p-IRF3 dimer:PIN1 p-IRF3:p-IRF3 Interaction of PIN1 with p-IRF3 Authored: Garapati, P V, 2010-08-02 Edited: Garapati, P V, 2010-08-02 Pubmed16699525 Pubmed16715065 Pubmed19125153 Reactome Database ID Release 43936380 Reactome, http://www.reactome.org ReactomeREACT_25077 Reviewed: Kawai, T, Akira, S, 2010-10-30 Two cluster of serine residues in the C-terminus of IRF3 are essential for its activation. Cluster 1, comprising Ser385 and Ser386, is essential for the formation of IRF3 dimers. The second cluster include a series of serine and threonine residues between Ser396 and Ser405. Phosphorylation of residues in both clusters has been noted in response to virus infection and dsRNA treatment, and the IKKi/TBK1 kinase complex has been shown to phosphorylate both clusters. <br>Yamaoka et al has shown that IRF3 is also phosphorylated on Ser339 after dsRNA stimulation, however this phosphorylation is associated with destabilization rather than activation of IRF3. This Ser339 precedes a proline residue 340 (Pro340) and this serine-proline motif acts as a binding site for the protein PIN1, a peptidyl-prolyl-isomerase. PIN1 consist of two distinct domains, a short N-terminal WW domain and a C-terminal catalytic domain. The WW domain of PIN1 is involved in binding the ser339-pro340 region. Yamaoka et al showed that exogenous expression of PIN1 suppresses IRF3 activation and type I interferon production and, conversely, that siRNA silencing of PIN1 leads to enhancement of IRF3 activation and IFNB production.