Research Projects

Oral squamous cell carcinoma of the gingivobuccal sulcus (OSCC-GB) is an aggressive disease responsible for high incidence and mortality in the Indian population primarily due to tobacco chewing habits (Singh et al., 2015). Treatment failure and disease recurrence remains the primary cause of mortality in these patients. A rare subpopulation of cancer-initiating stem-like cells, known as cancer stem cells (CSCs), is suggested to be involved in treatment resistance and disease recurrence (Naik et al., 2016). Epigenetic mechanisms, including DNA methylation and histone modification, have emerged as key players in cancer initiation and progression, especially in CSC maintenance and plasticity (Irimie et al., 2018). Thus, understanding the epigenetic landscape of oral CSCs will provide novel anti-cancer treatment options. Enhancer of zeste homolog (EZH2) is a histone methyltransferase and the catalytic subunit of the PRC2 complex which is responsible for the trimethylation of H3 at lysine 27 leading to gene silencing (Kim and Roberts, 2016). Literature suggests high EZH2 expression is required for the maintenance of cancer stemness in various solid tumors including pancreatic and colorectal cancers (van Vlerken et al., 2013, Chen et al., 2016). However, low EZH2 expression was reported in CD44high/CD24low breast CSCs and in side-population sorted from hepatocarcinoma cells (Yasuda et al., 2010), suggesting that the role of EZH2 in the maintenance of cancer stemness is cell type specific and context-dependent. Yet, the role of EZH2 in the regulation of oral cancer stemness and drug resistance remains unexplored. Bivalent chromatin are genomic regions marked by the histone modifications H3K4me3 and H3K27me3 associated with gene activation and silencing, respectively (Bernstein et al., 2006). Importantly, their co-existence in the same promoter maintains gene expression in a repressed but transcription-ready (poised) state. EZH2 is known to modulate transcriptional silencing of multiple genes involved in cell-fate decision by maintaining their bivalent state (Bernstein et al., 2006, Béguelin et al., 2016). However, the role of EZH2 in the regulation of bivalency-mediated priming of key oral cancer stemness genes is still unexplored. In preliminary study using IIOC019 cell line (Indian OSCC-GB patient-derived cell line recently established in PI’s lab), we have observed reduced expression of EZH2 and reduced global levels of H3K27Me3 in CSC-enriched orospheres compared to their adherent (differentiated) counterparts. We hypothesize that the loss of EZH2 expression in CSC-enriched orospheres disrupt bivalency of important genes that control oral CSC maintenance and plasticity (switch between stem and non-stem states). We propose to undertake genome-wide ChIP-seq to identify bivalent marks and compare with gene expression profile to identify key regulators of oral cancer stemness, and provide newer targets for improving therapeutic efficiency.