Background: Tissue plasminogen activator (tPA) is the major activator of plasminogen in plasma. This serine protease is overexpressed by exocrine pancreas tumor cells, where it promotes tumor cell proliferation, growth and invasion. Here we have explored the signaling pathways used by tPA to activate the proliferation of pancreatic cancer cells.
Methods: Comparative transcriptional profiling on cDNA micro arrays were used to analyze the pattern of gene expression of tPA with respect to known growth factors like epidermal growth factor (EGF) and platelet-derived growth factor (PDGF). Results were confirmed using different biochemical assays in which specific kinase inhibitors or RNA interference were used.
Results: The transcriptional profiling showed that tPA modulates the expression of a set of genes commonly regulated by EGF, but distinct from the major set of genes modulated by PDGF. This suggested that tPA and EGF share signaling pathways, a conclusion supported by further experimental evidence. First, we found that tPA induced a rapid and transient phosphorylation of the EGFR. Second, specific EGFR kinase inhibitors, but not PDGFR kinase inhibitors, abolished the tPA-induced phosphorylation of the ERK1/2 kinases and cell proliferation. The mitogenic activity of tPA was also inhibited by siRNA depletion of EGFR, thus confirming the involvement of this receptor and in tPA-triggered signaling. Third, we show that the signaling and mitogenic effects of tPA require its proteolytic activity, the activity of the metalloprotease-9 and active hb-EGF.
Conclusion: Our results suggest that tPA induces proliferation by triggering a proteolytic cascade that sequentially activates plasmin, MMP-9 and hb-EGF. These events are required to activate the EGFR signaling pathway and cell proliferation.
- EGF receptor
- pancreas cancer
- tissue plasminogen activator