The Transcription Factors PU.1 and IRF4 Determine Dendritic Cell-Specific Expression of RALDH2.

RALDH2 expressed in dendritic cells (DCs) plays a critical role in the development of regulatory T cells in mesenteric lymph nodes. Despite the importance of RALDH2 in intestinal immunity, little is known about the mechanism of DC-specific expression of RALDH2. In the current study, we focused on the hematopoietic cell-specific transcription factors PU.1 and IRF4 as the determinants of gene expression. The mRNA level of , and subsequently the enzyme activity, were decreased by knockdown of PU.1 and IRF4 in bone marrow-derived DCs (BMDCs) of BALB/c mice. Chromatin immunoprecipitation assays showed that PU.1 and IRF4 bound to the gene ∼2 kb upstream from the transcription start site in BMDCs. A reporter assay and an EMSA revealed that the promoter was synergistically transactivated by a heterodimer composed with PU.1 and IRF4 via the EICE motif at -1961/-1952 of the gene. The effect of small interfering RNAs for and and specific binding of PU.1 and IRF4 on the gene were also observed in DCs freshly isolated from spleen and mesenteric lymph nodes, respectively. GM-CSF stimulation upregulated the transcription in Flt3 ligand-generated BMDCs, in which the IRF4 expression and the PU.1 recruitment to the promoter were enhanced. We conclude that PU.1 and IRF4 are transactivators of the gene in vitro and ex vivo.