12 DOC1-dependent recruitment of NURD reveals antagonism with SWI/SNF during epithelial-mesenchymal transition in oral cancer cells

Introduction The molecular basis of the association between mutations in specific remodeler subunits and particular types of cancer is poorly understood. To understand how remodelers are targeted in a cell-type specific manner, we aim to explore the mechanisms of the Nucleosome Remodelling and Deacetylase (NURD) complex during cancer progression. Loss of the NURD subunit Deleted in Oral Cancer 1 (DOC1) is associated with human oral squamous cell carcinomas (OSCCs). Here, we show that restoration of DOC1 expression in OSCCs leads to a reversal of Epithelial-mesenchymal transition (EMT). Material and methods We examined DOC1 expression in normal and cancerous tongue tissue with immunohistochemistry. Besides, 4 different human OSCC cell lines were examined using immunofluorescence and immunoblotting. To study its role in these cells, we re-expressed DOC1 and utilised shRNA-mediated knockdowns (remodelers, EMT regulators). Subsequently we carried out proteomics, genomics, cell-based and biochemistry assays. Results and discussions The loss of DOC1 in oral cancer cells leads to a failure of NURD to bind and repress master transcriptional regulators of EMT. Re-expression of DOC1 in OSCC cells restores NURD recruitment to key target genes, a switch from open to closed chromatin, transcriptional repression, and reversal of EMT (MET). We speculate that, during the development of oral cancer, DOC1 is lost after the inactivation of p53 and INK4a. Our genome-wide binding site analysis showed that DOC1 is crucial for NURD recruitment to a subset of target loci; in particular, promoter regions harbouring CpG islands. DOC1-mediated NURD binding to the Twist1/2 and Zeb2 promoters leads to eviction of SWI/SNF involving nucleosome repositioning, epigenetic reprogramming, and shutdown of transcription. Binding of either SWI/SNF or NURD determines opposite epigenetic states, thereby committing OSCC cells to either EMT or MET. Conclusion Re-expression of DOC1 in OSCC cells restores the switch from open- to closed chromatin and reversal of EMT. We suggest that subunit-dependent gene selection is a major cause of the association between the loss of specific remodeler subunits and particular types of cancer. Our results emphasise that gene control involves a dynamic equilibrium between opposing chromatin modulating enzymes rather than a static chromatin state. Disturbances in this balance can initiate a cascade of chromatin reprogramming events that drives oncogenesis.