Abstract
Invasion is a hallmark of malignant gliomas and is the main reason for therapeutic failure and recurrence of the tumor. CXCR4 is a key chemokine receptor implicated in glioma cell migration whose expression is regulated by hypoxia. Here, we report that hepatocyte growth factor (HGF) upregulated CXCR4 protein expression in glioma cells. HGF pre-treatment increased migration of U87MG and LN229 glioma cells towards the CXCR4 ligand, stromal cell-derived factor-1alpha (SDF-1alpha). AMD3100, a CXCR4 inhibitor, inhibited the increased migration of HGF pre-treated LN229 glioma cells towards SDF-1alpha. Following exposure to HGF and hypoxia, both cell lines showed nuclear translocation of NF-kappaB (p65). The HGF- and hypoxia-induced nuclear translocation of NF-kappaB (p65) involved phosphorylation and degradation of IkappaB-alpha. Knock-down of NF-kappaB expression inhibited the induction of CXCR4 expression in response to HGF, but not to hypoxia. However, knock-down of NF-kappaB expression inhibited the induction of CXCR4 expression in response to hypoxia in the presence of HGF. NF-kappaB mediated migration towards SDF-1alpha in response to HGF. Knock-down of NF-kappaB expression resulted in decreased migration of HGF pre-treated glioma cells towards SDF-1alpha. Therefore, HGF upregulates CXCR4 expression via NF-kappaB and leads to enhanced migration. To our knowledge, this is the first report to show that a crosstalk mediated by NF-kappaB exists between the SDF-1alpha/CXCR4 and HGF/c-Met axes relevant to glioma cell migration. These findings imply that effective inhibition of glioma invasion should be directed against several ligand/receptor signaling pathways.