title: Sequence variation in promoter of Ica1 gene, which encodes protein implicated in type 1 diabetes, causes transcription factor autoimmune regulator (AIRE) to increase its binding and down-regulate expression.
abstract: ICA69 (islet cell autoantigen 69 kDa) is a protein implicated in type 1 diabetes mellitus in both the non-obese diabetic (NOD) mouse model and humans. ICA69 is encoded by the Ica1 gene on mouse chromosome 6 A1-A2. We previously reported reduced ICA69 expression in the thymus of NOD mice compared with thymus of several non-diabetic mouse strains. We propose that reduced thymic ICA69 expression could result from variations in transcriptional regulation of the gene and that polymorphisms within the Ica1 core promoter may partially determine this transcriptional variability. We characterized the functional promoter of Ica1 in NOD mice and compared it with the corresponding portions of Ica1 in non-diabetic C57BL/6 mice. Luciferase reporter constructs demonstrated that the NOD Ica1 promoter region exhibited markedly reduced luciferase expression in transiently transfected medullary thymus epithelial (mTEC(+)) and B-cell (M12)-derived cell lines. However, in a non-diabetic strain, C57BL/6, the Ica1 promoter region was transcriptionally active when transiently transfected into the same cell lines. We concomitantly identified five single nucleotide polymorphisms within the NOD Ica1 promoter. One of these single nucleotide polymorphisms increases the binding affinity for the transcription factor AIRE (autoimmune regulator), which is highly expressed in thymic epithelial cells, where it is known to play a key role regulating self-antigen expression. We conclude that polymorphisms within the NOD Ica1 core promoter may determine AIRE-mediated down-regulation of ICA69 expression in medullary thymic epithelial cells, thus providing a novel mechanistic explanation for the loss of immunologic tolerance to this self-antigen in autoimmunity.
authors.affiliation: Laboratory of Immunogenetics, Brehm Center for Diabetes Research, Department of Internal Medicine, University of Michigan Medical School, Ann Arbor, Michigan 48105.
authors.forename: Samantha M
authors.initials: SM
authors.lastname: Bonner
authors.affiliation: Laboratory of Immunogenetics, Brehm Center for Diabetes Research, Department of Internal Medicine, University of Michigan Medical School, Ann Arbor, Michigan 48105.
authors.forename: Susan L
authors.initials: SL
authors.lastname: Pietropaolo
authors.affiliation: Division of Immunogenetics, Department of Pediatrics, Rangos Research Center, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15224.
authors.forename: Yong
authors.initials: Y
authors.lastname: Fan
authors.affiliation: Laboratory of Immunogenetics, Brehm Center for Diabetes Research, Department of Internal Medicine, University of Michigan Medical School, Ann Arbor, Michigan 48105.
authors.forename: Yigang
authors.initials: Y
authors.lastname: Chang
authors.affiliation: Department of Genetics, University of North Carolina, Chapel Hill, North Carolina 27599.
authors.forename: Praveen
authors.initials: P
authors.lastname: Sethupathy
authors.affiliation: Laboratory of Immunogenetics, Brehm Center for Diabetes Research, Department of Internal Medicine, University of Michigan Medical School, Ann Arbor, Michigan 48105.
authors.forename: Michael P
authors.initials: MP
authors.lastname: Morran
authors.affiliation: Laboratory of Immunogenetics, Brehm Center for Diabetes Research, Department of Internal Medicine, University of Michigan Medical School, Ann Arbor, Michigan 48105.
authors.forename: Megan
authors.initials: M
authors.lastname: Beems
authors.affiliation: Division of Immunogenetics, Department of Pediatrics, Rangos Research Center, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15224; Department of Pathology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15213.
authors.forename: Nick
authors.initials: N
authors.lastname: Giannoukakis
authors.affiliation: Department of Pathology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15213.
authors.forename: Giuliana
authors.initials: G
authors.lastname: Trucco
authors.affiliation: Endocrine Genetics Laboratory, Montreal Children Hospital-Research Institute, McGill University Health Center, Montreal, Quebec H3H 1P3, Canada.
authors.forename: Michael O
authors.initials: MO
authors.lastname: Palumbo
authors.affiliation: Department of Molecular Diabetology, Paul Langerhans Institute Dresden, Carl Gustav Carus School of Medicine, Dresden University of Technology, 01307 Dresden, Germany.
authors.forename: Michele
authors.initials: M
authors.lastname: Solimena
authors.affiliation: Immunogenetics Program, Diabetes Research Institute, Department of Medicine, Division of Endocrinology, Diabetes and Metabolism, Miller School of Medicine, University of Miami, Miami, Florida 33136.
authors.forename: Alberto
authors.initials: A
authors.lastname: Pugliese
authors.affiliation: Endocrine Genetics Laboratory, Montreal Children Hospital-Research Institute, McGill University Health Center, Montreal, Quebec H3H 1P3, Canada.
authors.forename: Constantin
authors.initials: C
authors.lastname: Polychronakos
authors.affiliation: Division of Immunogenetics, Department of Pediatrics, Rangos Research Center, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15224.
authors.forename: Massimo
authors.initials: M
authors.lastname: Trucco
authors.affiliation: Laboratory of Immunogenetics, Brehm Center for Diabetes Research, Department of Internal Medicine, University of Michigan Medical School, Ann Arbor, Michigan 48105. Electronic address: maxtp@umich.edu.
authors.forename: Massimo
authors.initials: M
authors.lastname: Pietropaolo
mesh_terms: D000818:Animals; D001324:Autoantigens / Q000096:biosynthesis* / Q000235:genetics; D002460:Cell Line; D003922:Diabetes Mellitus, Type 1 / Q000235:genetics / Q000378:metabolism*; D015536:Down-Regulation; D006801:Humans; D051379:Mice; D016688:Mice, Inbred NOD; D020641:Polymorphism, Single Nucleotide; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic; D000096927:AIRE Protein
chemical_list: D001324:Autoantigens; D014157:Transcription Factors; D000096927:AIRE Protein; C087054:ICA1 protein, human; C490184:Ica1 protein, mouse