Ubiquitination of tumor suppressor PML regulates prometastatic and immunosuppressive tumor microenvironment

The tumor microenvironment plays an important role in tumor growth and metastasis. However, the mechanism by which tumor cells regulate the cell and non-cell constituents of surrounding stroma remains incompletely understood. Promyelocytic leukemia (PML) is a pleiotropic tumor suppressor, but its role in tumor microenvironment regulation is poorly characterized. PML is frequently downregulated in many cancer types, including lung cancer. Here, we identify a PML ubiquitination pathway that is mediated by WD repeat 4-containing cullin-RING ubiquitin ligase 4 ([CRL4.sup.WDR4]). Clinically, this PML degradation pathway is hyperactivated in lung cancer and correlates with poor prognosis. The WDR4/PML axis induces a set of cell-surface or secreted factors, including CD73, urokinase-type plasminogen activator receptor (uPAR), and serum amyloid A2 (SAA2), which elicit paracrine effects to stimulate migration, invasion, and metastasis in multiple lung cancer models. In xenograft and genetically engineered mouse models, the WDR4/PML axis elevates intratumoral Tregs and M2-like macrophages and reduces [CD8.sup.+] T cells to promote lung tumor growth. These immunosuppressive effects were all reversed by CD73 blockade. Our study identifies WDR4 as an oncoprotein that negatively regulates PML via ubiquitination to promote lung cancer progression by fostering an immunosuppressive and prometastatic tumor microenvironment, suggesting the potential of immune-modulatory approaches for treating lung cancer with aberrant PML degradation.
Introduction Lung cancer is one of the most devastating diseases. Despite advances in treatment, the 5-year survival rate is only slightly better than 10%, and the majority of late-stage patients [...]