Hypermethylation of NF-κB-Activating Protein-Like (NKAPL) Promoter in Hepatocellular Carcinoma Suppresses Its Expression and Predicts a Poor Prognosis

Abstract

Hepatocellular carcinoma (HCC) is a complicated disease with low survival rate partially due to frequent recurrence and no efficient therapy. Promoter hypermethylation of tumor suppressor genes has been demonstrated as one of the molecular mechanisms contributing to tumorigenesis and progression in HCC. This study aims to investigate regulation of NKAPL expression by promoter methylation and its clinical relevance as a biomarker for HCC. We measured mRNA expression of NKAPL in 5 HCC cell lines and a cohort of 62 pairs of primary HCC tumor and their adjacent non-cancer liver tissues. NKAPL protein expression on HCC cell lines and clinical samples was assessed by Western blot and immunohistochemistry, respectively. Association analyses between NKAPL expression and clinicopathologic characteristics in the cohort were conducted. Methylation statuses of NKAPL promoter in 18 pairs of tumor and adjacent non-tumor HCC samples were studied using methylation-specific PCR. Biological functions of NKAPL in HCC were investigated by ectopic expression of NKAPL in HCC cells, and cell viability and cell cycle analyses were performed. Our present study showed suppressed expression and promoter hypermethylation are common events in HCC. Demethylation experiment in HCC cells demonstrated that the NKAPL expression was regulated by promoter methylation. In addition, high methylation level of NKAPL and its low expression predict poor outcome. Furthermore, ectopic expression of NKAPL in the HCC cells inhibited cell growth. Our findings suggest that methylation of NKAPL is a frequent event and is a potential prognosis biomarker in HCC.