Regulation of HGF Expression by ΔEGFR-Mediated c-Met Activation in Glioblastoma Cells

Abstract

The hepatocyte growth factor receptor (c-Met) and a constitutively active mutant of the epidermal growth factor receptor (ΔEGFR/EGFRvIII) are frequently overexpressed in glioblastoma (GBM) and promote tumorigenesis. The mechanisms underlying elevated hepatocyte growth factor (HGF) production in GBM are not understood. We found higher, coordinated mRNA expression levels of HGF and c-Met in mesenchymal (Mes) GBMs, a subtype associated with poor treatment response and shorter overall survival. In an HGF/c-Met-dependent GBM cell line, HGF expression declined upon silencing of c-Met using RNAi or by inhibiting its activity with SU11274. Silencing c-Met decreased anchorage-independent colony formation and increased the survival of mice bearing intracranial GBM xenografts. Consistent with these findings, c-Met activation by ΔEGFR also elevated HGF expression, and the inhibition of ΔEGFR with AG1478 reduced HGF levels. Interestingly, c-Met expression was required for ΔEGFR-mediated HGF production, anchorage-independent growth, and in vivo tumorigenicity, suggesting that these pathways are coupled. Using an unbiased mass spectrometry-based screen, we show that signal transducer and activator of transcription 3 (STAT3) Y705 is a downstream target of c-Met signaling. Suppression of STAT3 phosphorylation with WP1193 reduced HGF expression in ΔEGFR-expressing GBM cells, whereas constitutively active STAT3 partially rescued HGF expression and colony formation in c-Met knockdown cells expressing ΔEGFR. These results suggest that the c-Met/HGF signaling axis is enhanced by ΔEGFR through increased STAT3-dependent HGF expression and that targeting c-Met in Mes GBMs may be an important strategy for therapy.

Nuclear phosphorylated Y142 β-catenin accumulates in astrocytomas and glioblastomas and regulates cell invasion

“…These results confirm a key role of c-Met in GBM progression. 29,[48][49][50][51] The lack of regulation of PY142 b-catenin by a c-Met inhibitor does not allow us to conclude if c-Met is phosphorylating this b-catenin site in GBM cells and rather suggests the involvement of other kinases. The proteolytic processing of c-Met is well described and nuclear c-Met has been linked to invasive cancers.…”

“…22,23 Crosstalk between EGFR, c-Met and Wnt/b-catenin is well documented in cancer cells, thereby linking b-catenin signaling and cell migration induced by growth factors. [24][25][26][27][28][29] Thus, stimulation of epithelial cells with EGF or HGF through the phosphorylation of cell adhesion proteins diminishes cell adhesion while promoting epithelial-mesenchymal transition (EMT). Phosphorylation of Y142 b-catenin by c-Met affects b-catenin interaction with a-catenin 30 and promotes a b-catenin switch from adhesive to transcriptional functions that facilitates promigratory phenotypes.…”

NF-κB and STAT3 in glioblastoma: therapeutic targets coming of age

“…EGFR is increasingly seen as an important STAT3 activator in GBM. For example, EGFRvIII (a constitutively active mutant missing exons 2–7) cooperates with wild-type EGFR to cause hyperactivation of STAT3 and STAT5—but not Akt or ERK—in GBM [89], and STAT3-mediated coordination between EGFRvIII and c-MET has also been described [90]. (Of note, however, is the recent observation that EGFR varieties are rarely coexpressed at the single cell level in GBM [24]. )…”

“…Thus, when antiangiogenic therapy is applied to GBM, MET becomes hyperactivated, and indeed, inhibition of VEGF and MET effectively reduced invasive capacity of GBM tumors while improving survival [109]. As previously mentioned, MET is capable of driving STAT3 activation [90]. In bevacizumab-resistant GBM models, MET is upregulated, and p-Tyr705-STAT3 levels are increased twofold in bevacizumab resistant versus non-resistant GBM [110].…”

EGFR wild type antagonizes EGFRvIII-mediated activation of Met in glioblastoma

“…9 A number of studies have reported a pro-oncogenic role of Met in glioma and that inhibition of Met is effective in inhibiting glioma growth in preclinical models. 10–12 Transactivation of Met by EGFR signaling has been reported for EGFRwt as well as EGFRvIII in GBMs and other cancers. 13,14 Phosphorylation of Y1234 is required for Met activity and is particularly responsive to the presence of EGFRvIII.…”