The effect and related mechanisms of RAC1 GTP on radiotherapy for hepatocellular carcinoma.

BACKGROUND: Ras-related C3 botulinum toxin substrate 1 (RAC1), a pivotal Rho guanosine triphosphatases (GTPase) implicated in oncogenic processes and radiotherapeutic resistance across malignancies, has not been extensively examined within the context of hepatocellular carcinoma (HCC) radiotherapy. Therefore, this study aimed to evaluate the expression and prognostic significance of RAC1 in HCC, investigate the molecular mechanisms by which radiation-induced RAC1 GTPase activity mediates radioresistance, and validate targeted inhibition of this activity as a potential strategy to enhance HCC radiosensitivity. METHODS: RAC1 expression was assessed in HCC versus adjacent tissues via The Cancer Genome Atlas (TCGA) and immunohistochemical (IHC) staining of clinical specimens. Its prognostic significance was rigorously evaluated using Cox regression models and visualized via nomogram construction. Radiation-induced RAC1 GTP activity in MHCC97-H cells was quantified by G-protein-linked immunosorbent assay (G-LISA), with downstream signaling (p-IκBα/Bcl-xL) and cell cycle dynamics analyzed via Western blotting and flow cytometry. NSC23766, a RAC1 GTP inhibitor, was employed to identify the pathway-specific effects. RESULTS: RAC1 exhibited marked overexpression in HCC tissues, correlating with advanced pathological stages and inferior prognosis. Radiation triggered RAC1 GTP activation in MHCC97-H cells, driving p-IκBα/Bcl-xL antiapoptotic signaling and G2/M arrest. NSC23766 suppressed radiation-induced IκBα phosphorylation (P<0.05), Bcl-xL upregulation, and cell cycle arrest attenuating radioresistance. CONCLUSIONS: RAC1 overexpression portends poor HCC prognosis and mediates radioresistance through GTP-dependent activation of antiapoptotic pathways and cell cycle modulation. Targeting RAC1 GTP activity may enhance the radiosensitivity of HCC.