The SWI/SNF complex regulates the expression of miR-222, a tumor suppressor microRNA in lung adenocarcinoma

Mammalian SWI/SNF complexes are considered as key epigenetic regulators and they are recurrently mutated in many types of cancer. Most of the studies of these chromatin remodeling complexes are focused on their role in regulating protein-coding genes. However, here we show that the SWI/SNF complex is able to control the expression of microRNAs. We used a SMARCA4-deficient model of lung adenocarcinoma where we could track changes of the miRNome upon SMARCA4 restoration. We found that exogenous SMARCA4 was successfully incorporated into endogenous SWI/SNF complexes and that these SMARCA4-SWI/SNF complexes induced significant changes in the expression of cancer-related microRNAs. The most significantly dysregulated miRNA was miR-222, whose expression was promoted by SMARCA4-SWI/SNF complexes but not by SMARCA2-SWI/SNF complexes via their direct binding to a miR-222 enhancer region. Importantly, miR-222 expression decreased cell viability and impaired cell clonogenicity, phenocopying the tumor-suppressor role of the SMARCA4-SWI/SNF complex in lung cancer. Finally, we showed that the miR-222 enhancer does not interact with any cancer-related protein-coding genes, supporting that its tumor suppressor effect may be exerted via miR-222. Overall, this study highlights the relevant role of the SWI/SNF complex in regulating the expression of the non-coding genome. A549 cell line was transfected with an empty vector and a vector for restoration of SMARCA4 expression. Three independent biological replicates were analysed.