A collagen-binding glycoprotein on the surface of mouse fibroblasts is identified as dipeptidyl peptidase IV

Abstract

A dipeptidyl aminopeptidase (DPP) was detected in plasma membranes from normal (3T3) and transformed (3T12) mouse fibroblasts. This enzyme was active in cleaving the prolyl bond in the synthetic dipeptide nitroanilide Gly-Pro-NH-Np, which is a specific substrate for DPP IV (Km 0.63 mM and Vmax 6.1 nmol/min per mg at pH 6.0 and 37 degrees C). However, it did not degrade Pro-NH-Np or other dipeptide nitroanilides such as Gly-Arg-NH-Np or Val-Ala-NH-Np. The enzyme was totally inhibited by di-isopropyl phosphorofluoridate (Pri2-P-F) and by phenylmethanesulphonyl fluoride, indicating a serine catalytic site for the proteinase. DPP IV is a glycoprotein that specifically recognized immobilized gelatin and type I collagen. Upon molecular exclusion chromatography, the proteinase exhibited an apparent Mr of 100,000. SDS/polyacrylamide-gel electrophoresis under non-reducing and reducing conditions revealed that the [3H]Pri2-P-protein was exclusively represented by a polypeptide of Mr 55,000. This suggested that DPP IV consists of two non-covalently linked 55,000-Mr subunits. Fibroblast adhesion to native or denatured collagen was significantly inhibited by the two dipeptide inhibitors of DPP IV, Gly-Pro-Ala and Ala-Pro-Gly, but not by the peptides Gly-Pro and Gly-Gly-Gly, which are not inhibitors of the proteinase. Moreover, preliminary fractionation of DPP IV by molecular exclusion chromatography and affinity chromatography indicated that this material was active in disrupting cell adhesion to collagens. Taken together, the above data suggest that a fibroblast membrane-associated collagen-binding glycoprotein, DPP IV, may play a role in cell attachment to collagen.