title: Hyaluronan promotes signaling interaction between CD44 and the transforming growth factor beta receptor I in metastatic breast tumor cells.
abstract: In this study we have examined the interaction between CD44 (a hyaluronan (HA) receptor) and the transforming growth factor beta (TGF-beta) receptors (a family of serine/threonine kinase membrane receptors) in human metastatic breast tumor cells (MDA-MB-231 cell line). Immunological data indicate that both CD44 and TGF-beta receptors are expressed in MDA-MB-231 cells and that CD44 is physically linked to the TGF-beta receptor I (TGF-betaRI) (and to a lesser extent to the TGF-beta receptor II (TGF-betaRII)) as a complex in vivo. Scatchard plot analyses and in vitro binding experiments show that the cytoplasmic domain of CD44 binds to TGF-betaRI at a single site with high affinity (an apparent dissociation constant (K(d)) of approximately 1.78 nm). These findings indicate that TGF-betaRI contains a CD44-binding site. Furthermore, we have found that the binding of HA to CD44 in MDA-MB-231 cells stimulates TGF-betaRI serine/threonine kinase activity which, in turn, increases Smad2/Smad3 phosphorylation and parathyroid hormone-related protein (PTH-rP) production (well known downstream effector functions of TGF-beta signaling). Most importantly, TGF-betaRI kinase activated by HA phosphorylates CD44, which enhances its binding interaction with the cytoskeletal protein, ankyrin, leading to HA-mediated breast tumor cell migration. Overexpression of TGF-betaRI by transfection of MDA-MB-231 cells with TGF-betaRIcDNA stimulates formation of the CD44.TGF-betaRI complex, the association of ankyrin with membranes, and HA-dependent/CD44-specific breast tumor migration. Taken together, these findings strongly suggest that CD44 interaction with the TGF-betaRI kinase promotes activation of multiple signaling pathways required for ankyrin-membrane interaction, tumor cell migration, and important oncogenic events (e.g. Smad2/Smad3 phosphorylation and PTH-rP production) during HA and TGF-beta-mediated metastatic breast tumor progression.
authors.affiliation: Department of Medicine, University of California, San Francisco, and the Endocrine Unit, Veterans Affairs Medical Center, San Francisco, California 94121, USA. lillyb@itsa.ucsf.edu
authors.forename: Lilly Y W
authors.initials: LY
authors.lastname: Bourguignon
authors.forename: Patrick A
authors.initials: PA
authors.lastname: Singleton
authors.forename: Hongbo
authors.initials: H
authors.lastname: Zhu
authors.forename: Bo
authors.initials: B
authors.lastname: Zhou
mesh_terms: D030201:Activin Receptors, Type I / Q000378:metabolism*; D000818:Animals; D001943:Breast Neoplasms / Q000378:metabolism*; D019556:COS Cells; D002460:Cell Line; D002465:Cell Movement; D003593:Cytoplasm / Q000378:metabolism; D018076:DNA, Complementary / Q000378:metabolism; D004926:Escherichia coli / Q000378:metabolism; D006801:Humans; D018960:Hyaluronan Receptors / Q000378:metabolism*; D006820:Hyaluronic Acid / Q000737:chemistry* / Q000378:metabolism; D007700:Kinetics; D009362:Neoplasm Metastasis; D010766:Phosphorylation; D011233:Precipitin Tests; D011485:Protein Binding; D017346:Protein Serine-Threonine Kinases; D017434:Protein Structure, Tertiary; D000077293:Receptor, Transforming Growth Factor-beta Type I; D018125:Receptors, Transforming Growth Factor beta / Q000378:metabolism*; D015398:Signal Transduction; D014162:Transfection; D014407:Tumor Cells, Cultured
chemical_list: D018076:DNA, Complementary; D018960:Hyaluronan Receptors; D018125:Receptors, Transforming Growth Factor beta; D006820:Hyaluronic Acid; D017346:Protein Serine-Threonine Kinases; D030201:Activin Receptors, Type I; D000077293:Receptor, Transforming Growth Factor-beta Type I