Functional Characterization of Integrin a6b4 Adhesion Interactions Using Soluble Integrin Constructs Reveals the Involvement of Different Functional Domains in the b4 Subunit

Integrin a6b4-mediated adhesion interactions play key roles in keratinocyte and epithelial tumor cell biology. In order to evaluate how a6b4 adhesion interactions contribute to these important cellular processes, the authors generated soluble versions of the integrin by recombinant expression of the subunit ectodomains fused to a human immunoglobulin G (IgG) Fc constant domain. Coexpression of the appropriate subunits enabled dimerization, secretion and purification of stable Fc-containing a6b4 heterodimers. The soluble proteins exhibited the same metal ion and ligand dependency in their binding characteristics as intact a6b4. Using these reagents in combination with anti-b4 antibodies, the authors identified two distinct functional epitopes on the b4 subunit. They demonstrated the involvement of one epitope in adhesion interactions and the other in regulating adhesion-independent growth in a6b4-expressing tumor cell lines. The availability of these soluble integrin reagents and the data provided herein help to further delineate the structure-function relationships regulating a6b4 signaling biology.