Dynamic interactions of epidermal collagen XVII with the extracellular matrix: laminin 332 as a major binding partner.

Transmembrane collagen XVII, a major component of the hemidesmosomes, is crucial for stable adhesion of the epidermis and dermis in the skin, and its dysfunction results in blistering diseases. The ectodomain of collagen XVII (Ecto-ColXVII) is constitutively shed from the cell surface, but its binding partner(s) in the extracellular matrix (ECM) and the physiologic roles of the ligand interactions remain elusive. Herein, we used a new cleavage site-specific antibody to address the dynamics of collagen XVII shedding and the interactions of Ecto-ColXVII with the ECM. Ecto-ColXVII was present in the migration tracks of primary human keratinocytes and co-localized with laminin 332. The presence of this laminin, but also of collagen IV and Matrigel, in the ECM enhanced shedding and incorporation of Ecto-ColXVII into the matrix. Laminin 332 is a major, but not exclusive, interaction partner in vivo because Ecto-ColXVII deposited in the ECM of laminin 332-deficient keratinocytes was drastically reduced, but Ecto-ColXVII was present in laminin 332-negative human skin. Expression of collagen XVII deletion mutants in HEK 293 cells identified the C-terminal ectodomain stretch Ser(978)-Pro(1497) as necessary for ECM binding. Taken together, migrating keratinocytes shed the Ecto-ColXVII, and this dynamically binds via its C-terminal domain to distinct partners in the ECM.