Effects of beta subunit cytoplasmic domain deletions on the recruitment of the integrin alpha v beta 6 to focal contacts.

The integrin alpha v beta 6 is expressed primarily in epithelial cells and mediates attachment to the extracellular matrix protein fibronectin. We recently observed that alpha v beta 6 localizes to focal contacts when cells that express the receptor are plated on fibronectin. To determine which regions of the beta 6 cytoplasmic domain are required for recruitment to focal contacts, the wild type human beta 6 cytoplasmic domain are required for recruitment to focal contacts, the wild type human beta 6 subunit and mutants containing selective deletions within the beta 6 cytoplasmic domain were stably expressed in Chinese Hamster Ovary cells. The beta 6 cytoplasmic domain is composed of a 41 amino acid region that is highly conserved among integrin beta subunits, and a unique 11 amino acid carboxy terminal extension. The 11 amino acid extension was not required for localization to focal contacts; in fact, its removal appeared to increase receptor localization. However, removal of any of the 3 conserved regions previously identified as important for the localization of beta 1 integrins to focal contacts (Reszka, et al., 1992, J. Cell Biol. 117:1321-30) eliminated recruitment of beta 6 to focal contacts. These data suggest that, as with the integrin beta 1 subunit, multiple regions within the first 41 amino acids of the beta 6 cytoplasmic domain are necessary for recruitment of alpha v beta 6 to focal contacts. However, the unique 11 amino acid carboxy terminus of beta 6 is not required for this recruitment, and may actually play a negative regulatory role.