The Bmi-1 oncogene induces telomerase activity and immortalizes human mammary epithelial cells.
The vast majority of breast cancers are carcinomas that arise from mammary epithelial cells (MECs). One of the key early events in tumorigenic transformation is the ability of cells to overcome replicative senescence. However, the precise genetic changes that are responsible for this event in MECs is largely unknown. Here, we report that Bmi-1, originally identified as a c-Myc cooperating oncoprotein, can bypass senescence, extend the replicative life span, and immortalize MECs. Furthermore, Bmi-1 was overexpressed in immortal MECs and several breast cancer cell lines. Overexpression of Bmi-1 in MECs led to activation of human telomerase reverse transcriptase (hTERT) transcription and induction of telomerase activity. Telomerase induction by Bmi-1 was an early event in the extension of the replicative life span and immortalization. Bmi-1 was not overexpressed in hTERT-immortalized MECs, suggesting that Bmi-1 functions upstream of hTERT. Although, c-Myc has been reported to induce telomerase in MECs, Bmi-1 appeared to act independently of c-Myc binding sequences in the hTERT promoter. Deletion analysis of the Bmi-1 protein suggested that the RING finger, as well as a conserved helix-turn-helix-turn domain, were required for its ability to induce telomerase and immortalize MECs. These data suggest that Bmi-1 regulates telomerase expression in MECs and plays a role in the development of human breast cancer.
Dimri
Goberdhan P
GP
Division of Radiation and Cancer Biology, Department of Radiation Oncology, New England Medical Center, Boston, Massachusetts 02111, USA. GDimri@Lifespan.org
Martinez
Jose-Luis
JL
Jacobs
Jacqueline J L
JJ
Keblusek
Petra
P
Itahana
Koji
K
Van Lohuizen
Maarten
M
Campisi
Judith
J
Wazer
David E
DE
Band
Vimla
V
D001665:Binding Sites; D001940:Breast / Q000166:cytology / Q000201:enzymology / Q000502:physiology*; D001943:Breast Neoplasms / Q000201:enzymology / Q000235:genetics / Q000378:metabolism; D002471:Cell Transformation, Neoplastic / Q000235:genetics* / Q000378:metabolism; D002478:Cells, Cultured; D004268:DNA-Binding Proteins; D015536:Down-Regulation; D004790:Enzyme Induction; D004847:Epithelial Cells / Q000166:cytology / Q000201:enzymology / Q000502:physiology; D006801:Humans; D009687:Nuclear Proteins / Q000096:biosynthesis / Q000235:genetics* / Q000502:physiology; D063150:Polycomb Repressive Complex 1; D011401:Promoter Regions, Genetic; D011518:Proto-Oncogene Proteins / Q000096:biosynthesis / Q000235:genetics* / Q000502:physiology; D016271:Proto-Oncogene Proteins c-myc / Q000378:metabolism; D012097:Repressor Proteins; D019098:Telomerase / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D015533:Transcriptional Activation; D014407:Tumor Cells, Cultured; D025803:Tumor Suppressor Protein p14ARF / Q000096:biosynthesis / Q000235:genetics
C069077:BMI1 protein, human; D004268:DNA-Binding Proteins; D009687:Nuclear Proteins; D011518:Proto-Oncogene Proteins; D016271:Proto-Oncogene Proteins c-myc; D012097:Repressor Proteins; D025803:Tumor Suppressor Protein p14ARF; D063150:Polycomb Repressive Complex 1; D019098:Telomerase