Loss of hepatocyte growth factor activator inhibitor type 1 participates in metastatic spreading of human pancreatic cancer cells in a mouse orthotopic transplantation model

Hepatocyte growth factor activator inhibitor type 1 ( HAI ‐1) is a membrane‐bound serine protease inhibitor that is expressed on the surface of epithelial and carcinoma cells. On the cell surface, HAI ‐1 regulates membrane‐anchored serine proteases, with matriptase being the most critical target. Matriptase is involved in pericellular processing of biologically active molecules, including protease‐activated receptor‐2 ( PAR ‐2). Previously we reported that S2‐ CP 8 cells, a metastatic variant of the SUIT ‐2 human pancreatic adenocarcinoma cell line, showed markedly decreased HAI ‐1 expression. To assess the significance of HAI ‐1 loss in invasion and spontaneous metastasis of S2‐ CP 8 cells, we established stable S2‐ CP 8 sublines that expressed HAI ‐1 under the control of a tetracycline‐regulated promoter. In vitro migration and invasion assays revealed inhibitory effects of HAI ‐1 on S 2‐ CP 8 cell migration and invasion. Matriptase activity was suppressed by the expression of HAI ‐1. As the enhanced invasiveness in the absence of HAI‐1 was alleviated by knockdown of matriptase by 81% and of PAR ‐2 completely, and PAR ‐2 antagonist also suppressed the invasion, matriptase‐mediated PAR ‐2 activation is involved in HAI ‐1 loss‐induced invasion of S 2‐ CP 8 cells. We then analyzed the effect of HAI ‐1 expression on metastasis of S 2‐ CP 8 cells in vivo using a nude mouse orthotopic xenograft model. Although approximately 50% of the control mice developed distant metastasis, mice treated with doxycycline to induce HAI ‐1 expression did not develop metastasis. These data indicate that HAI ‐1 loss contributes to invasion and dissemination of a highly metastatic subline of SUIT ‐2, suggesting crucial roles for the balance of pericellular serine proteases/inhibitors in pancreatic cancer progression.