SLE-Associated rs2295613(A) Allele Strengthens a Predicted c-MYC Motif and Enhances SLAMF1 Promoter Reporter Activity in B Cells

SLAMF1 encodes CD150, an immunoregulatory receptor involved in lymphocyte activation, T–B-cell interactions, and humoral immune responses. The SLAMF1 promoter polymorphism rs2295613(G>A) was previously associated with systemic lupus erythematosus (SLE) susceptibility in a Chinese case–control cohort. Here, we investigated the regulatory activity of rs2295613 in the transformed B-cell lines Raji and MP1 and in primary human CD19+ B cells. The rs2295613(A)-containing reporter showed higher promoter activity than the rs2295613(G)-containing reporter in all three cellular systems. Bioinformatic analysis predicted that the G to A substitution strengthens a pre-existing MYC-compatible motif. Substitutions disrupting the motif-containing region attenuated the rs2295613(A)-associated increase in reporter activity and reduced enrichment of the promoter fragment in anti-c-MYC DNA pull-down assays. Partial siRNA-mediated reduction in MYC mRNA also decreased the activity of the rs2295613(A)-containing reporter in Raji cells. Together, these findings identify rs2295613 as a functional SLAMF1 promoter variant in B-cell reporter systems and support a contribution of c-MYC-associated regulation to the enhanced activity of the rs2295613(A)-containing promoter.