Type XVII collagen (BP180) can function as a cell-matrix adhesion molecule via binding to laminin 332

Collagen XVII (COL17) is a transmembrane glycoprotein that is expressed on the basal surface of basal epidermal keratinocytes. Previous observations have led to the hypothesis that an interaction between COL17 and laminin 332, an extracellular matrix protein, contributes to the attachment of the basal keratinocyte to the basement membrane. In order to isolate and manipulate COL17 interactions with ECM components, we induced COL17 expression in two cells lines, SK-MEL1 and K562, that exhibit little or no capacity to attach to our test substrates, including laminin 332, types I and IV collagen, and fibronectin. Cells expressing high levels of COL17 preferentially adhered to a laminin 332 matrix, and, to a lesser extent, type IV collagen, while showing little or no binding to type I collagen or fibronectin. A quantitative analysis of cell adhesive forces revealed that, compared with COL17-negative cells, COL17-positive cells required over 7-fold greater force to achieve 50% detachment from a laminin 332 substrate. When a cell preparation (either K562 or SK-MEL1) with heterogeneous COL17 expression levels was allowed to attach to a laminin 332 matrix, the COL17-positive and COL17-negative cells differentially sorted to the bound and unbound cell fractions, respectively. COL17-dependent attachment to laminin 332 could be reduced or abolished by siRNA-mediated knock-down of COL17 expression or by adding to the assay wells specific antibodies against COL17 or laminin 332. These findings provide strong support for the hypothesis that cell surface COL17 can interact with laminin 332 and, together, participate in the adherence of a cell to the extracellular matrix.