Role of Hepatocyte-Derived Osteopontin in Liver Carcinogenesis

Osteopontin (OPN) expression correlates with tumor progression in many cancers, including hepatocellular carcinoma (HCC); however, its role in the onset of HCC remains unclear. We hypothesized that increased hepatocyte-derived OPN is a driver of hepatocarcinogenesis. Analysis of a tissue microarray of 366 human samples revealed a continuous increase in OPN expression during hepatocarcinogenesis. In patients with cirrhosis, a transcriptome-based OPN correlation network was associated with HCC incidence along 10 years of follow-up, together with messenger RNA (mRNA) signatures of carcinogenesis. After diethylnitrosamine (DEN) injection, mice with conditional overexpression of Opn in hepatocytes (Opn(Hep) transgenic [Tg]) showed increased tumor burden. Surprisingly, mice with conditional ablation of Opn in hepatocytes (Opn(Delta Hep)) expressed a similar phenotype. The acute response to DEN was reduced in Opn(Delta Hep), which also showed more cancer stem/progenitor cells (CSCs, CD44(+)AFP(+)) at 5 months. CSCs from Opn(Hep) Tg mice expressed several mRNA signatures known to promote carcinogenesis, and mRNA signatures from Opn(Hep) Tg mice were associated with poor outcome in human HCC patients. Treatment with rOPN had little effect on CSCs, and their progression to HCC was similar in Opn(-/-) compared with wild-type mice. Finally, ablation of Cd44, an OPN receptor, did not reduce tumor burden in Cd44(-/-)Opn(Hep) Tg mice. Conclusions: Hepatocyte-derived OPN acts as a tumor suppressor at physiological levels by controlling the acute response to DEN and the presence of CSCs, while induction of OPN is pro-tumorigenic. This is primarily due to intracellular events rather that by the secretion of the protein and receptor activation.