Functional Characterization of Integrin α6β4 Adhesion Interactions Using Soluble Integrin Constructs Reveals the Involvement of Different Functional Domains in the β4 Subunit

Integrin 64-mediated adhesion interactions play key roles in keratinocyte and epithelial tumor cell biology. In order to evaluate how 64 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 64 heterodimers. The soluble proteins exhibited the same metal ion and ligand dependency in their binding characteristics as intact 64. Using these reagents in combination with anti-4 antibodies, the authors identified two distinct functional epitopes on the 4 subunit. They demonstrated the involvement of one epitope in adhesion interactions and the other in regulating adhesion-independent growth in 64-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 64 signaling biology.