Cyclin-dependent kinase-associated protein phosphatase is overexpressed in alcohol-related hepatocellular carcinoma and influences xenograft tumor growth

The cyclin-dependent kinase (Cdk)-associated protein phosphatase (KAP) is a dual-specificity phosphatase that dephosphorylates Cdk2 and inhibits cell cycle progression. The overexpression of KAP has been found in breast, prostate and renal cell carcinomas. However, the role of KAP in hepatocellular carcinoma (HCC) remains unclear. Therefore, the aim of this study was to investigate the expression of KAP in HCC and elucidate its role in tumorigenesis. HCC tissues from 117 patients undergoing surgical resection were collected for western blot analysis and immunohistochemichal analysis to establish clinical correlation. The antisense-mediated inhibition of KAP expression was performed in Huh-7 cell lines for tumorigenicity and growth regulation experiments. Clinicopathological analysis indicated that KAP was overexpressed in HCC tissue from alcoholic patients (P<0.001). It was significantly overexpressed in patients with a tumor number of <3 (P=0.0271), suggesting the potential role of KAP in tumorigenesis during early-stage alcohol-related HCC. Additionally, the antisense-mediated inhibition of KAP in Huh-7 HCC cells interfered with cell cycle progression, decreased cell proliferation, reduced the colony-forming ability of the cells and increased apoptosis. Tumorigenicity experiments showed that the KAP knockdown in Huh-7 cells generated smaller tumors in nude mice compared with the mock controls (P=0.018). In the cells in which KAP had been knocked down, the physical interaction between KAP and Cdk2 significantly increased, despite the reduced expression levels of KAP. The phosphorylation of cell proliferation and apoptosis-associated proteins, including phosphatase and tensin homolog (PTEN), glycogen synthase kinase (GSK), p44/42 and Akt, was decreased. Therefore, it can be concluded that KAP is overexpressed in alcohol-related HCC. The antisense-mediated knockdown of KAP in Huh-7 cells decreased cell proliferation, reduced the colony-forming ability of the cells, interfered with cell cycle progression and suppressed xenograft tumor formation, partly through enhanced KAP and Cdk2 interaction.