The association between bromodomain proteins and cancer stemness in different solid tumor types.

Cancer stemness, which covers the stem cell-like molecular traits of cancer cells, is essential for tumor development, progression and relapse. Both transcriptional and epigenetic aberrations are essentially connected with cancer stemness. The engagement of bromodomain (BrD) proteins-a family of epigenetic factors-has been presented in the pathogenesis of several tumor types, although their association with cancer stemness remains largely unknown. Here, we harnessed TCGA and GEO databases and used several bioinformatic tools (ie, Oncomine, PrognoScan, GEPIA2, TIMER2.0, TISIDB, GSEA, R2 platform) to characterize the association between the BrD family members' expression and cancer stemness in solid tumors. Our results demonstrate that significant upregulation of ATAD2 and SMARCA4, and downregulation of SMARCA2 is consistently associated with enriched cancer stem cell-like phenotype, respectively. Especially, higher-grade tumors that display stem cell-like properties overexpress ATAD2. In contrast to most BrD members, the gene expression profiles of ATAD2 HIGH expressing tumors are strongly enriched with known markers of stem cells and with specific targets for c-Myc transcription factor. For other BrD proteins, the association with cancer de-differentiation status is rather tumor-specific. Our results demonstrate for the first time the relation between distinct BrD family proteins and cancer stemness across 27 solid tumor types. Specifically, our approach allowed us to discover a robust association of high ATAD2 expression with cancer stemness and reveal its' versatility in tumors. As bromodomains are attractive targets from a chemical and structural perspective, we propose ATAD2 as a novel druggable target for de-differentiated tumors, especially those overexpressing MYC.