Actin and Src-family kinases regulate nuclear YAP1 and its export

The transcriptional regulator YAP1 is critical for the pathological activation of fibroblasts. In normal fibroblasts YAP1 is predominantly located in the cytoplasm, while in activated cancer-associated fibroblasts it exhibits nuclear localization and promotes the expression of many genes required for pro-tumorigenic functions. Here, we investigate the dynamics of YAP1 shuttling in normal and activated fibroblasts, using EYFP-YAP1, quantitative photo-bleaching methods, and mathematical modeling. We find that both 14-3-3 and TEAD binding modulate YAP1 shuttling, but neither affects nuclear import. Instead, we find that YAP1 serine phosphorylation is required for nuclear export. Furthermore, YAP1 nuclear accumulation in activated fibroblasts results from Src and actomyosin-dependent suppression of phosphorylated YAP1 export. Finally, we show that nuclear constrained YAP1, upon XPO1 depletion, remains sensitive to blockade of actomyosin function. Together, these data place nuclear export at the center of YAP1 regulation and indicate that the cytoskeleton can regulate YAP1 within the nucleus.