Background and Aims: Cancer stem cells (CSCs) contribute to therapy resistance in HCC. Linear ubiquitin chain assembly complex (LUBAC) has been reported to accelerate the progression of cancers, yet its role in the sorafenib response of HCC is poorly defined. Herein, we investigated the impact of LUBAC on sorafenib resistance and the CSC properties of HCC, and explored the potential targeted drugs. Approach and Results: We found that HOIL-1, but not the other components of LUBAC, played a contributing role in LUBAC-mediated HCC sorafenib resistance, independent of its ubiquitin ligase activity. Both in vitro and in vivo assays revealed that the upregulated HOIL-1 expression enhanced the CSC properties of HCC. Mechanistically, HOIL-1 promoted sorafenib resistance and the CSC properties of HCC through Notch1 signaling. Mass spectrometry, co-immunoprecipitation, western blot, and immunofluorescence were used to determine that the A64/Q65 residues of HOIL-1 bound with the K78 residue of Numb, resulting in impaired Numb-mediated Notch1 lysosomal degradation. Notably, pixantrone was screened out by Autodock Vina, which was validated to disrupt HOIL-1/Numb interaction to inhibit Notch1 signaling and CSC properties by targeting the Q65 residue of HOIL-1. Moreover, pixantrone exerted synergistic effects with sorafenib for the treatment of HCC in different HCC mouse models. Conclusions: HOIL-1 is critical in promoting sorafenib resistance and CSC properties of HCC through Notch1 signaling. Pixantrone targeting HOIL-1 restrains the sorafenib resistance and provides a potential therapeutic intervention for HCC.

The linear ubiquitin chain assembly complex (LUBAC) has been implicated in both cancer progression and viral activity; however, its role in the progression of hepatitis B virus (HBV)-associated hepatocellular carcinoma (HBV-HCC) remains unclear. Here we found that the expression of LUBAC components and Met1-linked ubiquitination was significantly upregulated and associated with poor prognosis in HCC; however, blocking the LUBAC activity with HOIPIN-1 did not affect the malignancy of HCC cells or their sensitivity to sorafenib treatment. Targeting HOIL-1 inhibited the progression of HCC in vitro and in vivo. Interestingly, we found that HOIL-1 , but not other LUBAC components, was exclusively upregulated in HBV-HCC. Functionally, HOIL-1 knockdown suppressed tumor growth, metastasis and stemness in HBV-infected HCC cells. Mechanistically, HOIL-1 interacted with HBx, but not other HBV proteins, and facilitated its stabilization by recruiting deubiquitinatinase USP15, thereby reducing HBx K48-linked ubiquitination. Notably, the clinical analysis indicated that the association between high HOIL-1 expression and poor prognosis was evident only in patients with HBV-HCC with high USP15 expression and not in those with low USP15 expression. Collectively, our results demonstrated that HOIL-1 acts as an oncogene to promote HBV-HCC progression independent of LUBAC activity and may serve as a potential therapeutic target for HBV-HCC.