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Abstract

Toll-like receptors (TLR) play an essential role in innate immunity, in which they indentify invasive pathogens and initiate the immune responses to eliminate the pathogens. Interleukine-1receptor-associated kinases are key kinases in the TLR signalling pathway where they integrate signals from activated receptor complexes to then induce the activation of downstream transcription factors NF-κB, AP-1 and IRFs. It is known that IRAK4 deficiency in humans is related with recurrent pyogenic bacterial infections which can be lethal without any facilitation of health care and antibiotics. In light of this fact, this study focuses on analysing the general role of IRAK2 on the pathogenesis of certain kinds of diseases. Known non-synonymous single nucleotide polymorphisms (SNPs) of IRAK2 were selected from the NCBI SNP database, which served as probes to gain insights of the molecular functions of IRAK2. The SNPs of interest were screened by overexpressing the constructs of variants into a human cell line and detecting the activation of NF-κB. IRAK2 R214G and L392V decreased the activation of NF-κB and the production of IL-8. Although R214G and L392V varied the interaction intensity with IRAK2 and IRAK4, these two variants still maintained the interaction with the downstream signalling partner TRAF6. Interestingly, IRAK2 R214G and L392V both reduced the ubiquitination levels of TRAF6. The ubiquitination of TRAF6 is an essential step for the NF-κB activation. Moreover, when stimulating human IRAK2 WT reconstituted murine Irak2 knockout macrophages with TLR2, 4 and 7 ligands, the TNF-α production was massively enhanced. Meanwhile, phosphorylation of p38, p65, ERK was enhanced as well. Intriguingly, the phosphorylation of Akt was only observed in the IRAK2 WT reconstituted macrophages. Additionally, the R214G and L392V reconstituted macrophages reduced the transcriptional activation of Il-1β and Il-6 in comparison to IRAK2 WT. The epidemiological analyses revealed that IRAK2 R214G (rs35060588) reduced the survival time of colorectal cancer patients; IRAK2 L392V (rs3855283) significantly reduced the auto clearance of HCV in patients who are then susceptible to become a chronic HCV infection; additionally L392V also increased the possibility of progression from gastritis to gastric cancer. Collectively, this information would be helpful for the future personalized therapy.