Plasmin(ogen) carbohydrate chains mediate binding to dipeptidyl peptidase IV (CD 26) in rheumatoid arthritis human synovial fibroblasts

Objective: To assess the reactivity between dipeptidyl peptidase IV (DPP IV ) and the alpha 2,3-linked sialic acid of the plasminogen (Pg)Thr(345) O-li nked carbohydrate chain as the mechanism enabling plasmin (Pm) to induce in tracellular Ca2+ via DPP IV on rheumatoid synovial fibroblasts, and identif y the DPP IV region responsible for this interaction. Methods: Cytosolic Ca 2+ mobilization in rheumatoid synovial fibroblasts was assayed by Digital I maging Microscopy (DIM). DPP IV was purified by affinity chromatography on an immobilized polysaccharide structurally analogous to the last two residu es of the Pg 2 carbohydrate chain. Binding of Pg to DPP IV and identificati on of the: DPP IV reactive site were determined by an enzyme-linked immunos orbent assay (ELISA) and inhibition of Pm-induced intracellular Ca2+ mobili zation in these cells by peptides comprising three regions of DPP IV primar y structure. Results: Cytosolic Ca2+ mobilization induced by Pm on rheumato id synovial fibroblasts is inhibited by L-lactose, a sugar that interferes with sialic acid binding to lectins. Asialo Pg which binds and can be conve rted into Pm on the surface of these cells is not able to induce intracellu lar Ca2+ mobilization. A peptide comprising the DPP IV primary sequence L(3 13)QWLRRI inhibits both Pg binding to DPP IV and Pm-induced intracellular C a2+ mobilization on these cells. Conclusion: The intracellular Ca2+ mobiliz ation resulting from the reaction between Pg/Pm and DPP IV is mediated by a lectin-like region in DPP IV. This region is structurally analogous to the sequence (QxW)(3), previously identified as a carbohydrate-binding region in several lectin families.