Regulatory mechanism of matrix metalloproteinase activity.

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Matrix metalloproteinases (MMPs) are involved in various physiological and pathological conditions including arthritis and tumor metastasis. The activity of MMPs are regulated by three mechanisms : regulation of synthesis, activation of their latent proenzymes, and regulation of active enzymes by natural inhibitors. Proenzymes of most MMPs are known to be activated by some serine proteinases, whereas only the activating enzymes of pro-gelatinase A remain unknown. The present study aimed to clarify the natural activators of pro-gelatinase A.Pro-gelatinase A was purified in TIMP-2 bound and -free forms from conditioned medium of T98G human glioblastoma cell line. The TIMP-2-free pro-gelatinase A of 64 kDa (apparent molecular size under nonreducing conditions) was rapidly activated to the 57-kDa and then the 41-kDa mature forms by treatment with p-aminophenylmercuric acetate (APMA). When the TIMP-2-free form was incubated with stromelysin, a member of MMP family, its gelatinolytic activity increased to about 70% of the activity obtained by APMA activation, forming the 41-kDa form. The treatment of the TIMP-2-bound pro-gelatinase A with stromelysin also increased its gelatinolytic activity but hardly produced any mature forms. Analysis of interaction of the TIMP-2-bound proenzyme and stromelysin demonstrated that stromelysin bound to the TIMP-2 molecule in the TIMP-2/pro-gelatinase A complex, forming a tertiary protein complex with a significant gelatinolytic activity. These results suggest that stromelysin may function as a natural activator of pro-gelatinase A under some conditions.