Axl-EGFR receptor tyrosine kinase hetero-interaction provides EGFR with access to pro-invasive signalling in cancer cells

Abstract

Acquired resistance to conventional and targeted therapies is becoming a major hindrance in cancer management. It is increasingly clear that cancer cells are able to evolve and rewire canonical signalling pathways to their advantage, thus evading cell death and promoting cell invasion. The Axl receptor tyrosine kinase (RTK) has been shown to modulate acquired resistance to EGFR-targeted therapies in both breast and lung cancers. Glioblastoma multiforme (GBM) is a highly infiltrative and invasive form of brain tumour with little response to therapy. Both Axl and EGFR have been identified as major players in gliomagenesis and invasiveness. However, the mechanisms underlying a potential signalling crosstalk between EGFR and Axl RTKs are unknown. The purpose of this study was to investigate this novel and unconventional interaction among RTKs of different families in human GBM cells. With the use of western blotting, in vitro kinase activity, co-immunoprecipitation and bimolecular fluorescence complementation assays, we show that EGF stimulates activation of Axl kinase and that there is a hetero-interaction between the two RTKs. Through small interfering RNA knockdown and quantitative PCR screening, we identified distinct gene expression patterns in GBM cells that were specifically regulated by signalling from EGFR-EGFR, Axl–Axl and EGFR-Axl RTK parings. These included genes that promote invasion, which were activated only via the EGFR-Axl axis (MMP9), while EGFR-EGFR distinctly regulated the cell cycle and Axl–Axl regulated invasion. Our findings provide critical insights into the role of EGFR-Axl hetero-dimerisation in cancer cells and reveal regulation of cell invasion via Axl as a novel function of EGFR signalling.

HGF-induced formation of the MET–AXL–ELMO2–DOCK180 complex promotes RAC1 activation, receptor clustering, and cancer cell migration and invasion

“…In our system, we found that only the high molecular weight species, p140, but not the GAS6-dependent lower molecular species, p120, of the AXL proteins, is phosphorylated by HGF/MET on Y779 ( Figure 2E). Our data are consistent with the data showing that activation of p140 form of AXL by EGFR, which was very recently reported to form an EGFR-AXL protein complex to activate AXL via the EGFR-mediated trans-phosphorylation of Y779 in AXL (41). The p140 form, which likely represents the more glycosylated form of AXL than that of p120 (30), may facilitate AXL to interact with other RTKs in the extracellular domains.…”

Cross-talk between the receptor tyrosine kinases AXL and ERBB3 regulates invadopodia formation in melanoma cells

“…Cross-talk between AXL and EGFR family members was previously proposed by studies in several cancer systems as a potential mechanism for drug resistance, usually in the form of AXL activation following EGFR inhibition (33)(34)(35). Moreover, in breast cancer cells, the opposite process was found, when prolonged inhibition of AXL leads to an increase in ERBB3 expression and phosphorylation (36).…”

Loss of Gas6 and Axl signaling results in extensive axonal damage, motor deficits, prolonged neuroinflammation, and less remyelination following cuprizone exposure

“…Tyro3, Axl, MerTK (TAMs) and their respective ligands, Gas6 and ProS1, play major roles in regulating inflammation and homeostasis (Lemke & Rothlin, ; Rothlin et al, ). Gas6 is the sole ligand for Axl; however, Axl can bind or heterodimerize with other receptors including Tyro3, MerTK, epidermal growth factor receptor (EGFR), and type I interferon receptor (IFNAR) to initiate intracellular signaling (Rothlin et al, ; Vouri et al, ). Gas6 is highly expressed in the healthy mouse CNS by microglia, endothelial cells, and neurons (Prieto, Weber, Tracy, Heeb, & Lai, ; Zhang et al, ).…”