scholarly journals New Bone Marrow Failure Genes: DNAJC21 and ERCC6L2

Blood ◽  
2017 ◽  
Vol 130 (Suppl_1) ◽  
pp. SCI-22-SCI-22
Author(s):  
Inderjeet Dokal
Keyword(s):  
Bone Marrow ◽  
Dna Damage ◽  
Nuclear Export ◽  
Conflicts Of Interest ◽  
Excision Repair ◽  
Bone Marrow Failure ◽  
Retinal Dystrophy ◽  
Ribosomal Subunit ◽  
Genotoxic Stress ◽  
Biallelic Mutations

A significant number of cases with bone marrow failure present with one or more extra-hematopoietic abnormality. This suggests a constitutional or genetic basis, and yet many of them remain uncharacterized. Through exome sequencing, we have recently identified two sub groups of these cases, one defined by germline biallelic mutations in DNAJC21 (DNAJ homolog subfamily C member 21) and the other in ERCC6L2 (excision repair cross complementing 6 like-2). Patients with DNAJC21 mutations are characterized by global bone marrow failure in early childhood. They can also have a variable number of extra-hematopoietic abnormalities such as short stature and retinal dystrophy. The encoded protein associates with ribosomal RNA (rRNA) and plays a highly conserved role in the maturation of the 60S ribosomal subunit. Lymphoblastoid patient cells exhibit increased sensitivity to the transcriptional inhibitor actinomycin D and reduced levels of rRNA. Characterisation of mutations has revealed impairment in interactions with cofactors (PA2G4, HSPA8 and ZNF622) involved in 60S maturation. DNAJC21 deficiency results in cytoplasmic accumulation of the 60S nuclear export factor PA2G4, aberrant ribosome profiles and increased cell death. Collectively these findings demonstrate that biallelic mutations in DNAJC21 cause disease due to defects in early nuclear rRNA biogenesis and late cytoplasmic maturation of the 60S subunit. Patients harbouring biallelic ERCC6L 2 mutations are characterized by bone marrow failure (in childhood or early adulthood) and one or more extra-hematopoietic abnormality such as microcephaly. Knockdown of ERCC6L2 in human cells significantly reduces their viability upon exposure to the DNA damaging agent irofulven but not etoposide and camptothecin suggesting a role in nucleotide excision repair. ERCC6L2 knockdown cells and patient cells harbouring biallelic ERCC6L2 mutations also display H2AX phosphorylation that significantly increases upon genotoxic stress, suggesting an early DNA damage response. ERCC6L2 is seen to translocate to mitochondria as well as the nucleus in response to DNA damage and its knockdown induces intracellular reactive oxygen species (ROS). Treatment with the ROS scavenger, N-acetyl-cysteine, attenuates the irofulven-induced cytotoxicity in ERCC6L2 knockdown cells and abolishes its traffic to mitochondria and nucleus in response to this DNA damaging agent. Collectively, these observations suggest that ERCC6L2has a pivotal rolein DNA repair and mitochondrial function. In conclusion, ERCC6L2 and DNAJC21 have an important role in maintaining genomic stability and ribosome biogenesis, respectively. They bring into focus new biological connections/pathways whose constitutional disruption is associated with defective hematopoiesis since patients harbouring germline biallelic mutations in these genes uniformly have bone marrow failure. Disclosures No relevant conflicts of interest to declare.

Both p53-Dependent and -Independent Pathways Contribute to Erythroid Dysplasia in a Zebrafish Model for Diamond Blackfan Anemia.

Blood ◽  
2009 ◽  
Vol 114 (22) ◽  
pp. 177-177 ◽  
Author(s):  
Elspeth Payne ◽  
Hong Sun ◽  
Barry H. Paw ◽  
A. Thomas Look ◽  
Arati Khanna-Gupta
Keyword(s):  
Bone Marrow ◽  
Ribosomal Protein ◽  
Conflicts Of Interest ◽  
Bone Marrow Failure ◽  
Ribosomal Subunit ◽  
Specific Effect ◽  
Independent Component ◽  
Diamond Blackfan Anemia ◽  
Increased Risk ◽  
Erythroid Maturation

Abstract Abstract 177 Diamond Blackfan Anemia (DBA) is a congenital autosomal dominant bone marrow failure syndrome of childhood manifested as profound anemia. The disease is characterized by enhanced sensitivity of hematopoietic progenitors to apoptosis with evidence of stressed erythropoiesis. In addition to bone marrow defects, DBA patients often have craniofacial, genitourinary, cardiac and limb abnormalities and have an increased risk of developing hematopoietic malignancies and osteosarcoma. Twenty-five percent of patients with DBA have heterozygous mutations in the ribosomal protein S19 (RPS19) gene, which encodes a component of the 40S ribosomal subunit. Additionally, a growing percentage of DBA patients lacking a mutation in the RPS19 gene have been shown to have mutations in other ribosomal protein genes. These observations support the hypothesis that DBA is a disease of altered ribosome assembly and function. It is unclear how defects in ribosomal proteins have such a specific effect on erythroid maturation and cause increased apoptosis in the erythroid compartment. An attempt to model DBA by homozygous deletion of the Rps19 gene in mice proved to be embryonic lethal, and heterozygous mice appeared to fully compensate for the loss of one Rps19 allele, in contrast to the disease observed in humans. However, two groups have successfully modeled DBA in zebrafish using an antisense morpholino (MO) approach. These studies demonstrated that similar to the human disease, rps19 deficiency leads to defective erythropoiesis, increased apoptosis and to developmental abnormalities. A central role for the tumor suppressor p53 was suggested in one of these studies. It has previously been shown that any MO injection into zebrafish embryos can lead to the activation of the p53 pathway. Therefore, in order to clarify whether p53-independent effects also contributed to the DBA phenotype in zebrafish, we utilized the p53e7/e7 line that harbors a mutation within the p53 DNA-binding domain. Splice site and validated 5'UTR MOs targeting zebrafish rps19 were injected into one-cell stage embyros that were wildtype (WT) for p53 (AB) or mutated p53e7/e7. Staining for hemoglobin at 48 hours post fertilization showed a profound reduction in circulating blood in both p53 wild-type and p53 mutant embryos. Although p53 mutants injected with rps19 MO show a similar reduction in hemoglobin expression to WT morphants, they have a marked improvement in their developmental defects. A 20% decrease in expression of the transcription factor GATA-1 was observed in the rps19 morphants in the p53 mutant background compared to control MO injection. The implications of this finding are being further investigated and extended to include a panel of additional erythroid-specific factors. We have observed no increase in the levels of cell death, as measured by acridine orange (AO) staining or expression of the p53-regulated apoptosis associated gene PUMA, in the p53 mutant background. Taken together, our observations indicate that the phenotype observed in DBA has both a p53-dependent and a p53-independent component. We hypothesize that the p53-dependent component of DBA is likely responsible for the increased apoptosis associated with DBA while the erythroid maturation defect is associated, in large part, with a p53-independent component. Our studies are currently focused on identifying the players in the latter pathway. These investigations should shed light on thus far undefined pathways that will likely open new avenues for drug design and development for DBA. Disclosures: No relevant conflicts of interest to declare.

scholarly journals Phosphorylation of the Mdm2 oncoprotein by the c-Abl tyrosine kinase regulates p53 tumor suppression and the radiosensitivity of mice

2016 ◽  
Vol 113 (52) ◽  
pp. 15024-15029 ◽  
Author(s):  
Michael I. Carr ◽  
Justine E. Roderick ◽  
Hong Zhang ◽  
Bruce A. Woda ◽  
Michelle A. Kelliher ◽  
...  
Keyword(s):  
Bone Marrow ◽  
Dna Damage ◽  
Tumor Suppression ◽  
Bone Marrow Failure ◽  
Genotoxic Stress ◽  
Whole Body ◽  
Atm Kinase ◽  
Radiation Induced

The p53 tumor suppressor acts as a guardian of the genome by preventing the propagation of DNA damage-induced breaks and mutations to subsequent generations of cells. We have previously shown that phosphorylation of the Mdm2 oncoprotein at Ser394 by the ATM kinase is required for robust p53 stabilization and activation in cells treated with ionizing radiation, and that loss of Mdm2 Ser394 phosphorylation leads to spontaneous tumorigenesis and radioresistance in Mdm2S394A mice. Previous in vitro data indicate that the c-Abl kinase phosphorylates Mdm2 at the neighboring residue (Tyr393) in response to DNA damage to regulate p53-dependent apoptosis. In this present study, we have generated an Mdm2 mutant mouse (Mdm2Y393F) to determine whether c-Abl phosphorylation of Mdm2 regulates the p53-mediated DNA damage response or p53 tumor suppression in vivo. The Mdm2Y393F mice develop accelerated spontaneous and oncogene-induced tumors, yet display no defects in p53 stabilization and activity following acute genotoxic stress. Although apoptosis is unaltered in these mice, they recover more rapidly from radiation-induced bone marrow ablation and are more resistant to whole-body radiation-induced lethality. These data reveal an in vivo role for c-Abl phosphorylation of Mdm2 in regulation of p53 tumor suppression and bone marrow failure. However, c-Abl phosphorylation of Mdm2 Tyr393 appears to play a lesser role in governing Mdm2-p53 signaling than ATM phosphorylation of Mdm2 Ser394. Furthermore, the effects of these phosphorylation events on p53 regulation are not additive, as Mdm2Y393F/S394A mice and Mdm2S394A mice display similar phenotypes.

scholarly journals Congenital bone marrow failure in DNA-PKcs mutant mice associated with deficiencies in DNA repair

2011 ◽  
Vol 193 (2) ◽  
pp. 295-305 ◽  
Author(s):  
Shichuan Zhang ◽  
Hirohiko Yajima ◽  
HoangDinh Huynh ◽  
Junke Zheng ◽  
Elsa Callen ◽  
...  
Keyword(s):  
Bone Marrow ◽  
Dna Damage ◽  
Dna Repair ◽  
Bone Marrow Failure ◽  
Genotoxic Stress ◽  
Nonhomologous End Joining ◽  
End Joining ◽  
Hematopoietic Stem ◽  
Dependent Protein ◽  
P53 Activation

The nonhomologous end-joining (NHEJ) pathway is essential for radioresistance and lymphocyte-specific V(D)J (variable [diversity] joining) recombination. Defects in NHEJ also impair hematopoietic stem cell (HSC) activity with age but do not affect the initial establishment of HSC reserves. In this paper, we report that, in contrast to deoxyribonucleic acid (DNA)–dependent protein kinase catalytic subunit (DNA-PKcs)–null mice, knockin mice with the DNA-PKcs3A/3A allele, which codes for three alanine substitutions at the mouse Thr2605 phosphorylation cluster, die prematurely because of congenital bone marrow failure. Impaired proliferation of DNA-PKcs3A/3A HSCs is caused by excessive DNA damage and p53-dependent apoptosis. In addition, increased apoptosis in the intestinal crypt and epidermal hyperpigmentation indicate the presence of elevated genotoxic stress and p53 activation. Analysis of embryonic fibroblasts further reveals that DNA-PKcs3A/3A cells are hypersensitive to DNA cross-linking agents and are defective in both homologous recombination and the Fanconi anemia DNA damage response pathways. We conclude that phosphorylation of DNA-PKcs is essential for the normal activation of multiple DNA repair pathways, which in turn is critical for the maintenance of diverse populations of tissue stem cells in mice.

scholarly journals NIPA As a Novel Regulator of Aging and Stress Response of the Primitive HSC Pool

Blood ◽  
2015 ◽  
Vol 126 (23) ◽  
pp. 1155-1155
Author(s):  
Stefanie Kreutmair ◽  
Rouzanna Istvanffy ◽  
Cathrin Klingeberg ◽  
Christine Dierks ◽  
Christian Peschel ◽  
...  
Keyword(s):  
Bone Marrow ◽  
Dna Damage ◽  
Stress Response ◽  
Progenitor Cells ◽  
Conflicts Of Interest ◽  
Bone Marrow Failure ◽  
Hematopoietic Stem ◽  
Age Related

Abstract Accumulation of DNA damage in hematopoietic stem cells (HSCs) is associated with aging, bone marrow failure and development of hematological malignancies. Although HSCs numerically expand with age, their functional activity declines over time and the protection mechanism from DNA damage accumulation remains to be elucidated. NIPA (Nuclear Interaction Partner of ALK) is highly expressed in hematopoietic stem and progenitor cells, especially in the most primitive long-term repopulating HSCs (CD34-Flt3-Lin-Sca1+cKit+). Loss of NIPA leads to a significant exhaustion of primitive hematopoietic cells, where Lin-Sca1+cKit+ (LSK) cells were reduced to 40% of wildtype (wt) littermates (p<0.001). All LSK-subgroups, LT-HSCs (p<0.001), ST-HSCs (CD34+Flt3-LSK; p<0.01) and MPPs (CD34+Flt3+LSK; p<0.05) of NIPA deficient animals are affected and failed to age-related increase, whereas the lineage differentiation of Nipako/ko progenitor cells showed no gross differences. Myeloid depression by 5-FU treatment led to severely reduced HSC self renewal in Nipako/ko mice independent of age (p<0.001). Moreover, weekly 5-FU activation showed reduced survival of Nipako/ko vs. wt animals (11 vs. 14.5 days). To further examine the role of NIPA in HSC maintenance and exhaustion, we performed in vivo repopulationexperiments, where Nipa deletion causes bone marrow failure in case of competition, as Nipako/ko cells contributed to less than 10% of transplanted BM cells 6 month after transplantation (TX). According to this, colony formation assays and limiting dilution transplantation showed a dramatic reduction of competitive repopulation units (p<0.0001) in Nipako/ko animals. Serial LSK transplantation assays revealed loss of Nipa-deficient LSKs shortly after TX, whereas long-term repopulation capacity seemed to be maintained, suggesting a role of NIPA in critical stress response. To further investigate the stress response in Nipa-deficient HSCs, we irradiated LSKs with 3 Gy and stained for DNA-Damage foci by pH2ax. Remarkably, loss of NIPA led to significant higher numbers of pH2ax foci in irradiated HSCs (46% > 6 foci vs. 17% > 6 foci in wt cells) and highly increased the rates of apoptotic cells especially in the primitive CD34-LSK population. Taken together our results highlight the importance of the DNA damage response at HSC level for lifelong hematopoiesis and establish NIPA as a novel regulator of aging and stress response of the primitive HSC pool. Disclosures No relevant conflicts of interest to declare.

scholarly journals Genomic Instability in Fanconi Anemia Results from a Combination of Chromosome Mis-Segregation in Mitosis and Unresolved Interphase DNA Damage

Blood ◽  
2014 ◽  
Vol 124 (21) ◽  
pp. 357-357 ◽  
Author(s):  
Donna Cerabona ◽  
Zahi Abdul Sater ◽  
Rikki Enzor ◽  
Grzegorz Nalepa
Keyword(s):  
Bone Marrow ◽  
Dna Damage ◽  
Genomic Instability ◽  
Fanconi Anemia ◽  
Chromosomal Instability ◽  
Conflicts Of Interest ◽  
Bone Marrow Failure ◽  
Genetic Disorder ◽  
Biological Significance

Abstract Fanconi anemia (FA) is a complex genetic disorder characterized by bone marrow failure, multiple congenital anomalies, and genomic instability resulting in predisposition to cancer. Disruption of the FA signaling network impairs multiple genome-housekeeping processes, including DNA damage recognition and repair in interphase, DNA replication as well as high-fidelity chromosome segregation during mitosis. Recent data published by several groups, including our work (J Clin Invest 2013; 123: 3839-3847), implicated FA signaling in the control of several cell division events essential for chromosomal stability, including the spindle assembly checkpoint (SAC), centrosome maintenance, resolution of ultrafine anaphase bridges and cytokinesis. Understanding the mechanistic origins of chromosomal instability leading to carcinogenesis and bone marrow failure has important scientific and clinical implications. However, the relative contribution of the interphase and mitotic events leading to genomic instability in Fanconi anemia has not been systematically evaluated. In this work, we dissected the origins and mechanistic significance of chromosomal instability in Fanconi anemia ex vivo and in vivo. We employed the cytochalasin micronucleus assay to quantify the patterns of spontaneous and chemotherapy-induced genomic lesions in FA-A patient-derived primary fibroblasts and Fancc-/- mouse embryonic fibroblasts (MEFs). In this assay, dividing cells are treated with cytochalasin to inhibit cytokinesis and generate binucleated daughter cells. The presence of micronuclei in the resulting cells is indicative of genomic instability caused by either interphase DNA damage or chromosome mis-segregation. Centromere-negative micronuclei (CNMs) represent chromosomal fragments due to unresolved ds-DNA damage. Centromere-positive micronuclei (CPMs) result from whole-chromosome mis-segregation during mitosis. The frequency of both CPMs and CNMs was significantly increased in FA-deficient human and murine cells compared to gene-corrected isogenic control cells. These results indicate that genomic instability in FA is caused by a combination of interphase DNA damage and disordered mitosis. We confirmed the biological significance of these findings by showing that FA patient cells are hypersensitive to low concentrations of taxol (a spindle checkpoint-activating chemotherapeutic) similarly to mitomycin C (a cross-linking agent). Finally, we found increased frequency of micronuclei in Fancc-/- murine red blood cells compared to age-matched wild-type mice, which indicates that spontaneous chromosome mis-segregation occurs in FA-deficient bone marrow in vivo. Our study supports the emerging model of the FA family of proteins as holistic guardians of the genome during interphase and mitosis (see figure based on F1000Prime Rep. 2014; 6: 23, modified). This model furthers our understanding of genomic instability in Fanconi anemia and FA-deficient cancers, and opens new inroads towards targeted therapeutic interventions in these diseases. Figure 1 Figure 1. Disclosures No relevant conflicts of interest to declare.

The Zebrafish Provides Mechanistic Insights into the Role of Poly(A)-Specific Ribonuclease (PARN) in Hematopoietic Stem Cell (HSC) Homeostasis and Bone Marrow Failure

Blood ◽  
2015 ◽  
Vol 126 (23) ◽  
pp. 668-668
Author(s):  
Adam P Deveau ◽  
Andrew J Coombs ◽  
Santhosh Dhanraj ◽  
Gretchen Wagner ◽  
Yigal Dror ◽  
...  
Keyword(s):  
Bone Marrow ◽  
Stem Cell ◽  
Hematopoietic Stem Cell ◽  
Conflicts Of Interest ◽  
Bone Marrow Failure ◽  
Hematopoietic Stem ◽  
Phosphohistone H3 ◽  
Biallelic Mutations ◽  
Insight Into

Abstract Development of tissues during embryogenesis and their homeostasis after formation are highly regulated by expression of coding and non-coding RNAs. Deadenylation is a core mechanism that regulates RNA function and fate by controlling turnover, abundance and maturation of RNA. Factors that promote or inhibit deadenylation control hematopoietic stem cell (HSC) homeostasis, and inhibition of deadenylation limits differentiation of the HSCs. Importantly, RNA biogenesis has emerged as a mechanism underlying several inherited bone marrow failure syndromes (IBMFSs), such as Diamond Blackfan anemia, dyskeratosis congenita (DC) and Shwachman-Diamond syndrome. Poly(A)-specific ribonuclease (PARN) is a major deadenylation factor and demonstrates high specificity for single-stranded poly (A) tails of various RNA species. We recently identified biallelic mutations in PARN as a cause of hematopoietic failure and profound hypomyelination, similar to the severe form of DC, Hoyeraal-Hreidersson syndrome. We developed a zebrafish model to characterize the hematopoietic phenotype of a patient identified to have severe inherited bone marrow failure resulting from a combined deletion of PARN on one allele and missense mutation in the other. Zebrafish posses a single parn ortholog. Zebrafish parn protein shares homology and high sequence identity (~64%) to its human counterpart. Embryos were injected with either translation start-site or splice-site-blocking morpholino at the one-cell stage. Both morpholino injections resulted in anemic embryos at 48 hours post fertilization (hpf), as evidenced by reduced o-dianisidine staining and gata1 expression by whole-mount in situ hybrization and GFP+ red cell numbers by fluorescence-activated cell sorting (FACS). Morphant embryos also demonstrated reduced expression of myeloid cell markers including l-plastin, myeloperoxidase, and macrophage expressed gene 1 and were leukopenic as evidenced by reduced number of GFP+ myeloid cells. FACS analysis revealed that fluorescently labeled HSCs were increased in parn morphants. Early hematopoietic markers, lmo2 and fli1, expressed in hemogenic and vascular tissue respectively, were also overexpressed in parn morphants. Furthermore, there was reduced global cell proliferation in morphant embryos as determined by phosphohistone H3 antibody staining. These findings suggest that the absence of parn results in a developmental arrest at the HSC stage with an inability to differentiate into leukocyte or erythroid lineages. Similarly, human cell culture data from PARN-deficient HSC/progenitor cells demonstrated markedly reduced colony forming capacity. By modeling parn deficiency in the zebrafish, we validate for the first time an IBMFS that results from biallelic mutations in a major deadenylating protein. Moreover, our zebrafish studies provide insight into the role of parn in maintaining HSC homeostasis/differentiation as the origin of the pancytopenia observed in this patient. Permanent knockouts in the zebrafish using CRISPR/Cas9 technology are underway, which will enable tracking the hematopoietic phenotype into adulthood. These studies have set the stage for critical translational research in a rare form of bone marrow failure as well as new insight into HSC regulation. Disclosures No relevant conflicts of interest to declare.

scholarly journals Monitoring and treatment of MDS in genetically susceptible persons

Hematology ◽  
2019 ◽  
Vol 2019 (1) ◽  
pp. 105-109 ◽  
Author(s):  
Stella M. Davies
Keyword(s):  
Bone Marrow ◽  
Dna Damage ◽  
Bone Marrow Failure ◽  
Treatment Strategies ◽  
Informed Choice ◽  
Dyskeratosis Congenita ◽  
Careful Consideration ◽  
Host Susceptibility ◽  
Bone Marrow Failure Syndromes ◽  
Severe Infections

Abstract Genetic susceptibility to myelodysplastic syndrome (MDS) occurs in children with inherited bone marrow failure syndromes, including Fanconi anemia, Shwachman Diamond syndrome, and dyskeratosis congenita. Available evidence (although not perfect) supports annual surveillance of the blood count and bone marrow in affected persons. Optimal treatment of MDS in these persons is most commonly transplantation. Careful consideration must be given to host susceptibility to DNA damage when selecting a transplant strategy, because significant dose reductions and avoidance of radiation are necessary. Transplantation before evolution to acute myeloid leukemia (AML) is optimal, because outcomes of AML are extremely poor. Children and adults can present with germline mutations in GATA2 and RUNX1, both of which are associated with a 30% to 40% chance of evolution to MDS. GATA2 deficiency may be associated with a clinically important degree of immune suppression, which can cause severe infections that can complicate transplant strategies. GATA2 and RUNX1 deficiency is not associated with host susceptibility to DNA damage, and therefore, conventional treatment strategies for MDS and AML can be used. RUNX1 deficiency has a highly variable phenotype, and MDS can occur in childhood and later in adulthood within the same families, making annual surveillance with marrow examination burdensome; however, such strategies should be discussed with affected persons, allowing an informed choice.

Biallelic mutations in EXOC3L2 cause a novel syndrome that affects the brain, kidney and blood

2018 ◽  
Vol 56 (5) ◽  
pp. 340-346
Author(s):  
Adel Shalata ◽  
Supanun Lauhasurayotin ◽  
Zvi Leibovitz ◽  
Hongbing Li ◽  
Diane Hebert ◽  
...  
Keyword(s):  
Bone Marrow ◽  
Bone Marrow Failure ◽  
Renal Dysplasia ◽  
Chromosomal Microarray ◽  
Chromosomal Microarray Analysis ◽  
Dandy Walker Malformation ◽  
Whole Exome ◽  
Pituitary Hypoplasia ◽  
Walker Malformation ◽  
Biallelic Mutations

BackgroundDandy-Walker malformation features agenesis/hypoplasia of the cerebellar vermis, cystic dilatation of the fourth ventricle and enlargement of posterior fossa. Although Dandy-Walker malformation is relatively common and several genes were linked to the syndrome, the genetic cause in the majority of cases is unknown.ObjectiveTo identify the mutated gene responsible for Dandy-Walker malformation, kidney disease and bone marrow failure in four patients from two unrelated families.MethodsMedical assessment, sonographic, MRI and pathological studies were used to define phenotype. Chromosomal microarray analysis and whole-exome sequence were performed to unravel the genotype.ResultsWe report four subjects from two unrelated families with homozygous mutations in the Exocyst Complex Component 3-Like-2 gene (EXOC3L2).EXOC3L2 functions in trafficking of post-Golgi vesicles to the plasma membrane. In the first family a missense mutation in a highly conserved amino acid, p.Leu41Gln, was found in three fetuses; all had severe forms of Dandy-Walker malformation that was detectable by prenatal ultrasonography and confirmed by autopsy. In the second family, the affected child carried a nonsense mutation, p.Arg72*, and no detected protein. He had peritrigonal and cerebellar white matter abnormalities with enlargement of the ventricular trigones, developmental delay, pituitary hypoplasia, severe renal dysplasia and bone marrow failure.ConclusionWe propose that biallelic EXOC3L2 mutations lead to a novel syndrome that affects hindbrain development, kidney and possibly the bone marrow.

scholarly journals PARP Inhibitor Olaparib Causes No Potentiation of the Bleomycin Effect in VERO Cells, Even in the Presence of Pooled ATM, DNA-PK, and LigIV Inhibitors

2020 ◽  
Vol 21 (21) ◽  
pp. 8288
Author(s):  
Valentina Perini ◽  
Michelle Schacke ◽  
Pablo Liddle ◽  
Salomé Vilchez-Larrea ◽  
Deborah J. Keszenman ◽  
...  
Keyword(s):  
Dna Damage ◽  
Homologous Recombination ◽  
Synthetic Lethality ◽  
Excision Repair ◽  
Parp Inhibitor ◽  
Genotoxic Stress ◽  
Vero Cells ◽  
Limiting Factor ◽  
Parp Activation ◽  
Alternative Hypotheses

Poly(ADP-ribosyl)polymerase (PARP) synthesizes poly(ADP-ribose) (PAR), which is anchored to proteins. PAR facilitates multiprotein complexes’ assembly. Nuclear PAR affects chromatin’s structure and functions, including transcriptional regulation. In response to stress, particularly genotoxic stress, PARP activation facilitates DNA damage repair. The PARP inhibitor Olaparib (OLA) displays synthetic lethality with mutated homologous recombination proteins (BRCA-1/2), base excision repair proteins (XRCC1, Polβ), and canonical nonhomologous end joining (LigIV). However, the limits of synthetic lethality are not clear. On one hand, it is unknown whether any limiting factor of homologous recombination can be a synthetic PARP lethality partner. On the other hand, some BRCA-mutated patients are not responsive to OLA for still unknown reasons. In an effort to help delineate the boundaries of synthetic lethality, we have induced DNA damage in VERO cells with the radiomimetic chemotherapeutic agent bleomycin (BLEO). A VERO subpopulation was resistant to BLEO, BLEO + OLA, and BLEO + OLA + ATM inhibitor KU55933 + DNA-PK inhibitor KU-0060648 + LigIV inhibitor SCR7 pyrazine. Regarding the mechanism(s) behind the resistance and lack of synthetic lethality, some hypotheses have been discarded and alternative hypotheses are suggested.

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