[Show abstract][Hide abstract] ABSTRACT: For many plant species, reproductive success relies on the proper timing of flowering, and photoperiod provides a key environmental input. Photoperiod-dependent flowering depends on timely expression of FLOWERING LOCUS T (FT); however, the coordination of various cis-regulatory elements in the FT promoter is not well understood. Here, we provide evidence that long-distance chromatin loops bring distal enhancer elements into close association with the proximal promoter elements bound by CONSTANS (CO). Additionally, we show that NUCLEAR FACTOR Y (NF-Y) binds a CCAAT box in the distal enhancer element and that CCAAT disruption dramatically reduces FT promoter activity. Thus, we propose the recruitment model of photoperiod-dependent flowering where NF-Y complexes, bound at the FT distal enhancer element, help recruit CO to proximal cis-regulatory elements and initiate the transition to reproductive growth.
[Show abstract][Hide abstract] ABSTRACT: To elucidate the mechanisms behind the high sensitivity of myxoid/round cell liposarcoma (MRCL) to trabectedin and the suggested selectivity for specific subtypes, we have developed and characterized three MRCL xenografts, namely ML017, ML015 and ML004 differing for the break point of the fusion gene FUS-CHOP, respectively of type I, II and III. FUS-CHOP binding to the promoters of some target genes such as Pentraxin 3 or Fibronectin 1, assessed by chromatin immunoprecipitation, was strongly reduced in the tumor 24 h after the first or the third weekly dose of trabectedin, indicating that the drug at therapeutic doses causes a detachment of the FUS-CHOP chimera from its target promoters as previously shown in vitro. Moreover, the higher sensitivity of MRCL types I and II appears to be related to a more prolonged block of the transactivating activity of the fusion protein. Doxorubicin did not affect the binding of FUS-CHOP to target promoters. Histologically, the response to trabectedin in ML017 and ML015 was associated with a marked depletion of non-lipogenic tumoral cells and vascular component, as well as lipidic maturation as confirmed by PPARγ2 expression in western Blot. By contrast, in ML004 no major changes either in the cellularity or in the amount of mature were found, and consistently PPARγ2 was null. In conclusion, the data support the view that the selective mechanism of action of trabectedin in MRCL is specific and related to its ability to cause a functional inactivation of the oncogenic chimera with consequent derepression of the adypocytic differentiation.Oncogene advance online publication, 11 November 2013; doi:10.1038/onc.2013.462.
[Show abstract][Hide abstract] ABSTRACT: Core histones are the building block of chromatin and among the most highly conserved proteins in eukaryotes. The related "deviant" histones share the histone-fold domain, and serve various roles in DNA metabolism. We provide here a structural and functional outlook of H2A/H2B-like deviant histones in transcription, replication and remodeling.
[Show abstract][Hide abstract] ABSTRACT: NF-Y, a trimeric transcription factor (TF) composed of two histone-like subunits (NF-YB and NF-YC) and a sequence-specific subunit (NF-YA), binds to the CCAAT motif, a common promoter element. Genome-wide mapping reveals 5,000-15,000 NF-Y binding sites depending on the cell type, with the NF-YA and NF-YB subunits binding asymmetrically with respect to the CCAAT motif. Despite being characterized as a proximal promoter TF, only 25% of NF-Y sites map to promoters. A comparable number of NF-Y sites are located at enhancers, many of which are tissue specific, and nearly half of the NF-Y sites are in select subclasses of HERV LTR repeats. Unlike most TFs, NF-Y can access its target DNA motif in inactive (non-modified) or polycomb-repressed chromatin domains. Unexpectedly, NF-Y extensively co-localizes with FOS in all genomic contexts, and this often occurs in the absence of JUN and the AP-1 motif. NF-Y also co-associates with a select cluster of growth-controlling and oncogenic TFs, consistent with the abundance of CCAAT motifs in the promoters of genes overexpressed in cancer. Interestingly, NF-Y and several growth-controlling TFs bind in a stereo-specific manner, suggesting a mechanism for cooperative action at promoters and enhancers. Our results indicate that NF-Y is not merely a commonly-used, proximal promoter TF, but rather performs a more diverse set of biological functions, many of which are likely to involve co-association with FOS.
[Show abstract][Hide abstract] ABSTRACT: The Y box is an important sequence motif found in promoters and enhancers containing a CCAAT box - one of the few elements enriched in promoters of large sets of genes overexpressed in cancer. The search for the transcription factor(s) acting on it led to the biochemical purification of the nuclear factor Y (NF-Y) heterotrimer, and to the cloning - through the screening of expression libraries - of Y box-binding protein 1 (YB-1), an oncogene, overexpressed in aggressive tumors and associated with drug resistance. These two factors have been associated with Y/CCAAT-dependent activation of numerous growth-related genes, notably multidrug resistance protein 1. We review two decades of data indicating that NF-Y ultimately acts on Y/CCAAT in cancer cells, a notion recently confirmed by genome-wide data. Other features of YB-1, such as post-transcriptional control of mRNA biology, render it important in cancer biology.Cell Death and Differentiation advance online publication, 1 March 2013; doi:10.1038/cdd.2013.13.
Cell death and differentiation 03/2013; · 8.24 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The sequence-specific transcription factor NF-Y binds the CCAAT box, one of the sequence elements most frequently found in eukaryotic promoters. NF-Y is composed of the NF-YA and NF-YB/NF-YC subunits, the latter two hosting histone-fold domains (HFDs). The crystal structure of NF-Y bound to a 25 bp CCAAT oligonucleotide shows that the HFD dimer binds to the DNA sugar-phosphate backbone, mimicking the nucleosome H2A/H2B-DNA assembly. NF-YA both binds to NF-YB/NF-YC and inserts an α helix deeply into the DNA minor groove, providing sequence-specific contacts to the CCAAT box. Structural considerations and mutational data indicate that NF-YB ubiquitination at Lys138 precedes and is equivalent to H2B Lys120 monoubiquitination, important in transcriptional activation. Thus, NF-Y is a sequence-specific transcription factor with nucleosome-like properties of nonspecific DNA binding and helps establish permissive chromatin modifications at CCAAT promoters. Our findings suggest that other HFD-containing proteins may function in similar ways.
[Show abstract][Hide abstract] ABSTRACT: The CCAAT box is one of the most common cis-elements present in eukaryotic promoters and is bound by the transcription factor NUCLEAR FACTOR Y (NF-Y). NF-Y is composed of three subunits, NF-YA, NF-YB, and NF-YC. Unlike animals and fungi, plants have significantly expanded the number of genes encoding NF-Y subunits. We provide a comprehensive classification of NF-Y genes, with a separation of closely related, but distinct, histone fold domain proteins. We additionally review recent experiments that have placed NF-Y at the center of many developmental stress-responsive processes in the plant lineage.
[Show abstract][Hide abstract] ABSTRACT: Totipotency of embryonic stem cells (ESCs) is controlled at the transcriptional level by a handful of transcription factors (TFs) that promote stemness and prevent differentiation. One of the most enriched DNA elements in promoters and enhancers of genes specifically active in ESCs is the CCAAT box, which is recognized by NF-Y, a trimer with histone-like subunits-NF-YB/NF-YC-and the sequence-specific NF-YA. We show that the levels of the short NF-YA isoform-NF-YAs-is high in mouse ESCs (mESCs) and drops after differentiation; a dominant negative mutant affects expression of important stem cells genes, directly and indirectly. Protein transfections of TAT-NF-YAs stimulate growth and compensate for withdrawal of leukemia inhibitory factor (LIF) in cell cultures. Bioinformatic analysis identifies NF-Y sites as highly enriched in genomic loci of stem TFs in ESCs. Specifically, 30%-50% of NANOG peaks have NF-Y sites and indeed NF-Y-binding is required for NANOG association to DNA. These data indicate that NF-Y belongs to the restricted circle of TFs that govern mESCs, and, specifically, that NF-YAs is the active isoform in these cells. STEM CELLS2012;30:2450-2459.
[Show abstract][Hide abstract] ABSTRACT: NF-Y is a transcription factor that recognizes with high specificity and affinity the widespread CCAAT box promoter element. It is formed by three subunits: NF-YA and the NF-YB/NF-YC- heterodimer containing histone fold domains (HFDs). We previously identified a large NF-Y gene family in Arabidopsis thaliana, composed of 29 members, and characterized their expression patterns in various plant tissues.
We used yeast Two-hybrids assays (Y2H), pull-down and Electrophoretic Mobility Shift Assay (EMSA) in vitro experiments with recombinant proteins to dissect AtNF-YB/AtNF-YC interactions and DNA-binding with different AtNF-YAs.
Consistent with robust conservation within HFDs, we show that heterodimerization is possible among all histone-like subunits, including the divergent and related LEC1/AtNF-YB9 and L1L/AtNF-YB6 required for embryo development. DNA-binding to a consensus CCAAT box was investigated with specific AtNF-YB/AtNF-YC combinations and observed with some, but not all AtNF-YA subunits.
Our results highlight (i) the conserved heterodimerization capacity of AtNF-Y histone-like subunits, and (ii) the different affinities of AtNF-YAs for the CCAAT sequence. Because of the general expansion of NF-Y genes in plants, these results most likely apply to other species.
PLoS ONE 08/2012; 7(8):e42902. · 3.53 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We investigated the mechanism of action of the histone deacetylase inhibitor Givinostat (GVS) in Janus kinase 2 (JAK2)(V617F) myeloproliferative neoplasm (MPN) cells. GVS inhibited colony formation and proliferation and induced apoptosis at doses two- to threefold lower in a panel of JAK2(V617F) MPN compared to JAK2 wild-type myeloid leukemia cell lines. By global gene expression analysis, we observed that at 6 hours, GVS modulated 293 common genes in the JAK2(V617F) cell lines HEL and UKE1, of which 19 are implicated in cell cycle regulation and 33 in hematopoiesis. In particular, the hematopoietic transcription factors NFE2 and C-MYB were downmodulated by the drug specifically in JAK2(V617F) cells at both the RNA and protein level. GVS also inhibited JAK2-signal transducer and activator of transcription 5-extracellular signal-regulated kinase 1/2 phosphorylation, but modulation of NFE2 and C-MYB was JAK2-independent, as shown using the JAK2 inhibitor TG101209. GVS had a direct effect on the NFE2 promoters, as demonstrated by specific enrichment of associated histone H3 acetylated at lysine 9. Modulation by GVS of NFE2 was also observed in freshly isolated CD34(+) cells from MPN patients, and was accompanied by inhibition of their proliferation and differentiation toward the erythroid lineage. We conclude that GVS acts on MPN cells through dual JAK2-signal transducer and activator of transcription 5-extracellular signal-regulated kinase 1/2 inhibition and downmodulation of NFE2 and C-MYB transcription.
[Show abstract][Hide abstract] ABSTRACT: The basement membrane (BM) is a layer of specialized extracellular matrix that surrounds normal prostate glands and preserves tissue integrity. Lack or discontinuity of the BM is a prerequisite for tumor cell invasion into interstitial spaces, thus favoring metastasis. Therefore, BM maintenance represents a barrier against cancer development and progression. In the study, we show that miR-205 participates in a network involving ΔNp63α, which is essential for maintenance of the BM in prostate epithelium. At the molecular level, ΔNp63α is able to enhance miR-205 transcription by binding to its promoter, whereas the microRNA can post-transcriptionally limit the amount of ΔNp63α protein, mostly by affecting ΔNp63α proteasomal degradation rather than through a canonical miRNA/target interaction. Functionally, miR-205 is able to control the deposition of laminin-332 and its receptor integrin-β4. Hence, pathological loss of miR-205, as widely observed in prostate cancer, may favor tumorigenesis by creating discontinuities in the BM. Here we demonstrate that therapeutic replacement of miR-205 in prostate cancer (PCa) cells can restore BM deposition and 3D organization into normal-like acinar structures, thus hampering cancer progression.
Cell death and differentiation 05/2012; 19(11):1750-60. · 8.24 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: p53 and p63 are transcription factors -TFs- playing master roles in the DNA-damage response and in the development and maintenance of pluristratified epithelia, respectively. p53 mutations are common in epithelial tumors and HaCaT keratinocytes harbor two p53 alleles -H179Y and R282Q- with gain-of-function (GOF) activity. Indeed, functional inactivation of mutp53 affects the growth rate of HaCaT. We investigated the strategy of mutp53, by performing ChIP-Seq experiments of mutp53 and p63 and analyzed the transcriptome after mutp53 inactivation. Mutp53 bind to 7135 locations in vivo, with a robust overlap with p63. De novo motifs discovery recovered a p53/p63RE with high information content in sites bound by p63 and mutp53/p63, but not by mutp53 alone: these sites are rather enriched in elements of other TFs. The HaCaT p63 locations are only partially overlapping with those of normal keratinocytes; importantly, and enriched in mutp53 sites which delineate a functionally different group of target genes. Our data favour a model whereby mutp53 GOF mutants act both by tethering growth-controlling TFs and highjacking p63 to new locations.
[Show abstract][Hide abstract] ABSTRACT: NF-Y is a sequence-specific transcription factor - TF - targeting the common CCAAT promoter element. p53 is a master TF controlling the response to stress signals endangering genome integrity, often mutated in human cancers. The NF-Y/p53 - and p63, p73 - interaction results in transcriptional repression of a subset of genes within the vast NF-Y regulome under DNA-damage conditions. Recent data shows that NF-Y is also involved in pro-apoptotic activities, either directly, by mediating p53 transcriptional activation, or indirectly, by being targeted by a non coding RNA, PANDA. The picture is subverted in cells carrying Gain-of-function mutant p53, through interactions with TopBP1, a protein also involved in DNA repair and replication. In summary, the connection between p53 and NF-Y is crucial in determining cell survival or death.
Biochimica et Biophysica Acta 11/2011; 1825(2):131-9. · 4.66 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The CCAAT box promoter element and NF-Y, the transcription factor (TF) that binds to it, were among the first cis-elements and trans-acting factors identified; their interplay is required for transcriptional activation of a sizeable number of eukaryotic genes. NF-Y consists of three evolutionarily conserved subunits: a dimer of NF-YB and NF-YC which closely resembles a histone, and the "innovative" NF-YA. In this review, we will provide an update on the functional and biological features that make NF-Y a fundamental link between chromatin and transcription. The last 25 years have witnessed a spectacular increase in our knowledge of how genes are regulated: from the identification of cis-acting sequences in promoters and enhancers, and the biochemical characterization of the corresponding TFs, to the merging of chromatin studies with the investigation of enzymatic machines that regulate epigenetic states. Originally identified and studied in yeast and mammals, NF-Y - also termed CBF and CP1 - is composed of three subunits, NF-YA, NF-YB and NF-YC. The complex recognizes the CCAAT pentanucleotide and specific flanking nucleotides with high specificity (Dorn et al., 1997; Hatamochi et al., 1988; Hooft van Huijsduijnen et al, 1987; Kim & Sheffery, 1990). A compelling set of bioinformatics studies clarified that the NF-Y preferred binding site is one of the most frequent promoter elements (Suzuki et al., 2001, 2004; Elkon et al., 2003; Mariño-Ramírez et al., 2004; FitzGerald et al., 2004; Linhart et al., 2005; Zhu et al., 2005; Lee et al., 2007; Abnizova et al., 2007; Grskovic et al., 2007; Halperin et al., 2009; Häkkinen et al., 2011). The same consensus, as determined by mutagenesis and SELEX studies (Bi et al., 1997), was also retrieved in ChIP-on-chip analysis (Testa et al., 2005; Ceribelli et al., 2006; Ceribelli et al., 2008; Reed et al., 2008). Additional structural features of the CCAAT box - position, orientation, presence of multiple Transcriptional Start Sites - were previously reviewed (Dolfini et al., 2009) and will not be considered in detail here.
Critical Reviews in Biochemistry and Molecular Biology 11/2011; 47(1):29-49. · 5.58 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Myxoid Liposarcomas (MLS), characterized by the expression of FUS-CHOP fusion gene are clinically very sensitive to the DNA binding antitumor agent, trabectedin. However, resistance eventually occurs, preventing disease eradication. To investigate the mechanisms of resistance, a trabectedin resistant cell line, 402-91/ET, was developed. The resistance to trabectedin was not related to the expression of MDR related proteins, uptake/efflux of trabectedin or GSH levels that were similar in parental and resistant cells. The 402-91/ET cells were hypersensitive to UV light because of a nucleotide excision repair defect: XPG complementation decreased sensitivity to UV rays, but only partially to trabectedin. 402-91/ET cells showed collateral sensitivity to temozolomide due to the lack of O(6) -methylguanine-DNA-methyltransferase (MGMT) activity, related to the hypermethylation of MGMT promoter. In 402-91 cells chromatin immunoprecipitation (ChIP) assays showed that FUS-CHOP was bound to the PTX3 and FN1 gene promoters, as previously described, and trabectedin caused FUS-CHOP detachment from DNA. Here we report that, in contrast, in 402-91/ET cells, FUS-CHOP was not bound to these promoters. Differences in the modulation of transcription of genes involved in different pathways including signal transduction, apoptosis and stress response between the two cell lines were found. Trabectedin activates the transcription of genes involved in the adipogenic-program such as c/EBPα and β, in 402-91 but not in 402-91/ET cell lines. The collateral sensitivity of 402-91/ET to temozolomide provides the rationale to investigate the potential use of methylating agents in MLS patients resistant to trabectedin.
International Journal of Cancer 07/2011; 131(1):59-69. · 6.20 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Heterozygous mutations of p63, a key transcription factor in epithelial development, are causative in a variety of human ectodermal dysplasia disorders. Although the mutation spectrum of these disorders displays a striking genotype-phenotype association, the molecular basis for this association is only superficially known. Here, we characterize the transcriptional activity and protein stability of ΔNp63 mutants (that is, mutants of a p63 isoform that lacks the N-terminal transactivation domain) that are found in ectrodactyly-ectodermal dysplasia-cleft syndrome (EEC), ankyloblepharon-ectodermal dysplasia-clefting syndrome (AEC) and nonsyndromic split-hand/split-foot malformation (SHFM). DNA-binding and sterile alpha motif (SAM) domain mutants accumulate in the skin of EEC and AEC syndrome patients, respectively, and show extended half lives in vitro. By contrast, C-terminal mutations found in SHFM patients have half-lives similar to that of the wild-type protein. The increased half-life of EEC and AEC mutant proteins was reverted by overexpression of wild-type ΔNp63. Interestingly, the mutant proteins exhibit normal binding to and degradation by the E3 ubiquitin ligase Itch. Finally, EEC and AEC mutant proteins have reduced transcriptional activity on several skin-specific gene promoters, whereas SHFM mutant proteins are transcriptionally active. Our results, therefore, provide evidence for a regulatory feedback mechanism for p63 that links transcriptional activity to regulation of protein homeostasis by an unknown mechanism. Disruption of this regulatory mechanism might contribute to the pathology of p63-related developmental disorders.
[Show abstract][Hide abstract] ABSTRACT: The inhibitor of DNA binding 2, dominant negative helix-loop-helix protein, ID2, acts as an oncogene and elevated levels of ID2 have been reported in several malignancies. Whereas some inducers of the ID2 gene have been characterized, little is known regarding the proteins capable to repress its expression. We developed siRNA microarrays to perform a large scale loss-of-function screen in human adult keratinocytes engineered to express GFP under the control of the upstream region of ID2 gene. We screened the effect of siRNA-dependent inhibition of 220 cancer-associated genes on the expression of the ID2::GFP reporter construct. Three genes NBN, RAD21, and p63 lead to a repression of ID2 promoter activity. Strikingly NBN and RAD21 are playing on major role in cell cycle progression and mitosis arrest. These results underline the pregnant need to silence ID2 expression at transcript level to promote cell cycle exit. Central to this inhibitory mechanism we find p63, a key transcription factor in epithelial development and differentiation, which binds specific cis-acting sequence within the ID2 gene promoter both in vitro and in vivo. P63 would not suppress ID2 expression, but would rather prevent excessive expression of that protein to enable the onset of keratinocyte differentiation.
Journal of Biological Chemistry 06/2011; 286(23):20870-9. · 4.60 Impact Factor