Biased signaling downstream of epidermal growth factor receptor regulates proliferative versus apoptotic response to ligand

Abstract

Inhibition of epidermal growth factor receptor (EGFR) signaling by small molecule kinase inhibitors and monoclonal antibodies has proven effective in the treatment of multiple cancers. In contrast, metastatic breast cancers (BC) derived from EGFR-expressing mammary tumors are inherently resistant to EGFR-targeted therapies. Mechanisms that contribute to this inherent resistance remain poorly defined. Here, we show that in contrast to primary tumors, ligand-mediated activation of EGFR in metastatic BC is dominated by STAT1 signaling. This change in downstream signaling leads to apoptosis and growth inhibition in response to epidermal growth factor (EGF) in metastatic BC cells. Mechanistically, these changes in downstream signaling result from an increase in the internalized pool of EGFR in metastatic cells, increasing physical access to the nuclear pool of STAT1. Along these lines, an EGFR mutant that is defective in endocytosis is unable to elicit STAT1 phosphorylation and apoptosis. Additionally, inhibition of endosomal signaling using an EGFR inhibitor linked to a nuclear localization signal specifically prevents EGF-induced STAT1 phosphorylation and cell death, without affecting EGFR:ERK1/2 signaling. Pharmacologic blockade of ERK1/2 signaling through the use of the allosteric MEK1/2 inhibitor, trametinib, dramatically biases downstream EGFR signaling toward a STAT1-dominated event, resulting in enhanced EGF-induced apoptosis in metastatic BC cells. Importantly, combined administration of trametinib and EGF also facilitated an apoptotic switch in EGFR-transformed primary tumor cells, but not normal mammary epithelial cells. These studies reveal a fundamental distinction for EGFR function in metastatic BC. Furthermore, the data demonstrate that pharmacological biasing of EGFR signaling toward STAT1 activation is capable of revealing the apoptotic function of this critical pathway.

EGF Induces Migration Independent of EMT or Invasion in A549 Lung Adenocarcinoma Cells

“…This would be in line with the "go or grow hypothesis" suggesting that cells will favor either proliferation or migration but not both at the same time (Giese et al, 1996). Although EGF was shown to stimulate cell survival in multiple models (Henson and Gibson, 2006), the lack of serum-contained survival factors in our experiments might result in oncogene-induced cell death, a phenomenon described for activation of both EGFR (Ali et al, 2018) and Ras (Chi et al, 1999). FIGURE 7 | EGF does not contribute to EMT or invasion either alone or in combination with TGFβ.…”

Binding of single-mutant epidermal growth factor (EGF) ligands alter the stability of the EGF receptor dimer and promote growth signaling

“…Treatment with EGF has been observed to promote STAT1 dependent apoptosis (40). This pathway is dependent on the internalization of the ligand-receptor complex by the endocytosis process, a key factor in the ligand-induced biased signaling (16). In our experiments, A431 cells treated with mutant EGF ligands show a higher growth rate, therefore a decreased rate of apoptosis compared to WT.…”

Growth Hormone/Insulin Growth Factor Axis in Sex Steroid Associated Disorders and Related Cancers

“…Growth factors have been found to be involved in all steps of tumour invasion and metastasis (reviewed by Witsch et al, 2010 ). Additionally although signalling via growth factor receptors can be oncogenic the same receptors can also drive apoptosis within cancer cells ( Ali et al, 2018 ).…”