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Address correspondence to Cheryl B. Knudson, Dept. of Biochemistry, Rush Medical College, Rush University Medical Center, 1653 West Congress Parkway, Chicago, IL 60612. Tel.: (312) 942-8249. Fax: (312) 942-3053. email: cheryl_knudson{at}rush.edu
Bone morphogenetic protein 7 (BMP-7) regulates cellular metabolism in embryonic and adult tissues. Signal transduction occurs through the activation of intracellular Smad proteins. In this paper, using a yeast two-hybrid screen, Smad1 was found to interact with the cytoplasmic domain of CD44, a receptor for the extracellular matrix macromolecule hyaluronan. Coimmunoprecipitation experiments confirmed the interaction of Smad1 with full-length CD44interactions that did not occur when CD44 receptors truncated within the cytoplasmic domain were tested. Chondrocytes overexpressing a truncated CD44 on a background of endogenous full-length CD44 no longer exhibited Smad1 nuclear translocation upon BMP-7 stimulation. Further, pretreatment of chondrocytes with Streptomyces hyaluronidase to disrupt extracellular hyaluronancell interactions inhibited BMP-7mediated Smad1 phosphorylation, nuclear translocation of Smad1 or Smad4, and SBE4luciferase reporter activation. These results support a functional link between the BMP signaling cascade and CD44. Thus, changes in hyaluronancell interactions may serve as a means to modulate cellular responsiveness to BMP.
Key Words: CD44; bone morphogenetic protein; hyaluronan; chondrocyte; Smad1
Abbreviations used in this paper: BMP, bone morphogenetic protein; SBE, Smad-binding element.
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