TLR3 signaling in a hepatoma cell line is skewed towards apoptosis.

Toll-like receptors (TLRs) recognize pathogen-associated molecular patterns (PAMPS) leading to the activation of the innate immune response and subsequently to the shaping of the adaptive immune response. Of the known human TLRs, TLR3, 7, 8, and 9 were shown to recognize nucleic acid ligands. TLR3 signaling is induced by double-stranded (ds)RNA, a molecular signature of viruses, and is mediated by the TRIF (TIR domain-containing adaptor-inducing IFNbeta) adaptor molecule. Thus, TLR3 plays an important role in the host response to viral infections. The liver is constantly exposed to a large variety of foreign substances, including pathogens such as HBV (hepatitis B virus) and HCV (hepatitis C virus), which frequently establish persistent liver infections. In this work, we investigated the expression and signaling pathway of TLR3 in different hepatoma cell lines. We show that hepatocyte lineage cells express relatively low levels of TLR3 mRNA. TLR3 signaling in HEK293 cells (human embryonic kidney cells) activated NF-kappaB and IRF3 (interferon regulatory factor 3) and induced IFNbeta (interferon beta) promoter expression, which are known to lead to pro-inflammatory cytokine secretion. In Huh7 cells, there was only a short-term IRF3 activation, and a very low level of IFNbeta expression. In HepG2 cells on the other hand, while no induction of pro-inflammatory factors was observed, signaling by TLR3 was skewed towards the induction of apoptosis. These results indicate preferential induction of the apoptotic pathway over the cytokine induction pathway by TLR3 signaling in hepatocellular carcinoma cells with potential implications for therapeutic strategies.

Khvalevsky E ，Rivkin L ，Rachmilewitz J ，Galun E ，Giladi H ... -  《JOURNAL OF CELLULAR BIOCHEMISTRY》

Dual topology of functional Toll-like receptor 3 expression in human hepatocellular carcinoma: differential signaling mechanisms of TLR3-induced NF-kappaB activation and apoptosis.

Yoneda K ，Sugimoto K ，Shiraki K ，Tanaka J ，Beppu T ，Fuke H ，Yamamoto N ，Masuya M ，Horie R ，Uchida K ，Takei Y ... -  《INTERNATIONAL JOURNAL OF ONCOLOGY》

Synthetic double-stranded RNA induces multiple genes related to inflammation through Toll-like receptor 3 depending on NF-kappaB and/or IRF-3 in airway epithelial cells.

Matsukura S ，Kokubu F ，Kurokawa M ，Kawaguchi M ，Ieki K ，Kuga H ，Odaka M ，Suzuki S ，Watanabe S ，Takeuchi H ，Kasama T ，Adachi M ... -  《CLINICAL AND EXPERIMENTAL ALLERGY》

Functional evolution of the TICAM-1 pathway for extrinsic RNA sensing.

Seya T ，Matsumoto M ，Ebihara T ，Oshiumi H ... -  《-》

Transcriptional regulation of the human TRIF (TIR domain-containing adaptor protein inducing interferon beta) gene.

Hardy MP ，McGGettrick AF ，O'Neill LA 《-》