A genetic screening identifies a component of the SWI/SNF complex, Arid1b as a senescence regulator

Abstract

Senescence is an important tumour suppressor mechanism, which prevents the proliferation of stressed or damaged cells. The use of RNA interference to identify genes with a role in senescence is an important tool in the discovery of novel cancer genes. In this work, a protocol was established for conducting bypass of senescence screenings, using shRNA libraries together with next-generation sequencing. Using this approach, the SWI/SNF subunit Arid1b was identified as a regulator of cellular lifespan in MEFs. SWI/SNF is a large multi-subunit complex that remodels chromatin. Mutations in SWI/SNF proteins are frequently associated with cancer, suggesting that SWI/SNF components are tumour suppressors. Here the role of ARID1B during senescence was investigated. Depletion of ARID1B extends the proliferative capacity of primary mouse and human fibroblasts. Furthermore, in cells expressing mutant RASG12V and PIK3CAH1047R, ARID1B is necessary for the maintenance of oncogene-induced senescence (OIS). Knockdown of ARID1B during OIS results in reduced expression of the CKIs p21Cip1 and p16INK4a. Many SWI/SNF proteins are post-transcriptionally induced during both replicative senescence and OIS, suggesting a broader role for the SWI/SNF complex in senescence. Ectopic expression of components of the SWI/SNF complex induced premature senescence associated with an increase in p21Cip1 and p16INK4a protein levels. SILAC analysis of global changes in protein levels identified enrichment of mitochondrial proteins and depletion of mitotic proteins upon ARID1B expression. Mitochondrial dysfunction and ROS production are important in ARID1B expressing cells as growth arrest was rescued using antioxidant N-acetyl-cysteine. Finally, analysis of cancer genome sequencing data has identified ARID1B as a mutational-driver gene in some cancers. In these tumours, ARID1B mutations are often associated with mutations in TP53 and PTEN. Altogether the present evidence suggests that regulation of senescence by different mechanisms contributes to explain the tumour suppressive properties of the SWI/SNF complex.