Endogenous plasmin converts Glu‐plasminogen to Lys‐plasminogen on the monocytoid cell surface

• Published in: Journal of thrombosis and haemostasis 2003-06, Vol.1 (6), p.1264-1270
• Main Authors: Zhang, L., Gong, Y., Grella, D. K., Castellino, F. J., Miles, L. A.
• Format: Article
• Language: English
• Subjects: Cell Line; Enzyme Activation; Fibrinolysin - metabolism; Humans; monocyte; Monocytes - metabolism; Mutation; Peptide Fragments - biosynthesis; plasmin; plasminogen; Plasminogen - analysis; Plasminogen - biosynthesis; Plasminogen - genetics; Plasminogen - metabolism; plasminogen activation; Plasminogen Activators - metabolism; Recombinant Proteins - genetics; Recombinant Proteins - metabolism; RNA, Messenger - analysis
• ISSN: 1538-7933; 1538-7836; 1538-7836
• DOI: 10.1046/j.1538-7836.2003.00155.x

Recently, we showed that localization of Glu‐plasminogen on cell surfaces enhances its conversion to Lys‐plasminogen by exogenous plasmin. This leads to stimulation of plasminogen activation because Lys‐plasminogen is the preferred substrate on cell surfaces. Here, we show that Glu‐plasminogen was converted to Lys‐plasminogen on monocytoid cells in the absence of exogenous plasmin. Culture of cells under serum‐free conditions did not affect this conversion, suggesting that the enzymatic activity was cell‐derived. Therefore, we tested whether endogenous monocytoid plasminogen could provide a source of plasmin to convert cell‐associated Glu‐plasminogen to Lys‐plasminogen because plasmin is the only enzyme known to effect this reaction. We used a recombinant human plasminogen mutant, [D(646)E]Pg, which can be cleaved by plasminogen activators, but cannot catalyze the generation of Lys‐plasminogen. Upon incubation with either THP‐1 or U937 monocytoid cells, 35 and 38%, respectively, of the cell‐bound ligand was converted to Lys‐[D(646)E]Pg. Trasylol, α2‐antiplasmin, and an anticatalytic antiplasminogen monoclonal antibody decreased Lys‐[D(646)E]Pg formation to < 5% on monocytoid cells, consistent with a plasmin‐dependent mechanism. Plasminogen was detected in these cells by Northern blotting and RT‐PCR. Our results suggest that plasmin converts cell‐bound Glu‐plasminogen to Lys‐plasminogen and that this enzyme is produced by activation of monocytoid plasminogen by endogenous monocytoid plasminogen activators to enhance plasminogen activation on the monocytoid cell surface.