Low expression of NKD2 is associated with enhanced cell proliferation and poor prognosis in human hepatocellular carcinoma

Abstract

NKD2 is a member of the Naked cuticle (Nkd) protein family and functions as a negative regulator of the Wnt signaling pathway. We investigated the prognostic value of NKD2 expression in hepatocellular carcinoma (HCC). Western blot and immunohistochemical analyses revealed that NKD2 was significantly downregulated in HCC specimens compared with adjacent nontumorous tissues. Next, we found that NKD2 expression correlated significantly with several clinicopathologic features, such as tumor grade, tumor size, and Ki-67 expression. Univariate and multivariate analyses demonstrated that NKD2 was an independent prognostic factor for the survival of HCC patients. In particular, Kaplan-Meier survival curves suggested that low NKD2 was statistically associated with poor overall survival. Furthermore, serum refeeding of cultured HCC cells led to impaired amounts of NKD2 and induced HepG2 and Huh7 cells to transition from the G1 to the S phase. Small interfering RNA-mediated depletion of NKD2 in LO2 hepatocytes caused accelerated cell growth. To further clarify the role of NKD2 in cell cycle progression, a Flag-tagged NKD2 construct was used to overexpress NKD2 exogenously in Huh7 cells. These results showed that overexpression of NKD2 induced G1-phase cell cycle arrest. Reduced expression of NKD2 correlated with hyperactivation of the Wnt/β-catenin pathway and doxorubicin resistance in HCC cells. On the basis of these findings, we conclude that NKD2 may be a novel prognostic marker and therapeutic target in HCC.