Ezrin/Radixin/Moesin (ERM) Proteins Bind to a Positively Charged Amino Acid Cluster in the Juxta-Membrane Cytoplasmic Domain of CD44, CD43, and ICAM-2

Abstract

Abstract. CD44 has been identified as a membrane-binding partner for ezrin/radixin/moesin (ERM) proteins, plasma membrane/actin filament cross-linkers. ERM proteins, however, are not necessarily colocalized with CD44 in tissues, but with CD43 and ICAM-2 in some types of cells. We found that glutathione-S-transferase fusion proteins with the cytoplasmic domain of CD43 and ICAM-2, as well as CD44, bound to moesin in vitro. The regions responsible for the in vitro binding of CD43 and CD44 to moesin were narrowed down to their juxta-membrane 20–30–amino acid sequences in the cytoplasmic domain. These sequences and the cytoplasmic domain of ICAM-2 (28 amino acids) were all characterized by the positively charged amino acid clusters. When E-cadherin chimeric molecules bearing these positively charged amino acid clusters of CD44, CD43, or ICAM-2 were expressed in mouse L fibroblasts, they were co-concentrated with ERM proteins at microvilli, whereas those lacking these clusters were diffusely distributed on the cell surface. The specific binding of ERM proteins to the juxta-membrane positively charged amino acid clusters of CD44, CD43, and ICAM-2 was confirmed by immunoprecipitation and site-directed mutagenesis. From these findings, we conclude that ERM proteins bind to integral membrane proteins bearing a positively charged amino acid cluster in their juxta-membrane cytoplasmic domain.

Krp1, a novel kelch related protein that is involved in pseudopod elongation in transformed cells

“…This raises the question of whether these proteins might be interacting at the looped structure. It has been reported that ezrin links the cytoplasmic domain of CD44 to the actin cytoskeleton in baby hamster kidney cells and mouse L ®broblasts (Tsukita et al, 1994;Yonemura et al, 1998Yonemura et al, , 1999Legg and Isacke, 1998), but we do not know if this interaction occurs in FBR cells. None of our data allow us to conclude that Krp1 interacts with these proteins, but the presence of all of them at pseudopod tips upon transformation of 208F cells supports the hypothesis that AP-1 regulates the expression of these genes, and that they are recruited to a structure that is likely to allow transformed cells to become invasive (Guirguis et al, 1987;Hay, 1989;Lamb et al, 1997b;Liotta et al, 1991b;Nabi et al, 1999).…”

Directional sensing of a phorbol ester gradient requires CD44 and is regulated by CD44 phosphorylation

“…In the cell, approximately 75% of PKA is associated with AKAPs (Sim and Scott, 1999). A candidate AKAP in the phosphorylation of CD44 is ezrin (Dransfield et al, 1997), a member of the ERM family of proteins that interact with CD44 at a membrane proximal site in the CD44 cytoplasmic tail (Legg and Isacke, 1998;Yonemura et al, 1998). Alternatively, the four terminal amino acids (Lys-IleGly-Val) correspond to a consensus postsynaptic density protein/discs-large protein/zonula occludens-1 (PDZ) domain binding motif (Thorne et al, 2004).…”

RKIKK Motif in the Intracellular Domain Is Critical for Spatial and Dynamic Organization of ICAM-1: Functional Implication for the Leukocyte Adhesion and Transmigration

“…A striking feature of 507 RKIKK 511 residues is the presence of positively charged amino acids. A positively charged amino acid cluster in the juxta-membrane portion has been identified as an ERM protein-binding region in CD43, CD44, and ICAM-2 (Legg and Isacke, 1998;Yonemura et al, 1998). Therefore, instead of binding to ␣-actinin, this motif may also serve as a binding site for ERM proteins.…”