Integrative multi-omics analysis reveals conserved hierarchical mechanisms of FOXO3 pioneer-factor activity

FOXO transcription factors are critical for cellular homeostasis and have been implicated in longevity in several species. Yet how these factors directly affect aging, particularly in humans, is not well understood. Here, we take an integrated multi-omics approach to identify the chromatin-level mechanisms by which FOXO3 coordinates transcriptional programs. We find that FOXO3 functions as a pioneer factor in human cells, directly altering chromatin accessibility to regulate gene expression. Unexpectedly, FOXO3s pioneer activity at many sites is achieved through a two-step process, in which chromatin accessibility is initially reduced, then transitions to an open conformation. The direct FOXO3 network comprises chromatin remodelers, including the SWI/SNF remodeling complex, which we find is functionally required for FOXO3 activity. We also identify a novel secondary network of activator protein-1 (AP-1) transcription factors deployed by FOXO3, which orchestrate a neuronal-specific subnetwork. Together, this hierarchical FOXO3 pioneer network regulates key cellular processes including metabolism, proteostasis, epigenetics and proliferation, which must be tightly controlled under changing conditions that accompany aging.