Proteinases are isoform-specific regulators of the binding of transforming growth factor beta to alpha 2-macroglobulin.
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.
Webb
D J
DJ
Department of Pathology, University of Virginia Health Sciences Center, Charlottesville 22908, USA.
Weaver
A M
AM
Atkins-Brady
T L
TL
Gonias
S L
SL
D000818:Animals; D001011:Aorta; D002417:Cattle; D002455:Cell Division / Q000187:drug effects; D002478:Cells, Cultured; D004247:DNA / Q000096:biosynthesis; D004730:Endothelium, Vascular / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism*; D005341:Fibrinolysin / Q000378:metabolism* / Q000494:pharmacology; D006321:Heart; D006801:Humans; D007700:Kinetics; D009131:Muscle, Smooth, Vascular / Q000378:metabolism*; D010982:Platelet-Derived Growth Factor / Q000378:metabolism; D011485:Protein Binding; D051381:Rats; D017207:Rats, Sprague-Dawley; D020796:Receptor, Platelet-Derived Growth Factor alpha; D017479:Receptors, Platelet-Derived Growth Factor / Q000096:biosynthesis*; D013917:Thrombin / Q000378:metabolism* / Q000494:pharmacology; D016212:Transforming Growth Factor beta / Q000378:metabolism* / Q000494:pharmacology; D000511:alpha-Macroglobulins / Q000378:metabolism* / Q000494:pharmacology
D010982:Platelet-Derived Growth Factor; D016212:Transforming Growth Factor beta; D000511:alpha-Macroglobulins; C075278:platelet-derived growth factor A; D004247:DNA; D020796:Receptor, Platelet-Derived Growth Factor alpha; D017479:Receptors, Platelet-Derived Growth Factor; D013917:Thrombin; D005341:Fibrinolysin