NF90 interacts with components of RISC and modulates association of Ago2 with mRNA

Abstract

Background Nuclear factor 90 (NF90) is a double-stranded RNA-binding protein involved in a multitude of different cellular mechanisms such as transcription, translation, viral infection, and mRNA stability. Recent data suggest that NF90 might influence the abundance of target mRNAs in the cytoplasm through miRNA- and Argonaute 2 (Ago2)-dependent activity. Results Here, we identified the interactome of NF90 in the cytoplasm, which revealed several components of the RNA-induced silencing complex (RISC) and associated factors. Co-immunoprecipitation analysis confirmed the interaction of NF90 with the RISC-associated RNA helicase, Moloney leukemia virus 10 (MOV10), and other proteins involved in RISC-mediated silencing, including Ago2. Furthermore, NF90 association with MOV10 and Ago2 was found to be RNA-dependent. Glycerol gradient sedimentation of NF90 immune complexes indicates that these proteins occur in the same protein complex. At target RNAs predicted to bind both NF90 and MOV10 in their 3′ UTRs, NF90 association was increased upon loss of MOV10 and vice versa. Interestingly, loss of NF90 led to an increase in association of Ago2 as well as a decrease in the abundance of the target mRNA. Similarly, during hypoxia, the binding of Ago2 to vascular endothelial growth factor (VEGF) mRNA increased after loss of NF90, while the level of VEGF mRNA decreased. Conclusions These findings reveal that, in the cytoplasm, NF90 can associate with components of RISC such as Ago2 and MOV10. In addition, the data indicate that NF90 and MOV10 may compete for the binding of common target mRNAs, suggesting a role for NF90 in the regulation of RISC-mediated silencing by stabilizing target mRNAs, such as VEGF, during cancer-induced hypoxia.

The Polyvalent Role of NF90 in RNA Biology

“…Interestingly, NF90 has been identified as a subunit of P-bodies, and was recently shown to interact with RBPs involved in RISC-mediated silencing, such as Moloney leukemia virus 10 (MOV10) and Argonaute 2 (AGO2), in an RNA-dependent manner [ 26 , 64 ]. NF90 and MOV10 can bind a common set of target mRNAs.…”

“…NF90 and MOV10 can bind a common set of target mRNAs. However, RIP analyses suggest that the binding of MOV10 to target mRNAs might prevent or reduce the binding of NF90 to the same targets, and vice versa [ 26 ]. Interestingly, the loss of NF90 increases the association of AGO2 to the target mRNAs while reducing their abundance.…”

“…Interestingly, the loss of NF90 increases the association of AGO2 to the target mRNAs while reducing their abundance. These findings suggest that NF90 might have a role in RISC-mediated silencing by modulating AGO2 association with target mRNAs, and thereby enhancing their stability [ 26 ]. Similarly, the heterodimer NF90/NF45 was recently shown to compete with factors involved in Staufen-mediated mRNA decay (SMD) [ 65 ].…”

“…Despite the numerous examples of mRNAs regulated by NF90 at the post-transcriptional level, the exact mechanism of inhibition or the activation of translation or mRNA stabilization is still largely unknown. However, recent findings suggest that the function of NF90 in mRNA translational regulation and stability might be mediated by RISC and SMD activity [ 26 , 65 ].…”

“…It is implicated in transcription [ 21 ], splicing [ 22 ], post-transcriptional modification, translation, and mRNA stability [ 23 , 24 , 25 ]. To add to this list, functions in circular RNA formation, miRNA processing, and RNA decay pathways have more recently been described [ 16 , 26 , 27 ]. Here, we review the polyvalent role of NF90 in RNA biology.…”