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1.
PNAS Nexus ; 3(7): pgae242, 2024 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-38957451

RESUMO

The Fanconi anemia (FA) repair pathway governs repair of highly genotoxic DNA interstrand crosslinks (ICLs) and relies on translesion synthesis (TLS). TLS is facilitated by REV1 or site-specific monoubiquitination of proliferating cell nuclear antigen (PCNA) (PCNA-Ub) at lysine 164 (K164). A PcnaK164R/K164R but not Rev1-/- mutation renders mammals hypersensitive to ICLs. Besides the FA pathway, alternative pathways have been associated with ICL repair (1, 2), though the decision making between those remains elusive. To study the dependence and relevance of PCNA-Ub in FA repair, we intercrossed PcnaK164R/+; Fancg-/+ mice. A combined mutation (PcnaK164R/K164R; Fancg-/- ) was found embryonically lethal. RNA-seq of primary double-mutant (DM) mouse embryonic fibroblasts (MEFs) revealed elevated levels of replication stress-induced checkpoints. To exclude stress-induced confounders, we utilized a Trp53 knock-down to obtain a model to study ICL repair in depth. Regarding ICL-induced cell toxicity, cell cycle arrest, and replication fork progression, single-mutant and DM MEFs were found equally sensitive, establishing PCNA-Ub to be critical for FA-ICL repair. Immunoprecipitation and spectrometry-based analysis revealed an unknown role of PCNA-Ub in excluding mismatch recognition complex MSH2/MSH6 from being recruited to ICLs. In conclusion, our results uncovered a dual function of PCNA-Ub in ICL repair, i.e. exclude MSH2/MSH6 recruitment to channel the ICL toward canonical FA repair, in addition to its established role in coordinating TLS opposite the unhooked ICL.

2.
Int J Mol Sci ; 24(13)2023 Jul 05.
Artigo em Inglês | MEDLINE | ID: mdl-37446306

RESUMO

Fanconi anemia (FA) develops due to a mutation in one of the FANC genes that are involved in the repair of interstrand crosslinks (ICLs). FANCG, a member of the FA core complex, is essential for ICL repair. Previous FANCG-deficient mouse models were generated with drug-based selection cassettes in mixed mice backgrounds, leading to a disparity in the interpretation of genotype-related phenotype. We created a Fancg-KO (KO) mouse model using CRISPR/Cas9 to exclude these confounders. The entire Fancg locus was targeted and maintained on the immunological well-characterized C57BL/6J background. The intercrossing of heterozygous mice resulted in sub-Mendelian numbers of homozygous mice, suggesting the loss of FANCG can be embryonically lethal. KO mice displayed infertility and hypogonadism, but no other developmental problems. Bone marrow analysis revealed a defect in various hematopoietic stem and progenitor subsets with a bias towards myelopoiesis. Cell lines derived from Fancg-KO mice were hypersensitive to the crosslinking agents cisplatin and Mitomycin C, and Fancg-KO mouse embryonic fibroblasts (MEFs) displayed increased γ-H2AX upon cisplatin treatment. The reconstitution of these MEFs with Fancg cDNA corrected for the ICL hypersensitivity. This project provides a new, genetically, and immunologically well-defined Fancg-KO mouse model for further in vivo and in vitro studies on FANCG and ICL repair.


Assuntos
Cisplatino , Anemia de Fanconi , Humanos , Animais , Camundongos , Cisplatino/metabolismo , Anemia de Fanconi/genética , Anemia de Fanconi/metabolismo , Camundongos Endogâmicos C57BL , Sistemas CRISPR-Cas , Proteínas de Ligação a DNA/metabolismo , Fibroblastos/metabolismo , Mitomicina , Fenótipo , Proteína do Grupo de Complementação G da Anemia de Fanconi/genética
3.
Proc Natl Acad Sci U S A ; 120(4): e2216055120, 2023 Jan 24.
Artigo em Inglês | MEDLINE | ID: mdl-36669105

RESUMO

DNA damage threatens genomic integrity and instigates stem cell failure. To bypass genotoxic lesions during replication, cells employ DNA damage tolerance (DDT), which is regulated via PCNA ubiquitination and REV1. DDT is conserved in all domains of life, yet its relevance in mammals remains unclear. Here, we show that inactivation of both PCNA-ubiquitination and REV1 results in embryonic and adult lethality, and the accumulation of DNA damage in hematopoietic stem and progenitor cells (HSPCs) that ultimately resulted in their depletion. Our results reveal the crucial relevance of DDT in the maintenance of stem cell compartments and mammalian life in unperturbed conditions.


Assuntos
Dano ao DNA , Animais , Reparo do DNA , Replicação do DNA , Células-Tronco Hematopoéticas/metabolismo , Mamíferos/metabolismo , Antígeno Nuclear de Célula em Proliferação/metabolismo , Ubiquitinação
4.
Front Pharmacol ; 12: 596535, 2021.
Artigo em Inglês | MEDLINE | ID: mdl-33679394

RESUMO

The antihelmintic drug ABZ and its metabolites belong to the chemical family of benzimidazoles (BZM) that act as potent tubulin polymerization inhibitors, suggesting a potential re-direction of BZMs for cancer therapy. Applying UV-Vis spectrometry we here demonstrate ABZ as a DNA intercalator. This insight led us to determine the primary mode of ABZ action in mammalian cells. As revealed by RNA sequencing, ABZ did neither grossly affect replication as analyzed by survival and replication stress signaling, nor the transcriptome. Actually, unbiased transcriptome analysis revealed a marked cell cycle signature in ABZ exposed cells. Indeed, short-term exposure to ABZ arrested mammalian cells in G2/M cell cycle stages associated with frequent gains and losses of chromatin. Cellular analyses revealed ABZ as a potent mammalian spindle poison for normal and malignant cells, explaining the serious chromosome segregation defects. Since chromosomal aberrations promote both cancer development and cell death, we determined if besides its general cytotoxicity, ABZ could predispose to tumor development. As measured by loss of heterozygosity (LOH) in vitro and in vivo ABZ was found as a potent inducer of LOH and accelerator of chromosomal missegregation.

5.
Front Immunol ; 12: 807015, 2021.
Artigo em Inglês | MEDLINE | ID: mdl-35069591

RESUMO

Upon antigen recognition, activation-induced cytosine deaminase initiates affinity maturation of the B-cell receptor by somatic hypermutation (SHM) through error-prone DNA repair pathways. SHM typically creates single nucleotide substitutions, but tandem substitutions may also occur. We investigated incidence and sequence context of tandem substitutions by massive parallel sequencing of V(D)J repertoires in healthy human donors. Mutation patterns were congruent with SHM-derived single nucleotide mutations, delineating initiation of the tandem substitution by AID. Tandem substitutions comprised 5,7% of AID-induced mutations. The majority of tandem substitutions represents single nucleotide juxtalocations of directly adjacent sequences. These observations were confirmed in an independent cohort of healthy donors. We propose a model where tandem substitutions are predominantly generated by translesion synthesis across an apyramidinic site that is typically created by UNG. During replication, apyrimidinic sites transiently adapt an extruded configuration, causing skipping of the extruded base. Consequent strand decontraction leads to the juxtalocation, after which exonucleases repair the apyramidinic site and any directly adjacent mismatched base pairs. The mismatch repair pathway appears to account for the remainder of tandem substitutions. Tandem substitutions may enhance affinity maturation and expedite the adaptive immune response by overcoming amino acid codon degeneracies or mutating two adjacent amino acid residues simultaneously.


Assuntos
Mutação , Sequências de Repetição em Tandem , Alelos , Códon , Reparo de Erro de Pareamento de DNA , Sequenciamento de Nucleotídeos em Larga Escala , Humanos , Cadeias Pesadas de Imunoglobulinas/genética , Receptores de Antígenos de Linfócitos B/genética , Hipermutação Somática de Imunoglobulina , Recombinação V(D)J
6.
Nucleic Acids Res ; 47(14): 7163-7181, 2019 08 22.
Artigo em Inglês | MEDLINE | ID: mdl-31251805

RESUMO

The DNA damage response network guards the stability of the genome from a plethora of exogenous and endogenous insults. An essential feature of the DNA damage response network is its capacity to tolerate DNA damage and structural impediments during DNA synthesis. This capacity, referred to as DNA damage tolerance (DDT), contributes to replication fork progression and stability in the presence of blocking structures or DNA lesions. Defective DDT can lead to a prolonged fork arrest and eventually cumulate in a fork collapse that involves the formation of DNA double strand breaks. Four principal modes of DDT have been distinguished: translesion synthesis, fork reversal, template switching and repriming. All DDT modes warrant continuation of replication through bypassing the fork stalling impediment or repriming downstream of the impediment in combination with filling of the single-stranded DNA gaps. In this way, DDT prevents secondary DNA damage and critically contributes to genome stability and cellular fitness. DDT plays a key role in mutagenesis, stem cell maintenance, ageing and the prevention of cancer. This review provides an overview of the role of DDT in these aspects.


Assuntos
Adaptação Fisiológica/genética , Envelhecimento/genética , Dano ao DNA , Mutagênese , Neoplasias/genética , Células-Tronco/metabolismo , Animais , Reparo do DNA , Humanos , Modelos Genéticos , Neoplasias/terapia
7.
Front Immunol ; 10: 438, 2019.
Artigo em Inglês | MEDLINE | ID: mdl-30915081

RESUMO

Somatic hypermutation (SHM) of immunoglobulin (Ig) genes plays a key role in antibody mediated immunity. SHM in B cells provides the molecular basis for affinity maturation of antibodies. In this way SHM is key in optimizing antibody dependent immune responses. SHM is initiated by targeting the Activation-Induced Cytidine Deaminase (AID) to rearranged V(D)J and switch regions of Ig genes. The mutation rate of this programmed mutagenesis is ~10-3 base pairs per generation, a million-fold higher than the non-AID targeted genome of B cells. AID is a processive enzyme that binds single-stranded DNA and deaminates cytosines in DNA. Cytosine deamination generates highly mutagenic deoxy-uracil (U) in the DNA of both strands of the Ig loci. Mutagenic processing of the U by the DNA damage response generates the entire spectrum of base substitutions characterizing SHM at and around the initial U lesion. Starting from the U as a primary lesion, currently five mutagenic DNA damage response pathways have been identified in generating a well-defined SHM spectrum of C/G transitions, C/G transversions, and A/T mutations around this initial lesion. These pathways include (1) replication opposite template U generates transitions at C/G, (2) UNG2-dependent translesion synthesis (TLS) generates transversions at C/G, (3) a hybrid pathway comprising non-canonical mismatch repair (ncMMR) and UNG2-dependent TLS generates transversions at C/G, (4) ncMMR generates mutations at A/T, and (5) UNG2- and PCNA Ubiquitination (PCNA-Ub)-dependent mutations at A/T. Furthermore, specific strand-biases of SHM spectra arise as a consequence of a biased AID targeting, ncMMR, and anti-mutagenic repriming. Here, we review mammalian SHM with special focus on the mutagenic DNA damage response pathways involved in processing AID induced Us, the origin of characteristic strand biases, and relevance of the cell cycle.


Assuntos
Citidina Desaminase/genética , Dano ao DNA/genética , Reparo do DNA/genética , Hipermutação Somática de Imunoglobulina/genética , Linfócitos B/imunologia , Citidina Desaminase/metabolismo , DNA/genética , Desaminação/fisiologia , Humanos , Éxons VDJ/genética
8.
Oncotarget ; 9(27): 18832-18843, 2018 Apr 10.
Artigo em Inglês | MEDLINE | ID: mdl-29721165

RESUMO

DNA damage tolerance (DDT) enables replication to continue in the presence of a damaged template and constitutes a key step in DNA interstrand crosslink repair. In this way DDT minimizes replication stress inflicted by a wide range of endogenous and exogenous agents, and provides a critical first line defense against alkylating and platinating chemotherapeutics. Effective DDT strongly depends on damage-induced, site-specific PCNA-ubiquitination at Lysine (K) 164 by the E2/E3 complex (RAD6/18). A survey of The Cancer Genome Atlas (TCGA) revealed a high frequency of tumors presents RAD6/RAD18 bi-allelic inactivating deletions. For instance, 11% of renal cell carcinoma and 5% of pancreatic tumors have inactivating RAD18-deletions and 7% of malignant peripheral nerve sheath tumors lack RAD6B. To determine the potential benefit for tumor-specific DDT defects, we followed a genetic approach by establishing unique sets of DDT-proficient PcnaK164 and -defective PcnaK164R lymphoma and breast cancer cell lines. In the absence of exogenous DNA damage, PcnaK164R tumors grew comparably to their PcnaK164 controls in vitro and in vivo. However, DDT-defective lymphomas and breast cancers were compared to their DDT-proficient controls hypersensitive to the chemotherapeutic drug cisplatin (CsPt), both in vitro and in vivo. CsPt strongly inhibited tumor growth and the overall survival of tumor bearing mice greatly improved in the DDT-defective condition. These insights open new therapeutic possibilities for precision cancer medicine with DNA damaging chemotherapeutics and optimize Next-Generation-Sequencing (NGS)-based cancer-diagnostics, -therapeutics, and -prognosis.

9.
Immunity ; 47(5): 848-861.e5, 2017 11 21.
Artigo em Inglês | MEDLINE | ID: mdl-29126798

RESUMO

CD4+ T cells optimize the cytotoxic T cell (CTL) response in magnitude and quality, by unknown molecular mechanisms. We here present the transcriptomic changes in CTLs resulting from CD4+ T cell help after anti-cancer vaccination or virus infection. The gene expression signatures revealed that CD4+ T cell help during priming optimized CTLs in expression of cytotoxic effector molecules and many other functions that ensured efficacy of CTLs throughout their life cycle. Key features included downregulation of PD-1 and other coinhibitory receptors that impede CTL activity, and increased motility and migration capacities. "Helped" CTLs acquired chemokine receptors that helped them reach their tumor target tissue and metalloprotease activity that enabled them to invade into tumor tissue. A very large part of the "help" program was instilled in CD8+ T cells via CD27 costimulation. The help program thus enhances specific CTL effector functions in response to vaccination or a virus infection.


Assuntos
Ligante CD27/fisiologia , Linfócitos T CD4-Positivos/fisiologia , Linfócitos T Citotóxicos/imunologia , Membro 7 da Superfamília de Receptores de Fatores de Necrose Tumoral/fisiologia , Animais , Receptor 1 de Quimiocina CX3C/fisiologia , Diferenciação Celular , Movimento Celular , Regulação para Baixo , Camundongos , Camundongos Endogâmicos C57BL , Receptores CXCR4/fisiologia
10.
Proc Natl Acad Sci U S A ; 114(33): E6875-E6883, 2017 08 15.
Artigo em Inglês | MEDLINE | ID: mdl-28761001

RESUMO

DNA damage tolerance (DDT) enables bypassing of DNA lesions during replication, thereby preventing fork stalling, replication stress, and secondary DNA damage related to fork stalling. Three modes of DDT have been documented: translesion synthesis (TLS), template switching (TS), and repriming. TLS and TS depend on site-specific PCNA K164 monoubiquitination and polyubiquitination, respectively. To investigate the role of DDT in maintaining hematopoietic stem cells (HSCs) and progenitors, we used PcnaK164R/K164R mice as a unique DDT-defective mouse model. Analysis of the composition of HSCs and HSC-derived multipotent progenitors (MPPs) revealed a significantly reduced number of HSCs, likely owing to increased differentiation of HSCs toward myeloid/erythroid-associated MPP2s. This skewing came at the expense of the number of lymphoid-primed MPP4s, which appeared to be compensated for by increased MPP4 proliferation. Furthermore, defective DDT decreased the numbers of MPP-derived common lymphoid progenitor (CLP), common myeloid progenitor (CMP), megakaryocyte-erythroid progenitor (MEP), and granulocyte-macrophage progenitor (GMP) cells, accompanied by increased cell cycle arrest in CMPs. The HSC and MPP phenotypes are reminiscent of premature aging and stressed hematopoiesis, and indeed progressed with age and were exacerbated on cisplatin exposure. Bone marrow transplantations revealed a strong cell intrinsic defect of DDT-deficient HSCs in reconstituting lethally irradiated mice and a strong competitive disadvantage when cotransplanted with wild-type HSCs. These findings indicate a critical role of DDT in maintaining HSCs and progenitor cells, and in preventing premature aging.


Assuntos
Dano ao DNA , Replicação do DNA/genética , Células-Tronco Hematopoéticas/metabolismo , Células-Tronco Multipotentes/metabolismo , Envelhecimento/genética , Animais , Diferenciação Celular/genética , Reparo do DNA , Hematopoese/genética , Camundongos Endogâmicos C57BL , Camundongos Knockout , Antígeno Nuclear de Célula em Proliferação/genética
11.
Nucleic Acids Res ; 44(10): 4734-44, 2016 06 02.
Artigo em Inglês | MEDLINE | ID: mdl-26926109

RESUMO

PrimPol is a DNA damage tolerant polymerase displaying both translesion synthesis (TLS) and (re)-priming properties. This led us to study the consequences of a PrimPol deficiency in tolerating mutagenic lesions induced by members of the APOBEC/AID family of cytosine deaminases. Interestingly, during somatic hypermutation, PrimPol counteracts the generation of C>G transversions on the leading strand. Independently, mutation analyses in human invasive breast cancer confirmed a pro-mutagenic activity of APOBEC3B and revealed a genome-wide anti-mutagenic activity of PRIMPOL as well as most Y-family TLS polymerases. PRIMPOL especially prevents APOBEC3B targeted cytosine mutations within TpC dinucleotides. As C transversions induced by APOBEC/AID family members depend on the formation of AP-sites, we propose that PrimPol reprimes preferentially downstream of AP-sites on the leading strand, to prohibit error-prone TLS and simultaneously stimulate error-free homology directed repair. These in vivo studies are the first demonstrating a critical anti-mutagenic activity of PrimPol in genome maintenance.


Assuntos
Citidina Desaminase/metabolismo , DNA Primase/fisiologia , DNA Polimerase Dirigida por DNA/fisiologia , Antígenos de Histocompatibilidade Menor/metabolismo , Enzimas Multifuncionais/fisiologia , Mutagênese , Animais , Linfócitos B/enzimologia , Neoplasias da Mama/enzimologia , Neoplasias da Mama/genética , Sistemas CRISPR-Cas , Linhagem Celular , Sobrevivência Celular/efeitos da radiação , Células Cultivadas , Citidina Desaminase/antagonistas & inibidores , DNA/metabolismo , Replicação do DNA , Feminino , Humanos , Switching de Imunoglobulina , Camundongos Endogâmicos C57BL , Hipermutação Somática de Imunoglobulina , Linfócitos T/enzimologia , Raios Ultravioleta
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