Ikaros tumor suppression and epigenetic regulation [ATAC-seq]

Ikaros encodes a transcription factor that functions as a tumor suppressor in T-ALL. The mechanisms through which Ikaros regulates gene expression and cellular proliferation in T-ALL are unknown. Re-introduction of Ikaros into Ikaros-null T-ALL cells results in cessation of cellular proliferation and induction of T-cell differentiation. We performed dynamic global epigenomic and gene expression analyses to determine the role of Ikaros in tumor suppression during this process. Our results identified novel Ikaros functions in the epigenetic regulation of gene expression: Ikaros directly regulates de novo formation and depletion of enhancers, as well as de novo formation of active enhancers and activation of poised enhancers; Ikaros directly induces the formation of super-enhancers; and Ikaros demonstrates pioneering activity by directly regulating chromatin accessibility. Dynamic analyses demonstrate the long-lasting effect of Ikaros DNA binding on enhancer activation, de novo formation of enhancers and super-enhancers, and chromatin accessibility. Ikaros induces profound, global re-distribution of HDAC1 via recruitment of HDAC1 to promoter and enhancer regions of different target genes. Expression analysis identified a large number of novel signaling pathways that are directly regulated by Ikaros and Ikaros-induced enhancers, and that are responsible for the cessation of proliferation and induction of T-cell differentiation in T-ALL cells. DN3 cells were transduced with retrovirus that contains HA-tagged wild-type murine Ikaros for 1 day, 2 days and 3 days. ATAC-seqs were performed for cells from these four time points.