Filamin binds to the cytoplasmic domain of the β1-integrin -: Identification of amino acids responsible for this interaction

Integrins play an important role in regulating cell adhesion, motility, and activation. In an effort to identify intracellular proteins expressed by activated T cells that interact with the cytoplasmic domain of beta(1)-integrin (CD29), we used the beta(1)-integrin cytoplasmic domain as bait in the yeast two-hybrid system. Here we report that the cytoplasmic domain of beta(1)-integrin specifically interacts with the cytoskeletal protein filamin. This interaction required all but the most carboxyl-terminal three residues of the cytoplasmic domain of beta(1), and the carboxyl-terminal 477 residues of filamin containing the terminal 4.5 similar to 96-residue tandem repeats of filamin. To verify this interaction in vivo, we showed that filamin specifically coprecipitated with beta(1) in mammalian cells. We also showed that recombinant filamin chimeric proteins were able to bind to the beta(1) cytoplasmic domain in vitro. We observed that a subset of single point mutations in the cytoplasmic domain of beta(1), which had been previously reported to impair its function, disrupt the interaction between beta(1) and filamin, Taken together, these findings suggest that the interaction between beta(1) and filamin, which in turn can bind actin, provides a mechanism for the interaction of this cell surface receptor with cytoskeletal proteins and that this interaction plays a role in normal receptor function.