Toll-like receptor 3-mediated tumor invasion in head and neck cancer.

Chronic inflammation associated with some infectious agents can lead to cancer. The Toll-like receptor (TLR) family is one of the largest and best-studied families of pathogen-associated molecular patterns. TLR3 recognizes double-stranded RNA and is a major effector of the immune response against viral pathogens. We investigated TLR3 protein expression in 153 oral squamous cell carcinoma (OSCC) specimens using tissue microarray. Furthermore, we used polyinosinic-polycytidylic acid (poly I:C) to stimulate head and neck cancer cells and an inhibitor of endosomal acidification bafilomycin A1 to block the TLR 3 signaling pathway to clarify the role of TLR 3 in OSCC. Cytoplasmic TLR3 staining was observed in the vast majority of OSCC tissues (73.2%). Strong TLR3 expression was significantly correlated with patients whose tumors were poorly differentiated (P=0.028) and with perineural invasion (P=0.023). Three of the four head and neck cell lines tested (Fadu, OC2, and SCC4) expressed TLR3 mRNA, although at various levels. The stimulation of TLR3-expressing OC2 cells with poly I:C caused the phosphorylation of IFN regulatory factor 3 and IκB and sequentially induced the secretion of interleukin-6 and chemokine (C-C motif) ligand 5 (CCL5) in a dose- and time-dependent manner. Moreover, poly I:C stimulation promoted CCL5-mediated migration in OC2 cells. In this report, we provide a novel mechanism for tumor invasion and the TLR3-dependent inflammatory response that could have therapeutic implications for OSCC.