Abstract
MADDAM (Metalloprotease And Disintegrin Dendritic Cell Antigen Marker, ADAM19), a human metalloprotease belonging to the ADAM-family, is strongly expressed during in vitro differentiation of monocytes into dendritic cells (DC), whereas differentiation of monocytes into macrophages (MAC) is associated with a loss of MADDAM transcription. To investigate the mechanisms underlying this cell-type specific expression pattern we defined the transcriptional start site and the proximal promoter of the MADDAM gene. Gene bank analysis of the CpG island promoter and first intron revealed putative binding sites for several transcription factors, including VDR, NF-kB and Sp1-family factors. EMSA demonstrated binding of Sp1, Sp3, NF-kB and VDR to their putative binding sites in the proximal promoter region and mutation of these elements led to a decreased reporter activity of the proximal promoter in luciferase assays. A minimal promoter construct of 150-bp showed weak reporter activity in primary monocyte-derived MAC and a threefold higher activity in monocyte-derived DC, indicating that differential binding of transcription factors contributes to the cell-type specific regulation of MADDAM. Transfection of monocytic THP-1 cells with the 150-bp fragment also resulted in significant reporter activity, despite the lack of endogenous MADDAM expression. Interestingly, Trichostatin A (TSA), a known inhibitor of histone deacetylation, lead to a dose dependent induction of MADDAM mRNA in THP-1 cells. Chromatin immunoprecipitation (ChIP) assays demonstrate increased levels of acetylated histones H3 and H4 in DC as compared to MAC, indicating an important role of histone acetylation in the cell-type specific regulation of the MADDAM gene.
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