Insulin-like Growth Factor II Induced by Hypoxia May Contribute to Angiogenesis of Human Hepatocellular Carcinoma

Abstract Insulin-like growth factor II (IGF-II) is highly expressed during hepatocarcinogenesis (P. Schirmacher et al. , Cancer Res., 52: 2549–2556, 1992; B. C. Park et al. , J. Hepatol., 22: 286–294, 1995). However, the mechanism of its enhanced expression is largely unknown. In this study, we show that IGF-II mRNA levels are increased within six h of exposing human hepatoma cell cultures to hypoxia, suggesting that hypoxia may be a strong stimulus for the induction of IGF-II expression in the process of hepatocarcinogenesis. This finding and the fact that hepatocellular carcinoma (HCC) is a typical hypervascular tumor (M. Mise et al. , Hepatology, 23: 455–464, 1996) imply that IGF-II may play an important role in the development of neovascularization of HCC. Here we demonstrate that IGF-II substantially increases vascular endothelial growth factor (VEGF) mRNA and protein levels in a time-dependent manner in human hepatoma cells. The induction of VEGF by IGF-II was additively increased by hypoxia. Moreover, the direct angiogenic activity of IGF-II was observed in the quantitative chick chorioallantoic membrane assay (M. Nguyen et al. , Microvasc. Res., 47: 31–40, 1994). These data suggest that IGF-II may be a hypoxia-inducible angiogenic factor in HCC.