Nuclear force transmission drives cancer-associated fibroblast activation under BRAF inhibition.

Cancer-associated fibroblasts (CAFs) exhibit striking plasticity, enabling them to adapt to external cues such as therapeutic and mechanical stress in the tumor microenvironment (TME). Here, we uncover a shared mechanotransduction pathway through which both BRAF inhibition and matrix stiffness converge in nuclear remodeling to drive CAF activation. Mechanistically, BRAF inhibitors (BRAFis) accelerate RAS-dependent RAF homo and heterodimerization and ERK signaling, leading to GSK-3β inactivation and Rho kinase (ROCK) activation. In parallel, stiff substrates engage integrin receptors to directly activate ROCK signaling. Activation of ROCK induces actin stress fiber assembly, generating mechanical forces that deform the nucleus. In both contexts, nuclear reshaping promotes β-catenin translocation and actin polymerization through a feedback loop that continuously enforces CAF activation and promotes melanoma progression. Notably, pharmacological inhibition of ROCK activity blocks both BRAFi- and stiffness-induced nuclear remodeling and β-catenin accumulation, identifying the ROCK-cytoskeleton-nucleus axis as a critical regulator of CAF adaptation and functionality. Collectively, these findings reveal a mechanically tuned nuclear signaling hub that integrates chemical and physical cues to promote stromal adaptation and suggest ROCK inhibition as a strategy to counteract therapy-induced fibroblast reprogramming and improve therapy response.