AN INTERACTION BETWEEN ALPHA-ACTININ AND THE BETA-1 INTEGRIN SUBUNIT INVITRO

A number of cytoskeletal-associated proteins that are concentrated in focal contacts, namely α-actinin, vinculin, talin, and integrin, have been shown to interact in vitro such that they suggest a potential link between actin filaments and the membrane. Because some of these interactions are of low affinity, we suspect that additional linkages also exist. Therefore, we have used a synthetic peptide corresponding to the cytoplasmic domain of β1 integrin and affinity chromatography to identify additional integrinbinding proteins. Here we report our finding of an interaction between the cytoplasmic domain of β1 integrin and the actin-binding protein α-actinin. β1-integrin cytoplasmic domain peptide columns bound several proteins from Triton extracts of chicken embryo fibroblasts. One protein at ∼100 kD was identified by immunoblot analysis as α-actinin. Solid phase binding assays indicated that α-actinin bound specifically and directly to the β1 peptide with relatively high affinity. Using purified heterodimeric chicken smooth muscle integrin (a β1 integrin) or the platelet integrin glycoprotein IIb/IIIa complex (a β3 integrin), binding of α-actinin was also observed in similar solid phase assays, albeit with a lower affinity than was seen using the β1 peptide. β-Actinin also bound specifically to phospholipid vesicles into which glycoprotein IIb/IIIa had been incorporated. These results lead us to suggest that this integrin-α-actinin linkage may contribute to the attachment of actin filaments to the membrane in certain locations.