GSE121052
AP-1 is a temporally regulated dual gatekeeper of reprogramming to pluripotency (RNA-Seq)
Somatic cell transcription factors are critical to maintaining cellular identity and constitute a barrier to human somatic cell reprogramming, yet a comprehensive understanding of the mechanism of action is lacking. To gain insight, we examined epigenome remodeling at the onset of human nuclear reprogramming by profiling human fibroblasts after fusion with murine embryonic stem cells. By ATAC-seq and ChIP-seq we identified enrichment for the AP-1 transcription factor c Jun at regions of early transient accessibility at fibroblast-specific enhancers. Expression of a dominant negative AP-1 mutant (dnAP 1) reduced accessibility and expression of fibroblast genes, overcoming the barrier to reprogramming. Remarkably, efficient reprogramming of human fibroblasts to iPSC was achieved by transduction with vectors expressing SOX2, KLF4, and inducible dnAP 1 demonstrating that dnAP-1 can substitute for exogenous human OCT4. Mechanistically, we show that the AP-1 component c-Jun has two unexpected temporally distinct functions in human reprogramming: i) to potentiate fibroblast enhancer accessibility and fibroblast-specific gene expression and ii) to bind to and repress OCT4 as a complex with MBD3. Our findings highlight AP-1 as a previously unrecognized potent dual gatekeeper of the somatic cell state. Overall design: Human fibroblasts are fused with mouse embryonic stem cells (mESCs) with or without induction of dominant negative AP-1 (dnAP-1) to make heterokaryons. Heterokaryons are sorted at the specified timepoint post-fusion. Fibroblasts alone, fibroblasts co-cultured with mESCs (co-culture), and fibroblasts fused with each other (homokaryon) are used as controls. RNA is extracted for RNA-seq library preparation and sequencing.