FEN1 plays a key role in the transition from HSIL to CSCC.

Cervical high-grade squamous intraepithelial lesion (HSIL) is a well-recognized precursor to cervical squamous cell carcinoma (CSCC). This study aims to explore molecular mechanisms underlying this transition. The datasets of HSIL and CSCC were downloaded from gene expression omnibus database (GEO). HSIL and CSCC coexpression modules were analyzed by Weighted gene coexpression network analysis (WGCNA). Enrichment analysis were analyzed by Gene Ontology (GO) analysis and Kyoto Encyclopedia of Genes and Genomes (KEGG). The immune microenvironment (TIME) was analyzed by CIBERSORT. Receiver operating characteristic (ROC) curve, and survival analysis were performed. The binding of FEN1 and its upstream regulator PCNA was determined by protein interaction, correlation analysis and rigid docking. Immune infiltration, immune checkpoint and docking with small molecule inhibitors was also analyzed. In vitro experiments were conducted to investigate the function and underlying mechanisms of FEN1 in HSIL and CSCC. A total of 30 sequentially expressed shared genes were identified as potential drug targets. Immune infiltration revealed an imbalance of M1/M2 macrophages, T γδ cells and T cells CD4 memory resting were negatively associated with tumor progression, forming a pro-cancer effect at the HSIL stage and progressing toward CSCC. The key gene FEN1 was over-expressed in HSIL and CSCC, and correlated with the prognosis of CSCC (P < 0.05). FEN1 interacts with PCNA to regulate macrophage-mediated immune infiltration, increase the risk of immune escape, and decrease the sensitivity to immune checkpoints. Small molecule inhibitor binds to FEN1 docking and inhibits its regulation. FEN1 expression is upregulated in both HSIL and CSCC, with a more pronounced increase in CSCC. Knockdown of FEN1 significantly inhibits the proliferation of cervical cancer cells. This study identifies FEN1 as a biomarker and therapeutic target to truncate or reverse CSCC progression at the HSIL stage.