The Tumour Suppressor CYLD Is Required for Clathrin-Mediated Endocytosis of EGFR and Cetuximab-Induced Apoptosis in Head and Neck Squamous Cell Carcinoma

Simple Summary Epidermal growth factor receptor (EGFR) is a target for the therapeutic antibody cetuximab (CTX) in head and neck squamous cell carcinoma (HNSCC). Identification of its predictive biomarkers and potentiation of CTX-based therapies are important. In this study, we found that the N-terminal portion of cylindromatosis (CYLD) was required for clathrin-mediated endocytosis (CME) and degradation of EGFR. Loss of CYLD limited EGFR to lipid rafts and inhibited CTX-induced apoptosis. Destruction of lipid rafts by cholesterol removers restored EGFR CME and CTX activity in CYLD-downregulated cells. Our findings provide novel insights into the molecular mechanisms underlying EGFR trafficking and resistance to CTX, and suggest the usefulness of CTX-based therapy combined with cholesterol-lowering drugs in HNSCC. Epidermal growth factor receptor (EGFR) is frequently overexpressed in head and neck squamous cell carcinoma (HNSCC) and is a target for the therapeutic antibody cetuximab (CTX). However, because only some patients have a significant clinical response to CTX, identification of its predictive biomarkers and potentiation of CTX-based therapies are important. We have recently reported a frequent downregulation of cylindromatosis (CYLD) in primary HNSCC, which led to increased cell invasion and cisplatin resistance. Here, we show that CYLD located mainly in lipid rafts was required for clathrin-mediated endocytosis (CME) and degradation of the EGFR induced by EGF and CTX in HNSCC cells. The N-terminus containing the first cytoskeleton-associated protein-glycine domain of CYLD was responsible for this regulation. Loss of CYLD restricted EGFR to lipid rafts, which suppressed CTX-induced apoptosis without impeding CTX's inhibitory activity against downstream signalling pathways. Disruption of the lipid rafts with cholesterol-removing agents overcame this resistance by restoring CME and the degradation of EGFR. Regulation of EGFR trafficking by CYLD is thus critical for the antitumour activity of CTX. Our findings suggest the usefulness of a combination of cholesterol-lowering drugs with anti-EGFR antibody therapy in HNSCC.