DKC1 is an evolutionarily conserved c‐Myc target

Objectives: We have identified dyskeratosis congenita 1 (DKC1) as a direct c‐Myc transcriptional target in human cells. In these studies, we sought to determine if c‐Myc‐mediated DKC1 regulation is conserved across species. Methods: Murine p53‐null colonocytes and Rat 1a fibroblasts, both expressing an inducible, c‐Myc‐estrogen receptor (MYC‐ER) fusion protein, were incubated in media with 0.25% serum for 48 hrs; then stimulated with 250 nM 4‐hydroxytamoxifen (4‐OHT) for up to 72 hrs. At various time points, total RNA was harvested and Dkc1 levels were determined by quantitative RT‐PCR. Telomerase reverse transcriptase (Tert), a known direct target of c‐Myc; and vimentin (Vim) and β‐actin, neither of which is regulated by c‐Myc, served as controls for MYC‐ER activation. All mRNA levels were normalized to β‐actin expression. Results: Dkc1 was significantly upregulated in mouse (Figure 1) and rat cells following MYC‐ER activation. A comparison between the human and mouse DKC1 genomic sequences revealed conservation of five c‐Myc‐binding E‐box motifs within a region encompassing the promoter, exon 1 and intron 1. Through the use of chromatin immunoprecipitati on, we have previously demonstrated that endogenous c‐Myc binds to these same sites in human cells, thus inferring a functional conservation. Conclusion: c‐Myc‐mediated DKC1 transcriptional regulation is not species or cell‐type specific. 1Dkcl expression is upregulated in MYC‐ER mouse colonocytes