Initiation of the breakage-fusion-bridge mechanism through common fragile site activation in human breast cancer cells: the model of PIP gene duplication from a break at FRA7I.
Gene amplification plays a critical role in tumor progression. Hence, understanding the factors triggering this process in human cancers is an important concern. Unfortunately, the structures formed at early stages are usually unavailable for study, hampering the identification of the initiating events in tumors. Here, we show that the region containing the PIP gene, which is overexpressed in 80% of primary and metastatic breast cancers, is duplicated in the breast carcinoma cell line T47D. The two copies are organized as a large palindrome, lying 'in loco' on one chromosome 7. Such features constitute the landmark of the breakage-fusion-bridge (BFB) cycle mechanism. In hamster cells selected in vitro to resist cytotoxic drugs, common fragile site (CFS) activation has been shown to trigger this mechanism. Here, we characterize FRA7I at the molecular level and demonstrate that it lies 2 Mb telomeric to the PIP gene and sets the distal end of the repeated sequence. Moreover, our results suggest that the BFB process was frozen within the first cycle by healing of the broken chromosome. T47D cells thus offer a unique opportunity to observe the earliest products of the BFB cycle mechanism. Our findings constitute the first evidence that this amplification mechanism can be initiated in vivo by fragile site activation.
Ciullo
Marina
M
Génomique Fonctionnelle et Biologie Systémique en Santé, FRE 2571, Centre National de la Recherche Scientifique, 19 rue Guy Moquet, 94801 Villejuif, France.
Debily
Marie-Anne
MA
Rozier
Lorène
L
Autiero
Monica
M
Billault
Alain
A
Mayau
Véronique
V
El Marhomy
Sandrine
S
Guardiola
John
J
Bernheim
Alain
A
Coullin
Philippe
P
Piatier-Tonneau
Dominique
D
Debatisse
Michelle
M
D000818:Animals; D001053:Apolipoproteins; D053399:Apolipoproteins D; D019677:Artificial Gene Fusion; D001943:Breast Neoplasms / Q000235:genetics*; D016466:CHO Cells; D002352:Carrier Proteins / Q000235:genetics*; D019457:Chromosome Breakage / Q000235:genetics*; D043283:Chromosome Fragile Sites; D002873:Chromosome Fragility / Q000235:genetics*; D002897:Chromosomes, Human, Pair 7 / Q000235:genetics; D006224:Cricetinae; D015342:DNA Probes; D020440:Gene Duplication; D015723:Gene Library; D006023:Glycoproteins; D006801:Humans; D017404:In Situ Hybridization, Fluorescence; D066298:In Vitro Techniques; D007621:Karyotyping; D026901:Membrane Transport Proteins; D012091:Repetitive Sequences, Nucleic Acid; D016615:Telomere / Q000235:genetics; D014407:Tumor Cells, Cultured
C024328:APOD protein, human; D001053:Apolipoproteins; D053399:Apolipoproteins D; D002352:Carrier Proteins; D015342:DNA Probes; D006023:Glycoproteins; D026901:Membrane Transport Proteins