HIST1H4L promotes small cell lung cancer tumorigenesis by regulating the PI3K/Akt pathway and serves as a potential diagnostic biomarker.

Objective: Despite advances in treatment, small cell lung cancer (SCLC) remains highly aggressive and prone to relapse, leading to poor patient outcomes. Histone HIST1H4L is a key protein that maintains chromatin structure, but its role in SCLC is still unclear. This study aims to define its oncogenic role in SCLC and to determine whether it drives malignant progression by activating the PI3K/AKT signaling pathway. Materials and methods: Public datasets were used to integrate HIST1H4L expression with differentially expressed genes. Functional bioinformatics investigations and survival association analyses were then conducted. Additionally, stable HIST1H4L knockdown cell lines were generated. Knockdown efficiency was confirmed at the mRNA and protein levels by qRT-PCR and Western blot (WB). Cell proliferation was measured using CCK-8 and EdU staining. Cell invasion was assessed with Transwell assays. Cellular senescence and apoptosis were evaluated by β-galactosidase staining and flow cytometry, respectively. Finally, WB was used to detect changes in key proteins of the PI3K/AKT signaling pathway after HIST1H4L knockdown. Results: HIST1H4L was significantly upregulated in SCLC tumors versus normal tissues and enriched in DNA transcription-related pathways. Critically, high HIST1H4L expression correlated with poor patient survival. HIST1H4L knockdown markedly suppressed proliferation, migration, and invasion. It also reduced senescence and apoptosis. HIST1H4L knockdown weakened the activation of the PI3K/AKT signaling pathway. The levels of p-AKT and p-PI3K decreased, while total AKT and PI3K levels remained unchanged. Conclusion: HIST1H4L is significantly overexpressed in SCLC and correlates with poor prognosis. It functions as a key oncogenic driver by activating the PI3K/AKT pathway, promoting tumor proliferation and invasion.