1104 - Radiation-Induced HACE1 Suppression Drives Metastatic Progression in Lung Cancer through Actin Cytoskeletal Remodeling
Presenter(s)
H. Huang1, and L. N. Zhao2; 1Department of Radiation Oncology, First Affiliated Hospital of Air Force Medical University, Xian, China, 2Department of radiation oncology, Xijing Hospital, the Fourth Military Medical University, Xi'an, China
Purpose/Objective(s): Emerging evidence indicates that tumor cells develop radioresistance phenotypes during radiation therapy. While some preclinical studies have demonstrated the pro-metastatic potential of X-ray irradiation for lung cancer cells, the precise molecular mediators and underlying regulatory mechanisms driving this process remain poorly characterized.
Materials/Methods: The pro-metastatic effect of X-ray irradiation was measured using an in vivo pulmonary metastasis model. To identify radiation-responsive genes associated with radioresistance, we performed transcriptomic sequencing on irradiated lung cancer cells and followed with differentially expressed genes (DEGs) screening (p<0.05, |log2FC|>1.0). Subsequently, we employed proteomic profiling to characterize protein interaction networks associated with the identified DEGs. Functional validation for identified DEGs was achieved through systematic loss-of-function and gain-of-function experiments. Finally, we elucidated the molecular interactions between key DEGs and their target proteins using integrated biochemical and cellular biology approaches.
Results: Firstly, in vivo metastasis assays showed a 1.51-fold increase (p<0.05) in pulmonary metastatic nodules in X-ray-irradiated A549 cells compared to non-irradiated controls. Then the analysis for sequencing data revealed significant radiation-induced downregulation of the E3 ubiquitin ligase HACE1 and elevated RAC2 protein expression in lung cancer cells. Immunohistochemical analysis of lung tissues confirmed this phenotype, revealing decreased HACE1 expression (1.88-fold reduction, p<0.01) concomitant with increased RAC2 levels (2.11-fold elevation, p<0.001) in irradiated groups. Bioinformatics interrogation of TCGA datasets revealed a significant inverse correlation between HACE1 and RAC2 expression in LUAD (r = -0.142, p = 1.09e-03) and LUSC (r = -0.293, p = 2.15e-11). At the molecular level, HACE1 upregulation increased free barbed end (FBE) formation (2.23 ± 1.2 vs control, p<0.001), while RAC2 silencing reduced FBE density by 59.6% (p<0.001). Subsequent investigations confirmed that HACE1 directly interacts with RAC2 and mediates its ubiquitination and proteasomal degradation, establishing the pivotal role of the HACE1/RAC2 axis in radiation-induced cytoskeletal remodeling.
Conclusion: In summary, our study identifies HACE1 as a novel radiation-responsive regulator of cytoskeleton remodeling. Mechanistically, X-ray irradiation suppresses the HACE1 expression and disrupts the RAC2 ubiquitination and proteasomal degradation, thus promoting RAC2 expression and strengthening the FBE formation. These findings provide new insights into radiation-induced radioresistance mechanisms in lung cancer. and reveal potential therapeutic targets for improving the efficacy of radiotherapy while mitigating metastasis risk.