Mutant epidermal growth factor receptor
enhances induction of vascular endothelial growth factor by hypoxia and
insulin-like growth factor-1 via a PI3 kinase dependent pathway
Clarke K, Smith K, Gullick WJ, Harris AL
Growth Factor Group, Molecular Oncology Laboratories, Imperial
Cancer Research Fund, John Radcliffe Hospital, Oxford, OX3 9DU, UK
Over-expression of truncated epidermal growth factor receptor (EGFR) occurs in a
variety of malignancies including glioblastoma multiforme, breast and lung
The truncation deletes an extracellular domain and results in constitutive
activation of the receptor.
NIH3T3 cells were transfected with full length or truncated human EGFR and
differences in growth rates in vivo and in vitro analysed.
A growth advantage was seen for cells expressing mutant receptor compared to
full length EGFR in vivo only.
Administration of an anti-mutant EGFR antibody to mice transiently reduced the
growth rates of mutant tumours, confirming that the mutant receptor itself was
important in this enhanced tumorigenicity.
This showed that stimuli present in vivo and not in vitro may be contributing to
We therefore analysed the regulation of the angiogenic factor vascular
endothelial growth factor (VEGF).
Although levels of secreted VEGF did not differ significantly between wild-type
and mutant EGFR cell lines when grown in vitro under normoxic conditions,
following exposure to 0.1% hypoxia levels of VEGF produced by mutant cells
increased 3.5-6.6 fold compared to 2 or less for full length EGFR cells.
The fold induction was influenced by experimental conditions, including cell
confluence and percentage of fetal bovine serum, but was consistently higher for
mutant cell lines.
The increase in VEGF under hypoxic conditions was blocked by the addition of PI3
kinase inhibitors, indicating that the latter pathway is important in the
hypoxic stress response.
Basal levels were not affected.
Addition of insulin-like growth factor-1 also increased levels of VEGF under
normoxic conditions in the mutant cells and no further increase was seen when
added to cells exposed to 0.1% oxygen, indicating that levels of VEGF were
already maximally stimulated.
These results show that the mutant EGFR interacts with other growth factors and
hypoxia to regulate VEGF via a PI3 kinase pathway, and suggests a specific role
for anti-mutant EGFR antibodies and PI3 kinase inhibitors as therapy of this
specific tumour target.
Copyright 2001 Cancer Research Campaign.
PMID: 11355942 [PubMed - indexed for MEDLINE]