Hu Antigen R Regulates Antiviral Innate Immune Responses through the Stabilization of mRNA for Polo-like Kinase 2

Abstract

Retinoic acid-inducible gene I (RIG-I)-like receptors (RLRs), RIG-I, and melanoma differentiation-associated gene 5 (MDA5) play a critical role in inducing antiviral innate immune responses by activating IFN regulatory factor 3 (IRF3) and NF-κB, which regulates the transcription of type I IFN and inflammatory cytokines. Antiviral innate immune responses are also regulated by posttranscriptional and translational mechanisms. In this study, we identified an RNA-binding protein HuR as a regulator for RLR signaling. Overexpression of HuR, but not of other Hu members, increased IFN-β promoter activity. HuR-deficient macrophage cells exhibited decreased expression after RLR stimulation, whereas they showed normal induction after stimulation with bacterial LPS or immunostimulatory DNA. Moreover, HuR-deficient cells displayed impaired nuclear translocation of IRF3 after RLR stimulation. In HuR-deficient cells, the mRNA expression of Polo-like kinase (PLK) 2 was markedly reduced. We found that HuR bound to the 3' untranslated region of mRNA and increased its stabilization. PLK2-deficient cells also showed reduced IRF3 nuclear translocation and mRNA expression during RLR signaling. Together, these findings suggest that HuR bolsters RLR-mediated IRF3 nuclear translocation by controlling the stability of mRNA.

Innate immune responses through Toll-like receptor 3 require human-antigen-R-mediated Atp6v0d2 mRNA stabilization

“…Therefore, in this study, we investigated the contribution of HuR to the posttranscriptional regulation of genes involved in the innate immune system. In a previous study, we showed that HuR regulates the innate antiviral immune response by stabilizing the mRNA of polo-like kinase 2 (PLK2), which facilitates nuclear translocation of IRF3 induced by RLRs 20 . Here, we provide evidence suggesting that HuR is involved in the TLR3-mediated antiviral innate immune response by stabilizing the mRNA of Atp6v0d2 , which encodes a subunit of vacuolar-type H + adenosine triphosphatase (V-ATPase) required for the acidification of intracellular vesicles.…”

RNA Recognition and Immunity—Innate Immune Sensing and Its Posttranscriptional Regulation Mechanisms

“…In contrast to TTP and other ARE-biding proteins, ELAVL1 is an ARE-binding protein that stabilizes mRNAs. This protein predominantly localizes in the nucleus but translocates into the cytoplasm in response to viral infection, hypoxic stress, and DNA damage [102][103][104]. Subsequently, ELAVL1 competes against other ARE-binding proteins for ARE sites and therefore enhances the stability and translation of target mRNA.…”

“…HuR is also involved in viral responses through the activation of RLR. HuR promotes IRF3 nuclear translocation via the increased stability of Plk2 mRNA [104]. In contrast, mice specifically lacking ELAVL1 in macrophages show exacerbated inflammatory responses in chemically induced colitis [135].…”

PtdIns3P phosphatases MTMR3 and MTMR4 negatively regulate innate immune responses to DNA through modulating STING trafficking

“…RT-PCR was performed with the following primers: Mtm1, sense 5Ј-ATCTTAGGAG-GATCGCAACG-3Ј, reverse 5Ј-TACCGACAAGAGGCTGA-CTG-3Ј; Mtmr1, sense 5Ј-TCCATTTATGGGAGCAGTGA-3Ј, reverse 5Ј-TGCACCAATCTTCTCCACTC-3Ј; Mtmr2, sense 5Ј-AGCAGAAATGGAGGAACCAG-3Ј, reverse 5Ј-CGCTCCATGCTCTTGAAATA-3Ј; Mtmr3, sense 5Ј-TGGG-AATGTATTCTGCTCCA-3Ј, reverse 5Ј-CAATGCTG-GAGCTTGTAGGA-3Ј; Mtmr4, sense 5Ј-TGTGTCCT-GGAAATGAAGA-3Ј, reverse 5Ј-AAACTGTTCAGGTGGC-TTCC-3Ј; Mtmr6, sense 5Ј-TTCCGGTCCTATCCTACTGC-3Ј, reverse 5Ј-TGAAGCAAATGCTCATCCTC-3Ј; Mtmr7, sense 5Ј-CCAGTTTGGGAACTTCCTGT-3Ј, reverse 5Ј-GGCAGCTCGATTCTTCCACA-3Ј; Mtmr8 sense 5Ј-GGCT-CTCTGGGTACCATCAT-3Ј, reverse 5Ј-GAGTGGACAAT-GCCTCAATG-3Ј. Primer for Ifnb, Il6, Il10, Cxcl10, and 18s were described previously (33,34).…”

“…Other plasmids were described previously (33). After 24-h transfection, luciferase activity was measured as described previously (33,34).…”