The histone methyltransferase NSD3 contributes to sister chromatid cohesion and to cohesin loading at mitotic exit.

Sister chromatid cohesion is a multi-step process implemented throughout the cell cycle to ensure the correct transmission of chromosomes to daughter cells. Although cohesion establishment and mitotic cohesion dissolution have been extensively explored, the regulation of cohesin loading is still poorly understood. Here, we report that the methyltransferase NSD3 is essential for mitotic sister chromatid cohesion before mitosis entry. NSD3 interacts with the cohesin loader complex kollerin (composed of NIPBL and MAU2) and promotes the chromatin recruitment of MAU2 and cohesin at mitotic exit. We also show that NSD3 associates with chromatin in early anaphase, prior to the recruitment of MAU2 and RAD21, and dissociates from chromatin when prophase begins. Among the two NSD3 isoforms present in somatic cells, the long isoform is responsible for regulating kollerin and cohesin chromatin-loading, and its methyltransferase activity is required for efficient sister chromatid cohesion. Based on these observations, we propose that NSD3-dependent methylation contributes to sister chromatid cohesion by ensuring proper kollerin recruitment and thus cohesin loading.

HDAC8 mutations in Cornelia de Lange syndrome affect the cohesin acetylation cycle.

Cornelia de Lange syndrome (CdLS) is a dominantly inherited congenital malformation disorder, caused by mutations in the cohesin-loading protein NIPBL for nearly 60% of individuals with classical CdLS, and by mutations in the core cohesin components SMC1A (~5%) and SMC3 (<1%) for a smaller fraction of probands. In humans, the multisubunit complex cohesin is made up of SMC1, SMC3, RAD21 and a STAG protein. These form a ring structure that is proposed to encircle sister chromatids to mediate sister chromatid cohesion and also has key roles in gene regulation. SMC3 is acetylated during S-phase to establish cohesiveness of chromatin-loaded cohesin, and in yeast, the class I histone deacetylase Hos1 deacetylates SMC3 during anaphase. Here we identify HDAC8 as the vertebrate SMC3 deacetylase, as well as loss-of-function HDAC8 mutations in six CdLS probands. Loss of HDAC8 activity results in increased SMC3 acetylation and inefficient dissolution of the 'used' cohesin complex released from chromatin in both prophase and anaphase. SMC3 with retained acetylation is loaded onto chromatin, and chromatin immunoprecipitation sequencing analysis demonstrates decreased occupancy of cohesin localization sites that results in a consistent pattern of altered transcription seen in CdLS cell lines with either NIPBL or HDAC8 mutations.

CDK11(p58) kinase activity is required to protect sister chromatid cohesion at centromeres in mitosis.

The cyclin-dependent kinase CDK11(p58) is specifically expressed at G2/M phase. CDK11(p58) depletion leads to different cell cycle defects such as mitotic arrest, failure in centriole duplication and centrosome maturation, and premature sister chromatid separation. We report that upon CDK11 depletion, loss of sister chromatid cohesion occurs during mitosis but not during G2 phase. CDK11(p58) depletion prevents Bub1 and Shugoshin 1 recruitment but has no effect on the dimethylation of histone H3 lysine 4 at centromeres. We also report that a construct expressing a kinase dead version of CDK11(p58) fails to prevent CDK11 depletion-induced sister chromatid separation, showing that CDK11(p58) kinase activity is required for protection of sister chromatid cohesion at centromeres during mitosis. Thus, CDK11(p58) kinase activity appears to be involved in early events in the establishment of the centromere protection machinery.

Genome-wide distribution of histone trimethylation reveals a global impact of bisphenol A on telomeric binding proteins and histone acetyltransferase factors: a pilot study with human and in vitro data.

OBJECTIVE: To assess the genetic and epigenetic effects promoted by Bisphenol A (BPA) exposure in adolescent males from the Spanish INMA-Granada birth cohort, and in human cells. METHODS: DNA methylation was analysed using MEDIP. Repeat number variation in genomic DNA was evaluated, along with the analysis of H3K4me3 by using chromatin immunoprecipitation followed by high-throughput sequencing (ChIP-seq). Analyses were performed with material extracted from whole blood of the adolescents, complemented by in vitro assessments of human (HeLa) cells exposed to 10 nM BPA, specifically, immunofluorescence evaluation of protein levels, gene expression analysis and ChIP‒qPCR analysis. RESULTS: Adolescents in the high urinary BPA levels group presented a higher level of Satellite A (SATA) repetitive region copy numbers compared to those in the low BPA group and a tendency towards increase in telomere length. We also observed decreased DNA methylation at the promoters of the imprinted genes H19, KCNQ1, and IGF2; at LINE1 retroelements; and at the ARID2, EGFR and ESRRA and TERT genes. Genome-wide sequencing revealed increased H3K4me3 occupancy at the promoters of genes encoding histone acetyltransferases, telomeric DNA binding factors and DNA repair genes. Results were supported in HeLa cells exposed to 10 nM BPA in vitro. In accordance with the data obtained in blood samples, we observed higher H3K4me3 occupancy and lower DNA methylation at some specific targets in HeLa cells. In exposed cells, changes in the expression of genes encoding DNA repair factors (ATM, ARID2, TRP53) were observed, and increased expression of several genes encoding telomeric DNA binding factors (SMG7, TERT, TEN1, UPF1, ZBTB48) were also found. Furthermore, an increase in ESR1/ERa was observed in the nuclei of HeLa cells along with increased binding of ESR1 to KAT5, KMT2E and TERF2IP promoters and decreased ESR1 binding at the RARA promoter. The DNA damage marker p53/TP53 was also increased. CONCLUSION: In this pilot study, genome-wide analysis of histone trimethylation in adolescent males exposed to BPA revealed a global impact on the expression of genes encoding telomeric binding proteins and histone acetyltransferase factors with similar results in HeLa cells. Nevertheless, larger studies should confirm our findings.

Calpain 2 is required for sister chromatid cohesion.

Calpains form a family of Ca(2+)-dependent cysteine proteases involved in diverse cellular processes. However, the specific functions of each calpain isoform remain unknown. Recent reports have shown that calpain 2 (Capn2) is essential for cell viability. We have recently shown that Capn2 is a nuclear protease associated with chromosomes during mitosis in mammalian embryonic cells. We now report that Capn2 depletion impairs mitosis and induces apoptosis in murine cells. Low Capn2 levels induce chromosome alignment defects, the loss of histone H3 threonine 3 phosphorylation at centromeres, and premature sister chromatid separation. Thus, Capn2 may play a role in fundamental mitotic functions, such as the maintenance of sister chromatid cohesion.

Histone deacetylase inhibitors induce premature sister chromatid separation and override the mitotic spindle assembly checkpoint.

Histone deacetylase inhibitors (HDACI) are powerful antiproliferative drugs, and are currently undergoing clinical trials as antitumor agents. It would be valuable for both cancer therapy and our knowledge of basic cellular processes to understand the mechanisms by which HDACIs block cell proliferation. Most current models postulate that HDACIs allow the reexpression of tumor suppressor genes silenced in cancer cells. However, other mechanisms, distinct from transcription regulation, may participate in HDACI antiproliferative properties. We report that HDACI treatment induces premature sister chromatid separation in cells in which the mitotic spindle assembly checkpoint (SAC) has already been activated. This effect was transcription-independent. In addition, HDACI-treated mitotic cells displayed SAC inactivation characteristics, including anaphase-promoting complex/cyclosome target degradation, cyclin-dependent kinase 1 inactivation, histone H3 dephosphorylation, and loss of the SAC component MAD2 from the kinetochore. Thus, HDAC inhibition renders the SAC ineffective. Our findings help elucidate the molecular mechanisms of proliferative cell death induced by HDACI treatment and may allow new HDACI-based preclinical and clinical trial protocols to be redesigned so as to target mitosis.

Aurora A Protein Kinase: To the Centrosome and Beyond.

Accurate chromosome segregation requires the perfect spatiotemporal rearrangement of the cellular cytoskeleton. Isolated more than two decades ago from Drosophila, Aurora A is a widespread protein kinase that plays key roles during cell division. Numerous studies have described the localisation of Aurora A at centrosomes, the mitotic spindle, and, more recently, at mitotic centromeres. In this review, we will summarise the cytoskeletal rearrangements regulated by Aurora A during cell division. We will also discuss the recent discoveries showing that Aurora A also controls not only the dynamics of the cortical proteins but also regulates the centromeric proteins, revealing new roles for this kinase during cell division.

Aurora A-dependent CENP-A phosphorylation at inner centromeres protects bioriented chromosomes against cohesion fatigue.

Sustained spindle tension applied to sister centromeres during mitosis eventually leads to uncoordinated loss of sister chromatid cohesion, a phenomenon known as "cohesion fatigue." We report that Aurora A-dependent phosphorylation of serine 7 of the centromere histone variant CENP-A (p-CENP-AS7) protects bioriented chromosomes against cohesion fatigue. Expression of a non-phosphorylatable version of CENP-A (CENP-AS7A) weakens sister chromatid cohesion only when sister centromeres are under tension, providing the first evidence of a regulated mechanism involved in protection against passive cohesion loss. Consistent with this observation, p-CENP-AS7 is detected at the inner centromere where it forms a discrete domain. The depletion or inhibition of Aurora A phenocopies the expression of CENP-AS7A and we show that Aurora A is recruited to centromeres in a Bub1-dependent manner. We propose that Aurora A-dependent phosphorylation of CENP-A at the inner centromere protects chromosomes against tension-induced cohesion fatigue until the last kinetochore is attached to spindle microtubules.

Bloom's syndrome and PICH helicases cooperate with topoisomerase IIα in centromere disjunction before anaphase.

Centromeres are specialized chromosome domains that control chromosome segregation during mitosis, but little is known about the mechanisms underlying the maintenance of their integrity. Centromeric ultrafine anaphase bridges are physiological DNA structures thought to contain unresolved DNA catenations between the centromeres separating during anaphase. BLM and PICH helicases colocalize at these ultrafine anaphase bridges and promote their resolution. As PICH is detectable at centromeres from prometaphase onwards, we hypothesized that BLM might also be located at centromeres and that the two proteins might cooperate to resolve DNA catenations before the onset of anaphase. Using immunofluorescence analyses, we demonstrated the recruitment of BLM to centromeres from G2 phase to mitosis. With a combination of fluorescence in situ hybridization, electron microscopy, RNA interference, chromosome spreads and chromatin immunoprecipitation, we showed that both BLM-deficient and PICH-deficient prometaphase cells displayed changes in centromere structure. These cells also had a higher frequency of centromeric non disjunction in the absence of cohesin, suggesting the persistence of catenations. Both proteins were required for the correct recruitment to the centromere of active topoisomerase IIα, an enzyme specialized in the catenation/decatenation process. These observations reveal the existence of a functional relationship between BLM, PICH and topoisomerase IIα in the centromere decatenation process. They indicate that the higher frequency of centromeric ultrafine anaphase bridges in BLM-deficient cells and in cells treated with topoisomerase IIα inhibitors is probably due not only to unresolved physiological ultrafine anaphase bridges, but also to newly formed ultrafine anaphase bridges. We suggest that BLM and PICH cooperate in rendering centromeric catenates accessible to topoisomerase IIα, thereby facilitating correct centromere disjunction and preventing the formation of supernumerary centromeric ultrafine anaphase bridges.

Histone deacetylase inhibitors and genomic instability.

Histone deacetylase inhibitors (HDACIs) are a promising new class of anticancer drugs. However, their mechanism of action has not been fully elucidated. Most studies have investigated the effect of HDACIs on the regulation of gene transcription. HDAC inhibition also leads to genomic instability by a variety of mechanisms. This phenomenon, which has been largely overlooked, may contribute to the cytotoxic effects of these drugs. Indeed, HDACIs sensitize DNA to exogenous genotoxic damage and induce the generation of reactive oxygen species. Moreover, HDACIs target mitosis resulting in chromosome segregation defects. Here, we review the effects of HDACI treatment on DNA damage and repair, and chromosome segregation control.

Histone deacetylase 3 is required for centromeric H3K4 deacetylation and sister chromatid cohesion.

We describe here the role of histone deacetylase 3 (HDAC3) in sister chromatid cohesion and the deacetylation of histone H3 Lys 4 (H3K4) at the centromere. HDAC3 knockdown induced spindle assembly checkpoint activation and sister chromatid dissociation. The depletion of Polo-like kinase 1 (Plk1) or Aurora B restored cohesion in HDAC3-depleted cells. HDAC3 was also required for Shugoshin localization at centromeres. Finally, we show that HDAC3 depletion results in the acetylation of centromeric H3K4, correlated with a loss of dimethylation at the same position. These findings provide a functional link between sister chromatid cohesion and the mitotic "histone code".

Histone deacetylase activity is necessary for chromosome condensation during meiotic maturation in Xenopus laevis.

Chromosome condensation is thought to be an essential step for the faithful transmission of genetic information during cellular division or gamete formation. The folding of DNA into metaphase chromosomes and its partition during the cell cycle remains a fundamental cellular process that, at the molecular level, is poorly understood. Particularly, the role of histone deacetylase (HDAC) activities in establishing and maintaining meiotic metaphase chromosome condensation has been little documented. In order to better understand how metaphase chromosome condensation is achieved during meiosis, we explored, in vivo, the consequences of HDAC activities inhibition in a Xenopus oocyte model. Our results show that deacetylase activity plays a crucial role in chromosome condensation. This activity is necessary for correct chromosome condensation since the earlier stages of meiosis, but dispensable for meiosis progression, meiosis exit and mitosis entry. We show that HDAC activity correlates with chromosome condensation, being higher when chromosomes are fully condensed and lower during interphase, when chromosomes are decondensed. In addition, we show that, unlike histone H4, Xenopus maternal histone H3 is stored in the oocyte as a hypoacetylated form and is rapidly acetylated when the oocyte exits meiosis.