Hepatic tumor–stroma crosstalk guides epithelial to mesenchymal transition at the tumor edge

Abstract

The tumor–stroma crosstalk is a dynamic process fundamental in tumor development. In hepatocellular carcinoma (HCC), the progression of malignant hepatocytes frequently depends on transforming growth factor (TGF)-β provided by stromal cells. TGF-β induces an epithelial to mesenchymal transition (EMT) of oncogenic Ras-transformed hepatocytes and an upregulation of platelet-derived growth factor (PDGF) signaling. To analyse the influence of the hepatic tumor–stroma crosstalk onto tumor growth and progression, we co-injected malignant hepatocytes and myofibroblasts (MFBs). For this, we either used in vitro-activated p19ARF MFBs or in vivo-activated MFBs derived from physiologically inflamed livers of Mdr2/p19ARF double-null mice. We show that co-transplantation of MFBs with Ras-transformed hepatocytes strongly enhances tumor growth. Genetic interference with the PDGF signaling decreases tumor cell growth and maintains plasma membrane-located E-cadherin and β-catenin at the tumor–host border, indicating a blockade of hepatocellular EMT. We further generated a collagen gel-based three dimensional HCC model in vitro to monitor the MFB-induced invasion of micro-organoid HCC spheroids. This invasion was diminished after inhibition of TGF-β or PDGF signaling. These data suggest that the TGF-β/PDGF axis is crucial during hepatic tumor–stroma crosstalk, regulating both tumor growth and cancer progression.