Parkin Facilitates Proteasome Inhibitor-Induced Apoptosis via Suppression of NF-κB Activity in Hepatocellular Carcinoma

Abstract

Background: The ubiquitin-proteasome system (UPS) is a tight homeostatic control mechanism of intracellular protein degradation and turnover involved in many human diseases. Proteasome inhibitors were initially developed as anticancer agents with potentially beneficial in the suppression of tumor growth. However, clinical trials of patients with solid tumors fail to demonstrate the same efficacy of these proteasome inhibitors. Methods: The expression of Parkin was examined by quantitative PCR and western blotting analyses and immunohistochemical assay. The effect of Parkin on tumor suppression in hepatocellular carcinoma (HCC) cells in vitro was measured using cell viability assay and cell death assay, soft agar clonogenic assay in vitro and a Xenografted tumor model in vivo. The underlying mechanisms in which Parkin -mediated NF-κB activity inhibition were determined via luciferase reporter assays, immunofluorescence staining, nuclear protein extraction assay, immunoprecipitation, and western blot analysis. Findings: Lower Parkin expression correlates with poor survival in patients with HCC. Ectopic Parkin expression enhances proteasome inhibitor-induced apoptosis and tumor suppression in HCC cells in vitro and in vivo. In contrast, knockdown of Parkin expression promotes apoptosis resistance and tumor growth. Mechanically, Parkin promotes TNF receptor-associated factor (TRAF) 2 and TRAF6 degradation and thus facilitates nuclear factor-kappa B (NF-κB) inhibition, which finally results in apoptosis. Interpretation: These findings reveal a direct molecular link between Parkin and protein degradation in the control of NF-κB pathway and may provide a novel UPS-dependent strategy for the treatment of HCC by induction of apoptosis. Funding: This work was supported by the Natural Science Foundation of China (grant numbers 81672874, 81502194), the Guangdong Province Universities and Colleges Pearl River Scholar Funded Scheme (GDUPS), the Distinguished Young Scholar of Guangdong Province (grant number 2015A030306033), the Natural Science Foundation of Guangdong Province (grant number 2015A030313468), the Young Scholar of Science and Technology of Guangdong Province (grant number 2016TQ03R801), the Innovative Academic Team of Guangzhou Education System (grant number 1201610014), the Natural Science Foundation research team of Guangdong Province (grant number 2018B030312001), the Research Team of Department of Education of Guangdong Province (grant number 2017KCXTD027),the Guangzhou key medical discipline construction project fun, Guangdong traditional Chinese medicine bureau project (grant number 20161178), and Guangzhou traditional Chinese medicine and traditional Chinese and western medicine science and technology project (grant numbers 2016A011020, 20182A011025). Declaration of Interest: The authors have no professional, personal or financial conflicts of interests relating to this publication. Ethical Approval: For the clinical materials used in our study, prior patient consent and approval from the Institutional Research Ethics Committee of Taizhou hospital were obtained.