Knockdown of DEAD-box RNA helicase DDX5 selectively attenuates serine 311 phosphorylation of NF-κB p65 subunit and expression level of anti-apoptotic factor Bcl-2.

NF-κB plays a key role in the transcriptional regulation of genes involved in immunity, inflammation, cell proliferation, and oncogenesis. The NF-κB activation process includes nuclear translocation, followed by association with basal transcription machinery. These steps are tightly regulated by posttranslational modification of the proteins involved in this pathway. We recently reported that NF-κB transactivation activity is enhanced by knockdown of diacylglycerol kinase ζ (DGKζ), which belongs to an enzyme family that phosphorylates lipidic second messenger diacylglycerol to phosphatidic acid. To investigate details of the regulatory mechanism exerted by DGKζ, we identified DEAD-box RNA helicase DDX5 as a novel DGKζ-interacting protein and examined functional role of DDX5 in NF-κB transactivation activity. Here we show that DDX5 knockdown exerts no significant effect on nuclear translocation, but specifically attenuates Ser311 phosphorylation of p65 subunit. Luciferase reporter assay reveals that the NF-κB transcriptional activity is repressed in DDX5-knockdown cells. Furthermore, we found that DDX5 knockdown selectively downregulates the expression level of Bcl-2 of the NF-κB-inducible anti-apoptotic factors upon TNF-α stimulation. Considering the evidence collectively, we can infer that DGKζ-interacting multi-protein complex modulates the NF-κB transactivation activity in a negative and positive manner under conditions in which the expression level of a component of the complex is altered.

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