Abstract
MicroRNAs (miRNAs) are small, noncoding RNAs that post-transcriptionally regulate gene expression. For example, miRNAs repress gene expression by recruiting the miRNA-induced silencing complex (miRISC), a ribonucleoprotein complex that contains miRNA-engaged Argonaute (Ago) and the scaffold protein GW182. Recently, ubiquitin-protein ligase E3 component N-recognin 5 (UBR5) has been identified as a component of miRISC. UBR5 directly interacts with GW182 proteins and participates in miRNA silencing by recruiting downstream effectors, such as the translation regulator DEAD-box helicase 6 (DDX6) and transducer of ERBB2,1/2,2 (Tob1/2), to the Ago-GW182 complex. However, the regulation of miRISC-associated UBR5 remains largely elusive. In the present study, we showed that UBR5 down-regulates the levels of TNF receptor-associated factor 3 (TRAF3), a key component of Toll-like receptor signaling, via the miRNA pathway. We further demonstrated that p90 ribosomal S6 kinase (p90RSK) is an upstream regulator of UBR5. p90RSK phosphorylates UBR5 at Thr637, Ser1227, and Ser2483, and this phosphorylation is required for the translational repression of TRAF3 mRNA. Phosphorylated UBR5 co-localized with GW182 and Ago2 in cytoplasmic speckles, which implies that miRISC is affected by phospho-UBR5. Collectively, these results indicated that the p90RSK-UBR5 pathway stimulates miRNA-mediated translational repression of TRAF3. Our work has added another layer to the regulation of miRISC.
Highlights
MicroRNAs are small, noncoding RNAs that post-transcriptionally regulate gene expression
We further demonstrated that p90 ribosomal S6 kinase (p90RSK) is an upstream regulator of ubiquitin–protein ligase E3 component N-recognin 5 (UBR5). p90RSK phosphorylates UBR5 at Thr637, Ser1227, and Ser2483, and this phosphorylation is required for the translational repression of TNF receptor-associated factor 3 (TRAF3) mRNA
We showed that the p90 ribosomal S6 kinase (p90RSK)–UBR5 pathway negatively regulates the translation of TRAF3 through miRNA-mediated translational repression
Summary
TRAF3 is one of the substrates for DUBA in TLR-mediated type I IFN production [20]. To elucidate the roles of UBR5 in the regulation of TRAF3-mediated TLR signaling, we generated HeLa cell lines stably expressing shRNA targeting control or UBR5. Overexpression of RSK CA in HeLa cells significantly decreased Luc–KRAS 3Ј-UTR activity (Fig. 5D) These data suggest that the regulation of miRNA-mediated gene silencing by the p90RSK–UBR5 pathway may be a general phenomenon. The treatment of BI-D1870 or siRNA transfection of p90RSK in HeLa cells resulted in increase in the p60 katanin protein level (supplemental Fig. 4, B and C) These data suggested the possibility that the abundance of p60 katanin protein may be controlled through the p90RSK–UBR5 pathway–regulated miRNA pathway as well as the UBR5–DYRK2–DDB1–VPRBP E3 complex. In agreement with these results, the UBR5 3E mutant further decreased Luc–KRAS 3Ј-UTR activity in comparison with wild-type UBR5 in UBR5-depleted HEK293 cells, but the UBR5 3A mutant did not (Fig. 5G and supplemental Fig. 4D) Together these results suggested that phosphorylation of UBR5 at Thr637, Ser1227, and Ser2483 by p90RSK was required for miRNA-mediated gene silencing
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
