Regulation and Localization of the Bloom Syndrome Protein in Response to DNA Damage

Life Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA..
The Journal of Cell Biology (Impact Factor: 9.83). 05/2001; 153(2):367-80.
Source: PubMed


Bloom syndrome (BS) is an autosomal recessive disorder characterized by a high incidence of cancer and genomic instability. BLM, the protein defective in BS, is a RecQ-like helicase, presumed to function in DNA replication, recombination, or repair. BLM localizes to promyelocytic leukemia protein (PML) nuclear bodies and is expressed during late S and G2. We show, in normal human cells, that the recombination/repair proteins hRAD51 and replication protein (RP)-A assembled with BLM into a fraction of PML bodies during late S/G2. Biochemical experiments suggested that BLM resides in a nuclear matrix-bound complex in which association with hRAD51 may be direct. DNA-damaging agents that cause double strand breaks and a G2 delay induced BLM by a p53- and ataxia-telangiectasia mutated independent mechanism. This induction depended on the G2 delay, because it failed to occur when G2 was prevented or bypassed. It coincided with the appearance of foci containing BLM, PML, hRAD51 and RP-A, which resembled ionizing radiation-induced foci. After radiation, foci containing BLM and PML formed at sites of single-stranded DNA and presumptive repair in normal cells, but not in cells with defective PML. Our findings suggest that BLM is part of a dynamic nuclear matrix-based complex that requires PML and functions during G2 in undamaged cells and recombinational repair after DNA damage.

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Available from: Oliver Bischof
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    • "WRN is associated with a variegated translocation mosaicism, a prolongation of the S phase of the cell cycle, hypersensitivity to DNA cross-linking and DSBs provoking agents, and a reduction in recombinational DSB repair [Salk et al., 1981; Poot et al., 1992, 2001, 2002; Ogburn et al., 1997; Melcher et al., 2000; Dhillon et al., 2007]. In BLM, rates of sister chromatid exchanges and hypersensitivity to DSB-causing agents are elevated [Bischof et al., 2001]. Cultured lymphoblastic cells from both WRN and BLM patients show spontaneously elevated levels of micronuclei, which further increased after treatment with compounds that interfered with DNA replication [Honma et al., 2002]. "

    Full-text · Article · Oct 2015 · Molecular syndromology
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    • "Another differentiating hallmark of chromothripsis is the close clustering of breaks, analogous to the clustering of mutations (kataegis), resulting from the activity of editing cytosine deaminases of the APOBEC superfamily [Kloosterman et al., 2012; Lada et al., 2015], which can only be fully ascertained by paired-end and mate-pair sequencing . Chromothripsis-based rearrangements affect only a single haplotype, which suggests that it occurred just before or during meiosis I and indicates a possible involvement of BLM and its partners [Bischof et al., 2001; Holloway et al., 2010]. Chromothripsis took place in the paternal germline in all 4 of the cases that could thus be evaluated [Kloosterman and Hochstenbach, 2014]. "
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    ABSTRACT: Complex chromosome rearrangements (CCRs) are currently defined as structural genome variations that involve more than 2 chromosome breaks and result in exchanges of chromosomal segments. They are thought to be extremely rare, but their detection rate is rising because of improvements in molecular cytogenetic technology. Their population frequency is also underestimated, since many CCRs may not elicit a phenotypic effect. CCRs may be the result of fork stalling and template switching, microhomology-mediated break-induced repair, breakage-fusion-bridge cycles, or chromothripsis. Patients with chromosomal instability syndromes show elevated rates of CCRs due to impaired DNA double-strand break responses during meiosis. Therefore, the putative functions of the proteins encoded by ATM , BLM , WRN , ATR , MRE11 , NBS1 , and RAD51 in preventing CCRs are discussed. CCRs may exert a pathogenic effect by either (1) gene dosage-dependent mechanisms, e.g. haploinsufficiency, (2) mechanisms based on disruption of the genomic architecture, such that genes, parts of genes or regulatory elements are truncated, fused or relocated and thus their interactions disturbed – these mechanisms will predominantly affect gene expression – or (3) mixed mutation mechanisms in which a CCR on one chromosome is combined with a different type of mutation on the other chromosome. Such inferred mechanisms of pathogenicity need corroboration by mRNA sequencing. Also, future studies with in vitro models, such as inducible pluripotent stem cells from patients with CCRs, and transgenic model organisms should substantiate current inferences regarding putative pathogenic effects of CCRs. The ramifications of the growing body of information on CCRs for clinical and experimental genetics and future treatment modalities are briefly illustrated with 2 cases, one of which suggests KDM4C (JMJD2C) as a novel candidate gene for mental retardation.
    Full-text · Article · Aug 2015 · Molecular syndromology
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    • "This issue is complicated by the fact that it has been shown that BLM is required to stimulate end-resection of a DSB and thereby promote HR (Gravel et al, 2008; Nimonkar et al, 2008, 2011), whereas in contrast the RNF8-/RNF168-dependent relocalization of 53BP1 plays a role in limiting DNA end-resection and HR (Bunting et al, 2010; Bothmer et al, 2011). Moreover, given that BLM can function as both a pro-recombinogenic (Gravel et al, 2008; Nimonkar et al, 2008, 2011) and anti-recombinogenic factor during later stages of homology-directed DSB repair (Bischof et al, 2001; Sengupta et al, 2003; Bugreev et al, 2007; Tripathi et al, 2007, 2008; Srivastava et al, 2009), it is conceivable that it may also be required to moderate the levels of HR. In support of a role for RNF8 and RNF168 in facilitating the relocalization of BLM to DSBs, cells depleted of either E3 ligase fail to properly form BLM foci following exposure to laser-generated DSB tracks (Supplementary Figure 4). "
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    ABSTRACT: Limiting the levels of homologous recombination (HR) that occur at sites of DNA damage is a major role of BLM helicase. However, very little is known about the mechanisms dictating its relocalization to these sites. Here, we demonstrate that the ubiquitin/SUMO-dependent DNA damage response (UbS-DDR), controlled by the E3 ligases RNF8/RNF168, triggers BLM recruitment to sites of replication fork stalling via ubiquitylation in the N-terminal region of BLM and subsequent BLM binding to the ubiquitin-interacting motifs of RAP80. Furthermore, we show that this mechanism of BLM relocalization is essential for BLM's ability to suppress excessive/uncontrolled HR at stalled replication forks. Unexpectedly, we also uncovered a requirement for RNF8-dependent ubiquitylation of BLM and PML for maintaining the integrity of PML-associated nuclear bodies and as a consequence the localization of BLM to these structures. Lastly, we identified a novel role for RAP80 in preventing proteasomal degradation of BLM in unstressed cells. Taken together, these data highlight an important biochemical link between the UbS-DDR and BLM-dependent pathways involved in maintaining genome stability.
    Full-text · Article · May 2013 · The EMBO Journal
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