Cell-type-specific replication initiation programs set fragility of the FRA3B fragile site.
Common fragile sites have long been identified by cytogeneticists as chromosomal regions prone to breakage upon replication stress. They are increasingly recognized to be preferential targets for oncogene-induced DNA damage in pre-neoplastic lesions and hotspots for chromosomal rearrangements in various cancers. Common fragile site instability was attributed to the fact that they contain sequences prone to form secondary structures that may impair replication fork movement, possibly leading to fork collapse resulting in DNA breaks. Here we show, in contrast to this view, that the fragility of FRA3B--the most active common fragile site in human lymphocytes--does not rely on fork slowing or stalling but on a paucity of initiation events. Indeed, in lymphoblastoid cells, but not in fibroblasts, initiation events are excluded from a FRA3B core extending approximately 700 kilobases, which forces forks coming from flanking regions to cover long distances in order to complete replication. We also show that origins of the flanking regions fire in mid-S phase, leaving the site incompletely replicated upon fork slowing. Notably, FRA3B instability is specific to cells showing this particular initiation pattern. The fact that both origin setting and replication timing are highly plastic in mammalian cells explains the tissue specificity of common fragile site instability we observed. Thus, we propose that common fragile sites correspond to the latest initiation-poor regions to complete replication in a given cell type. For historical reasons, common fragile sites have been essentially mapped in lymphocytes. Therefore, common fragile site contribution to chromosomal rearrangements in tumours should be reassessed after mapping fragile sites in the cell type from which each tumour originates.
Institut Curie, Centre de Recherche, 26 rue d'Ulm, 75248 Paris, France.
Anne
A
Letessier
Gaël A
GA
Millot
Stéphane
S
Koundrioukoff
Anne-Marie
AM
Lachagès
Nicolas
N
Vogt
R Scott
RS
Hansen
Bernard
B
Malfoy
Olivier
O
Brison
Michelle
M
Debatisse
D017766:Acid Anhydride Hydrolases / Q000235:genetics*; D002460:Cell Line; D019457:Chromosome Breakage; D043283:Chromosome Fragile Sites / Q000235:genetics*; D002873:Chromosome Fragility / Q000235:genetics / Q000502:physiology*; D004261:DNA Replication / Q000235:genetics / Q000502:physiology*; D005347:Fibroblasts; D016147:Genes, Tumor Suppressor; D056426:Genetic Loci / Q000235:genetics; D006801:Humans; D008214:Lymphocytes / Q000378:metabolism; D008954:Models, Biological; D009363:Neoplasm Proteins / Q000235:genetics*; D009928:Organ Specificity; D018741:Replication Origin / Q000235:genetics*; D000099170:Bis(5'-adenosyl)triphosphatase
D017766:Acid Anhydride Hydrolases; D009363:Neoplasm Proteins; D000099170:Bis(5'-adenosyl)triphosphatase
Oncogene. 2008 May 22;27(23):3256-64
18084328
Genes Dev. 2000 Jan 1;14(1):1-10
10640269
Science. 2002 Jul 26;297(5581):602-6
12142538
Nat Rev Mol Cell Biol. 2010 Mar;11(3):220-8
20177397
Genome Res. 2008 Oct;18(10):1562-70
18669478
J Cell Biochem. 2008 Aug 1;104(5):1525-33
18393361
Cancer Lett. 2006 Jan 28;232(1):37-47
16242840
Cell. 2003 Aug 8;114(3):385-94
12914702
Chromosoma. 2010 Dec;119(6):575-87
20585795
Mol Biol Cell. 2006 Dec;17(12):5337-45
17005913
Annu Rev Biochem. 2010;79:89-130
20373915
Biotechniques. 2008 Dec;45(6):649-52, 654, 656-8
19238795
Cell Cycle. 2003 Jul-Aug;2(4):307-9
12851480
EMBO Rep. 2006 Aug;7(8):806-11
16799461
Proc Natl Acad Sci U S A. 2005 Dec 13;102(50):18069-74
16330769
PLoS Biol. 2008 Oct 7;6(10):e245
18842067
Proc Natl Acad Sci U S A. 2008 Jan 8;105(1):246-51
18162546
DNA Repair (Amst). 2007 Jul 1;6(7):900-13
17379579
Cancer Lett. 2006 Jan 28;232(1):13-26
16236432
Nat Rev Mol Cell Biol. 2010 Mar;11(3):208-19
20177396
Br J Cancer. 2003 May 19;88(10):1501-6
12771912
Nature. 2008 Sep 25;455(7212):557-60
18716622
Annu Rev Genet. 2007;41:169-92
17608616
Genome Res. 2010 Jun;20(6):761-70
20430782
Nature. 2010 Feb 18;463(7283):893-8
20164919
Hum Mol Genet. 1998 Apr;7(4):755-61
9499431
Proc Natl Acad Sci U S A. 2010 Jan 5;107(1):139-44
19966280
Genome Res. 2006 Oct;16(10):1222-30
16954539
Curr Opin Genet Dev. 1995 Jun;5(3):323-7
7549426
Science. 1997 Sep 5;277(5331):1518-23
9278517
EMBO Rep. 2006 Aug;7(8):812-6
16845368