NF-κB, Sp1 and NF-Y as transcriptional regulators of human SND1 gene

Staphylococcal nuclease domain-containing protein 1 (SND1), also called Tudor-SN, is required for many biological events ranging from gene expression to cell growth regulation. Promoter regulation of SND1 gene and its molecular mechanism have remained elusive to date. In this work, we have identified SND1 as a new target gene for NF-κB, Sp1 and NF-Y transcription factors. We isolated and characterized a 3808 bp sequence corresponding to the human SND1 gene promoter (GenBank ID: EF690304). It lacks the typical TATA-box element and contains a CpG island with several Sp1 binding sites at the 3' end, and a highly conserved 300 bp segment with two inverted CCAAT boxes that bind NF-Y, in addition to NF-κB sites and other cis-regulatory elements. Electrophoretic mobility shift assays and chromatin immunoprecipitation experiments confirmed the ability of SND1 promoter to bind NF-κB, Sp1 and NF-Y in vitro and in vivo. Deletion analysis of the 5'-flanking region by luciferase reporter assays, showed the minimum promoter activity 112 base-pair upstream from the transcription start site, and an enhancer region between -112 and -274 bp responsible for the maximal transcriptional activity of the promoter. Site-directed mutagenesis of the CCAAT and GC boxes and the NF-κB elements within the proximal region substantially reduced SND1 promoter activity. Proinflammatory cytokine TNF-α caused an increase of SND1 promoter activity that is mediated, at least in part, via NF-κB as mutation in the NF-κB sites impaired the promoter stimulation. We provide for the first time the characterization of the human SND1 promoter activity and establish a transcriptional network associated to the key transcription factors NF-κB, Sp1 and NF-Y that operates in the control of the SND1 gene expression.