Summary. Matrix metalloproteinases (MMPs) and tissue inhibitors of metalloproteinases (TIMPs) regulate the turnover of the extracellular matrix and may modulate the biology of haematopoietic cells. We investigated whether MMPs and TIMPs are produced in long-term marrow cultures (LTMCs) established from normal donors and acute myelogenous leukaemia (AML) patients, and by fibroblast-(F), granulocyte macrophage-(GM) and megakaryocyte-(Meg) colony-forming unit (CFU) and erythroid burst-forming unit (BFU-E)-derived precursor cells. ProMMP-9 levels were highest (. 400 ng/ml) at week 1 of normal LTMC, whereas proMMP-2, TIMP-1, TIMP-2 and TIMP-3 levels peaked (up to 1000 ng/ml) after the establishment of the adherent layer. In LTMC from AML patients, these patterns of secretion were reversed. Moreover, we found that after a 24 h incubation in serum-free media, normal CFU-GM-, BFU-E-and CFU-Meg-derived cells secreted proMMP-9 and CFU-F-derived cells proMMP-2, in contrast to cells from LTMC adherent layer which secreted both active and latent forms of MMP-2 and MMP-9 under serum-free conditions. However, when these adherent cells were incubated in 12´5% fetal calf or horse serum or complete LTMC growth media, active forms of MMP-2 and MMP-9 were no longer detectable, and TIMP levels increased. Hence, we concluded that (i) MMPs/TIMPs are secreted by normal human bone marrow haematopoietic and stromal cells and may play an important role in intercellular cross-talk in haematopoiesis; and (ii) only latent forms of MMPs are present under LTMC conditions, indicating that the specific media used for weekly re-feeding of LTMC can block activation of MMP-2 and MMP-9, maintaining the integrity of the stromal layer and supporting haematopoiesis in vitro.Keywords: matrix metalloproteinases, tissue inhibitors of metalloproteinases, long-term marrow cultures, haematopoietic progenitor cells, acute myelogenous leukaemia.Matrix metalloproteinases (MMPs) and tissue inhibitors of metalloproteinases (TIMPs) not only regulate the turnover of the extracellular matrix (ECM) but also cell survival, proliferation, differentiation, adhesion and migration (Werb, 1997). On the basis of their domain structure and substrate specificity, MMPs are classified into four major subgroups: collagenases, gelatinases, stromelysins and membrane-type MMPs (MT-MMPs) (Forget et al, 1999;Nagase & Woessner, 1999;Janowska-Wieczorek et al, 2000a;Lenz et al, 2000).The gelatinases (MMP-2/72-kDa type IV collagenase and MMP-9/92-kDa type IV collagenase) degrade denatured collagens (gelatins), native collagen types II, IV, V, VII, X and XI, fibronectin, vitronectin, elastin and aggrecan (Forget et al, 1999). The primary mechanism for MMP regulation occurs at the transcriptional level and involves a variety of extracellular factors including cytokines, growth factors and cell contact with the ECM (Nagase & Woessner, 1999;Westermarck & Kahari, 1999). Another level of regulation of MMP activity is through proenzyme activation, as most MMPs are secreted as latent enzymes. MT...
