Upregulation of USP22 and ABCC1 during Sorafenib Treatment of Hepatocellular Carcinoma Contribute to Development of Resistance.

Sorafenib is a small molecule that blocks tumor proliferation by targeting the activity of multi-kinases for the treatment of advanced hepatocellular carcinoma (HCC). Increasing sorafenib resistance following long-term treatment is frequently encountered. Mechanisms underlying sorafenib resistance remain not completely clear. To further understand the mechanism of sorafenib resistance in HCC, we established sorafenib-resistant cell lines by slowly increasing sorafenib concentration in cell culture medium. Upregulation of USP22 and ABCC1 were found in Sorafenib-resistant cells. Sorafenib-resistant cells treated with USP22 siRNA showed significant reduction in endogenous mRNA and protein levels of ABCC1. During sorafenib treatment, upregulation of USP22 increases ABCC1 expression and subsequently contributes to sorafenib resistance in HCC cells. Immunohistochemical analysis revealed a positive correlation between USP22 and ABCC1 expression in tissue samples from sorafenib-resistant patients (Pearson's correlation = 0.59, p = 0.03). Our findings indicate that upregulation of USP22 and ABCC1 expression during treatment contribute to sorafenib resistance in HCC cells and that USP22 has strong potential as a therapeutic target for overcoming sorafenib resistance in HCC patients.