Abstract: OBJECTIVE：To investigate biological function and prognostic value of lysyl hydroxylase 2 (PLOD2) in hepatocellular carcinoma (HCC)，as well as its impact on tumor immune infiltration. METHODS：PLOD2 expression in HCC was analyzed using data from The Cancer Genome Atlas (TCGA) database. Correlations between PLOD2 expression and clinicopathological characteristics and its prognostic value were evaluated by statistical analysis. Signaling pathways associated with PLOD2 expression were identified using gene set enrichment analysis (GSEA). A stable knockdown of PLOD2 in a human hepatocellular carcinoma cell line，Huh7，was achieved using lentivirus-mediated shRNA technology，and the knockdown effect was verified by Western blot. Effects of PLOD2 on biological behavior of Huh7 cells were assessed using CCK-8，Transwell，and scratch assays. Correlations between PLOD2 expression and HCC immune infiltration was investigated using single-sample gene set enrichment analysis (ssGSEA). RESULTS：Bioinformatics analysis revealed that PLOD2 was significantly overexpressed in HCC compared to normal liver tissues (P<0.05 or P<0.01) and was positively correlated with patient age，T stage，pathological stage，tumor status，histological grade，and AFP level (P<0.05). Survival analysis showed that the median survival time of the PLOD2 high-expression group was significantly shorter than that of the low-expression group (P<0.05). The area under the receiver operating characteristic (ROC) curve for PLOD2 in diagnosing HCC was 0.656，indicating that PLOD2 had reference value in the diagnosis and prognosis prediction of HCC. GSEA revealed that several signaling pathways were associated with high PLOD2 expression：cancer pathways，cell cycle，and adhesion junctions. Cell line validation experiments demonstrated that knockdown of PLOD2 significantly inhibited proliferation，invasion，and migration of Huh7 cells compared to control cells (P<0.05). Migration ability of Huh7 cells with PLOD2 knockdown was significantly reversed upon re-expression of PLOD2 (P<0.05). Expression of PLOD2 was positively correlated with Th2 cell infiltration (r=0.372，P<0.01) and negatively correlated with Th17 and pDC infiltration (r=-0.310，P<0.01). CONCLUSION：This study elucidated the critical role of PLOD2 in HCC progression，with high PLOD2 expression associated with poor prognosis in HCC patients. PLOD2 may play a key role in the immunosuppressive microenvironment by regulating immune cell infiltration and function.

Key words: lysyl hydroxylase 2, hepatocellular carcinoma, clinical value, immune infiltration