FBXO9 mediated the ubiquitination and degradation of YAP in a GSK-3β-dependent manner.

The Hippo signaling pathway effector YAP (Yes-associated protein) serves as a critical transcriptional regulator involved in a wide range of biological processes, including oncogenesis. Despite its potential as a therapeutic target, pharmacologically targeting the Hippo/YAP axis remains challenging, necessitating further exploration of the mechanisms governing YAP regulation. In this study, we identify the Cullin-RING E3 ligase complex SCF-FBXO9-CRL1 as a novel posttranslational regulator of YAP stability. Mechanistically, FBXO9 recognizes YAP through a conserved degron motif and facilitates its K48-linked polyubiquitination at lysine 76 (K76), thereby promoting proteasomal degradation. Notably, we demonstrate that phosphorylation of YAP at Ser338 and Thr342 by GSK-3β primes YAP for FBXO9 recognition, leading to subsequent ubiquitination. Furthermore, our analysis of the signaling cascade reveals that Akt kinase activity modulates this regulatory axis by influencing the phosphorylation status of GSK-3β. Pharmacological inhibition of Akt signaling leads to YAP degradation in a GSK-3β/FBXO9-dependent manner, significantly enhancing chemosensitivity in cancer models. These findings establish a previously unrecognized regulatory axis involving Akt, GSK-3β, FBXO9, and YAP that controls YAP protein turnover, providing a mechanistic basis for therapeutic strategies that combine Akt inhibitors with conventional chemotherapeutics. Our work advances the understanding of posttranslational YAP regulation and identifies several potential therapeutic targets for YAP-driven malignancies.