包装到外泌体中，泛素特异性蛋白酶 7 (USP7) 通过去泛素化稳定 hnRNPA1。重要的是，顺铂和紫杉醇通过激活 USP7/hnRNPA1 轴促进 CAF 分泌 miR-522，从而抑制 ALOX15 并减少癌细胞中脂质-ROS 的积累，最终导致化疗敏感性降低。结论本研究表明，CAF 分泌外泌体 miR-522，通过靶向 ALOX15 并阻止脂质-ROS 积累来抑制癌细胞中的铁死亡。细胞间通路由 USP7、hnRNPA1、exo-miR-522 和 ALOX15 组成，揭示了 GC 获得性化疗耐药的新机制。