Activation of matrix metalloproteinase-2 from hepatic stellate cells requires interactions with hepatocytes

Activation of matrix metalloproteinase (MMP)-2, the 72-kd collagenase IV/gelatinase A, is involved in extracellular matrix remodeling It has been suggested that a membrane-type MMP (MT-MMP-1) and the tissue inhibitor of metalloproteinase (TIMP)-2 are involved in MMP-2 processing, but the exact mechanism(s) of its activation remains unclear. We have investigated the role of cell-cell cooperation ill the activation of pro-MMP-2 in the liver, using pure cultures and cocultures of hepatocytes and hepatic stellate cells (HSCs). Northern blot analysis and in situ hybridization showed that, in both pure and cocultures, HSCs, but not hepatocytes, expressed MMP-2, TIMP-2, and MT-MMP-1 mRNA. Zymography analyses revealed the latent form of MMP-2 in medium from 2-day-old pure HSC cultures with higher amounts in medium from hepatocyte/HSC co-cultures. When hepatocytes were added to 10-day-old NSC cultures, the activated form of MMP-2 was detected, concomitantly with the deposition of all abundant extracellular matrix. Incubation of plasma membrane-enriched fractions from hepatocytes with conditioned medium from pure NSC cultures generated the activated species of MMP-2 (62 and 59 kd). Activation of pro-MMP-2 by hepatocyte membranes was inhibited by EDTA, heat, and trypsin but not by serine proteinase inhibitors. These data show that the co-expression of TIMP-2, MMP-2, and MT-MMP-1 by HSCs does not lead to secretion of the activated form of MMP-2. Hepatocytes, which do not express MMP-2, TIMP-2, or MT-MMP-1, induce MMP-2 activation through a plasma membrane-dependent mechanism(s), thus suggesting that cell-cell interactions are involved in this process in vivo.