RKIKK motif in the intracellular domain is critical for spatial and dynamic organization of ICAM-1: functional implication for the leukocyte adhesion and transmigration.

No direct evidence has been reported whether the spatial organization of ICAM-1 on the cell surface is linked to its physiological function in terms of leukocyte adhesion and transendothelial migration (TEM). Here we observed that ICAM-1 by itself directly regulates the de novo elongation of microvilli and is thereby clustered on the microvilli. However, truncation of the intracellular domain resulted in uniform cell surface distribution of ICAM-1. Mutation analysis revealed that the C-terminal 21 amino acids are dispensable, whereas a segment of 5 amino acids ((RKIKK511)-R-507) in the NH-terminal third of intracellular domain, is required for the proper localization and dynamic distribution of ICAM-1 and the association of ICAM-1 with F-actin, ezrin, and moesin. Importantly, deletion of the (RKIKK511)-R-507 significantly delayed the LFA-1-dependent membrane projection and decreased leukocyte adhesion and subsequent TEM. Endothelial cells treated with cell-permeant penetratin-ICAM-1 peptides comprising ICAM-1 RKIKK sequences inhibited leukocyte TEM. Collectively, these findings demonstrate that (RKIKK511)-R-507 is an essential motif for the microvillus ICAM-1 presentation and further suggest a novel regulatory role for ICAM-1 topography in leukocyte TEM.