Shedding of membrane type matrix metalloproteinase 5 by a furin-type convertase - A potential mechanism for down-regulation

The shedding of membrane-associated proteins has been recognized as a regul atory mechanism to either up-regulate or down-regulate cellular functions b y releasing membrane-bound growth factors or removing ectodomains of adhesi on molecules and receptors. We have reported previously that the ectoenzyme of membrane type matrix metalloproteinase 5 (MT5-MMP) is shed into extrace llular milieu (Pei, D. (1999) J. BioL Chem. 274, 8925-8932). Here we presen t evidence that MT5-MMP is shed by a furin-type convertase activity in the trans-Golgi network. Among proteinase inhibitors screened, only decanoyl-Ar g-Val-Lys-Arg-chloromethylketone, a known inhibitor for furin-type converta ses, blocked the shedding of MT5-MMP in a dose-dependent manner. As expecte d, decanoyl-Arg-Val-Lys-Arg-chloromethylketone also prevented the activatio n of MT5-MMP, raising the possibility that the observed shedding could be a utolytic. However, an active site mutant devoid of any catalytic activity, is also shed efficiently, thus ruling out the autolytic pathway. The sheddi ng cleavage was subsequently mapped to the stem region immediately upstream of the transmembrane domain, where a cryptic furin recognition site, (RRKE RR)-R-545, was recognized. Indeed, MT5-MMP and furin are co-localized in th e trans-Golgi network and the shed species could be detected inside the cel ls. Furthermore, deletion mutations removing this cryptic site prevented MT 5-MMP from shedding. The resulting mutants express a gain-of-function pheno type by mediating more robust activation of proMMP-2 than the wild type mol ecule. Thus, shedding provides a potential mechanism to regulate proteolyti c activity of membrane-bound MMPs.