151. Interleukin-1 receptor-associated kinase-1 (IRAK-1): A self-regulatory adapter molecule in the signaling cascade of the Toll/IL-1 receptor family
- Author
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Michael U. Martin and Christian Kollewe
- Subjects
Receptor complex ,Protein kinase domain ,Kinase ,Autophosphorylation ,Phosphorylation ,Cell Biology ,Biology ,Signal transduction ,Protein kinase A ,Molecular Biology ,Death domain ,Cell biology - Abstract
The human Interleukin-1 receptor-associated protein kinase IRAK-1 is a highly specific signaling molecule activated by the Toll/IL-1 receptor family. It is a multidomain protein consisting of an N-terminal death domain, a regulatory ProST (proline-, serine-, threonine-rich) region, a conventional serine/threonine protein kinase domain and a large C-terminal rest. IRAK-1 mediates between the active receptor complex and downstream signaling events such as activation of NFκB. This adapter function is guaranteed by protein interactions of the N-terminal death domain to MyD88 and of the C-terminus to TRAF6. The signaling function of IRAK-1 is independent of its enzymatic activity. The kinase domain and the ProST region serve as a self-activating kinetic switch module in IRAK-1. Two different phosphorylation events take place in a sequential fashion in IRAK-1. The first is an autophosphorylation of the kinase domain resulting in full enzymatic activity. This is followed by multiple phosphorylations in the ProST region. The introduction of negative charges adjacent to the death domain has two consequences: First hyperphosphorylated IRAK-1 dissociates from the upstream adapter MyD88 and thus leaves the active receptor complex allowing optimal interaction with the downstream adapter TRAF6. Second, hyperphosphorylated IRAK-1 is targeted to the proteasome where it is proteolytically degraded and thus removed out of the signaling chain. This self-limitation guarantees a transient IL-1 signal. This regulatory function is completely dispensable for IRAK-1's adapter function as a signaling molecule. In summary, IRAK-1 is a highly-sophisticated adapter molecule in the signaling pathway of the Toll/IL-1 receptor family which regulates its own availability as a signaling component by autophosphorylation and autoinduced proteolytical degradation (summarized in Fig. 1).
- Published
- 2001
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