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

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 10(6) to 8.0 x 10(6) m(-1)), but is reduced for t-PA lacking the finger and growth factor domains (K-a of 2.0 x 10(6) 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) mu m(-1).s(-1)). This is mainly the result of an enhanced affinity of t-PA for its substrate (K-m of 1.6 mu m vs. 89 mu m 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 10(6) m(-1)) and of miniplasminogen with fivefold lower affinity (K-a of 0.26 x 10(6) m(-1)) as compared to Glu-plasminogen (K-a of 1.2 x 10(6) 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.