In vivo perimenstrual activation of progelatinase B (proMMP-9) in the human endometrium and its dependence on stromelysin 1 (MMP-3) ex vivo

Most matrix metalloproteinases (MMPs) Lire secreted as inactive proenzymes. Their expression is well documented in several human tissues, but their ac tivators in vivo are still unknown, To address this question, the activatio n of progelatinase B (proMMP-9) in the human endometrium was selected as a model system. ProMMP-9 was detected by gelatin zymography in homogenates of fresh endometrial tissue sampled during all phases of the menstrual cycle, whereas its active form was observed only during the late secretory and me nstrual phases. Furthermore, proMMP-9 was expressed and activated in endome trial explants sampled outside the perimenstrual phase and cultured in the absence of both progesterone and oestradiol, mimicking the menstrual condit ion in vivo. Analysis of such tissue cultures by gelatin zymography and Wes tern blotting showed that activation of proMMP-9 depended on a secreted fac tor and was selectively inhibited by either a synthetic inhibitor of strome lysin I (MMP-3) or a monoclonal antibody that specifically blocks MMP-3, th us providing strong evidence for the activation of proMMP-9 in vivo by MMP- 3. The activation of proMMP-3 was itself inhibited by a broad-range MMP inh ibitor in most cultures, but seemed to involve multiple pathways, implying both serine proteinases and metalloproteinases, which could operate in para llel or sequentially.