Nuclear myc promoter-binding protein-1 (MBP-1) expression is a prognostic factor in invasive ductal breast carcinoma

Insulators are DNA elements that block the extension of a condensed chromatin domain into a transcriptionally active region or prevent the interaction of a distal enhancer with a promoter when placed between the two. Human c-Myc and Pvt-1 genes map close each other and are separated by an intergenic region rich of DNAseI hypersensitivity sites. Starting from the observation that PVT1 expression is restricted to a low number of normal tissues compared to the wide distribution of c-Myc mRNA we focus our studies on the function and structure of the regions surrounding the DHs present between the two genes. Stable and transient transfection, indicate that one of the regions (HB-2.8) has enhancer blocking activity. Further evidences indicate that HB.2.8 blocks the activity of c-Myc distal enhancer (PA-A) on the Pvt-1 promoter, suggesting that c-Myc and Pvt-1 genes are insulated in two distinct chromatin. A Matrix-attachment region (MAR) has been mapped in close proximity of the HB-2.8 region and we found it is associated to the core element responsible for the HB-2.8 enhancer-blocking activity. By means of DNA affinity chromatography and proteomic analysis we characterized two proteins interacting with HB-2.8, from nuclear extract of Hela cells: THAP11 and HP1BP3. Overexpression of THAP11 inhibits growth of different cells types and its function is mediated by its ability to repress transcription of c-Myc. HP1BP3 is a component of heterochromatin and may be involved in chromatin structure. Functional characterization of these proteins may contribute to define MYC chromatin domain.