Dipeptidyl Peptidase IV(CD 26) is a Receptor for Streptokinase and Fibronectin on Rheumatoid Arthritis Human Synovial Fibroblasts
Streptokinase (SK), a potent non-proteolytic plasminogen (Pg) activator, binds to synovial fibroblasts derived from patients with rheumatoid arthritis(RA) at very high affinity (Kd= 77 nM) either directly or via a complex with Pg. By contrast, SK does not bind specifically to normal synovial fibroblasts. Bound radiolabeled SK is displaced from the cell surface by both SK and fibronectin (FN), but not by Pg or plasmin-derived heavy chain. Our data suggest that RA synovial fibroblasts possess two distinct classes of receptors involved in Pg/Pm and FN/SK binding. The receptor for SK/FN in these cells is dipeptidyl peptidase IV (CD 26) [DPP IV]. Since FN shares the common sequence LTSRPA with SK, we used the "complementary peptide" approach to find the region in DPP IV which may serve as a binding region for this sequence. We found that the peptide QLRCSGPGLPL present in DPP IV may serve as an efficient ligand for the sequence LTSRPA common to both proteins. Since DPP IV is also a receptor for Pg/Pm, our experiments suggest that rheumatoid cells express receptors that may enhance mechanisms leading to the inflammatory response characteristic of RA.
Gonzalez-Gronow, M; Shearin, TV; Pizzo, SV
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