MMP-9 from TNFα-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 TNF alpha (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 TNF alpha. In contrast, the expression of MMP-2 was not influenced by TNF alpha. IFN gamma caused a significant dose-dependent inhibition in the TNF alpha-stimulated expression of MMP-9. TNF alpha did not markedly influence keratinocyte growth, while INF gamma 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. (C) 1998 Academic Press.