Nuclear Expression of the Deubiquitinase CYLD Is Associated with Improved Survival in Human Hepatocellular Carcinoma

BACKGROUND & AIMS: The deubiquitinase CYLD removes (K-63)-linked polyubiquitin chains from proteins involved in NF-κB, Wnt/ß-catenin and Bcl-3 signaling. Reduced CYLD expression has been reported in different tumor entities, including hepatocellular carcinoma (HCC). Furthermore, loss of CYLD has been shown to contribute to HCC development in knockout animal models. This study aimed to assess subcellular CYLD expression in tumor tissues and its prognostic significance in HCC patients undergoing liver resection or liver transplantation. METHODS: Subcellular localization of CYLD was assessed by immunohistochemistry in tumor tissues of 95 HCC patients undergoing liver resection or transplantation. Positive nuclear CYLD staining was defined as an immunhistochemical (IHC) score ≥3. Positive cytoplasmic CYLD staining was defined as an IHC score ≥6. The relationship with clinicopathological parameters was investigated. Cell culture experiments were performed to analyze subcellular CYLD expression in vitro. RESULTS: Cytoplasmic CYLD expression was observed in 57 out of 95 (60%) HCC specimens ((cyt)°CYLD(+)). Nuclear CYLD staining was positive in 52 out of 95 specimens (55%, (nuc)CYLD(+)). 13 out of 52 (nuc)CYLD(+) patients (25%) showed a lack of cytoplasmic CYLD expression. (nuc)CYLD(+) was associated with prolonged overall survival in patients after resection or liver transplantation (P = 0.007). 5-year overall survival rates were 63% in (nuc)CYLD(+) vs. 26% in (nuc)CYLD(-) patients. Nuclear CYLD staining strongly correlated with tumor grading (P<0.001) and Ki67 positivity (P = 0.005). (nuc)CYLD(+) did not prove to be an independent prognostic parameter. In vitro, Huh7, Hep3B and HepG2 showed reduced CYLD levels compared to the non-malignant liver cell line THLE-2. Induction of CYLD expression by doxorubicin treatment led to increased cytoplasmic and nuclear expression of CYLD. CONCLUSIONS: Expression of nuclear CYLD is a novel prognostic factor for improved survival in patients with HCC undergoing liver resection or transplantation.