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

Area of Science:

• Oncology
• Cell Biology
• Biochemistry

Background:

• Cancer-associated fibroblasts (CAFs) are key components of the tumor microenvironment (TME) that can be reprogrammed by external stimuli.
• Therapeutic agents and extracellular matrix (ECM) stiffness influence CAF behavior within the TME.

Purpose of the Study:

• To investigate the mechanism by which BRAF inhibitors (BRAFis) induce reprogramming of CAFs.
• To elucidate the role of nuclear β-catenin accumulation and mechanical forces in CAF adaptation.

Main Methods:

• Utilized BRAF inhibitors (BRAFis) and stiff substrates to treat CAFs.
• Investigated the role of actin polymerization, nuclear deformation, and β-catenin nuclear import.
• Examined the involvement of RAS, RAF, ERK, GSK-3β, and Rho kinase (ROCK) signaling pathways.
• Employed genetic ablation of RAS and RAF isoforms and pharmacological blockade of ROCK activity.

Main Results:

• BRAFis induce nuclear accumulation of β-catenin in CAFs via actin-mediated nuclear deformation.
• Stiff substrates also promote cytoskeletal reorganization and nuclear β-catenin entry in CAFs.
• BRAFi-induced nuclear import of β-catenin is mediated by the ROCK-cytoskeleton axis, involving RAS-RAF-ERK signaling.
• ROCK inhibition or ablation of RAS/RAF isoforms suppressed BRAFi-induced nuclear deformation and β-catenin entry.

Conclusions:

• ROCK-regulated actin polymerization is a critical pathway for CAF reprogramming in response to external signals.
• BRAFis reprogram CAFs by mechanically driving nuclear β-catenin transport through a noncanonical mechanism.
• Targeting the ROCK-cytoskeleton axis may offer a strategy to modulate CAF behavior in cancer therapy.