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
omental microvascular 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. Enzyme activity was assayed
at various pHs using the CathL-specific fluorogenic substrate FY-CHO. Activation of cell
signalling pathways was tested using a commercially available phosphokinase array and intact cellbased
Results: We showed 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 suggest that
these proangiogenic effects of CathL are mediated via a non-proteolytic mechanism. 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.