Identification of the protein kinases that activate the E3 ubiquitin ligase Pellino 1 in the innate immune system

• Main Authors: Goh, Eddy T. H., Arthur, J. Simon C., Cheung, Peter Ching For, Akira, Shizuo, Toth, Rachel, Cohen, Philip
• Other Authors: School of Biological Sciences
• Format: Article
• Language: English
• Published: 2013
• Subjects: DRNTU::Science::Biological sciences
• Online Access: https://hdl.handle.net/10356/98789; http://hdl.handle.net/10220/12739
• Institution: Nanyang Technological University

The E3 ubiquitin ligase Pellino 1 can be interconverted between inactive and active forms by a reversible phosphorylation mechanism. In vitro, phosphorylation and activation can be catalysed by either the IRAKs [IL (interleukin)-1-receptorassociated kinases] IRAK1 and IRAK4, or the IKK {IκB [inhibitor of NF-κB (nuclear factor κB)] kinase}-related kinases [IKKε andTBK1 (TANK{TRAF[TNF (tumour-necrosis-factor)- receptor-associated factor]-associated NF-κB activator}-binding kinase 1)]. In the present study we establish that IRAK1 is the major protein kinase that mediates the IL-1-stimulated activation of Pellino 1 in MEFs (mouse embryonic fibroblasts) or HEK (human embryonic kidney)-293 cells, whereas the IKK-related kinases activate Pellino 1 in TNFα-stimulated MEFs. The IKKrelated kinases are also the major protein kinases that activate Pellino 1 in response to TLR (Toll-like receptor) ligands that signal via the adaptors MyD88 (myeloid differentiation primary response gene 88) and/or TRIF [TIR (Toll/IL-1 receptor) domaincontaining adaptor protein inducing interferon β]. The present studies demonstrate that, surprisingly, the ligands that signal via MyD88 do not always employ the same protein kinase to activate Pellino 1. Our results also establish that neither the catalytic activity of IRAK1 nor the activation of Pellino 1 is required for the initial transient activation of NF-κB and MAPKs (mitogenactivated protein kinases) that is triggered by IL-1 or TNFα in MEFs, or by TLR ligands in macrophages. The activation of Pellino 1 provides the first direct readout for IRAK1 catalytic activity in cells.