MDA5 complements TLR3 in suppression of neuroblastoma.

Wen-Ming Hsu,Hui-Ching Chuang,Chao-Cheng Huang,Hsin-Yu Lee,Jiin-Haur Chuang,Pei-Yi Wu,Li-Ling Lin,Min-Tsui Wu

doi:10.18632/oncotarget.4511

Abstract

Toll-like receptor3 (TLR3) has been confirmed to be differentially expressed in neuroblastoma (NB), and predicts a favorable prognosis with a high expression in tumor tissues. Treatment with TLR3 agonist--polyinosinic-polycytidylic acid [poly(I:C)] could induce significant but limited apoptosis in TLR3-expressing NB cells, suggesting that other viral RNA sensors, including melanoma differentiation-associated gene 5 (MDA5) and retinoic acid-inducible gene-I (RIG-I) in the cytosolic compartment might also be implicated in poly(I:C)-induced NB cell death. MDA5 and RIG-I were induced by poly(I:C) to express in two of six NB cell lines, SK-N-AS (AS) and SK-N-FI, which were associated with up-regulation of caspase9 and active caspase3. While knockdown of either MDA5 or RIG-I alone is ineffective to decrease caspase9 and active caspase3, simultaneously targeting MDA5 and TLR3 showed the best effect to rescue poly(I:C) induced up-regulation of mitochondrial antiviral signaling protein (MAVS), caspase9, active caspase3, and apoptosis in AS cells. Over-expression of MDA5 in FaDu cells resulted in significantly less colony formation and more poly(I:C)-induced cell death. Further studies in human NB tissue samples revealed that MDA5 expression in NB tissues predicted a favorable prognosis synergistically with TLR3. Our findings indicate that MDA5 may serve as a complementary role in the TLR3 activated suppression of NB.

Highlights

Neuroblastoma (NB) is a pediatric solid tumor characterized by its wide range of clinical manifestations and poor outcome for those with high-risk clinical phenotypes, despite significant advance in the treatment in the last 10 years [1, 2]
All NB cell lines expressed a base-line level of Toll-like receptor3 (TLR3), the level was low in SK-N-DZ
melanoma differentiationassociated gene 5 (MDA5) and retinoic acid-inducible gene-I (RIG-I) are cytosolic receptors responsible for the detection of viral RNA, which have been expected to respond to synthetic dsRNA— poly(I:C) similar to TLR3 in NB [3]

Summary

Introduction

Neuroblastoma (NB) is a pediatric solid tumor characterized by its wide range of clinical manifestations and poor outcome for those with high-risk clinical phenotypes, despite significant advance in the treatment in the last 10 years [1, 2]. One of the TLR family members - TLR3 has been confirmed to be differentially expressed in NB, and predict a favorable prognosis with a high expression in tumor tissues by our group [3, 4]. TLR3 agonist polyinosinic-polycytidylic acid [poly(I:C)] could induce apoptosis in TLR3-expressing NB cells, preferentially through mitochondrial pathway [5]. In addition to TLR3, there are other viral RNA sensors in the cells, including melanoma differentiation-associated gene 5 (MDA5) and retinoic acid-inducible gene-I (RIG-I), which have been implicated in mitochondrial apoptosis www.impactjournals.com/oncotarget of human melanoma cells, as well as proimmunogenic apoptosis of human ovarian cancer cells [6, 7]. RIG-I was isolated by differential display-PCR from acute promyelocytic leukemia cells treated with all-trans retinoic acid, and initially known as RIG-E [9]

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Results

Conclusion