Assembly of the beta 4-Integrin Interactome Based on Proximal Biotinylation in the Presence and Absence of Heterodimerization

Abstract

Integrin-mediated laminin adhesions mediate epithelial cell anchorage to basement membranes and are critical regulators of epithelial cell polarity. Integrins assemble large multiprotein complexes that link to the cytoskeleton and convey signals into the cells. Comprehensive proteomic analyses of actin network-linked focal adhesions (FA) have been performed, but the molecular composition of intermediate filament-linked hemidesmosomes (HD) remains incompletely characterized. Here we have used proximity-dependent biotin identification (BioID) technology to label and characterize the interactome of epithelia-specific beta 4-integrin that, as alpha 6 beta 4-heterodimer, forms the core of HDs. The analysis identified similar to 150 proteins that were specifically labeled by BirA-tagged integrin-beta 4. In addition to known HDs proteins, the interactome revealed proteins that may indirectly link integrin-beta 4 to actin-connected protein complexes, such as FAs and dystrophin/dystroglycan complexes. The specificity of the screening approach was validated by confirming the HD localization of two candidate beta 4-interacting proteins, utrophin (UTRN) and ELKS/Rab6-interacting/CAST family member 1 (ERC1). Interestingly, although establishment of functional HDs depends on the formation of alpha 6 beta 4-heterodimers, the assembly of beta 4-interactome was not strictly dependent on alpha 6-integrin expression. Our survey to the HD interactome sets a precedent for future studies and provides novel insight into the mechanisms of HD assembly and function of the beta 4-integrin.