The lipogenic regulator SREBF2 induces Transferrin in circulating melanoma cells and suppresses ferroptosis [TF KD RNA-Seq]

Circulating tumor cells (CTCs) are shed by cancer into the bloodstream, where a viable subset overcomes oxidative stress to initiate metastatic outgrowth. Here we show that CTCs from patients with BRAF-mutant melanoma coordinately upregulate both lipogenesis and iron homeostasis pathways. In clonally-derived cultures of melanoma CTCs these pathways are correlated with both intrinsic and acquired resistance to BRAF inhibitors. The lipogenesis regulator SREBF2 directly induces transcription of the iron carrier Transferrin (TF), reducing intracellular iron pools, reactive oxygen species (ROS) and lipid peroxidation, and conferring resistance to both BRAF inhibitors and inducers of ferroptosis. Knockdown of endogenous TF impairs tumor formation by melanoma CTCs, and their tumorigenic defects are partially rescued by the lipophilic anti-oxidants Ferrostatin-1 and Vitamin E. In a cohort of patient-derived melanoma CTCs, single cell RNA-seq identifies a subset with high lipogenic, iron metabolic and proliferative signatures, which are correlated with adverse clinical outcome, irrespective of treatment regimen. Thus, SREBF2-driven iron homeostatic pathways contribute to cancer progression, drug resistance and metastasis. Overall design: We performed in triplicate shRNA knock-down of Transferrin in cells from a culture grown from CTCs from a melanoma patient.

循环肿瘤细胞（Circulating Tumor Cells, CTCs）由癌细胞脱落进入血液循环系统，其中具有生存活性的亚群可克服氧化应激，启动转移性增殖。本研究发现，BRAF突变型黑色素瘤患者的循环肿瘤细胞可协同上调脂肪生成与铁稳态通路。在黑色素瘤循环肿瘤细胞的克隆源性培养体系中，上述通路与BRAF抑制剂的固有耐药及获得性耐药均存在相关性。脂肪生成调控因子SREBF2可直接诱导铁转运蛋白转铁蛋白（Transferrin, TF）的转录，降低细胞内铁储备、活性氧（Reactive Oxygen Species, ROS）水平与脂质过氧化程度，同时赋予细胞对BRAF抑制剂及铁死亡诱导剂的耐药性。对内源性转铁蛋白进行敲低会削弱黑色素瘤循环肿瘤细胞的成瘤能力，而亲脂性抗氧化剂铁司他汀-1（Ferrostatin-1）与维生素E可部分挽救其致瘤缺陷。在一组患者来源的黑色素瘤循环肿瘤细胞队列中，单细胞RNA测序（single cell RNA-seq）可鉴定出一类兼具高脂肪生成、铁代谢与增殖特征的亚群，该亚群与不良临床结局显著相关，且不受治疗方案的影响。综上，SREBF2介导的铁稳态通路可促进癌症进展、耐药与转移。实验设计：我们对1例黑色素瘤患者循环肿瘤细胞来源的培养细胞进行了3次重复的转铁蛋白短发夹RNA（shRNA）敲低实验。