A SNP identified as rs548234, which is found in PRDM1, the gene that encodes BLIMP1, is a risk allele associated with systemic lupus erythematosus (SLE). BLIMP1 expression was reported to be decreased in women with the PRDM1 rs548234 risk allele compared with women with the nonrisk allele in monocyte-derived DCs (MO-DCs). In this study, we demonstrate that BLIMP1 expression is regulated by the binding of Kruppel-like factor 4 (KLF4) to the risk SNP. KLF4 is highly expressed in MO-DCs but undetectable in B cells, consistent with the lack of altered expression of BLIMP1 in B cells from risk SNP carriers. Female rs548234 risk allele carriers, but not nonrisk allele carriers, exhibited decreased levels of BLIMP1 in MO-DCs, showing that the regulatory function of KLF4 is influenced by the risk allele. In addition, KLF4 directly recruits histone deacetylases (HDAC4, HDAC6, and HDAC7), established negative regulators of gene expression. Finally, the knock down of KLF4 expression reversed the inhibitory effects of the risk SNP on promoter activity and BLIMP1 expression. Therefore, the binding of KLF4 and the subsequent recruitment of HDACs represent a mechanism for reduced BLIMP1 expression in MO-DCs bearing the SLE risk allele rs548234.
Authors
Su Hwa Jang, Helen Chen, Peter K. Gregersen, Betty Diamond, Sun Jung Kim
(A) Diagram of reporter constructs containing genomic DNA (gDNA) (purple box). 100 bpgDNA (± 50 bp from SNP) from nonrisk allele (middle) or from risk allele (bottom; red arrowhead indicates risk allele) was inserted upstream of promoter region (P, blue box). (B and C) Each cell type was transfected with plasmid as indicated. Tk-Renilla with CMV promoter plasmid was cotransfected as a control. Cells were harvested 6 hours (MO-DC, THP-1, and Raji) or 48 hours (HEK293) after transfection, and luciferase level was measured. In the box-and-whisker plot, horizontal bars indicate the medians, boxes indicate 25th to 75th percentiles, and whiskers indicate 10th and 90th percentiles (n = 5). The nonparametric, Mann-Whitney test was used for statistics.