Abstract
Epidermal growth factor receptor (EGFR) is highly expressed in head and neck squamous cell carcinoma (HNSCC) and related to cancer progression. The resistance to anti-EGFR therapy remains a major clinical problem in HNSCC. In this study, we found that TOLL-like receptor 4 (TLR4) was highly expressed in 50% of EGFR overexpressed HNSCC biopsies, which correlated to worse prognosis in patients. In HNSCC cell lines, activation of TLR4 reversed cetuximab-induced the inhibition of proliferation, migration and invasion. LPS induced of TLR4 signaling was potentiated under cetuximab treatment, showing increased activation of downstream NF-κB and MAPK pathways. Accordingly, cetuximab treatment also increased expression of TNF-α, COX2, and other molecules involved in TLR4 induced tumor inflammation. Mechanistically, we found inhibition of EGFR by cetuximab led to decreased phosphorylation of Src and sequentially Src-medicated activation of Cbl-b. This inhibited Cbl-b-mediated degradation of the key TLR4 adaptor protein MyD88 and activated TLR4 signaling. TLR4 or MyD88 overexpressed CAL27 and SCC4 cells grew faster and were more resistant to cetuximab and gefitinib both in vitro and in vivo. Out study delineates a crosstalk between EGFR and TLR4 pathways and identified TLR4 as a potential biomarker as well as a therapeutic target in overcoming the resistance to anti-EGFR therapy of HNSCC.