SMARCA4 Inhibits Breast Cancer Progression and Metastasis through RHOA Suppression.

Triple-negative breast cancer (TNBC) is the most challenging subtype of the disease due to its aggressive nature and lack of targeted therapy options. To identify regulators of TNBC, we conducted a genome-wide CRISPR knockout screen in both three-dimensional (3D) tumor spheroid and two-dimensional cell culture models. The 3D spheroid model displayed unique potential in identifying putative tumor suppressors because of its closer mimicry of in vivo tumor growth conditions. Notably, the chromatin remodeling SWI/SNF complex emerged as a potent suppressor of tumor spheroid growth. Specifically, loss of the SWI/SNF ATPase subunit SMARCA4 promoted tumor spheroid growth with reduced compactness and enhanced primary tumor growth and metastasis across multiple TNBC models. SMARCA4 was required for the transcription of the Rho GTPase-activating factor ARHGAP29 by enhancing DNA accessibility through direct binding to its promoter. SMARCA4 loss resulted in reduced ARHGAP29 levels and hyperactive RHOA signaling, subsequently disrupting cell adhesion, facilitating the formation of a loose spheroid structure in vitro, and enhancing breast cancer growth and metastasis in vivo. These results establish SMARCA4 and SWI/SNF as tumor suppressors of TNBC through suppression of RHOA activity. Significance: CRISPR-knockout screen in 3D tumor spheroid revealed that SMARCA4, a SWI/SNF ATPase subunit, suppresses triple-negative breast cancer growth and metastasis by increasing ARHGAP29 transcription and inhibiting the RHOA signaling pathway.