The Uptake of Heparanase into Mast Cells Is Regulated by Its Enzymatic Activity to Degrade Heparan Sulfate.

Mast cells take up extracellular latent heparanase and store it in secretory granules. The present study examined whether the enzymatic activity of heparanase regulates its uptake efficiency. Recombinant mouse heparanase mimicking both the latent and mature forms (L-Hpse and M-Hpse, respectively) was internalized into mastocytoma MST cells, peritoneal cell-derived mast cells, and bone marrow-derived mast cells. The internalized amount of L-Hpse was significantly higher than that of M-Hpse. In MST cells, L-Hpse was continuously internalized for up to 8 h, while the uptake of M-Hpse was saturated after 2 h of incubation. L-Hpse and M-Hpse are similarly bound to the MST cell surface. The expression level of cell surface heparan sulfate was reduced in MST cells incubated with M-Hpse. The internalized amount of M-Hpse into mast cells was significantly increased in the presence of heparastatin (SF4), a small molecule heparanase inhibitor that does not affect the binding of heparanase to immobilized heparin. Enzymatically quiescent M-Hpse was prepared with a point mutation at Glu335. The internalized amount of mutated M-Hpse was significantly higher than that of wild-type M-Hpse but similar to that of wild-type and mutated L-Hpse. These results suggest that the enzymatic activity of heparanase negatively regulates the mast cell-mediated uptake of heparanase, possibly via the downregulation of cell surface heparan sulfate expression.

A new algorithm to convert a normal antibody into the corresponding catalytic antibody.

Over thousands of monoclonal antibodies (mAbs) have been produced so far, and it would be valuable if these mAbs could be directly converted into catalytic antibodies. We have designed a system to realize the above concept by deleting Pro95, a highly conserved residue in CDR-3 of the antibody light chain. The deletion of Pro95 is a key contributor to catalytic function of the light chain. The S35 and S38 light chains have identical amino acid sequences except for Pro95. The former, with Pro95 did not show any catalytic activity, whereas the latter, without Pro95, exhibited peptidase activity. To verify the generality of this finding, we tested another light chain, T99wt, which had Pro95 and showed little catalytic activity. In contrast, a Pro95-deleted mutant enzymatically degraded the peptide substrate and amyloid-beta molecule. These two cases demonstrate the potential for a new method of creating catalytic antibodies from the corresponding mAbs.