title: Inhibition of human telomerase reverse transcriptase gene expression by BRCA1 in human ovarian cancer cells.
abstract: Human telomerase reverse transcriptase (hTERT), the catalytic subunit of human telomerase, is responsible for the synthesis and maintenance of the telomeric repeats at the distal ends of human chromosomes. Telomerase expression is repressed in normal human cells and is activated in immortal cells and during tumorigenesis, but the mechanism by which telomerase expression is regulated is not fully understood. Previous studies have shown that c-Myc stimulates hTERT transcription through the binding sites located on the hTERT promoter. In this study, we sought to determine whether BRCA1 inhibits hTERT transcription through its direct interaction with c-Myc. In ovarian cancer cells, c-Myc increased hTERT expression by threefold and BRCA1 completely abrogated this activity. A mutation in the c-Myc-binding site (E-box) of the hTERT promoter resulted in the loss of activation by c-Myc and in the loss of inhibition by BRCA1. Deletion of the c-Myc-binding domain in BRCA1 resulted in the loss of BRCA1's ability to inhibit transcription of the hTERT promoter. In addition, BRCA1 associates with c-Myc and inhibits the binding activity of c-Myc to the hTERT promoter. Our data indicate that BRCA1 is involved in regulating cellular immortalization through the modulation of c-Myc on the hTERT promoter.
authors.affiliation: Department of Pathology, Division of Pathology and Laboratory Medicine, Unit 85, The University of Texas M.D. Anderson Cancer Center, 1515 Holcombe Boulevard, Houston, TX 77030-4095, USA.
authors.forename: Chenyi
authors.initials: C
authors.lastname: Zhou
authors.forename: Jinsong
authors.initials: J
authors.lastname: Liu
mesh_terms: D019313:BRCA1 Protein / Q000378:metabolism*; D001665:Binding Sites; D015153:Blotting, Western; D002467:Cell Nucleus / Q000378:metabolism; D004268:DNA-Binding Proteins; D004789:Enzyme Activation; D005260:Female; D006367:HeLa Cells; D006801:Humans; D008156:Luciferases / Q000378:metabolism; D009154:Mutation; D009369:Neoplasms / Q000378:metabolism; D010053:Ovary / Q000201:enzymology* / Q000378:metabolism*; D010957:Plasmids / Q000378:metabolism; D011233:Precipitin Tests; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D016271:Proto-Oncogene Proteins c-myc / Q000378:metabolism; D019098:Telomerase / Q000037:antagonists & inhibitors*; D015533:Transcriptional Activation; D014162:Transfection; D014407:Tumor Cells, Cultured
chemical_list: D019313:BRCA1 Protein; D004268:DNA-Binding Proteins; D016271:Proto-Oncogene Proteins c-myc; D008156:Luciferases; D019098:Telomerase