scholarly journals DIPG-14. TARGETING POLO-LIKE KINASE 1 IN COMBINATION WITH KEY ONCOGENIC DRIVERS IN DIPG: FROM SINGLE AGENT TO COMBINATION STRATEGIES

2020 ◽  
Vol 22 (Supplement_3) ◽  
pp. iii289-iii289
Author(s):  
Laura Franshaw ◽  
Elisha Hayden ◽  
Swapna Joshi ◽  
Jie Liu ◽  
Anahid Ehteda ◽  
...  
Keyword(s):  
Gene Expression ◽  
Cell Cycle ◽  
Cell Growth ◽  
Single Agent ◽  
Treatment Strategies ◽  
Therapeutic Effects ◽  
Loss Of Function ◽  
Microtubule Organization

Abstract Diffuse Intrinsic Pontine Glioma (DIPG) are devastating paediatric brainstem tumours. Loss of function mutations in DIPG decrease genetic stability and impair DNA damage response pathways promoting tumourigenesis. Polo-like Kinase 1 (PLK1) is a pivotal controller of cell growth, regulating key intermediaries of DNA replication, homologous repair, the cell cycle and cell division. We have found DIPG cultures consistently overexpress PLK1 with inhibition resulting in decreased tumour cell growth, heightened cell cycle arrest and apoptosis. Single agent treatment using PLK1 inhibitors unprecedentedly doubled the median survival of animals harbouring DIPG tumours. Through gene expression analysis, we’ve showed PLK1 inhibition affected multiple pathways which control the cell cycle, cell death regulation, microtubule organization and regulation of cell migration. We found these pathways of differentially expressed genes were significantly enriched for known targets of both E2F1 and E2F4. Analysis of gene expression and proteomic studies also revealed PLK1 inhibition decreased the activation and expression of key tumour promoting mediators within multiple phases of the cell cycle, decreased expression of tumour promoters including MYC and the PI3K/mTOR pathway and reactivated tumour suppressors p53 and PTEN. Assessing these changes in the treated transcriptome and proteome, we aim to develop multiple potentially translatable combination treatment strategies for DIPG. We have performed mechanistic studies and identified synergism with PLK1 inhibitors and the epigenetic regulator panobinostat, bet/bromodomain inhibitor JQ1, dual PI3K/mTOR inhibitor bimiralisib and PI3K inhibitor BKM120. Finally, we found PLK1 inhibitors act as potent radiosensitizers, enhancing the therapeutic effects of radiotherapy in vitro and in vivo.

scholarly journals Identification of Wee1 as Target in Combination with Avapritinib for the Treatment of Gastrointestinal Stromal Tumor

2020 ◽  
Author(s):  
Shuai Ye ◽  
Dinara Sharipova ◽  
Marya Kozinova ◽  
Lilli Klug ◽  
Jimson D’Souza ◽  
...  
Keyword(s):  
Tyrosine Kinase ◽  
Gastrointestinal Stromal Tumor ◽  
Single Agent ◽  
Treatment Strategies ◽  
Clinical Problem ◽  
Stromal Tumor ◽  
Loss Of Function ◽  
Rtk Inhibitors

AbstractManagement of gastrointestinal stromal tumor (GIST) has been revolutionized by the identification of activating mutations in KIT and PDGFRA, and the clinical application of receptor tyrosine kinase (RTK) inhibitors in the advanced disease setting. Stratification of GIST into molecularly defined subsets provides insight into clinical behavior and response to approved targeted therapies. Although these RTK inhibitors are effective in the majority of GIST, resistance to these agents remains a significant clinical problem. Development of effective treatment strategies for refractory GIST subtypes requires identification of novel targets to provide additional therapeutic options. Global kinome profiling has the potential to identify critical signaling networks and reveal protein kinases that are essential in GIST. Using Multiplexed Inhibitor Beads and Mass Spectrometry, we explored the majority of the kinome in GIST specimens from the three most common molecular subtypes to identify novel kinase targets. Kinome profiling revealed distinct signatures in GIST subtypes and identified kinases that are universally activated in all GIST, as well as kinases that are unique to each subtype. Kinome profiling in combination with loss-of-function assays identified a significant role for the G2-M tyrosine kinase, Wee1, in GIST cell survival. In vitro and in vivo studies revealed significant efficacy of MK-1775 (Wee1 inhibitor) in combination with avapritinib in KIT and PDGFRA-mutant GIST cell lines, and notable efficacy of MK-1775 as a single agent in the PDGFRA-mutant line. These studies provide strong preclinical justification for the use of MK-1775 in GIST.

scholarly journals TAM Inhibitor ONO-7475 Combination with Sorafenib Is Effective Using in Vitro and In Vivo Models of FLT3 ITD Acute Myeloid Leukemia

Blood ◽  
2018 ◽  
Vol 132 (Supplement 1) ◽  
pp. 2642-2642
Author(s):  
Peter P. Ruvolo ◽  
Huaxian Ma ◽  
Vivian Ruvolo ◽  
Xiaorui Zhang ◽  
Hong Mu ◽  
...  
Keyword(s):  
Gene Expression ◽  
Cell Cycle ◽  
Myeloid Leukemia ◽  
Research Funding ◽  
Single Agent ◽  
Xenograft Model ◽  
Cell Cycle Regulators ◽  
Flt3 Inhibitor

Abstract Background: Internal tandem duplication (ITD) mutation in Fems-like kinase 3 (FLT3) occur in ~ 25% of newly diagnosed acute myeloid leukemia (AML) patients and are associated with poor survival outcome. We recently demonstrated that highly specific AXL/MER inhibitor ONO-7475 (Ono Pharmaceutical Co, Osaka, Japan) was effective as a single agent against FLT3 ITD AML cells studied with in vitro co-culture and murine xenograft models (Ruvolo et al Haematologica, 2017). Based on expression of TAM kinases in the AML cells tested, mechanism for ONO-7475 killing in the FLT3 ITD AML cells was due to AXL inhibition. Here we report on the in vitro and in vivo effects of ONO-7475 when combined with FLT3 inhibitor Sorafenib in FLT3 ITD AML models. Methods: FLT3 ITD AML cell lines Molm13 and MV4;11 as well as Sorafenib resistant Molm13 cells were treated with varying doses of ONO-7475 in the presence and absence of FLT3 inhibitor Sorafenib and effect on cell viability and induction of apoptosis was assessed by flow cytometry using DAPI, Annexin V, and counting beads. RNA was isolated and gene expression profiling (GEP) analysis using microarray was performed on ONO-7475 treated cells. GEP results for a number of genes including CDK1, PLK1, and other cell cycle regulators were validated by qRT-PCR. The efficacy of ONO-7475 combination with Sorafenib in an in vivo AML xenograft model was tested using Molm13 cells expressing luciferase/GFP in NSG mice. Both drugs were given by oral gavage (ONO-7475 at 10 mg/kg and Sorafenib at 5 mg/kg). Drugs were given 5 days a week. Leukemia burden was assessed by IVIS imaging. Results: Molm13 and MV4;11 cells were highly sensitive to ONO-7475 combination with Sorafenib. A dose of 50 nM ONO-7475 with 25 nM Sorafenib potently induces apoptosis and eliminates > 90% of cells after 72 hours. Sorafenib resistant Molm13 cells were more resistant to either drug compared to parental cells. However, combination of 50 nM ONO-7475 with 100 nM Sorafenib potently induces apoptosis in the Sorafenib resistant cells with nearly all leukemic cells eliminated after 72 hour treatment. GEP analysis of cells treated with the AXL inhibitor revealed suppression of many genes involved in cell cycle control including various CDKs (e.g. CDK1, CDK4), Cyclins (e.g Cyclin B1), and other cell cycle regulators such as PLK1. ONO-7475 inhibition of gene expression of these genes was verified by qRT-PCR. GEP also revealed induction of genes associated with more mature myeloid cells including HLA-DR, CD114, and CD115. Finally, single agent use of ONO-7475 (10 mg/kg) or Sorafenib (5 mg/kg) had limited effect in the FLT3 ITD AML xenograft model; however, the combination of both drugs at single agent dose was effective reducing leukemia burden and significantly enhancing survival of mice bearing the Molm13 leukemia cells. Conclusions: These results suggest that ONO-7475 combination with Sorafenib is effective killing AML cells with FLT3 ITD including those that are resistant to the FLT3 inhibitor. The identification of gene expression of cell cycle regulators as novel targets of the drug suggests for the first time that AXL regulates cell cycle via a complex transcriptional mechanism. The ability of the drug to induce expression of genes associated with mature myeloid cells suggest the drug may have the potential to promote differentiation of FLT3 AML cells. Finally, combination of ONO-7475 with Sorafenib proved effective in an in vivo AML xenograft model suggesting that combination of ONO-7475 with a FLT3 inhibitor could be efficacious for therapy of AML patients with FLT3 ITD. Disclosures Yasuhiro: Ono Pharmaceutical: Employment. Tanaka:Ono Pharmaceutical: Employment. Yoshizawa:Ono Pharmaceutical: Employment. Cortes:Pfizer: Consultancy, Research Funding; Astellas Pharma: Consultancy, Research Funding; Novartis: Consultancy, Research Funding; Daiichi Sankyo: Consultancy, Research Funding; Arog: Research Funding. Andreeff:AstraZeneca: Research Funding.

scholarly journals β-elemene alleviates airway stenosis via the ILK/Akt pathway modulated by MIR143HG sponging miR-1275

2021 ◽  
Vol 26 (1) ◽  
Author(s):  
Guoying Zhang ◽  
Cheng Xue ◽  
Yiming Zeng
Keyword(s):  
Cell Cycle ◽  
Cell Viability ◽  
Cell Model ◽  
Protective Efficacy ◽  
Rabbit Model ◽  
Akt Pathway ◽  
Loss Of Function ◽  
Airway Stenosis

Abstract Background We have previously found that β-elemene could inhibit the viability of airway granulation fibroblasts and prevent airway hyperplastic stenosis. This study aimed to elucidate the underlying mechanism and protective efficacy of β-elemene in vitro and in vivo. Methods Microarray and bioinformatic analysis were used to identify altered pathways related to cell viability in a β-elemene-treated primary cell model and to construct a β-elemene-altered ceRNA network modulating the target pathway. Loss of function and gain of function approaches were performed to examine the role of the ceRNA axis in β-elemene's regulation of the target pathway and cell viability. Additionally, in a β-elemene-treated rabbit model of airway stenosis, endoscopic and histological examinations were used to evaluate its therapeutic efficacy and further verify its mechanism of action. Results The hyperactive ILK/Akt pathway and dysregulated LncRNA-MIR143HG, which acted as a miR-1275 ceRNA to modulate ILK expression, were suppressed in β-elemene-treated airway granulation fibroblasts; β-elemene suppressed the ILK/Akt pathway via the MIR143HG/miR-1275/ILK axis. Additionally, the cell cycle and apoptotic phenotypes of granulation fibroblasts were altered, consistent with ILK/Akt pathway activity. In vivo application of β-elemene attenuated airway granulation hyperplasia and alleviated scar stricture, and histological detections suggested that β-elemene's effects on the MIR143HG/miR-1275/ILK axis and ILK/Akt pathway were in line with in vitro findings. Conclusions MIR143HG and ILK may act as ceRNA to sponge miR-1275. The MIR143HG/miR-1275/ILK axis mediates β-elemene-induced cell cycle arrest and apoptosis of airway granulation fibroblasts by modulating the ILK/Akt pathway, thereby inhibiting airway granulation proliferation and ultimately alleviating airway stenosis.

scholarly journals Long noncoding RNA LINC00941 promotes pancreatic cancer progression by competitively binding miR-335-5p to regulate ROCK1-mediated LIMK1/Cofilin-1 signaling

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Jie Wang ◽  
Zhiwei He ◽  
Jian Xu ◽  
Peng Chen ◽  
Jianxin Jiang
Keyword(s):  
Pancreatic Cancer ◽  
Cell Growth ◽  
Cell Lines ◽  
Cancer Progression ◽  
Noncoding Rna ◽  
Epithelial Mesenchymal Transition ◽  
Loss Of Function ◽  
Mesenchymal Transition

AbstractAn accumulation of evidence indicates that long noncoding RNAs are involved in the tumorigenesis and progression of pancreatic cancer (PC). In this study, we investigated the functions and molecular mechanism of action of LINC00941 in PC. Quantitative PCR was used to examine the expression of LINC00941 and miR-335-5p in PC tissues and cell lines, and to investigate the correlation between LINC00941 expression and clinicopathological features. Plasmid vectors or lentiviruses were used to manipulate the expression of LINC00941, miR-335-5p, and ROCK1 in PC cell lines. Gain or loss-of-function assays and mechanistic assays were employed to verify the roles of LINC00941, miR-335-5p, and ROCK1 in PC cell growth and metastasis, both in vivo and in vitro. LINC00941 and ROCK1 were found to be highly expressed in PC, while miR-335-5p exhibited low expression. High LINC00941 expression was strongly associated with larger tumor size, lymph node metastasis, and poor prognosis. Functional experiments revealed that LINC00941 silencing significantly suppressed PC cell growth, metastasis and epithelial–mesenchymal transition. LINC00941 functioned as a molecular sponge for miR-335-5p, and a competitive endogenous RNA (ceRNA) for ROCK1, promoting ROCK1 upregulation, and LIMK1/Cofilin-1 pathway activation. Our observations lead us to conclude that LINC00941 functions as an oncogene in PC progression, behaving as a ceRNA for miR-335-5p binding. LINC00941 may therefore have potential utility as a diagnostic and treatment target in this disease.

scholarly journals Propofol attenuates lung ischemia/reperfusion injury though the involvement of the MALAT1/microRNA-144/GSK3β axis

2021 ◽  
Vol 27 (1) ◽  
Author(s):  
Jian-Ping Zhang ◽  
Wei-Jing Zhang ◽  
Miao Yang ◽  
Hua Fang
Keyword(s):  
Cell Apoptosis ◽  
Ischemia Reperfusion Injury ◽  
Glycogen Synthase ◽  
Ischemia Reperfusion ◽  
Inflammatory Factors ◽  
Therapeutic Effects ◽  
Protective Effects ◽  
Loss Of Function

Abstract Background Propofol, an intravenous anesthetic, was proven to protect against lung ischemia/reperfusion (I/R) injury. However, the detailed mechanism of Propofol in lung I/R injury is still elusive. This study was designed to explore the therapeutic effects of Propofol, both in vivo and in vitro, on lung I/R injury and the underlying mechanisms related to metastasis-associated lung adenocarcinoma transcript 1 (MALAT1)/microRNA-144 (miR-144)/glycogen synthase kinase-3β (GSK3β). Methods C57BL/6 mice were used to establish a lung I/R injury model while pulmonary microvascular endothelial cells (PMVECs) were constructed as hypoxia/reperfusion (H/R) cellular model, both of which were performed with Propofol treatment. Gain- or loss-of-function approaches were subsequently employed, followed by observation of cell apoptosis in lung tissues and evaluation of proliferative and apoptotic capabilities in H/R cells. Meanwhile, the inflammatory factors, autophagosomes, and autophagy-related proteins were measured. Results Our experimental data revealed that Propofol treatment could decrease the elevated expression of MALAT1 following I/R injury or H/R induction, indicating its protection against lung I/R injury. Additionally, overexpressing MALAT1 or GSK3β promoted the activation of autophagosomes, proinflammatory factor release, and cell apoptosis, suggesting that overexpressing MALAT1 or GSK3β may reverse the protective effects of Propofol against lung I/R injury. MALAT1 was identified to negatively regulate miR-144 to upregulate the GSK3β expression. Conclusion Overall, our study demonstrated that Propofol played a protective role in lung I/R injury by suppressing autophagy and decreasing release of inflammatory factors, with the possible involvement of the MALAT1/miR-144/GSK3β axis.

scholarly journals p53 upregulated by HIF-1α promotes hypoxia-induced G2/M arrest and renal fibrosis in vitro and in vivo

2018 ◽  
Vol 11 (5) ◽  
pp. 371-382 ◽  
Author(s):  
Limin Liu ◽  
Peng Zhang ◽  
Ming Bai ◽  
Lijie He ◽  
Lei Zhang ◽  
...  
Keyword(s):  
Cell Cycle ◽  
Transcriptional Activation ◽  
Renal Fibrosis ◽  
Intraperitoneal Administration ◽  
Luciferase Reporter ◽  
Loss Of Function ◽  
P53 Expression ◽  
Tubular Cells

Abstract Hypoxia plays an important role in the genesis and progression of renal fibrosis. The underlying mechanisms, however, have not been sufficiently elucidated. We examined the role of p53 in hypoxia-induced renal fibrosis in cell culture (human and rat renal tubular epithelial cells) and a mouse unilateral ureteral obstruction (UUO) model. Cell cycle of tubular cells was determined by flow cytometry, and the expression of profibrogenic factors was determined by RT-PCR, immunohistochemistry, and western blotting. Chromatin immunoprecipitation and luciferase reporter experiments were performed to explore the effect of HIF-1α on p53 expression. We showed that, in hypoxic tubular cells, p53 upregulation suppressed the expression of CDK1 and cyclins B1 and D1, leading to cell cycle (G2/M) arrest (or delay) and higher expression of TGF-β, CTGF, collagens, and fibronectin. p53 suppression by siRNA or by a specific p53 inhibitor (PIF-α) triggered opposite effects preventing the G2/M arrest and profibrotic changes. In vivo experiments in the UUO model revealed similar antifibrotic results following intraperitoneal administration of PIF-α (2.2 mg/kg). Using gain-of-function, loss-of-function, and luciferase assays, we further identified an HRE3 region on the p53 promoter as the HIF-1α-binding site. The HIF-1α–HRE3 binding resulted in a sharp transcriptional activation of p53. Collectively, we show the presence of a hypoxia-activated, p53-responsive profibrogenic pathway in the kidney. During hypoxia, p53 upregulation induced by HIF-1α suppresses cell cycle progression, leading to the accumulation of G2/M cells, and activates profibrotic TGF-β and CTGF-mediated signaling pathways, causing extracellular matrix production and renal fibrosis.

scholarly journals BET bromodomain inhibitor birabresib in mantle cell lymphoma: in vivo activity and identification of novel combinations to overcome adaptive resistance

ESMO Open ◽  
2018 ◽  
Vol 3 (6) ◽  
pp. e000387 ◽  
Author(s):  
Chiara Tarantelli ◽  
Elena Bernasconi ◽  
Eugenio Gaudio ◽  
Luciano Cascione ◽  
Valentina Restelli ◽  
...  
Keyword(s):  
Mantle Cell Lymphoma ◽  
Cell Lines ◽  
Cell Lymphoma ◽  
Antitumour Activity ◽  
Single Agent ◽  
Treatment Strategies ◽  
Bet Inhibitor ◽  
Mantle Cell

BackgroundThe outcome of patients affected by mantle cell lymphoma (MCL) has improved in recent years, but there is still a need for novel treatment strategies for these patients. Human cancers, including MCL, present recurrent alterations in genes that encode transcription machinery proteins and of proteins involved in regulating chromatin structure, providing the rationale to pharmacologically target epigenetic proteins. The Bromodomain and Extra Terminal domain (BET) family proteins act as transcriptional regulators of key signalling pathways including those sustaining cell viability. Birabresib (MK-8628/OTX015) has shown antitumour activity in different preclinical models and has been the first BET inhibitor to successfully undergo early clinical trials.Materials and methodsThe activity of birabresib as a single agent and in combination, as well as its mechanism of action was studied in MCL cell lines.ResultsBirabresib showed in vitro and in vivo activities, which appeared mediated via downregulation of MYC targets, cell cycle and NFKB pathway genes and were independent of direct downregulation of CCND1. Additionally, the combination of birabresib with other targeted agents (especially pomalidomide, or inhibitors of BTK, mTOR and ATR) was beneficial in MCL cell lines.ConclusionOur data provide the rationale to evaluate birabresib in patients affected by MCL.

Upregulation of SGOL2 Predicts Poor Prognosis and Facilitates Hepatocellular Carcinoma Progression via Dysregulating the Cell Cycle by Directly Activating MAD2

2021 ◽  
Author(s):  
Qingqing Hu ◽  
Xiaochu Hu ◽  
Yalei Zhao ◽  
Lingjian Zhang ◽  
Ya Yang ◽  
...  
Keyword(s):  
Hepatocellular Carcinoma ◽  
Cell Cycle ◽  
The Cancer Genome Atlas ◽  
Loss Of Function ◽  
Protein Levels ◽  
Cancer Genome Atlas ◽  
Centromeric Protein ◽  
Hcc Cells

Abstract Background: Hepatocellular carcinoma (HCC) is the third leading cause of cancer-related death worldwide. Shugoshin-like protein 2 (SGOL2) is a centromeric protein that ensures the correct and orderly process of mitosis by protecting and maintaining centripetal adhesions during meiosis and mitosis. However, the role of SGOL2 in cancer is not well understood. Methods: The mRNA and protein levels of SGOL2 and survival analysis were conducted in The Cancer Genome Atlas (TCGA) and further validated in 2 independent cohorts. Differential genes correlated with SGOL2 and mitotic arrest deficient 2 like 1 (MAD2) were obtained using LinkedOmics. Subsequently, loss-of-function and rescue assays were carried out in vitro and in vivo to assess the functions of SGOL2 in hepatic tumorigenisis. Findings: We found that SGOL2 was significantly overexpressed in HCC and predicted unfavorable overall survival in HCC patients. Next, we identified 47 differentially expressed genes positively correlated with both SGOL2 and MAD2 to be mainly involved in the cell cycle. In addition, SGOL2 downregulation suppressed the migration, invasion, proliferation, stemness and EMT of HCC cells and inhibited tumorigenesis in vivo. Furthermore, SGOL2 promoted tumor proliferation by activating MAD2-induced cell cycle dysregulation, which could be reversed by the MAD2 inhibitor M2I-1. We also proved that SGOL2 activated MAD2 by directly binding with MAD2. Conclusions: The results of this study showed that SGOL2 acts as an oncogene in HCC cells by directly activating MAD2 and then dysregulating the cell cycle, thereby providing a potential target for HCC patients in the future.

Effect and mechanism of YB-1 knockdown on glioma cell growth, migration, and apoptosis

2020 ◽  
Vol 52 (2) ◽  
pp. 168-179 ◽  
Author(s):  
Huilin Gong ◽  
Shan Gao ◽  
Chenghuan Yu ◽  
Meihe Li ◽  
Ping Liu ◽  
...  
Keyword(s):  
Cell Cycle ◽  
Cell Proliferation ◽  
Cell Growth ◽  
Glioma Cell ◽  
Cell Transformation ◽  
Malignant Cell ◽  
Protein Levels ◽  
Glioma Progression

Abstract Y-box binding protein 1 (YB-1) is manifested as its involvement in cell proliferation and differentiation and malignant cell transformation. Overexpression of YB-1 is associated with glioma progression and patient survival. The aim of this study is to investigate the influence of YB-1 knockdown on glioma cell progression and reveal the mechanisms of YB-1 knockdown on glioma cell growth, migration, and apoptosis. It was found that the knockdown of YB-1 decreased the mRNA and protein levels of YB-1 in U251 glioma cells. The knockdown of YB-1 significantly inhibited cell proliferation, colony formation, and migration in vitro and tumor growth in vivo. Proteome and phosphoproteome data revealed that YB-1 is involved in glioma progression through regulating the expression and phosphorylation of major proteins involved in cell cycle, adhesion, and apoptosis. The main regulated proteins included CCNB1, CCNDBP1, CDK2, CDK3, ADGRG1, CDH-2, MMP14, AIFM1, HO-1, and BAX. Furthermore, it was also found that YB-1 knockdown is associated with the hypo-phosphorylation of ErbB, mTOR, HIF-1, cGMP-PKG, and insulin signaling pathways, and proteoglycans in cancer. Our findings indicated that YB-1 plays a key role in glioma progression in multiple ways, including regulating the expression and phosphorylation of major proteins associated with cell cycle, adhesion, and apoptosis.

scholarly journals Growth Suppression by Acute PromyelocyticLeukemia-Associated Protein PLZF Is Mediated by Repression ofc-mycExpression

2003 ◽  
Vol 23 (24) ◽  
pp. 9375-9388 ◽  
Author(s):  
Melanie J. McConnell ◽  
Nathalie Chevallier ◽  
Windy Berkofsky-Fessler ◽  
Jena M. Giltnane ◽  
Rupal B. Malani ◽  
...  
Keyword(s):  
Cell Cycle ◽  
Cell Growth ◽  
Cell Cycle Arrest ◽  
Target Genes ◽  
Ectopic Expression ◽  
Growth Suppression ◽  
Quiescent State ◽  
Cycle Arrest

ABSTRACT The transcriptional repressor PLZF was identified by its translocation with retinoic acid receptor alpha in t(11;17) acute promyelocytic leukemia (APL). Ectopic expression of PLZF leads to cell cycle arrest and growth suppression, while disruption of normal PLZF function is implicated in the development of APL. To clarify the function of PLZF in cell growth and survival, we used an inducible PLZF cell line in a microarray analysis to identify the target genes repressed by PLZF. One prominent gene identified was c-myc. The array analysis demonstrated that repression of c-myc by PLZF led to a reduction in c-myc-activated transcripts and an increase in c-myc-repressed transcripts. Regulation of c-myc by PLZF was shown to be both direct and reversible. An interaction between PLZF and the c-myc promoter could be detected both in vitro and in vivo. PLZF repressed the wild-type c-myc promoter in a reporter assay, dependent on the integrity of the binding site identified in vitro. PLZF binding in vivo was coincident with a decrease in RNA polymerase occupation of the c-myc promoter, indicating that repression occurred via a reduction in the initiation of transcription. Finally, expression of c-myc reversed the cell cycle arrest induced by PLZF. These data suggest that PLZF expression maintains a cell in a quiescent state by repressing c-myc expression and preventing cell cycle progression. Loss of this repression through the translocation that occurs in t(11;17) would have serious consequences for cell growth control.

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