Non-coding RNAs (ncRNAs)-mediated high expression of Ras-related C3 botulinum toxin substrate 1 (RAC1) correlates with poor prognosis and tumor immune infiltration of liver hepatocellular carcinoma.

BACKGROUND: Liver hepatocellular carcinoma (LIHC) is a highly malignant tumor with a poor prognosis, and there is an urgent need to identify reliable prognostic markers and therapeutic targets. Ras-related C3 botulinum toxin substrate 1 (RAC1), a key member of the Rho GTPase family, has been reported to play a role in the development of various cancers. Nevertheless, its specific regulatory mechanisms and its influence on the tumor immune microenvironment in hepatocellular carcinoma (HCC) are not yet fully elucidated. In our study, we aimed to comprehensively investigate the expression pattern, prognostic value, regulatory mechanisms and immune infiltration role of RAC1 in LIHC.

METHODS: In this study, we systematically evaluated the expression profile of RAC1 and its clinical relevance using RNA sequencing data from The Cancer Genome Atlas (TCGA) and the Genotype-Tissue Expression (GTEx) database. Potential upstream non-coding RNA (ncRNA) regulators were predicted through integrated bioinformatics approaches and further verified by correlation and survival analyses. The relationship between RAC1 expression and immune cell infiltration in the tumor microenvironment was investigated using the TIMER and GEPIA platforms. Experimental validation was conducted using clinical HCC tissue specimens and hepatocellular carcinoma cell lines.

RESULTS: RAC1 expression was significantly elevated in HCC tissues and cell lines compared to normal controls. High RAC1 expression was associated with more advanced clinicopathological stages and predicted a worse overall survival for patients. Epigenetic analysis indicated that DNA hypomethylation at specific CpG sites may contribute to the upregulation of RAC1. Mechanistically, we identified the LINC00662/miR-101-3p axis as a critical upstream regulatory circuit controlling RAC1 expression. Furthermore, RAC1 levels showed a positive correlation with the infiltration abundance of several immune cell populations, such as B cells, CD8+ T cells, and macrophages, as well as with the expression of immune checkpoint molecules including programmed death 1 (PD-1), programmed death ligand-1 (PD-L1), and cytotoxic T-lymphocyte associated protein 4 (CTLA-4). Notably, RAC1 expression was strongly linked to markers of M2-polarized macrophages, implying its potential involvement in fostering an immunosuppressive tumor microenvironment.

CONCLUSIONS: Our findings demonstrate that ncRNA-mediated overexpression of RAC1 acts as a novel prognostic factor and is closely associated with immune escape mechanisms in HCC. The LINC00662/miR-101-3p/RAC1 signaling axis represents a promising therapeutic target, and RAC1 itself may serve as a valuable biomarker to stratify patients for immunotherapy in hepatocellular carcinoma.