THE ACTIVITY OF COLLAGENASE-1 IS REQUIRED FOR KERATINOCYTE MIGRATION ON A TYPE-I COLLAGEN MATRIX

We have shown in a variety of human wounds that collagenase-1 (MMP-1), a matrix metalloproteinase that cleaves fibrillar type I collagen, is invariably expressed by basal keratinocytes migrating across the derm al matrix. Furthermore, we have demonstrated that MMP-1 expression is induced in primary keratinocytes by contact with native type I collage n and not by basement membrane proteins or by other components of the dermal or provisional (wound) matrix. Based on these observations, we hypothesized that the catalytic activity of MMP-1 is necessary for ker atinocyte migration on type I collagen. To test this idea, we assessed keratinocyte motility on type I collagen using colony dispersion and colloidal gold migration assays. In both assays, primary human keratin ocytes migrated efficiently on collagen. The specificity of MMP-1 in p romoting cell movement was demonstrated in four distinct experiments. One, keratinocyte migration was completely blocked by peptide hydroxym ates, which are potent inhibitors of the catalytic activity of MMPs. T wo, HaCaTs, a line of human keratinocytes that do not express MMP-1 in response to collagen, did not migrate on a type I collagen matrix but moved efficiently on denatured type I collagen (gelatin). EGF, which induces MMP-1 production by HaCaT cells, resulted in the ability of th ese cells to migrate across a type I collagen matrix. Three, keratinoc ytes did not migrate on mutant type I collagen lacking the collagenase cleavage site, even though this substrate induced MMP-1 expression. F our, cell migration on collagen was completely blocked by recombinant tissue inhibitor of metalloproteinase-1 (TIMP-1) and by affinity-purif ied anti-MMP-1 antiserum. In addition, the collagen-mediated induction of collagenase-1 and migration of primary keratinocytes on collagen w as blocked by antibodies against the alpha 2 integrin subunit but not by antibodies against the alpha 1 or alpha 3 subunits. We propose that interaction of the alpha 2 beta 1 integrin with dermal collagen media tes induction of collagenase-1 in keratinocytes at the onset of healin g and that the activity of collagenase-1 is needed to initiate cell mo vement. Furthermore, we propose that cleavage of dermal collagen provi des keratinocytes with a mechanism to maintain their directionality du ring reepithelialization.