A promoter polymorphism in the central MHC gene, IKBL, influences the binding of transcription factors USF1 and E47 on disease-associated haplotypes.
The human major histocompatibility complex (MHC) contains genes that affect susceptibility to numerous immunopathological diseases. We propose that genes in the central MHC between TNFA and HLA-B explain associations between the 8.1 haplotype (HLA-A1, B8, DR3) and disease. IKBL encodes a protein resembling members of the IkappaB protein family that regulate bioavailability of NFkappaB. We have identified two polymorphisms in the 500 bp upstream of the transcription start site of IKBL that distinguish the 8.1 haplotype from the resistant 7.1 haplotype (HLA-A3, B7, DR15). A single nucleotide polymorphism at -62 disrupts a putative E-box binding sequence. To investigate binding of transcription factors in vitro, we exposed 32P-labeled DNA fragments carrying both alleles to nuclear extracts, showing allele-specific binding of nuclear proteins from Jurkat cells but not from other lineages. Supershift studies using Jurkat nuclear extract showed that the E-box protein, E47, and ubiquitously expressed transcription factor USF1 bind to the E-box element of the 7.1 haplotype. Transient transfections of luciferase reporter constructs carrying promoter alleles of IKBL into Jurkat cells showed an effect of IKBL-62 alleles. In contrast, alleles at -421 did not affect transcription factor binding or transcription. IKBL was expressed at low levels in Jurkat cells but not in blood mononuclear cells, and expression declined following mitogenic stimulation. The restriction of IKBL expression to Jurkat cells is consistent with evidence that E47 is expressed in thymocytes and suggests IKBL may affect autoimmunity through an effect on T-cell selection.
University of Mauritius, Reduit, Mauritius, Western Australia.
Alvin
A
Boodhoo
Agnes M L
AM
Wong
David
D
Williamson
Dominic
D
Voon
Silvia
S
Lee
Richard J N
RJ
Allcock
Patricia
P
Price
D048868:Adaptor Proteins, Signal Transducing; D000483:Alleles; D001483:Base Sequence; D002467:Cell Nucleus / Q000235:genetics; D002478:Cells, Cultured; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D005786:Gene Expression Regulation; D008040:Genetic Linkage; D020022:Genetic Predisposition to Disease; D006239:Haplotypes; D006367:HeLa Cells; D000949:Histocompatibility Antigens Class II / Q000235:genetics*; D006801:Humans; D019169:Jurkat Cells; D007700:Kinetics; D009687:Nuclear Proteins / Q000378:metabolism; D009841:Oligonucleotides / Q000235:genetics; D011110:Polymorphism, Genetic; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D051820:TCF Transcription Factors; D058125:Transcription Factor 7-Like 1 Protein; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D051720:Upstream Stimulatory Factors
D048868:Adaptor Proteins, Signal Transducing; D004268:DNA-Binding Proteins; D000949:Histocompatibility Antigens Class II; C120111:NFKBIL1 protein, human; D009687:Nuclear Proteins; D009841:Oligonucleotides; D051820:TCF Transcription Factors; C544912:TCF7L1 protein, human; D058125:Transcription Factor 7-Like 1 Protein; D014157:Transcription Factors; C497181:USF1 protein, human; D051720:Upstream Stimulatory Factors