Impaired FANCD2 monoubiquitination and hypersensitivity to camptothecin uniquely characterize Fanconi anemia complementation group M - PubMed (original) (raw)

. 2009 Jul 2;114(1):174-80.

doi: 10.1182/blood-2009-02-207811. Epub 2009 May 7.

Sietske T Bakker, Sheba Agarwal, Michael Jansen, Elke Grassman, Barbara C Godthelp, Abdullah Mahmood Ali, Chang-hu Du, Martin A Rooimans, Qiang Fan, Kebola Wahengbam, Jurgen Steltenpool, Paul R Andreassen, David A Williams, Hans Joenje, Johan P de Winter, Amom Ruhikanta Meetei

Affiliations

Impaired FANCD2 monoubiquitination and hypersensitivity to camptothecin uniquely characterize Fanconi anemia complementation group M

Thiyam Ramsing Singh et al. Blood. 2009.

Abstract

FANCM is a component of the Fanconi anemia (FA) core complex and one FA patient (EUFA867) with biallelic mutations in FANCM has been described. Strikingly, we found that EUFA867 also carries biallelic mutations in FANCA. After correcting the FANCA defect in EUFA867 lymphoblasts, a "clean" FA-M cell line was generated. These cells were hypersensitive to mitomycin C, but unlike cells defective in other core complex members, FANCM(-/-) cells were proficient in monoubiquitinating FANCD2 and were sensitive to the topoisomerase inhibitor camptothecin, a feature shared only with the FA subtype D1 and N. In addition, FANCM(-/-) cells were sensitive to UV light. FANCM and a C-terminal deletion mutant rescued the cross-linker sensitivity of FANCM(-/-) cells, whereas a FANCM ATPase mutant did not. Because both mutants restored the formation of FANCD2 foci, we conclude that FANCM functions in an FA core complex-dependent and -independent manner.

PubMed Disclaimer

Figures

Figure 1

Figure 1

EUFA867 has biallelic FANCA mutations. (A) Introduction of FANCA in EUFA867 lymphoblasts stably expressing FANCM restores FANCD2 monoubiquitination. EUFA867 lymphoblasts were transduced with SF91-FANCM to obtain EUFA867 + FANCM. Subsequently these cells were transduced with bicistronic retroviruses encoding the indicated FA proteins. Cells were treated with 2 mM HU for 16 hours and immunoblotted for FANCD2 and FANCM. (B) EUFA867 has a nonsense mutation 2557C>T (R853X) in FANCA. (C) Mutation IVS7 + 5G>A affects the normal splice donor in FANCA intron 7 and results in a 30-bp insertion of intron 7 sequence in the cDNAs of EUFA867 and her mother. The sequence shown is from an isolated cDNA clone of EUFA867. (D) FANCA cDNA derived from the IVS7 + 5G>A mutation does not correct FANCD2 monoubiquitination. FANCA-deficient HSC72 lymphoblasts were transduced with bicistronic retrovirus encoding either wild-type FANCA or the FANCA mutant derived from the mutation IVS7 + 5G>A. Cells were treated with 1 mM HU to stimulate FANCD2 monoubiquitination.

Figure 2

Figure 2

Stable expression of FANCA in EUFA867 lymphoblasts partially corrects the phenotype of this cell line. (A) EUFA867 lymphoblasts stably expressing wild-type FANCA are still hypersensitive to growth inhibition by mitomycin C. FANCA-deficient HSC72 and EUFA867 lymphoblasts were transduced with SF91-FANCA. Viable cells were measured with the Cell Titer 96 Proliferation Assay. The data represent the percentage growth compared with untreated cells and show 1 representative result of 3 independent experiments with standard deviations. (B) EUFA867 lymphoblasts stably expressing wild-type FANCA show melphalan-induced G2 arrest. (C) EUFA867 lymphoblasts stably expressing wild-type FANCA have reduced FANCD2 monoubiquitination. Cells were treated with either 2 mM HU or 240 nM MMC for 16 hours or left untreated. Total lysates were immunoblotted for FANCM, FANCD2, and FANCA.

Figure 3

Figure 3

Ectopic expression of both FANCA and FANCM can correct the FA phenotype of EUFA867 lymphoblasts. (A) Ectopic expression of FANCA and FANCM in EUFA867 restores the chromatin localization of monoubiquitinated FANCD2, which coincides with an enhanced FANCD2 monoubiquitination. EUFA867 cells stably expressing FANCA (EUFA867-FANCA) were generated with pMMP-FANCA. Subsequently, these cells were transduced with either MIEG3 bicistronic retroviral vector or MIEG3 encoding wild-type FANCM. EGFP-positive cells were treated with 240 nM MMC for 16 hours or left untreated and subcellular fractions were made: S100 cytoplasmic and nucleoplasmic proteins, S400 chromatin-bound proteins. (B) The ATPase activity and the C-terminus of FANCM are not required for efficient FANCD2 monoubiquitination. EUFA867 lymphoblasts stably expressing FANCA were transduced with either MIEG3 retroviral vector or MIEG3 encoding wild-type FANCM, an ATPase-dead FANCM mutant (K117R-FANCM) or a C-terminal FANCM deletion mutant (delC-FANCM). EGFP-positive cells were treated with either 2 mM HU (top panel) or 240 mM MMC (bottom panel) for 16 hours. Total lysates were immunoblotted for FANCD2. (C) FANCM, but not its ATPase activity or its C-terminus, is required for the assembly of FANCD2 foci. Cells were either left untreated or exposed to 450 nM MMC or 2 mM HU for 24 hours, and the percentage of cells with 5 or more FANCD2 foci was determined in at least 150 cells. The result shows the average of 3 independent experiments with standard deviations. (D) The ATPase activity, but not the C-terminus of FANCM, is required for MMC resistance. Viable cells were measured with the Cell Titer 96 Proliferation Assay. The data represent the percentage growth compared with untreated cells and show 1 representative result of 3 independent experiments with standard deviations. (E) The FANCM ATPase mutant does not rescue the melphalan-induced G2 arrest in EUFA867 lymphoblasts. (F) FANCM is required for chromatin targeting of the FA core complex proteins. Subcellular fractions of EUFA867 lymphoblast and stably transduced derivatives were immunoblotted for FANCM, FANCA, FANCG, FANCL, and FAAP24. H2A was used as a loading control for the chromatin fraction.

Figure 4

Figure 4

Camptothecin sensitivity in human lymphoblasts. (A) EUFA867 lymphoblasts are sensitive to the topoisomerase I inhibitor camptothecin. Lymphoblasts were continuously exposed to different doses of camptothecin and cell growth was compared with untreated cells by cell counting. Wild-type, and FANCC- and FANCJ-deficient lymphoblasts were included as camptothecin-resistant controls. (B) Camptothecin sensitivity of EUFA867 lymphoblasts is due to a defect in FANCM. The FANCA defect in EUFA867 was corrected by stable transfection of flag-tagged FANCA (EUFA867+FANCA-flag); the FANCM defect was corrected by cell fusion with FANCA-deficient lymphoblasts HSC72 (EUFA867xHSC72OT fusion). Four independent cell fusions are depicted. (C) The C-terminus of FANCM is involved in camptothecin resistance. EUFA867 cells were stably transduced with FANCA and wild-type FANCM (FANCM) or a C-terminal deletion mutant of FANCM (delC-FANCM).

Figure 5

Figure 5

Camptothecin and UV sensitivity and Rad51 focus formation in human lymphoblasts. (A) FA-D1 lymphoblasts with a defect in FANCD1/BRCA2 are as sensitive to growth inhibition by camptothecin as EUFA867 lymphoblasts. (B) FA-N lymphoblasts with a defect in FANCN/PALB2 are as sensitive to growth inhibition by camptothecin as EUFA867 lymphoblasts. EUFA1341R is a MMC-resistant reverted derivative of EUFA1341 lymphoblasts. (C) EUFA867 lymphoblasts are sensitive to UV. Lymphoblasts were exposed to different doses of UVC light and cell growth was compared with untreated cells by cell counting. Lymphoblasts of xeroderma pigmentosum patient XP3BE were used as a positive control. Results show mean values of at least 5 experiments with SEM. (D) Normal Rad51 focus formation in EUFA867 lymphoblasts. Kinetics of Rad51 foci formation in response to x-ray irradiation (12 Gy) or MMC treatment (2.4 μg/mL for 1 hour) analyzed 7 and 24 hours after treatment. A cell with more than 5 distinct foci in the nucleus was considered positive. Results show the mean values of at least 2 experiments with standard error of the mean.

Similar articles

Cited by

References

    1. Wang W. Emergence of a DNA-damage response network consisting of Fanconi anaemia and BRCA proteins. Nat Rev Genet. 2007;8:735–748. - PubMed
    1. de Winter JP, Joenje H. The genetic and molecular basis of Fanconi anemia. Mutat Res. Prepublished on November 14, 2008, as DOI <10.1016/j.mrfmmm.2008.11.004>. - DOI - PubMed
    1. Meetei A, de Winter J, Medhurst A, et al. A novel ubiquitin ligase is deficient in Fanconi anemia. Nat Genet. 2003;35:165–170. - PubMed
    1. Machida YJ, Machida Y, Chen Y, et al. UBE2T is the E2 in the Fanconi anemia pathway and undergoes negative autoregulation. Mol Cell. 2006;23:589–596. - PubMed
    1. Alpi A, Langevin F, Mosedale G, Machida YJ, Dutta A, Patel KJ. UBE2T, the Fanconi anemia core complex, and FANCD2 are recruited independently to chromatin: a basis for the regulation of FANCD2 monoubiquitination. Mol Cell Biol. 2007;27:8421–8430. - PMC - PubMed

Publication types

MeSH terms

Substances

LinkOut - more resources