MMP-9 from TNF alpha-stimulated keratinocytes binds to cell membranes and type I collagen: a cause for extended matrix degradation in inflammation?

Activated keratinocytes synthesize increased amounts of matrix metalloproteinases during inflammation. Incubation of mucosal keratinocytes with TNFalpha (24 h) increased their expression of MMP-9 mRNA, which was followed by the corresponding increase in the expression of MMP-9 protein. This stimulation was dose dependent and continued for several days after the initial exposure to TNFalpha. In contrast, the expression of MMP-2 was not influenced by TNFalpha. IFNgamma caused a significant dose-dependent inhibition in the TNFalpha-stimulated expression of MMP-9. TNFalpha did not markedly influence keratinocyte growth, while INFgamma potently inhibited cell growth. Cytokine-stimulated keratinocytes secreted most MMP-2 and MMP-9 extracellularly into the culture medium, but MMP-9 was also found in the membrane extract of keratinocytes. Furthermore, wild-type and recombinant MMP-9 were bound to noncollageneous and nonintegrin components of the mucosal keratinocyte cell surface. MMP-9 was not, however, found in the extracellular matrix deposited by the keratinocytes in culture. Type I and IV collagens and gelatin but no other purified extracellular matrix nor basement membrane proteins (types I and IV collagen, laminin-1 and -5, fibronectin) were able to bind MMP-9 from the conditioned medium. Binding of MMP-9 from keratinocyte conditioned medium was demonstrated along the collagen fibers using immunoelectron microscopy. These phenomena may participate in extended matrix degradation in chronic inflammation. Copyright 1998 Academic Press.