title: Combined protein- and nucleic acid-level effects of rs1143679 (R77H), a lupus-predisposing variant within ITGAM.
abstract: Integrin alpha M (ITGAM; CD11b) is a component of the macrophage-1 antigen complex, which mediates leukocyte adhesion, migration and phagocytosis as part of the immune system. We previously identified a missense polymorphism, rs1143679 (R77H), strongly associated with systemic lupus erythematosus (SLE). However, the molecular mechanisms of this variant are incompletely understood. A meta-analysis of published and novel data on 28 439 individuals with European, African, Hispanic and Asian ancestries reinforces genetic association between rs1143679 and SLE [Pmeta = 3.60 × 10(-90), odds ratio (OR) = 1.76]. Since rs1143679 is in the most active region of chromatin regulation and transcription factor binding in ITGAM, we quantitated ITGAM RNA and surface protein levels in monocytes from patients with each rs1143679 genotype. We observed that transcript levels significantly decreased for the risk allele ('A') relative to the non-risk allele ('G'), in a dose-dependent fashion: ('AA' < 'AG' < 'GG'). CD11b protein levels in patients' monocytes were directly correlated with RNA levels. Strikingly, heterozygous individuals express much lower (average 10- to 15-fold reduction) amounts of the 'A' transcript than 'G' transcript. We found that the non-risk sequence surrounding rs1143679 exhibits transcriptional enhancer activity in vivo and binds to Ku70/80, NFKB1 and EBF1 in vitro, functions that are significantly reduced with the risk allele. Mutant CD11b protein shows significantly reduced binding to fibrinogen and vitronectin, relative to non-risk, both in purified protein and in cellular models. This two-pronged contribution (nucleic acid- and protein-level) of the rs1143679 risk allele to decreasing ITGAM activity provides insight into the molecular mechanisms of its potent association with SLE.
authors.affiliation: Arthritis and Clinical Immunology Research Program, Oklahoma Medical Research Foundation, Oklahoma City, OK, USA.
authors.forename: Amit K
authors.initials: AK
authors.lastname: Maiti
authors.affiliation: Arthritis and Clinical Immunology Research Program, Oklahoma Medical Research Foundation, Oklahoma City, OK, USA.
authors.forename: Xana
authors.initials: X
authors.lastname: Kim-Howard
authors.affiliation: Arthritis and Clinical Immunology Research Program, Oklahoma Medical Research Foundation, Oklahoma City, OK, USA.
authors.forename: Prasenjeet
authors.initials: P
authors.lastname: Motghare
authors.affiliation: National Institute of Immunohematology, Mumbai, India.
authors.forename: Vandana
authors.initials: V
authors.lastname: Pradhan
authors.affiliation: Department of Biomedical Science, University of Malaya, Kuala Lumpur, Malaysia.
authors.forename: Kek Heng
authors.initials: KH
authors.lastname: Chua
authors.affiliation: Arthritis and Clinical Immunology Research Program, Oklahoma Medical Research Foundation, Oklahoma City, OK, USA.
authors.forename: Celi
authors.initials: C
authors.lastname: Sun
authors.affiliation: Center for Autoimmune Diseases Research (CREA), School of Medicine and Health Sciences, Universidad del Rosario, Bogotá, Colombia.
authors.forename: María Teresa
authors.initials: MT
authors.lastname: Arango-Guerrero
authors.affiliation: National Institute of Immunohematology, Mumbai, India.
authors.forename: Kanjaksha
authors.initials: K
authors.lastname: Ghosh
authors.affiliation: Division of Rheumatology and Department of Immunology, Mayo Clinic, Rochester, MN, USA.
authors.forename: Timothy B
authors.initials: TB
authors.lastname: Niewold
authors.affiliation: Cincinnati Children's Hospital Medical Center and the US Department of Veterans Affairs Medical Center, Cincinnati, OH, USA.
authors.forename: John B
authors.initials: JB
authors.lastname: Harley
authors.affiliation: Center for Autoimmune Diseases Research (CREA), School of Medicine and Health Sciences, Universidad del Rosario, Bogotá, Colombia.
authors.forename: Juan-Manual
authors.initials: JM
authors.lastname: Anaya
authors.affiliation: Howard Hughes Medical Institute, Janelia Farm Research Campus, Ashburn, VA, USA.
authors.forename: Loren L
authors.initials: LL
authors.lastname: Looger
authors.affiliation: Arthritis and Clinical Immunology Research Program, Oklahoma Medical Research Foundation, Oklahoma City, OK, USA swapan-nath@omrf.org.
authors.forename: Swapan K
authors.initials: SK
authors.lastname: Nath
mesh_terms: D000483:Alleles; D034961:Antigens, Nuclear / Q000235:genetics / Q000378:metabolism; D039481:CD11b Antigen / Q000235:genetics* / Q000378:metabolism; D002843:Chromatin / Q000378:metabolism / Q000473:pathology; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D005260:Female; D005340:Fibrinogen / Q000235:genetics / Q000378:metabolism; D005786:Gene Expression Regulation; D005787:Gene Frequency; D020022:Genetic Predisposition to Disease; D006801:Humans; D000072200:Ku Autoantigen; D008180:Lupus Erythematosus, Systemic / Q000208:ethnology / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D008297:Male; D009000:Monocytes / Q000378:metabolism* / Q000473:pathology; D052002:NF-kappa B p50 Subunit / Q000235:genetics / Q000378:metabolism; D016017:Odds Ratio; D011110:Polymorphism, Genetic; D011485:Protein Binding; D012333:RNA, Messenger / Q000235:genetics* / Q000378:metabolism; D044469:Racial Groups; D012306:Risk; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism; D014158:Transcription, Genetic; D019096:Vitronectin / Q000235:genetics / Q000378:metabolism
chemical_list: D034961:Antigens, Nuclear; D039481:CD11b Antigen; D002843:Chromatin; D004268:DNA-Binding Proteins; C081976:EBF1 protein, human; C509295:ITGAM protein, human; D052002:NF-kappa B p50 Subunit; C489548:NFKB1 protein, human; D012333:RNA, Messenger; D015534:Trans-Activators; D019096:Vitronectin; D005340:Fibrinogen; C000606509:Xrcc6 protein, human; D000072200:Ku Autoantigen