Phosphatidylinositol 4,5-Bisphosphate Clusters the Cell Adhesion Molecule CD44 and Assembles a Specific CD44-Ezrin Heterocomplex, as Revealed by Small Angle Neutron Scattering

• Published in: The Journal of biological chemistry Vol. 290; no. 10; pp. 6639 - 6652
• Main Authors: Chen, Xiaodong, Khajeh, Jahan Ali, Ju, Jeong Ho, Gupta, Yogesh K., Stanley, Christopher B., Do, Changwoo, Heller, William T., Aggarwal, Aneel K., Callaway, David J.E., Bu, Zimei
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 06-03-2015; American Society for Biochemistry and Molecular Biology
• Subjects: Animals; CD44; Cell Adhesion; Cell Adhesion Molecule; Cytoskeletal Proteins - biosynthesis; Cytoskeletal Proteins - chemistry; Cytoskeletal Proteins - metabolism; Cytoskeleton - chemistry; Cytoskeleton - metabolism; Cytosol - chemistry; Cytosol - metabolism; Ezrin; Guinea Pigs; Hyaluronan Receptors - biosynthesis; Hyaluronan Receptors - chemistry; Hyaluronan Receptors - metabolism; INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; Multiprotein Complexes - chemistry; Multiprotein Complexes - isolation & purification; Neutron Scattering; Phosphatidylinositol; Phosphatidylinositol 4,5-Diphosphate - chemistry; Phosphatidylinositol 4,5-Diphosphate - metabolism; Protein Binding; Protein Structure and Folding; Protein Structure, Tertiary; Scattering, Small Angle; Signal Transduction - genetics; Phosphatidylinositol; Cell Adhesion Molecule; Cell Adhesion; Neutron Scattering; CD44; Ezrin
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M114.589523

The cell adhesion molecule CD44 regulates diverse cellular functions, including cell-cell and cell-matrix interaction, cell motility, migration, differentiation, and growth. In cells, CD44 co-localizes with the membrane-cytoskeleton adapter protein Ezrin that links the CD44 assembled receptor signaling complexes to the cytoskeletal actin network, which organizes the spatial and temporal localization of signaling events. Here we report that the cytoplasmic tail of CD44 (CD44ct) is largely disordered. Upon binding to the signaling lipid phosphatidylinositol 4,5-bisphosphate (PIP2), CD44ct clusters into aggregates. Further, contrary to the generally accepted model, CD44ct does not bind directly to the FERM domain of Ezrin or to the full-length Ezrin but only forms a complex with FERM or with the full-length Ezrin in the presence of PIP2. Using contrast variation small angle neutron scattering, we show that PIP2 mediates the assembly of a specific heterotetramer complex of CD44ct with Ezrin. This study reveals the role of PIP2 in clustering CD44 and in assembling multimeric CD44-Ezrin complexes. We hypothesize that polyvalent electrostatic interactions are responsible for the assembly of CD44 clusters and the multimeric PIP2-CD44-Ezrin complexes.
Background: The mechanism by which the conserved CD44 cytoplasmic tail (CD44ct) functions is not well understood.
Results: The disordered CD44ct interacts with FERM only in the presence of phosphatidylinositol 4,5-bisphosphate (PIP2).
Conclusion: PIP2 clusters CD44ct and facilitates the assembly of a specific CD44-Ezrin heterotetramer complex.
Significance: The study reveals the role of PIP2 in clustering CD44 and in assembling multimeric CD44-Ezrin signaling complexes.