Proteinases are isoform-specific regulators of the binding of transforming growth factor beta to alpha 2-macroglobulin

• Published in: Biochemical journal 1996-12, Vol.320 ( Pt 2) (Pt 2), p.551-555
• Main Authors: Webb, D J, Weaver, A M, Atkins-Brady, T L, Gonias, S L
• Format: Article
• Language: English
• Subjects: alpha-Macroglobulins - metabolism; alpha-Macroglobulins - pharmacology; Animals; Aorta; Cattle; Cell Division - drug effects; Cells, Cultured; DNA - biosynthesis; Endothelium, Vascular - cytology; Endothelium, Vascular - drug effects; Endothelium, Vascular - metabolism; Fibrinolysin - metabolism; Fibrinolysin - pharmacology; Heart; Humans; Kinetics; Muscle, Smooth, Vascular - metabolism; Platelet-Derived Growth Factor - metabolism; Protein Binding; Rats; Rats, Sprague-Dawley; Receptor, Platelet-Derived Growth Factor alpha; Receptors, Platelet-Derived Growth Factor - biosynthesis; Thrombin - metabolism; Thrombin - pharmacology; Transforming Growth Factor beta - metabolism; Transforming Growth Factor beta - pharmacology
• ISSN: 0264-6021; 1470-8728

alpha 2-Macroglobulin (alpha 2M) regulates growth and gene expression in many cell types by binding and neutralizing transforming growth factor beta (TGF-beta). In this study we characterized the effects of the serine proteinase, plasmin, on the interaction of alpha 2M with TGF-beta 1 and TGF-beta 2. Binding of both TGF-beta isoforms to purified alpha 2M-plasmin complex was primarily non-covalent and reversible. The binding affinity of alpha 2M for TGF-beta 1 was increased by plasmin; the Kd values were 320 and 84 nM for native alpha 2M and alpha 2M-plasmin respectively. In contrast the affinity of alpha 2M for TGF-beta 2 was decreased by plasmin; the Kd values were 14 and 80 nM for native alpha 2M and alpha 2M-plasmin respectively. Thrombin decreased the affinity of alpha 2M for TGF-beta 2 in a similar manner to plasmin. In assays of DNA synthesis in fetal bovine heart endothelial cells, native alpha 2M neutralized the activity of exogenously added TGF-beta 2, whereas alpha 2M-plasmin, at equivalent concentrations, had almost no effect. Native alpha 2M and methylamine-modified alpha 2M increased platelet-derived growth factor alpha-receptor expression in vascular smooth-muscle cells, an activity attributed to the neutralization of autocrine TGF-beta activity, whereas alpha 2M-plasmin was less effective at the same concentration. These studies demonstrate that the effects of proteinases on the cytokine-binding and cytokine-neutralizing activities of alpha 2M are cytokine-dependent. By reacting with alpha 2M, proteinases might regulate not only the availability of cytokines in the extracellular spaces but also the composition of the cytokine milieu.