BRAF Inhibition-Associated Nuclear Remodeling is Linked to Cancer-Associated Fibroblast Activation.

Cancer-associated fibroblasts (CAFs) display remarkable plasticity, enabling them to adapt to therapeutic and mechanical stress within the tumor microenvironment. In this study, we identify a shared mechanotransduction pathway by which BRAF inhibition and matrix stiffness converge on ROCK-dependent cytoskeletal remodeling, nuclear deformation, and β-catenin nuclear accumulation in CAFs. Mechanistically, BRAF inhibitors (BRAFi) accelerate RAS-dependent RAF homodimerization and heterodimerization and promote ERK signaling, accompanied by GSK-3β inactivation and activation of the ROCK pathway. ROCK activation induces actin stress fiber assembly and nuclear deformation. Stiff substrates recapitulate BRAFi-induced actin remodeling and nuclear deformation in CAFs. In both contexts, nuclear remodeling is associated with β-catenin nuclear accumulation and CAF activation. Functionally, constitutive β-catenin activation in mouse fibroblasts enhanced CAF-like features in vitro and promoted melanoma growth and matrix remodeling in vivo. Pharmacologic ROCK inhibition blocked both BRAFi- and stiffness-induced nuclear remodeling and β-catenin accumulation, identifying the ROCK-cytoskeleton-nucleus axis as a mediator of CAF responses to therapeutic and mechanical cues. Collectively, these findings reveal a mechanically tuned signaling mechanism that contributes to CAF activation, supporting ROCK inhibition as a potential strategy to limit tumor-promoting stromal adaptation during targeted therapy. SIGNIFICANCE: This study shows that CAFs respond to BRAF inhibition and mechanical cues via a shared ROCK-cytoskeleton-nucleus pathway. ROCK-dependent nuclear remodeling is associated with β-catenin accumulation and CAF activation, whereas ROCK inhibition disrupts this response, highlighting a mechanotransduction pathway that may contribute to stromal adaptation during targeted therapy.