Myc pathways provoking cell suicide and cancer

Selection of cell-type specific antibodies on tissue-sections using phage display

With the advent of modern technologies enabling single cell analysis, it has become clear that small sub-populations of cells or even single cells can drive the phenotypic appearance of tissue, both diseased and normal. Nucleic acid based technologies allowing single cell analysis has been faster to mature, while technologies aimed at analysing the proteome at a single cell level is still lacking behind, especially technologies which allow single cell analysis in tissue. Introducing methods, that allows such analysis, will pave the way for discovering new biomarkers with more clinical relevance, as these may be unique for microenvironments only present in tissue and will avoid artifacts introduced by in vitro studies. Here, we introduce a technology enabling biomarker identification on small sub-populations of cells within a tissue section. Phage antibody libraries are applied to the tissue sections, followed by washing to remove non-bound phage particles. To eliminate phage antibodies binding to antigens ubiquitously expressed and retrieve phage antibodies binding specifically to antigens expressed by the sub-population of cells, the area of interest is protected by a ‘shadow stick’. The phage antibodies on the remaining areas on the slide are exposed to UV light, which introduces cross-links in the phage genome, thus rendering them non-replicable. In this work we applied the technology, guided by CD31 expressing endothelial cells, to isolate recombinant antibodies specifically binding biomarkers expressed either by the cell or in the microenvironment surrounding the endothelial cell.

Oncogenesis and induced pluripotency - commonalities of signalling pathways

Rapid progress in the field of adult cells reprogramming back into a stem cell-like fate revealed shared mechanisms of action with tumoural reprogramming. A hallmark of stem cells - self-renewal and differentiation potential - seems to be tightly interlaced with large proliferation capacity and cellular plasticity of cancer cells. In this review, we briefly summarise the core transcription factors critical to maintenance of ES cell signature and overexpressed in many types of cancer, as well as signalling pathways involved in both induced pluripotency and oncogenesis, with particular regard to the role of tumour suppressor p53.

Higher gene expression variability in the more aggressive subtype of chronic lymphocytic leukemia

Background

Chronic lymphocytic leukemia (CLL) presents two subtypes which have drastically different clinical outcomes, IgVH mutated (M-CLL) and IgVH unmutated (U-CLL). So far, these two subtypes are not associated to clear differences in gene expression profiles. Interestingly, recent results have highlighted important roles for heterogeneity, both at the genetic and at the epigenetic level in CLL progression.

Methods

We analyzed gene expression data of two large cohorts of CLL patients and quantified expression variability across individuals to investigate differences between the two subtypes using different measures and statistical tests. Functional significance was explored by pathway enrichment and network analyses. Furthermore, we implemented a random forest approach based on expression variability to classify patients into disease subtypes.

Results

We found that U-CLL, the more aggressive type of the disease, shows significantly increased variability of gene expression across patients and that, overall, genes that show higher variability in the aggressive subtype are related to cell cycle, development and inter-cellular communication. These functions indicate a potential relation between gene expression variability and the faster progression of this CLL subtype. Finally, a classifier based on gene expression variability was able to correctly predict the disease subtype of CLL patients.

Conclusions

There are strong relations between gene expression variability and disease subtype linking significantly increased expression variability to phenotypes such as aggressiveness and resistance to therapy in CLL.

Electronic supplementary material

The online version of this article (doi:10.1186/s13073-014-0125-z) contains supplementary material, which is available to authorized users.

Myc-induced liver tumors in transgenic zebrafish can regress in tp53 null mutation

Hepatocellular carcinoma (HCC) is currently one of the top lethal cancers with an increasing trend. Deregulation of MYC in HCC is frequently detected and always correlated with poor prognosis. As the zebrafish genome contains two differentially expressed zebrafish myc orthologs, myca and mycb, it remains unclear about the oncogenicity of the two zebrafish myc genes. In the present study, we developed two transgenic zebrafish lines to over-express myca and mycb respectively in the liver using a mifepristone-inducible system and found that both myc genes were oncogenic. Moreover, the transgenic expression of myca in hepatocytes caused robust liver tumors with several distinct phenotypes of variable severity. ~5% of myca transgenic fish developing multinodular HCC with cirrhosis after 8 months of induced myca expression. Apoptosis was also observed with myca expression; introduction of homozygous tp53^-/- mutation into the myca transgenic fish reduced apoptosis and accelerated tumor progression. The malignant status of hepatocytes was dependent on continued expression of myca; withdrawal of the mifepristone inducer resulted in a rapid regression of liver tumors, and the tumor regression occurred even in the tp53^-/- mutation background. Thus, our data demonstrated the robust oncogenicity of zebrafish myca and the requirement of sustained Myc overexpression for maintenance of the liver tumor phenotype in this transgenic model. Furthermore, tumor regression is independent of the function of Tp53.

A pan-cancer modular regulatory network analysis to identify common and cancer-specific network components

Many human diseases including cancer are the result of perturbations to transcriptional regulatory networks that control context-specific expression of genes. A comparative approach across multiple cancer types is a powerful approach to illuminate the common and specific network features of this family of diseases. Recent efforts from The Cancer Genome Atlas (TCGA) have generated large collections of functional genomic data sets for multiple types of cancers. An emerging challenge is to devise computational approaches that systematically compare these genomic data sets across different cancer types that identify common and cancer-specific network components. We present a module- and network-based characterization of transcriptional patterns in six different cancers being studied in TCGA: breast, colon, rectal, kidney, ovarian, and endometrial. Our approach uses a recently developed regulatory network reconstruction algorithm, modular regulatory network learning with per gene information (MERLIN), within a stability selection framework to predict regulators for individual genes and gene modules. Our module-based analysis identifies a common theme of immune system processes in each cancer study, with modules statistically enriched for immune response processes as well as targets of key immune response regulators from the interferon regulatory factor (IRF) and signal transducer and activator of transcription (STAT) families. Comparison of the inferred regulatory networks from each cancer type identified a core regulatory network that included genes involved in chromatin remodeling, cell cycle, and immune response. Regulatory network hubs included genes with known roles in specific cancer types as well as genes with potentially novel roles in different cancer types. Overall, our integrated module and network analysis recapitulated known themes in cancer biology and additionally revealed novel regulatory hubs that suggest a complex interplay of immune response, cell cycle, and chromatin remodeling across multiple cancers.

New insights in hepatocellular carcinoma: from bench to bedside

Hepatocarcinogenesis is a multistep process involving different genetic alterations that ultimately lead to malignant transformation of the hepatocyte. The liver is one of the main targets for different metastatic foci, but it represents an important and frequent locus of degeneration in the course of chronic disease. In fact, Hepatocellular carcinoma (HCC) represents the outcome of the natural history of chronic liver diseases, from the condition of fibrosis, to cirrhosis and finally to cancer. HCC is the sixth most common cancer in the world, some 630,000 new cases being diagnosed each year. Furthermore, about the 80% of people with HCC, have seen their clinical history developing from fibrosis, to cirrhosis and finally to cancer. The three main causes of HCC development are represented by HBV, HCV infection and alcoholism. Moreover, metabolic disease [starting from Non Alcoholic Fatty Liver Disease (NAFLD), Non Alcoholic Steatohepatitis (NASH)] and, with reduced frequency, some autoimmune disease may lead to HCC development. An additional rare cause of carcinogenetic degeneration of the liver, especially developed in African and Asian Countries, is represented by aflatoxin B1. The mechanisms by which these etiologic factors may induce HCC development involve a wide range of pathway and molecules, currently under investigation. In summary, the hepatocarcionogenesis results from a multifactorial process leading to the common condition of genetic changes in mature hepatocytes mainly characterized by uncontrolled proliferation and cell death. Advances in understanding the mechanism of action are fundamental for the development of new potential therapies and results primarily from the association of the research activities coming from basic and clinical science. This review article analyzes the current models used in basic research to investigate HCC activity, and the advances obtained from a basic and clinical point of view.

Putting the pieces together: How is the mitochondrial pathway of apoptosis regulated in cancer and chemotherapy?

In order to solve a jigsaw puzzle, one must first have the complete picture to logically connect the pieces. However, in cancer biology, we are still gaining an understanding of all the signaling pathways that promote tumorigenesis and how these pathways can be pharmacologically manipulated by conventional and targeted therapies. Despite not having complete knowledge of the mechanisms that cause cancer, the signaling networks responsible for cancer are becoming clearer, and this information is serving as a solid foundation for the development of rationally designed therapies. One goal of chemotherapy is to induce cancer cell death through the mitochondrial pathway of apoptosis. Within this review, we present the pathways that govern the cellular decision to undergo apoptosis as three distinct, yet connected puzzle pieces: (1) How do oncogene and tumor suppressor pathways regulate apoptosis upstream of mitochondria? (2) How does the B-cell lymphoma 2 (BCL-2) family influence tumorigenesis and chemotherapeutic responses? (3) How is post-mitochondrial outer membrane permeabilization (MOMP) regulation of cell death relevant in cancer? When these pieces are united, it is possible to appreciate how cancer signaling directly impacts upon the fundamental cellular mechanisms of apoptosis and potentially reveals novel pharmacological targets within these pathways that may enhance chemotherapeutic success.

Therapeutic potential of siRNA and DNAzymes in cancer

Cancer is characterized by uncontrolled cell growth, invasion, and metastasis and possess threat to humans worldwide. The scientific community is facing numerous challenges despite several efforts to cure cancer. Though a number of studies were done earlier, the molecular mechanism of cancer progression is not completely understood. Currently available treatments like surgery resection, adjuvant chemotherapy, and radiotherapy are not completely effective in curing all the cancers. Recent advances in the antisense technology provide a powerful tool to investigate various cancer pathways and target them. Small interfering RNAs (siRNAs) could be effective in downregulating the cancer-associated genes, but their in vivo delivery is the main obstacle. DNA enzymes (DNAzymes) have great potential in the treatment of cancer due to high selectivity and significant catalytic efficiency. In this review, we are focusing on antisense molecules such as siRNA and DNAzymes in cancer therapeutics development. This review also describes the challenges and approaches to overcome obstacles involved in using siRNA and DNAzymes in the treatment of cancers.

MYC and EGR1 synergize to trigger tumor cell death by controlling NOXA and BIM transcription upon treatment with the proteasome inhibitor bortezomib

The c-MYC (MYC afterward) oncogene is well known for driving numerous oncogenic programs. However, MYC can also induce apoptosis and this function of MYC warrants further clarification. We report here that a clinically relevant proteasome inhibitor significantly increases MYC protein levels and that endogenous MYC is necessary for the induction of apoptosis. This kind of MYC-induced cell death is mediated by enhanced expression of the pro-apoptotic BCL2 family members NOXA and BIM. Quantitative promoter-scanning chromatin immunoprecipitations (qChIP) further revealed binding of MYC to the promoters of NOXA and BIM upon proteasome inhibition, correlating with increased transcription. Both promoters are further characterized by the presence of tri-methylated lysine 4 of histone H3, marking active chromatin. We provide evidence that in our apoptosis models cell death occurs independently of p53 or ARF. Furthermore, we demonstrate that recruitment of MYC to the NOXA as well as to the BIM gene promoters depends on MYC's interaction with the zinc finger transcription factor EGR1 and an EGR1-binding site in both promoters. Our study uncovers a novel molecular mechanism by showing that the functional cooperation of MYC with EGR1 is required for bortezomib-induced cell death. This observation may be important for novel therapeutic strategies engaging the inherent pro-death function of MYC.

The lncRNA-MYC regulatory network in cancer

Long non-coding RNAs (lncRNAs) have been widely studied in recent years, and accumulating evidence identified lncRNAs as crucial regulators of various biological processes, including cell cycle progression, chromatin remodeling, gene transcription, and posttranscriptional processing. In addition, the fact that lncRNAs interact with the MYC gene family in human carcinomas has been discovered. This review summarizes the latest progress on the investigation of lncRNAs and MYC, particularly focusing on the interplay between lncRNAs and MYC in cancer to reveal the significance of lncRNA-MYC network in regulating initiation, development, and metastasis of tumors. Further research and collection of clinical data would provide a better understanding of lncRNA-MYC network in cancer diagnosis and treatment.

CRTC1/MAML2 gain-of-function interactions with MYC create a gene signature predictive of cancers with CREB-MYC involvement

Chimeric oncoproteins created by chromosomal translocations are among the most common genetic mutations associated with tumorigenesis. Malignant mucoepidermoid salivary gland tumors, as well as a growing number of solid epithelial-derived tumors, can arise from a recurrent t (11, 19)(q21;p13.1) translocation that generates an unusual chimeric cAMP response element binding protein (CREB)-regulated transcriptional coactivator 1 (CRTC1)/mastermind-like 2 (MAML2) (C1/M2) oncoprotein comprised of two transcriptional coactivators, the CRTC1 and the NOTCH/RBPJ coactivator MAML2. Accordingly, the C1/M2 oncoprotein induces aberrant expression of CREB and NOTCH target genes. Surprisingly, here we report a gain-of-function activity of the C1/M2 oncoprotein that directs its interactions with myelocytomatosis oncogene (MYC) proteins and the activation of MYC transcription targets, including those involved in cell growth and metabolism, survival, and tumorigenesis. These results were validated in human mucoepidermoid tumor cells that harbor the t (11, 19)(q21;p13.1) translocation and express the C1/M2 oncoprotein. Notably, the C1/M2-MYC interaction is necessary for C1/M2-driven cell transformation, and the C1/M2 transcriptional signature predicts other human malignancies having combined involvement of MYC and CREB. These findings suggest that such gain-of-function properties may also be manifest in other oncoprotein fusions found in human cancer and that agents targeting the C1/M2-MYC interface represent an attractive strategy for the development of effective and safe anticancer therapeutics in tumors harboring the t (11, 19) translocation.

Inactivation of MYC reverses tumorigenesis

The MYC proto-oncogene is an essential regulator of many normal biological programmes. MYC, when activated as an oncogene, has been implicated in the pathogenesis of most types of human cancers. MYC overexpression in normal cells is restrained from causing cancer through multiple genetically and epigenetically controlled checkpoint mechanisms, including proliferative arrest, apoptosis and cellular senescence. When pathologically activated in the correct epigenetic and genetic contexts, MYC bypasses these mechanisms and drives many of the 'hallmark' features of cancer, including uncontrolled tumour growth associated with DNA replication and transcription, cellular proliferation and growth, protein synthesis and altered cellular metabolism. MYC also dictates tumour cell fate by enforcing self-renewal and by abrogating cellular senescence and differentiation programmes. Moreover, MYC influences the tumour microenvironment, including activating angiogenesis and suppressing the host immune response. Provocatively, brief or even partial suppression of MYC back to its physiological levels of activation can lead to the restoration of intrinsic checkpoint mechanisms, resulting in acute and sustained tumour regression associated with tumour cells undergoing proliferative arrest, differentiation, senescence and apoptosis, as well as remodelling of the tumour microenvironment, recruitment of an immune response and shutdown of angiogenesis. Hence, tumours appear to be addicted to the MYC oncogene because of both tumour cell intrinsic and host-dependent mechanisms. MYC is important for the regulation of both the initiation and maintenance of tumorigenesis.

Partition of Myc into immobile vs. mobile complexes within nuclei

Myc levels are highly regulated and usually low in vivo. Dimerized with Max, it regulates most expressed genes and so directly and indirectly controls most cellular processes. Intranuclear diffusion of a functional c-Myc-eGFP, expressed from its native locus in murine fibroblasts and 3T3 cells or by transient transfection, was monitored using Two Photon Fluorescence Correlation Spectroscopy, revealing concentration and size (mobility) of complexes. With increased c-Myc-eGFP, a very immobile pool saturates as a ‘mobile' pool increases. Both pools diffuse too slowly to be free Myc-Max dimers. Following serum stimulation, eGFP-c-Myc accumulated in the presence of the proteasome inhbitor MG132. Stimulating without MG132, Myc peaked at 2.5 hrs, and at steady was ~8 ± 1.3 nM. Inhbiting Myc-Max dimerization by Max-knockdown or drug treatment increased the ‘mobile' c-Myc pool size. These results indicate that Myc populates macromolecular complexes of widely heterogenous size and mobility in vivo.

Genetic mechanisms and signaling pathways in autosomal dominant polycystic kidney disease

Recent advances in defining the genetic mechanisms of disease causation and modification in autosomal dominant polycystic kidney disease (ADPKD) have helped to explain some extreme disease manifestations and other phenotypic variability. Studies of the ADPKD proteins, polycystin-1 and -2, and the development and characterization of animal models that better mimic the human disease, have also helped us to understand pathogenesis and facilitated treatment evaluation. In addition, an improved understanding of aberrant downstream pathways in ADPKD, such as proliferation/secretion-related signaling, energy metabolism, and activated macrophages, in which cAMP and calcium changes may play a role, is leading to the identification of therapeutic targets. Finally, results from recent and ongoing preclinical and clinical trials are greatly improving the prospects for available, effective ADPKD treatments.

MYC activation is a hallmark of cancer initiation and maintenance

The MYC proto-oncogene has been implicated in the pathogenesis of most types of human tumors. MYC activation alone in many normal cells is restrained from causing tumorigenesis through multiple genetic and epigenetically controlled checkpoint mechanisms, including proliferative arrest, apoptosis, and cellular senescence. When pathologically activated in a permissive epigenetic and/or genetic context, MYC bypasses these mechanisms, enforcing many of the "hallmark" features of cancer, including relentless tumor growth associated with DNA replication and transcription, cellular proliferation and growth, protein synthesis, and altered cellular metabolism. MYC mandates tumor cell fate, by inducing stemness and blocking cellular senescence and differentiation. Additionally, MYC orchestrates changes in the tumor microenvironment, including the activation of angiogenesis and suppression of the host immune response. Provocatively, brief or even partial suppression of MYC back to its physiological levels of activation can result in the restoration of intrinsic checkpoint mechanisms, resulting in acute and sustained tumor regression, associated with tumor cells undergoing proliferative arrest, differentiation, senescence, and apoptosis, as well as remodeling of the tumor microenvironment, recruitment of an immune response, and shutdown of angiogenesis. Hence, tumors appear to be "addicted" to MYC because of both tumor cell-intrinsic, cell-autonomous and host-dependent, immune cell-dependent mechanisms. Both the trajectory and persistence of many human cancers require sustained MYC activation. Multiscale mathematical modeling may be useful to predict when tumors will be addicted to MYC. MYC is a hallmark molecular feature of both the initiation and maintenance of tumorigenesis.

The activities of MYC, MNT and the MAX-interactome in lymphocyte proliferation and oncogenesis

The MYC family of proteins plays essential roles in embryonic development and in oncogenesis. Efforts over the past 30 years to define the transcriptional activities of MYC and how MYC functions to promote proliferation have produced evolving models of MYC function. One picture that has emerged of MYC and its partner protein MAX is of a transcription factor complex with a seemingly unique ability to stimulate the transcription of genes that are epigenetically poised for transcription and to amplify the transcription of actively transcribed genes. During lymphocyte activation, MYC is upregulated and stimulates a pro-proliferative program in part through the upregulation of a wide variety of metabolic effector genes that facilitate cell growth and cell cycle progression. MYC upregulation simultaneously sensitizes cells to apoptosis and activated lymphocytes and lymphoma cells have pro-survival attributes that allow MYC-driven proliferation to prevail. For example, the MAX-interacting protein MNT is upregulated in activated lymphocytes and was found to protect lymphocytes from MYC-dependent apoptosis. Here we review the activities of MYC, MNT and other MAX interacting proteins in the setting of T and B cell activation and oncogenesis. This article is part of a Special Issue entitled: Myc proteins in cell biology and pathology.

Inhibition of malignant phenotypes of human osteosarcoma cells by a gene silencer, a pyrrole-imidazole polyamide, which targets an E-box motif

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We generated pyrrole–imidazole (PI) polyamides that could bind to an E-box motif.

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PI polyamide Myc-6 induces G1 arrest and apoptosis in human osteosarcoma MG63 cells.

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Myc-6 represses tumor growth both in vitro and in vivo.

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Myc-6 binds to the 5′-upstream region of noncoding RNA MALAT1 and reduces its expression.

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Myc-6 exerts its tumor-suppressive ability through the down-regulation of MALAT1.

Gene amplification and/or overexpression of the transcription factor c-MYC, which binds to the E-box sequence (5′-CACGTG-3′), has been observed in many human tumors. In this study, we have designed 5 pyrrole–imidazole (PI) polyamides recognizing E-box, and found that, among them, Myc-6 significantly suppresses malignant phenotypes of human osteosarcoma MG63 cells both in vitro and in vivo. Intriguingly, knockdown of the putative Myc-6 target MALAT1 encoding long noncoding RNA remarkably impaired cell growth of MG63 cells. Collectively, our present findings strongly suggest that Myc-6 exerts its tumor-suppressive ability at least in part through the specific down-regulation of MALAT1.

A novel PTEN/mutant p53/c-Myc/Bcl-XL axis mediates context-dependent oncogenic effects of PTEN with implications for cancer prognosis and therapy

Phosphatase and tensin homolog located on chromosome 10 (PTEN) is one of the most frequently mutated tumor suppressors in human cancer including in glioblastoma. Here, we show that PTEN exerts unconventional oncogenic effects in glioblastoma through a novel PTEN/mutant p53/c-Myc/Bcl-XL molecular and functional axis. Using a wide array of molecular, genetic, and functional approaches, we demonstrate that PTEN enhances a transcriptional complex containing gain-of-function mutant p53, CBP, and NFY in human glioblastoma cells and tumor tissues. The mutant p53/CBP/NFY complex transcriptionally activates the oncogenes c-Myc and Bcl-XL, leading to increased cell proliferation, survival, invasion, and clonogenicity. Disruption of the mutant p53/c-Myc/Bcl-XL axis or mutant p53/CBP/NFY complex reverses the transcriptional and oncogenic effects of PTEN and unmasks its tumor-suppressive function. Consistent with these data, we find that PTEN expression is associated with worse patient survival than PTEN loss in tumors harboring mutant p53 and that a small molecule modulator of p53 exerts greater antitumor effects in PTEN-expressing cancer cells. Altogether, our study describes a new signaling pathway that mediates context-dependent oncogenic/tumor-suppressive role of PTEN. The data also indicate that the combined mutational status of PTEN and p53 influences cancer prognosis and anticancer therapies that target PTEN and p53.

miR-100 induces epithelial-mesenchymal transition but suppresses tumorigenesis, migration and invasion

Whether epithelial-mesenchymal transition (EMT) is always linked to increased tumorigenicity is controversial. Through microRNA (miRNA) expression profiling of mammary epithelial cells overexpressing Twist, Snail or ZEB1, we identified miR-100 as a novel EMT inducer. Surprisingly, miR-100 inhibits the tumorigenicity, motility and invasiveness of mammary tumor cells, and is commonly downregulated in human breast cancer due to hypermethylation of its host gene MIR100HG. The EMT-inducing and tumor-suppressing effects of miR-100 are mediated by distinct targets. While miR-100 downregulates E-cadherin by targeting SMARCA5, a regulator of CDH1 promoter methylation, this miRNA suppresses tumorigenesis, cell movement and invasion in vitro and in vivo through direct targeting of HOXA1, a gene that is both oncogenic and pro-invasive, leading to repression of multiple HOXA1 downstream targets involved in oncogenesis and invasiveness. These findings provide a proof-of-principle that EMT and tumorigenicity are not always associated and that certain EMT inducers can inhibit tumorigenesis, migration and invasion.

Induction of epithelial-mesenchymal transition (EMT) in epithelial tumor cells has been shown to enhance migration, invasion and cancer ‘stemness’. Here we demonstrate that a miRNA downregulated in human breast tumors, miR-100, can simultaneously induce EMT and inhibit tumorigenesis, migration and invasion through direct targeting of distinct genes. This is the first report of an EMT inducer that suppresses cell movement and tumor invasion, which indicates that EMT is not always associated with increased tumorigenesis, migration and invasion, and that all EMT inducers are not equal: while some of them can promote tumorigenicity, motility and invasiveness, others inhibit these properties owing to their ability to concurrently target both EMT-repressing genes and oncogenic/pro-invasive genes. These findings provide new insights into the complex roles of EMT inducers.

MYC and transcription elongation

Most transcription factors specify the subset of genes that will be actively transcribed in the cell by stimulating transcription initiation at these genes, but MYC has a fundamentally different role. MYC binds E-box sites in the promoters of active genes and stimulates recruitment of the elongation factor P-TEFb and thus transcription elongation. Consequently, rather than specifying the set of genes that will be transcribed in any particular cell, MYC's predominant role is to increase the production of transcripts from active genes. This increase in the transcriptional output of the cell's existing gene expression program, called transcriptional amplification, has a profound effect on proliferation and other behaviors of a broad range of cells. Transcriptional amplification may reduce rate-limiting constraints for tumor cell proliferation and explain MYC's broad oncogenic activity among diverse tissues.

Regulation of TRAIL receptor expression by β-catenin in colorectal tumours

Tumour-necrosis-factor-related apoptosis-inducing ligand (TRAIL) is being investigated as a targeted cancer therapeutic and the expression of its pro-apoptotic receptors, DR4 and DR5, increases during colorectal carcinogenesis. This study investigated the role of β-catenin in the regulation of these receptors. In human colorectal adenoma and carcinoma cell lines, downregulation of β-catenin resulted in lower total DR4 and DR5 protein levels. Similarly, cell membrane expression of DR4 and DR5 was reduced after downregulation of β-catenin in colon carcinoma cells, whereas induction of β-catenin in HeLa cells led to increased cell membrane expression of DR4 and DR5. Downregulation of β-catenin decreased the recombinant human TRAIL sensitivity of human colon carcinoma cells. Activation of the transcription factor T-cell factor-4 (TCF-4) is an important function of β-catenin. Dominant-negative TCF-4 overexpression, however, did not significantly affect TRAIL receptor expression or recombinant human TRAIL sensitivity. Human colorectal adenomas (N = 158) with aberrant (cytoplasmic and nuclear) β-catenin expression had a higher percentage of immunohistochemical DR4 and DR5 staining per tumour (mean: 73 and 88%, respectively) than those with membranous β-catenin staining only (mean: 50 and 70%, respectively, P < 0.01 for both). Furthermore, aberrant β-catenin staining co-localized with DR4 and DR5 expression in 92% of adenomas. In 53 human colorectal carcinomas, aberrant β-catenin expression was present in most cases and DR4/5 expression was largely homogenous. Similarly, in adenomas from APC(min) mice, cytoplasmic β-catenin staining co-localized with staining for the murine TRAIL death receptor. In conclusion, the gradual increase in TRAIL receptor expression during colorectal carcinogenesis is at least partially mediated through increased β-catenin expression, independently of TCF-4-signalling.

Impact of c-MYC protein expression on outcome of patients with early-stage HER2+ breast cancer treated with adjuvant trastuzumab NCCTG (alliance) N9831

PURPOSE

This study investigated the association between tumor MYC protein expression and disease-free survival (DFS) of patients randomized to receive chemotherapy alone (Arm A) or chemotherapy with sequential (Arm B) or concurrent trastuzumab (Arm C) in the N9831 (Alliance) adjuvant HER2(+) trastuzumab breast cancer trial.

EXPERIMENTAL DESIGN

This analysis included 1,736 patients randomized to Arms A, B, and C on N9831. Nuclear MYC protein expression was determined in tissue microarray sections containing three biopsies per patient or whole tissue sections using standard immunohistochemistry (clone 9E10). A tumor was considered positive for MYC protein overexpression (MYC(+)) if the nuclear 3+ staining percentage was more than 30%.

RESULTS

Five hundred and seventy-four (33%) tumors were MYC(+). MYC(+) was associated with hormone receptor positivity (χ(2), P = 0.006), tumors 2 cm or more (χ(2), P = 0.02), and a higher rate of nodal positivity (χ(2), P < 0.001). HRs for DFS (median follow-up: 6.1 years) for Arm C versus A were 0.52 (P = 0.006) and 0.65 (P = 0.006) for patients with MYC(+) and MYC(-) tumors, respectively (P(interaction) = 0.40). For Arm B versus A, HRs for patients with MYC(+) and MYC(-) tumors were 0.79 (P = 0.21) and 0.74 (P = 0.04), respectively (P(interaction) = 0.71). For Arm C versus B, HRs for patients with MYC(+) and MYC(-) tumors were 0.56 (P = 0.02) and 0.89 (P = 0.49), respectively (P(interaction) = 0.17).

CONCLUSIONS

Our data do not support an impact of tumor MYC protein expression on differential benefit from adjuvant trastuzumab.

Runx transcription factors repress human and murine c-Myc expression in a DNA-binding and C-terminally dependent manner

The transcription factors Runx1 and c-Myc have individually been shown to regulate important gene targets as well as to collaborate in oncogenesis. However, it is unknown whether there is a regulatory relationship between the two genes. In this study, we investigated the transcriptional regulation of endogenous c-Myc by Runx1 in the human T cell line Jurkat and murine primary hematopoietic cells. Endogenous Runx1 binds to multiple sites in the c-Myc locus upstream of the c-Myc transcriptional start site. Cells transduced with a C-terminally truncated Runx1 (Runx1.d190), which lacks important cofactor interaction sites and can block C-terminal-dependent functions of all Runx transcription factors, showed increased transcription of c-Myc. In order to monitor c-Myc expression in response to early and transiently-acting Runx1.d190, we generated a cell membrane-permeable TAT-Runx1.d190 fusion protein. Murine splenocytes treated with TAT-Runx1.d190 showed an increase in the transcription of c-Myc within 2 hours, peaking at 4 hours post-treatment and declining thereafter. This effect is dependent on the ability of Runx1.d190 to bind to DNA. The increase in c-Myc transcripts is correlated with increased c-Myc protein levels. Collectively, these data show that Runx1 directly regulates c-Myc transcription in a C-terminal- and DNA-binding-dependent manner.

Urinary bladder cancer susceptibility markers. What do we know about functional mechanisms?

Genome-wide association studies (GWAS) have been successful in the identification of the several urinary bladder cancer (UBC) susceptibility loci, pointing towards novel genes involved in tumor development. Despite that, functional characterization of the identified variants remains challenging, as they mostly map to poorly understood, non-coding regions. Recently, two of the UBC risk variants (PSCA and UGT1A) were confirmed to have functional consequences. They were shown to modify bladder cancer risk by influencing gene expression in an allele-specific manner. Although the role of the other UBC risk variants is unknown, it can be hypothesized-based on studies from different cancer types-that they influence cancer susceptibility by alterations in regulatory networks. The insight into UBC heritability gained through GWAS and further functional studies can impact on cancer prevention and screening, as well as on the development of new biomarkers and future personalized therapies.

Toll-like receptor agonists induce apoptosis in mouse B-cell lymphoma cells by altering NF-κB activation

Toll-like receptor 9 (TLR9) recognizes microbial DNA containing unmethylated cytosyl guanosyl (CpG) sequences, induces innate immune responses, and facilitates antigen-specific adaptive immunity. Recent studies report that in addition to stimulating innate immunity, TLR9 ligands induce apoptosis of TLR9 expressing cancer cells. To understand the mechanism of TLR9-induced apoptosis, we compared the effects of CpG containing oligodeoxynucleotides (CpG ODN) on a mouse B-cell lymphoma line, CH27, with those on mouse splenic B cells. CpG ODN inhibited constitutive proliferation and induced apoptosis in the CH27 B-cell lymphoma line. In contrast, CpG ODN-treated primary B cells were stimulated to proliferate and were rescued from spontaneous apoptosis. The induction of apoptosis required the ODNs to contain the CpG motif and the expression of TLR9 in lymphoma B cells. A decrease in Bcl-xl expression and an increase in Fas and Fas ligand expression accompanied lymphoma B-cell apoptosis. Treatment with the Fas ligand-neutralizing antibody inhibited CpG ODN-induced apoptosis. CpG ODN triggered a transient NF-κB activation in the B-cell lymphoma cell line, which constitutively expresses a high level of c-Myc, while CpG ODN induced sustained increases in NF-κB activation and c-Myc expression in primary B cells. Furthermore, an NF-κB inhibitor inhibited the proliferation of the CH27 B-cell lymphoma line. Our data suggest that the differential responses of lymphoma and primary B cells to CpG ODN are the result of differences in NF-κB activation. The impaired NF-κB activation in the CpG ODN-treated B-cell lymphoma cell line alters the balance between NF-κB and c-Myc, which induces Fas/Fas ligand-dependent apoptosis.

mTOR, metabolism, and the regulation of T-cell differentiation and function

Upon antigen recognition, naive T cells undergo rapid expansion and activation. The energy requirements for this expansion are formidable, and T-cell activation is accompanied by dramatic changes in cellular metabolism. Furthermore, the outcome of antigen engagement is guided by multiple cues derived from the immune microenvironment. Mammalian target of rapamycin (mTOR) is emerging as a central integrator of these signals playing a critical role in driving T-cell differentiation and function. Indeed, multiple metabolic programs are controlled by mTOR signaling. In this review, we discuss the role of mTOR in regulating metabolism and how these pathways intersect with the ability of mTOR to integrate cues that guide the outcome of T-cell receptor engagement.

Methods to quantify microRNAs in the Myc gene network for posttranscriptional gene repression

As a global transcription factor, Myc regulates both protein-coding genes and noncoding microRNA genes. Myc-activated or repressed miRNAs are involved in various pathways to affect tumorigenesis, mediate apoptosis, proliferation, angiogenesis, metastasis, and metabolism downstream of Myc. Functional characterization of miRNAs in the Myc network requires the accurate detection and quantification of miRNA expression levels. Here, we describe two widely used methodologies to determine miRNA expression, including miRNA real-time PCR and miRNA northern analysis.

ORAI3 silencing alters cell proliferation and cell cycle progression via c-myc pathway in breast cancer cells

Members of the Orai family are highly selective calcium ion channels that play an important role in store-operated calcium entry. Among the three known Orai isoforms, Orai3 has gained increased attention, notably for its emerging role in cancer. We recently demonstrated that Orai3 channels are over-expressed in breast cancer (BC) biopsies, and involved specifically in proliferation, cell cycle progression and survival of MCF-7 BC cells. Here, we investigate the downstream signaling mechanisms affected by Orai3 silencing, leading to the subsequent functional impact specifically seen in MCF-7 cancer cells. We report a correlation between Orai3 and c-myc expression in tumor tissues and in the MCF-7 cancer cell line by demonstrating that Orai3 down-regulation reduces both expression and activity of the proto-oncogene c-myc. This is likely mediated through the MAP Kinase pathway, as we observed decreased pERK1/2 levels and cell-cycle arrest in G1 phase after Orai3 silencing. Our results provide strong evidence that the c-myc proto-oncogene is influenced by the store-operated calcium entry channel Orai3 through the MAP kinase pathway. This connection provides new clues in the downstream mechanism linking Orai3 channels and proliferation, cell cycle progression and survival of MCF-7 BC cells.

Not all G-quadruplexes are created equally: an investigation of the structural polymorphism of the c-Myc G-quadruplex-forming sequence and its interaction with the porphyrin TMPyP4

G-quadruplexes, DNA tertiary structures highly localized to functionally important sites within the human genome, have emerged as important new drug targets. The putative G-quadruplex-forming sequence (Pu27) in the NHE-III(1) promoter region of the c-Myc gene is of particular interest as stabilization of this G-quadruplex with TMPyP4 has been shown to repress c-Myc transcription. In this study, we examine the Pu27 G-quadruplex-forming sequence and its interaction with TMPyP4. We report that the Pu27 sequence exists as a heterogeneous mixture of monomeric and higher-order G-quadruplex species in vitro and that this mixture can be partially resolved by size exclusion chromatography (SEC) separation. Within this ensemble of configurations, the equilibrium can be altered by modifying the buffer composition, annealing procedure, and dialysis protocol thereby affecting the distribution of G-quadruplex species formed. TMPyP4 was found to bind preferentially to higher-order G-quadruplex species suggesting the possibility of stabilization of the junctions of the c-Myc G-quadruplex multimers by porphyrin end-stacking. We also examined four modified c-Myc sequences that have been previously reported and found a narrower distribution of G-quadruplex configurations compared to the parent Pu27 sequence. We could not definitively conclude whether these G-quadruplex structures were selected from the original ensemble or if they are new G-quadruplex structures. Since these sequences differ considerably from the wild-type promoter sequence, it is unclear whether their structures have any actual biological relevance. Additional studies are needed to examine how the polymorphic nature of G-quadruplexes affects the interpretation of in vitro data for c-Myc and other G-quadruplexes. The findings reported here demonstrate that experimental conditions contribute significantly to G-quadruplex formation and should be carefully considered, controlled, and reported in detail.

Transcriptional amplification in tumor cells with elevated c-Myc

Elevated expression of the c-Myc transcription factor occurs frequently in human cancers and is associated with tumor aggression and poor clinical outcome. The effect of high levels of c-Myc on global gene regulation is poorly understood but is widely thought to involve newly activated or repressed "Myc target genes." We report here that in tumor cells expressing high levels of c-Myc the transcription factor accumulates in the promoter regions of active genes and causes transcriptional amplification, producing increased levels of transcripts within the cell's gene expression program. Thus, rather than binding and regulating a new set of genes, c-Myc amplifies the output of the existing gene expression program. These results provide an explanation for the diverse effects of oncogenic c-Myc on gene expression in different tumor cells and suggest that transcriptional amplification reduces rate-limiting constraints for tumor cell growth and proliferation.

The MYC-associated protein CDCA7 is phosphorylated by AKT to regulate MYC-dependent apoptosis and transformation

Cell division control protein A7 (CDCA7) is a recently identified target of MYC-dependent transcriptional regulation. We have discovered that CDCA7 associates with MYC and that this association is modulated in a phosphorylation-dependent manner. The prosurvival kinase AKT phosphorylates CDCA7 at threonine 163, promoting binding to 14-3-3, dissociation from MYC, and sequestration to the cytoplasm. Upon serum withdrawal, induction of CDCA7 expression in the presence of MYC sensitized cells to apoptosis, whereas CDCA7 knockdown reduced MYC-dependent apoptosis. The transformation of fibroblasts by MYC was reduced by coexpression of CDCA7, while the non-MYC-interacting protein Δ(156-187)-CDCA7 largely inhibited MYC-induced transformation. These studies provide insight into a new mechanism by which AKT signaling to CDCA7 could alter MYC-dependent growth and transformation, contributing to tumorigenesis.

A critical role for Mnt in Myc-driven T-cell proliferation and oncogenesis

Mnt (Max's next tango) is a Max-interacting transcriptional repressor that can antagonize both the proproliferative and proapoptotic functions of Myc in vitro. To ascertain the physiologically relevant functions of Mnt and to help define the relationship between Mnt and Myc in vivo, we generated a series of mouse strains in which Mnt was deleted in T cells in the absence of endogenous c-Myc or in the presence of ectopic c-Myc. We found that apoptosis caused by loss of Mnt did not require Myc but that ectopic Myc expression dramatically decreased the survival of both Mnt-deficient T cells in vivo and Mnt-deficient MEFs in vitro. Consequently, Myc-driven proliferative expansion of T cells in vitro and thymoma formation in vivo were prevented by the absence of Mnt. Consistent with T-cell models, mouse embryo fibroblasts (MEFs) lacking Mnt were refractory to oncogenic transformation by Myc. Tumor suppression caused by loss of Mnt was linked to increased apoptosis mediated by reactive oxygen species (ROS). Thus, although theoretically and experimentally a Myc antagonist, the dominant physiological role of Mnt appears to be suppression of apoptosis. Our results redefine the physiological relationship between Mnt and Myc and requirements for Myc-driven oncogenesis.

Coordinated silencing of MYC-mediated miR-29 by HDAC3 and EZH2 as a therapeutic target of histone modification in aggressive B-Cell lymphomas

We investigated the transcriptional and epigenetic repression of miR-29 by MYC, HDAC3, and EZH2 in mantle cell lymphoma and other MYC-associated lymphomas. We demonstrate that miR-29 is repressed by MYC through a corepressor complex with HDAC3 and EZH2. MYC contributes to EZH2 upregulation via repression of the EZH2 targeting miR-26a, and EZH2 induces MYC via inhibition of the MYC targeting miR-494 to create positive feedback. Combined inhibition of HDAC3 and EZH2 cooperatively disrupted the MYC-EZH2-miR-29 axis, resulting in restoration of miR-29 expression, downregulation of miR-29-targeted genes, and lymphoma growth suppression in vitro and in vivo. These findings define a MYC-mediated miRNA repression mechanism, shed light on MYC lymphomagenesis mechanisms, and reveal promising therapeutic targets for aggressive B-cell malignancies.

DNA-damaging drug-induced apoptosis sensitized by N-myc in neuroblastoma cells

Neuroblastoma is one of the most common solid tumours in children (8-10% of all malignancies). Over 22% of cases have N-myc amplification associated with aggressively growing neuroblastomas. Oncogene-induced sensitization of cells to apoptosis is an important mechanism for suppression of tumorigenesis. Tumour suppressors often play a critical role in linking oncogenes to apoptotic machinery. For example, activated p53 then targets both intrinsic and extrinsic pathways to promote apoptosis through transcription-dependent and -independent mechanisms. Understanding of the involved mechanisms has important clinical implications. We have employed DNA-damaging drug-induced apoptosis sensitized by oncogene N-myc as a model. DNA damaging drugs trigger high levels of p53, leading to caspase-9 activation in neuroblastoma cells. Inactivation of p53 protects cells from drug-triggered apoptosis sensitized by N-myc. These findings thus define a molecular pathway for mediating DNA-damaging drug-induced apoptosis sensitized by oncogene, and suggest that inactivation of p53 or other components of this apoptotic pathway may confer drug resistance in neuroblastoma cells. The data also suggests that inactivation of apoptotic pathways through co-operating oncogenes may be necessary for the pathogenesis of neuroblastoma with N-myc amplification.

N-myc and noncoding RNAs in neuroblastoma

Neuroblastoma is a pediatric tumor of the sympathetic nervous system. Amplification and overexpression of the MYCN proto-oncogene occurs in approximately 20% of neuroblastomas and is associated with advanced stage disease, rapid tumor progression, and poor prognosis. MYCN encodes the transcriptional regulator N-myc, which has been shown to both up- and downregulate many target genes involved in cell cycle, DNA damage, differentiation, and apoptosis in neuroblastoma. During the last years, it has become clear that N-myc also modulates the expression of several classes of noncoding RNAs, in particular microRNAs. MicroRNAs are the most widely studied noncoding RNA molecules in neuroblastoma. They function as negative regulators of gene expression at the posttranscriptional level in diverse cellular processes. Aberrant regulation of miRNA expression has been implicated in the pathogenesis of neuroblastoma. While the N-myc protein is established as an important regulator of several miRNAs involved in neuroblastoma tumorigenesis, tumor suppressor miRNAs have also been documented to repress MYCN expression and inhibit cell proliferation of MYCN-amplified neuroblastoma cells. It is now becoming increasingly evident that N-myc also regulates the expression of long noncoding RNAs such as T-UCRs and ncRAN. This review summarizes the current knowledge about the interplay between N-myc and noncoding RNAs in neuroblastoma and how this contributes to neuroblastoma tumorigenesis.

In vitro and in vivo anti-colon cancer effects of Garcinia mangostana xanthones extract

Background

Xanthones are a group of oxygen-containing heterocyclic compounds with remarkable pharmacological effects such as anti-cancer, antioxidant, anti-inflammatory, and antimicrobial activities.

Methods

A xanthones extract (81% α-mangostin and 16% γ-mangostin), was prepared by crystallization of a toluene extract of G. mangostana fruit rinds and was analyzed by LC-MS. Anti-colon cancer effect was investigated on HCT 116 human colorectal carcinoma cells including cytotoxicity, apoptosis, anti-tumorigenicity, and effect on cell signalling pathways. The in vivo anti-colon cancer activity was also investigated on subcutaneous tumors established in nude mice.

Results

The extract showed potent cytotoxicity (median inhibitory concentration 6.5 ± 1.0 μg/ml), due to induction of the mitochondrial pathway of apoptosis. Three key steps in tumor metastasis including the cell migration, cell invasion and clonogenicity, were also inhibited. The extract and α-mangostin up-regulate the MAPK/ERK, c-Myc/Max, and p53 cell signalling pathways. The xanthones extract, when fed to nude mice, caused significant growth inhibition of the subcutaneous tumor of HCT 116 colorectal carcinoma cells.

Conclusions

Our data suggest new mechanisms of action of α-mangostin and the G. mangostana xanthones, and suggest the xanthones extract of as a potential anti-colon cancer candidate.

Identification of novel cellular transcription factors that regulate early promoters of human papillomavirus types 18 and 16

BACKGROUND

The long control region (LCR) of human papillomavirus (HPV) regulates early gene transcription by interaction with several viral and cellular transcription factors (TFs).

METHODS

To identify novel TFs that could influence early expression of HPV type 18 (HPV-18) and HPV type 16 (HPV-16), a high-throughput transfection array was used.

RESULTS

Among the 704 TFs tested, 28 activated and 36 inhibited the LCR of HPV-18 by more than 2-fold. For validation, C33 cells were cotransfected with increasing amounts of selected TF expression plasmids in addition to LCR-luciferase vectors of different molecular variants of HPV-18 and HPV-16. Among the TFs identified, only GATA3, FOXA1, and MYC have putative binding sites within the LCR sequence, as indicated using the TRANSFAC database. Furthermore, we demonstrated FOXA1 and MYC in vivo binding to the LCR of both HPV types using chromatin immunoprecipitation assay.

CONCLUSIONS

We identified new TFs implicated in the regulation of the LCR of HPV-18 and HPV-16. Many of these factors are mutated in cancer or are putative cancer biomarkers and could potentially be involved in the regulation of HPV early gene expression.

Anticancer activity and cellular repression of c-MYC by the G-quadruplex-stabilizing 11-piperazinylquindoline is not dependent on direct targeting of the G-quadruplex in the c-MYC promoter

This G-rich region of the c-MYC promoter has been shown to form a G-quadruplex structure that acts as a silencer element for c-MYC transcriptional control. In the present work, we have synthesized a series of 11-substituted quindoline analogues as c-MYC G-quadruplex-stabilizing compounds, and the cell-free and in vitro activity of these compounds were evaluated. Two lead compounds (4 and 12) demonstrated good cell-free profiles, and compound 4 (2-(4-(10H-indolo[3,2-b]quinolin-11-yl)piperazin-1-yl)-N,N-dimethylethanamine) significantly down-regulated c-MYC expression. However, despite the good cell-free activity and the effect of these compounds on c-MYC gene expression, we have demonstrated, using a cellular assay in a Burkitt's lymphoma cell line (CA46-specific), that these effects were not mediated through targeting of the c-MYC G-quadruplex. Thus, caution should be used in assigning the effects of G-quadruplex-interactive compounds that lower c-MYC to direct targeting of these promoter elements unless this assay, or similar ones, demonstrates direct targeting of the G-quadruplex in cells.

Activated ALK collaborates with MYCN in neuroblastoma pathogenesis

Amplification of the MYCN oncogene in childhood neuroblastoma is often accompanied by mutational activation of ALK (anaplastic lymphoma kinase), suggesting their pathogenic cooperation. We generated a transgenic zebrafish model of neuroblastoma in which MYCN-induced tumors arise from a subpopulation of neuroblasts that migrate into the adrenal medulla analog following organogenesis. Coexpression of activated ALK with MYCN in this model triples the disease penetrance and markedly accelerates tumor onset. MYCN overexpression induces adrenal sympathetic neuroblast hyperplasia, blocks chromaffin cell differentiation, and ultimately triggers a developmentally-timed apoptotic response in the hyperplastic sympathoadrenal cells. Coexpression of activated ALK with MYCN provides prosurvival signals that block this apoptotic response and allow continued expansion and oncogenic transformation of hyperplastic neuroblasts, thus promoting progression to neuroblastoma.

MicroRNAs/TP53 feedback circuitry in glioblastoma multiforme

MicroRNAs (miRNAs) are increasingly implicated in regulating cancer initiation and progression. In this study, two miRNAs, miR-25 and -32, are identified as p53-repressed miRNAs by p53-dependent negative regulation of their transcriptional regulators, E2F1 and MYC. However, miR-25 and -32 result in p53 accumulation by directly targeting Mdm2 and TSC1, which are negative regulators of p53 and the mTOR (mammalian target of rapamycin) pathway, respectively, leading to inhibition of cellular proliferation through cell cycle arrest. Thus, there is a recurrent autoregulatory circuit involving expression of p53, E2F1, and MYC to regulate the expression of miR-25 and -32, which are miRNAs that, in turn, control p53 accumulation. Significantly, overexpression of transfected miR-25 and -32 in glioblastoma multiforme cells inhibited growth of the glioblastoma multiforme cells in mouse brain in vivo. The results define miR-25 and -32 as positive regulators of p53, underscoring their role in tumorigenesis in glioblastoma.

Liver hyperplasia after tamoxifen induction of Myc in a transgenic medaka model

Myc is a global transcriptional regulator and one of the most frequently overexpressed oncoproteins in human tumors. It is well established that activation of Myc leads to enhanced cell proliferation but can also lead to increased apoptosis. The use of animal models expressing deregulated levels of Myc has helped to both elucidate its function in normal cells and give insight into how Myc initiates and maintains tumorigenesis. Analyses of the medaka (Oryzias latipes) genome uncovered the unexpected presence of two Myc gene copies in this teleost species. Comparison of these Myc versions to other vertebrate species revealed that one gene, myc17, differs by the loss of some conserved regulatory protein motifs present in all other known Myc genes. To investigate how such differences might affect the basic biological functions of Myc, we generated a tamoxifen-inducible in vivo model utilizing a natural, fish-specific Myc gene. Using this model we show that, when activated, Myc17 leads to increased proliferation and to apoptosis in a dose-dependent manner, similar to human Myc. We have also shown that long-term Myc17 activation triggers liver hyperplasia in adult fish, allowing this newly established transgenic medaka model to be used to study the transition from hyperplasia to liver cancer and to identify Myc-induced tumorigenesis modifiers.

Expression of candidate genes related to metabolism, immunity and cellular stress during massive mortality in the American oyster Crassostrea virginica larvae in relation to biochemical and physiological parameters

Quantification of mRNA of genes related to metabolism, immunity and cellular stress was examined in relation to a massive mortality event during the culture of American oyster larvae, Crassostrea virginica which was probably, in regard to previous microbiological analysis, induced by Vibrio infection. To document molecular changes associated with the mortality event, mRNA levels were compared to biochemical and physiological data, previously described in a companion paper. Among the 18 genes studied, comparatively to the antibiotic control, 10 showed a lower relative gene expression when the massive mortality occurred. Six of them are presumed to be related to metabolism, corroborating the metabolic depression associated with the mortality event suggested by biochemical and physiological analyses. Relationships between the regulation of antioxidant enzyme activities, lipid peroxidation, and the mRNA abundance of genes linked to oxidative stress, cytoprotection, and immune response are also discussed. Finally, we observed an increase in the transcript abundance of two genes involved in apoptosis and cell regulation simultaneously with mortality, suggesting that these processes might be linked.

Inhibition of the intrinsic but not the extrinsic apoptosis pathway accelerates and drives MYC-driven tumorigenesis towards acute myeloid leukemia

Myc plays an important role in tumor development, including acute myeloid leukemia (AML). However, MYC is also a powerful inducer of apoptosis, which is one of the major failsafe programs to prevent cancer development. To clarify the relative importance of the extrinsic (death receptor-mediated) versus the intrinsic (mitochondrial) pathway of apoptosis in MYC-driven AML, we coexpressed MYC together with anti-apoptotic proteins of relevance for AML; BCL-X(L)/BCL-2 (inhibiting the intrinsic pathway) or FLIP(L) (inhibiting the extrinsic pathway), in hematopoietic stems cells (HSCs). Transplantation of HSCs expressing MYC into syngeneic recipient mice resulted in development of AML and T-cell lymphomas within 7-9 weeks as expected. Importantly, coexpression of MYC together with BCL-X(L)/BCL-2 resulted in strongly accelerated kinetics and favored tumor development towards aggressive AML. In contrast, coexpression of MYC and FLIP(L) did neither accelerate tumorigenesis nor change the ratio of AML versus T-cell lymphoma. However, a change in distribution of immature CD4(+)CD8(+) versus mature CD4(+) T-cell lymphoma was observed in MYC/FLIP(L) mice, possibly as a result of increased survival of the CD4+ population, but this did not significantly affect the outcome of the disease. In conclusion, our findings provide direct evidence that BCL-X(L) and BCL-2 but not FLIP(L) acts in synergy with MYC to drive AML development.

The Warburg effect in 2012

PURPOSE OF REVIEW

A revival of interest in tumor metabolism is underway and here we discuss recent results with a focus on the central theme of the Warburg effect, aerobic glycolysis.

RECENT FINDINGS

The M2 tumor-specific isoform of pyruvate kinase has generated much interest, but it has now been reported that PKM2 is not specific to tumors. Despite this setback, the reciprocal regulation of PKM2, prolyl hydroxylase 3 and HIF-1 in a positive feedback loop shows that PKM2 is important to tumor metabolism. Hexokinase II was reported to be a crucial regulator of glycolysis in glioblastoma multiforme, and the importance of lactate dehydrogenase was underlined by evidence that a 'lactate-based dialog' exists between cancer cells and endothelial cells. A growing appreciation of the role of oncogenes and tumor suppressor genes in the Warburg effect was reflected in reports of the regulation of glutamine metabolism by p53, the role of c-Myc in the high glucose uptake of tumors, and the regulation of ectonucleoside triphosphate diphosphohydrolase 5 (ENTPD5) and ATP consumption by AKT. The sirtuins, SIRT3 and SIRT6, were also shown to play central roles in aerobic glycolysis and other aspects of tumor metabolism.

SUMMARY

The results discussed illustrate the growing integration of the previously distinct fields of molecular biological and metabolic cancer research and show that this synergy is beginning to yield a more complete and comprehensive understanding of the tumor cell.

Embryonic stem cell-specific signatures in cancer: insights into genomic regulatory networks and implications for medicine

Embryonic stem (ES) cells are of great interest as a model system for studying early developmental processes and because of their potential therapeutic applications in regenerative medicine. Obtaining a systematic understanding of the mechanisms that control the 'stemness' - self-renewal and pluripotency - of ES cells relies on high-throughput tools to define gene expression and regulatory networks at the genome level. Such recently developed systems biology approaches have revealed highly interconnected networks in which multiple regulatory factors act in combination. Interestingly, stem cells and cancer cells share some properties, notably self-renewal and a block in differentiation. Recently, several groups reported that expression signatures that are specific to ES cells are also found in many human cancers and in mouse cancer models, suggesting that these shared features might inform new approaches for cancer therapy. Here, we briefly summarize the key transcriptional regulators that contribute to the pluripotency of ES cells, the factors that account for the common gene expression patterns of ES and cancer cells, and the implications of these observations for future clinical applications.

The direct Myc target Pim3 cooperates with other Pim kinases in supporting viability of Myc-induced B-cell lymphomas

The Pim kinases are weak oncogenes. However, when co-expressed with a strong oncogene, such as c-Myc, Pim kinases potentiate the oncogenic effect resulting in an acceleration of tumorigenesis. In this study we show that the least studied Pim kinase, Pim-3, is encoded by a gene directly regulated by c-Myc via binding to one of the conserved E-boxes within the Pim3 gene. Accordingly, lymphomas arising in Myc-transgenic mice and Burkitt lymphoma cell lines exhibit elevated levels of Pim-3. Interestingly, inhibition of Pim kinases by a novel pan-Pim kinase inhibitor, Pimi, in Myc-induced lymphoma results in cell death that appears independent of caspases. The data indicate that Pim kinase inhibition could be a viable treatment strategy in certain human lymphomas that rely on Pim-3 kinase expression.