AXL-TBK1 driven nuclear AKT3 promotes metastasis

Abstract

Epithelial-to-mesenchymal transition (EMT) contributes to tumor cell survival, immune evasion, migration, invasion, and therapy resistance. Across human cancer, tumors that are high grade, poorly differentiated, and have undergone EMT carry a worse prognosis with a higher likelihood of metastasis. AXL, a receptor tyrosine kinase, drives EMT and is implicated in tumor progression, metastasis, and therapy resistance in multiple cancer types including pancreatic cancer and breast cancer. TANK-binding kinase 1 (TBK1) is central to AXL-driven EMT yet, the mechanism of how TBK1 induces EMT remains unclear. Here, we report that AXL activation stimulates TBK1 binding and phosphorylation of AKT3. TBK1 activation of AKT3 drives binding and phosphorylation of slug/snail resulting in protection from proteasomal degradation and translocation of the complex into the nucleus. We show that nuclear translocation of AKT3 is required for AXL-driven EMT and metastasis. Congruently, nuclear AKT3 expression correlates with worse outcome in aggressive breast cancer. To advance AKT3 as a therapeutic target, an AKT3-isoform selective allosteric small molecule inhibitor, BGB214, was developed. BGB214 inhibits AKT3 nuclear translocation, EMT-TF stability, AKT3-mediated invasion of breast cancer cells and reduces tumor initiation in vivo. Our results suggest that AKT3 nuclear activity is an important feature of AXL-driven epithelial plasticity and that selective AKT3 inhibition represents a novel therapeutic avenue for treating aggressive cancer. SignificanceNuclear AKT3 activity is an important feature of AXL-TBK1 driven EMT and metastasis, thus selective AKT3 targeting represents a novel approach to treat aggressive cancer.