Abstract
BackgroundSynthetic double-stranded RNA poly(I:C) is a useful immune adjuvant and exhibits direct antitumor effects against several types of cancers. In this study, we elucidated the mechanisms underlying the effects induced in poly(I:C)-transfected human renal cell carcinoma (RCC) cells.ResultsIn contrast to the lack of an effect of adding poly(I:C), poly(I:C) transfection drastically decreased RCC cell viability. Poly(I:C) transfection induced reactive oxygen species (ROS)-dependent apoptosis in RCC cells and decreased the mitochondrial membrane potential (ΔΨm). Treatment with N-acetyl-l-cysteine (NAC), a ROS scavenger, suppressed apoptosis and restored the ΔΨm. Although the levels of phosphorylated γH2A.X, an indicator of DNA damage, increased in poly(I:C)-transfected RCC cells, NAC treatment decreased their levels, suggesting ROS-mediated DNA damage. Furthermore, poly(I:C) transfection increased the levels of phosphorylated p53, NOXA, and tBid. Immunoblots and assays with a panel of caspase inhibitors revealed that poly(I:C) transfection-induced apoptosis was dependent on caspase-8 and -9, as well as caspase-2. Alternatively, poly(I:C) transfection increased mRNA expression of interferon (IFN)-β, and treatment with IFN-β suppressed growth of RCC cells without apoptosis. In addition, cyclinD1 and c-Myc expression decreased in poly(I:C)-transfected RCC cells. Moreover, RNA interference experiments revealed that poly(I:C) transfection exerted apoptotic effects on RCC cells through innate adjuvant receptors and the 2-5A system, the latter of which induces apoptosis in virus-infected cells.ConclusionsThese results suggest that poly(I:C) transfection induced two types of effects against RCC cells such as apoptosis, as a result of ROS-mediated DNA damage, and IFN-β-mediated growth arrest, both of which were exerted via innate adjuvant receptors and the 2-5A system.Electronic supplementary materialThe online version of this article (doi:10.1186/1476-4598-13-217) contains supplementary material, which is available to authorized users.
Highlights
Synthetic double-stranded RNA poly(I:C) is a useful immune adjuvant and exhibits direct antitumor effects against several types of cancers
These results suggest that poly(I:C) transfection induced two types of effects against renal cell carcinoma (RCC) cells such as apoptosis, as a result of reactive oxygen species (ROS)-mediated DNA damage, and IFN-β-mediated growth arrest, both of which were exerted via innate adjuvant receptors and the 2-5A system
Our results suggest that poly(I:C) transfection induces two types of effects against RCC cells: apoptosis, as a result of ROS-mediated DNA damage, and interferon (IFN)β-mediated suppression of cell growth
Summary
Synthetic double-stranded RNA poly(I:C) is a useful immune adjuvant and exhibits direct antitumor effects against several types of cancers. We have reported that poly (I:C) transfection exhibits apoptotic effects against human breast cancer cells, whereas recovery of their viability by selective MDA5 knockdown is only partial [11]. The mechanism by which apoptosis is induced and the identities of receptors and/or mechanisms other than MDA5 that participate in the effects in poly(I:C)-transfected cancer cells have not been fully elucidated. Apoptosis is triggered mainly through the extrinsic or intrinsic caspase-dependent pathways, and caspase-8 and −9, respectively, play central roles in these pathways [12]. Caspase-2 has been suggested to participate in ROS-mediated cellular apoptosis [15], but the precise roles of this “orphan” caspase in cancer cell apoptosis have not been fully explained [16]
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