Cathepsin L induces proangiogenic changes in human omental microvascular endothelial cells via activation of the ERK1/2 pathway.

BACKGROUND: Metastasis still remains the major cause of therapeutic failure, poor prognosis and high mortality in epithelial ovarian cancer (EOC) patients. Previously, we showed that EOC cells secrete a range of factors with potential pro-angiogenic activity, in disease-relevant human microvascular omental endothelial cells (HOMECs), including the lysosomal protease cathepsin L (CathL). Thus, the aim of this study was to examine potential pro-proliferative and pro-migratory effects of CathL in HOMECs and the activated signalling pathways, and whether these proangiogenic responses are dependent on CathL-catalytic activity.

METHODS: HOMECs proliferation was investigated using WST-1, BrdU and CyQUANT assays. Cell migration was examined using a Cultrex Cell 96 transwell migration assay. A range of pHs were assayed to assess enzyme activity in the presence of CathL-specific fluorogenic substrate FY-CHO. Activation of cell signalling pathways was tested using commercially available phosphokinase array and intact cell-based ELISAs.

RESULTS: We show for the first time that CathL has a potent pro-proliferative and pro-migratory effect on HOMECs. For instance, CathL significantly increases HOMEC proliferation (134.8±14.7% vs control 100%) and migration (146.6±17.3% vs control 100%). Our data strongly suggests that these proangiogenic effects of CathL are mediated via a non-proteolytic manner. Finally, we show that CathL-induced activation of the ERK1/2 pathway is involved in inducing these cellular effects in HOMECs.

CONCLUSION: These data suggest that CathL acts as an extracellular ligand and plays an important pro-angiogenic, and thus pro-metastatic, role during EOC metastasis to the omentum, by activating the omental microvasculature, and thus can potentially be targeted therapeutically in the future.