Ku86 autoantigen related protein-1 transcription initiates from a CpG island and is induced by p53 through a nearby p53 response element

The human Ku86 gene and an isoform, KARP-1 (Ku86 autoantigen related protein-1), encode overlapping, but differentially regulated, transcripts. Ku86 is constitutively transcribed at high levels and, although it plays a seminal role in DNA double-strand break repair, its expression is not induced by DNA damage. KARP-1, in contrast, is expressed constitutively only at low levels and its expression is induced by DNA damage in a p53-dependent fashion. The regulatory elements promoting KARP-1 gene expression and p53 responsiveness, however, were unknown. Here, we report that a strong DNase I hypersensitive site (DHS) resides ∼25 kb upstream from the Ku86 promoter. This DHS is encompassed by a hypomethylated CpG island. Reporter assays demonstrated that this region corresponded to a promoter(s), which promoted transcription of peroxisomal trans-2-enoyl CoA reductase in the centromeric direction and KARP-1 in the telomeric direction. KARP-1 primer extension products were mapped to this CpG island in the correct transcriptional orientation confirming that KARP-1 transcription initiates from this site. Moreover, a p53 response element within the first intron of the KARP-1 transcriptional unit was identified using chromatin immunoprecipitation and antibodies specific to activated forms of p53. These data expand our understanding of this important DNA repair locus.