The role of reactive oxygen species production in activation of innate adjuvant receptor signals in thyroid carcinoma

Abstract

Background/Aims

Innate adjuvant receptors recognize various pathogen associated molecules, and they have a major role in the innate and adaptive immunity through the production of type I interferon and other proinflammatory cytokines. Recently, the anti-tumor effects inducing apoptosis and growth arrest after cytoplasmic delivery of an innate adjuvant receptor ligand, polyinosinic-polycytidylic acid [poly(I:C)] has been reported in cancers. Intracellular reactive oxygen species have also been known to have regulatory function of cell proliferation, apoptosis involved in innate immune and proinflammatory responses. We hypothesized that reactive oxygen species production had the role influencing the innate adjuvant receptor signals in thyroid cancer cells. We aimed to validate the role of innate adjuvant receptors activation and intracellular reactive oxygen species generation and furthermore their correlation in the process of papillary thyroid cancer cell death.

Methods

Immunohistochemical analysis of innate adjuvant receptors including Toll-like receptor (TLR) 3, melanoma differentiation-associated gene (MDA) 5, and retinoic acid inducible gene-1 (RIG-I) was performed in 40 paraffin-embedded post-surgical papillary thyroid cancer tissues. The existence of functioning innate adjuvant receptors and the biological effects of their activation following poly(I:C) transfection on thyroid cancer cell deaths were evaluated in TPC-1 and 8505C cell lines. Detailed downstream molecular signaling mediated by interferon-β and reactive oxygen species production were investigated in TPC-1, papillary thyroid cancer cells.

Results

TLR3, MDA5 and interferon-β were expressed in papillary thyroid cancer tissues with variable intensity, but RIG-I expression was not definite. Poly(I:C) transfection induced innate adjuvant receptors dependent apoptosis of papillary thyroid cancer cells which was revealed to be extrinsic caspase-3 and caspase-8 mediated. Increased mRNA expression of innate adjuvant receptors and downstream interferon-β were induced by poly(I:C) transfection. Intracellular reactive oxygen species production was also increased following activation of innate adjuvant receptors. Reactive oxygen species scavenging and interferon-β signal blocking both reduced the effect of poly(I:C) transfection. However, interferon-β expression was not attenuated by reactive oxygen species scavengers.

Conclusion

Innate adjuvant receptor signaling of TLR3 and MDA5 are functioning in papillary thyroid cancer cells and induce the cancer cell deaths. Both interferon-β signal and reactive oxygen species production contribute the innate adjuvant receptors mediated cell death, but intracellular ROS is not mandatory for IFN-β activation in papillary thyroid cancers.