ENDOPROTEOLYSIS OF GLUCAGON-LIKE PEPTIDE (GLP)-1(7-36) AMIDE BY ECTOPEPTIDASES IN RINM5F CELLS

This study concerns whether the pancreatic beta cell expresses cell-su rface ectopeptidases that are capable of proteolysis of peptide hormon es and neuropeptides that modify glucose-dependent insulin release. Th ese biochemical investigations of the RINm5F cell line found that thes e cells express ectopeptidases. We have characterized the limited endo proteolysis of GLP-1 (7-36) amide that occurs in the presence of RINm5 F plasma membranes. The products and the sensitivity to specific pepti dase inhibitors of the proteolysis is characteristic of neutral endope ptidase (NEP) 24.11. Vasoactive intestinal polypeptide (VIP), pituitar y adenylate cyclase-activating peptide (PACAP), amylin, glucagon, gluc ose-dependent insulinotropic polypeptide (GTP), and exendin-4 also und ergo proteolysis in the presence of RIN cell membranes. NEP 24.11-acti vity in RIN cell membranes was confirmed using a specific fluorogenic assay, by histochemistry, and by comparison with the recombinant enzym e with respect to the kinetics of proteolysis of GLP-1 (7-36) amide an d of a fluorogenic substrate. Specific fluorogenic assays revealed the presence of aminopeptidase N and the absence of aminopeptidase A and of dipeptidylpeptidase IV. (C) 1997 Elsevier Science Inc.