Disease relevance of BLM

• BLM-/- cells showed hypersensitivities to the genotoxic agents as well as ultraviolet (UV) light, in addition to a 10-fold increase in targeted integration rate and an 11-fold increase in SCE frequency [1].
• We tested the hypothesis whether three polymorphic, non-conservative amino acid exchanges in WRN and BLM act as low-penetrance familial breast cancer risk factors [2].
• Of the five human RecQ helicases identified, three are associated with genetic disorders characterized by an elevated incidence of cancer or premature aging: Werner syndrome, Bloom syndrome, and Rothmund-Thomson syndrome [3].
• BLM physically associates with ATR (ataxia telangiectasia and rad3(+) related) protein and is phosphorylated on two residues in the N-terminal domain, Thr-99 and Thr-122, by this kinase [4].
• We show that, consistent with a role for BLM in protection of human cells against the toxicity associated with arrest of DNA replication, BS cells are hypersensitive to HU [4].

Psychiatry related information on BLM

• These disorders are xeroderma pigmentosum, Cockayne syndrome, trichothiodystrophy, Bloom syndrome, Werner syndrome, X-linked alpha-thalassemia/mental retardation syndrome, and Juberg-Marsidi syndrome [5].

High impact information on BLM

• This suggests that defects in the suppression of rearrangements involving divergent, repeated sequences may underlie the genome instability seen in BLM and WRN patients and in cancer cases associated with defects in these genes [6].
• Bloom syndrome is a disorder associated with genomic instability that causes affected people to be prone to cancer [7].
• In this novel mapping method, cells were used from persons with BS that had undergone intragenic recombination within BLM. cDNA analysis of the candidate gene identified a 4437 bp cDNA that encodes a 1417 amino acid peptide with homology to the RecQ helicases, a subfamily of DExH box-containing DNA and RNA helicases [8].
• A candidate for BLM was identified by direct selection of a cDNA derived from a 250 kb segment of the genome to which BLM had been assigned by somatic crossover point mapping [8].
• Sterility of Drosophila with mutations in the Bloom syndrome gene--complementation by Ku70 [9].

Chemical compound and disease context of BLM

• Liblomycin (LBM), a novel bleomycin analogue, and bleomycin A2 (BLM A2) were compared with respect to their relative potential to inhibit growth in a human head and neck squamous carcinoma cell line and to produce DNA damage within cellular DNA and nuclei DNA and against isolated naked DNA [10].
• The role of integrin alpha(v)beta(3) expression in the process of metastasis was tested by transfection of BLM, but did not lead to an altered pattern of metastasis [11].
• In study 1, a 0.5-mm-deep artificial plaque containing Streptococcus oralis cells was exposed to 10% sucrose for one min, and a 0.1-mm-thick film of sucrose-free artificial saliva was then flowed over the plaque surface at the unstimulated salivary film velocities previously found at the BLM and LLM sites [12].
• Forty-five patients with epidermoid cancer of the head and neck were either treated with cisplatin and bleomycin (DDP-BLM) or with vincristine, bleomycin and methotrexate (VBM) as neoadjuvant chemotherapy before radical radiation therapy (XRT) [13].
• We have cloned malignant cells carrying specific antigens associated with ovarian cancer (OVC) and malignant lymphoma (ML) from BS-SHI-4M cells, a line derived from a 1-methyl-3-nitro-1-nitrosoguanidine-treated B-lymphoblastoid cell line isolated from a patient with Bloom syndrome [14].

Biological context of BLM

• These results indicate that p53 and BLM functionally interact during resolution of stalled DNA replication forks and provide insight into the mechanism of genomic fidelity maintenance by these nuclear proteins [15].
• 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 [16].
• We also find that the FA core complex is necessary for BLM phosphorylation and assembly in nuclear foci in response to crosslinked DNA [17].
• BLM colocalizes with a select subset of telomeres in normal cells and with large telomeric clusters seen in simian virus 40-transformed normal fibroblasts [18].
• BLM is likely to be part of a DNA surveillance mechanism operating during S phase [18].

Anatomical context of BLM

• Moreover, BLM and WRN colocalized to nuclear foci in three human cell lines [19].
• We produced WRN-/-, BLM-/- and WRN(-/-)/BLM(-/-) mutants in the chicken B-cell line DT40 [1].
• Human males homozygous for BLM mutations are infertile and heterozygous individuals display increased frequencies of structural chromosome abnormalities in their spermatozoa [20].
• Our antibodies raised against the C terminus of the human protein specifically recognize both mouse and human BLM in western blots of cell lines and in successive developmental stages of spermatocytes, but fail to detect BLM protein in a cell line with a C-terminally truncated protein [20].
• Bone marrow cells from mice heterozygous for BLM mutation, BLM(Cin/+), transfected with BCR/ABL display increased sensitivity to cisplatin compared to those obtained from the wild-type littermates [21].

Associations of BLM with chemical compounds

• Moreover, lymphoblastoid cell lines (LCLs) derived from BS donors are resistant to both gamma-radiation and doxorubicin-induced cell killing, and sensitivity can be restored by the stable expression of normal BLM [22].
• Finally, we demonstrate that exposure to UVC and hydroxyurea treatment both induce BLM phosphorylation via an ATM-independent pathway [23].
• The results demonstrate that BLM and WRN proteins exhibit similar sensitivity profiles to these DNA-binding ligands and are most potently inhibited by the structurally related minor groove binders distamycin A and netropsin (K(i) </=1 microM) [24].
• The caspase 3 recognition sequence (412)TEVD(415) was verified by mutating aspartate 415 to glycine and showing that this mutation rendered BLM resistant to caspase 3 cleavage [25].
• Here, we show that BCR/ABL tyrosine kinase, which also modulates DNA repair capacity, is associated with elevated expression of BLM [21].

Physical interactions of BLM

• Biochemical experiments suggested that BLM resides in a nuclear matrix-bound complex in which association with hRAD51 may be direct [16].
• BLM helicase-dependent transport of p53 to sites of stalled DNA replication forks modulates homologous recombination [15].
• Amino acids 125 to 244 of Mus81 interact with the C-terminal region (amino acids 1,007-1,417) of BLM [26].
• The C terminus of BLM interacts directly with MLH1 in the yeast-two hybrid assay; far Western analysis and co-immunoprecipitations confirmed the interaction [27].

Enzymatic interactions of BLM

• Moreover, recombinant BLM was cleaved to 47- and 110-kDa fragments by caspase 3, but not caspase 6, in vitro [25].
• Finally, we present data demonstrating that, in response to ionizing radiation, BLM protein is phosphorylated and accumulates through an ATM-dependent pathway [28].
• We also demonstrate that BLM is directly phosphorylated at multiple sites in vitro by the mitotic cdc2 kinase, and identify two new sites of mitotic BLM phosphorylation: Ser-714 and Thr-766 [29].
• In the presence of ATP, BLM is phosphorylated and dissociates from DNA in a strictly DNA-PKcs-dependent manner [30].

Co-localisations of BLM

• BLM is found primarily in nuclear domain 10 except during S phase when it colocalizes with the Werner syndrome gene product, WRN, in the nucleolus [18].
• Following camptothecin treatment, T99p-BLM colocalized with gamma-H2AX but not with Top3alpha or PML [31].
• BLM co-localizes with TRF2 in foci actively synthesizing DNA during late S and G2/M; co-localization increases in late S and G2/M when ALT is thought to occur [32].

Regulatory relationships of BLM

• We show that the RAD51L3-XRCC2 complex stimulates BLM to disrupt synthetic 4-way junctions that model the Holliday junction [33].
• Certain BLM mutants (C1055S or Delta133-237) that have a reduced ability to localize to the NBs when expressed in normal cells can impair the localization of wild type BLM to NBs and block p53-mediated apoptosis, suggesting a dominant-negative effect [22].
• Telomere-binding protein TRF2 binds to and stimulates the Werner and Bloom syndrome helicases [34].
• Intra-nuclear trafficking of the BLM helicase to DNA damage-induced foci is regulated by SUMO modification [35].
• Functionally, BLM inhibited the exonuclease activity of WRN [19].

Other interactions of BLM

• DNA-damaging agents that cause double strand breaks and a G2 delay induced BLM by a p53- and ataxia-telangiectasia mutated independent mechanism [16].
• BLM localizes to promyelocytic leukemia protein (PML) nuclear bodies and is expressed during late S and G2 [16].
• These BLM foci recruited BRCA1 and NBS1 [36].
• We provide evidence that BLM and FANCD2 colocalise and co-immunoprecipitate following treatment with either DNA crosslinkers or agents inducing replication arrest [17].
• These conditions, however, did not prevent the DNA damage response in BLM-ablated cells, suggesting a distinct role for WRN in DNA homeostasis in vivo [37].
• SUV3 helicase ( SUPV3L1) was found to interact in vitro with BLM and WRN helicases

Analytical, diagnostic and therapeutic context of BLM

• BLM and FEN-1 are associated with each other in human nuclei as shown by their reciprocal co-immunoprecipitation from HeLa nuclear extracts [38].
• Like its RecQ helicase family member, WRN, the defective protein in Werner syndrome, dissection of the BLM protein revealed that its HRDC domain is sufficient for its recruitment to the damaged sites [39].
• Immunofluorescence and cellular fractionation demonstrate that BLM partitions to different sub-cellular compartments after replication stress [40].
• We have investigated the quaternary structure of BLM using a combination of size-exclusion chromatography and electron microscopy with reference-free image processing [41].
• To analyze its biochemical properties, we have overexpressed an oligohistidine-tagged version of the BLM gene product in Saccharomyces cerevisiae and purified the protein to apparent homogeneity using nickel chelate affinity chromatography [42].

References