Basal transcriptional regulation of human damage-specific DNA-binding protein genes DDB1 and DDB2 by Sp1, E2F, N-myc and NF1 elements

Abstract

The human DDB1 and DDB2 genes encode the 127 and 48 kDa subunits, respectively, of the damage-specific DNA-binding protein (DDB). Mutations in the DDB2 gene have been correlated with the hereditary disease xeroderma pigmentosum group E. We have investigated the proximal promoters of the DDB genes, both of which are G/C-rich and do not contain a TATA box. Transient expression analysis in HeLa cells using a luciferase reporter system indicated the presence of core promoters located within 292 bp (DDB1) and 220 bp (DDB2) upstream of the putative transcription initiation sites. Both core promoters contain multiple active Sp1 sites, with those of DDB1 at -123 to -115 and of DDB2 at -29 to -22 being critical determinants of promoter activity. In addition, an N-myc site at -56 to -51 for DDB1 is an essential transcription element, and mutations in a DDB1 NF-1 site at -104 to -92, a DDB2 NF-1 site at -68 to -56 and a DDB2 E2F site at +36 to +43 also reduce promoter activity. Taken together, these results suggest a regulation of basal transcription typical of cell cycle-regulated genes, and therefore support conjectures that the DDB heterodimer and/or its subunits have functions other than direct involvement in DNA repair.

E2F regulates DDB2: consequences for DNA repair in Rb-deficient cells

“…The DDB2 mouse gene (Ensembl Gene ID ENSMUS-G00000002109) was analysed and a putative E2F binding site, also reported by others (Nichols et al, 2003), was identified located 143-136 nucleotides upstream of the translation initiation site.…”

“…This finding provides for the first time, a plausible mechanism for the cell cycle regulation of expression of DDB2 as upon Rb phosphorylation in G1/S, E2F activity also increases to peak in S phase (for reviews, see Dyson, 1998;Muller and Helin, 2000). Whether E2F transcriptionally regulates DDB2 in other species remains to be confirmed, but the identification of an E2F site downstream of the initiation of transcription site in human DDB2 suggests that this may also be the case in human cells (Nichols et al, 2003).…”

“…E2F activates transcription of DDB2 with consequences for global DNA repair As Rb deletion does not require functional p53 to affect DDB2 expression levels (Figure 2b), we analysed the mouse DDB2 promoter region (Ensembl Gene ID ENSMUSG00000002109) and identified a putative E2F binding site (also mentioned in Nichols et al, 2003) located 143-136 nucleotides upstream of the translation initiation site. We have previously shown that E2F transcriptional activity is elevated in Rb null hepatocytes (Sheahan et al, 2004).…”

Regulation of epidermal apoptosis and DNA repair by E2F1 in response to ultraviolet B radiation

“…One possibility is that E2F1 regulates the expression of one or more rate-limiting factors involved in NER. E2F1 overexpression can transcriptionally activate several genes whose products have been implicated in the repair of UV-induced DNA damage, including DDB2, BRCA1 and MSH2 (Wang et al, 1999;Hartman and Ford, 2002;Meira et al, 2002;Polager et al, 2002;Ren et al, 2002;Takimoto et al, 2002;Nichols et al, 2003;Young et al, 2003). To determine if inactivation of endogenous E2f1 would affect the expression of DNA repair genes, microarray gene expression analysis was performed using RNA isolated from the epidermis of wild-type and E2f1 À/À mice (data not shown).…”

DDB2 gene disruption leads to skin tumors and resistance to apoptosis after exposure to ultraviolet light but not a chemical carcinogen

“…However, the removal from DNA of many bulky lesions, including photoproducts, occurs in the absence of DDB (8,12,13), and DDB2 is induced by UV-irradiation at a time by which NER has been completed. Moreover, the DDB2 promoter resembles that of a cell cycleregulated gene (1,14), and DDB2 is part of the COP9 signalosome complex (15,16). Instead, DDB2 has been proposed to be a transcription transactivator through its stimulation of E2F1 (17), and we recently observed that DDB2 controls p53-mediated apoptosis after UV-irradiation of human diploid fibroblasts and that XP group E (XP-E) primary skin fibroblasts are abnormally resistant to killing by UV-irradiation (18).…”