FBXO31 is down-regulated and may function as a tumor suppressor in hepatocellular carcinoma.

The F-box protein family member FBXO31 has rarely been studied in human hepatocellular carcinoma (HCC). This study was designed to investigate the expression profile of FBXO31 in HCC and the possibility that FBXO31 might function as a tumor suppressor in HCC cell lines. We report that FBXO31 is strongly down-regulated in HCC cell lines and specimens. Ectopic expression of FBXO31 inhibited cell proliferation and colony formation in HepG2 and Hep3B cells. The endogenous expression of FBXO31 was fluctuated through cell cycle in the HepG2 cells with maximal expression from late G2 to early G1 phase. Ectopic expression of FBXO31 in HepG2 resulted in the accumulation of cells at the G1 phase of the cell cycle. Possible mechanism might be cyclin D1 degradation mediate by FBXO31 through ubiquitin ligase pathway. Ectopic overexpression of FBXO31 resulted in down-regulation of cyclin D1 which leads to the accumulation of cells at the G1 phase of the cell cycle. Cytoplasmic location of FBXO31 was consistent with cyclin D1 degradation in cytoplasm. Together, our findings suggested that down-regulation of FBXO31 might function as a tumor suppressor in HCC.