Involvement of MMP-7 in invasion of pancreatic cancer cells through activation of the EGFR mediated MEK–ERK signal transduction pathway

Aims: To clarify the involvement of matrix metalloproteinase-7 (MMP-7) in cell dissociation and the subsequent invasion of pancreatic cancer cells. Methods: Western blotting, in vitro invasion assay, immunocytochemistry, and immunohistochemistry were performed in pancreatic cancer cell lines or pancreatic cancer tissue. Results: The active form of the MMP-7 protein was expressed exclusively in the conditioned medium of dissociated (PC-1.0 and AsPC-1) pancreatic cancer cells, whereas proMMP-7 protein was only detected in the conditioned medium of non-dissociated (PC-1 and Capan-2) cells. Both intracellular and conditioned medium localised MMP-7 was greatly reduced by treatment with the epidermal growth factor receptor (EGFR) inhibitor AG1478 and the mitogen activated protein kinase kinase (MEK) inhibitor U0126 in pancreatic cancer cells. MMP-7 treatment significantly induced the disruption of tight junction (TJ) structures and subsequent cell dissociation, and activation of the EGFR mediated MEK– ERK (extracellular signal regulated protein kinase) signalling pathway in the non-dissociated pancreatic cancer cells. Moreover, the strong in vitro invasiveness of dissociated cells was inhibited by AG1478 and U0126 treatment, whereas the weak invasiveness of non-dissociated cells was apparently induced by MMP-7 treatment. In addition, MMP-7 expression was stronger at the invasive front than at the centre of human pancreatic tumours. Conclusion: MMP-7 is involved in cell dissociation and the subsequent invasion of pancreatic cancer cells. It induces the disruption of TJ structures and forms a positive feedback loop with activation of the EGFR mediated MEK–ERK signalling pathway.