科研之友
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摘要
Osteopontin (OPN) is a secreted phosphoprotein, originally characterized in malignant-transformed epithelial cells. OPN is associated with tumor metastasis of several tumors and is overexpressed in hepatocellular carcinoma (HCC) tissue involving HCC invasion and metastasis. Importantly, OPN is significantly up-regulated in liver injury, inflammation, and hepatitis C virus (HCV)-associated HCC. However, the underlying mechanisms of OPN activation and its role in HCV-mediated liver disease pathogenesis are not known. In this study, we investigated the mechanism of OPN activation in HCV-infected cells. We demonstrate that HCV-mediated Ca2+ signaling, elevation of reactive oxygen species, and activation of cellular kinases such as p38 MAPK, JNK, PI3K, and MEK1/2 are involved in OPN activation. Incubation of HCV-infected cells with the inhibitors of AP-1 and Sp1 and site-directed mutagenesis of AP-1- and Sp1-binding sites on the OPN promoter suggest the critical role of AP-1 and Sp1 in OPN promoter activation. In addition, we show the in vivo interactions of AP-1 and Sp1 with the OPN promoter using chromatin immunoprecipitation assay. We also show the calpain-mediated processing of precursor OPN (approximate to 75 kDa) into approximate to 55-, approximate to 42-, and approximate to 36-kDa forms of OPN in HCV-infected cells. Furthermore, we demonstrate the critical role of HCV-induced OPN in increased phosphorylation of Akt and GSK-3 followed by the activation of -catenin, which can lead to EMT of hepatocytes. Taken together, these studies provide an insight into the mechanisms of OPN activation that is relevant to the metastasis of HCV-associated HCC.
- 出版日期2013-12-27
