Pioneer factors orchestrate tissue-specific cohesin-NIPBL chromatin entry and 3D genome organization [ATAC-seq]

Cohesin complex shapes 3D genome organization by extruding DNA loops, yet the mechanisms underlying its chromatin entry remain poorly understood. Here, we reveal that the cohesin loader NIPBL exhibits highly tissue-specific chromatin binding, in stark contrast to the conserved binding profiles of CTCF and RAD21. We identify pioneer transcription factors (TFs), notably FOXA1, as key mediators of NIPBL recruitment to chromatin. FOXA1 directs NIPBL to intra-TAD regions, enabling symmetric loop extrusion, while factors like ETS1 target NIPBL to TAD boundaries, supporting one-sided extrusion. Rapid depletion of FOXA1 disrupts NIPBL binding and intra-TAD loops, whereas loss of NIPBL impairs both intra-TAD and inter-TAD interactions, highlighting their roles in 3D genome folding. Strikingly, a recurrent FOXA1 mutation (R219S) in prostate cancer redirects NIPBL to TAD boundaries by recognizing a non-canonical motif, fostering a more insulated and tumor-aggressive genome. Evolutionary analysis points to a potential conserved role for TF-NIPBL cooperation in cohesin chromatin entry across species with tissue-specific adaptations. Our findings reveal that pioneer factors orchestrate cohesin loading to shape tissue-specific chromatin accessibility and 3D genome dynamics, a mechanism hijacked in diseases like cancer to rewire gene expression.