FOS deficiency activates NRF2 signaling and CAF-mediated metabolic symbiosis to induce ferroptosis resistance in lung cancer initiation and brain metastasis. FOS deficiency activates NRF2 signaling and CAF-mediated metabolic symbiosis to induce ferroptosis resistance in lung cancer initiation and brain metastasis

Lung cancer brain metastasis (LCBM) is a leading cause of mortality in lung cancer patients, with a median survival of merely 4-6 months post-metastasis. Ferroptosis, an iron-dependent form of programmed cell death, has emerged as a key regulator of cancer metastasis, yet its role and underlying mechanisms in LCBM remain elusive. This study investigates the involvement of ferroptosis resistance and the transcription factor FOS in LCBM progression. Through single-cell RNA sequencing (scRNA-seq) and clinical sample validation, we identified prominent ferroptosis resistance in LCBM tissues, characterized by elevated expression of resistance markers (e.g., GPX4, SLC7A11) and reduced pro-ferroptotic factors (e.g., ACSL4, TFRC). Functional assays demonstrated that ferroptosis activation inhibits epithelial-mesenchymal transition (EMT) and LCBM both in vitro and in vivo. Notably, FOS expression was progressively downregulated from normal lung tissues to primary lung cancer and LCBM tissues, and FOS overexpression significantly suppressed ferroptosis resistance and brain metastasis. Mechanistically, FOS transcriptionally inhibits the NRF2-SLC3A2-GPX4 axis while promoting the SLC39A8-ACSF2 axis, thereby regulating iron and lipid metabolism to induce ferroptosis. Additionally, FOS overexpression disrupts aberrant crosstalk between lung cancer epithelial cells and cancer-associated fibroblasts (CAFs), blocking CAF-mediated extracellular matrix (ECM) remodeling and cancer cell PD-L1-driven immunosuppression. Notably, FOS overexpression also enhances cisplatin sensitivity in chemo-resistant lung cancer cells, reinforcing its therapeutic potential. Our findings reveal FOS as a critical regulator of ferroptosis and CAF function in LCBM, highlighting targeting FOS and ferroptosis as a novel therapeutic strategy to improve outcomes for lung cancer patients with brain metastasis. Overall design: Comparative transcriptome analysis of PC-9 lung cancer cells with FOS overexpression (OE) versus control PC-9 cells (Con). The experiment includes 3 biological replicates per group to investigate the regulatory mechanisms of FOS in lung cancer.

肺癌是全球范围内男女癌症相关死亡的首要病因。肺腺癌（LUAD）是肺癌最常见的组织学亚型，其整体5年生存率不足20%。我们发现，相较于癌旁正常对照组织，c-Fos在肺腺癌临床样本中的mRNA表达水平显著降低。过表达c-Fos可抑制肺腺癌细胞的增殖与集落形成，并诱导细胞凋亡；而敲低c-Fos则可促进细胞增殖与集落形成，抑制细胞凋亡。细胞周期检测结果显示，敲低c-Fos后细胞周期无显著变化，但过表达c-Fos可使G1期细胞占比升高，同时降低G2期细胞比例。敲低c-Fos会降低肺腺癌细胞对顺铂（cisplatin）的敏感性，而过表达c-Fos则在体内外均能增强顺铂的抗肿瘤效果。在肺腺癌细胞中过表达c-Fos后，丝裂原活化蛋白激酶（mitogen-activated protein kinase, MAPK）信号通路出现显著富集。c-Fos过表达会显著抑制c-Jun、c-Myc及DUSP1的表达，而敲低c-Fos则上调这些分子的表达，提示c-Fos在肺腺癌细胞中调控MAPK信号通路。进一步研究显示，c-Fos可与c-Jun发生相互作用；过表达c-Jun可部分恢复c-Fos过表达所下调的c-Jun、c-Myc及DUSP1的表达水平，同时也能挽救因c-Fos过表达引起的细胞增殖抑制，缓解其诱导的细胞凋亡。与之相反，敲低c-Jun会下调c-Jun、c-Myc及DUSP1的表达水平，进而抑制肺腺癌细胞增殖并促进细胞凋亡。综上，在部分肺腺癌中，c-Fos可通过与c-Jun相互作用调控MAPK信号通路，从而抑制肺腺癌细胞增殖、促进细胞凋亡，并增强其对顺铂的敏感性。实验设计：本研究包含两组mRNA表达谱测序对照比较，分别为SOX9短发夹RNA #1（SOX9 shRNA #1）组与阴性对照短发夹RNA（shCtrl）组，以及SOX9短发夹RNA #2（SOX9 shRNA #2）组与shCtrl组。