A Dock8-dependent mechanosensitive central actin pool maintains T cell shape and protects the nucleus during migration

Immune cells navigate through complex tissue architectures by extensive cellular deformation, low adhesion, and high cell velocities. Loss-of-function mutations in dedicator of cytokinesis 8 (Dock8) are associated with immunodeficiency as immune cells becoming entangled during migration through dense environments, but their migration on two-dimensional surfaces remains entirely intact. Here, we investigated the specific cytoskeletal defect of Dock8-deficient activated T cells and describe a central pool of F-actin in wild-type murine and human T cells that is absent in Dock8 knockout T cells. The appearance of the central actin pool is mechanoresponsive and emerges only when cells are very confined. We identified mammalian sterile 20-like (Mst1) as a necessary component in this mechanosensitive pathway in addition to Dock8, allowing for cell shape integrity and survival during migration through complex environments. Our work shows that loss of the central actin pool results in greater nuclear deformation, accrual of DNA damage, and premature cell senescence.