BINDING OF THE CYTOPLASMIC DOMAIN OF INTERCELLULAR-ADHESION MOLECULE-2 (ICAM-2) TO ALPHA-ACTININ

Intercellular adhesion molecule-2 (ICAM-2) functions as a ligand for l ymphocyte function-associated antigen-1 (LFA-1) and is involved in leu kocyte adhesion, We studied intracellular associations of ICAM-2 using a peptide encompassing the cytoplasmic amino acids 231-254 as an affi nity matrix, Among the proteins from placental lysates that bound to t he peptide was alpha-actinin as demonstrated by immunoblotting. Purifi ed, I-125-labeled alpha-actinin also bound to the peptide. Confocal mi croscopic analysis of Eahy926 cells demonstrated a colocalization of I CAM-2 and alpha-actinin. Of overlapping octapeptides covering the enti re ICAM-2 cytoplasmic amino acids, ICAM-2(241-248) bound alpha-actinin most avidly and effectively competed with the longer cytoplasmic pept ide for binding. The site of interaction in alpha-actinin was studied using bacterially expressed alpha-actinin fusion proteins, Several con structs covering nonoverlapping regions of alpha-actinin bound to the ICAM-2 cytoplasmic peptide suggesting that multiple regions in alpha-a ctinin can mediate the interaction, These results, together with previ ously demonstrated interactions between alpha-actinin and the adhesion proteins ICARS-1, L-selectin, beta(1)- and beta(2)-integrins emphasiz e the role of alpha-actinin as a linker between cell surface adhesion molecules and the actin containing cytoskeleton.