Arsenic trioxide promotes a glue‑like interaction to drive STUB1-mediated NPM-ALK degradation in ALK⁺ ALCL

The nucleophosmin-anaplastic lymphoma kinase (NPM-ALK) fusion constitutively activates ALK tyrosine kinase, driving oncogenesis in anaplastic large cell lymphoma (ALCL). While arsenic trioxide (ATO) exhibits therapeutic potential, its precise mechanism remains elusive, limiting clinical application. Here, we used a combined approach of E3 ligase library screening, ATO chemical proteomics, and NPM-ALK immunoprecipitation-mass spectrometry to reveal that ATO regulates NPM-ALK stability via the E3 ligase STUB1. Clinically, high STUB1 expression correlates with improved survival, identifying it as a candidate favorable prognostic biomarker in NPM-ALK⁺ ALCL. Mechanistically, ATO promotes a glue‑like interaction that stabilizes the ternary complex of STUB1 and NPM-ALK, promoting ubiquitination at K174 and subsequent proteasomal degradation. Furthermore, structural modeling, domain mapping, and point mutations support a proposed arsenic-dependent interaction model involving STUB1 Cys83, Cys103, and NPM-ALK Cys599, which may modulate the STUB1-NPM-ALK interface and enhance their interaction, thereby promoting ubiquitin-mediated degradation. Crucially, we demonstrate that STUB1 overexpression or pharmacological activation using the FDA-approved cardiac glycoside Deslanoside synergizes profoundly with ATO to inhibit tumor growth both in vitro and in vivo. These findings provide novel mechanistic insight into ATO's action in NPM-ALK⁺ ALCL and reveal new therapeutic strategies and candidate prognostic biomarkers for patient management.