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J. Cell Biol.,
Volume 140, Number 4, February 23, 1998 885-895
* Department of Cell Biology, Faculty of Medicine, Kyoto University, Sakyo-ku, Kyoto 606-01, Japan; 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.
Department of Surgery
II, § Second Department of Internal Medicine, Osaka University Medical School, Suita, Osaka 565, Japan; and College of
Medical Technology, Kyoto University, Sakyo-ku, Kyoto 606, Japan
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