Meta-Biol

• Pathways

The role of IRAK1 kinase activity in the activation of NF-kappa-B by IL-1/TLR is still uncertain. It has been shown that a kinase-dead IRAK1 mutants can still activate NF-kappa-B. Furthermore, stimulation of IRAK1-deficient I1A 293 cells with LMP1 (latent membrane protein 1- a known viral activator of NF-kappa-B) leads to TRAF6 polyubiquitination and IKKbeta activation [Song et al 2006]. On the other hand, IRAK1 enhances p65 Ser536 phosphorylation [Song et al 2006] and p65 binding to the promoter of NF-kappa-B dependent target genes [Liu G et al 2008].

IRAK1 has also been shown to be itself Lys63-polyubiquitinated (probably by Pellino proteins, which have E3 ligase activity). Mutation of the ubiquitination sites on IRAK1 prevented interaction with the NEMO subunit of IKK complex and subsequent IL-1/TLR-induced NF-kappa-B activation [Conze et al 2008]. These data suggest that kinase activity of IRAK1 is not essential for its ability to activate NF-kappa-B, while its Lys63-polyubuquitination allows IRAK1 to bind NEMO thus facilitating association of TRAF6 and TAK1 complex with IKK complex followed by induction of NF-kappa-B.

Upon IL-1/TLR stimulation IRAK1 protein can undergo covalent modifications including phosphorylation [Kollewe et al 2004], ubiquitination [Conze DB et al 2008] and sumoylation [Huang et al 2004]. Depending upon the nature of its modification, IRAK1 may perform distinct functions including activation of IRF5/7 [Uematsu et al 2005, Schoenemeyer et al 2005], NF-kappa-B [Song et al 2006], and Stat1/3 [Huang et al 2004, Nguyen et al 2003].

Innate immunity encompases the nonspecific part of immunity tha are part of an individual's natural biologic makeup

Humans are exposed to millions of potential pathogens daily, through contact, ingestion, and inhalation. Our ability to avoid infection depends on the adaptive immune system and during the first critical hours and days of exposure to a new pathogen, our innate immune system.