An Apoptotic Signaling Pathway in the Interferon Antiviral Response Mediated by RNase L and c-Jun NH2-terminal Kinase

Abstract

Cellular stress responses induced during viral infections are critical to the health and survival of organisms. In higher vertebrates, interferons (IFNs) mediate the innate antiviral response in part through the action of RNase L, a uniquely regulated enzyme. RNase L is activated by 5 -phosphorylated, 2 -5 oligoadenylates (2-5A) produced from IFN-inducible and double stranded RNA-dependent synthetases. We show that viral activation of the c-Jun NH 2 -terminal kinases (JNK) family of MAP kinases and viral induction of apoptosis are both deficient in mouse cells lacking RNase L. Also, JNK phosphorylation in response to 2-5A was greatly reduced in RNase L ؊/؊ mouse cells. In addition, 2-5A treatment of the human ovarian carcinoma cell line, Hey1b, resulted in specific ribosomal RNA cleavage products coinciding with JNK activation. Furthermore, suppression of JNK activity with the chemical inhibitor, SP600125, prevented apoptosis induced by 2-5A. In contrast, inhibition of alternative MAP kinases, p38 and ERK, failed to prevent 2-5A-mediated apoptosis. Short interfering RNA to JNK1/JNK2 mRNAs resulted in JNK ablation while also suppressing 2-5A-mediated apoptosis. Moreover, Jnk1 ؊/؊ Jnk2 ؊/؊ cells were highly resistant to the apoptotic effects of IFN and 2-5A. These findings suggest that JNK and RNase L function in an integrated signaling pathway during the IFN response that leads to elimination of virus-infected cells through apoptosis.

Dual role of TMS1/ASC in death receptor signaling

“…To further investigate the role of the JNK pathway, we also examined the response of TMS1 to TNFa treatment in the presence of small interfering RNA (siRNA) directed against JNK1 and 2 ( Li et al, 2004). We found that knockdown of JNK1/2 resulted in a slight upregulation (1.5-fold) in the basal levels of TMS1 mRNA and protein.…”

“…The sequence of the TMS1 siRNA was: 5 0 -CGA GGG UCA CAA ACG UUG A dTdT-3 0 (sense), and the sequence of the p65 siRNA was: 5 0 -GCC CUA UCC CUU UAC GUC A dTdT-3 0 (sense). The JNK siRNA was purchased from Sigma (St Louis, MO, USA) and targets a common sequence in both Jnk1 and Jnk2 mRNA (Li et al, 2004). The sequence of the JNK1/2 siRNA was: 5 0 -AAA GAA UGU CCU ACC UUC U dTdT-3 0 (sense).…”

A scientific journey through the 2-5A/RNase L system

“…However, we and others have shown that activation of RNase L beyond an ill-defined threshold causes apoptosis [69,[79][80][81][82][83]. Therefore, activation of RNase L could lead to elimination of virus-infected cells under some circumstances.…”

“…Induction of the MIC-1 gene in response to 2-5A required stimulation of the MAP kinases, JNK and ERK, and the catalytic function of RNase L. There are significant gaps in our understanding of the transcriptional signaling pathways mediated by 2-5A activation of RNase L. For example, how RNase L activity stimulates JNK and ERK and the downstream events to gene induction are unknown. However, JNK is activated in response to different treatments that cleave or modify rRNA in intact ribosomes (including ricin A, alpha sarcin, uv light, and RNase L) [81,87,88]. Because some of the RNase L-induced genes have antiviral functions, this phenomenon could be contributing to the antiviral effect of 2-5A.…”

“…Therefore, activation of RNase L could lead to elimination of virus-infected cells under some circumstances. RNase L mediated apoptosis is the result of a JNK-dependent stressresponse pathway leading to cytochrome c release from mitochondria and caspase-dependent apoptosis [80,81]. …”