Differential activation of epidermal growth factor (EGF) receptor downstream signaling pathways by betacellulin and EGF.
To determine the downstream signaling pathways regulated by betacellulin (BTC) in comparison with epidermal growth factor (EGF), we used Chinese hamster ovary cells overexpressing the human EGF receptor (ErbB1/EGFR). The overall time-dependent activation of EGFR autophosphorylation was identical in cells treated with 1 nm BTC or 1.5 nm EGF. Analysis of site-specific EGFR phosphorylation demonstrated that the BTC and EGF tyrosine phosphorylation of Y1086 was not significantly different. In contrast, the autophosphorylation of Y1173 was markedly reduced in BTC-stimulated cells, compared with EGF stimulation that directly correlated with a reduced BTC stimulation of Shc tyrosine phosphorylation, Ras, and Raf-1 activation. On the other hand, Y1068 phosphorylation was significantly increased after BTC stimulation, compared with EGF in parallel with a greater extent of Erk phosphorylation. Expression of a dominant interfering MEK kinase 1 (MEKK1) and Y1068F EGFR more efficiently blocked the enhanced Erk activation by BTC, compared with EGF. Interestingly BTC had a greater inhibitory effect on apoptosis, compared with EGF, and expression of Y1068F EGFR abolished this enhanced inhibitory effect. Together, these data indicated that although BTC and EGF share overlapping signaling properties, the ability of BTC to enhance Erk activation occurs independent of Ras. The increased BTC activation results from a greater extent of Y1068 EGFR tyrosine phosphorylation and subsequent increased recruitment of the Grb2-MEKK1 complex to the plasma membrane, compared with EGF stimulation. The increased Erk activation by BTC associated with antiapoptotic function.
Saito
Tsugumichi
T
Department of Medicine and Molecular Science, Gunma University Graduate School of Medicine, Gunma 371-8511, Japan. okadash@showa.gunma-u.ac.jp.
Okada
Shuichi
S
Ohshima
Kihachi
K
Yamada
Eijiro
E
Sato
Minoru
M
Uehara
Yutaka
Y
Shimizu
Hiroyuki
H
Pessin
Jeffrey E
JE
Mori
Masatomo
M
D048868:Adaptor Proteins, Signal Transducing; D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D066259:Betacellulin; D016466:CHO Cells; D006224:Cricetinae; D004815:Epidermal Growth Factor / Q000378:metabolism / Q000494:pharmacology*; D066246:ErbB Receptors / Q000235:genetics / Q000378:metabolism*; D051380:GRB2 Adaptor Protein; D006801:Humans; D036341:Intercellular Signaling Peptides and Proteins / Q000378:metabolism / Q000494:pharmacology*; D008024:Ligands; D048369:MAP Kinase Kinase 1; D048370:MAP Kinase Kinase 2; D048728:MAP Kinase Kinase Kinase 1; D020930:MAP Kinase Kinase Kinases / Q000378:metabolism; D020929:Mitogen-Activated Protein Kinase Kinases / Q000378:metabolism; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D011506:Proteins / Q000378:metabolism; D019908:Proto-Oncogene Proteins c-raf / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects* / Q000502:physiology; D020664:Son of Sevenless Proteins / Q000378:metabolism; D014443:Tyrosine / Q000378:metabolism; D018631:ras Proteins / Q000378:metabolism; D018909:src Homology Domains / Q000502:physiology
D048868:Adaptor Proteins, Signal Transducing; C587851:BTC protein, human; D066259:Betacellulin; D051380:GRB2 Adaptor Protein; C495948:GRB2 protein, human; D036341:Intercellular Signaling Peptides and Proteins; D008024:Ligands; D011506:Proteins; D020664:Son of Sevenless Proteins; D014443:Tyrosine; D004815:Epidermal Growth Factor; C482128:MAP2K2 protein, human; D066246:ErbB Receptors; D011505:Protein-Tyrosine Kinases; D019908:Proto-Oncogene Proteins c-raf; D020928:Mitogen-Activated Protein Kinases; D048728:MAP Kinase Kinase Kinase 1; D020930:MAP Kinase Kinase Kinases; C482576:MAP3K1 protein, human; D048369:MAP Kinase Kinase 1; D048370:MAP Kinase Kinase 2; C482125:MAP2K1 protein, human; D020929:Mitogen-Activated Protein Kinase Kinases; D018631:ras Proteins