Hypoxia Enhances Tumor-Stroma Crosstalk that Drives the Progression of Hepatocellular Carcinoma

Crosstalk between tumor cells and their microenvironment plays a crucial role in the progression of hepatocellular carcinoma (HCC). Hypoxia, a common feature of advanced HCC, has been shown to modulate the evolution of the tumor microenvironment. In this study, we investigated the effect of hypoxia on tumor-stroma crosstalk in HCC. Human HCC cell lines (Huh-BAT, SNU-475) were cocultured with an activated human hepatic stellate cell line (HSCs; LX-2) under either normoxic or hypoxic conditions. Cell growth was evaluated with the MTS assay. Apoptotic signaling cascades were assessed by immunoblot analysis. Expression of CD31 and phosphorylated (p-) Akt in HCC tissues was detected by immunohistochemistry. Coculturing HCC cells with HSCs under hypoxic conditions enhanced their proliferation, migration, and resistance to bile acid (BA)-induced apoptosis compared to coculturing under normoxic conditions. Under hypoxia, of various HSC-derived growth factors, PDGF-BB was the most up-regulated, leading to the activation of the phosphatidylinositol 3-kinase (PI3K)/Akt pathway in HCC cells. Immunohistochemical study also revealed that p-Akt was highly expressed in hypoxic, hypovascular HCC as compared to hypervascular HCC. Neutralizing antisera to PDGF-BB or a PI3K inhibitor attenuated the proliferation of HCC cells cocultured with HSCs, and sensitized HCC cells to BA-induced apoptosis, especially under hypoxic conditions. In conclusion, hypoxic HSC-derived PDGF-BB stimulates the proliferation of HCC cells through activation of the PI3K/Akt pathway, while the inhibition of PDGF-BB or PI3K/Akt pathways enhances apoptotic cell death. Targeting tumor-stroma crosstalk might be a novel therapy in the management of human HCCs.