Complement receptor 2 polymorphisms associated with systemic lupus erythematosus modulate alternative splicing

Abstract

Genetic factors influence susceptibility to systemic lupus erythematosus (SLE). A recent family-based analysis in Caucasian and Chinese populations provided evidence for association of single-nucleotide polymorphisms (SNPs) in the complement receptor 2 (CR2/CD21) gene with SLE. Here we confirmed this result in a case-control analysis of an independent European-derived population including 2084 patients with SLE and 2853 healthy controls. A haplotype formed by the minor alleles of three CR2 SNPs (rs1048971, rs17615, rs4308977) showed significant association with decreased risk of SLE (30.4% in cases vs. 32.6% in controls, P = 0.016, OR = 0.90 [0.82-0.98]). Two of these SNPs are in exon 10, directly 5′ of an alternatively spliced exon preferentially expressed in follicular dendritic cells (FDC), and the third is in the alternatively spliced exon. Effects of these SNPs as well as a fourth SNP in exon 11 (rs17616) on alternative splicing were evaluated. We found that the minor alleles of these SNPs decreased splicing efficiency of exon 11 both in vitro and ex vivo. These findings further implicate CR2 in the pathogenesis of SLE and suggest that CR2 variants alter the maintenance of tolerance and autoantibody production in the secondary lymphoid tissues where B cells and FDCs interact.

Expression of complement receptors 1 (CR1/CD35) and 2 (CR2/CD21), and co-signaling molecule CD19 in cattle

“…Cattle encoded CR1 and CR2 by alternative splicing of a single gene as is observed in mice Molina et al, 1990). Cattle also alternatively spliced an exon encoding the 16 th CCP domain, which corresponds to the alternatively spliced CCP 10a domain in humans (Braun et al, 1998;Douglas et al, 2009;Ilges et al, 1997;Liu et al, 1997). As the human Cr2 gene has lost the ability to encode CR1 domains (Holguin et al, 1990;Jacobson & Weis, 2008) and mice appear to have lost the ability to encode the alternatively spliced CCP 10a domain, it is likely that cattle have a more phylogenetically ancient Cr2 gene.…”

“…However, mRNA transcripts of both the long and short sub--isoforms have been detected in peripheral blood cells (Braun et al, 1998;Douglas et al, 2009) and in lymphoid tissues where both sub--isoforms were expressed in what appears to be equal proportions (Ilges et al, 1997). Only the short form of CR2 has been detected in mice (Accession: NP_031784, Validated Reference Sequence).…”

“…Support for functional differences has been found in studies of single nucleotide polymorphisms (SNPs) in the Cr2 gene that are associated with an increased risk of systemic lupus erythematosus (SLE). Two of these SNPs decreased inclusion of the 11 th exon (corresponding to the 16 th CCP domain in cattle) in Cr2 mRNA transcripts (Douglas et al, 2009). It has been suggested that this domain may play a role in activation--induced ectodomain shedding (Ling et al, 1998;Masilamani et al, 2003) Many transmembrane proteins, including those associated with signaling in lymphocytes, undergo ectodomain shedding wherein the extracellular region of a transmembrane protein is cleaved by plasma or membrane proteases (reviewed in Dello Sbarba et al, 2002).…”

“…Ectodomain shedding generates soluble receptors, resulting in down--modulation of ligand dependent cell signaling by reducing the density of membrane bound receptors and removing potential ligands from the surrounding environment. Soluble CR2 (sCR2) has been found in serum and plasma from healthy humans (Douglas et al, 2009;Ling et al, 1998;Masilamani et al, 2003;Masilamani et al, 2004a); decreased plasma concentration of sCR2 has been associated with rheumatoid arthritis, SLE, Sjögren's syndrome and pregnancy (Masilamani et al, 2004a;Masilamani et al, 2004b;Masilamani et al, 2008). sCR2 is not a product of an alternatively spliced mRNA transcript that lacks the transmembrane domain (Illges et al, 1997); it is derived from cleavage of the membrane protein's extracellular domains (Frémeaux--Bacchi et al, 1996;Masilamani et al, 2003) through proteolysis by matrix metalloproteases (Aichem et al, 2006).…”

Autoimmune Diseases: The Role of Environment and Gene Interactions

“…Cr2 polymorphism that function to encode the complement receptor type 2, a B-cell co-receptor known to contribute to the Sle1c1 phenotypes (Boackle et al, 2001;Chen et al, 2005b). SLE patients do carry a common CR2 haplotype more frequently than in healthy controls; and follicular dendritic cells (FDC) express a novel CR2 splice variants of SLE patients (Douglas et al, 2009;Wu et al, 2007). Sle1b corresponds to polymorphisms in four signaling lymphocytic activation molecule (SLAM) family member genes (Wandstrat et al, 2004), including Ly108 directly implicated in the regulation of B-cell tolerance (Kumar et al, 2006).…”