Hepatocellular carcinoma (HCC) is a prototype of inflammation-associated cancer. Oncoprotein Gankyrin, which mostly increases in HCC, plays a critical role in HCC development and metastasis. However, the exact mechanism of Gankyrin up-regulation in HCC remains unclear. A Gankyrin luciferase reporter was developed to screen a potential regulator for Gankyrin from a list of proinflammatory cytokines, and interleukin (IL)-1β was found as one of its activators. In clinical premalignant and malignant liver disease samples, enhanced IL-1β/interleukin-1 receptor-associated kinase 1 (IRAK-1) signaling accompanied by increased Gankyrin was observed. Lower expression of Gankyrin and phospho-IRAK-1 are favorable prognostic markers for HCC. A similar correlation was observed in the diethylnitrosamine (DEN) model of rat hepatocarcinogenesis. The results from Gankyrin reporter activity, real-time polymerase chain reaction, or immunoblotting further confirmed the up-regulation of Gankyrin by IL-1β/IRAK-1 inflammatory signaling. Moreover, a series of Gankyrin's truncated reporters were constructed, and electrophoretic mobility shift assay (EMSA) and chromatin immunoprecipitation (ChIP) were performed to analyze the properties of Gankyrin promoter. Mechanistically, the core promoter of Gankyrin contains the binding site of nuclear factor Y (NF-Y) family members, which can recruit histone acetyltransferase coactivator E1A-binding protein p300 (p300) or CREB-binding protein (CBP) to promote Gankyrin transcription. Conversely, knockdown of NF-Y, p300, or CBP inhibits Gankyrin expression. IL-1β stimulation causes sequential phosphorylation of IRAK-1, c-Jun N-terminal kinase (JNK), and p300 and enhances recruitment of the p300/CBP/NF-Y complex to Gankyrin promoter. Inhibition of phospho-JNK impairs IL-1β/IRAK-1 signaling-mediated up-regulation of Gankyrin.
Conclusion: The finding of IL-1β/IRAK-1 signaling promoting Gankyrin expression through JNK and NF-Y/p300/CBP complex provides a fresh view on inflammation-enhanced hepatocarcinogenesis.
© 2014 by the American Association for the Study of Liver Diseases.