AXL is a novel ERK5/KLF4 target in MEKi-treated melanoma

RAS/RAF/MEK/ERK1/2 MAPK pathway-based treatments, typically combination therapies with inhibitors for oncogenic BRAF V600 (BRAFi) and MEK1/2 (MEKi), are important treatment alternatives to immunotherapy in advanced BRAF-mutated melanoma. However, their benefit is limited by frequent therapy resistance, i.e. persistence and tumor progression/metastasis under sustained treatment. Furthermore, approximately 50% of the patients, including the NRAS-mutated subset, lack targetable BRAF oncogenes and profit poorly from MEKi. Recent preclinical studies suggest that co-inhibition of the MEK5/ERK5 MAPK pathway, which in different MAPK-activated tumors is compensatorily activated by MEKi, represents a promising strategy to overcome therapy resistance and trigger apoptosis and/or sustained cell cycle arrest. In NRAS-mutant melanoma compensatory ERK5 activation is accompanied by the induction of the two Krüppel-like factors KLF2 and KLF4 Their functional relevance in MEKi resistance, however,is unclear. Using siRNA and CRISPR/Cas9, we examined their contribution to MEKi resistance through functional assays and RNA sequencing. Surprisingly, KLF2 and KLF4 were dispensable for the proliferative and anti-apoptotic effects of compensatory ERK5 activation in MEKi-exposed melanoma. Instead, we identified AXL, a key receptor tyrosine kinase associated with metastasis and phenotypic switching, as critical ERK5/KLF4 target induced during MEKi resistance and demonstrate that KLF4 loss or AXL depletion results in reduced melanoma cell migration and invasion. Our study describes a novel ERK5/KLF4/AXL signaling axis that drives MEKi resistance and metastatic potential in NRAS-mutant melanoma. Targeting this pathway may enhance the efficacy of MAPK-directed therapies and potentially improve responses to immune therapy, where AXL expression similarly promotes tumor progression.