Bikunin down-regulates heterodimerization between CD44 and growth factor receptors and subsequently suppresses agonist-mediated signaling.
We provided evidence previously that bikunin, a Kunitz-type protease inhibitor, can disrupt dimerization of CD44 proteins, which may result in suppression of receptor-mediated MAP kinase signaling. However, to what extent dimerization may alter ligand-induced signaling has not been documented. Given the recent recognition that some growth factor receptors can form heterodimers with CD44, the present study was undertaken to determine whether the CD44 and growth factor receptors (e.g., EGFR, FGFR, HGFR, VEGFR, TGF-betaRI, or TGF-betaRII) can form heterodimers in cancer cells and, if so, to investigate the potential functional consequences of such heterodimerization. We also examined whether bikunin can abrogate these heterodimerizations and inhibit CD44/growth factor-dependent signaling. Here, we show direct evidence for heterodimerization of CD44-FGFR and CD44-TGF-betaRI in human chondrosarcoma HCS-2/8 cells, CD44-EGFR complex in human glioma U87MG cells, and CD44-TGF-betaRI heterodimer in human ovarian cancer HRA cells. Coupling of CD44 and growth factor receptor may be selective, depending on a cell type. Bikunin does not alter the ligand binding, whereas functionally reduces heterodimerization between CD44 and growth factor receptors. The disruption of heterodimerization substantially reduces receptor-induced tyrosine phosphorylation and ERK1/2 activation. Taken together, our data suggest that bikunin-mediated suppression of heterodimerization between CD44 and growth factors may inhibit the agonist-promoted activation of the signaling pathway.
Wakahara
Kiyoshi
K
NetForce Co. Ltd., Taiko 3-1-18, Nakamura, Nagoya, Aichi 453-0801, Japan.
Kobayashi
Hiroshi
H
Yagyu
Tatsuo
T
Matsuzaki
Hidenori
H
Kondo
Toshiharu
T
Kurita
Noriyuki
N
Sekino
Hideo
H
Inagaki
Kiyokazu
K
Suzuki
Mika
M
Kanayama
Naohiro
N
Terao
Toshihiko
T
D045744:Cell Line, Tumor; D019281:Dimerization; D015536:Down-Regulation / Q000187:drug effects*; D004789:Enzyme Activation; D005260:Female; D005434:Flow Cytometry; D006801:Humans; D018960:Hyaluronan Receptors / Q000378:metabolism*; D047468:Immunoprecipitation; D008562:Membrane Glycoproteins / Q000494:pharmacology*; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D010766:Phosphorylation; D018125:Receptors, Transforming Growth Factor beta / Q000378:metabolism*; D015398:Signal Transduction; D014360:Trypsin Inhibitor, Kunitz Soybean / Q000494:pharmacology*
D018960:Hyaluronan Receptors; D008562:Membrane Glycoproteins; D018125:Receptors, Transforming Growth Factor beta; C109148:SPINT2 protein, human; D014360:Trypsin Inhibitor, Kunitz Soybean; D020928:Mitogen-Activated Protein Kinases