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Differential activation of Epidermal Growth Factor (EGF) receptor downstream signaling pathways by betacellulin and EGF

Department of Medicine and Molecular Science, Gunma University Graduate School of Medicine, Gunma 371-8511, Japan. .
Endocrinology (Impact Factor: 4.64). 10/2004; 145(9):4232-43. DOI: 10.1210/en.2004-0401
Source: PubMed

ABSTRACT 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.

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    • "BTC has anti-apoptotic effects on intestinal epithelial cells Western blots carried out employing protein extracts from the small intestine epithelium revealed markedly lower levels of activated caspase-3 in samples from BTC-tg mice, as compared to control mice (Fig. 3D). This result confirms previous observations indicating that BTC has stronger anti-apoptotic actions as compared to EGF [26]. Furthermore, this finding suggests that BTC overexpression creates an anti-apoptotic environment in the gut epithelium, supporting the survival of newly formed adenomas. "
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    • "The α v integrin subunit induced the phosphorylation of 845, 1068, 1086, and 1173 (Moro et al., 2002). In addition, ionizing radiation induced phosphorylation of 992 and 1173 while betacellulin induced 1068 (Sturla et al., 2005; Saito et al., 2004). While these are major sites of phosphorylation in response to EGF, it is interesting that differential phosphorylation occurs in response to specific biologic activation. "
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    • "BTC acts by binding to members of the tyrosine kinase erbB receptor family. This triggers receptor phosphorylation and signaling to the cell nucleus through a cascade of mediators, resulting in modulation of gene transcription [30] [31]. The modulated genes may include key b-cell transcription factors such as Pdx1, NeuroD, Nkx2.2, and Nkx6.1, whose expression was observed to be induced by BTC in PHID cells. "
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