Prostromelysin-1 (proMMP-3) stimulates plasminogen activation by tissue-type plasminogen activator

Abstract

Matrix metalloproteinase-3 (MMP-3 or stromelysin-1) specifically binds to tissue-type plasminogen activator (t-PA), without however, hydrolyzing the protein. Binding affinity to proMMP-3 is similar to single chain t-PA, two chain t-PA and active site mutagenized t-PA (K(a) of 6.3 x 106 to 8.0 x 106 M-1), but is reduced for t-PA lacking the finger and growth factor domains (K(a) of 2.0 x 106 M-1). Activation of native Glu-plasminogen by t-PA in the presence of proMMP-3 obeys Michaelis-Menten kinetics; at saturating concentrations of proMMP-3, the catalytic efficiency of two chain t-PA is enhanced 20-fold (k(cat)/K(m) of 7.9 x 10-3 vs. 4.1 x 10-4 μM-1.s-1). This is mainly the result of an enhanced affinity of t-PA for its substrate (K(m) of 1.6 μM vs. 89 μM in the absence of proMMP-3), whereas the k(cat) is less affected (k(cat) of 1.3 x 10-2 vs. 3.6 x 10-2 s-1). Activation of Lys-plasminogen by two chain t-PA is stimulated about 13-fold at a saturating concentration of proMMP-3, whereas that of miniplasminogen is virtually unaffected (1.4-fold). Plasminogen activation by single chain t-PA is stimulated about ninefold by proMMP-3, whereas that by the mutant lacking finger and growth factor domains is stimulated only threefold. Biospecific interaction analysis revealed binding of Lys-plasminogen to proMMP-3 with 18-fold higher affinity (K(a) of 22 x 106 M-1) and of miniplasminogen with fivefold lower affinity (K(a) of 0.26 x 106 M-1) as compared to Glu-plasminogen (K(a) of 1.2 x 106 M-1). Plasminogen and t-PA appear to bind to different sites on proMMP-3. These data are compatible with a model in which both plasminogen and t-PA bind to proMMP-3, resulting in a cyclic ternary complex in which t-PA has an enhanced affinity for plasminogen, which may be in a Lys-plasminogen-like conformation. Maximal binding and stimulation require the N-terminal finger and growth factor domains of t-PA and the N-terminal kringle domains of plasminogen.