Mediator Subunit MED4 Enforces Metastatic Dormancy in Breast Cancer (RNA-seq_shMed4)

Through rigorous genetic screening in mice, we identified the mediator complex subunit 4 gene, Med4, as a novel tumor-cell intrinsic gatekeeper in metastatic reactivation. Med4 downregulation effectively awakened dormant breast cancer cells, prompting reactivation and macroscopic metastatic outgrowth in the lungs.

Med4 depletion results in profound changes in nuclear size and three-dimensional (3D) chromatin architecture from compacted to relaxed states in contrast to the known canonical function of the Mediator complex. These changes rewire the expression of extracellular matrix (ECM) proteins, integrins, and signaling components resulting in integrin-mediated mechano-transduction and activation of YAP and MRTF. In parallel, assembly of stress fibers pulls on the nuclear membrane, and thereby contributes to mediating and reinforcing the overall chromatin modifications that occur subsequent to Med4 depletion.