Aim: This study aims to comprehensively analyse the Ribosomal Protein S6 Kinase A4 (RPS6KA4) and determine the prognostic value for hepatocellular carcinoma (HCC).

Background: Liver cancer is a common type of tumor worldwide, and HCC accounts for about 75 to 85% of all primary liver cancer cases. The Ribosomal S6 protein kinases (RSK) family plays an important regulatory role in cell growth, movement, survival, and proliferation.

Methods: We collected the expression and clinicopathological features of RPS6KA4 in The Cancer Genome Atlas (TCGA) cohort and evaluated the prognostic value of RPS6KA4 in HCC. Gene Ontology (GO)/ Kyoto Encyclopedia of Genes and Genomes (KEGG) and Gene Set Enrichment Analysis (GSEA) were performed to determine the enrichment pathways of RPS6KA4. Correlation between RPS6KA4 expression and immune infiltration was analyzed. Protein-protein interaction (PPI) network analysis was performed to screen hub genes.

Results: RPS6KA4 overexpression is statistically significant in HCC relative to normal tissues (P < 0.001). Increased expression of RPS6KA4 is associated with higher T stage (p=0.021), pathological stage (p=0.006), α-fetoprotein (AFP) value (p=0.026), and vascular invasion (p=0.023) of HCC. Overexpression of RPS6KA4 predicted worse overall survival (OS, P=0.002), disease-specific survival (DSS, P=0.012), and progress-free interval (PFI, P=0.031) for HCC. Univariate/multivariate Cox regression analysis confirmed that RPS6KA4 was an independent risk factor for HCC (P=0.002 in univariate analysis; P=0.014 in multivariate analysis). GO/KEGG analysis and GSEA analysis suggest that RPS6KA4 plays a precancer role in HCC through epigenetics, cell adhesion, tumor-driven GTPase pathways, infection-related carcinogenesis, and adaptive immunity. Immune infiltration analysis confirmed the strong negative relationship between RPS6KA4 and B cells, CD4+ T cells, macrophages, neutrophils, as well as dendritic cells. Protein-protein interactions (PPI) analysis and hub gene identification revealed the cancer-promoting effects of RPS6KA4 related to RSKs, AP-2, clathrin, and MAPK/ ERK pathways.

Conclusion: RPS6KA4 is a potentially valuable molecule for understanding HCC tumorigenesis. Increased RPS6KA4 might be a promising prognostic factor for low HCC survival.