Extracellular matrix (ECM) fragments or cryptic sites unmasked by proteinases have been postulated to affect tissue remodeling and cancer progression. Therefore, the elucidation of their identities and functions is of great interest. Here, we show that matrix metalloproteinases (MMPs) generate a domain (DIII) from the ECM macromolecule laminin-5. Binding of a recombinant DIII fragment to epidermal growth factor receptor stimulates downstream signaling (mitogen-activated protein kinase), MMP-2 gene expression, and cell migration. Appearance of this cryptic ECM ligand in remodeling mammary gland coincides with MMP-mediated involution in wild-type mice, but not in tissue inhibitor of metalloproteinase 3 ( TIMP-3 )–deficient mice, supporting physiological regulation of DIII liberation. These findings indicate that ECM cues may operate via direct stimulation of receptor tyrosine kinases in tissue remodeling, and possibly cancer invasion.

Keratinocytes and other epithelial cells express two receptors for the basement membrane (BM) extracellular matrix component laminin-5 (Ln-5), integrins α3β1 and α6β4. While α3β1 mediates adhesion, spreading, and migration (Kreidberg, J.A. 2000. Curr. Opin. Cell Biol. 12:548–553), α6β4 is involved in BM anchorage via hemidesmosomes (Borradori, L., and A. Sonnenberg. 1999. J. Invest. Dermatol . 112:411–418). We investigated a possible regulatory interplay between α3β1 and α6β4 in cell motility using HaCaT keratinocytes as a model. We found that α6β4 antibodies inhibit α3β1-mediated migration on Ln-5, but only when migration is haptotactic (i.e., spontaneous or stimulated by α3β1 activation), and not when chemotactic (i.e., triggered by epidermal growth factor receptor). Inhibition of migration by α6β4 depends upon phosphoinositide 3-kinase (PI3-K) since it is abolished by PI3-K blockers and by dominant-negative PI3-K, and constitutively active PI3-K prevents haptotaxis. In HaCaT cells incubated with anti–α6β4 antibodies, activation of PI3-K is mediated by α6β4-associated erbB-2, as indicated by erbB-2 autophosphorylation and erbB-2/p85 PI3-K coprecipitation. Furthermore, dominant-negative erbB-2 abolishes inhibition of haptotaxis by anti–α6β4 antibodies. These results support a model whereby (a) haptotactic cell migration on Ln-5 is regulated by concerted action of α3β1 and α6β4 integrins, (b) α6β4-associated erbB-2 and PI3-K negatively affect haptotaxis, and (c) chemotaxis on Ln-5 is not affected by α6β4 antibodies and may require PI3-K activity. This model could be of general relevance to motility of epithelial cells in contact with BM.