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Supplementary figure legends.

Supplementary Figure 1: Metastatic inhibtion by Jagged2 depletion in BxPC-3 using another shRNA.

Supplementary Figure 3: Jagged1 knockdown had no effect on MIA PaCa-2 cells migration.

Supplementary Figure 4: Gamma-secretase inhibition did not impair MIA PaCa-2 cell migration.

Supplementary Figure 2: Jagged2-depleted MIA PaCa-2 cells exhibited metastatic defects.

Supplementary Figure 5: Jagged1 and Jagged2-Fc are capable of inducing Notch signaling pathway.

Supplementary Tables 1 and 2: Primer sequences used in the study.

Purpose: Notch1 deregulation is assuming a focal role in T-cell acute lymphoblastic leukemia (T-ALL). Despite tremendous advances in our understanding of Notch1 transcriptional programs, the mechanisms by which Notch1 stability and turnover are regulated remain obscure. The goal of the current study is to identify intracellular Notch1 (ICN1, the activated form of Notch1) binding partner(s) regulating its stability and activity.Experimental Design: We employed immunoaffinity purification to identify ICN1-associating partner(s) and used coimmunoprecipitation to verify the endogenous protein interaction. Pharmacologic or short hairpin RNA–mediated inhibition was applied in loss-of-function assays to assess the role of tentative binding partner(s) in modulating ICN1 protein stability as well as affecting T-ALL cell expansion in vitro and in vivo. Mechanistic analysis involved protein degradation and polyubiquitination assays.Results: We identify the Hsp90 chaperone as a direct ICN1-binding partner essential for its stabilization and transcriptional activity. T-ALL cells exhibit constitutive endogenous ICN1–Hsp90 interaction and Hsp90 depletion markedly decreases ICN1 levels. The Hsp90-associated E3 ubiquitin ligase Stub1 mediates the ensuring proteasome-dependent ICN1 degradation. Administration of 17-AAG or PU-H71, two distinct Hsp90 inhibitors, depletes ICN1, inhibits T-ALL cell proliferation, and triggers dramatic apoptotic cell death. Systemic treatment with PU-H71 reduces ICN1 expression and profoundly inhibits murine T-ALL allografts as well as human T-ALL xenografts.Conclusions: Our findings demonstrate Hsp90 blockade leads to ICN1 destabilization, providing an alternative strategy to antagonize oncogenic Notch1 signaling with Hsp90-selective inhibitors. Clin Cancer Res; 23(14); 3834–46. ©2017 AACR.

MYCN amplification in neuroblastoma leads to aberrant expression of MYCN oncoprotein, which binds active genes promoting transcriptional amplification. Yet, how MYCN coordinates transcription elongation to meet productive transcriptional amplification and which elongation machinery represents MYCN-driven vulnerability remain to be identified. We conducted a targeted screen of transcription elongation factors and identified the super elongation complex (SEC) as a unique vulnerability in MYCN -amplified neuroblastomas. MYCN directly binds EAF1 and recruits SEC to enhance processive transcription elongation. Depletion of EAF1 or AFF1/AFF4, another core subunit of SEC, leads to a global reduction in transcription elongation and elicits selective apoptosis of MYCN -amplified neuroblastoma cells. A combination screen reveals SEC inhibition synergistically potentiates the therapeutic efficacies of FDA-approved BCL-2 antagonist ABT-199, in part due to suppression of MCL1 expression, both in MYCN -amplified neuroblastoma cells and in patient-derived xenografts. These findings identify disruption of the MYCN-SEC regulatory axis as a promising therapeutic strategy in neuroblastoma.

Supplementary tables, figures and materials

T-cell acute lymphoblastic leukemia (T-ALL) is an aggressive hematological cancer that frequently occurs in children and adolescents, which results from the transformation of immature T-cell progenitors. Aberrant cell growth and proliferation of T-ALL lymphoblasts are sustained by activation of strong oncogenic drivers. Mounting evidence highlights the critical role of the NOTCH1-MYC highway toward the initiation and progression of T-ALL. MYC has been emphasized as a primary NOTCH1 transcriptional target impinging in leukemia-initiating cell activity particularly responsible for disease onset and relapse. These findings lay a foundation of T-ALL as an ideal disease model for studying MYC-mediated cancer. The biology of MYC deregulation in T-ALL supports innovative strategies for therapeutic targeting of MYC. To summarize the relevant literature and data in recent years, we here provide a comprehensive overview of the functional importance of MYC in T-ALL development, and the molecular mechanisms underlying MYC deregulation in T-ALL. Finally, we illustrate the innovative MYC-targeted approaches that have been evaluated in pre-clinical models and shown significant efficacy. Given the complexity of T-ALL molecular pathogenesis, we propose that a combination of anti-MYC strategies with conventional chemotherapies or other targeted/immunotherapies may provide the most durable response, especially for those patients with relapsed and refractory T-ALL.

Despite the development of metabolism-based therapy for a variety of malignancies, resistance to single-agent treatment is common due to the metabolic plasticity of cancer cells. Improved understanding of how malignant cells rewire metabolic pathways can guide the rational selection of combination therapy to circumvent drug resistance. Here, we show that human T-ALL cells shift their metabolism from oxidative decarboxylation to reductive carboxylation when the TCA cycle is disrupted. The α-ketoglutarate dehydrogenase complex (KGDHC) in the TCA cycle regulates oxidative decarboxylation by converting α-ketoglutarate (α-KG) to succinyl-CoA, while isocitrate dehydrogenase (IDH) 1 and 2 govern reductive carboxylation. Metabolomics flux analysis of T-ALL reveals enhanced reductive carboxylation upon genetic depletion of the E2 subunit of KGDHC, dihydrolipoamide-succinyl transferase (DLST), mimicking pharmacological inhibition of the complex. Mechanistically, KGDHC dysfunction causes increased demethylation of nuclear DNA by α-KG-dependent dioxygenases (e.g., TET demethylases), leading to increased production of both IDH1 and 2. Consequently, dual pharmacologic inhibition of the TCA cycle and TET demethylases demonstrates additive efficacy in reducing the tumor burden in zebrafish xenografts. These findings provide mechanistic insights into how T-ALL develops resistance to drugs targeting the TCA cycle and therapeutic strategies to overcome this resistance.

Deregulation of v-myc avian myelocytomatosis viral oncogene homolog (MYC) occurs in a broad range of human cancers and often predicts poor prognosis and resistance to therapy. However, directly targeting oncogenic MYC remains unsuccessful, and indirectly inhibiting MYC emerges as a promising approach. Checkpoint kinase 1 (CHK1) is a protein kinase that coordinates the G2/M cell cycle checkpoint and protects cancer cells from excessive replicative stress. Using c-MYC-mediated T-cell acute lymphoblastic leukemia (T-acute lymphoblastic leukemia) and N-MYC-driven neuroblastoma as model systems, we reveal that both c-MYC and N-MYC directly bind to the CHK1 locus and activate its transcription. CHIR-124, a selective CHK1 inhibitor, impairs cell viability and induces remarkable synergistic lethality with mTOR inhibitor rapamycin in MYC-overexpressing cells. Mechanistically, rapamycin inactivates carbamoyl-phosphate synthetase 2, aspartate transcarbamoylase, and dihydroorotase (CAD), the essential enzyme for the first three steps of de novo pyrimidine synthesis, and deteriorates CHIR-124-induced replicative stress. We further demonstrate that dual treatments impede T-acute lymphoblastic leukemia and neuroblastoma progression in vivo. These results suggest simultaneous targeting of CHK1 and mTOR as a novel and powerful co-treatment modality for MYC-mediated tumors.

Efforts to therapeutically target EZH2 have generally focused on inhibition of its methyltransferase activity, although it remains less clear whether this is the central mechanism whereby EZH2 promotes cancer. In the current study, we show that EZH2 directly interacts with both MYC family oncoproteins, MYC and MYCN, and promotes their stabilization in a methyltransferase-independent manner. By competing against the SCFFBW7 ubiquitin ligase to bind MYC and MYCN, EZH2 counteracts FBW7-mediated MYC(N) polyubiquitination and proteasomal degradation. Depletion, but not enzymatic inhibition, of EZH2 induces robust MYC(N) degradation and inhibits tumor cell growth in MYC(N) driven neuroblastoma and small cell lung carcinoma. Here, we demonstrate the MYC family proteins as global EZH2 oncogenic effectors and EZH2 pharmacologic degraders as potential MYC(N) targeted cancer therapeutics, pointing out that MYC(N) driven cancers may develop inherent resistance to the canonical EZH2 enzymatic inhibitors currently in clinical development., While inhibition of the EZH2 methyltransferase activity has been used for targeting EZH2, its role in cancer progression remains unclear. Here, the authors use neuroblastoma and small cell lung carcinoma model systems and reveal the crosstalk between EZH2 and MYC(N) in the regulation of tumour formation.

The MYC family oncoproteins are deregulated in more than 50 % of human cancers through a variety of mechanisms, such as gene amplification or translocation, super-enhancer activation, aberrant upstream signaling, and altered protein stability. As one of the major drivers in tumorigenesis, MYC regulates the expression of a large number of noncoding genes involved in multiple oncogenic processes. Noncoding RNAs, including miRNA, lncRNA, circRNA, rRNA and tRNA, are also deeply involved in the oncogenic MYC network by functioning as MYC regulators/effectors. In this review, we summarize representative studies depicting the crosstalk between oncogenic MYC and noncoding RNAs in carcinogenesis with the aim of providing potential implications for both basic science and clinical applications.

Cancer cells must rewire cellular metabolism to satisfy the demands of unbridled growth and proliferation. As such, most human cancers differ from normal counterpart tissues by a plethora of energetic and metabolic reprogramming. Transcription factors of the MYC family are deregulated in up to 70% of all human cancers through a variety of mechanisms. Oncogenic levels of MYC regulates almost every aspect of cellular metabolism, a recently revisited hallmark of cancer development. Meanwhile, unrestrained growth in response to oncogenic MYC expression creates dependency on MYC-driven metabolic pathways, which in principle provides novel targets for development of effective cancer therapeutics. In the current review, we summarize the significant progress made toward understanding how MYC deregulation fuels metabolic rewiring in malignant transformation.

T-cell acute lymphoblastic leukemia (T-ALL) is a heterogeneous group of hematological tumors composed of distinct subtypes that vary in their genetic abnormalities. In the past decade, large-scale genomic analysis has shed new light on providing potentially important oncogenic or tumor suppressive candidates involved in the disease progression. Following in silico analysis, functional studies are usually performed to vigorously investigate the biological roles of candidate genes. For this purpose, animal models faithfully recapitulating the human disease are widely applied to decipher the mechanism underlying T-cell transformation. Conversely, an increased understanding of T-ALL biology, including identification of oncogene NOTCH1, TAL1 and MYC as well as tumor suppressor phosphatase and tensin homolog (PTEN), has significantly improved the development of T-ALL animal models. These progresses have opened opportunities for development of new therapeutic strategy to benefit T-ALL patients. In this review, we particularly summarize the mouse and zebrafish models used in T-ALL research and also the most recent advances from these in vivo studies. Key words: hematopoietic stem cell transplant; T-cell acute lymphoblastic leukemia; transgenetic mice; transgenic zebrafish; xenograft

The MYC family oncogene is deregulated in >50% of human cancers, and this deregulation is frequently associated with poor prognosis and unfavorable patient survival. Myc has a central role in almost every aspect of the oncogenic process, orchestrating proliferation, apoptosis, differentiation, and metabolism. Although Myc inhibition would be a powerful approach for the treatment of many types of cancers, direct targeting of Myc has been a challenge for decades owing to its “undruggable” protein structure. Hence, alternatives to Myc blockade have been widely explored to achieve desirable anti-tumor effects, including Myc/Max complex disruption, MYC transcription and/or translation inhibition, and Myc destabilization as well as the synthetic lethality associated with Myc overexpression. In this review, we summarize the latest advances in targeting oncogenic Myc, particularly for cancer therapeutic purposes., Cancer: Therapeutic strategies target myc from all directions The cancer gene myc is the subject of a variety of research strategies aimed at developing anti-cancer therapies. Myc, which regulates at least 15% of all genes including those involved in cell development and survival, is mutated and overexpressed in many cancer types. While inhibiting myc is an obvious anti-cancer strategy, directly targeting myc has proved difficult. Dr Guoliang Qing and colleagues from Wuhan University have reviewed advances in myc-targeting strategies as potential cancer therapies. Current strategies include indirectly targeting myc by inhibiting its regulation and stability, and interaction with its partner Max, which is necessary for its regulation of gene expression. Other strategies involve inducing a mutation in a gene that interacts with myc to kill cancer cells. These and future innovative approaches provide promise for effective therapeutics against myc-dependent cancers.

Most tumor cells exhibit obligatory demands for essential amino acids (EAAs), but the regulatory mechanisms whereby tumor cells take up EAAs and EAAs promote malignant transformation remain to be determined. Here, we show that oncogenic MYC, solute carrier family (SLC) 7 member 5 (SLC7A5), and SLC43A1 constitute a feedforward activation loop to promote EAA transport and tumorigenesis. MYC selectively activates Slc7a5 and Slc43a1 transcription through direct binding to specific E box elements within both genes, enabling effective EAA import. Elevated EAAs, in turn, stimulate Myc mRNA translation, in part through attenuation of the GCN2-eIF2α-ATF4 amino acid stress response pathway, leading to MYC-dependent transcriptional amplification. SLC7A5/SLC43A1 depletion inhibits MYC expression, metabolic reprogramming, and tumor cell growth in vitro and in vivo. These findings thus reveal a MYC-SLC7A5/SLC43A1 signaling circuit that underlies EAA metabolism, MYC deregulation, and tumorigenesis.

Aggressive NK-cell leukemia (ANKL) is a rare form of NK cell neoplasm that is more prevalent among people from Asia and Central and South America. Patients usually die within days to months, even after receiving prompt therapeutic management. Here we performed the first comprehensive study of ANKL by integrating whole genome, transcriptome and targeted sequencing, cytokine array as well as functional assays. Mutations in the JAK-STAT pathway were identified in 48% (14/29) of ANKL patients, while the extracellular STAT3 stimulator IL10 was elevated by an average of 56-fold (P < 0.0001) in the plasma of all patients examined. Additional frequently mutated genes included TP53 (34%), TET2 (28%), CREBBP (21%) and MLL2 (21%). Patient NK leukemia cells showed prominent activation of STAT3 phosphorylation, MYC expression and transcriptional activities in multiple metabolic pathways. Functionally, STAT3 activation and MYC expression were critical for the proliferation and survival of ANKL cells. STAT signaling regulated the MYC transcription program, and both STAT signaling and MYC transcription were required to maintain the activation of nucleotide synthesis and glycolysis. Collectively, the JAK-STAT pathway represents a major target for genomic alterations and IL10 stimulation in ANKL. This newly discovered JAK/STAT-MYC-biosynthesis axis may provide opportunities for the development of novel therapeutic strategies in treating this subtype of leukemia.

Summary Deregulation of MYC plays an essential role in T cell acute lymphoblastic leukemia (T-ALL), yet the mechanisms underlying its deregulation remain elusive. Herein, we identify a molecular mechanism responsible for reciprocal activation between Aurora B kinase (AURKB) and MYC. AURKB directly phosphorylates MYC at serine 67, counteracting GSK3β-directed threonine 58 phosphorylation and subsequent FBXW7-mediated proteasomal degradation. Stabilized MYC, in concert with T cell acute lymphoblastic leukemia 1 (TAL1), directly activates AURKB transcription, constituting a positive feedforward loop that reinforces MYC-regulated oncogenic programs. Therefore, inhibitors of AURKB induce prominent MYC degradation concomitant with robust leukemia cell death. These findings reveal an AURKB-MYC regulatory circuit that underlies T cell leukemogenesis, and provide a rationale for therapeutic targeting of oncogenic MYC via AURKB inhibition.

Aberrant activation of Wnt signaling pathway is crucial for the onset and progression of human colorectal cancer (CRC). Owing to the persistent dependence on Wnt signaling for growth and survival, inhibition of this pathway is an attractive approach for new therapies. 11α, 12α-epoxyleukamenin E (EPLE) is a novel ent-kaurane diterpenoid that we previously isolated from Salvia cavaleriei, exhibiting antitumor activities in a variety of cancer cells. Herein, we found that whereas sparing normal human colon mucosal epithelial cells, EPLE selectively inhibited the proliferation of CRC cell lines as well as primary tumor cells. Mechanistically, we demonstrated EPLE exerted its function through suppressing Wnt signaling pathway, as evidenced by EPLE-mediated downregulation of Wnt target genes such as c-Myc, Axin2 and Survivin. Consistently, luciferase reporter assays showed that the EPLE directly blocked Wnt/β-catenin-mediated transcriptional activation. In combination of co-immunoprecipitation and protein structure-based analyses, we determined that the EPLE entered the interface of β-catenin/TCF4 complexes and blocked their interaction that is required for β-catenin-mediated transcriptional activation. Moreover, overexpression of β-catenin alleviated the cytotoxicity of EPLE in CRC cells, supporting Wnt signaling is a major and specific target of EPLE. Combined treatments of EPLE and 5-fluorouracil, the first-line chemotherapy for CRC patients, achieved a synergistic effect. More importantly, EPLE hampered tumor development in a CRC xenograft model. Our data thus establish EPLE as a novel inhibitor of Wnt signaling that holds great promise as a potential candidate for further preclinical evaluation for CRC treatments.

Pancreatic ductal adenocarcinoma (PDAC) is an aggressive and lethal disease with a high rate of metastasis. Numerous signaling events have been implicated in the molecular pathogenesis of this neoplasm. Aberrantly high expression of JAGGED2, one of the NOTCH ligands, often occurs in human PDAC. However, what role JAGGED2 plays in the disease development and whether JAGGED2 executes its function through activating NOTCH signaling remain to be determined. We report here that JAGGED2 plays a critical role in promoting PDAC metastasis in vitro and in vivo. Depletion of JAGGED2, but not its homolog JAGGED1, profoundly inhibited both migration and invasion without influencing cell proliferation. Furthermore, reconstitution of JAGGED2 expression rescued the migratory defect. Surprisingly, neither pharmacologic nor genetic inhibition of NOTCH downstream signaling resulted in obvious defect in metastasis. Instead, depletion of NOTCH1 expression per se gave rise to migratory defects similar to JAGGED2 ablation. Moreover, blockade of ligand–receptor interaction by a specific JAGGED2-Fc fusion protein dramatically inhibited PDAC cell migration, suggesting that tumor metastasis relies on physical interactions of JAGGED2-NOTCH1 but not Notch downstream signaling activation. Taken together, our data reveal a novel role of NOTCH in regulation of PDAC metastasis, and identify JAGGED2 as a critical mediator in this event. These findings also provide rationale for developing small molecules or biologic agents targeting JAGGED2 for therapeutic intervention. Mol Cancer Ther; 14(1); 289–97. ©2014 AACR.

Over-expression of ATP-binding cassette (ABC) transporters, a large family of integral membrane proteins that decrease cellular drug uptake and accumulation by active extrusion, is one of the major causes of cancer multi-drug resistance (MDR) that frequently leads to failure of chemotherapy. Carbon nanotubes (CNTs)-based drug delivery devices hold great promise in enhancing the efficacy of cancer chemotherapy. However, CNTs' effects on the ABC transporters remain under-investigated. In this study, we found that multiwalled carbon nanotubes (MWCNTs) reduced transport activity and expression of ABC transporters including ABCB1/Pgp and ABCC4/MRP4 in human colon adenocarcinoma Caco-2 cells. Proto-oncogene c-Myc, which directly regulates ABC gene expression, was concurrently decreased in MWCNT-treated cells and forced over-expression of c-Myc reversed MWCNTs' inhibitory effects on ABCB1 and ABCC4 expression. MWCNT-cell membrane interaction and cell membrane oxidative damage were observed. However, antioxidants such as vitamin C, β-mecaptoethanol and dimethylthiourea failed to antagonize MWCNTs' down-regulation of ABC transporters. These data suggest that MWCNTs may act on c-Myc, but not through oxidative stress, to down-regulate ABC transporter expression. Our findings thus shed light on CNTs' novel cellular effects that may be utilized to develop CNTs-based drug delivery devices to overcome ABC transporter-mediated cancer chemoresistance.

Notch transcription complexes (NTCs) drive target gene expression by binding to two distinct types of genomic response elements, NTC monomer–binding sites and sequence-paired sites (SPSs) that bind NTC dimers. SPSs are conserved and have been linked to the Notch responsiveness of a few genes. To assess the overall contribution of SPSs to Notch-dependent gene regulation, we determined the DNA sequence requirements for NTC dimerization using a fluorescence resonance energy transfer (FRET) assay and applied insights from these in vitro studies to Notch-“addicted” T cell acute lymphoblastic leukemia (T-ALL) cells. We found that SPSs contributed to the regulation of about a third of direct Notch target genes. Although originally described in promoters, SPSs are present mainly in long-range enhancers, including an enhancer containing a newly described SPS that regulates HES5 expression. Our work provides a general method for identifying SPSs in genome-wide data sets and highlights the widespread role of NTC dimerization in Notch-transformed leukemia cells.

Amplification of the MYCN gene in human neuroblastoma predicts poor prognosis and resistance to therapy. We previously showed that MYCN-amplified neuroblastoma cells constantly require large amounts of glutamine to support their unabated growth. However, the identity and regulation of the transporter(s) that capture glutamine in MYCN-amplified neuroblastoma cells and the clinical significance of the transporter(s) in neuroblastoma diagnosis remain largely unknown. Here, we performed a systemic glutamine influx analysis and identified that MYCN-amplified neuroblastoma cells predominantly rely on activation of ASCT2 (solute carrier family 1 member 5, SLC1A5) to maintain sufficient levels of glutamine essential for the TCA cycle anaplerosis. Consequently, ASCT2 depletion profoundly inhibited glutaminolysis, concomitant with a substantial decrease in cell proliferation and viability in vitro and inhibition of tumourigenesis in vivo. Mechanistically, we identified ATF4 as a novel regulator which coordinates with N-Myc to directly activate ASCT2 expression. Of note, ASCT2 expression, which correlates with that of N-Myc and ATF4, is markedly elevated in high-stage neuroblastoma tumour samples compared with low-stage ones. More importantly, high ASCT2 expression is significantly associated with poor prognosis and survival of neuroblastoma patients. In aggregate, these findings elucidate a novel mechanism depicting how cell autonomous insults (MYCN amplification) and microenvironmental stresses (ATF4 induction) in concert coordinate ASCT2 activation to promote aggressive neuroblastoma progression, and establish ASCT2 as a novel biomarker in patient prognosis and stratification.

// Chong Li 1,2 , Ji Wang 3 , Hong Zhang 3 , Mingao Zhu 3 , Feifei Chen 3 , Yufeng Hu 4 , Hudan Liu 4 and Hong Zhu 1 1 Department of Oncology, the First Affiliated Hospital of Soochow University, Suzhou, China 2 CAS Key Laboratory of Infection and Immunity, Institute of Biophysics, Chinese Academy of Sciences (CAS), Beijing, China 3 Department of Oncology, the Second Affiliated Hospital of Soochow University, Suzhou, China 4 School of Pharmacy, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, China Correspondence: Hong Zhu, email: // Keywords : ISG15, HCC, Metastasis, Tumorigenesis Received : June 04, 2014 Accepted : August 05, 2014 Published : August 06, 2014 Abstract Hepatocellular carcinoma (HCC) is one of the most common cancers worldwide with poor prognosis. IFN-stimulated genes 15 (ISG15) is an ubiquitin-like molecule that is strongly upregulated by type I interferons as a primary response to diverse microbial and cellular stress stimuli. However, the role of ISG15 in HCC remains unclear. In this study, we investigated the function of ISG15 during HCC progression and related mechanism using clinicopathological data, cell line and xenograft model. Our results indicated that ISG15 is highly expressed in HCC tissues and multiple HCC cell lines. ISG15 expression is significantly associated with the differentiation grade, metastatic of tumor and survival of HCC patients. However, the expression of ISG15 is not affected by HBV infection. ISG15 promotes the proliferation and migration of hepatocarcinoma cells through maintaining Survivin protein stabilization via sequestering XIAP from interacting with Survivin. Knowing down ISG15 with SiRNA inhibited the xenografted tumor growth and prolonged the lifespan of tumor-bearing mice. All these results support that ISG15 high expression is an intrinsic feature for HCC and a trigger for tumorigenesis and metastasis. ISG15 may be a prognostic biomarker and the inhibition of ISG15 could provide a therapeutic advantage for HCC patients over-expressing ISG15.

The aberrant activation of oncogene MYC (also termed c-MYC) is one of the most common features in human cancer. The unleashed MYC oncogene frequently produces abundant MYC protein, which mediates a transcriptional response involved in a variety of biological processes, contributing to almost every aspect of tumorigenesis. The significance of MYC deregulation has been recognized in T-cell acute lymphoblastic leukemia (T-ALL), a life-threatening hematological malignancy with dismal outcome due to disease relapse and drug resistance. Therapeutic efforts aimed at inhibiting MYC expression or activity should have an important clinical relevance. However, attempts to directly disrupt MYC function have met with limited success, in part due to its "undruggable" protein structure. Aurora kinases, a multi-genic family of serine/threonine kinases, consist Aurora A (AURKA), Aurora B (AURKB) and Aurora C (AURKC). They are known to play an integral role in the regulation of cell division and chromosomal segregation. Amplification or overexpression of Aurora kinases is frequently found in human cancers with clear evidence of oncogenic potential, implicating Aurora kinases as rational anti-tumor targets. AURKB is the catalytic subunit of the chromosomal passenger protein complex (CPPC) which regulates multiple facets of cell division. Overexpression of AURKB has been reported in a variety of cancers and predicts poor overall survival. AZD1152 is a highly potent and selective inhibitor of Aurora B; preclinical evidence of anti-tumor efficacy with AZD1152 has extended to the clinical setting with tolerable toxicity. Despite considerable study, it remains largely unclear how expression of AURKB is elevated and, in particular, how elevated levels of AURKB reprogram cells to promote the cancer progression. We identified AURKB as a novel MYC binding partner using liquid chromatography tandem mass spectrometry (LC-MS/MS) analysis. To assess the potential role of AURKB in regulating MYC, we inhibited AURKB in multiple T-ALL cell lines and found that MYC protein expression was diminished significantly. Notably, depletion of AURKB failed to downregulate MYC mRNA, suggesting a post-transcriptional regulation of the MYC protein. We then assessed MYC protein decay in the presence or absence of AURKB expression. Time course experiments revealed that knockdown of AURKB significantly shortened the half-life of endogenous MYC in T-ALL cells. Consistently, AURKB depletion resulted in significant downregulation of MYC-induced gene expression programs, corroborating an essential role of AURKB in sustaining MYC transcriptional activities. Regulation of MYC degradation by ubiquitin-proteasome system is dependent on MYC phosphorylation. Initiation of MYC turnover requires GSK3b-mediated phosphorylation of threonine 58 (p-T58). Time-course analysis showed that treatment with AZD1152 in T-ALL cells resulted in a notable increase in MYC p-T58. We performed in vitro kinase assays and found that MYC is phosphorylated directly by AURKB. This phosphorylation counteracted GSK3b-directed Thr58 phosphorylation and subsequent FBW7-mediated proteasomal degradation and enhanced the MYC protein stability. The AURKB mRNA and protein are generally more abundant in human T-ALL than normal thymocytes. We demonstrated that MYC, in concert with TAL1, directly binds to the AURKB promoter and activates its transcription, thus constituting a reciprocal regulation between MYC and AURKB. In order to clarify the biological significance of the AURKB-MYC circuit, we co-injected the one-cell-stage zebrafish embryos with the rag2:EGFP-Myc construct alone or together with rag2:AURKB followed by fluorescent microscopy analysis. Our results demonstrate that AURKB phosphorylation of MYC is functionally important for T cell leukemogenesis in vivo. Moreover, inhibition of AURKB elicits dramatic MYC degradation in association with robust apoptosis in wild type-FBW7 T-ALL cells, suggesting that FBW7 mutational status may serve as a genetic predictor of sensitivity to AURKB inhibitors. In this study, we unravel a non-mitotic role of AURKB in promoting MYC stabilization via direct MYC phosphorylation at an unconventional site. Our findings decipher a previously unsuspected mechanism involved in MYC deregulation and highlight disruption of the AURKB-MYC signaling circuit as a promising T-ALL therapeutic strategy. Disclosures No relevant conflicts of interest to declare.

Aberrant activation of the NOTCH signaling pathway is crucial for the onset and progression of T cell leukemia. Yet recent studies also suggest a tumor suppressive role of NOTCH signaling in acute myeloid leukemia (AML) and reactivation of this pathway offers an attractive opportunity for anti-AML therapies. N-methylhemeanthidine chloride (NMHC) is a novel Amaryllidaceae alkaloid that we previously isolated from Zephyranthes candida, exhibiting inhibitory activities in a variety of cancer cells, particularly those from AML. Here, we report NMHC not only selectively inhibits AML cell proliferation in vitro but also hampers tumor development in a human AML xenograft model. Genome-wide gene expression profiling reveals that NMHC activates the NOTCH signaling. Combination of NMHC and recombinant human NOTCH ligand DLL4 achieves a remarkable synergistic effect on NOTCH activation. Moreover, pre-inhibition of NOTCH by overexpression of dominant negative MAML alleviates NMHC-mediated cytotoxicity in AML. Further mechanistic analysis using structure-based molecular modeling as well as biochemical assays demonstrates that NMHC docks in the hydrophobic cavity within the NOTCH1 negative regulatory region (NRR), thus promoting NOTCH1 proteolytic cleavage. Our findings thus establish NMHC as a potential NOTCH agonist that holds great promises for future development as a novel agent beneficial to patients with AML.

MYCN amplification in human cancers predicts poor prognosis and resistance to therapy. However, pharmacological strategies that directly target N-Myc, the protein encoded by MYCN, remain elusive. Here, we identify a molecular mechanism responsible for reciprocal activation between Polo-like kinase-1 (PLK1) and N-Myc. PLK1 specifically binds to the SCFFbw7 ubiquitin ligase, phosphorylates it, and promotes its autopolyubiquitination and proteasomal degradation, counteracting Fbw7-mediated degradation of N-Myc and additional substrates, including cyclin E and Mcl1. Stabilized N-Myc in turn directly activates PLK1 transcription, constituting a positive feedforward regulatory loop that reinforces Myc-regulated oncogenic programs. Inhibitors of PLK1 preferentially induce potent apoptosis of MYCN-amplified tumor cells from neuroblastoma and small cell lung cancer and synergistically potentiate the therapeutic efficacies of Bcl2 antagonists. These findings reveal a PLK1-Fbw7-Myc signaling circuit that underlies tumorigenesis and validate PLK1 inhibitors, alone or with Bcl2 antagonists, as potential effective therapeutics for MYC-overexpressing cancers.

Notch signaling regulates myriad cellular functions by activating transcription, yet how Notch selectively activates different transcriptional targets is poorly understood. The core Notch transcriptional activation complex can bind DNA as a monomer, but it can also dimerize on DNA-binding sites that are properly oriented and spaced. However, the significance of Notch dimerization is unknown. Here, we show that dimeric Notch transcriptional complexes are required for T-cell maturation and leukemic transformation but are dispensable for T-cell fate specification from a multipotential precursor. The varying requirements for Notch dimerization result from the differential sensitivity of specific Notch target genes. In particular, c-Myc and pre-T-cell antigen receptor α (Ptcra) are dimerization-dependent targets, whereas Hey1 and CD25 are not. These findings identify functionally important differences in the responsiveness among Notch target genes attributable to the formation of higher-order complexes. Consequently, it may be possible to develop a new class of Notch inhibitors that selectively block outcomes that depend on Notch dimerization (e.g., leukemogenesis).

MicroRNAs (miRNAs) are endogenous single-stranded RNA molecules of about 21 nucleotides in length that are fundamental post-transcriptional regulators of gene expression. Although the transcriptional and processing events involved in the generation of miRNAs have been extensively studied, very little is known pertaining to components that regulate the stability of individual miRNAs. All RNAs have distinct inherent half-lives that dictate their level of accumulation and miRNAs would be expected to follow a similar principle. Here we demonstrate that although most miRNA appear to be stable, like mRNAs, miRNAs possess differential stability in human cells. In particular, we found that miR-382, a miRNA that contributes to HIV-1 provirus latency, is unstable in cells. To determine the region of miR-382 responsible for its rapid decay, we developed a cell-free system that recapitulated the observed cell-based-regulated miR-382 turnover. The system utilizes in vitro-processed mature miRNA derived from pre-miRNA and follows the decay of the processed miRNA. Using this system, we demonstrate that instability of miR-382 is driven by sequences outside its seed region and required the 3′ terminal seven nucleotides where mutations in this region increased the stability of the RNA. Moreover, the exosome 3′–5′ exoribonuclease complex was identified as the primary nuclease involved in miR-382 decay with a more modest contribution by the Xrn1 and no detectable contribution by Xrn2. These studies provide evidence for an miRNA element essential for rapid miRNA decay and implicate the exosome in this process. The development of a biochemically amendable system to analyze the mechanism of differential miRNA stability provides an important step in efforts to regulate gene expression by modulating miRNA stability.

Contains fulltext : 88453.pdf (Publisher’s version ) (Open Access) Somatic activating mutations in Notch1 contribute to the pathogenesis of T cell acute lymphoblastic lymphoma (T-ALL), but how activated Notch1 signaling exerts this oncogenic effect is not completely understood. Here we identify HIV-1 Rev-binding protein (Hrb), a component of the clathrin-mediated endocytosis machinery, as a critical mediator of Notch-induced T-ALL development in mice. Hrb was found to be a direct transcriptional target of Notch1, and Hrb loss reduced the incidence or delayed the onset of T-ALL in mouse models in which activated Notch1 signaling either contributes to or drives leukemogenesis. Consistent with this observation, Hrb supported survival and proliferation of hematopoietic and T cell precursor cells in vitro. We demonstrated that Hrb accelerated the uptake of transferrin, which was required for upregulation of the T cell protooncogene p21. Indeed, iron-deficient mice developed Notch1-induced T-ALL substantially more slowly than control mice, further supporting a critical role for iron uptake during leukemogenesis. Taken together, these results reveal that Hrb is a critical Notch target gene that mediates lymphoblast transformation and disease progression via its ability to satisfy the enhanced demands of transformed lymphoblasts for iron. Further, our data suggest that Hrb may be targeted to improve current treatment or design novel therapies for human T-ALL patients.

The human scavenger decapping enzyme, DcpS, functions to hydrolyze the resulting cap structure following cytoplasmic mRNA decay yet is, surprisingly, a nuclear protein by immunofluorescence. Here, we show that DcpS is a nucleocytoplasmic shuttling protein that contains separable nuclear import and Crm-1-dependent export signals. We postulated that the presence of DcpS in both cellular compartments and its ability to hydrolyze cap structure may impact other cellular events dependent on cap-binding proteins. An shRNA-engineered cell line with markedly diminished DcpS levels led to a corresponding reduction in cap-proximal intron splicing of a reporter minigene and endogenous genes. The impaired cap catabolism and resultant imbalanced cap concentrations were postulated to sequester the cap-binding complex (CBC) from its normal splicing function. In support of this explanation, DcpS efficiently displaced the nuclear cap-binding protein Cbp20 from cap structure, and complementation with Cbp20 reversed the reduced splicing, indicating that modulation of splicing by DcpS is mediated through Cbp20. Our studies demonstrate that the significance of DcpS extends beyond its well-characterized role in mRNA decay and involves a broader range of functions in RNA processing including nuclear pre-mRNA splicing.

Messenger RNA (mRNA) decay utilizes both exoribonucleolytic and endoribonucleolytic enzymes where the latter are generally more prone to be transcript-specific. An erythroid-enriched endoribonuclease, ErEN, can destabilize the alpha-globin mRNA through directing a site-specific cleavage within the 3' untranslated region (3' UTR) both in vitro and in vivo. ErEN activity is sequence- and/or local structure-specific as the minimal recognition/cleavage sequence can be conferred onto a heterologous RNA and mutations at the cleavage site immunize the mRNA from ErEN hydrolysis. Interestingly, the ErEN cleavage activity is regulated by an mRNA stability complex (alpha-complex). An interaction between the alpha-complex and the poly(A)-binding protein (PABP) accentuates alpha-complex binding to a region overlapping the ErEN cleavage site and further prevents premature ErEN-mediated decay. At present the identity of ErEN remains elusive, yet its identification will provide mechanistic and functional insights into the general processes of endoribonuclease-mediated mRNA turnover and erythropoiesis.