IRAK2 (Interleukin-1 Receptor-Associated Kinase 2) is a serine/threonine protein kinase that plays a critical role in Toll-like receptor (TLR) and interleukin-1 receptor (IL-1R) signaling pathways. It is primarily involved in the innate immune response and neuroinflammation, making it a highly relevant target in neurodegenerative disease research. Unlike IRAK1 and IRAK4, IRAK2 has relatively weak intrinsic kinase activity and functions more as a scaffolding protein that stabilizes the signaling complex while also contributing to downstream activation. @flannagan2012
Gene Information
Function
TLR/IL-1R Signaling Cascade
IRAK2 is a key mediator in the TLR/IL-1R signaling cascade:
Receptor activation: Upon TLR or IL-1R activation by pathogen-associated molecular patterns (PAMPs) or damage-associated molecular patterns (DAMPs), IRAK2 is recruited to the receptor complex through interactions with MYD88 adaptor protein
Complex formation: IRAK2 forms a complex with IRAK4 and MYD88 at the activated receptor
IRAK4 phosphorylation: IRAK4 phosphorylates IRAK2 on threonine residues
Downstream signaling: Phosphorylated IRAK2 activates TRAF6, leading to NF-κB and MAPK activation
NF-κB activation: The IRAK2/TRAF6 pathway leads to IKK activation and NF-κB nuclear translocation
MAPK activation: IRAK2 also contributes to MAPK (p38, JNK, ERK) signaling pathways
Inflammatory gene expression: The TLR/IRAK2 pathway drives transcription of pro-inflammatory cytokines including TNF-α, IL-1β, IL-6, and IL-8 @gottipati2008
Kinase Activity
Unlike IRAK1 and IRAK4 which have robust kinase activity, IRAK2 has relatively weak intrinsic kinase activity:
Residual kinase activity: Low but detectable autophosphorylation capability
Scaffolding function: Primary role is as a scaffold for complex assembly
Activation loop: Contains an activation loop that can be phosphorylated
Death domain: Contains an N-terminal death domain for protein-protein interactions @kawagoe2009
Substrate Specificity
IRAK2 phosphorylates several downstream substrates:
TRAF6: Primary substrate, activation of E3 ubiquitin ligase activity
TAB proteins: TAK1 complex activation
IRAK1: Cross-phosphorylation
Disease Associations
Alzheimer's Disease
IRAK2 is strongly implicated in Alzheimer's disease through neuroinflammation:
Elevated expression: IRAK2 expression is significantly elevated in AD brain tissue, particularly in microglia surrounding amyloid plaques
Amyloid response: IRAK2 is activated by amyloid-beta through TLR4 and CD14
Genetic association: Genetic variants in IRAK2 have been associated with increased AD risk in some population studies
Tau pathology: IRAK2-mediated neuroinflammation contributes to tau pathology progression
Therapeutic targeting: IRAK2 is being explored as a therapeutic target to reduce chronic neuroinflammation in AD @genetic2022