An interaction between alpha-actinin and the beta 1 integrin subunit in vitro.

Abstract

A number of cytoskeletal-associated proteins that are concentrated in focal contacts, namely .alpha.-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 .beta.1 integrin and affinity chormatography to identify additional integrin-binding proteins. Here we report our finding of an interaction between the cytoplasmic domain of .beta.1 integrin and the actin-binding protein .alpha.-actinin. .beta.1-integrin cytoplasmic domain peptide columns bound several proteins from Triton extracts of chicken embryo fibroblasts. One protein at .apprx. 100 kD was identified by immunoblot analysis as .alpha.-actinin. Solid phase binding assays indicated that .alpha.-actinin bound specifically and directly of the .beta.1 peptide with relatively high affinity. Using purified heterodimeric chicken smooth muscle integrin (a .beta.1 integrin) or the platelet integrin glycoprotein IIb/IIIa complex (a .beta.3 integrin), binding of .alpha.-actinin was also observed in similar solid phase assays, albeit with a lower affinity than was seen using the .beta.1 peptide. .alpha.-Actinin also bound specifically to phospholipid vesicles into which glycoprotein IIb/IIIa had been incorporated. These results lead us to suggest that this integrin-.alpha.-actinin linkage may contribute to the attachment of actin filaments to the membrane in certain locations.