EGF Receptor Substrate 2 Phospho-Tyr5

Colorectal cancer is the third most common cancer worldwide, with 1.2 million patients diagnosed annually. In late-stage colorectal cancer, the most commonly used targeted therapies are the monoclonal antibodies cetuximab and panitumumab, which prevent epidermal growth factor receptor (EGFR) activation. Recent studies have identified alterations in KRAS and other genes as likely mechanisms of primary and secondary resistance to anti-EGFR antibody therapy. Despite these efforts, additional mechanisms of resistance to EGFR blockade are thought to be present in colorectal cancer and little is known about determinants of sensitivity to this therapy. To examine the effect of somatic genetic changes in colorectal cancer on response to anti-EGFR antibody therapy, here we perform complete exome sequence and copy number analyses of 129 patient-derived tumour grafts and targeted genomic analyses of 55 patient tumours, all of which were KRAS wild-type. We analysed the response of tumours to anti-EGFR antibody blockade in tumour graft models and in clinical settings and functionally linked therapeutic responses to mutational data. In addition to previously identified genes, we detected mutations in ERBB2, EGFR, FGFR1, PDGFRA, and MAP2K1 as potential mechanisms of primary resistance to this therapy. Novel alterations in the ectodomain of EGFR were identified in patients with acquired resistance to EGFR blockade. Amplifications and sequence changes in the tyrosine kinase receptor adaptor gene IRS2 were identified in tumours with increased sensitivity to anti-EGFR therapy. Therapeutic resistance to EGFR blockade could be overcome in tumour graft models through combinatorial therapies targeting actionable genes. These analyses provide a systematic approach to evaluating response to targeted therapies in human cancer, highlight new mechanisms of responsiveness to anti-EGFR therapies, and delineate new avenues for intervention in managing colorectal cancer.

Activated epidermal growth factor receptors (EGFRs) are crucial for inducing metastasis in cancer cells by promoting matrix metalloproteinase (MMP) expression. The present study was designed to investigate the effects of 1‑palmitoyl‑2‑linoleoyl‑3‑acetyl‑rac‑glycerol (PLAG) on MMP expression in epidermal growth factor (EGF)‑stimulated breast cancer cells in vitro. EGF stimulation induced internalization of its cognate receptor, EGFR, for stimulus‑desensitization. These internalized receptors, complexed with the ubiquitin ligase c‑Cbl and EGFR pathway substrate 15 (EPS15) (for degradation), were evaluated by confocal microscopy at 5‑90 min time intervals. During intracellular trafficking of EGFRs, EGF‑induced signaling cascades were analyzed by examining EGFR and SHC phosphorylation. Modulation of MMP expression was assessed by evaluating the activity of transcription factor AP‑1 using a luciferase assay. PLAG accelerated the assembly of EGFRs with c‑Cbl and EPS15 and promoted receptor degradation. This faster intracellular EGFR degradation reduced AP‑1‑mediated MMP expression. PLAG stimulation upregulated thioredoxin‑interacting protein (TXNIP) expression, and this mediated the accelerated receptor internalization. This PLAG‑induced increase in EGFR trafficking was blocked in TXNIP‑silenced cells. By downregulating MMP expression, PLAG effectively attenuated EGF‑induced mobility and invasiveness in these cancer cells. These data suggest that PLAG may be a potential therapeutic agent for blocking metastasis.

The epidermal growth factor receptor (EGF-R) and the erbB-2 proto-oncogene product protein are closely related by their structural homology and their shared enzymatic activity as autophosphorylating tyrosine kinases. We show that in mammary tumor cells (SK-BR-3) EGF causes a rapid increase in tyrosine phosphorylation of the erbB-2 protein. Phosphorylation of erbB-2 does not occur in cells lacking the EGF-R (MDA-MB-453). Phosphorylation of erbB-2 in SK-BR-3 cells is blocked if EGF is prevented from interacting with its receptor by specific monoclonal antibodies. While EGF induces the down-regulation of its receptor in SK-BR-3 cells, EGF has no effect on the stability of the erbB-2 protein. This result suggests that the erbB-2 protein is a substrate of the EGF-R and indicates the possibility of communication between these two proteins early in the signal transduction process.