ABSTRACTThe tumor stroma and its cellular components are known to play an important role in tumor resilience towards treatment. Here, we report a novel resistance mechanism in melanoma that is elicited by BRAF inhibitors (BRAFi)-induced non-canonical nuclear β-catenin signaling in cancer-associated fibroblasts (CAFs). Our study reveals that BRAFi leads to an expanded CAF population with increased β-catenin nuclear accumulation and enhances their biological properties. This CAF subpopulation is essential for melanoma cells to grow and resist to BRAFi/MEK inhibitors (MEKi). Mechanistically, BRAFi induces BRAF and CRAF dimerization and subsequently the activation of ERK signaling in CAFs, leading to the inactivation of the β-catenin destruction complex. By RNA-Seq, periostin (POSTN) is identified as a major downstream effector of β catenin in CAFs and can compensate for the loss of β-catenin in CAFs in conferring melanoma cell BRAFi/MEKi resistance. Moreover, POSTN reactivates the ERK pathway, which is inhibited by BRAFi/MEKi, in melanoma cells through PI3K/AKT signaling. Our data underscore the roles of BRAFi-induced CAF reprogramming in matrix remodeling and therapeutic escape of melanoma cells and reveal POSTN as an important matrix target to eliminate BRAFi/MEKi resistance in melanoma.
Matrix remodeling‐associated protein 8 is a marker of a subset of cancer‐associated fibroblasts in pancreatic cancer
