LAUSR

The recurrent mutation (S34F) in splicing factor U2AF1 is frequently observed in lung adenocarcinoma, but its function remains largely unknown. To determine the mechanistic basis and consequences of U2AF1 mutations, we established non–small cell lung carcinoma A549 cell lines with exogenous expression of wildtype (U2AF1‐WT) or mutant (U2AF1‐S34F). Splicing analysis revealed that U2AF1‐S34F mainly caused aberrant exon usage and affected splicing of numerous DNA damage repair genes. Compared to A549 cells expressing U2AF1‐WT, cells expressing U2AF1‐S34F showed enhanced DNA damage and cell death in response to ATR inhibitors (ATRi). Mechanistically, U2AF1‐S34F induced mis‐splicing and downregulation of a key homologous recombination protein RAD51. Overexpression of RAD51 could largely rescue the defective DNA damage response in cells expressing U2AF1‐S34F. Moreover, A549 cells expressing U2AF1‐S34F, but not U2AF1‐WT, were highly sensitive to treatment even with low dose of RAD51 inhibitor on ATRi‐induced DNA damage. Our results suggest that U2AF1‐S34F causes mis‐splicing of DNA damage repair factors in lung cancer and sensitizes cells to RAD51 inhibition.