Differential gene expression analysis reveals generation of an autocrine loop by a mutant epidermal growth factor receptor in glioma cells.
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-alpha (TGF-alpha) 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-alpha 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.
Ramnarain
Deepti B
DB
Department of Neurology, University of Texas Southwestern Medical Center, 6001 Forest Park ND4.136, Dallas, TX 75390, USA.
Park
Seongmi
S
Lee
Diana Y
DY
Hatanpaa
Kimmo J
KJ
Scoggin
Shane O
SO
Otu
Hasan
H
Libermann
Towia A
TA
Raisanen
Jack M
JM
Ashfaq
Raheela
R
Wong
Eric T
ET
Wu
Julian
J
Elliott
Robert
R
Habib
Amyn A
AA
D019898:Autocrine Communication; D001932:Brain Neoplasms / Q000235:genetics* / Q000473:pathology; D002471:Cell Transformation, Neoplastic; D066246:ErbB Receptors / Q000235:genetics*; D020869:Gene Expression Profiling; D005909:Glioblastoma / Q000235:genetics* / Q000473:pathology; D006801:Humans; D007150:Immunohistochemistry; D009154:Mutation; D015398:Signal Transduction; D015854:Up-Regulation
D066246:ErbB Receptors