Bcr-Abl Regulates USP1 Subcellular Localization through Kinase-Dependent Mechanisms in Chronic Myeloid Leukemia

Abstract Chronic myelogenous leukemia (CML) is driven by the constitutively active Bcr-Abl tyrosine kinase, which persistently remodels intracellular signaling networks through phosphorylation-dependent mechanisms. Although tyrosine kinase inhibitors have significantly improved clinical outcomes, resistance remains a major therapeutic challenge, underscoring the need to define additional regulatory layers of Bcr-Abl signaling. Ubiquitin-specific protease 1 (USP1) is a deubiquitination enzyme that has been identified as one of the Bcr-Abl partner proteins, suggesting a potential functional interaction between the deubiquitination and phosphorylation signaling axes in CML cells. In the present study, we investigated the phosphorylation status of USP1 and evaluated the contribution of Bcr-Abl kinase activity to the regulation of USP1 subcellular localization in K562 cells. Pharmacological inhibition of Bcr-Abl tyrosine kinase activity did not disrupt its colocalization with USP1, indicating that kinase activity is dispensable for complex formation. However, kinase inhibition induced a pronounced redistribution of USP1 from the nucleus to the cytoplasm, suggesting that Bcr-Abl-dependent phosphorylation signaling contributes to the maintenance of USP1 nuclear localization. We assume that activated USP1 may, in turn, facilitate the stabilization of Bcr-Abl, potentially forming a positive feedback mechanism. Importantly, activated USP1 may stabilize Bcr-Abl, supporting the existence of a positive regulatory loop. In this context, Bcr-Abl-dependent signaling maintains USP1 activity or localization, while USP1-mediated deubiquitination enhances Bcr-Abl protein stability. Such reciprocal regulation may sustain oncogenic signaling and promote leukemic progression in CML.