archives@tulane.edu / 0 / Anna Smith

Epigenetic regulators are commonly mutated in cancer. Activating mutations and overexpression of EZH2 occur in lymphoma and other malignancies, while loss-of-function mutations are found in myeloid malignancies. This thesis is a study of this apparent contradiction, examining the importance of cellular context for Ezh2 loss during the evolution of a single malignancy, Acute Myeloid Leukaemia (AML). This work demonstrates diametrically opposite functions for Ezh2 at early and late stages during the evolution of leukemias generated by disparate AML-associated fusion-oncogenes. Ezh2 functions as an oncogene that may be therapeutically targeted during disease maintenance. In contrast, Ezh2 behaves as a tumour suppressor gene during AML induction. Integrated genomic analysis demonstrates that largely different expression programmes are de-repressed during disease induction and maintenance following Ezh2 loss. Studying disease induction, Ezh2 represses a subset of bivalent promoters that resolve towards gene activation upon Ezh2 loss, inducing a feto-oncogene programme including genes like Plag1, whose overexpression phenocopies Ezh2 loss to accelerate AML induction in mouse models. This data highlights the importance of cellular context and phase of disease evolution for Ezh2 function. Moreover, the work herein identifies EZH2 as a potential target in AML, whilst providing reassurance of the safety of this therapeutic strategy.

No description available.

No description available.

archives@tulane.edu / 1 / Anna Smith

EGR1, one of the immediate-early response genes, plays an important role as a mediator for transmitting extracellular stimuli. EGR1 is down regulated in many cancers. Many studies show that it functions as a tumor suppressor gene in a variety of cancers. EGR1 also acts as an oncogene in number of cancers. We found that in rhabdomyosarcoma (RMS), which is a muscle derived pediatric cancer, EGR1 was expressed in both RMS subtypes, embryonal and alveolar, but with a much higher expression profile in embryonal RMS. This suggests different mechanisms of down regulation of EGR1 in these two subtypes. Molecular and cellular approaches were used to characterize the functional role of EGR1 in RMS. We found that over expression of EGR1 in alveolar RMS significantly decreased cell proliferation, mobility, and anchorage-independent growth. We showed that exogenous EGR1 up regulated the cell cycle regulator, p21, which is normally repressed in RMS. EGR1 also promoted differentiation in RMS cells by up regulating several genes involved in muscle differentiation including myosin heavy chain (MyHC), MyoD and myogenin. We found that EGR1 interacts with the oncogene TBX2 in RMS cells and that TBX2 inhibits EGR1 function. To understand how TBX2 inhibits EGR1, we depleted TBX2 in RMS and we found an up regulation of the EGR1 targeted tumor suppressor gene, PTEN, and the cysteine protease inhibitor gene, CST6. Also, we performed luciferase assays and found that TBX2 decreased the expression of luciferase constructs fused with the PTEN promoter when TBX2 was co-transfected with EGR1. Our novel findings on the EGR1 function in RMS highlights the significant role of EGR1 in muscle development and tumor growth. Significantly, our work also suggests the EGR1 could promote tumor regression in RMS through inducing programmed cell death, or apoptosis. We found that EGR1 induced apoptosis through triggering the intrinsic apoptosis pathway and activating caspase cascades involving caspase 3 and caspase 9, which are essential mitochondrial apoptotic factors. Also, we observed the activation of two pro-apoptotic factors, BAX and dephosphorylated BAD, which are both located upstream of the caspase cascades in the intrinsic pathway. Also, we found in our study that EGR1 is repressed by the catalytic subunit of PRC2 complex, EZH2, which mediates gene silencing through methylation of lysine 27 on histone 3 (H3K27me3). EGR1 also sensitized RMS cells to chemotherapeutic agents, which could be a future direction for improved therapeutic targeting. Therefore, this work provides a novel and powerful molecular therapeutic target for RMS cancer.

TBX2 and TBX3, which function as repressors, are members of the T-Box transcription factor family which are conserved throughout the metazoan lineage. TBX2 is highly expressed in rhabdomyosarcoma (RMS), the most common soft tissue sarcoma in children, and many other cancers. Previously, our lab dissected the oncogenic properties of TBX2 and its regulation of p14, p21 and PTEN. TBX3 is also expressed in some cancer types, however, its expression profile in RMS is severely down-regulated. TBX3 is shown to repress TBX2 in chondrocytes, but the characterization and regulation of TBX3 is poorly understood in the muscle lineage. Polycomb Repressive Complex 2 (PRC2), a gene silencing complex, acts to methylate histone H3 lysine 27 (H3K27me) of target gene promoters. The catalytic subunit of PRC2, EZH2, is up-regulated in RMS and data from our lab has shown that depletion of EZH2 up-regulated TBX3 and down-regulated TBX2 in C2C12 cells, an immortalized murine cell line. The hypothesis of this project was that there would be a PRC2-TBX3-TBX2 axis in RMS cells. To examine if TBX3 represses TBX2, TBX3 was transiently expressed in RMS cells representing both subtypes of RMS and we found that TBX2 was downregulated in each cell line. In a stable RH30 cell line with ectopic TBX3, TBX2 was down-regulated and PTEN expression was up-regulated. To determine if TBX2 repression by TBX3 was direct, a TBX3 ChIP assay was performed on the TBX2 promoter as well as the PTEN promoter. We found a strong enrichment of TBX3 on the TBX2 promoter but not on the PTEN promoter. Accordingly, we also observed that TBX3 over-expression impaired tumorigenesis through reduced cell proliferation, migration, and anchorage dependent growth. Also, we found that a stable RD cell line with ectopic TBX3 could promote differentiation, strongly suggesting that these results could have therapeutic value. Next, a shEZH2 plasmid was transfected into RMS cell lines ask if TBX3 was regulated by the PRC2 complex as we had observed in C2C12 cells. Just as we hypothesized, TBX3 was up-regulated and TBX2 was down-regulated. Similar to the previous TBX3 overexpression experiments, the EZH2 depleted RMS cell lines also showed decreased cell proliferation and migration rate. Also, an EZH2 knock down treatment induced differentiation in RMS cell lines. Therefore, understanding this potent regulation axis could provide an excellent opportunity for treatment of RMS cancer in the future.

No description available.

The developing brain is highly sensitive to environmental influences. Unfavorable nutrition is one kind of stress that can cause acute metabolic disorders during the neonatal period [1,2,3] and severe diseases in later life [4,5]. These early life experiences occurring during heightened periods of brain plasticity help determine the lifelong structural and functional aspects of brain and behavior. In humans, for example, weight gain during the first week of life increased the propensity for developing obesity several decades later [5]. This susceptibility is, if not all, related to the dynamic reversible epigenetic imprints left on the histones [6,7,8], especially during the prenatal and postpartum period [9]. Histones are highly dynamic and responsive towards environmental stress [10,11]. Through covalent modification of the histone tail, histones are able to direct DNA scaffolding and regulate gene expression [10,12]. Thus far, various types of post translational modifications have been identified on various histones tails [12]. Among them, the methylation and acetylation on lysine residue (K) 27 on histone 3 (H3) has been tightly linked to gene repression [13,14] and activation [15], respectively. EZh2 (enhancer of zeste 2) in the polycomb repressive complex 2 (PRC2) is the only methyltransferase that has been linked to catalyze this methylation reaction. In addition, SUZ (suppressor of zeste) and EED (embryonic ectoderm development) are two other key proteins in PRC2 function core that help EZH2. As previous reported, increased H3K27 methylation was monitored after fasting stress during neonatal period in chicks' paraventricular nucleus (PVN). In this study, we investigated the detailed mechanism behind changes in H3K27 methylation following fasting stress. After 24 hours fasting on 3 days-of-age (D3), chicks exhibited elevated mRNA levels of PRC2 key components, including EZH2, SUZ and EED, in the PVN on D4. Western blots confirmed this finding by showing increased global methylation status at the H3K27 site in the PVN on D4. In addition, until 38 days post fasting, SUZ and EZH2 remained inhibited. A newly identified anorexigenic factor, Brain-derived neurotrophic factor (BDNF), was used as an example of multiple hormones expressed in PVN to verify this finding. Both BDNF protein and mRNA exhibited compatible changes to global changes of tri- (me3) and di-methylated (me2) H327. Furthermore, by using chromatin immunoprecipitation assays (ChIP), we were able to monitor the changes of H3K27me2/me3 deposition along the Bdnf gene. Fasting significantly increased H3K27me2/me3 as well as EZH2 at the Bdnf's promoter, transcription start site and 3'-untranslated region. These data show that fasting stress during the early life period could leave epigenetic imprinting in PVN for a long time. Next, we tried to understand the function of this epigenetic imprinting in the chicks' PVN. Thus, we compared naive chicks (never fasted) to chicks that received either a single 24 hour fast on D3 or two 24 hour fast on both D3 and 10 days-of-age (D10). We found that the D3 fasted group significantly increased the level of PRC2 key components and its product H3K27me2/me3 compared to the naive group. However, D3 fasting and D10 fasting together decreased the surges of H3K27me2/me3, SUZ and EED (not EZH2) compared to the naive group. We called this phenomenon "epigenetic memory". The Western blot, qPCR and CHIP assay results from BDNF all confirmed the existence of "epigenetic memory" for PRC2. These data suggested that fasting stress during the early period of brain development could leave long term epigenetic modifications in neurons. These changes could be beneficial to the body, which keeps homeostasis of inner environment and prevent massive response to future same stress. The EZH2 protein was knocked down and the H3K27 methylation status changes were monitored after applying the same treatment. We first confirmed that EZH2 antisense oligonucleotides (5.5 ug), but not EZH2 siRNA and artificial cerebrospinal fluid (ACSF), inhibit EZH2 protein by 86 % in the PVN. Then, on D3, chicks were subjected to a 24 hour fasting stress (D3-fasting) post either EZH2 antisense or ACSF injection. The EZH2 antisense blocked the surge of both EZH2 mRNA and H3K27 methylation after D3-fasting. At the same time, BDNF exhibited elevated expression levels and less methylated H3K27 deposition along the Bdnf gene. In addition, we were also interested in the changes of "epigenetic memory" post EZH2 antisense injection. We found that after EZH2 antisense injection, chicks' PVN no longer exhibited any "epigenetic memory" to repetitive fasting stress. While EZH2 mRNA was constantly inhibited, SUZ, EED and H3K27me2/3 levels were unpredictable. These findings suggested that neurons in the PVN utilized PRC2 as a major H3K27 methylation tool. Knockdown of EZH2 in the PRC2 impaired the proper response in PVN to fasting stress and PVN's ability to acclimate to repetitive fasting stresses. Thus, EZH2 is an important H3K27 methyltransferase inside chicken hypothalamus to maintain homeostasis. In conclusion, fasting stress during the early life period could leave epigenetic markers on chromosomes of neurons in the feeding regulation center. These epigenetic markers will be left on chromosomes for a long period of time and have a beneficial role in keeping homeostasis when individuals face future fasting stress again. H3K27 methylation is one of these epigenetic markers and inhibits expression of various genes inside neurons. EZH2 is so far the only detected methyltransferases for H3K27 that form the PRC2. Thus EZH2 plays a key function in the body's response to fasting. / Ph. D.

A esquistossomose é um grave problema de saúde pública, com alta mortalidade e morbidade em países endêmicos, causada pelo verme trematódeo do gênero Schistosoma. O praziquantel é a única droga disponível para tratamento da doença, é usada em larga escala para tratamento de populações de áreas endêmicas, porém não previne a reinfecção e tem efeito somente em vermes adultos. Drogas estudadas em câncer como inibidores de histona deacetilases (iHDACs) modificam o padrão epigenético da célula desencadeando a morte celular, e em Schistosoma mansoni já foi mostrado que a inibição de HDACs além de aumentar a acetilação de histonas alterou o fenótipo de miracídios e provocou morte em esquistossômulos e vermes adultos. O presente estudo investigou o efeito do iHDAC Trichostatin A (TSA) na regulação da transcrição gênica em esquistossômulos, detectando por meio de ensaios de microarray centenas de genes diferencialmente expressos, relacionados a replicação de DNA, metabolismo e complexos modificadores de histonas. A inibição de HDAC em vermes adultos levou a um aumento da acetilação nas marcas de histonas H3K9ac, H3K14ac e H4K5ac relacionadas à indução de transcrição. Com imunoprecipitação de cromatina seguida de PCR (ChIP-qPCR) detectou-se o aumento de deposição de H3K9ac e H3K14ac na região promotora de genes com expressão aumentada ou diminuída, porém a marca de repressão H3K27me3 não sofreu alteração na região promotora de nenhum gene analisado. Análises adicionais indicaram um conjunto de genes diferencialmente expressos que codificam proteínas histone readers, que fazem parte de complexos modificadores de histonas, como EED capaz de identificar a marca de repressão H3K27me3 e regular a atividade de EZH2, apontando um novo alvo terapêutico. O efeito sinérgico entre iHDAC e um iEZH2 foi testado e detectou-se o aumento da mortalidade de esquistossômulos. A estrutura de SmEZH2 foi modelada por homologia e usada para análises computacionais que sugeriram uma alta afinidade de ligação de SmEZH2 com o iEZH2, abrindo uma perspectiva de desenvolvimento de novas drogas específicas para tratamento da esquistossomose. / Schistosomiasis is a serious public health problem, with high mortality and morbidity in endemic countries, caused by trematode worms of the genus Schistosoma. Praziquantel is the only available drug for treatment of the disease; it is used extensively to treat populations in endemic areas, but does not prevent reinfection and is effective only in adult worms. Drugs studied in cancer as histone deacetylase inhibitors (iHDACs) modify the epigenetic status of the cell, triggering cell death, and it has been shown in Schistosoma mansoni that inhibition of HDACs increase histone acetylation, alter the phenotype of miracidia and cause death in schistosomules and adult worms. The present study investigated the effect of iHDAC Trichostatin A (TSA) on the regulation of gene transcription in schistosomules, detecting by means of microarray assays hundreds of differentially expressed genes related to DNA replication, metabolism and histone remodeling complexes. Inhibition of HDAC in adult worms led to an increase in histone acetylation marks H3K9ac, and H3K14ac H4K5ac related to transcriptional induction. With chromatin immunoprecipitation followed PCR (ChIP-qPCR) we detected an increased deposition of H3K9ac and H3K14ac at the promoter region of genes with increased or decreased expression, but the repressive mark H3K27me3 was not changed at all analyzed gene promoter regions. Additional analysis indicated a set of differentially expressed genes that encode histone reader proteins that are part of histone modifier complexes such as EED, which is able to identify the repression mark H3K27me3 and to regulate EZH2 activity, pointing to a new therapeutic target. The synergistic effect between iHDAC and one iEZH2 has been tested and found to cause an increase in schistosomules mortality. The SmEZH2 structure was modeled by homology and used for computational analyses, which suggested a high affinity binding of SmEZH2 with iEZH2, opening the opportunity for development of new specific drugs for treatment of schistosomiasis.