Targeting FEN1 disrupts EIF4A3-mediated MUC1-C autoregulation: a novel strategy to suppress lung adenocarcinoma progression

Abstract Flap endonuclease 1 (FEN1), a key enzyme in DNA metabolism, exhibits oncogenic properties in various cancers. However, its functional role and underlying mechanisms in lung adenocarcinoma (LUAD) progression and tumor immunity remain poorly defined. Here, we demonstrate that FEN1 is significantly upregulated in LUAD tissues and serves as an independent prognostic factor for poor survival. Genetic depletion of FEN1 suppressed LUAD cell proliferation by inducing G0/G1 cell cycle arrest and cellular senescence, while significantly impairing migration and invasion capabilities. Mechanistically, integrated proteomic and molecular analyses revealed that FEN1 knockdown disrupts the carboxyl-terminal subunit of mucin 1 (MUC1-C)/PI3K/AKT autoregulatory loop, a critical driver of oncogenic signaling. Furthermore, FEN1 downregulation inhibited the MUC1-C/p65/ programmed death-ligand 1 (PD-L1) signaling axis, thereby alleviating tumor-mediated immunosuppression. This was evidenced by enhanced antitumor immunity, characterized by the local expansion of CD4 + T cells and restored effector function of CD8 + T cells, both in vitro and in vivo. Mechanistically, independent of its nuclease activity, FEN1 interacts with the N-terminus of eukaryotic translation initiation factor 4A3 (EIF4A3) to facilitate its binding to MUC1-C mRNA. Specifically, FEN1 is required for EIF4A3-mediated maintenance of both the transcript stability and translation efficiency of MUC1-C. Clinically, FEN1, MUC1-C, and PD-L1 are coordinately upregulated in LUAD tissues, and their co-expression predicts poor patient survival irrespective of EGFR mutation status. Our findings establish the FEN1/EIF4A3/MUC1-C axis as a novel mechanism driving LUAD progression by concurrently regulating intrinsic malignancy and extrinsic immune evasion, presenting FEN1 targeting as a promising dual-hit therapeutic strategy.