A canonical role of SMAD4 in safeguarding 3D genome architecture to suppress lung tumorigenesis.

Dysregulation of three-dimensional (3D) genome architecture is a hallmark of cancer, yet the mechanisms by which its disruption drives tumorigenesis remain incompletely understood. Here, we demonstrated that SMAD4 regulated 3D genome organization through its canonical transcription factor activity by directly binding chromatin, thereby suppressing lung tumorigenesis. Hi-C analyses of human lung tumors identify SMAD4 as a potential regulator of 3D genome integrity. Using PTEN-deficient human bronchial epithelial cells and genetically engineered mouse models, we showed that SMAD4 loss induced widespread reorganization of chromatin compartments, topologically associating domain (TAD) boundaries, and chromatin loops, leading to oncogenic transcriptional rewiring during early tumorigenesis. Mechanistically, SMAD4 directly bound chromatin loops and spatially connected gene promoters with active or repressive regulatory elements to control transcription. Upon SMAD4 ablation, enhancer-promoter rewiring dysregulated critical oncogenic drivers, including ELF3. Functional manipulation of an SMAD4-regulated ELF3-associated chromatin loop altered ELF3 expression and cell survival both in vitro and in vivo. Collectively, our findings establish SMAD4 as a direct regulator of 3D genome architecture through classical transcription factor binding to chromatin loops and reveal enhancer-promoter rewiring as a key mechanism driving lung tumorigenesis and a potential therapeutic vulnerability in SMAD4-deficient lung cancer.