SMARCA4 regulates SMARCAD1 expression for toleration of replication stress in non-small cell lung cancer

Objectives: SMARCA4, a core component of the SWI/SNF chromatin remodeling complex, is frequently mutated in non-small cell lung cancer (NSCLC). SMARCA4-deficient cancer cells are associated with increased replication stress, one of the major causes of genomic instability, which may lead to cancer. SMARCAD1, a chromatin remodeler, is known as replication fork progressor, and SMARCAD1 dysregulation is also closely related to cancer development. This study aimed to investigate the role of the SMARCA4-SMARCAD1 axis in the toleration of replication stress in NSCLC, focusing on the regulatory relationship between SMARCA4 and SMARCAD1 during replication stress conditions. Methods: Human NSCLC cell lines (Calu-6, NCI-H1975, Calu-1, and NCI-H460) were used for experiments. SMARCA4 and SMARCAD1 expression levels were analyzed by quantitative RT-PCR and immunoblotting. Transcriptional regulation of SMARCAD1 was analyzed by chromatin immunoprecipitation assay. Immunofluorescent analysis was performed to assess SMARCAD1 accumulation at stalled replication forks. Clonogenic assays were conducted to evaluate the roles of SMARCA4 and SMARCAD1 in cell survival. Results: SMARCAD1 was highly expressed in SMARCA4-depleted cells under replication stress. Immunofluorescent analysis revealed significant accumulation of SMARCAD1 at stalled replication forks in SMARCA4-depleted cells. Chromatin immunoprecipitation assays demonstrated that SMARCA4 bound to the transcriptional regulatory region of SMARCAD1, and that this efficacy was decreased under replication stress, suggesting that SMARCA4 is a transcriptional suppressor of SMARCAD1. In a clonogenic analysis either SMARCA4 or SMARCAD1 is required for cell survival. Conclusions: The SMARCA4-SMARCAD1 axis is a novel mechanism that provides tolerance for replication stress.