UMR3348 – Intégrité du génome, ARN et cancer

Publications de l’unité

Année de publication : 2002

Stefania Millevoi, Finola Geraghty, Bernadine Idowu, Jennifer L Y Tam, Michael Antoniou, Stéphan Vagner (2002 Sep 1)

A novel function for the U2AF 65 splicing factor in promoting pre-mRNA 3′-end processing.

EMBO reports : 869-74 : DOI : 10.1093/embo-reports/kvf173 En savoir plus
Résumé

Splicing and 3′-end processing (including cleavage and polyadenylation) of vertebrate pre-mRNAs are tightly coupled events that contribute to the extensive molecular network that coordinates gene expression. Sequences within the terminal intron of genes are essential to stimulate pre-mRNA 3′-end processing, although the factors mediating this effect are unknown. Here, we show that the pyrimidine tract of the last splice acceptor site of the human beta-globin gene is necessary to stimulate mRNA 3′-end formation in vivo and binds the U2AF 65 splicing factor. Naturally occurring beta-thalassaemia-causing mutations within the pyrimidine tract reduces both U2AF 65 binding and 3′-end cleavage efficiency. Significantly, a fusion protein containing U2AF 65, when tethered upstream of a cleavage/polyadenylation site, increases 3′-end cleavage efficiency in vitro and in vivo. Therefore, we propose that U2AF 65 promotes 3′-end processing, which contributes to 3′-terminal exon definition.

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Mouna Ababou, Virginie Dumaire, Yann Lécluse, Mounira Amor-Guéret (2002 Jul 1)

Cleavage of BLM and sensitivity of Bloom’s syndrome cells to hydroxurea and UV-C radiation.

Cell cycle (Georgetown, Tex.) : 262-6 : DOI : 10.4161/cc.1.4.136 En savoir plus
Résumé

Patients with Bloom’s syndrome (BS) show a strong genetic instability and a predisposition to all types of cancer. Here, we report that the Bloom’s syndrome protein (BLM) is cleaved in response to hydroxyurea (HU)- or UVC-induced apoptosis. The appearance and solubility of BLM proteolytic products differed according to whether proteolysis occurred in response to HU or UVC. One BS cell line homozygous for a null mutation in BLM was resistant to both UVC- and HU-induced apoptosis, while another one expressing a mutated BLM protein was resistant to HU-induced apoptosis but displayed normal sensitivity to UVC. Thus, UVC and HU appear to induce apoptosis through distinct pathways.

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Mouna Ababou, Virginie Dumaire, Yann Lécluse, Mounira Amor-Guéret (2002 Mar 27)

Bloom’s syndrome protein response to ultraviolet-C radiation and hydroxyurea-mediated DNA synthesis inhibition.

Oncogene : 2079-88 : DOI : 10.1038/sj.onc.1205246 En savoir plus
Résumé

Bloom’s syndrome (BS) arises through mutations in both copies of the BLM gene that encodes a RecQ 3′-5′ DNA helicase. BS patients are predisposed to developing all the cancers that affect the general population, and BS cells exhibit marked genetic instability. We showed recently that BLM protein contributes to the cellular response to ionizing radiation by acting as downstream ATM kinase effector. We now show that following UVC treatment, BLM-deficient cells exhibit a reduction in the number of replicative cells, a partial escape from the G2/M cell cycle checkpoint, and have an altered p21 response. Surprisingly, we found that hydroxyurea-treated BLM-deficient cells exhibit an intact S phase arrest, proper recovery from the S phase arrest, and intact p53 and p21 responses. We also show that the level of BLM falls sharply in response to UVC radiation. This UVC-induced reduction in BLM does not require a functional ATM gene and does not result from a subcellular compartment change. Finally, we demonstrate that exposure to UVC and hydroxyurea treatment both induce BLM phosphorylation via an ATM-independent pathway. These results are discussed in the light of their potential physiological significance with regard to the role of BLM in the cellular pathways activated by UVC radiation or HU-mediated inhibition of DNA synthesis.

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Stéphanie Dutertre, Redha Sekhri, Lionel A Tintignac, Rosine Onclercq-Delic, Bruno Chatton, Christian Jaulin, Mounira Amor-Guéret (2002 Feb 22)

Dephosphorylation and subcellular compartment change of the mitotic Bloom’s syndrome DNA helicase in response to ionizing radiation.

The Journal of biological chemistry : 6280-6 : DOI : 10.1074/jbc.M105735200 En savoir plus
Résumé

Bloom’s syndrome is a rare human autosomal recessive disorder that combines a marked genetic instability and an increased risk of developing all types of cancers and which results from mutations in both copies of the BLM gene encoding a RecQ 3′-5′ DNA helicase. We recently showed that BLM is phosphorylated and excluded from the nuclear matrix during mitosis. We now show that the phosphorylated mitotic BLM protein is associated with a 3′-5′ DNA helicase activity and interacts with topoisomerase III alpha. We demonstrate that in mitosis-arrested cells, ionizing radiation and roscovitine treatment both result in the reversion of BLM phosphorylation, suggesting that BLM could be dephosphorylated through the inhibition of cdc2 kinase. This was supported further by our data showing that cdc2 kinase activity is inhibited in gamma-irradiated mitotic cells. Finally we show that after ionizing radiation, BLM is not involved in the establishment of the mitotic DNA damage checkpoint but is subjected to a subcellular compartment change. These findings lead us to propose that BLM may be phosphorylated during mitosis, probably through the cdc2 pathway, to form a pool of rapidly available active protein. Inhibition of cdc2 kinase after ionizing radiation would lead to BLM dephosphorylation and possibly to BLM recruitment to some specific sites for repair.

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Année de publication : 2000

M Ababou, S Dutertre, Y Lécluse, R Onclercq, B Chatton, M Amor-Guéret (2000 Dec 7)

ATM-dependent phosphorylation and accumulation of endogenous BLM protein in response to ionizing radiation.

Oncogene : 5955-63 : DOI : 10.1038/sj.onc.1204003 En savoir plus
Résumé

Bloom’s syndrome (BS), a rare genetic disease, arises through mutations in both alleles of the BLM gene which encodes a 3′-5′ DNA helicase identified as a member of the RecQ family. BS patients exhibit a high predisposition to development of all types of cancer affecting the general population and BLM-deficient cells display a strong genetic instability. We recently showed that BLM protein expression is regulated during the cell cycle, accumulating to high levels in S phase, persisting in G2/M and sharply declining in G1, suggesting a possible implication of BLM in a replication (S phase) and/or post-replication (G2 phase) process. Here we show that, in response to ionizing radiation, BLM-deficient cells exhibit a normal p53 response as well as an intact G1/S cell cycle checkpoint, which indicates that ATM and p53 pathways are functional in BS cells. We also show that the BLM defect is associated with a partial escape of cells from the gamma-irradiation-induced G2/M cell cycle checkpoint. Finally, we present data demonstrating that, in response to ionizing radiation, BLM protein is phosphorylated and accumulates through an ATM-dependent pathway. Altogether, our data indicate that BLM participates in the cellular response to ionizing radiation by acting as an ATM kinase downstream effector.

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A Barakat, M Ababou, R Onclercq, S Dutertre, E Chadli, N Hda, A Benslimane, M Amor-Guéret (2000 Jun 1)

Identification of a novel BLM missense mutation (2706T>C) in a Moroccan patient with Bloom’s syndrome.

Human mutation : 584-5 En savoir plus
Résumé

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S Dutertre, M Ababou, R Onclercq, J Delic, B Chatton, C Jaulin, M Amor-Guéret (2000 May 25)

Cell cycle regulation of the endogenous wild type Bloom’s syndrome DNA helicase.

Oncogene : 2731-8 : DOI : 10.1038/sj.onc.1203595 En savoir plus
Résumé

Bloom’s syndrome (BS) is a rare human autosomal recessive disorder characterized by an increased risk to develop cancer of all types. BS cells are characterized by a generalized genetic instability including a high level of sister chromatid exchanges. BS arises through mutations in both alleles of the BLM gene which encodes a 3′ – 5′ DNA helicase identified as a member of the RecQ family. We developed polyclonal antibodies specific for the NH2- and COOH-terminal region of BLM. Using these antibodies, we analysed BLM expression during the cell cycle and showed that the BLM protein accumulates to high levels in S phase, persists in G2/M and sharply declines in G1, strongly suggestive of degradation during mitosis. The BLM protein is subject to post-translational modifications in mitosis, as revealed by slow migrating forms of BLM found in both demecolcine-treated cells and in mitotic cells isolated from non-treated asynchronous populations. Phosphatase treatment indicated that phosphorylation events were solely responsible for the appearance of the retarded moieties, a possible signal for subsequent degradation. Together, these results are consistent with a role of BLM in a replicative (S phase) and/or post-replicative (G2 phase) process. Oncogene (2000).

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