In this paper Alban Ordureau, Karine Enesa and Sambit Nanda in Philip Cohen's lab have identified DEAF1 as a new transcription factor required for the production of Type 1 interferons (IFNs). These findings have enhanced our understanding of the signaling networks that regulate the production of the interferons needed to fight infection by viruses.
Double-stranded (ds) RNA, formed as an intermediate in the replication of some RNA viruses, activates the dsRNA receptors TLR3 and MDA5, which are located on the endosomal membranes and in the cytosol of host cells, respectively. The engagement of these receptors induces the activation of the protein kinase TBK1, which then phosphorylates the transcription factor IRF3. This stimulates the translocation of IRF3 to the nucleus, where it dimerises and activates the IFNÃ_Â_ promoter. In earlier papers, the Cohen lab had reported that TBK1 also phosphorylates and activates the E3 ubiquitin ligase Pellino1 (Smith et al, 2011, Biochem. J. 434, 537-548) and that the TLR3- or MDA5-induced production of IFNÃ_Â_ was greatly reduced in cells from mice in which Pellino1 had been replaced by an E3 ligase-inactive mutant (Enesa et al, 2012, J. Biol. Chem. 287,34825-34835). In the new paper the lab identified the transcription factor Deformed Epidermal Associated Factor 1 DEAF1 as a Pellino1-interacting protein and went on to show that IFNÃ_Â_ production induced by synthetic dsRNA or by infection with Sendai virus was greatly reduced in fibroblasts or macrophages from DEAF1 knock-out mice. Interestingly, they also found that the phosphorylation of Pellino1 induced its dissociation from DEAF1, that DEAF1 interacted with IRF3 and the related transcription factor IRF7, and that DEAF1 interacted with the same region of the IFNÃ_Â_ promoter as IRF3.
Although Pellino1 and DEAF1 were both known to be required for the production of the anti-bacterial peptides Drosomycin and Metchnikowin in Drosophila following bacterial infection of the fruit fly, the idea that these proteins might actually interact, or that DEAF1 might have a function in the mammalian innate immune system had not been considered previously. Instead, a number of other roles for DEAF1 have been identified in mammalian cells. For example, it has been linked to depression and suicide through its role in controlling the production of serotonin, and to diseases such as cancer and type1 diabetes.
The phosphorylation of Pellino1 induces its dissociation from DEAF1 in vitro, which may enable DEAF1 to translocate to the nucleus and control IFNÃ_Â_ gene transcription. Similar observations were made with an E3 ligase-inactive mutant of Pellino1, and no ubiquitylation of DEAF1 by Pellino1 could be detected in co-transfection experiments. The reversible interaction of Pellino1 and DEAF1 does not therefore explain why the E3 ligase activity of Pellino1 is needed for IFNÃ_Â_ production and further research is clearly needed to identify how the E3 ligase activity of Pellino1 regulates IFNÃ_Â_ production.
Double-stranded (ds) RNA, formed as an intermediate in the replication of some RNA viruses, activates the dsRNA receptors TLR3 and MDA5, which are located on the endosomal membranes and in the cytosol of host cells, respectively. The engagement of these receptors induces the activation of the protein kinase TBK1, which then phosphorylates the transcription factor IRF3. This stimulates the translocation of IRF3 to the nucleus, where it dimerises and activates the IFNÃ_Â_ promoter. In earlier papers, the Cohen lab had reported that TBK1 also phosphorylates and activates the E3 ubiquitin ligase Pellino1 (Smith et al, 2011, Biochem. J. 434, 537-548) and that the TLR3- or MDA5-induced production of IFNÃ_Â_ was greatly reduced in cells from mice in which Pellino1 had been replaced by an E3 ligase-inactive mutant (Enesa et al, 2012, J. Biol. Chem. 287,34825-34835). In the new paper the lab identified the transcription factor Deformed Epidermal Associated Factor 1 DEAF1 as a Pellino1-interacting protein and went on to show that IFNÃ_Â_ production induced by synthetic dsRNA or by infection with Sendai virus was greatly reduced in fibroblasts or macrophages from DEAF1 knock-out mice. Interestingly, they also found that the phosphorylation of Pellino1 induced its dissociation from DEAF1, that DEAF1 interacted with IRF3 and the related transcription factor IRF7, and that DEAF1 interacted with the same region of the IFNÃ_Â_ promoter as IRF3.
Although Pellino1 and DEAF1 were both known to be required for the production of the anti-bacterial peptides Drosomycin and Metchnikowin in Drosophila following bacterial infection of the fruit fly, the idea that these proteins might actually interact, or that DEAF1 might have a function in the mammalian innate immune system had not been considered previously. Instead, a number of other roles for DEAF1 have been identified in mammalian cells. For example, it has been linked to depression and suicide through its role in controlling the production of serotonin, and to diseases such as cancer and type1 diabetes.
The phosphorylation of Pellino1 induces its dissociation from DEAF1 in vitro, which may enable DEAF1 to translocate to the nucleus and control IFNÃ_Â_ gene transcription. Similar observations were made with an E3 ligase-inactive mutant of Pellino1, and no ubiquitylation of DEAF1 by Pellino1 could be detected in co-transfection experiments. The reversible interaction of Pellino1 and DEAF1 does not therefore explain why the E3 ligase activity of Pellino1 is needed for IFNÃ_Â_ production and further research is clearly needed to identify how the E3 ligase activity of Pellino1 regulates IFNÃ_Â_ production.