Induction of hepatocyte growth factor activator gene expression under hypoxia activates the hepatocyte growth factor/c‐Met system via hypoxia inducible factor‐1 in pancreatic cancer

Abstract

Hepatocyte growth facor activator (HGFA) is a serine protease that converts hepatocyte growth factor (HGF) into its active form. Our previous study demonstrated that tumor–stromal interaction under hypoxia augments the aggressive invasive features of pancreatic cancer line PK8 through activated HGF/c‐Met signaling. The present study investigated whether or not hypoxia increases HGFA expression in PK8 cells and promotes the processing of HGF, and leads to c‐Met activation. Moreover, HGFA promoter assays were performed to define whether hypoxia inducible factor‐1 alpha (HIF‐1α) directly activates the HGFA promoter in a hypoxia‐dependent fashion. As a result, hypoxia induced the HGFA mRNA and protein expression in PK8 and the elevation under hypoxia was inhibited by the transfection of HIF‐1α siRNA, thus indicating HIF‐1α‐dependent induction of HGFA. The transfection of siRNA against HGFA to PK8 cells suppressed the conversion to the active HGF, which is secreted from fibroblast MRC5. Furthermore, the phosphorylation of c‐Met and cancer invasion of PK8 cells were decreased by the transfection of HGFA siRNA under hypoxia. Using the luciferase reporter system, HIF‐1α was shown to transactivate the HGFA promoter under hypoxia. These experiments demonstrated for the first time that HGFA is a novel HIF‐1 target gene. Under hypoxia, HGFA might be overexpressed and secreted from pancreatic cancer cells, which contributes to accelerate processing of HGF from fibroblast, resulting in the activation of the c‐Met pathway. HGF/HGFA/c‐Met recruited between cancer‐stromal fibroblasts is activated under hypoxic conditions and therefore might play a central role in the aggressive invasion of pancreatic cancer. (Cancer Sci 2008; 99: 1341–1347)