Rabgap1 promotes recycling of active ß1 integrins to support effective cell migration.

Integrin function depends on the continuous internalization of integrins and their subsequent endosomal recycling to the plasma membrane to drive adhesion dynamics, cell migration and invasion. Here we assign a pivotal role for Rabgap1 (GAPCenA) in the recycling of endocytosed active ß1 integrins to the plasma membrane. The phosphotyrosine-binding (PTB) domain of Rabgap1 binds to the membrane-proximal NPxY motif in the cytoplasmic domain of ß1 integrin subunits on endosomes. Silencing Rabgap1 in mouse fibroblasts leads to the intracellular accumulation of active ß1 integrins, alters focal adhesion formation, and decreases cell migration and cancer cell invasion. Functionally, Rabgap1 facilitates active ß1 integrin recycling to the plasma membrane through attenuation of Rab11 activity. Taken together, our results identify Rabgap1 as an important factor for conformation-specific integrin trafficking and define the role of Rabgap1 in ß1-integrin-mediated cell migration in mouse fibroblasts and breast cancer cells.

LCP1 preferentially binds clasped αMß2 integrin and attenuates leukocyte adhesion under flow.

Integrins are α/ß heterodimers that interconvert between inactive and active states. In the active state the α/ß cytoplasmic domains recruit integrin-activating proteins and separate the transmembrane and cytoplasmic (TMcyto) domains (unclasped TMcyto). Conversely, in the inactive state the α/ß TMcyto domains bind integrin-inactivating proteins, resulting in the association of the TMcyto domains (clasped TMcyto). Here, we report the isolation of integrin cytoplasmic tail interactors using either lipid bicelle-incorporated integrin TMcyto domains (α5, αM, αIIb, ß1, ß2 and ß3 integrin TMcyto) or a clasped, lipid bicelle-incorporated αMß2 TMcyto. Among the proteins found to preferentially bind clasped rather than the isolated αM and ß2 subunits was L-plastin (LCP1, also known as plastin-2), which binds to and maintains the inactive state of αMß2 integrin in vivo and thereby regulates leukocyte adhesion to integrin ligands under flow. Our findings offer a global view on cytoplasmic proteins interacting with different integrins and provide evidence for the existence of conformation-specific integrin interactors.