REPOSITORY > RESULTS

Abstract

Epidermal growth factor receptor (EGFR) belongs to the ErbB family of receptor tyrosine kinases and plays an essential role in cell differentiation, migration, proliferation, and metabolism. Alterations in EGFR signalling were found in a number of cancers like lung, breast, colorectal cancer and gliomas, shown to be more aggressive and resistant to therapeutics. Consequently, EGFR has been intensively studied as an important anticancer therapeutic target. Signalling through EGFR is commonly triggered by ligand binding. However, deletions in the extracellular region of EGFR can also cause constitutive activation, such as in the case of the EGFRvIII variant. Such deletions can influence receptor activation and downstream signalling cascades. Also, due to its constitutive phosphorylation, cancer cells expressing this variant are highly tumorigenic. EGFR was also identified as a substrate of extracellularly present cysteine cathepsins, known to cleave ectodomains of membrane proteins, including receptors, cytokines, and adhesion proteins.
In this study, we confirmed extracellular cathepsin L-mediated cleavage of epidermal growth factor receptor (EGFR) and identified the cleavage site in the extracellular domain after R224. To further evaluate the relevance of this cleavage, we cloned and expressed a truncated version of EGFR, starting at G225, in HeLa cells. We confirmed the constitutive activation of the truncated protein in the absence of ligand binding and determined possible changes in intracellular signalling. Furthermore, we determined the effect of truncated EGFR protein expression on HeLa cell viability and response to the EGFR inhibitors erlotinib and cetuximab. Our data reveal the nuclear localization and phosphorylation of EGFR and signal transducer and activator of transcription 3 (STAT3) in cells that express the truncated EGFR protein and suggest that these phenomena cause resistance to EGFR inhibitors. Also, we determined the effects of truncated EGFR expression on HeLa cell migration. However, our findings open new questions about EGFR and could possibly lead to more effective strategies in anticancer therapy.