Cellular uptake of mammalian heparanase precursor involves low density lipoprotein receptor-related proteins, mannose 6-phosphate receptors, and heparan sulfate proteoglycans

Mammalian heparanase, strongly implicated in the regulation of cell growth, migration, and differentiation, plays a crucial role in inflammation, angiogenesis, and metastasis. There is thus a clear need for understanding how heparanase activity is regulated. Cells can generate an active form of the enzyme from a larger inactive precursor protein by a process of secretion-recapture, internalization, and proteolytic processing in late endosomes/lysosomes. Cell surface heparan sulfate proteoglycans are the sole known components with a role in this trafficking of the heparanase precursor. Here, we provide evidence that heparan sulfate proteoglycans are not strictly required for this process. More importantly, by heparanase transfection, binding, and uptake experiments and by using a combination of specific inhibitors and receptor-defective cells, we have identified low density lipoprotein receptor-related proteins and mannose 6-phosphate receptors as key elements of the receptor system that mediates the capture of secreted heparanase precursor and its trafficking to the intracellular site of processing/activation.