CD44 Interaction with Tiam1 Promotes Rac1 Signaling and Hyaluronic Acid-mediated Breast Tumor Cell Migration*
- From the Department of Cell Biology and Anatomy, School of Medicine, University of Miami, Miami, Florida 33101
Abstract
In this study we have explored the interaction between CD44 (the hyaluronic acid (HA)-binding receptor) and Tiam1 (a guanine nucleotide exchange factor) in metastatic breast tumor cells (SP1 cell line). Immunoprecipitation and immunoblot analyses indicate that both the CD44v3 isoform and the Tiam1 protein are expressed in SP1 cells and that these two proteins are physically associated as a complex in vivo. Using an Escherichia coli-derived calmodulin-binding peptide-tagged Tiam1 fragment (i.e. the NH2-terminal pleckstrin homology (PHn) domain and an adjacent protein interaction domain designated as PHn-CC-Ex, amino acids 393–738 of Tiam1) and an in vitrobinding assay, we have detected a specific binding interaction between the Tiam1 PHn-CC-Ex domain and CD44. Scatchard plot analysis indicates that there is a single high affinity CD44 binding site in the PHn-CC-Ex domain of Tiam1 with an apparent dissociation constant (K d) of 0.2 nm, which is comparable with CD44 binding (K d = ∼0.13 nm) to intact Tiam1. These findings suggest that the PHn-CC-Ex domain is the primary Tiam1-binding region for CD44. Most importantly, the binding of HA to CD44v3 of SP1 cells stimulates Tiam1-catalyzed Rac1 signaling and cytoskeleton-mediated tumor cell migration. Transfection of SP1 cells with Tiam1cDNA promotes Tiam1 association with CD44v3 and up-regulates Rac1 signaling as well as HA/CD44v3-mediated breast tumor cell migration. Co-transfection of SP1 cells with PHn-CC-Ex cDNA and Tiam1 cDNA effectively inhibits Tiam1 association with CD44 and efficiently blocks tumor behaviors. Taken together, we believe that the linkage between CD44v3 isoform and the PHn-CC-EX domain of Tiam1 is required for HA stimulated Rac1 signaling and cytoskeleton-mediated tumor cell migration during breast cancer progression.
Footnotes
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↵* This work was supported by United States Public Health Grants CA66163 and CA 78633 and Department of Defense Grants DAMD 17-94-J-4121, DAMD 17-97-1-7014, and DAMD 17-99-1-9291.The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
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↵‡ To whom reprint request should be addressed: Dept. of Cell Biology and Anatomy, University of Miami Medical School, 1600 N.W. 10th Ave., Miami, FL 33136. Tel.: 305-243-6985; Fax: 305-545-7166; E-mail: Lbourgui@mednet.med.miami.edu.
- Abbreviations:
- HA
-
hyaluronic acid
- PHn
-
pleckstrin homology
- PHc
-
PH domain located at the COOH-terminal region of the molecule
- CC
-
coiled coil region
- Ex
-
extra region
- CBP
-
calmodulin-binding peptide
- GFP
-
green fluorescent protein
- GST
-
glutathione S-transferase
- PBS
-
phosphate-buffered saline
- PCR
-
polymerase chain reaction
- GTPγS
-
guanosine 5′-3-O-(thio)triphosphate
- Rh
-
rhodamine
- FITC
-
fluorescein isothiocyanate
-
- Received September 3, 1999.
- Revision received October 19, 1999.
- The American Society for Biochemistry and Molecular Biology, Inc.
