Poly(I:C) treatment influences the expression of calreticulin and profilin-1 in a human HNSCC cell line: a proteomic study

Polyinosinic:polycytidylic acid (poly (I:C)) has been formerly known to be an interferon inducer but the mechanism of its action was not revealed until the discovery of Toll-like receptors (TLRs). TLRs are members of transmembrane proteins that recognize conserved molecular motifs of viral and bacterial origin and initiate innate immune response. Recent studies have shown that they are also expressed on tumor cells, but their role in these cells is still not clear. TLR3 recognizes double-stranded RNA (poly (I:C)) and is primarily involved in the defense against viruses. TLR3 ligand binding initiates the activation of transcription factors NF-κB, IRF family members, and AP-1, which can induce wide cascading effect on the cell and consequently activate many cellular processes. Since little is known about TLR3 target genes, we have used the proteomic approach to widen the current knowledge. In this study, we have discovered 15 differentially expressed proteins, mostly connected with protein metabolic processes. Furthermore, we have confirmed by Western blot that calreticulin and profilin-1, proteins which have been shown previously to be involved in processes connected with tumor progression, are differentially expressed after poly(I:C) treatment. By using TLR3 small interfering RNA, we showed that calreticulin expression might be TLR3 dependent, unlike profilin-1.