NPXY motifs control the recruitment of the α5β1 integrin in focal adhesions independently of the association of talin with the β1 chain

With the exception of the divergent β4 and β8 chains, the integrin β subunit cytoplasmic domains are short and highly conserved sequences. Consensus motifs are found among the different cytoplasmic β chains. Experiments using chimeric receptors demonstrated that the 47 amino acids of the β1 subunit cytoplasmic domain contain sufficient information to target integrins to adhesion plaques. Three clusters of amino acids, named cyto-1, cyto-2 and cyto-3, seem to contribute to this localization. Cyto-2 and cyto-3 exhibit NPXY motifs. At present, the exact function of these motifs remains unknown but it is likely that these sequences are involved in proteinprotein interactions. Although NPXY motifs often act as internalization signals at the cytoplasmic tail of membrane receptors, our previous results showed that the two NPXY motifs are not responsible for the α5β1 integrin endocytosis. Herein, we address the question of the role of the two highly conserved NPXY motifs found in the β1 cytoplasmic domain, and which correspond to the conserved domains cyto-2 and cyto-3. We demonstrate that, within the integrin β1 cytoplasmic tail, the two NPXY motifs are required for the recruitment of the integrin in focal adhesions. In addition, our results indicate that these two motifs control but do not belong to the talin-binding sites. Finally, the analysis of the phenotypes of NPXY mutants reveals that the interaction of talin with the β1 cytosolic domain is not sufficient to target the integrins to focal adhesions.