A polymorphism in the upstream regulatory region of the interleukin-1α gene confers differential binding by transcription factors of the AP-1 family

AimsPrevious genetic studies have shown that a C/T polymorphism at position − 889 of the IL1A promoter, specifically allele 2 (− 889 T), increases the risk for development of several inflammation-related disorders, such as periodontitis, osteomyelitis, toxoplasmic retinochoroiditis, contact dermatitis, as well as neurodegenerative conditions such as Alzheimer's disease. We sought to determine the differential abilities of C- and T- containing versions of the − 889 sequence to bind nuclear proteins from microglia.Main methodsMicroglial cells were subjected to inflammatory activation prior to the harvest of nuclear proteins. Electrophoretic mobility shift assays (EMSA) were performed using oligonucleotide probes representing 25 base pairs surrounding the IL1A − 889 polymorphism. Antibodies reactive against transcription factors were used to identify the specific proteins involved in complexes with DNA.Key findingsEMSA revealed multiple differences in DNA-binding profiles when microglial nuclear extracts were incubated with the polymorphic probes. The allele-2 probe formed specific complexes that were not detected with the allele-1 (− 889 C) probe, and vice versa. Formation of allele-2 nucleoprotein complexes was increased in activated microglia. Antibody supershift analysis indicated that multiple Jun-family members but not Fos-family proteins contributed to the LPS-activated allele-2 EMSA complexes. LPS-activation of allele-2 EMSA complexes could be blocked by the specific c-Jun N-terminal kinase (JNK) inhibitor SP600125.SignificanceThese results suggest that the − 889 polymorphism creates differential interactions with transcription factors that could lead to differential expression rates under proinflammatory conditions.