Novel view on the mechanism of activation of matrix metalloproteinase (mmp): binding of mmp-9 (gelatinase b) to extracellular matrix molecules in vivo and in vitro leads to activation od the enzyme without removal of its n-terminal propeptide.

GB Bannikov, PhD, T.V.Karelina, M.D., Ph.D., I.E.Collier, Ph.D., B.L.Marmer, G.I.Goldberg, Ph.D.

Washington University Medical School, St . Louis, MO USA

AIM: Expression of MMP-9, a member of the MMP's family, has been implicated to variety of tissue remodeling processes, including tumor cell invasion and metastasis. Removal of the N-terminal propeptide is required for activation of MMP's in vitro. It is commonly accepted that expression of MMP-9 in the placenta plays an important role in the invasion of the trophoblasts into the decidua. Judging by molecular weight, however, this enzyme extracted from placenta was found in its proform. Present investigation addresses the question: does a non-proteolytic mechanism of MMP-9 activation exist? METHODS: We used in situ zymography in combination with function blocking antibody, gel zymography, western blot and immunohistochemistry to asses localization, enzymatic activity and molecular weight of MMP-9 in term human placenta. MMP-9 activity upon its binding to ECM-coated surface was conducted by measurement of cleavage of the peptide substrate and 3H-gelatin. RESULTS: Gelatinolytic activity in tissue sections of term placenta is co-localized with MMP-9, however, the enzyme had its propeptide unprocessed. Upon binding of the MMP-9 proenzyme to gelatin and to a type IV collagen coated surface, it required enzymatic activity, while its propeptide remained intact. CONCLUSIONS: Our results suggest the existence of alternative non-proteolytic mechanism of activation of MMPs. Binding to a ligand or to a substrate may lead to a disengagement of the propeptide from the active center of the enzyme and may represent a physiological pathway of its activation in vivo.

KEY WORDS: non-proteolytic activation, invasion.

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Paper presented at the International Symposium on Predictive Oncology and Intervention Strategies; Paris, France; February 9 - 12, 2002; in the section on Metastasis.