Fanconi Anemia and Ubiquitination

Fanconi anemia （FA） is a rare recessive hereditary disease characterized clinically by congenital defects, progressive bone-marrow failure, and cancer predisposition. Cells from FA patients exhibit hypersensitivity to DNA cross-linking agents, such as mitomycin C （MMC）. To date, at least 12 FA genes have been found deleted or mutated in FA cells, and 10 FA gene products form a core complex involved in FA/BRCA2 DNA repair pathway-FA pathway. The ubiquitin E3 ligase FANCL, an important factor of FA core complex, co-functions with a new ubiquitin conjugating enzyme UBE2T to catalyze the monoubiquitination of FANCD2. FANCD2-Ub binds BRCA2 to form a new complex located in chromatin foci and then take part in DNA repair process. The deubiquitylating enzyme USP1 removes the mono-ubiquitin from FANCD2-Ub following completion of the repair process, then restores the blocked cell cycle to normal order by shutting off the FA pathway. In a word, the FANCD2 activity adjusted exquisitely by ubiquitination and/or deubiquitination in vivo may co-regulate the FA pathway involving in variant DNA repair pathway.

DTL facilitates the Fanconi anemia pathway for ultraviolet-induced DNA repair in retinal pigment epithelial cells

The excessive energy of light,especially the invisible rays with lower wavelength,is basically absorbed by retinal pigment epithelium(RPE)and usually causes DNA damage.The molecular mechanism behind DNA damage repair response to this frequent stress in RPE is not clearly understood.In this study,we determined that the Fanconi anemia(FA)pathway was activated in human RPE ARPE-19 cells after ultraviolet(UV)B and C treatment.Moreover,immunoprecipitation(IP)of FANCD2 indicated that denticleless E3 ubiquitin protein ligase homolog(DTL)closely interacted with FANCD2.Knockdown of DTL weakened the activity of the FA pathway in ARPE-19 cells responding to UV treatment.Finally,the DTL promoter was incubated with a biotin-labeled probe and pulled down by streptavidin beads followed by the genomic DNA sonication.p53 was indicated by mass spectrum and further determined by chromatin IP assay.Taken together,our results demonstrated that DTL regulated by p53 could activate the FA pathway for UV-induced DNA damage repair in retinal pigment epithelial cells.

Effect of a Nutrient Mixture on Fanconi Anemia Fibroblast and Normal Human Dermal Fibroblast: A Comparison

Fanconi anemia (FA) is a fatal heterogeneous autosomal recessive disorder, characterized by progressive bone marrow failure, congenital defect and cancer predisposition. Cell culture from FA fibroblast (FAF) displays certain abnormalities as compared to normal human dermal fibroblast (NHDF). This prompted us to investigate the effect of a specific nutrient mixture (NM) containing ascorbic acid, lysine, proline and green tea extract, which has demonstrated a broad spectrum of pharmacological activities, on FAF compared to NHDF. We investigated the in vitro effect of NM on FAF and NHDF cell proliferation by MTT assay, MMPs secretion by zymography, morphology by H&E staining and apoptosis by green caspase assay. FAF (FA-A: PD20, FA-A: PD220) and NHDF were cultured in modified Dulbecco Eagle media. At near confluence, the cells were treated with different concentrations of NM (0, 50, 100, 250, 500 and 1000 μg/ml) in triplicate. The cells were also treated with PMA to induce MMP-9 activity. NM had no effect on FAF cell viability in both cell lines compared to control. In contrast NM exhibited 20% at 50 and 100, 50% at 250, 60% at 500 and 70% toxicity at 1000 μg/ml on NHDF cells. Zymography demonstrated MMP-2 and MMP-9 on PMA stimulation in FAF and NM inhibited the activity of both MMP-2 and MMP-9 in a dose response fashion with total block at 500 μg/ml. In contrast, NHDF exhibited only MMP-2, both active and inactive forms, and NM inhibited their activities in a dose-dependent manner with total block at 1000 μg/ml. H&E staining did not indicate any morphological changes in FAF nor induced apoptosis at higher concentrations, as seen by caspases assay. However, although no morphological changes in NHDF were noted up to NM 100 μg/ml, progressive changes in cell shrinkage, rounding and nuclear condensation, pertaining to apoptosis, were observed at higher concentrations. These changes were consistent with the results from the green caspases apoptosis assay. Our data demonstrate that NM exhibited different responses toward FAF and NHDF. This may in part be due to elevated chromosomal break, deletion and hypersensitivity to cross linking agents, a DNA repair disorder in FAF that is lacking in NHDF.

TGF-β2-induced NEAT1 regulates lens epithelial cell proliferation,migration and EMT by the miR-26a-5p/FANCE axis

AIM:To explore the regulatory mechanism of nuclear paraspeckle assembly transcript 1(NEAT1)in the pathogenesis of posterior capsule opacification(PCO).METHODS:Quantitative reverse transcription polymerase chain reaction(RT-q PCR)was executed to analyze NEAT1 and micro RNA(miR)-26a-5p expression in transforming growth factor-beta 2(TGF-β2)-disposed lens epithelial cells(LECs).The proliferation,cell cycle progression,apoptosis,and migration of TGF-β2-disposed LECs were evaluated.The relationship between NEAT1 or fanconi anemia(FA)complementation group E(FANCE)and miR-26a-5p was verified by dual-luciferase reporter assay.RESULTS:TGF-β2 induced NEAT1 expression in LECs.NEAT1 inhibition accelerated apoptosis,cell cycle arrest,decreased proliferation,epithelial-mesenchymal transition(EMT),and migration of TGF-β2-disposed LECs.NEAT1 sponged miR-26a-5p to further regulate FANCE expression.Rescue experiments presented that miR-26a-5p downregulation overturned NEAT1 silencing-mediated impacts on TGF-β2-disposed LEC biological behaviors.Additionally,FANCE overexpression reversed miR-26a-5p mimic-mediated impacts on TGF-β2-disposed LEC biological behaviors.CONCLUSION:TGF-β2-induced NEAT1 facilitates LEC proliferation,migration,and EMT by upregulating FANCE via sequestering miR-26a-5p.

Disulfiram enhances the antitumor activity of cisplatin by inhibiting the Fanconi anemia repair pathway

A series of chemotherapeutic drugs that induce DNA damage,such as cisplatin(DDP),are standard clinical treatments for ovarian cancer,testicular cancer,and other diseases that lack effective targeted drug therapy.Drug resistance is one of the main factors limiting their application.Sensitizers can overcome the drug resistance of tumor cells,thereby enhancing the antitumor activity of chemotherapeutic drugs.In this study,we aimed to identify marketable drugs that could be potential chemotherapy sensitizers and explore the underlying mechanisms.We found that the alcohol withdrawal drug disulfiram(DSF)could significantly enhance the antitumor activity of DDP.JC-1 staining,propidium iodide(PI)staining,and western blotting confirmed that the combination of DSF and DDP could enhance the apoptosis of tumor cells.Subsequent RNA sequencing combined with Gene Set Enrichment Analysis(GSEA)pathway enrichment analysis and cell biology studies such as immunofluorescence suggested an underlying mechanism:DSF makes cells more vulnerable to DNA damage by inhibiting the Fanconi anemia(FA)repair pathway,exerting a sensitizing effect to DNA damaging agents including platinum chemotherapy drugs.Thus,our study illustrated the potential mechanism of action of DSF in enhancing the antitumor effect of DDP.This might provide an effective and safe solution for combating DDP resistance in clinical treatment.

Demethylation of FANCF gene may be a potential treatment through inhibiting the proliferation of cervical cancer

Objective: The aim of the study was to explore the effect of demethylating agent 5-Aza-2'-deoxycytidine (5-ADC) on expression of Fanconi anemia complementation group F (FANCF) gene and the proliferation of cervical cancer cells, to observe cell's sensitivity to chemotherapeutic drug taxol, and to explore the antitumor effect of 5-ADC as well as the new treatment of cervical cancer. Methods: Cervical cancer cell lines SiHa (FANCF gene full-methylated) and Hela (unmethylated) were treated with 5-ADC. We used the methylation-specific PCR (MSP), reverse transcription-polymerase chain reaction (RT-PCR) and Western blot to detect the FANCF methylation, mRNA and protein respectively. The 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay was used to detect the proliferation of cells. The cytotoxicity of taxol was measured by flow cytometer. The nude mice bearing SiHa was used to observe the effect of 5-ADC in vivo. Results: Inhibition of DNA promoter methylation by 5-ADC reactivated the expression of FANCF mRNA and protein in SiHa cells, consistent with decreased growth speed and increased taxol resistance. These results were proven in experiments in vivo. Conclusion: The 5-ADC probably become a potential treatment drug through inhibiting the proliferation of cervical cancer cells in taxol-resistant patients.

The Fanconi anemia pathway and DNA interstrand cross-link repair

Fanconi anemia(FA)is an autosomal or X-linked recessive disorder characterized by chromosomal instability,bone marrow failure,cancer susceptibility,and a profound sensitivity to agents that produce DNA interstrand cross-link(ICL).To date,15 genes have been identified that,when mutated,result in FA or an FA-like syndrome.It is believed that cellular resistance to DNA interstrand cross-linking agents requires all 15 FA or FAlike proteins.Here,we review our current understanding of how these FA proteins participate in ICL repair and discuss the molecular mechanisms that regulate the FA pathway to maintain genome stability.

Diagnosis of Fanconi anemia in children with atypical clinical features： a primary study

Background Fanconi anemia is a severe congenital disorder associated with mutations in a cluster of genes responsible for DNA repair.Arriving at an accurate and timely diagnosis can be difficult in cases of Fanconi anemia with atypical clinical features.It is very important to increase the rate of accurate diagnosis for such cases in a clinical setting.The purpose of this study is to explore the clinical diagnosis of Fanconi anemia in children with atypical clinical features.Methods Six cases of Fanconi anemia with atypical clinical features were enrolled in the study,and their clinical features were recorded,their FANCA gene transcription was assessed by RT-PCR,and FANCA mutations and the ubiquitination of FANCD2 protein were analyzed using DNA sequencing and western blotting respectively.Results All six cases showed atypical clinical features including no apparent deformities,lack of response to immune therapy,and progressively increasing bone marrow failure.They also have significantly increased fetal hemoglobin,negative mitomycin-induced fracture test results,and carry a FANCA gene missense mutation.Single protein ubiquitination of FANCD2 was not observed in those patients.Conclusion The combination of clinical features,FANCA pathogenic gene mutation genotype and the absence of FANCD2 protein ubiquitination are helpful in the accurate and timely diagnosis of Fanconi anemia in children.

Fanconi anemia gene-associated germline predisposition in aplastic anemia and hematologic malignancies

Whether Fanconi anemia(FA)heterozygotes are predisposed to bone marrow failure and hematologic neoplasm is a crucial but unsettled issue in cancer prevention and family consulting.We retrospectively analyzed rare possibly significant variations(PSVs)in the five most obligated FA genes,BRCA2,FANCA,FANCC,FANCD2,and FANCG,in 788 patients with aplastic anemia(AA)and hematologic malignancy.Sixty-eight variants were identified in 66 patients(8.38%).FANCA was the most frequently mutated gene(n=29),followed by BRCA2(n=20).Compared with that of the ExAC East Asian dataset,the overall frequency of rare PSVs was higher in our cohort(P=0.016).BRCA2 PSVs showed higher frequency in acute lymphocytic leukemia(P=0.038),and FANCA PSVs were significantly enriched in AA and AML subgroups(P=0.020;P=0.008).FA-PSV-positive MDS/AML patients had a higher tumor mutation burden,higher rate of cytogenetic abnormalities,less epigenetic regulation,and fewer spliceosome gene mutations than those of FA-PSV-negative MDS/AML patients(P=0.024,P=0.029,P=0.024,and P=0.013).The overall PSV enrichment in our cohort suggests that heterozygous mutations of FA genes contribute to hematopoietic failure and leukemogenesis.

Novel diagnostic approaches for Fanconi anemia (FA) by single-cell sequencing and capillary nano-immunoassay

Next-generation sequencing technology has been widely utilized for the diagnosis of Fanconi anemia(FA).However,mixed cell sequencing and chimerism of FA patients may lead to unconfirmed genetic subtypes.Herein,we introduced two novel diagnostic methods,including single-cell sequencing and capillary nano-immunoassay.One FA case with FANCM c.4931G>A p.R1644Q and FANCD1 c.6325G>A p.V2109I was studied.The DNA of 28 cells was amplified and eight types of cells were observed after Sanger sequencing.There were two homozygous mutations(FANCM/FANCD1).Furthermore,the capillary nano-immunoassay was conducted to analyze the expression profile of FA-associated proteins.Abnormal FANCM and FANCD1 expressions simultaneously existed.This case was thus diagnosed as FA-D1/FA-M dual subtype.Compared with mixed cell sequencing,single-cell sequencing data shows more accuracy for the FA subtype evaluation,while the capillary nano-immunoassay is a good method to detect the expression profile of abnormal or modified FA protein.

DNAH2 facilitates the homologous recombination repair of Fanconi anemia pathway through modulating FANCD2 ubiquitination

Fanconi anemia(FA),an X-linked genetic or autosomal recessive disease,exhibits complicated pathogenesis.Previously,we detected the mutated Dynein Axonemal Heavy Chain 2(DNAH2)gene in 2 FA cases.Herein,we further investigated the potential association between DNAH2 and the homologous recombination repair pathway of FA.The assays of homologous recombination repair,mitomycin C(MMC)sensitivity,immunofluorescence,and ubiquitination modification were performed in U2OS and DR-U2OS cell lines.In MMC-treated U2OS cells,the downregulation of the DNAH2 gene increased the sensitivity of cells to DNA inter-strand crosslinks.We also observed the reduced enrichment of FANCD2 protein to DNA damage sites.Furthermore,the ubiquitination modification level of FANCD2 was influenced by the deficiency of DNAH2.Thus,our results suggest that DNAH2 may modulate the cell homologous recombination repair partially by increasing the ubiquitination and the enrichment to DNA damage sites of FANCD2.DNAH2 may act as a novel co-pathogenic gene of FA patients.

Formation and repair of DNA-protein crosslink damage

DNA is constantly exposed to a wide array of genotoxic agents, generating a variety of forms of DNA damage. DNA-protein crosslinks(DPCs)—the covalent linkage of proteins with a DNA strand—are one of the most deleterious and understudied forms of DNA damage, posing as steric blockades to transcription and replication. If not properly repaired, these lesions can lead to mutations, genomic instability, and cell death. DPCs can be induced endogenously or through environmental carcinogens and chemotherapeutic agents. Endogenously, DPCs are commonly derived through reactions with aldehydes, as well as through trapping of various enzymatic intermediates onto the DNA. Proteolytic cleavage of the protein moiety of a DPC is a general strategy for removing the lesion. This can be accomplished through a DPC-specific protease and and/or proteasome-mediated degradation.Nucleotide excision repair and homologous recombination are each involved in repairing DPCs, with their respective roles likely dependent on the nature and size of the adduct. The Fanconi anemia pathway may also have a role in processing DPC repair intermediates. In this review, we discuss how these lesions are formed, strategies and mechanisms for their removal, and diseases associated with defective DPC repair.