|
|
Differential Gene Expression
Analysis Reveals Generation of an Autocrine Loop by a Mutant Epidermal
Growth Factor Receptor in Glioma Cells
Deepti B. Ramnarain1,
Seongmi Park1,3,
Diana Y. Lee5,6,
Kimmo J. Hatanpaa2,3,
Shane O. Scoggin4,
Hasan Otu7, Towia
A. Libermann7, Jack
M. Raisanen2,3, Raheela
Ashfaq2, Eric T.
Wong5, Julian Wu6,
Robert Elliott5
and Amyn A. Habib1,3,4
Departments of 1Neurology
and 2Pathology, 3Annette G. Strauss Center in
Neuro-Oncology, and 4Harold C. Simmons Comprehensive Cancer
Center, University of Texas Southwestern Medical Center, Dallas, Texas
and Departments of 5Neurology and 6Neurosurgery
and 7Genomics Center, Beth Israel Deaconess Medical Center
and Harvard Medical School, Boston Massachusetts. Requests for
reprints: Amyn A. Habib, University of Texas Southwestern Medical
Center, Mail Code 8813, 6001 Forest Park ND4.136, Dallas, TX
75390-8813. Phone: 214-645-6237; Fax: 214-645-6240; E-mail: Amyn.Habib@UTSouthwestern.edu
.
The epidermal growth factor receptor
(EGFR) gene is commonly amplified and rearranged in
glioblastoma multiforme leading to overexpression of
wild-type and mutant EGFRs.
Expression of wild-type EGFR ligands, such as transforming
growth factor-α (TGF-α) or heparin-binding EGF (HB-EGF),
is also often increased in gliomas resulting in an
autocrine loop that contributes to the growth autonomy of
glioma cells.
Glioblastoma multiformes express a characteristic EGFR
mutant (EGFRvIII, de 2-7) that does not bind ligand,
signals constitutively, and is more tumorigenic than the
wild-type receptor.
However, the downstream signals that mediate this increased
tumorigenicity are not well understood.
We hypothesized that signals induced specifically by EGFRvIII and
not the wild-type receptor are more likely to mediate its increased
tumorigenic activity and examined the gene expression profiles
resulting from inducible expression of comparable levels of
either wild-type EGFR or EGFRvIII in a U251-MG glioma cell line.
Expression of EGFRvIII resulted in specific up-regulation of
a small group of genes.
Remarkably, all these genes, which include TGFA, HB-EGF,
EPHA2, IL8, MAP4K4, FOSL1, EMP1, and DUSP6, influence
signaling pathways known to play a key role in oncogenesis and
function in interconnected networks.
Increased expression of EGFRvIII-induced genes was
validated by real-time PCR.
The mutant receptor does not bind ligand, and EGFRvIII-induced
expression of TGF-α and HB-EGF suggests that EGFRvIII
plays a role in generating an autocrine loop using the
wild-type EGFR in glioma.
It also raises the possibility that EGFRvIII may signal, at
least in part, through the wild-type receptor.
Indeed, we show that inhibiting the activity of HB-EGF, a
potent mitogen, with neutralizing antibodies reduces cell
proliferation induced by expression of EGFRvIII.
This suggests that the EGFRvIII-HB-EGF-wild-type EGFR
autocrine loop plays an important role in signal transduction by
EGFRvIII in glioma cells.
We also show by immunohistochemistry that HB-EGF expression
correlates with the presence of EGFRvIII in glioblastoma
multiforme.
Thus, our study provides a new insight into oncogenic
signaling by EGFRvIII and improves our understanding of how
autocrine loops are generated in glioma.
(Cancer Res 2006; 66(2): 867-74)
|
