Double-stranded RNA-induced TLR3 activation inhibits angiogenesis and triggers apoptosis of human hepatocellular carcinoma cells

Toll-like receptor 3 (TLR3) is a member of the Toll-like receptors whichrecognize pathogen-associated molecular patterns leading to the activation ofthe innate immune response. Recent reports have strongly indicated that they playimportant roles in cancer cells. Since TLR3 has been recently suggested as a possibletherapeutic target in certain types of cancers, in the present study, TLR3 expressionand its function were explored in hepatocellular carcinoma (HCC) and human umbilicalvein endothelial cells (HUVECs). The expression of TLR3 in various HCC cell linesand HUVECs was detected using quantitative real-time PCR (qRT-PCR) and immunocytochemistry.TLR3 activity was determined by Luciferase reporter assays. The effects of TLR3double-stranded RNA (dsRNA) agonists on angiogenesis were tested by aortic ringassay and HUVEC tube formation experiments. After dsRNA treatment, cell apoptosiswas assessed by Annexin V and PI staining through FACS, and the migration abilitywas measured by a migration assay. The results showed that TLR3 was expressedin HCC cell lines and HUVECs at the mRNA and protein level. Luciferase reporterassays demonstrated that TLR3 was activated by the dsRNA analog BM-06 or poly(I:C).Rat aortic ring outgrowth and endothelial cell tube formation were suppressedafter treatment with dsRNA. In addition, dsRNA triggered apoptosis in MHCC97H,SMMC-7721 and HUVEC cell lines and inhibited cell migration. In conclusion, TLR3agonists not only affect tumor microenvironment by suppressing angiogenesis butalso directly induce tumor cell apoptosis and inhibit tumor cell migration. TLR3may be a new target for HCC therapy.