Characterization of the plasminogen receptors of normal and rheumatoid arthritis human synovial fibroblasts.

Plasminogen (Pg) activation on the surface of rheumatoid arthritis (RA) synovial fibroblasts by the urinary-type Pg activator induced a significant increase in cytosolic free Ca2+ concentration. This response was not observed in normal synovial fibroblasts, suggesting different Pg binding and activation mechanisms in these cell types. Pg receptors from both cell types were isolated by affinity chromatography using Pg covalently bound to Sepharose 4B. RA synovial fibroblasts express a Pg receptor complex composed of a glycoprotein IIb/IIIa-related protein in association with a 130-kDa protein that is antigenically related to the alpha 2-macroglobulin receptor-associated protein and dipeptidyl peptidase IV. This receptor complex appears to bind to both Pg and fibronectin. The Pg "receptor" in normal synovial fibroblasts is composed of a 97-kDa protein also antigenically related to the alpha 2-macroglobulin receptor-associated protein. Both cell types express the urinary-type Pg activator receptor on their surfaces. Our results suggest that RA synovial fibroblasts express novel proteins involved in Pg binding, activation, and signal transduction, which are absent in normal synovial fibroblasts.