Dataset Information

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.

SUBMITTER: Maiti AK

PROVIDER: S-EPMC4082363 | biostudies-literature | 2014 Aug

REPOSITORIES: biostudies-literature

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Combined protein- and nucleic acid-level effects of rs1143679 (R77H), a lupus-predisposing variant within ITGAM.

Maiti Amit K AK Kim-Howard Xana X Motghare Prasenjeet P Pradhan Vandana V Chua Kek Heng KH Sun Celi C Arango-Guerrero María Teresa MT Ghosh Kanjaksha K Niewold Timothy B TB Harley John B JB Anaya Juan-Manual JM Looger Loren L LL Nath Swapan K SK

Human molecular genetics 20140307 15

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 ancestr ...[more]

PMID: 24608226

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Project description:Multiple studies have demonstrated that single-nucleotide polymorphisms (SNPs) in the ITGAM locus (including the nonsynonymous SNPs rs1143679, rs1143678, and rs1143683) are associated with systemic lupus erythematosus (SLE). ITGAM encodes the protein CD11b, a subunit of the ?2 integrin Mac-1. The purpose of this study was to determine the effects of ITGAM genetic variation on the biologic functions of neutrophil Mac-1.Neutrophils from ITGAM-genotyped and -sequenced healthy donors were isolated for functional studies. The phagocytic capacity of neutrophil ITGAM variants was probed with complement-coated erythrocytes, serum-treated zymosan, heat-treated zymosan, and IgG-coated erythrocytes. The adhesion capacity of ITGAM variants, in adhering to either purified intercellular adhesion molecule 1 or tumor necrosis factor ?-stimulated endothelial cells, was assessed in a flow chamber. Expression levels of total CD11b and activation of CD11b were assessed by flow cytometry.Mac-1-mediated neutrophil phagocytosis, determined in cultures with 2 different complement-coated particles, was significantly reduced in individuals with nonsynonymous variant alleles of ITGAM. This reduction in phagocytosis was related to variation at either rs1143679 (in the ?-propeller region) or rs1143678/rs1143683 (highly linked SNPs in the cytoplasmic/calf-1 regions). Phagocytosis mediated by Fc? receptors was also significantly reduced in donors with variant ITGAM alleles. Similarly, firm adhesion of neutrophils was significantly reduced in individuals with variant ITGAM alleles. These functional alterations were not attributable to differences in total receptor expression or activation.The nonsynonymous ITGAM variants rs1143679 and rs1143678/rs113683 contribute to altered Mac-1 function on neutrophils. These results underscore the need to consider multiple nonsynonymous SNPs when assessing the functional consequences of ITGAM variation on immune cell processes and the risk of SLE.

Dataset Information

Combined protein- and nucleic acid-level effects of rs1143679 (R77H), a lupus-predisposing variant within ITGAM.

Publications

Combined protein- and nucleic acid-level effects of rs1143679 (R77H), a lupus-predisposing variant within ITGAM.

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