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 amissense polymorphism, rs1143679 (R77H), strongly associated with systemic lupus erythematosus (SLE). However, the molecularmechanismsof this variant are incompletely understood. Ameta-analysis of publishedandnovel 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) 5 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 inmonocytes from patients with each rs1143679 genotype.Weobserved that transcript levels significantly decreased for the risk allele ('A') relative to the non-risk allele ('G'), in a dose-dependent fashion: ('AA' < 'AG'