ERM family members as molecular linkers between the cell surface glycoprotein CD44 and actin-based cytoskeletons.

Abstract

Abstract. The ERM family members, ezrin, radixin, and moesin, localizing just beneath the plasma membranes, are thought to be involved in the actin iliamerit/plasma membrane association. To identify the integral membrane protein directly associated with ERM family members, we performed immunoprecipitation studies using antimoesin mAb and cultured baby hamster kidney (BHK) cells metabolically labeled with [35S]methionine or surface-labeled with biotin. The results indicated that moesin is directly associated with a 140-kD integral membrane protein. Using BHK cells as antigens, we obtained a mAb that recognized the 140-kD membrane protein. We next cloned a cDNA encoding the 140-kD membrane protein and identified it as CD44, a broadly distributed cell surface glycoprotein. Immunoprecipitation with various anti-CIM4 mAbs showed that ezrin and radixin, as well as moesin, are associated with CIM4, not only in BHK cells, but also in mouse L fibroblasts. Furthermore, immunofluorescence microscopy revealed that in both BHK and L cells, the Triton X-100-insoluble CIM4 is precisely colocalized with ERM family members. We concluded that ERM family members work as molecular linkers between the cytoplasmic domain of CIM4 and actin-based cytoskeletons.

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).…”

“…CD44 antisense oligonucleotides caused a reduction in invasiveness in both of these cells. The expression of ezrin, which is a member of the ezrin/radixin/moesin (ERM) family and is thought to link CD44 to the cell's cytoskeleton, was also shown to be upregulated (Lamb et al, 1997b;Jooss and Muller, 1995;Tsukita et al, 1994). Ezrin is located at the tips of pseudopodia in FBR cells and EGF-treated 208F cells, and removal of it from pseudopodia using the micro-CALI technique resulted in retraction of pseudopodia, suggesting that ezrin has a role in pseudopod extension (Lamb et al, 1997b).…”

Inhibition of the hyaluronan-CD44 interaction by merlin contributes to the tumor-suppressor activity of merlin

“…Merlin and the ERM proteins are members of the band 4.1 superfamily, all of which contain a FERM (4.1, ezrin, radixin, moesin) domain at their NH 2 -termini. Like the ERM proteins, merlin regulates actin cytoskeletal organization, cell architecture and motility (Algrain et al, 1993;Tsukita et al, 1994).…”

“…CD44, the principal cell-surface receptor for hyaluronan (HA; Stamenkovic et al, 1989;Aruffo et al, 1990), is one of the transmembrane proteins that interact with ERM proteins and merlin (Tsukita et al, 1994;Hirao et al, 1996;Sainio et al, 1997;Tsukita and Yonemura, 1997;Morrison et al, 2001). There are numerous isoforms of CD44, the most commonly expressed isoform is the standard form of CD44 (CD44s) that lacks variant exon products.…”

“…Only merlin isoform I has been shown to exhibit tumor-suppressing activity (Sherman et al, 1997). The NH 2 -terminus of merlin shares high sequence homology with the NH 2 -terminal halves of ERM proteins that mediate the binding of these proteins to a variety of molecules in the plasma membrane (Tsukita et al, 1994;Hirao et al, 1996;Yonemura et al, 1998). Accordingly, merlin mutants that lack part of the NH 2 -terminal ERM-homology domains lose their ability to associate with the plasma membrane (Deguen et al, 1998;Koga et al, 1998).…”