JNK signaling plays a critical role in both tumor promotion and tumor suppression. Here, we identified clustered microRNAs (miRNAs) miR-306 and miR-79 as novel tumor-suppressor miRNAs that specifically eliminate JNK-activated tumors in Drosophila. While showing only a slight effect on normal tissue growth, miR-306 and miR-79 strongly suppressed growth of multiple tumor models, including malignant tumors caused by Ras activation and cell polarity defects. Mechanistically, these miRNAs commonly target the mRNA of an E3 ubiquitin ligase ring finger protein 146 (RNF146). We found that RNF146 promotes degradation of tankyrase (Tnks), an ADP-ribose polymerase that promotes JNK activation in a noncanonical manner. Thus, downregulation of RNF146 by miR-306 and miR-79 leads to hyper-enhancement of JNK activation. Our data show that, while JNK activity is essential for tumor growth, elevation of miR-306 or miR-79 overactivate JNK signaling to the lethal level via noncanonical JNK pathway and thus eliminate tumors, providing a new miRNA-based strategy against cancer.

The small interfering RNA (siRNA) pathway is a highly conserved antiviral defense mechanism in vertebrates and invertebrates. Although the core components of this pathway are well characterized, its upstream regulatory networks remain poorly understood. Here, we identify the integrated stress response (ISR) as a negative regulator of the siRNA pathway, and demonstrate that the picorna-like virus CrPV (Cricket Paralysis Virus) exploits this mechanism for immune evasion. Mechanistically, the picorna-like virus triggers the ISR through transcriptional suppression of ppp1r15 , a key regulator of eukaryotic initiation factor 2α (eIF2α) dephosphorylation. ISR activation subsequently induces the autophagy-lysosomal pathway by up-regulating Atg1 transcription in an ATF4-dependent manner. This process leads to selective degradation of Argonaute 2 (Ago2) and other core components of the RNA-induced silencing complex (RISC), thereby suppressing the host RNA interference (RNAi) machinery and enhancing viral replication. Our findings uncover an unconventional immune evasion strategy employed by a picorna-like virus and establish a previously unrecognized crosstalk between the ISR and siRNA pathways.

Translin/TRAX complex, also named as C3PO, is evolutionarily conserved and participates in diverse cellular processes in different organisms from yeast to human. C3PO plays a critical role in the activation of RNA-induced silencing complexes by promoting the unwinding and degradation of passenger strand of exogenous siRNAs (exo-siRNAs) in Drosophila and human. Moreover, human C3PO (hC3PO) has been found to broadly repress miRNAs by degrading miRNA precursors. However, the effect of Drosophila melanogaster C3PO (dmC3PO) on endogenous siRNA (endo-siRNA) and miRNA pathways remains unknown. Here, we found that the loss of dmC3PO promoted the accumulation of the passenger strand of esi-2.1 (hp-CG4068B), and resulted in the de-repression of the DNA-damage-response gene mutagensensitive 308 (mus308), which is an endogenous slicer target of esi-2.1 in Drosophila. Moreover, we also found that depletion of dmC3PO increased the accumulation of miR-bantam. Taken together, our findings indicated that dmC3PO not only involves in siRNA pathway triggered by dsRNA, but also regulates the abundance of certain endogenous small RNAs in Drosophila.

The cGAS (cyclic GMP-AMP synthase)-STING (Stimulator of interferon genes) pathway plays a central role in antiviral innate immunity in vertebrates. Recent studies have shown that invertebrates possess a related cGLR (cGAS-like receptor)-STING pathway. However, due to the lack of direct evidence demonstrating viral evasion of cGLR-STING-mediated immunity, the functional importance of cGLR-STING pathway in antiviral responses remains uncertain in invertebrates. Here, we show that an insect picorna-like virus CrPV (Cricket Paralysis virus) inhibits STING-mediated antiviral activity by altering the transcription start site of STING . Mechanistically, CrPV infection down-regulates several spliceosomal genes and disrupts pre-mRNA splicing. This splicing impairment is sufficient to stall RNA polymerase II in transcriptional initiation condensates, reduce global transcription efficiency, and reprogram the transcription start site of STING . Such a shift diverts STING expression from a functional antiviral isoform to a nonantiviral variant that partially suppresses STING activity, thereby disabling the cGLR-STING pathway. Our findings uncover an unconventional viral immune evasion strategy and an unexpected link between splicing suppression and STING-mediated antiviral response. Given the evolutionary conservation of splicing mechanisms and STING-like pathways, this mechanism may represent a broadly applicable regulatory principle in immune defense across species.