Knockdown of HURP inhibits the proliferation of hepacellular carcinoma cells via downregulation of gankyrin and accumulation of p53

We determined earlier that the hepatoma upregulated protein (HURP) is overexpressed in hepatocellular carcinoma (HCC), but the role of this protein during cancer development and progression remains unknown. Here, we observed that the overexpression of HURP in HEK293 cells promoted the ubiquitination of p53 and its degradation by the proteasome. In contrast, HURP knockdown using short-hairpin RNA reversed these effects. Knockdown of HURP promoted the accumulation of p53 in SK-Hep-1 cells (p53+/-), and these cells showed reduced proliferation, while the p53-mutant Mahlavu cells were not affected. HURP knockdown did not affect the proliferation of H1299 lung carcinoma cells and Hep3B HCC cells which lack p53. Knockdown of HURP also sensitized SK-Hep-1 cells to cisplatin. On the other hand, the expression of exogenous p53 in H1299 and Hep3B cells was decreased following overexpression of HURP, and these cells showed decreased sensitivity to cisplatin-induced apoptosis. Importantly, overexpression of HURP promoted the proliferation of HEK293 cells in an anchorage-independent manner, and inoculation of SK-Hep-1 cancer cells that expressed short-hairpin RNA to knockdown HURP resulted in smaller tumors in nude mice. Gankyrin, a positive regulator of the E3 ubiquitin ligase MDM2, was found to be upregulated following HURP expression, and gankyrin knockdown decreased the HURP-mediated downregulation of p53. Notably, we detected a positive correlation between elevated HURP and gankyrin protein levels in HCC patients (r(2) = 0.778: N = 9). Taken together, these results indicate that HURP represents an oncogene that may play a role in HCC progression and chemoresistance. (C) 2011 Elsevier Inc. All rights reserved.