GADD45A Promoter Research Articles

EZH2 enhances proliferation and migration of trophoblast cell lines by blocking GADD45A-mediated p38/MAPK signaling pathway

ABSTRACT Impaired activity of the trophoblasts is a major contributor to the progression of pregnancy pathologies including preeclampsia (PE). This research probed the function of enhancer of zeste homolog 2 (EZH2) in activity of trophoblast cells and its correlation with growth arrest and DNA damage inducible alpha (GADD45A). EZH2 was predicted to be downregulated in placental tissues in PE according to a gene chip analysis, and reduced expression of EZH2 was detected in the placental tissues of patients with PE. Overexpression of EZH2 augmented proliferation and invasiveness of two trophoblast cell lines HTR-8/SVneo and JEG3 cells. EZH2 catalyzed trimethylation of lysine 27 on histone 3 (H3K27me3) in GADD45A promoter to suppress its transcription. GADD45A silencing increased the activity of the trophoblast cell lines and inactivated the p38/mitogen-activated protein kinase (MAPK) signaling pathway. Rescue experiments confirmed that either inhibition of GADD45A or p38 restored the proliferation, migration, and invasiveness of the trophoblast cell lines suppressed by EZH2 silencing. In conclusion, this work suggests that EZH2 enhances activity of trophoblast cell lines by suppressing GADD45A-mediated p38/MAPK signaling pathway.

Trimethylamine N-oxide mediated Y-box binding protein-1 nuclear translocation promotes cell cycle progression by directly downregulating Gadd45a expression in a cellular model of chronic kidney disease

AimsCell cycle arrest plays critical roles in preventing renal tubular epithelial cell (RTEC) injury and maladaptation after the onset of chronic kidney disease (CKD), but the underlying mechanism governing this arrest has not been fully elucidated. This study was designed to determine the underlying role of YB-1 in promoting cell cycle progression and nuclear translocation in HK-2 cells induced by trimethylamine N-oxide (TMAO). Main methodsYB-1 primarily accumulated in the cytoplasm in HK-2 cells after they were treated with TMAO for 30 min and 6 h. Gene expression was analysed using RNA sequencing in HK-2 cells treated with TMAO. Cell cycle progression was analysed via flow cytometry. Luciferase assay and ChIP-PCR were performed to determine the relationship between transcription factor YB-1 and Gadd45a promoter region. Additionally, mice were fed with TMAO to test renal dysfunction and measure the expression of YB-1, GADD45a and CCNA2 in the kidney sections through immunohistochemistry. Key findingsYB-1 primarily accumulated in the cytoplasm in HK-2 cells after they were treated with TMAO for 30 min and 6 h. RNA sequencing analysis showed that the cell cycle checkpoint genes growth arrest and DNA damage (Gadd)45a, Gadd45g, cyclin (Ccn)a2, Ccnb1, Ccne1 and Ccnf were differentially expressed in HK-2 cells after treated with 400 μM TMAO for 30 min. Flow cytometry results demonstrated that cell cycle progression was blocked at the G2/M checkpoint. In animal models, elevated dietary TMAO directly led to progressive renal tubulointerstitial dysfunction and inhibited the expression of YB-1 in kidney. Moreover, YB-1 was determined to regulate Gadd45a expression by directly binding to its promoter region. YB-1 expression was negatively correlated with the expression of Gadd45a and Gadd45g but positively correlated with Ccna2, Ccnb1, Ccne1 and Ccnf in CKD. SignificanceYB-1 may be a reliable molecular target and an effective prognostic biomarker for CKD.

KLF5-Modulated lncRNA NEAT1 Contributes to Tumorigenesis by Acting as a Scaffold for BRG1 to Silence GADD45A in Gastric Cancer

Long noncoding RNAs (lncRNAs), genomic “dark matter,” are deeply involved in diverse biological processes. The lncRNA nuclear paraspeckle assembly transcript 1 (NEAT1) is a highly participatory lncRNA; however, its roles in gastric cancer (GC) remain largely unexplored. Here, we demonstrated that the expression of NEAT1 was significantly increased and negatively correlated with prognosis in GC. Subsequent experiments confirmed that KLF5 can induce NEAT1 expression by binding to the NEAT1 promoter region. Further experiments revealed that NEAT1 silencing significantly suppressed cell proliferation both in vitro and in vivo and induced apoptosis. We used mRNA sequencing (mRNA-seq) to identify the preferentially affected genes linked to cell proliferation in cells with NEAT1 knockdown. Mechanistically, NEAT1 bound BRG1 (SMARCA4) directly, modulating H3K27me3 and H3K4me3 in the GADD45A promoter to regulate GADD45A-dependent G2/M cell cycle progression. In addition, BRG1 was significantly upregulated and correlated with outcomes in GC; moreover, it promoted cell proliferation both in vitro and in vivo. Taken together, our data support the importance of NEAT1 in promoting GC tumorigenesis and indicate that NEAT1 might be a diagnostic and therapeutic target in GC.

Hypermethylation of GADD45A Defines a Methylation Profile Distinct to Mutant IDH1/2, and Correlates with More Aggressive AML

We have previously reported that hypermethylationof the GADD45A promoter (GADD45AmeHI) occurs frequently in AML at a specific CpG residue (CpG1) and associates with poor overall survival for patients on standard chemotherapy (Perugini et al, Leukemia 2013). Sequenom multiplex analysis of 195 AML patients revealed a co-occurrence of GADD45AmeHI with recurrent mutations at conserved residues in IDH1 and IDH2 (p<0.0001, Fisher’s exact test). These mutations in IDH1 and IDH2 result in enzyme isoforms that produce high levels of the onco-metabolite 2-hydroxyglutarate with a wide-range of effects including inhibition of α-KG-dependent dioxygenases and association with a profound DNA hypermethylation phenotype in AML (Figueroa et al, Cancer Cell 2010). Furthermore these mutations are found in pre-leukemic AML clones (Shlush et al, Nature 2014) and lead to pre-leukaemic phenotypes in mouse models (Sasaki et al, Nature 2012, Kats et al, Cell Stem Cell 2014, Ogawara et al, Cancer Research 2015). Here we investigated the relationship between hypermethylation at GADD45A CpG1, IDH1/2 mutation status, global methylation patterns and patient survival.We performed survival analysis to determine disease-free survival (DFS) and relapse-free survival (RFS) for AML patients with GADD45AmeHI or IDH1/2-mutations. This showed that GADD45AmeHI is a significant independent predictor of poor DFS and RFS, particularly in normal karyotype AML (Cox regression analysis, NK-AML DFS, P=0.009 HR=2.55, RFS, P=0.003 HR=2.75). Despite the co-association of GADD45AmeHI with mutations in IDH1 and IDH2, the mutation status of IDH1/2 did not predict DFS or RFS in these patients. To examine further the relationship between GADD45AmeHI and IDH1/2-mutation, and to investigate how this might influence tumour cell biology in AML, we determined global methylation patterns for a panel of AML diagnosis (Dx) samples (base-pair-resolution analysis using enhanced reduced representation bisulfite sequencing; ERRBS) in which both GADD45AmeHI and IDH mutation status has been determined. Unsupervised analyses of global methylation patterns grouped the AML Dx samples into three clusters including cluster 1 (n=12) which was associated with GADD45AmeHI samples with IDH- mutations, cluster 2 (n=13) which was enriched for GADD45AmeHI lacking IDH- mutations, and cluster 3 (n=9) which was associated with GADD45AmeLO (low CpG1 methylation) IDH-WT AML. We propose that this CpG in the GADD45A promoter may be subject to alternative events affecting DNA methylation in AML pathogenesis, including events distinct from IDH1/2 mutation. Finally, in GADD45AmeHI AML we detected hypermethylated regions compared to CD34+ normal bone marrow controls within 2016 gene promoters, 848 of which were unique to the GADD45AmeHI samples and not present in IDH1/2-mutant samples. We hypothesize that these differentially methylated genes may contribute mechanistically to the poor survival observed for this subtype.To determine how GADD45AmeHI status might associate with disease progression, DNA methylation assessment was performed on the patient panel-matched relapse samples (Rx). While GADD45AmeHI occurs frequently in both cluster 1 and 2 there is a significant difference in level of GADD45A CpG1 methylation at Dx and Rx for samples in cluster 1 vs cluster 2 and 3 (Figure 1), consistent with mutant IDH1/2 activity influencing methylation levels at this CpG site. Given that GADD45A has an established basal role in the maintenance of genomic stability (Liebermann & Hoffman, Springer 2013), and is a determinant of HSC self-renewal and response to genotoxic insult (Wingert et al, Stem Cells 2016, Chen et al, Blood 2014) we are also investigating whether GADD45A methylation and silencing plays a direct role in determining aggressiveness and response to chemotherapy for GADD45AmeHIAML.In conclusion this data suggests that methylation at this specific CpGof the GADD45A promoter, in combination with IDH1/2 mutation status, associate with varying global methylation phenotypes. Importantly, we demonstrate that GADD45AmeHI better predicts poorer prognosis than IDH1/2 mutation status, despite the significant co-association of these characteristics in AML.SES and FEGB contributed equally to this work. [Display omitted] DisclosuresGuzman:Cellectis: Research Funding. Roboz:Agios, Amgen, Amphivena, Astex, AstraZeneca, Boehringer Ingelheim, Celator, Celgene, Genoptix, Janssen, Juno, MEI Pharma, MedImmune, Novartis, Onconova, Pfizer, Roche/Genentech, Sunesis, Teva: Consultancy; Cellectis: Research Funding. Levine:Qiagen: Membership on an entity's Board of Directors or advisory committees; Novartis: Consultancy. Melnick:Janssen: Research Funding.

Comparative genotoxicity of silver nanoparticles in human liver HepG2 and lung epithelial A549 cells.

With the rapid expanding of human exposure to silver nanoparticles (AgNPs), genotoxicity screening of nanosilver is necessary to ensure consumer safety. Here, we assessed one key DNA damage responsive pathway activated by GADD45a gene after 24 h of AgNPs exposure in stable luciferase reporter cell systems based on two widely used in vitro cell models, human liver HepG2 and lung epithelial A549 cells. The comet assay and micronucleus test were also conducted to confirm the genetic damage induced by AgNPs. Our results showed that AgNPs produced a strong dose-dependent increase in transcriptional activation of GADD45a promoter indicated by luciferase activity accompanying by the significant decreases in cell viability. Surprisingly, in HepG2-luciferase cells, the relative luciferase activity was greater than 4.5× the control level after being treated with 200 μg ml-1 AgNPs. These results were generally in line with the positive and dose-dependent responses in cytotoxicity, DNA strand breaks indicated by Olive tail moment, tail DNA (%) and tail length, and chromosome damage indicated by induction of micronuclei, nucleoplasmic bridges, and nuclear buds. Additionally, compared with the A549-luciferase cells, the HepG2-luciferase cells seemed to be more susceptible to AgNPs as higher levels of genotoxicity were induced. We concluded that our GADD45a promoter-driven luciferase reporter gene cell system, together with the comet assay and micronucleus test, can be used as valuable tools for rapid screening of genotoxic potential of nanosilver. Copyright © 2016 John Wiley & Sons, Ltd.

Derivate isocorydine inhibits cell proliferation in hepatocellular carcinoma cell lines by inducing G2/M cell cycle arrest and apoptosis.

We have previously demonstrated that isocorydine (ICD) can be served as a potential antitumor agent in hepatocellular carcinoma (HCC). A novel derivate of isocorydine (d-ICD) could significantly improve its anticancer activity in tumors. However, the molecular mechanisms of d-ICD on HCC cells remain to be unclear. In this study, we observed that d-ICD inhibited cell proliferation and induced apoptosis of HCC cells in a concentration-dependent manner. We found d-ICD induced G2/M cycle arrest of HCC cells via DNA damage 45 alpha (GADD45A) and p21 pathway in vitro and in vivo. In d-ICD-treated cells, cell cycle-related proteins cyclin B1 and p-CDC2 were upregulated and p-cyclin B1, CDC2, and E2F1 were inhibited. p21 expression can be reversed by knockdown of GADD45A in d-ICD-treated HCC cells. Enforced expression of CCAAT/enhancer-binding protein β (C/EBPβ) in combination with d-ICD enhanced the p21 expression in HCC cells. Furthermore, the luciferase reporter assay showed that upregulation of GADD45A by C/EBPβ was achieved through the increase of GADD45A promoter activity. These findings indicate that d-ICD inhibits cell proliferation and induces cell cycle arrest through activation of C/EBPβ-GADD45A-p21 pathway in HCC cells. d-ICD might be a promising chemotherapeutic agent for the treatment of HCC.

GADD45a promoter regulation by a functional genetic variant associated with acute lung injury.

RationaleGrowth arrest DNA damage inducible alpha (GADD45a) is a stress-induced gene we have shown to participate in the pathophysiology of ventilator-induced lung injury (VILI) via regulation of mechanical stress-induced Akt ubiquitination and phosphorylation. The regulation of GADD45a expression by mechanical stress and its relationship with acute lung injury (ALI) susceptibility and severity, however, remains unknown.ObjectivesWe examined mechanical stress-dependent regulatory elements (MSRE) in the GADD45a promoter and the contribution of promoter polymorphisms in GADD45a expression and ALI susceptibility.Methods and ResultsInitial studies in GADD45a knockout and heterozygous mice confirmed the relationship of GADD45a gene dose to VILI severity. Human lung endothelial cells (EC) transfected with a luciferase vector containing the full length GADD45a promoter sequence (−771 to +223) demonstrated a >4 fold increase in GADD45a expression in response to 18% cyclic stretch (CS, 4 h) compared to static controls while specific promoter regions harboring CS-dependent MSRE were identified using vectors containing serial deletion constructs of the GADD45a promoter. In silico analyses of GADD45a promoter region (−371 to −133) revealed a potential binding site for specificity protein 1 (SP1), a finding supported by confirmed SP1 binding with the GADD45a promoter and by the significant attenuation of CS-dependent GADD45a promoter activity in response to SP1 silencing. Separately, case-control association studies revealed a significant association of a GADD45a promoter SNP at −589 (rs581000, G>C) with reduced ALI susceptibility. Subsequently, we found allelic variation of this SNP is associated with both differential GADD45a expression in mechanically stressed EC (18% CS, 4 h) and differential binding site of interferon regulatory factor 7 (IRF7) at this site.ConclusionThese results strongly support a functional role for GADD45a in ALI/VILI and identify a specific gene variant that confers risk for ALI.

Nutlin-3a Efficacy in Sarcoma Predicted by Transcriptomic and Epigenetic Profiling

Nutlin-3a is a small-molecule antagonist of p53/MDM2 that is being explored as a treatment for sarcoma. In this study, we examined the molecular mechanisms underlying the sensitivity of sarcomas to Nutlin-3a. In an ex vivo tissue explant system, we found that TP53 pathway alterations (TP53 status, MDM2/MDM4 genomic amplification/mRNA overexpression, MDM2 SNP309, and TP53 SNP72) did not confer apoptotic or cytostatic responses in sarcoma tissue biopsies (n = 24). Unexpectedly, MDM2 status did not predict Nutlin-3a sensitivity. RNA sequencing revealed that the global transcriptomic profiles of these sarcomas provided a more robust prediction of apoptotic responses to Nutlin-3a. Expression profiling revealed a subset of TP53 target genes that were transactivated specifically in sarcomas that were highly sensitive to Nutlin-3a. Of these target genes, the GADD45A promoter region was shown to be hypermethylated in 82% of wild-type TP53 sarcomas that did not respond to Nutlin-3a, thereby providing mechanistic insight into the innate ability of sarcomas to resist apoptotic death following Nutlin-3a treatment. Collectively, our findings argue that the existing benchmark biomarker for MDM2 antagonist efficacy (MDM2 amplification) should not be used to predict outcome but rather global gene expression profiles and epigenetic status of sarcomas dictate their sensitivity to p53/MDM2 antagonists.

Methylation‐mediated repression of GADD45A and GADD45G expression in gastric cardia adenocarcinoma

The growth arrest DNA damage-inducible gene (GADD45) family, which is composed of GADD45A, GADD45B, and GADD45G, may play similar but not identical roles in tumorigenesis. Genetic changes associated with or responsible for their dysregulation are in general uncommon. This study was to detect the role of GADD45 gene family in gastric cardia adenocarcinoma (GCA) and the relationship of GADD45A and GADD45G methylation to a series of pathological parameters in a large GCA sample, in order to elucidate more information on the role of GADD45 gene family with regard to the pathogenesis of GCA. Decreased mRNA and protein expression of GADD45A and GADD45G but not GADD45B were found in 138 GCA tumor tissues. The methylation frequency of 5' 4 CpG region located in distal promoter of GADD45A and proximal promoter of GADD45G in GCA tumor tissues was significantly higher than that in corresponding normal tissues. The expression levels of GADD45A and GADD45G were inversely correlated with methylation levels. GADD45B expression was not correlated with GCA patients survival, while GADD45A and GADD45G methylation status and protein expression were independently associated with GCA patients' survival. These results suggest that GADD45A and GADD45G gene may act as functional tumor suppressor but being frequently inactivated epigenetically in patients with GCA. Silencing of GADD45A and GADD45G, negative regulator of cell growth, is most likely responsible for conferring a selective growth advantage during GCA evolution and outgrowth.

Regulation of Oct1/Pou2f1 transcription activity by O ‐GlcNAcylation

The Oct1 transcription factor is a potent regulator of stress responses, metabolism, and tumorigenicity. Although Oct1 is regulated by phosphorylation and ubiquitination, the presence and importance of other modifications is unknown. Here we show that Oct1 is modified by O-linked β-N-acetylglucosamine (O-GlcNAc) moieties. We map two sites of O-GlcNAcylation at positions T255 and S728 within human Oct1. Under anchorage-independent overgrowth conditions, Oct1 associates 3-fold more strongly with the Gadd45a promoter and mediates transcriptional repression. Increased binding correlates with quantitative reductions in Oct1 nuclear periphery-associated puncta, and a reduced association with lamin B1. The O-GlcNAc modification sites are important for both Gadd45a repression and anchorage-independent survival. In contrast to chronic overgrowth conditions, following acute nutrient starvation Oct1 mediates Gadd45a activation. The O-GlcNAc sites are also important for Gadd45a activation under these conditions. We also, for the first time, identify specific Oct1 ubiquitination sites. The findings suggest that Oct1 integrates metabolic and stress signals via O-GlcNAc modification to regulate target gene activity.

The BlueScreen-384 Assay as an Indicator of Genotoxic Hazard Potential in Early-Stage Drug Discovery

High-throughput cell-based techniques that permit early detection of compound-induced genotoxic damage have recently become available. Methods based on induction of the GADD45a promoter are attractive because multiple intracellular mechanisms that detect genetic damage intersect at this checkpoint gene. Consequently, assays such as GreenScreen HC, which uses p53-competant human TK6 lymphoblastoid cells and a GADD45a-GFP reporter, have been developed. GreenScreen HC allows weekly testing of dozens of compounds using 96-well microplates, with high interassay consistency. BlueScreen HC is a recent advancement, coupling GADD45a to Gaussia luciferase, with several advantages over GADD45a-GFP including the potential for miniaturization. Here we describe implementation of a 384-well BlueScreen assay. For drug discovery programs carrying out iterative analogue synthesis around a chemical lead series, these assays permit assessment of compound genotoxic potential in parallel to, rather than subsequent to, determination of activity at a therapeutic target. We demonstrate comparability of BlueScreen-384 to GreenScreen HC and illustrate the use of BlueScreen-384 to explore the structure-activity relationship around a genotoxic lead molecule to identify nongenotoxic analogues. BlueScreen-384 can reduce the need for costly and time-consuming analogue testing in more traditional genotoxicity tests, such as the Ames test.

Methylation of the Proximal Promoter of GADD45A Is Common in Acute Myeloid Leukemia and Is Associated with Poor Survival.

AbstractAbstract 2396 Background:Despite recent advances in understanding the key molecular mechanisms of leukemogenesis, the outcome for patients with Acute Myeloid Leukemia, particularly with a normal karyotype, remains poor. For this large group of patients, genetic alterations in genes such as FLT3, NPM1, CEBPA, IDH1/2, and DNMT3A provide useful prognostic information. However, risk stratification of this group remains only partially resolved and markers of response that can be therapeutically targeted would likely improve outcome for these patients. GADD45A is a tumor suppressor gene that plays cell-type dependent roles in cellular stress coordinating DNA repair and de-methylation, cell cycle arrest, and pro-apoptotic or pro-survival responses (Cancer Ther. 2009;7:268). Methylation of four discrete CpG residues in the proximal promoter of GADD45A is a hallmark of many solid tumours and has been associated with impaired cell stress signalling and reduced drug response (Cancer Res. 2009;69:1527; Oncogene. 2005;24:2705). In AML, GADD45A expression is broadly down-regulated both in normal karyotype and other cytogenetic classes. Down-regulation of GADD45A in AML has been associated with FLT3-ITD (Leukemia. 2009;23:729) and RUNX1 mutations (Satoh et al, Leukemia. 2011;Epub). For those patients without these mutations, the mechanism of GADD45A down-regulation and its prognostic significance remains unknown. We hypothesised that the promoter of GADD45A is methylated in AML and that this methylation is functionally important in patient response. Methods:Using the Sequenom MassARRAY methodology we screened for methylation of four GADD45A promoter CpG dinucleotides (CpG1–4) previously shown to be associated with silencing of GADD45A in breast and prostate cancer, in a retrospective cohort of 222 AML patients collected at diagnosis from the Royal Adelaide Hospital. We then determined association of CpG methylation with outcome and mutation status in our treated patient cohort of 167 patients. In AML cell lines and in primary patient samples we also determined the response to cytotoxic agents in vitro in the presence and absence of demethylating agents. Results:We observed hypermethylation of the CpG1–4 in the proximal promoter of GADD45A in 93 of 222 (42%) of AML patients and in 6 AML cell lines. In the 167 patients treated with standard induction chemotherapy regimes, 61 patients showed methylation of the GADD45A proximal promoter. Of the four CpG residues, methylation of CpG1 was associated with poor overall and event-free survival, in AML overall (Figure 1A) and in normal karyotype AML (Figure 1B). GADD45A CpG1 methylation was significantly associated with IDH1 and IDH2 mutations (p<0.001), but was not associated with FLT3-ITD or other high risk cytogenetic groups. Multivariate analysis (including age, wcc, FLT3-ITD, IDH1/2) revealed that methylation of GADD45A CpG1 is an independent predictor of poor survival in AML, overall (OS; HR 2.17, p=0.006: EFS; HR 2.43, p=0.001), and in normal karyotype AML (OS; HR 2.86, p=0.014: EFS; 5.25, p<0.001). Additionally, treatment of AML cell lines and patient blasts with decitabine (5-Aza-deoxycitidine) resulted in induction of GADD45A mRNA selectively in samples with GADD45A hyper-methylation, and this was associated with increased sensitivity to daunorubicin. Conclusions:DNA methylation of the GADD45A proximal promoter marks a large percentage AML patients, including those with with IDH1/2 mutations, and is an independent predictor of poor outcome, particularly in AML patients with normal karyotype. Our biological data shows that induction of GADD45A mRNA expression with decitabine in methylated samples is associated with increased response to cytotoxic agents. Thus GADD45A proximal promoter methylation represents a new biomarker that may provide prognostic information in the heterogeneous normal karyotype AML group. Given that recent clinical trials are combining Azacitidine with chemotherapy and other agents for induction therapy in AML (Blood;118:1472), this may represent a marker to help define patients that will benefit from this approach. [Display omitted] [Display omitted] Disclosures:Wei:Celgene: Research Funding.

Methylation of a Single CpG in the GADD45A Proximal Promoter Is Associated with Poor Survival in Acute Myeloid Leukemia,

Abstract 3540▪▪This icon denotes a clinically relevant abstract Background:GADD45A is a tumor suppressor gene that plays cell-type dependent roles in cellular stress, coordinating DNA repair and de-methylation, cell cycle arrest, and pro-apoptotic or pro-survival responses. GADD45A expression is normally rapidly induced in response to radiation and cytotoxic drugs1 and ectopic expression of GADD45A in the M1 leukemic cell line sensitises cells to stress-induced apoptosis in response to a range of genotoxic agents.2 Silencing of GADD45A by promoter methylation is a hallmark of many tumors,3–5 however to date there have been no investigations to determine whether this is associated with response to therapy. In AML, we have shown GADD45A expression is broadly down-regulated6 and here we investigate the mechanism of GADD45A repression in AML and its clinical significance. METHODS:We analysed 131 diagnostic bone marrow mononuclear cell samples from a retrospective cohort of patients with de novo AML. 93 of these patients were treated with induction chemotherapy. Patients 60 years or under were treated with chemotherapy regimens containing idarubicin and high dose cytarabine, and patients older than 60 received idarubicin and standard dose cytarabine. We used matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (Sequenom MassARRAY) to analyze methylation of 4 GADD45A promoter CpG dinucleotides previously shown to be associated with silencing of GADD45A in breast and prostate cancer.4,5 We determined association of CpG hyper-methylation with outcome in our treated patient cohort. For AML cells with GADD45A hyper-methylation, and for those with normal levels of GADD45A promoter methylation, we also determined the response to cytotoxic agents in vitro in the presence and absence of hypo-methylating agents. RESULTS:We observed hyper-methylation of the 4 CpG residues in the proximal promoter of GADD45A in 49 of 131 (37%) de novo AML patients and in 6 AML cell lines. Multivariable analysis showed that methylation of a single CpG (CpG1) was an independent predictor of poor survival in AML overall (median survival 281 days versus 794 days, HR 2.25, p=0.009), in normal karyotype AML (NK-AML) (median survival of 281 versus 793 days, HR 5.77, p=0.03, >250 days), and in the elderly patient group (>60 years, median survival of 218 versus 392 days, HR 2.64, p=0.03)(see Figure 1). Additionally, treatment of AML cell lines and patient blasts with decitabine resulted in selective induction of GADD45A mRNA in samples with GADD45A hyper-methylation, and this was associated with increased sensitivity to daunorubicin. [Display omitted] CONCLUSIONS:DNA methylation of the GADD45A proximal promoter is an independent predictor of poor outcome particularly in AML patients with normal karyotype and in the elderly group. Our biological data shows that induction of GADD45A mRNA expression with decitabine in hyper-methylated samples is associated with increased response to cytotoxic agents. Thus GADD45A promoter CpG methylation represents a new biomarker that may provide prognostic information in the heterogeneous NK-AML group, and in elderly patients. Given that recent trials are combining Azacitidine with chemotherapy and other agents for initial induction treatment of AML9, this may represent a marker to help define patients that will benefit from this approach. Elderly patients with GADD45A hyper-methylation may benefit from treatment with hypo-methylating agents which are associated with less toxicity (see Refs 7,8). Disclosures:Wei:Celgene: Honoraria, Research Funding.

Gadd45a Behaves as a Tumor Suppressor and Gadd45b Behaves as an Oncogene in myc-Mediated Block in Myeloid Differentiation.

We have observed that deregulated c-Myc expression in M1 myeloid leukemic cells blocks IL-6-induced differentiation at an intermediate stage, the cells fail to exit the cell cycle, proliferating indefinitely, with a portion of the cells always undergoing apoptotic cell death by prematurely recruiting the CD95/Fas apoptotic pathway. Similar results were also observed in normal myeloid cells from bone marrow (Amanullah et al. Oncogene 19:2967–77, 2000; Amanullah et al. Oncogene 21:1600–1610, 2002). Although there is evidence that c-myc represses the gadd45a promoter, this laboratory has observed elevated gadd45a expression in M1myc cells that are blocked during differentiation. In addition, microarray analysis indicated that gadd45b is a c-myc target gene. Because of these observations and the availability of gadd45a null and gadd45b null mice, the effect of deregulated myc expression in Hoxb8 immortalized macrophage progenitors was ascertained. It was observed that deregulated c-myc expression in gadd45a null cells blocked differentiation at the blast stage, compared to a block at the intermediate stage for wild type progenitors. In contrast, deregulated c-myc expression in gadd45b null progenitors resulted in rapid cell death. These observations suggest that in the context of myc mediated myeloid leukemias Gadd45a behaves as a tumor suppressor and Gadd45b behaves as an oncogene.

The Eukaryotic Initiation Factor-2 Kinase Pathway Facilitates Differential GADD45a Expression in Response to Environmental Stress

Phosphorylation of eukaryotic initiation factor-2 (eIF2) regulates general and gene-specific translation in response to diverse environmental stresses. Central to gene expression induced by eIF2 phosphorylation is the preferential translation of ATF4, a basic zipper transcription activator. Phosphorylation of eIF2 and its attendant induction of ATF4 can lead to different patterns of gene expression depending on the environmental stress. This is of fundamental importance because eIF2 kinases can induce the expression of genes involved in survival as well as in apoptosis. In this report, we explore the molecular basis for why there can be differential expression of GADD45a, a stress-responsive protein that regulates genome stability, apoptosis, and immune responses. We find that whereas ATF4 is required for GADD45a transcription during many different environmental stresses, GADD45a protein accumulates only during a limited number of stress arrangements. The basis for this difference between measurable GADD45a mRNA and protein lies in the observation that GADD45a protein is labile. Those stress agents that enhance ATF4-directed GADD45a transcription and impede the turnover of GADD45a protein by blocking ubiquitin/proteasome-mediated degradation elevate GADD45a protein levels. By comparison, those stress arrangements that trigger ATF4 levels and GADD45a transcription, but do not perturb the proteasome pathway, only elevate GADD45a mRNA levels. This study highlights the molecular mechanisms by which environmental stresses can differentially control central regulatory proteins targeted by the eIF2 kinase pathway.

Mechanism of Transcriptional Repression of GADD45a in Prostate Cancer and Its Potential Role as a Therapeutic Target.

Methylation-mediated repression of tumor-suppressor genes or genes involved in cell death pathway is a common event in most human malignancies. We examined the mechanism of regulation of a gene involved in cell-cycle and apoptotic pathways, Growth Arrest and DNA Damage inducible, alpha (GADD45a), in prostate cancer cells. GADD45a is expressed at a low level in LNCaP and Du145 prostate cancer cells as compared to PC3 prostate cancer cells. Bisulfite genomic sequencing was used to determine the methylation pattern of CpG dinucleotides in GADD45a promoter region. Transcriptional repression of GADD45a occurs by an atypical pattern of methylation. Unlike the commonly reported methylation pattern of tumor-suppressor genes in human malignancies, the CpG islands of the proximal promoter region are unmethylated in all three prostate cancer cell lines Du145, LNCaP and PC3. However, methylation of 4 CpGs located approximately 700 bp upstream of the transcriptional start site correlates inversely with the expression of GADD45a in Du145, LNCaP, and PC3 cells. Treatment of Du145 and LNCaP cells with DNA methyl transferase (DNMT) inhibitors, 5-Azacytidine and 5 Aza-2′deoxycytidine led to an enhanced GADD45a expression concomitant with demethylation of the 4 CpGs. Frequent methylation of the 4 CpGs was also seen in prostate cancer tissues. Methylation-mediated transcriptional repression involves binding of specific proteins, Methyl-CpG binding proteins (MBDs) at methylated CpG dinucleotides. Using chromatin immunoprecipitation (ChIP), we analyzed the interaction of GADD45a- 4-CpG region with MeCP2, the archetypical MBD protein. Cell specific interaction of MeCP2 was observed: MeCP2 was associated with the methylated four CpGs in Du145 whereas no binding was detected in LNCaP cells. Stable transfection of MeCP2 siRNA vector in Du145 (Du145-MeCP2-ve) resulted in down regulation of MeCP2, release of MeCP2 from GADD45a promoter and upregulation of GADD45a expression suggesting a role of MeCP2 in mediating transcriptional repression in Du145 cells. Since GADD45a has been implicated in cell cycle arrest and apoptosis, we hypothesized that induction of GADD45a expression in Du145 cells would lead to increased sensitivity to chemotherapeutic drugs. Consistent with this hypothesis, we observed thatDocetaxel treatment resulted in an increased cytotoxicity in MeCP2-ve Du145 cells that exhibit enhanced GADD45a expression as compared to the wt Du145 cells,Induction of GADD45a expression by prior treatment with DNMT inhibitor, 5-Azacytidine resulted in an enhanced cytotoxicity in wt Du145 cells andwt Du145 cells that were transfected with GADD45a expression vector exhibited an enhanced cyotoxicity to Docetaxel as compared to the mock-transfected cells.In conclusion, we show that methylation of CpG dinucleotides away from the transcriptional start site but not in the proximal promoter region correlates inversely with GADD45a expression in prostate cancer cells, cell-specific interaction of MeCP2 to the methylated GADD45a promoter, and a potential role of DNA methyltransferase inhibitors in enhancing sensitivity to cytotoxic agents through upregulation of GADD45a in prostate cancer cells.