scholarly journals Transcription-replication conflicts as a source of common fragile site instability caused by BMI1-RNF2 deficiency

2019 ◽  
Author(s):  
Anthony Sanchez ◽  
Angelo de Vivo ◽  
Peter Tonzi ◽  
Jeonghyeon Kim ◽  
Tony T. Huang ◽  
...  
Keyword(s):  
Protective Factor ◽  
Fragile Site ◽  
Fragile Sites ◽  
Polycomb Group ◽  
Polycomb Group Proteins ◽  
Genome Maintenance ◽  
Cancer Etiology ◽  
Genomic Aberration ◽  
Common Fragile Sites ◽  
Polycomb Proteins

AbstractCommon fragile sites (CFSs) are breakage-prone genomic loci, and are considered to be hotspots for genomic rearrangements frequently observed in cancers. Understanding the underlying mechanisms for CFS instability will lead to better insight on cancer etiology. Here we show that Polycomb group proteins BMI1 and RNF2 are suppressors of transcription-replication conflicts (TRCs) and CFS instability. Cells depleted of BMI1 or RNF2 showed slower replication forks and elevated fork stalling. These phenotypes are associated with increase occupancy of RNA Pol II (RNAPII) at CFSs, suggesting that the BMI1-RNF2 complex regulate RNAPII elongation at these fragile regions. Using proximity ligase assays, we showed that depleting BMI1 or RNF2 causes increased associations between RNAPII with EdU-labeled nascent forks and replisomes, suggesting increased TRC incidences. Increased occupancy of a fork protective factor FANCD2 and R-loop resolvase RNH1 at CFSs are observed in RNF2 CRISPR-KO cells, which are consistent with increased transcription-associated replication stress in RNF2-deficient cells. Depleting FANCD2 or FANCI proteins further increased genomic instability and cell death of the RNF2-deficient cells, suggesting that in the absence of RNF2, cells depend on these fork-protective factors for survival. These data suggest that the Polycomb proteins have non-canonical roles in suppressing TRC and preserving genomic integrity.Author summaryIncreasing evidence suggest that instabilities at common fragile sites (CFSs), breakage-prone genomic loci, may be source of genomic aberration seen in cancer cells. Among the proposed mechanisms that can cause CFSs instabilities is the conflict between transcription and replication, and the mechanisms or factors that resolve the possible conflicts are only beginning to be understood. Here we found that deficiency in the Polycomb group proteins BMI1 or RNF2 leads to the CFS instability, and is associated with transcription-associated replication fork stresses. We further found that in the absence of RNF2, cells depend on the Fanconi Anemia fork-protective proteins for genome maintenance and survival. These results underscore that the Polycomb proteins are important for genome maintenance.

scholarly journals Increased Common Fragile Site Expression, Cell Proliferation Defects, and Apoptosis following Conditional Inactivation of Mouse Hus1 in Primary Cultured Cells

2007 ◽  
Vol 18 (3) ◽  
pp. 1044-1055 ◽  
Author(s):  
Min Zhu ◽  
Robert S. Weiss
Keyword(s):  
Cell Cycle ◽  
Cultured Cells ◽  
Chromosomal Abnormalities ◽  
Fragile Site ◽  
Loxp Site ◽  
Fragile Sites ◽  
Cell Cycle Checkpoint ◽  
Dna Breaks ◽  
Common Fragile Sites ◽  
Histone H2ax

Targeted disruption of the mouse Hus1 cell cycle checkpoint gene results in embryonic lethality and proliferative arrest in cultured cells. To investigate the essential functions of Hus1, we developed a system for the regulated inactivation of mouse Hus1 in primary fibroblasts. Inactivation of a loxP site-flanked conditional Hus1 allele by using a cre-expressing adenovirus resulted in reduced cell doubling, cell cycle alterations, and increased apoptosis. These phenotypes were associated with a significantly increased frequency of gross chromosomal abnormalities and an S-phase–specific accumulation of phosphorylated histone H2AX, an indicator of double-stranded DNA breaks. To determine whether these chromosomal abnormalities occurred randomly or at specific genomic regions, we assessed the stability of common fragile sites, chromosomal loci that are prone to breakage in cells undergoing replication stress. Hus1 was found to be essential for fragile site stability, because spontaneous chromosomal abnormalities occurred preferentially at common fragile sites upon conditional Hus1 inactivation. Although p53 levels increased after Hus1 loss, deletion of p53 failed to rescue the cell-doubling defect or increased apoptosis in conditional Hus1 knockout cells. In summary, we propose that Hus1 loss leads to chromosomal instability during DNA replication, triggering increased apoptosis and impaired proliferation through p53-independent mechanisms.

Abnormalities of 16q in Multiple Myeloma Are Associated with Poor Prognosis: 500K Gene Mapping and Expression Correlations Identify Two Potential Tumor Suppressor Genes, WWOX and CYLD.

Blood ◽  
2006 ◽  
Vol 108 (11) ◽  
pp. 110-110
Author(s):  
Matthew W. Jenner ◽  
Paola E. Leone ◽  
Brian A. Walker ◽  
David C. Johnson ◽  
Laura Chiecchio ◽  
...  
Keyword(s):  
Tumor Suppressor ◽  
Gene Mapping ◽  
Tumor Suppressor Genes ◽  
Poor Prognosis ◽  
Fragile Site ◽  
Fragile Sites ◽  
Common Fragile Site ◽  
Chromosome 16 ◽  
Common Fragile Sites ◽  
Potential Tumor Suppressor

Abstract Abnormalities of 16q are important recurrent events in multiple myeloma (MM). We performed FISH on CD138 selected plasma cells from 701 newly diagnosed MM patients from the LRF UKMF cytogenetics database. Gene mapping, including paired normal controls, and gene expression analysis was performed on 55 cases using the Affymetrix Human Mapping 500K Array Set and U133 Plus 2.0 Arrays respectively. 16q deletion (del16q) was identified by FISH using probes for cMAF (Abbott Diagnostics) in 131/701 cases (18.7%) and was significantly associated with deletion 17p (16.5% vs. 8.9%, p=0.006), deletion 13 (60.8% vs. 48.5%, p=0.009), deletion of IgH (22.1% vs. 11.1%, p=0.0003) and non-hyperdiploid status (58.3% vs. 42.7%, p=0.006). Del16q showed a trend to poor overall survival, mean survival 43 vs. 61 months (p=0.09), and was associated with significantly worse survival in combination with t(4;14) compared with either t(4;14) or del16q alone, mean survival 15 vs. 26 vs. 45 months respectively (p=0.006). t(14;16) was identified by FISH in 31/701 cases (4.4%) and was associated with poor prognosis, mean survival 29 vs. 54 months (p=0.005). Mapping arrays revealed loss of heterozygosity (LOH) involving all or part of 16q in 20 of 55 cases (36%) in 3 distinct patterns: uniparental disomy (UPD) of chromosome 16 or 16q in 4/55 cases (7%); deletion of chromosome 16 or the whole of 16q in 11/55 cases (20%); and interstitial deletion of small regions of 16q in 5/55 cases (10%), focused on 16q12, the location of CYLD, and 16q23, the location of WWOX. 16q LOH was distributed across translocation groups but was identified in all 4 mapping cases containing 17p deletion, supporting the association identified by FISH. As WWOX is the site of the common fragile site FRA16D and deletions at common fragile sites have been associated with DNA instability in human cancers, we assessed this using gene mapping in these 55 MM cases. Although deletions spanning other common fragile sites were identified, they were not restricted to those with 16q LOH. However, in 2 t(14;16) cases, hemizygous deletions of approximately 100kb could be identified within WWOX at the presumed translocation breakpoint. One of the t(14;16) cases had a similar hemizygous deletion within FHIT, another tumor suppressor gene located within common fragile site FRA3B, consistent with findings in other cancer types. Cases with 16q LOH or t(14;16) all had significantly reduced WWOX expression relative to cases without 16q abnormalities, confirming gene inactivation by either LOH or translocation. Cases with 16q LOH also had significantly reduced expression of two other potential tumor suppressor genes located on 16q, CYLD and RBL2. In summary, our data confirms the adverse prognosis associated with 16q translocation or deletion. Array data reveals 16q LOH occurs due to deletion or UPD with two regions involved, one defined by CYLD and the other by WWOX. WWOX is also inactivated by translocation and is associated with interstitial deletions at this and other common fragile sites. WWOX is a likely candidate gene in MM pathogenesis because of its interaction with TP53 and CYLD via its effects on NF-κB.

scholarly journals Molecular Basis for Expression of Common and Rare Fragile Sites

2003 ◽  
Vol 23 (20) ◽  
pp. 7143-7151 ◽  
Author(s):  
Eitan Zlotorynski ◽  
Ayelet Rahat ◽  
Jennifer Skaug ◽  
Neta Ben-Porat ◽  
Efrat Ozeri ◽  
...  
Keyword(s):  
Molecular Basis ◽  
Fragile Site ◽  
Secondary Structures ◽  
Fragile Sites ◽  
Entire Genome ◽  
Common Fragile Sites ◽  
Dna Structures ◽  
Significant Difference ◽  
Minisatellite Repeats ◽  
Genomic Regions

ABSTRACT Fragile sites are specific loci that form gaps, constrictions, and breaks on chromosomes exposed to partial replication stress and are rearranged in tumors. Fragile sites are classified as rare or common, depending on their induction and frequency within the population. The molecular basis of rare fragile sites is associated with expanded repeats capable of adopting unusual non-B DNA structures that can perturb DNA replication. The molecular basis of common fragile sites was unknown. Fragile sites from R-bands are enriched in flexible sequences relative to nonfragile regions from the same chromosomal bands. Here we cloned FRA7E, a common fragile site mapped to a G-band, and revealed a significant difference between its flexibility and that of nonfragile regions mapped to G-bands, similar to the pattern found in R-bands. Thus, in the entire genome, flexible sequences might play a role in the mechanism of fragility. The flexible sequences are composed of interrupted runs of AT-dinucleotides, which have the potential to form secondary structures and hence can affect replication. These sequences show similarity to the AT-rich minisatellite repeats that underlie the fragility of the rare fragile sites FRA16B and FRA10B. We further demonstrate that the normal alleles of FRA16B and FRA10B span the same genomic regions as the common fragile sites FRA16C and FRA10E. Our results suggest that a shared molecular basis, conferred by sequences with a potential to form secondary structures that can perturb replication, may underlie the fragility of rare fragile sites harboring AT-rich minisatellite repeats and aphidicolin-induced common fragile sites.

scholarly journals Clustering of mammalian Hox genes with other H3K27me3 targets within an active nuclear domain

2015 ◽  
Vol 112 (15) ◽  
pp. 4672-4677 ◽  
Author(s):  
Maxence Vieux-Rochas ◽  
Pierre J. Fabre ◽  
Marion Leleu ◽  
Denis Duboule ◽  
Daan Noordermeer
Keyword(s):  
Hox Genes ◽  
Transcriptional Regulators ◽  
Polycomb Group ◽  
Polycomb Group Proteins ◽  
Cell Type ◽  
Polycomb Proteins ◽  
Chromosomal Distance ◽  
Nuclear Domain ◽  
Cell Type Specific ◽  
Nuclear Environment

Embryogenesis requires the precise activation and repression of many transcriptional regulators. The Polycomb group proteins and the associated H3K27me3 histone mark are essential to maintain the inactive state of many of these genes. Mammalian Hox genes are targets of Polycomb proteins and form local 3D clusters centered on the H3K27me3 mark. More distal contacts have also been described, yet their selectivity, dynamics, and relation to other layers of chromatin organization remained elusive. We report that repressed Hox genes form mutual intra- and interchromosomal interactions with other genes located in strong domains labeled by H3K27me3. These interactions occur in a central and active nuclear environment that consists of the HiC compartment A, away from peripheral lamina-associated domains. Interactions are independent of nearby H3K27me3-marked loci and determined by chromosomal distance and cell-type–specific scaling factors, thus inducing a moderate reorganization during embryogenesis. These results provide a simplified view of nuclear organization whereby Polycomb proteins may have evolved to repress genes located in gene-dense regions whose position is restricted to central, active, nuclear environments.

Direct cloning and analysis of DNA sequences from a region of the Chinese hamster genome associated with aphidicolin-sensitive fragility

1998 ◽  
Vol 111 (12) ◽  
pp. 1623-1634
Author(s):  
A.H. Palin ◽  
R. Critcher ◽  
D.J. Fitzgerald ◽  
J.N. Anderson ◽  
C.J. Farr
Keyword(s):  
Dna Sequences ◽  
Fragile Site ◽  
Integration Site ◽  
Consensus Sequence ◽  
Chinese Hamster ◽  
Fragile Sites ◽  
Chemical Agent ◽  
Fish Analysis ◽  
Common Fragile Sites ◽  
Direct Cloning

Fragile sites are reproducibly expressed and chemically induced decondensations on mitotic chromosomes observed under cytological conditions. They are classified both on the basis of the frequency with which they occur (rare and common) and in terms of the chemical agent used to induce expression in tissue culture cells. Aphidicolin-sensitive common fragile sites appear to be ubiquitous in humans and other mammals and have been considered as candidates of pathological importance. Recently DNA from FRA3B, the most highly expressed constitutive fragile site in the human genome, has been cloned although as yet the cause of the underlying fragility has not been identified. In this study we describe the isolation, using a direct cloning approach, of DNA from a region of the Chinese hamster genome associated with aphidicolin-inducible fragility. Cells of a human-hamster somatic cell hybrid were transfected with a pSV2HPRT vector while exposed to aphidicolin, an inhibitor of DNA polymerases alpha, delta and epsilon. FISH analysis of stable transfectant clones revealed that the ingoing plasmid DNA had preferentially integrated into fragile site-containing chromosomal bands. Plasmid rescue was used to recover DNA sequences flanking one such integration site in the hamster genome. We demonstrate by FISH analysis of metaphase cells induced with aphidicolin that the rescued DNA is from a region of fragility on Chinese hamster chromosome 2, distal to the DHFR locus. Analysis of the DNA sequences flanking the integration site revealed the overall A+T content of the 3,725 bp region sequenced to be 63.3%, with a highly [A].[T]-rich 156 bp region (86.5%) almost adjacent to the integration site. Computational analyses have identified strong homologies to Saccharomyces cerevisiae autonomous replicating sequences (ARS), polypyrimidine tracts, scaffold attachment site consensus sequences and a 24 bp consensus sequence highly conserved in eukaryotic replication origins, all of which appear to cluster around the [A].[T]-rich sequences. This domain also possesses structural characteristics which are common to both prokaryotic and eukaryotic origins of replications, in particular an unusually straight conformation of low thermal stability flanked either side by highly bent DNA segments. Further isolation and characterisation of DNA sequences from common fragile sites will facilitate studies into the underlying nature of these enigmatic regions of the mammalian genome, leading to a greater understanding of chromatin structure.

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