SMC1 involvement in fragile site expression.
Common fragile sites have been involved in neoplastic transformation, although their molecular basis is still poorly understood. Here, we demonstrate that inhibition of the SMC1 by RNAi is sufficient to induce fragile site expression. By investigating normal, ATM- and ATR-deficient cell lines, we provide evidence that the contribution of SMC1 in preventing the collapse of stalled replication fork is an Atr-dependent pathway. Using a fluorescent antibody specific for gamma-H2AX, we show that very rare discrete nuclear foci appear 1 and 2 h after exposure to aphidicolin and/or RNAi-SMC1, but became more numerous and distinct after longer treatment times. In this context, fragile sites might be viewed as an in vitro phenomenon originating from double-strand breaks formed because of a stalled DNA replication that lasted too long to be managed by physiological rescue acting through the Atr/Smc1 axis. We propose that in vivo, following an extreme replication block, rare cells could escape checkpoint mechanisms and enter mitosis with a defect in genome assembly, eventually leading to neoplastic transformation.
Musio
Antonio
A
Istituto di Tecnologie Biomediche, Consiglio Nazionale delle Ricerche, Via Fratelli Cervi, 93, 20090 Segrate, Milan, Italy. antonio.musio@itb.cnr.it
Montagna
Cristina
C
Mariani
Tullio
T
Tilenni
Manuela
M
Focarelli
Maria Luisa
ML
Brait
Lorenzo
L
Indino
Esterina
E
Benedetti
Pier Alberto
PA
Chessa
Luciana
L
Albertini
Alberto
A
Ried
Thomas
T
Vezzoni
Paolo
P
D016590:Aphidicolin / Q000494:pharmacology; D064007:Ataxia Telangiectasia Mutated Proteins; D018797:Cell Cycle Proteins / Q000037:antagonists & inhibitors / Q000502:physiology*; D002467:Cell Nucleus; D002868:Chromosomal Proteins, Non-Histone / Q000037:antagonists & inhibitors / Q000502:physiology*; D043283:Chromosome Fragile Sites; D002875:Chromosomes / Q000187:drug effects; D004261:DNA Replication / Q000187:drug effects; D004268:DNA-Binding Proteins / Q000502:physiology*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005347:Fibroblasts / Q000378:metabolism; D006367:HeLa Cells; D006657:Histones / Q000276:immunology / Q000378:metabolism; D006801:Humans; D016376:Oligonucleotides, Antisense / Q000494:pharmacology; D017346:Protein Serine-Threonine Kinases / Q000502:physiology*; D034622:RNA Interference; D025521:Tumor Suppressor Proteins / Q000502:physiology*; D000098550:Structural Maintenance of Chromosome Protein 1
D018797:Cell Cycle Proteins; D002868:Chromosomal Proteins, Non-Histone; D004268:DNA-Binding Proteins; D004791:Enzyme Inhibitors; C468783:H2AX protein, human; D006657:Histones; D016376:Oligonucleotides, Antisense; D025521:Tumor Suppressor Proteins; D000098550:Structural Maintenance of Chromosome Protein 1; D016590:Aphidicolin; C576324:ATM protein, human; C576597:ATR protein, human; D064007:Ataxia Telangiectasia Mutated Proteins; D017346:Protein Serine-Threonine Kinases