USP51/PD‐L1/ITGB1‐deployed juxtacrine interaction plays a cell‐intrinsic role in promoting chemoresistant phenotypes in non‐small cell lung cancer

BACKGROUND: Programmed death ligand 1 (PD‐L1) has been demonstrated to facilitate tumor progression and therapeutic resistance in an immune‐independent manner. Nevertheless, the function and underlying signaling network(s) of cancer cell‐intrinsic PD‐L1 action remain largely unknown. Herein, we sought to better understand how ubiquitin‐specific peptidase 51 (USP51)/PD‐L1/integrin beta‐1 (ITGB1) signaling performs a cell‐intrinsic role in mediating chemotherapeutic resistance in non‐small cell lung cancer (NSCLC). METHODS: Western blotting and flow cytometry were employed for PD‐L1 detection in NSCLC cell lines. Coimmunoprecipitation and pulldown analyses, protein deubiquitination assay, tissue microarray, bioinformatic analysis and molecular biology methods were then used to determine the significance of PD‐L1 in NSCLC chemoresistance and associated signaling pathways in several different cell lines, mouse models and patient tissue samples. Ubiquitin‐7‐amido‐4‐methylcoumarin (Ub‐AMC)‐based deubiquitinase activity, cellular thermal shift and surface plasmon resonance (SPR) analyses were performed to investigate the activity of USP51 inhibitors. RESULTS: We provided evidence that cancer cell‐intrinsic PD‐L1 conferred the development of chemoresistance by directly binding to its membrane‐bound receptor ITGB1 in NSCLC. At the molecular level, PD‐L1/ITGB1 interaction subsequently activated the nuclear factor‐kappa B (NF‐κB) axis to elicit poor response to chemotherapy. We further determined USP51 as a bona fide deubiquitinase that targeted the deubiquitination and stabilization of the PD‐L1 protein in chemoresistant NSCLC cells. Clinically, we found a significant direct relationship between the USP51, PD‐L1 and ITGB1 contents in NSCLC patients with chemoresistant potency. The elevated USP51, PD‐L1 and ITGB1 levels were strongly associated with worse patient prognosis. Of note, we identified that a flavonoid compound dihydromyricetin (DHM) acted as a potential USP51 inhibitor and rendered NSCLC cells more sensitive to chemotherapy by targeting USP51‐dependent PD‐L1 ubiquitination and degradation in vitro and in vivo. CONCLUSIONS: Together, our results demonstrated that the USP51/PD‐L1/ITGB1 network potentially contributes to the malignant progression and therapeutic resistance in NSCLC. This knowledge is beneficial to the future design of advanced cancer therapy.