Background: NEDD8 ultimate buster 1 (NUB1) is an interferon (IFN)-inducible protein that downregulates NEDD8 expression and its conjugation system. Although overexpression of NUB1 induces a growth-inhibitory effect in cells, the mechanisms underlying the anti-mitogenic actions of NUB1 in cancer cells remain uncertain. We investigated the anti-cancer effects of NUB1 in human renal cell carcinoma (RCC) cells.
Methods: Nine human RCC cells were used for this study. The proliferation of RCC cells exposed to IFN-alpha was measured by water-soluble tetrazolium salt assay. The expression level of NUB1 in cells was measured by quantitative reverse transcriptase PCR or western blot analysis. Apoptosis and cell-cycle analysis were performed by flow cytometry. Silencing of NUB1 was performed using a small interfering RNA.
Results: Both NUB1 messenger RNA and protein were significantly induced by IFN-alpha in seven out of nine selected RCC cell lines, and the NUB1 expressions induced by IFN-alpha correlated positively with cell growth inhibition. Overexpression of NUB1 remarkably induced S-phase transition during cell cycle and apoptosis in IFN-alpha-resistant A498 cells, in which NUB1 is not induced by IFN-alpha. The expression levels of two cell-cycle regulator proteins, cyclin E and p27, were increased under the aforementioned conditions. The knockdown of NUB1 enhanced cell proliferation of IFN-alpha-resistant A498 cells and suppressed IFN-alpha-induced growth inhibition in IFN-alpha-sensitive 4TUHR cells.
Conclusion: NUB1 may be a key factor involved not only in cell growth inhibition by IFN-alpha in RCC cells but also in the anti-cancer effect against IFN-alpha-resistant RCC cells.