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.
Su Hwa Jang, Helen Chen, Peter K. Gregersen, Betty Diamond, Sun Jung Kim
Frequencies and the level of PRDM1 expression of blood CD14+ monocytes (A) and total B cells (B) from leukocytes prepared from female or male individuals with nonrisk (T/T) or risk (C/C) allele. CD14+ monocytes were cultured with granulocyte-macrophage colony-stimulating factor (GM-CSF) and IL-4 for 7 days for the generation of MO-DCs. MO-DCs and freshly isolated total B cells were further processed for total RNA preparation and qPCR for BLIMP1 expression. Relative expression of BLIMP1 was normalized to the level of housekeeping gene, POLR2A. Each dot represents an individual sample, and the bar represents the mean ± SEM (n = 5). (C) BLIMP1 (also known as PRDM1) expression was compared in DC subsets in human blood. Human blood DCs (cDC: Lin–CD11c+CD123–BDCA2–; pDC: Lin–CD11c–CD123hiBDCA2+; BDCA3 DC: Lin–CD11c+CD123–BDCA2–CD141+) and MO-DCs were purified and total RNAs were extracted. qPCR was performed, and the relative level of BLIMP1 was normalized to the level of the housekeeping gene. Each dot represents an individual sample, and the bar represents the mean ± SEM (n = 4). (D) The level of ATG5 was compared in MO-DCs from female nonrisk (T/T) or risk (C/C) carriers. Relative expression was normalized to the level of the housekeeping gene. Each dot represents an individual sample, and the bar represents the mean ± SEM (n = 5). The nonparametric, Mann-Whitney test was used for statistics.