Cr2, a Candidate Gene in the Murine Sle1c Lupus Susceptibility Locus, Encodes a Dysfunctional Protein

Abstract

The major murine systemic lupus erythematosus (SLE) susceptibility locus, Sle1, corresponds to three loci independently affecting loss of tolerance to chromatin in the NZM2410 mouse. The congenic interval corresponding to Sle1c contains Cr2, which encodes complement receptors 1 and 2 (CR1/CR2, CD35/CD21). NZM2410/NZW Cr2 exhibits a single nucleotide polymorphism that introduces a novel glycosylation site, resulting in higher molecular weight proteins. This polymorphism, located in the C3d binding domain, reduces ligand binding and receptor-mediated cell signaling. Molecular modeling based on the recently solved CR2 structure in complex with C3d reveals that this glycosylation interferes with receptor dimerization. These data demonstrate a functionally significant phenotype for the NZM2410 Cr2 allele and strongly support its role as a lupus susceptibility gene.

Augmentation of NZB Autoimmune Phenotypes by the Sle1c Murine Lupus Susceptibility Interval

“…8, C and D) or intermediate (tetramers containing a higher dose of biotinylated anti-sIgM; data not shown) anti-sIgM stimulus was used to crosslink the BCR alone, B cells from both strains responded similarly in the numbers of cells responding and the amplitude of the response. These findings were similar to those demonstrated previously for the parental B6 and B6.Sle1c strains (10). To ensure that the decreased signaling mediated by CD35/CD21 was not due to altered expression of CD35/CD21 on (NZB ϫ B6.Sle1c)F 1 B cells, the binding of mAbs to CD35 (8C12; Fig.…”

“…There are several potential candidate genes for lupus susceptibility in these latter two regions, including a cluster of four novel genes containing fibronectin type III domain fragments and the protein tyrosine phosphatase Ptpn14 (also known as PTP36). We have already identified Cr2 to be a strong candidate gene for lupus susceptibility in the Sle1c interval based on the presence of a single nucleotide polymorphism in the ligand binding domain of CD21, which introduces a novel N-linked glycosylation site and results in decreased binding of C3d ligands and impaired B cell signaling (10). Furthermore, we have found that the NZW complement receptor-related gene Y (Crry), which lies within 10 kb of Cr2 in the Sle1c interval and encodes a potent complement regulatory protein in mice (22), has alterations in its structure and function (S. N. Tchepeleva and S. A. Boackle, unpublished data).…”

“…We have previously identified Cr2, which encodes complement receptors (CR) 1 and 2 (CR1/CR2, CD35/ CD21) in the mouse, to be a strong candidate gene for lupus susceptibility in this interval based on structural and functional alterations in its protein products (10). The primary autoimmune phenotype of congenic mice containing the Sle1c interval on a C57BL/6 (B6) background is a loss of tolerance to chromatin, resulting in the production of autoantibodies specific for chromatin.…”

“…cDNA was generated by reverse transcription using random hexamers (Applied Biosystems), and PCR products were generated from cDNA using primer sets described previously (10). PCR, performed in a GeneAmp PCR System 9700 (Applied Biosystems), generally used touchdown PCR cycling parameters (94°C for 2 min, 20 cycles of 94°C for 30 s, 65°C to 55°C for 30 s, and 72°C for 1 min, followed by 15 cycles of 94°C for 30 s, 55°C for 30 s, 72°C for 1 min, and then 72°C for10 min).…”

“…We had previously demonstrated that NZB shared the NZW allele for the single-nucleotide polymorphism identified at nucleotide 1700 in the Cr2 gene, based on restriction fragment length polymorphism analysis (10). To evaluate whether the NZB Cr2 gene contained other polymorphisms that might affect the function of its gene products, we determined the sequence of the coding region for the entire NZB Cr2 gene.…”