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Molecular and Cellular Biology, December 1998, p. 7192-7204, Vol. 18, No. 12
Ludwig Institute for Cancer Research,
Received 6 April 1998/Returned for modification 7 May 1998/Accepted 24 August 1998
Signalling by the epidermal growth factor (EGF) receptor (EGFR) has
been studied intensively, but for most cell types the analysis is
complicated by the fact that EGFR not only homodimerizes but can also
form heterodimers with other EGFR family members. Heterodimerization is a particular problem in the study of EGFR mutants, where the true phenotype of the mutants is confounded by the
contribution of the heterodimer partner to signal transduction. We have made use of the murine hemopoietic cell line BaF/3, which does
not express EGFR family members, to express wild-type (WT) EGFR,
three kinase-defective EGFR mutants (V741G, Y740F, and K721R), or
a C-terminally truncated EGFR (CT957) and have measured their responses
to EGF. We found that under the appropriate conditions EGF can
stimulate cell proliferation of BaF/3 cells expressing WT or CT957
EGFRs but not that of cells expressing the kinase-defective mutants.
However, EGF promotes the survival of BaF/3 cells expressing either of the kinase-defective receptors (V741G and Y740F), indicating that these receptors can still transmit a survival signal. Analysis of
the early signalling events by the WT, V741G, and Y740F mutant EGF
receptors indicated that EGF stimulates comparable levels of Shc
phosphorylation, Shc-GRB-2 association, and activation of Ras,
B-Raf, and Erk-1. Blocking the mitogen-activated protein kinase (MAPK)
signalling pathway with the specific inhibitor PD98059 abrogates
completely the EGF-dependent survival of cells expressing the
kinase-defective EGFR mutants but has no effect on the EGF-dependent proliferation mediated by WT and CT957 EGFRs. Similarly, the Src family
kinase inhibitor PP1 abrogates EGF-dependent survival without affecting
proliferation. However blocking phosphatidylinositol-3-kinase or JAK-2
kinase with specific inhibitors does arrest growth factor-dependent cell proliferation. Thus, EGFR-mediated mitogenic signalling in BaF/3
cells requires an intact EGFR tyrosine kinase activity and appears to
depend on the activation of both the JAK-2 and PI-3 kinase pathways.
Activation of the Src family of kinases or of the Ras/MAPK pathway can,
however, be initiated by a kinase-impaired EGFR and is linked to survival.
0270-7306/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Activation of the Ras/Mitogen-Activated Protein Kinase Pathway by
Kinase-Defective Epidermal Growth Factor Receptors Results in Cell
Survival but Not Proliferation
*
Corresponding author. Mailing address: Ludwig Institute
for Cancer Research, Post Office Royal Melbourne Hospital, Melbourne, Victoria 3050, Australia. Phone: 61-3-9341-3155. Fax: 61-3-9341-3104. E-mail: burgess{at}ludwig.edu.au.
Molecular and Cellular Biology, December 1998, p. 7192-7204, Vol. 18, No. 12
0270-7306/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
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