953 resultados para Olig bHLH transcription factors
Resumo:
Anthocyanin concentration is a primary determinant of plant colour. Fruit anthocyanin biosynthesis is controlled by a distinct clade of R2R3 MYB transcription factors. In apple, three recent papers describe the discovery of MYB genes activating skin, flesh and foliage anthocyanic colour. These findings lead the way to new approaches in the breeding and biotechnological development of fruit with new colour patterns.
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Oncogene-induced senescence (OIS) is a potent tumor-suppressive mechanism that is thought to come at the cost of aging. The Forkhead box O (FOXO) transcription factors are regulators of life span and tumor suppression. However, whether and how FOXOs function in OIS have been unclear. Here, we show a role for FOXO4 in mediating senescence by the human BRAFV600E oncogene, which arises commonly in melanoma. BRAFV600E signaling through mitogen-activated protein kinase/extracellular signal-regulated kinase kinase resulted in increased reactive oxygen species levels and c-Jun NH 2 terminal kinase-mediated activation of FOXO4 via its phosphorylation on Thr223, Ser226, Thr447, and Thr451. BRAFV600E-induced FOXO4 phosphorylation resulted in p21cip1-mediated cell senescence independent of p16 ink4a or p27kip1. Importantly, melanocyte-specific activation of BRAFV600E in vivo resulted in the formation of skin nevi expressing Thr223/Ser226-phosphorylated FOXO4 and elevated p21cip1. Together, these findings support a model in which FOXOs mediate a trade-off between cancer and aging.
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To gain insight into the mechanisms by which the Myb transcription factor controls normal hematopoiesis and particularly, how it contributes to leukemogenesis, we mapped the genome-wide occupancy of Myb by chromatin immunoprecipitation followed by massively parallel sequencing (ChIP-Seq) in ERMYB myeloid progenitor cells. By integrating the genome occupancy data with whole genome expression profiling data, we identified a Myb-regulated transcriptional program. Gene signatures for leukemia stem cells, normal hematopoietic stem/progenitor cells and myeloid development were overrepresented in 2368 Myb regulated genes. Of these, Myb bound directly near or within 793 genes. Myb directly activates some genes known critical in maintaining hematopoietic stem cells, such as Gfi1 and Cited2. Importantly, we also show that, despite being usually considered as a transactivator, Myb also functions to repress approximately half of its direct targets, including several key regulators of myeloid differentiation, such as Sfpi1 (also known as Pu.1), Runx1, Junb and Cebpb. Furthermore, our results demonstrate that interaction with p300, an established coactivator for Myb, is unexpectedly required for Myb-mediated transcriptional repression. We propose that the repression of the above mentioned key pro-differentiation factors may contribute essentially to Myb's ability to suppress differentiation and promote self-renewal, thus maintaining progenitor cells in an undifferentiated state and promoting leukemic transformation. © 2011 The Author(s).
Resumo:
Angiosperms represent a huge diversity in floral structures. Thus, they provide an attractive target for comparative developmental genetics studies. Research on flower development has focused on few main model plants, and studies on these species have revealed the importance of transcription factors, such as MADS-box and TCP genes, for regulating the floral form. The MADS-box genes determine floral organ identities, whereas the TCP genes are known to regulate flower shape and the number of floral organs. In this study, I have concentrated on these two gene families and their role in regulating flower development in Gerbera hybrida, a species belonging to the large sunflower family (Asteraceae). The Gerbera inflorescence is comprised of hundreds of tightly clustered flowers that differ in their size, shape and function according to their position in the inflorescence. The presence of distinct flower types tells Gerbera apart from the common model species that bear only single kinds of flowers in their inflorescences. The marginally located ray flowers have large bilaterally symmetrical petals and non-functional stamens. The centrally located disc flowers are smaller, have less pronounced bilateral symmetry and carry functional stamens. Early stages of flower development were studied in Gerbera to understand the differentiation of flower types better. After morphological analysis, we compared gene expression between ray and disc flowers to reveal transcriptional differences in flower types. Interestingly, MADS-box genes showed differential expression, suggesting that they might take part in defining flower types by forming flower-type-specific regulatory complexes. Functional analysis of a CYCLOIDEA-like TCP gene GhCYC2 provided evidence that TCP transcription factors are involved in flower type differentiation in Gerbera. The expression of GhCYC2 is ray-flower-specific at early stages of development and activated only later in disc flowers. Overexpression of GhCYC2 in transgenic Gerbera-lines causes disc flowers to obtain ray-flower-like characters, such as elongated petals and disrupted stamen development. The expression pattern and transgenic phenotypes further suggest that GhCYC2 may shape ray flowers by promoting organ fusion. Cooperation of GhCYC2 with other Gerbera CYC-like TCP genes is most likely needed for proper flower type specification, and by this means for shaping the elaborate inflorescence structure. Gerbera flower development was also approached by characterizing B class MADS-box genes, which in the main model plants are known regulators of petal and stamen identity. The four Gerbera B class genes were phylogenetically grouped into three clades; GGLO1 into the PI/GLO clade, GDEF2 and GDEF3 into the euAP3 clade and GDEF1 into the TM6 clade. Putative orthologs for GDEF2 and GDEF3 were identified in other Asteraceae species, which suggests that they appeared through an Asteraceae-specific duplication. Functional analyses indicated that GGLO1 and GDEF2 perform conventional B-function as they determine petal and stamen identities. Our studies on GDEF1 represent the first functional analysis of a TM6-like gene outside the Solanaceae lineage and provide further evidence for the role of TM6 clade members in specifying stamen development. Overall, the Gerbera B class genes showed both commonalities and diversifications with the conventional B-function described in the main model plants.
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The eukaryotic cell nucleoplasm is separated from the cytoplasm by the nuclear envelope. This compartmentation of eukaryotic cells requires that all nuclear proteins must be transported from the cytoplasm into the nucleus. Transport of macromolecules between the nucleus and the cytoplasm occurs through nuclear pore complexes (NPCs). Proteins to be targeted into the nucleus by the classical nuclear import system contain nuclear localization signals (NLSs), which are recognized by importin alpha, the NLS receptor. Importin alpha binds to importin beta, which docks the importin-cargo complex on the cytoplasmic side of the NPC and mediates the movement of the complex into the nucleus. Presently six human importin alpha isoforms have been identified. Transcription factors are among the most important regulators of gene expression in eukaryotic organisms. Transcription factors bind to specific DNA sequences on target genes and modulate the activity of the target gene. Many transcription factors, including signal transducers and activators of transcription (STAT) and nuclear factor kB (NF-kB), reside in the cytoplasm in an inactive form, and upon activation they are rapidly transported into the nucleus. In the nucleus STATs and NF-kB regulate the activity of genes whose products are critical in controlling numerous cellular and organismal processes, such as inflammatory and immune responses, cell growth, differentiation and survival. The aim of this study was to investigate the nuclear import mechanisms of STAT and NF-kB transcription factors. This work shows that STAT1 homodimers and STAT1/STAT2 heterodimers bind specifically and directly to importin alpha5 molecule via unconventional dimer-specific NLSs. Importin alpha molecules have two regions, which have been shown to directly interact with the amino acids in the NLS of the cargo molecule. The Arm repeats 2-4 comprise the N-terminal NLS binding site and Arm repeats 7-8 the C-terminal NLS binding site. In this work it is shown that the binding site for STAT1 homodimers and STAT1/STAT2 heterodimers is composed of Arm repeats 8 and 9 of importin alpha5 molecule. This work demonstrates that all NF-kB proteins are transported into the nucleus by importin alpha molecules. In addition, NLS was identified in RelB protein. The interactions between NF-kB proteins and importin alpha molecules were found to be directly mediated by the NLSs of NF-kB proteins. Moreover, we found that p50 binds to the N-terminal and p65 to the C-terminal NLS binding site of importin alpha3. The results from this thesis work identify previously uncharacterized mechanisms in nuclear import of STAT and NF-kB. These findings provide new insights into the molecular mechanisms regulating the signalling cascades of these important transcription factors from the cytoplasm into the nucleus to the target genes.
Resumo:
Mammalian gastrointestinal tract and liver are self-renewing organs that are able to sustain themselves due to stem cells present in their tissues. In constant, inflammation-related epithelial damage, vigorous activation of stem cells may lead to their uncontrolled proliferation, and further, to cancer. GATA-4, GATA-5, and GATA-6 regulate cell proliferation and differentiation in many mammalian organs. Lack of GATA-4 or GATA-6 leads to defective endodermal development and cell differentiation. GATA-4 and GATA-5 are considered the ones with tumor suppressive functions, whereas GATA-6 is more related to tumor promotion. In the digestive system their roles in inflammation and tumor-related molecular pathways remain unclear. In this study, we examined the GATA-related molecular pathways involved in normal tissue organization and renewal and in inflammation-related epithelial repair in the gastrointestinal tract and liver. The overall purpose of this study was to elucidate the relation of GATA factors to gastrointestinal and hepatic disease pathology and to evaluate their possible clinical significance in tumor biology. The results indicated distinct expression patterns for GATA-4, GATA-5, and GATA-6 in the human and murine gastrointestinal tract and liver, and their involvement in the regulation of intestine-specific genes. GATA-5 was confined to the intestines of suckling mice, suggesting an association with postnatal enzymatic changes. GATA-4 was upregulated in bowel inflammation concomitantly with TGF-β signaling. In gastrointestinal tumors, GATA-4 was restricted to benign neoplasias of the stomach, while GATA-6 was detected especially at the invasive edges of malignant tumors throughout the gut. In the liver, GATA-4 was upregulated in pediatric tumors along with erythropoietin (Epo), which was detected also in the sera of tumor patients. Furthermore, GATA-4 was enhanced in areas of vigorous hepatic regeneration in patients with tyrosinemia type I. These results suggest a central role for GATA-4 in pediatric tumor biology of the liver. To conclude, GATA-4, GATA-5, and GATA-6 are associated with normal gastrointestinal and hepatic development and regeneration. The appearance of GATA-4 along with TGF-β-signaling in the inflammatory bowel suggests a protective role in the response to inflammation-related epithelial destruction. However, in extremely malignant pediatric liver tumors, GATA-4 function is unlikely to be tumor-suppressing, probably due to the nature of the very primitive multipotent tumor cells. GATA-4, along with its possible downstream factor Epo, could be utilized as novel hepatic tumor markers to supplement the present diagnostics. They could also serve a function in future biological therapies for aggressive pediatric tumors.
Resumo:
Transcription factors play a key role in tumor development, in which dysfunction of genes regulating tissue growth and differentiation is a central phenomenon. The GATA family of transcription factors consists of six members that bind to a consensus DNA sequence (A/T)GATA(A/G) in gene promoters and enhancers. The two GATA factors expressed in the adrenal cortex are GATA-4 and GATA-6. In both mice and humans, GATA-4 can be detected only during the fetal period, whereas GATA-6 expression is abundant both throughout development and in the adult. It is already established that GATA factors are important in both normal development and tumorigenesis of several endocrine organs, and expression of GATA-4 and GATA-6 is detected in adrenocortical tumors. The aim of this study was to elucidate the function of these factors in adrenocortical tumor growth. In embryonal development, the adrenocortical cells arise and differentiate from a common pool with gonadal steroidogenic cells, the urogenital ridge. As the adult adrenal cortex undergoes constant renewal, it is hypothesized that undifferentiated adrenocortical progenitor cells reside adjacent to the adrenal capsule and give rise to daughter cells that differentiate and migrate centripetally. A diverse array of hormones controls the differentiation, growth and survival of steroidogenic cells in the adrenal gland and the gonads. Factors such as luteinizing hormone and inhibins, traditionally associated with gonadal steroidogenic cells, can also influence the function of adrenocortical cells in physiological and pathophysiological states. Certain inbred strains of mice develop subcapsular adrenocortical tumors in response to gonadectomy. In this study, we found that these tumors express GATA-4, normally absent from the adult adrenal cortex, while GATA-6 expression is downregulated. Gonadal markers such as luteinizing hormone receptor, anti-Müllerian hormone and P450c17 are also expressed in the neoplastic cells, and the tumors produce gonadal hormones. The tumor cells have lost the expression of melanocortin-2 receptor and the CYP enzymes necessary for the synthesis of corticosterone and aldosterone. By way of xenograft studies utilizing NU/J nude mice, we confirmed that chronic gonadotropin elevation is sufficient to induce adrenocortical tumorigenesis in susceptible inbred strains. Collectively, these studies suggest that subcapsular adrenocortical progenitor cells can, under certain conditions, adopt a gonadal fate. We studied the molecular mechanisms involved in gene regulation in endocrine cells in order to elucidate the role of GATA factors in endocrine tissues. Ovarian granulosa cells express both GATA-4 and GATA-6, and the TGF-β signaling pathway is active in these cells. Inhibin-α is both a target gene for, and an atypical or antagonistic member of the TGF-β growth factor superfamily. In this study, we show that GATA-4 is required for TGF-β-mediated inhibin-α promoter activation in granulosa cells, and that GATA-4 physically interacts with Smad3, a TGF-β downstream protein. Apart from the regulation of steroidogenesis and other events in normal tissues, TGF-β signaling is implicated in tumors of multiple organs, including the adrenal cortex. Another signaling pathway found often to be aberrantly active in adrenocortical tumors is the Wnt pathway. As both of these pathways regulate the expression of inhibin-α, a transcriptional target for GATA-4 and GATA-6, we wanted to investigate whether GATA factors are associated with the components of these signaling cascades in human adrenocortical tumors. We found that the expression of Wnt co-receptors LRP5 and LRP6, Smad3, GATA-6 and SF-1 was diminished in adrenocortical carcinomas with poor outcome. All of these factors drive inhibin-α expression, and their expression in adrenocortical tumors correlated with that of inhibin-α. The results support a tumor suppressor role previously suggested for inhibin-α in the mouse adrenal cortex, and offer putative pathways associated with adrenocortical tumor aggressiveness. Unraveling the role of GATA factors and associated molecules in human and mouse adrenocortical tumors could ultimately contribute to the development of diagnostic tools and future therapies for these diseases.
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Development of multidrug resistance (MDR) is a major deterrent in the effective treatment of metastatic cancers by chemotherapy. Even though MDR and cancer invasiveness have been correlated, the molecular basis of this link remains obscure. We show here that treatment with chemotherapeutic drugs increases the expression of several ATP binding cassette transporters (ABC transporters) associated with MDR, as well as epithelial-mesenchymal transition (EMT) markers, selectively in invasive breast cancer cells, but not in immortalized or non-invasive cells. Interestingly, the mere induction of an EMT in immortalized and non-invasive cell lines increased their expression of ABC transporters, migration, invasion, and drug resistance. Conversely, reversal of EMT in invasive cells by downregulating EMT-inducing transcription factors reduced their expression of ABC transporters, invasion, and rendered them more chemosensitive. Mechanistically, we demonstrate that the promoters of ABC transporters carry several binding sites for EMT-inducing transcription factors, and overexpression of Twist, Snail, and FOXC2 increases the promoter activity of ABC transporters. Furthermore, chromatin immunoprecipitation studies revealed that Twist binds directly to the E-box elements of ABC transporters. Thus, our study identifies EMT inducers as novel regulators of ABC transporters, thereby providing molecular insights into the long-standing association between invasiveness and MDR. Targeting EMT transcription factors could hence serve as novel strategies to curb both metastasis and the associated drug resistance. Cell Death and Disease (2011) 2, e179; doi:10.1038/cddis.2011.61; published online 7 July 2011
Resumo:
SEPALLATA (SEP) MADS box transcription factors mediate floral development in association with other regulators. Mutants in five rice (Oryza sativa) SEP genes suggest both redundant and unique functions in panicle branching and floret development. LEAFY HULL STERILE1/OsMADS1, from a grass-specific subgroup of LOFSEP genes, is required for specifying a single floret on the spikelet meristem and for floret organ development, but its downstream mechanisms are unknown. Here, key pathways and directly modulated targets of OsMADS1 were deduced from expression analysis after its knockdown and induction in developing florets and by studying its chromatin occupancy at downstream genes. The negative regulation of OsMADS34, another LOFSEP gene, and activation of OsMADS55, a SHORT VEGETATIVE PHASE-like floret meristem identity gene, show its role in facilitating the spikelet-to-floret meristem transition. Direct regulation of other transcription factor genes like OsHB4 (a class III homeodomain Leu zipper member), OsBLH1 (a BEL1-like homeodomain member), OsKANADI2, OsKANADI4, and OsETTIN2 show its role in meristem maintenance, determinacy, and lateral organ development. We found that the OsMADS1 targets OsETTIN1 and OsETTIN2 redundantly ensure carpel differentiation. The multiple effects of OsMADS1 in promoting auxin transport, signaling, and auxin-dependent expression and its direct repression of three cytokinin A-type response regulators show its role in balancing meristem growth, lateral organ differentiation, and determinacy. Overall, we show that OsMADS1 integrates transcriptional and signaling pathways to promote rice floret specification and development.