Abstract 5822: YAP inhibition via targeting MAP3K3-dependent lysosomal degradation pathway overcomes BRAF and CDK4/6 inhibitor resistance

Abstract The Hippo-yes-associated protein (YAP) signaling pathway activation underlies the resistance to a wide range of molecularly targeted anti-cancer agents. However, strategies to block YAP activity in cancer by promoting YAP degradation have been largely unsuccessful despite rigorous investigations into canonical Hippo-YAP regulatory mechanisms. Here, we report a novel mechanism of YAP stability regulation by MAP3K3 independently of LATS-mediated proteasomal degradation. We observed that MAP3K3 depletion significantly reduced YAP protein levels in both normal and malignant cells, and mass spectrometry analysis revealed that MAP3K3 phosphorylates YAP at its serine 405 residue. MAP3K3-mediated serine 405 YAP phosphorylation polarizes YAP interaction with BTRC while hindering its interaction with FBXW7, collectively preventing both proteasomal degradation and the p62-mediated lysosomal degradation of YAP. We investigated the role of this mechanism in overcoming anti-cancer resistance and observed robust YAP activation in CDK4/6 inhibitor-resistant luminal breast cancer cells. Genetic and pharmacological MAP3K3 inhibition suppressed YAP-induced drug resistance. Moreover, increased MAP3K3 expression supported the pro-survival activity of YAP in BRAF inhibitor-resistant melanoma cells, and MAP3K3 depletion downregulated YAP-dependent cell cycle gene signatures. Accordingly, the combination of vemurafenib and ponatinib was effective in reducing the survival of BRAF inhibitor-resistant melanoma cells. Collectively, our study identified a novel phosphorylation-mediated YAP stability regulation mechanism and underscored MAP3K3 inhibition as a promising strategy to overcome BRAF and CDK4/6 inhibitor resistance by directly promoting YAP degradation. Citation Format: Won-Ji Ryu, Sanghyun Park, Tae Yeong Kim, Yumi Hwang, Hyun Ju Han, Jeong Dong Lee, Gun Min Kim, Joohyuk Sohn, Sang Kyum Kim, Joon Kim, Min Hwan Kim. YAP inhibition via targeting MAP3K3-dependent lysosomal degradation pathway overcomes BRAF and CDK4/6 inhibitor resistance [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 5822.