SMARCD1 and Its Functional Relevance in SWI/SNF and Cancer

In vertebrates, SWI/SNF complexes, also known as BRG1/BRM-associated factor (BAF) complexes, come in three major subtypes, canonical BAF (cBAF or BAF), polybromo-associated BAF (PBAF) and non-canonical BAF (ncBAF), that are targeted to different types of chromosomal cis-regulatory gene expression control elements. Approximately 20% of malignancies exhibit mutations in genes coding for subunits of the SWI/SNF family of ATP-dependent chromatin remodelling complexes. SMARCD is an essential evolutionarily conserved subunit of these complexes in all eukaryotes. Whilst the integral role of SMARCD in targeting and stabilising the SWI/SNF complexes is conserved from yeast to plants to humans, the three human SMARCD paralogs display specific expression patterns underlying their functional divergence. Although, all three SMARCD paralogs exhibit context-dependent roles in cancer, acting as both tumour suppressors and oncogenes, it is SMARCD1 that appears to show the broadest oncogenic footprint across malignancies, driving proliferation, invasion and metastasis in diverse cancer types. Here we review the recent literature pertaining to the molecular and cellular roles of the mammalian SMARCD paralogs and discuss their roles in oncogenesis from those perspectives.