(DEAD)-box RNA helicase 3 modulates NF-κB signal pathway by controlling the phosphorylation of PP2A-C subunit

Abstract

Asp-Glu-Ala-Asp (DEAD)-box RNA helicase 3 (DDX3), an ATP-dependent RNA helicase, is associated with RNA splicing, mRNA export, transcription, translation, and RNA decay. Recent studies revealed that DDX3 participates in innate immune response during virus infection by interacting with TBK1 and regulating the production of IFN-β. In our studies, we demonstrated that DDX3 regulated NF-κB signal pathway. We found that DDX3 knockdown reduced the phosphorylation of p65 and IKK-β and ultimately attenuated the production of inflammatory cytokines induced by poly(I:C) or TNF-α stimulation. The regulatory effect of DDX3 on NF-κB signal pathway was not affected by the loss of its ATPase or helicase activity. We further identified PP2A C subunit (PP2A-C) as an interaction partner of DDX3 by co-immunoprecipitation and mass spectrum analysis. We confirmed that DDX3 formed the complex with PP2A-C/IKK-β and regulated the interaction between IKK-β and PP2A-C. Furthermore, we demonstrated that DDX3 modulated the activity of PP2A by controlling the phosphorylation of PP2A-C, which might enable PP2A-C to regulate NF-κB signal pathway by dephosphorylating IKK-β. All these findings suggested DDX3 plays multiple roles in modulating innate immune system.

Diverse Roles of DEAD/DEAH-Box Helicases in Innate Immunity and Diseases

“…The discrepancy between the effects is possibly due to different experimental conditions. The positive regulation was observed when the cells were stimulated by the synthetic dsRNA analog poly I:C [48], which resembles antiviral immune response, whereas the repression was observed during normal cell culture conditions [49]. This would suggest that DDX3 is an arbitrary regulator of NF-κB pathway whose activity depends on the cellular conditions.…”

“…[47] THF cells [52] hepatitis C [54À57] HIV-1 [55,58,59] norovirus, West Nile virus, Japanese encephalitis virus [55] MAVS À DDX3 can activate MAVS and act as a scaffolding adaptor in downstream signaling TRAF3 [46] À Interaction between DDX3 and TRAF3 triggers K63-linked polyubiquitination and oligomerization of TRAF3 IKKε [45,46] À IKKε and DDX3 phosphorylate each other to promote downstream signaling in the MAVS pathway TBK1 [47] À DDX3 undergoes phosphorylation by TBK1 before it can act as a transcription factor for IFN-β PP2A [48] À Positive regulation of NF-κB transcriptional activity by modulation of PP2A activity NF-κB subunit p65 [49] À Suppression of NF-κB transcriptional activity eIF4E and PABP1 [50] À Promotion of stress granule formation and inhibition of translation Sensor of bacterial and viral RNA, activates the NLRP3 inflammasome in macrophages. [85,86].…”

“…Besides the stimulation of interferon production, DDX3 has been implied in the regulation of NF-κB pathway [48,49]. Interestingly, while one study showed the positive regulatory effect achieved by modulation of PP2A (a phosphatase that inactivates the NF-κB activator IKK-β and NF-κB subunit p65) [48], another study showed that DDX3 interacts with p65 to suppress its transcriptional activity [49]. The discrepancy between the effects is possibly due to different experimental conditions.…”

“…Direct transcription factor for IFN-β upon Listeria monocytogenes infection [47]. Regulation of NF-κB pathway [48,49]. Assembly of processing bodies and stress granules [50,51].…”

“…Inhibition of hepatitis B virus polymerase [53]. hepatocyte lineage cells [43À46, 48,49,53] A549 cells [45,46]…”