Cell surface localization of heparanase on macrophages regulates degradation of extracellular matrix heparan sulfate.
Extravasation of peripheral blood monocytes through vascular basement membranes requires degradation of extracellular matrix components including heparan sulfate proteoglycans (HSPGs). Heparanase, the heparan sulfate-specific endo-beta-glucuronidase, has previously been shown to be a key enzyme in melanoma invasion, yet its involvement in monocyte extravasation has not been elucidated. We examined a potential regulatory mechanism of heparanase in HSPG degradation and transmigration through basement membranes in leukocyte trafficking using human promonocytic leukemia U937 and THP-1 cells. PMA-treated cells were shown to degrade 35S-sulfated HSPG in endothelial extracellular matrix into fragments of an approximate molecular mass of 5 kDa. This was not found with untreated cells. The gene expression levels of heparanase or the enzyme activity of the amount of cell lysates were no different between untreated and treated cells. Immunocytochemical staining with anti-heparanase mAb revealed pericellular distribution of heparanase in PMA-treated cells but not in untreated cells. Cell surface heparanase capped into a restricted area on PMA-treated cells when they were allowed to adhere. Addition of a chemoattractant fMLP induced polarization of the PMA-treated cells and heparanase redistribution at the leading edge of migration. Therefore a major regulatory process of heparanase activity in the cells seems to be surface expression and capping of the enzyme. Addition of the anti-heparanase Ab significantly inhibited enzymatic activity and transmigration of the PMA-treated cells, suggesting that the cell surface redistribution of heparanase is involved in monocyte extravasation through basement membranes.