The cell adhesion domain of type XVII collagen promotes integrin-mediated cell spreading by a novel mechanism

Type XVII collagen (BP180) is a keratinocyte transmembrane protein that exi sts as the full-length protein in hemidesmosomes and as a 120-kDa shed ecto domain in the extracellular matrix. The largest collagenous domain of type XVII collagen, COL15, has been described previously as a cell adhesion doma in (Tasanen, K., Eble, J. A., Aumailley, M., Schumann, H., Baetge, J, Tu, H ., Bruckner, P., and Bruckner-Tuderman, L. (2000) J: Biol Chem. 275, 3093-3 099). In the present work, the integrin binding of triple helical, human re combinant COL15 was tested. Solid phase binding assays using recombinant in tegrin alpha I-1, alpha I-2, and alpha I-10 domains and cell spreading assa ys with alpha (1)beta (1)- and alpha (2)beta (1)-expressing Chinese hamster ovary cells showed that, unlike other collagens, COL15 was not recognized by the collagen receptors. Denaturation of the COL15 domain increased the s preading of human HaCaT keratinocytes, which could migrate on the denatured COL15 domain as effectively as on fibronectin. Spreading of HaCaT cells on the COL15 domain was mediated by alpha (5)beta (1) and alpha (v)beta (1) i ntegrins, and it could be blocked by RGD peptides. The collagen alpha -chai ns in the COL15 domain do not contain RGD motifs but, instead, contain 12 c losely related KGD motifs, four in each of the three alpha -chains. Twenty- two overlapping, synthetic peptides corresponding to the entire COL15 domai n were tested; three peptides, all containing the KGD motif, inhibited the spreading of HaCaT cells on denatured COL15 domain. Furthermore, this effec t was lost by mutation from D to E (KGE instead of KGD). We suggest that th e COL15 domain of type XVII collagen represents a specific collagenous stru cture, unable to interact with the cellular receptors for other collagens. After being shed from the cell surface, it may support keratinocyte spreadi ng and migration.