The nuclear transport receptor Impβ is a regulator of actin polymerization

Nuclear transport receptors are best known for mediating nucleocytoplasmic transport (NCT) through nuclear pore complexes. Here, we uncover an unexpected function of the primary import receptor importin-β (Impβ) as a direct regulator of the actin cytoskeleton. Impβ associates with stress fibers and the cell cortex and promotes actin polymerization through direct interactions. Disrupting Impβ-actin binding impairs stress fiber formation and suppresses cell migration well before NCT is affected. In 3D spheroids, perturbing Impβ further compromises tissue integrity, as reflected in changes to nuclear curvature and ellipticity. Together, these findings identify Impβ as a regulator of actin organization in both 2D and 3D contexts, revealing a direct link between the nuclear transport machinery and the cytoskeleton.