Epidermal growth factor receptor regulates MET levels and invasiveness through hypoxia-inducible factor-1α in non-small cell lung cancer cells

Abstract

Recent studies have established that amplification of the MET proto-oncogene can cause resistance to epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors (TKIs) in non-small cell lung cancer (NSCLC) cell lines with EGFR-activating mutations. The role of non-amplified MET in EGFR-dependent signaling before TKI resistance, however, is not well understood. Using NSCLC cell lines and transgenic models, we demonstrate here that EGFR activation by either mutation or ligand binding increases MET gene expression and protein levels. Our analysis of 202 NSCLC patient specimens was consistent with these observations: levels of MET were significantly higher in NSCLC with EGFR mutations than in NSCLC with wild-type EGFR. EGFR regulation of MET levels in cell lines occurred through the hypoxia-inducible factor (HIF)-1α pathway in a hypoxia-independent manner. This regulation was lost, however, after MET gene amplification or overexpression of a constitutively active form of HIF-1α. EGFR- and hypoxia-induced invasiveness of NSCLC cells, but not cell survival, were found to be MET dependent. These findings establish that, absent MET amplification, EGFR signaling can regulate MET levels through HIF-1α and that MET is a key downstream mediator of EGFR-induced invasiveness in EGFR-dependent NSCLC cells.

Endothelial PAS domain-containing protein 1 confers TKI-resistance by mediating EGFR and MET pathways in non-small cell lung cancer cells

“…15,16 To test whether MET reacts to the interaction of EPAS1 and T790M EGFR, we expressed T790M EGFR and EPAS1 in HCC827 cells simultaneously and examined MET protein levels using anti-c-Met antibody. As previously reported, expression of wild-type and T790M EGFR alone was sufficient to trigger MET amplification, 25 even in the absence of EPAS1 (Fig. 3A, lanes 1 and 2 from left).…”

“…25 To explore if there are other factors mediating EGFR-MET interaction, we carried out a genome-wide search for HIF-1a homologs and EPAS1 (NCBI Reference Sequence: NP_001421.2) was returned as the top hit with 48% amino acid sequence identity (Fig. 1A).…”

“…24 The mechanisms for crosstalk between EGFR and MET remain largely elusive, except that EGFR regulates MET levels in NSCLC cells through the hypoxia-inducible factor (HIF)-1a pathway independently of hypoxia. 25 Here we have identified endothelial PAS domain-containing protein 1 (EPAS1), which has 48% sequence identity to HIF-1a, as a novel player mediating EGFR and MET interactions. We found that EPAS1 directly interacts with EGFR containing TKIresistant T790M mutation, but not with wild-type EGFR, in NSCLC cell lines.…”

Interplay between receptor tyrosine kinases and hypoxia signaling in cancer

“…EGFR-activating mutations have been found to associate with elevated levels of MET in both NSCLC transgenic murine models and clinical samples [138]. Using NSCLC cell lines, Xu et al have shown that the HIF-1α/MET axis plays an important role in regulating invasiveness induced not only by hypoxia but also by EGFR signaling.…”

“…As mentioned in section 1.1., hypoxia is a regulator of HGF, presumably through HIF-1α activity [55]. In this respect, Xu et al suggested that EGFR-activating mutations could promote production of HGF through HIF-1α and thus EGFR/HIF-1α activation may not only regulate MET levels, but also have an impact on MET signal transduction [138].…”