C-myc overexpression and p53 loss cooperate to promote genomic instability

Exploring Myc puzzle: Insights into cancer, stem cell biology, and PPI networks

"The grand orchestrator," "Universal Amplifier," "double-edged sword," and "Undruggable" are just some of the Myc oncogene so-called names. It has been around 40 years since the discovery of the Myc, and it remains in the mainstream of cancer treatment drugs. Myc is part of basic helix-loop-helix leucine zipper (bHLH-LZ) superfamily proteins, and its dysregulation can be seen in many malignant human tumors. It dysregulates critical pathways in cells that are connected to each other, such as proliferation, growth, cell cycle, and cell adhesion, impacts miRNAs action, intercellular metabolism, DNA replication, differentiation, microenvironment regulation, angiogenesis, and metastasis. Myc, surprisingly, is used in stem cell research too. Its family includes three members, MYC, MYCN, and MYCL, and each dysfunction was observed in different cancer types. This review aims to introduce Myc and its function in the body. Besides, Myc deregulatory mechanisms in cancer cells, their intricate aspects will be discussed. We will look at promising drugs and Myc-based therapies. Finally, Myc and its role in stemness, Myc pathways based on PPI network analysis, and future insights will be explained.

Lessons in aging from Myc knockout mouse models

Despite MYC being among the most intensively studied oncogenes, its role in normal development has not been determined as Myc-/- mice do not survival beyond mid-gestation. Myc ± mice live longer than their wild-type counterparts and are slower to accumulate many age-related phenotypes. However, Myc haplo-insufficiency likely conceals other important phenotypes as many high-affinity Myc targets genes continue to be regulated normally. By delaying Myc inactivation until after birth it has recently been possible to study the consequences of its near-complete total body loss and thus to infer its normal function. Against expectation, these "MycKO" mice lived significantly longer than control wild-type mice but manifested a marked premature aging phenotype. This seemingly paradoxical behavior was potentially explained by a >3-fold lower lifetime incidence of cancer, normally the most common cause of death in mice and often Myc-driven. Myc loss accelerated the accumulation of numerous "Aging Hallmarks", including the loss of mitochondrial and ribosomal structural and functional integrity, the generation of reactive oxygen species, the acquisition of genotoxic damage, the detrimental rewiring of metabolism and the onset of senescence. In both mice and humans, normal aging in many tissues was accompaniued by the downregulation of Myc and the loss of Myc target gene regulation. Unlike most mouse models of premature aging, which are based on monogenic disorders of DNA damage recognition and repair, the MycKO mouse model directly impacts most Aging Hallmarks and may therefore more faithfully replicate the normal aging process of both mice and humans. It further establishes that the strong association between aging and cancer can be genetically separated and is maintained by a single gene.

Multiple-Gene Regulation for Enhanced Antitumor Efficacy with Branch-PCR-Assembled TP53 and MYC Gene Nanovector

Multiple proteins are involved in network regulation through the crosstalk of different signaling pathways in cancers. Here, we propose a novel strategy of genome therapy with branch-PCR-assembled gene nanovectors to perform network-based gene regulation at multiple levels for cancer therapy. To validate network-based multiplex-gene regulation for genome therapy, we chose to simultaneously target one tumor suppressor gene (TP53) and one oncogene (MYC) in two different signaling pathways. The results showed that, compared to gene nanovectors targeting single genes (NP-TP53 and NP-shMYC), branch-PCR-assembled gene nanovectors simultaneously expressing p53 proteins and MYC shRNA arrays (NP-TP53-shMYC) showed enhanced antitumor efficacy in both MDA-MB-231 cancer cells and an MDA-MB-231-tumor-bearing mouse model. These findings indicate the feasibility and effectiveness of genome therapy in cancer therapy.

Normal and Neoplastic Growth Suppression by the Extended Myc Network

Among the first discovered and most prominent cellular oncogenes is MYC, which encodes a bHLH-ZIP transcription factor (Myc) that both activates and suppresses numerous genes involved in proliferation, energy production, metabolism and translation. Myc belongs to a small group of bHLH-ZIP transcriptional regulators (the Myc Network) that includes its obligate heterodimerization partner Max and six "Mxd proteins" (Mxd1-4, Mnt and Mga), each of which heterodimerizes with Max and largely opposes Myc's functions. More recently, a second group of bHLH-ZIP proteins (the Mlx Network) has emerged that bears many parallels with the Myc Network. It is comprised of the Myc-like factors ChREBP and MondoA, which, in association with the Max-like member Mlx, regulate smaller and more functionally restricted repertoires of target genes, some of which are shared with Myc. Opposing ChREBP and MondoA are heterodimers comprised of Mlx and Mxd1, Mxd4 and Mnt, which also structurally and operationally link the two Networks. We discuss here the functions of these "Extended Myc Network" members, with particular emphasis on their roles in suppressing normal and neoplastic growth. These roles are complex due to the temporal- and tissue-restricted expression of Extended Myc Network proteins in normal cells, their regulation of both common and unique target genes and, in some cases, their functional redundancy.

Targeted Downregulation of MYC through G-quadruplex Stabilization by DNAi

Modulating the expression or function of the enigmatic MYC protein has demonstrated efficacy in an array of cancer types and a marked potential therapeutic index and safety profile. Despite its high therapeutic value, specific and selective inhibitors or downregulating therapeutics have proven difficult to develop. In the current study, we expanded our work on a MYC promoter G-quadruplex (G4) stabilizing DNA clamp to develop an oligonucleotide interfering DNA (DNAi) therapeutic. We explored six DNAi for G4-stabilization through EMSA, DMS footprinting, and thermal stability studies, focusing on the DNAi 5T as the lead therapeutic. 5T, but not its scramble control 5Tscr, was then shown to enter the nucleus, modulate cell viability, and decrease MYC expression through G4-stabilization. DNAi 5T is thus described to be our lead DNAi, targeting MYC regulation through stabilization of the higher-order DNA G4 structure in the proximal promoter, and it is poised for further preclinical development as an anticancer therapeutic.

Polyploid giant cancer cells, stemness and epithelial-mesenchymal plasticity elicited by human cytomegalovirus

A growing body of evidence is recognizing human cytomegalovirus (HCMV) as a potential oncogenic virus. We hereby provide the first experimental in vitro evidence for HCMV as a reprogramming vector, through the induction of dedifferentiation of mature human mammary epithelial cells (HMECs), generation of a polyploid giant cancer cell (PGCC) phenotype characterized by sustained growth of blastomere-like cells, in concordance with the acquisition of embryonic stem cells characteristics and epithelial-mesenchymal plasticity. HCMV presence parallels the succession of the observed cellular and molecular events potentially ensuing the transformation process. Correlation between PGCCs detection and HCMV presence in breast cancer tissue further validates our hypothesis in vivo. Our study indicates that some clinical HCMV strains conserve the potential to transform HMECs and fit with a "blastomere-like" model of oncogenesis, which may be relevant in the pathophysiology of breast cancer and other adenocarcinoma, especially of poor prognosis.

Evolution of late-stage metastatic melanoma is dominated by aneuploidy and whole genome doubling

Although melanoma is initiated by acquisition of point mutations and limited focal copy number alterations in melanocytes-of-origin, the nature of genetic changes that characterise lethal metastatic disease is poorly understood. Here, we analyze the evolution of human melanoma progressing from early to late disease in 13 patients by sampling their tumours at multiple sites and times. Whole exome and genome sequencing data from 88 tumour samples reveals only limited gain of point mutations generally, with net mutational loss in some metastases. In contrast, melanoma evolution is dominated by whole genome doubling and large-scale aneuploidy, in which widespread loss of heterozygosity sculpts the burden of point mutations, neoantigens and structural variants even in treatment-naïve and primary cutaneous melanomas in some patients. These results imply that dysregulation of genomic integrity is a key driver of selective clonal advantage during melanoma progression.

Circadian Genes as Therapeutic Targets in Pancreatic Cancer

Pancreatic cancer is one of the most lethal cancers worldwide due to its symptoms, early metastasis, and chemoresistance. Thus, the mechanisms contributing to pancreatic cancer progression require further exploration. Circadian rhythms are the daily oscillations of multiple biological processes regulated by an endogenous clock. Several evidences suggest that the circadian clock may play an important role in the cell cycle, cell proliferation and apoptosis. In addition, timing of chemotherapy or radiation treatment can influence the efficacy and toxicity treatment. Here, we revisit the studies on circadian clock as an emerging target for therapy in pancreatic cancer. We highlight those potential circadian genes regulators that are commonly affected in pancreatic cancer according to most recent reports.

Oncogenic MYC Induces the Impaired Ribosome Biogenesis Checkpoint and Stabilizes p53 Independent of Increased Ribosome Content

The role of MYC in regulating p53 stability as a function of increased ribosome biogenesis is controversial. On the one hand, it was suggested that MYC drives the overexpression of ribosomal proteins (RP)L5 and RPL11, which bind and inhibit HDM2, stabilizing p53. On the other, it has been proposed that increased ribosome biogenesis leads the consumption of RPL5/RPL11 into nascent ribosomes, reducing p53 levels and enhancing tumorigenesis. Here, we show that the components that make up the recently described impaired ribosome biogenesis checkpoint (IRBC) complex, RPL5, RPL11, and 5S rRNA, are reduced following MYC silencing. This leads to a rapid reduction in p53 protein half-life in an HDM2-dependent manner. In contrast, MYC induction leads to increased ribosome biogenesis and p53 protein stabilization. Unexpectedly, there is no change in free RPL5/RPL11 levels, but there is a striking increase in IRBC complex bound to HDM2. Our data support a cell-intrinsic tumor-suppressor response to MYC expression, which is presently being exploited to treat cancer. SIGNIFICANCE: Oncogenic MYC induces the impaired ribosome biogenesis checkpoint, which could be potentially targeted for cancer treatment.

Microhomology-mediated end joining drives complex rearrangements and overexpression of MYC and PVT1 in multiple myeloma

MYC is a widely acting transcription factor and its deregulation is a crucial event in many human cancers. MYC is important biologically and clinically in multiple myeloma, but the mechanisms underlying its dysregulation are poorly understood. We show that MYC rearrangements are present in 36.0% of newly diagnosed myeloma patients, as detected in the largest set of next generation sequencing data to date (n=1,267). Rearrangements were complex and associated with increased expression of MYC and PVT1, but not other genes at 8q24. The highest effect on gene expression was detected in cases where the MYC locus is juxtaposed next to super-enhancers associated with genes such as IGH, IGK, IGL, TXNDC5/BMP6, FAM46C and FOXO3. We identified three hotspots of recombination at 8q24, one of which is enriched for IGH-MYC translocations. Breakpoint analysis indicates primary myeloma rearrangements involving the IGH locus occur through non-homologous end joining, whereas secondary MYC rearrangements occur through microhomology-mediated end joining. This mechanism is different to lymphomas, where non-homologous end joining generates MYC rearrangements. Rearrangements resulted in overexpression of key genes and chromatin immunoprecipitation-sequencing identified that HK2, a member of the glucose metabolism pathway, is directly over-expressed through binding of MYC at its promoter.

Emerging Roles of C-Myc in Cancer Stem Cell-Related Signaling and Resistance to Cancer Chemotherapy: A Potential Therapeutic Target Against Colorectal Cancer

Myc is a nuclear transcription factor that mainly regulates cell growth, cell cycle, metabolism, and survival. Myc family proteins contain c-Myc, n-Myc, and l-Myc. Among them, c-Myc can become a promising therapeutic target molecule in cancer. Cancer stem cells (CSCs) are known to be responsible for the therapeutic resistance. In the previous study, we demonstrated that c-Myc mediates drug resistance of colorectal CSCs using a patient-derived primary three-dimensional (3D) organoid culture. In this review, we mainly focus on the roles of c-Myc-related signaling in the regulation of CSCs, chemotherapy resistance, and colorectal cancer organoids. Finally, we introduce the various types of c-Myc inhibitors and propose the possibility of c-Myc as a therapeutic target against colorectal cancer.

Metabolic and oncogenic adaptations to pyruvate dehydrogenase inactivation in fibroblasts

Eukaryotic cell metabolism consists of processes that generate available energy, such as glycolysis, the tricarboxylic acid (TCA) cycle, and oxidative phosphorylation (Oxphos), and those that consume it, including macromolecular synthesis, the maintenance of ionic gradients, and cellular detoxification. By converting pyruvate to acetyl-CoA (AcCoA), the pyruvate dehydrogenase (PDH) complex (PDC) links glycolysis and the TCA cycle. Surprisingly, disrupting the connection between glycolysis and the TCA cycle by inactivation of PDC has only minor effects on cell replication. However, the molecular basis for this metabolic re-equilibration is unclear. We report here that CRISPR/Cas9-generated PDH-knockout (PDH-KO) rat fibroblasts reprogrammed their metabolism and their response to short-term c-Myc (Myc) oncoprotein overexpression. PDH-KO cells replicated normally but produced surprisingly little lactate. They also exhibited higher rates of glycolysis and Oxphos. In addition, PDH-KO cells showed altered cytoplasmic and mitochondrial pH, redox states, and mitochondrial membrane potential (ΔΨM). Conditionally activated Myc expression affected some of these parameters in a PDH-dependent manner. PDH-KO cells had increased oxygen consumption rates in response to glutamate, but not to malate, and were depleted in all TCA cycle substrates between α-ketoglutarate and malate despite high rates of glutaminolysis, as determined by flux studies with isotopically labeled glutamine. Malate and pyruvate were diverted to produce aspartate, thereby potentially explaining the failure to accumulate lactate. We conclude that PDH-KO cells maintain proliferative capacity by utilizing glutamine to supply high rates of AcCoA-independent flux through the bottom portion of the TCA cycle while accumulating pyruvate and aspartate that rescue their redox defects.

Expression of Mina53 and its Significance in Gastric Carcinoma

Aim

To study the expression of Mina53 and its relationships with clinicopathological characteristics, antioncogene inactivation and tumor proliferation in human gastric carcinoma, and to explore the role of Mina53 in carcinogenesis and tumor progression.

Methods

Expression of Mina53 and proliferating cell nuclear antigen (PCNA) was determined in gastric carcinoma (n=79), gastric dysplasia (n=21) and normal gastric tissues (n=20), while p53 was measured in gastric carcinoma tissues by immunohistochemistry.

Results

Mina53 was negatively expressed in all normal mucosa tissues. Dysplasia specimens showed weakly positive staining for Mina53 in 3 of 21 cases. Elevated expression of Mina53 was observed in 72 (91.1%) of the gastric carcinomas. No significant associations were found between Mina53 and clinicopathological characteristics such as sex, age, histological differentiation, distant metastasis and lymph node metastasis (p>0.05). There was a significant association with depth of invasion (χ2=5.385, p<0.05) and TMN stage (χ2=6.255, p<0.05). In gastric carcinoma, positive staining for p53 was detected in 53 of 79 cases (67.1%), showing a significant association with Mina53 (χ2=5.161, p<0.05). The mean (± SD) PCNA labeling index for gastric carcinoma was 39.47±16.92%. Mina53 expression was positively associated with PCNA level (r=0.756, p<0.01).

Conclusion

Mina53 was overexpressed in gastric carcinoma and associated with tumor proliferation and antioncogene inactivation. Mina53 could therefore play an important role in the carcinogenesis and progression of gastric carcinoma.

Sequential adaptive changes in a c-Myc-driven model of hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is a common cancer that frequently overexpresses the c-Myc (Myc) oncoprotein. Using a mouse model of Myc-induced HCC, we studied the metabolic, biochemical, and molecular changes accompanying HCC progression, regression, and recurrence. These involved altered rates of pyruvate and fatty acid β-oxidation and the likely re-directing of glutamine into biosynthetic rather than energy-generating pathways. Initial tumors also showed reduced mitochondrial mass and differential contributions of electron transport chain complexes I and II to respiration. The uncoupling of complex II's electron transport function from its succinate dehydrogenase activity also suggested a mechanism by which Myc generates reactive oxygen species. RNA sequence studies revealed an orderly progression of transcriptional changes involving pathways pertinent to DNA damage repair, cell cycle progression, insulin-like growth factor signaling, innate immunity, and further metabolic re-programming. Only a subset of functions deregulated in initial tumors was similarly deregulated in recurrent tumors thereby indicating that the latter can "normalize" some behaviors to suit their needs. An interactive and freely available software tool was developed to allow continued analyses of these and other transcriptional profiles. Collectively, these studies define the metabolic, biochemical, and molecular events accompanyingHCCevolution, regression, and recurrence in the absence of any potentially confounding therapies.

Links between DNA Replication, Stem Cells and Cancer

Cancers can be categorized into two groups: those whose frequency increases with age, and those resulting from errors during mammalian development. The first group is linked to DNA replication through the accumulation of genetic mutations that occur during proliferation of developmentally acquired stem cells that give rise to and maintain tissues and organs. These mutations, which result from DNA replication errors as well as environmental insults, fall into two categories; cancer driver mutations that initiate carcinogenesis and genome destabilizing mutations that promote aneuploidy through excess genome duplication and chromatid missegregation. Increased genome instability results in accelerated clonal evolution leading to the appearance of more aggressive clones with increased drug resistance. The second group of cancers, termed germ cell neoplasia, results from the mislocation of pluripotent stem cells during early development. During normal development, pluripotent stem cells that originate in early embryos give rise to all of the cell lineages in the embryo and adult, but when they mislocate to ectopic sites, they produce tumors. Remarkably, pluripotent stem cells, like many cancer cells, depend on the Geminin protein to prevent excess DNA replication from triggering DNA damage-dependent apoptosis. This link between the control of DNA replication during early development and germ cell neoplasia reveals Geminin as a potential chemotherapeutic target in the eradication of cancer progenitor cells.

Clinical and molecular relevance of mutant-allele tumor heterogeneity in breast cancer

PURPOSE

Intra-tumor heterogeneity (ITH) plays a pivotal role in driving breast cancer progression and therapeutic resistance. We used a mutant-allele tumor heterogeneity (MATH) algorithm to measure ITH and explored its correlation with clinical parameters and multi-omics data.

METHODS

We assessed 916 female breast cancer patients from The Cancer Genome Atlas. We calculated the MATH values from whole-exome sequencing data and further investigated their correlation with clinical characteristics, somatic mutations, somatic copy number alterations (SCNAs), and gene enrichment.

RESULTS

The patients were divided into low, intermediate, and high MATH groups. High T stage, African American race, and triple-negative or basal-like subtype were associated with a higher MATH level (all P < 0.001). In hormone receptor-positive and human epidermal growth factor receptor-negative patients, the high MATH group showed a tendency toward a worse overall survival (P = 0.052); Furthermore, the TP53 mutation rate increased as MATH was elevated (P < 0.001), whereas CDH1 mutations were correlated with a lower level of MATH (P = 0.002). Several focal and arm-level SCNA events were more common in the high MATH group (P < 0.05), including Chr8q24 with only the MYC gene in the "peak" region. Similarly, high MATH was associated with gene set enrichment related to the MYC pathway and proliferation.

CONCLUSION

Our integrative analysis reveals the clinical and genetic relevance of ITH in breast cancer. These results also suggest the origin and natural history of clonal evolution and intra-tumor genetic heterogeneity, which warrant further investigation.

Nucleic acid clamp-mediated recognition and stabilization of the physiologically relevant MYC promoter G-quadruplex

The MYC proto-oncogene is upregulated, often at the transcriptional level, in ∼80% of all cancers. MYC's promoter is governed by a higher order G-quadruplex (G4) structure in the NHE III₁ region. Under a variety of conditions, multiple isoforms have been described to form from the first four continuous guanine runs (G4_1–4) predominating under the physiologically relevant supercoiled conditions. In the current study, short oligonucleotides complementing the 5′- and 3′-regions flanking the G4 have been connected by an abasic linker to form G4 clamps, varying both linker length and G4 isoform being targeted. Clamp A with an 18 Å linker was found to have marked affinity for its target isomer (G4_1–4) over the other major structures (G4_2–5 and G4_1–5, recognized by clamps B and C, respectively), and to be able to shift equilibrating DNA to foster greater G4 formation. In addition, clamp A, but not B or C, is able to modulate MYC promoter activity with a significant and dose-dependent effect on transcription driven by the Del4 plasmid. This linked clamp-mediated approach to G4 recognition represents a novel therapeutic mechanism with specificity for an individual promoter structure, amenable to a large array of promoters.

Decoding c-Myc networks of cell cycle and apoptosis regulated genes in a transgenic mouse model of papillary lung adenocarcinomas

The c-Myc gene codes for a basic-helix-loop-helix-leucine zipper transcription factor protein and is reported to be frequently over-expressed in human cancers. Given that c-Myc plays an essential role in neoplastic transformation we wished to define its activity in lung cancer and therefore studied its targeted expression to respiratory epithelium in a transgenic mouse disease model. Using histological well-defined tumors, transcriptome analysis identified novel c-Myc responsive cell cycle and apoptosis genes that were validated as direct c-Myc targets using EMSA, Western blotting, gene reporter and ChIP assays.Through computational analyses c-Myc cooperating transcription factors emerged for repressed and up-regulated genes in cancer samples, namely Klf7, Gata3, Sox18, p53 and Elf5 and Cebpα, respectively. Conversely, at promoters of genes regulated in transgenic but non-carcinomatous lung tissue enriched binding sites for c-Myc, Hbp1, Hif1 were observed. Bioinformatic analysis of tumor transcriptomic data revealed regulatory gene networks and highlighted mortalin and moesin as master regulators while gene reporter and ChIP assays in the H1299 lung cancer cell line as well as cross-examination of published ChIP-sequence data of 7 human and 2 mouse cell lines provided strong evidence for the identified genes to be c-Myc targets. The clinical significance of findings was established by evaluating expression of orthologous proteins in human lung cancer. Taken collectively, a molecular circuit for c-Myc-dependent cellular transformation was identified and the network analysis broadened the perspective for molecularly targeted therapies.

Structurally diverse c-Myc inhibitors share a common mechanism of action involving ATP depletion

The c-Myc (Myc) oncoprotein is deregulated in a large proportion of diverse human cancers. Considerable effort has therefore been directed at identifying pharmacologic inhibitors as potential anti-neoplastic agents. Three such groups of small molecule inhibitors have been described. The first is comprised of so-called “direct” inhibitors, which perturb Myc's ability to form productive DNA-binding heterodimers in association with its partner, Max. The second group is comprised of indirect inhibitors, which largely function by targeting the BET-domain protein BRD4 to prevent the proper formation of transcriptional complexes that assemble in response to Myc-Max DNA binding. Thirdly, synthetic lethal inhibitors cause the selective apoptosis of Myc over-expressing either by promoting mitotic catastrophe or altering Myc protein stability. We report here a common mechanism by which all Myc inhibitors, irrespective of class, lead to eventual cellular demise. This involves the depletion of ATP stores due to mitochondrial dysfunction and the eventual down-regulation of Myc protein. The accompanying metabolic de-regulation causes neutral lipid accumulation, cell cycle arrest, and an attempt to rectify the ATP deficit by up-regulating AMP-activated protein kinase (AMPK). These responses are ultimately futile due to the lack of functional Myc to support the requisite anabolic response. Finally, the effects of Myc depletion on ATP levels, cell cycle arrest, differentiation and AMPK activation can be mimicked by pharmacologic inhibition of the mitochondrial electron transport chain without affecting Myc levels. Thus, all Myc inhibitors promote a global energy collapse that appears to underlie many of their phenotypic consequences.

Transmembrane domain is crucial to the subcellular localization and function of Myc target 1

Deregulation of c-MYC occurs in a variety of human cancers. Overexpression of c-MYC promotes cell growth, proliferation, apoptosis, transformation and genomic instability. MYC target 1 (MYCT1) is a direct target gene of c-MYC, and its murine homologue MT-MC1 recapitulated multiple c-Myc-related phenotypes. However, the molecular mechanism of MYCT1 remains unclear. Here, we identified the transmembrane (TM) domain of MYCT1, not the nuclear localization sequence, is indispensable to the vesicle-associated localization of MYCT1 protein in the cytoplasmic membrane vesicle. Overexpression of MYCT1, not MYCT1 (ΔTM), decreased cell viability under serum deprivation and increased tumour cell migration ability. We further identified CKAP4 interacted with MYCT1 and contributed to the function of MYCT1. In addition, we found that a mutation, A88D, which is observed in patient sample, changed the localization, and abolished the effect on cell viability and cell migration, suggesting that the TM domain is critical to MYCT1.

MDL-1, a growth- and tumor-suppressor, slows aging and prevents germline hyperplasia and hypertrophy in C. elegans

In C. elegans, increased lifespan in daf-2 insulin/IGF-1 receptor mutants is accompanied by up-regulation of the MDL-1 Mad basic helix-loop-helix leucine zipper transcription factor. Here we describe the role of mdl-1 in C. elegans germline proliferation and aging. The deletion allele mdl-1(tm311) shortened lifespan, and did so significantly more so in long-lived daf-2 mutants implying that mdl-1(+) contributes to effects of daf-2 on lifespan. mdl-1 mutant hermaphrodites also lay increased numbers of unfertilized oocytes. During aging, unfertilized oocytes in the uterus develop into tumors, whose development was accelerated by mdl-1(tm311). Opposite phenotypes were seen in daf-2 mutants, i.e. mdl-1 and daf-2 mutant germlines are hyperplastic and hypoplastic, respectively. Thus, MDL-1, like its mammalian orthologs, is an inhibitor of cell proliferation and growth that slows progression of an age-related pathology in C. elegans (uterine tumors). In addition, intestine-limited rescue of mdl-1 increased lifespan but not to wild type levels. Thus, mdl-1 likely acts both in the intestine and the germline to influence age-related mortality.

An unexpected role for caspase-2 in neuroblastoma

Caspase-2 has been implicated in various cellular functions, including cell death by apoptosis, oxidative stress response, maintenance of genomic stability and tumor suppression. The loss of the caspase-2 gene (Casp2) enhances oncogene-mediated tumorigenesis induced by E1A/Ras in athymic nude mice, and also in the Eμ-Myc lymphoma and MMTV/c-neu mammary tumor mouse models. To further investigate the function of caspase-2 in oncogene-mediated tumorigenesis, we extended our studies in the TH-MYCN transgenic mouse model of neuroblastoma. Surprisingly, we found that loss of caspase-2 delayed tumorigenesis in the TH-MYCN neuroblastoma model. In addition, tumors from TH-MYCN/Casp2^−/− mice were predominantly thoracic paraspinal tumors and were less vascularized compared with tumors from their TH-MYCN/Casp2^+/+ counterparts. We did not detect any differences in the expression of neuroblastoma-associated genes in TH-MYCN/Casp2^−/− tumors, or in the activation of Ras/MAPK signaling pathway that is involved in neuroblastoma progression. Analysis of expression array data from human neuroblastoma samples showed a correlation between low caspase-2 levels and increased survival. However, caspase-2 levels correlated with clinical outcome only in the subset of MYCN-non-amplified human neuroblastoma. These observations indicate that caspase-2 is not a suppressor in MYCN-induced neuroblastoma and suggest a tissue and context-specific role for caspase-2 in tumorigenesis.

Small-molecule inhibitors of the Myc oncoprotein

The c-Myc (Myc) oncoprotein is among the most attractive of cancer targets given that it is de-regulated in the majority of tumors and that its inhibition profoundly affects their growth and/or survival. However, its role as a seldom-mutated transcription factor, its lack of enzymatic activity for which suitable pharmaceutical inhibitors could be crafted and its expression by normal cells have largely been responsible for its being viewed as "undruggable". Work over the past several years, however, has begun to reverse this idea by allowing us to view Myc within the larger context of global gene regulatory control. Thus, Myc and its obligate heterodimeric partner, Max, are integral to the coordinated recruitment and post-translational modification of components of the core transcriptional machinery. Moreover, Myc over-expression re-programs numerous critical cellular functions and alters the cell's susceptibility to their inhibition. This new knowledge has therefore served as a framework upon which to develop new pharmaceutical approaches. These include the continuing development of small molecules which act directly to inhibit the critical Myc-Max interaction, those which act indirectly to prevent Myc-directed post-translational modifications necessary to initiate productive transcription and those which inhibit vital pathways upon which the Myc-transformed cell is particularly reliant. This article is part of a Special Issue entitled: Myc proteins in cell biology and pathology.

Mammalian MYC Proteins and Cancer

The MYC family of proteins is a group of basic-helix-loop-helix-leucine zipper transcription factors that feature prominently in cancer. Overexpression of MYC is observed in the vast majority of human malignancies and promotes an extraordinary set of changes that impact cell proliferation, growth, metabolism, DNA replication, cell cycle progression, cell adhesion, differentiation, and metastasis. The purpose of this review is to introduce the reader to the mammalian family of MYC proteins, highlight important functional properties that endow them with their potent oncogenic potential, describe their mechanisms of action and of deregulation in cancer cells, and discuss efforts to target the unique properties of MYC, and of MYC-driven tumors, to treat cancer.

Fumigaclavine C from a marine-derived fungus Aspergillus fumigatus induces apoptosis in MCF-7 breast cancer cells

Recently, much attention has been given to discovering natural compounds as potent anti-cancer candidates. In the present study, the anti-cancer effects of fumigaclavine C, isolated from a marine-derived fungus, Aspergillus fumigatus, was evaluated in vitro. In order to investigate the impact of fumigaclavine C on inhibition of proliferation and induction of apoptosis in breast cancer, MCF-7 cells were treated with various concentrations of fumigaclavine C, and fumigaclavine C showed significant cytotoxicity towards MCF-7 cells. Anti-proliferation was analyzed via cell mobility and mitogen-activated protein kinase (MAPK) signaling pathway. In addition, fumigaclavine C showed potent inhibition on the protein and gene level expressions of MMP-2, -9 in MCF-7 cells which were manifested in Western blot and reverse transcription polymerase chain reaction (RT-PCR) results. The apoptosis induction abilities of the fumigaclvine C was studied by analyzing the expression of apoptosis related proteins, cell cycle analysis, DNA fragmentation and molecular docking studies. It was found that fumigaclavine C fragmented the MCF-7 cell DNA and arrested the cell cycle by modulating the apoptotic protein expressions. Moreover, fumigaclavine C significantly down-regulated the NF-kappa-B cell survival pathway. Collectively, data suggest that fumigaclavine C has a potential to be developed as a therapeutic candidate for breast cancer.

Transcriptional control of DNA replication licensing by Myc

The c-myc protooncogene encodes the Myc transcription factor, a global regulator of fundamental cellular processes. Deregulation of c-myc leads to tumorigenesis, and c-myc is an important driver in human cancer. Myc and its dimerization partner Max are bHLH-Zip DNA binding proteins involved in transcriptional regulation of target genes. Non-transcriptional functions have also been attributed to the Myc protein, notably direct interaction with the pre-replicative complex (pre-RC) controlling the initiation of DNA replication. A key component of the pre-RC is the Cdt1 protein, an essential factor in origin licensing. Here we present data suggesting that the CDT1 gene is a transcriptional target of the Myc-Max complex. Expression of the CDT1 gene in v-myc-transformed cells directly correlates with myc expression. Also, human tumor cells with elevated c-myc expression display increased CDT1 expression. Occupation of the CDT1 promoter by Myc-Max is demonstrated by chromatin immunoprecipitation, and transactivation by Myc-Max is shown in reporter assays. Ectopic expression of CDT1 leads to cell transformation. Our results provide a possible direct mechanistic link of Myc's canonical function as a transcription factor to DNA replication. Furthermore, we suggest that aberrant transcriptional activation of CDT1 by deregulated myc alleles contributes to the genomic instabilities observed in tumor cells.

iTRAQ-based proteomic analysis of polyploid giant cancer cells and budding progeny cells reveals several distinct pathways for ovarian cancer development

Polyploid giant cancer cells (PGCCs) are a morphologically distinct subgroup of human tumor cells with increased nuclear size or multiple nuclei, but they are generally considered unimportant because they are presumed to be nondividing and thus nonviable. We have recently shown that these large cancer cells are not only viable but also can divide asymmetrically and yield progeny cancer cells with cancer stem-like properties via budding division. To further understand the molecular events involved in the regulation of PGCCs and the generation of their progeny cancer cells, we comparatively analyzed the proteomic profiles of PGCCs, PGCCs with budding daughter cells, and regular control cancer cells from the HEY and SKOv3 human ovarian cancer cell lines with and without CoCl2. We used a high-throughput iTRAQ-based proteomic methodology coupled with liquid chromatography-electrospray ionization tandem mass spectroscopy to determine the differentiated regulated proteins. We performed Western blotting and immunohistochemical analyses to validate the differences in the expression patterns of a variety of proteins between PGCCs or budding PGCCs and regular cancer cells identified by iTRAQ approach and also a selected group of proteins from the literature. The differentially regulated proteins included proteins involved in response to hypoxia, stem cell generation, chromatin remodeling, cell-cycle regulation, and invasion and metastasis. In particular, we found that HIF-1alpha and its known target STC1 are upregulated in PGCCs. In addition, we found that a panel of stem cell-regulating factors and epithelial-to-mesenchymal transition regulatory transcription factors were upregulated in budding PGCCs, whereas expression of the histone 1 family of nucleosomal linker proteins was consistently lower in PGCCs than in control cells. Thus, proteomic expression patterns provide valuable insight into the underlying mechanisms of PGCC formation and the relationship between PGCCs and cancer stem cells in patients with ovarian cancers.

Asperolide A, a marine-derived tetranorditerpenoid, induces G2/M arrest in human NCI-H460 lung carcinoma cells, is mediated by p53-p21 stabilization and modulated by Ras/Raf/MEK/ERK signaling pathway

Here we first demonstrate that asperolide A, a very recently reported marine-derived tetranorditerpenoid, leads to the inhibition of NCI-H460 lung carcinoma cell proliferation by G2/M arrest with the activation of the Ras/Raf/MEK/ERK signaling and p53-dependent p21 pathway. Treatment with 35 μM asperolide A (2 × IC₅₀) resulted in a significant increase in the proportion of G2/M phase cells, about a 2.9-fold increase during 48 h. Immunoblot assays demonstrated time-dependent inhibition of G2/M regulatory proteins. Moreover, asperolide A significantly activated MAP kinases (ERK1/2, JNK and p38 MAP kinase) by phosphorylation, and only the inhibition of ERK activation by PD98059 reversed downregulation of G2/M regulatory proteins CDC2, and suppressed upregulation of p21 and p-p53 levels. Transfection of cells with dominant-negative Ras (RasN17) mutant genes up-regulated asperolide A-induced the decrease of cyclin B1 and CDC2, suppressed Raf, ERK activity and p53-p21 expression, and at last, abolished G2/M arrest. This study indicates that asperolide A-induced G2/M arrest in human NCI-H460 lung carcinoma cells relys on the participation of the Ras/Raf/MEK/ERK signaling pathway in p53-p21 stabilization. An in vivo study with asperolide A illustrated a marked inhibition of tumor growth, and little toxcity compared to Cisplatin therapy. Overall, these findings provide potential effectiveness and a theoretical basis for the therapeutic use of asperolide A in the treatment of malignancies.

Expression of RAS-like family members, c-jun and c-myc mRNA levels in neoplastic hemocytes of soft-shell clams Mya arenaria using microsphere-based 8-plex branched DNA assay

The molecular mechanisms by which disseminated neoplasia (DN) is developed in soft shell clams Mya arenaria remain largely unknown. This study aims at quantifying Rho-like GTPase, RAS-Rho, RAS-related C3 botulinum (RAS C3), c-jun as well as c-myc transcript levels in clams sampled at North River (Charlottetown, Prince Edward Island, Canada). The transcripts were quantified using multiplex gene analysis (Quantigene(®) 2 Plex, Affymetrix) in 3 groups of clams: (1) Group C (healthy clams considered as control) with a low percentage of tetraploid hemocytes (<10%); (2) Group D (disease in development): individuals presenting a percentage of tetraploid cells ranging between 10% and 50%; (3) Group E (established disease): clams with a high percentage of tetraploid hemocytes (>50%). Data showed a down-regulation of Rho-like GTPase, Rho-like subfamily, RAS C3, c-jun and an up-regulation of c-myc gene expression. It is believed that a deregulation of the expression of these genes could partly unravel the molecular mechanisms involved in the development of DN in soft shell clams Mya arenaria. Further investigations should be pursued to determine the role of these gene products in clams' hemocytes.

Upregulated expression of Mina53 in cholangiocarcinoma and its clinical significance

The aim of this study was to determine the level of expression of Mina53 in human cholangiocarcinoma (CCA) and to explore the role of Mina53 in carcinogenesis and tumor progression and its clinical significance in CCA. The level of expression of Mina53, p53 and Ki67 was investigated by immunohistochemistry in 69 surgically resected CCA tissues and 21 adjacent non-cancerous tissues. The correlation between Mina53 expression and clinicopathological characteristics and the expression of p53 and Ki67 was examined. Positive expression of Mina53 was observed in 61 of 69 CCA cases (88.4%) and 1 case (4.8%) of adjacent non-cancerous tissue. The level of expression of Mina53 in CCA was markedly higher than in the adjacent non-cancerous tissues. An increased level of expression of Mina53 in CCA was significantly associated with histological differentiation (P<0.01), TNM stage (P<0.05) and lymph node metastasis (P<0.01). There was no significant correlation between the level of Mina53 expression and gender, age or distant metastasis (P>0.05). However, the expression of Mina53 was associated with the expression of p53 in CCA (P<0.05). In addition, increased levels of expression of Mina53 in CCA were positively associated with Ki67 levels (r=0.801, P<0.01, as calculated by association analysis). Therefore, the upregulation of Mina53 expression may be significant in the carcinogenesis and development of human CCA and could have significant clinical value.

Myc: the beauty and the beast

The iconic history of the Myc oncoprotein encompasses 3 decades of intense scientific discovery. There is no question that Myc has been a pioneer, advancing insight into the molecular basis of cancer as well as functioning as a critical control center for several diverse biological processes and regulatory mechanisms. This narrative chronicles the journey and milestones that have defined the understanding of Myc, and it provides an opportunity to consider future directions in this challenging yet rewarding field.

Mechanistic insight into Myc stabilization in breast cancer involving aberrant Axin1 expression

High expression of the oncoprotein Myc has been linked to poor outcome in human tumors. Although MYC gene amplification and translocations have been observed, this can explain Myc overexpression in only a subset of human tumors. Myc expression is in part controlled by its protein stability, which can be regulated by phosphorylation at threonine 58 (T58) and serine 62 (S62). We now report that Myc protein stability is increased in a number of breast cancer cell lines and this correlates with increased phosphorylation at S62 and decreased phosphorylation at T58. Moreover, we find this same shift in phosphorylation in primary breast cancers. The signaling cascade that controls phosphorylation at T58 and S62 is coordinated by the scaffold protein Axin1. We therefore examined Axin1 in breast cancer and report decreased AXIN1 expression and a shift in the ratio of expression of two naturally occurring AXIN1 splice variants. We demonstrate that this contributes to increased Myc protein stability, altered phosphorylation at S62 and T58, and increased oncogenic activity of Myc in breast cancer. Thus, our results reveal an important mode of Myc activation in human breast cancer and a mechanism contributing to Myc deregulation involving unique insight into inactivation of the Axin1 tumor suppressor in breast cancer.

Tripeptidyl Peptidase II Is Required for c-MYC-Induced Centriole Overduplication and a Novel Therapeutic Target in c-MYC-Associated Neoplasms

Centrosome aberrations are frequently detected in c-MYC-associated human malignancies. Here, we show that c-MYC-induced centrosome and centriole overduplication critically depend on the protease tripeptidyl peptidase II (TPPII). We found that TPPII localizes to centrosomes and that overexpression of TPPII, similar to c-MYC, can disrupt centriole duplication control and cause centriole multiplication, a process during which maternal centrioles nucleate the formation of more than a single daughter centriole. We report that inactivation of TPPII using chemical inhibitors or siRNA-mediated protein knockdown effectively reduced c-MYC-induced centriole overduplication. Remarkably, the potent and selective TPPII inhibitor butabindide not only potently suppressed centriole aberrations but also caused significant cell death and growth suppression in aggressive human Burkitt lymphoma cells with c-MYC overexpression. Taken together, these results highlight the role of TPPII in c-MYC-induced centriole overduplication and encourage further studies to explore TPPII as a novel antineoplastic drug target.

MYC in chronic myeloid leukemia: induction of aberrant DNA synthesis and association with poor response to imatinib

Untreated chronic myeloid leukemia (CML) progresses from chronic phase to blastic crisis (BC). Increased genomic instability, deregulated proliferation, and loss of differentiation appear associated to BC, but the molecular alterations underlying the progression of CML are poorly characterized. MYC oncogene is frequently deregulated in human cancer, often associated with tumor progression. Genomic instability and induction of aberrant DNA replication are described as effects of MYC. In this report, we studied MYC activities in CML cell lines with conditional MYC expression with and without exposure to imatinib, the front-line drug in CML therapy. In cells with conditional MYC expression, MYC did not rescue the proliferation arrest mediated by imatinib but provoked aberrant DNA synthesis and accumulation of cells with 4C content. We studied MYC mRNA expression in 66 CML patients at different phases of the disease, and we found that MYC expression was higher in CML patients at diagnosis than control bone marrows or in patients responding to imatinib. Further, high MYC levels at diagnosis correlated with a poor response to imatinib. MYC expression did not directly correlate with BCR-ABL levels in patients treated with imatinib. Overall our study suggests that, as in other tumor models, MYC-induced aberrant DNA synthesis in CML cells is consistent with MYC overexpression in untreated CML patients and nonresponding patients and supports a role for MYC in CML progression, possibly through promotion of genomic instability.

Hyperproliferation, cancer, and inflammation in mice expressing a Δ133p53-like isoform

The p53 protein is a pivotal tumor suppressor that is frequently mutated in many human cancers, although precisely how p53 prevents tumors is still unclear. To add to its complexity, several isoforms of human p53 have now been reported. The Δ133p53 isoform is generated from an alternative transcription initiation site in intron 4 of the p53 gene (Tp53) and lacks the N-terminus. Elevated levels of Δ133p53 have been observed in a variety of tumors. To explore the functions of Δ133p53, we created a mouse expressing an N-terminal deletion mutant of p53 (Δ122p53) that corresponds to Δ133p53. Δ122p53 mice show decreased survival and a different and more aggressive tumor spectrum compared with p53 null mice, implying that Δ122p53 is a dominant oncogene. Consistent with this, Δ122p53 also confers a marked proliferative advantage on cells and reduced apoptosis. In addition to tumor development, Δ122p53 mice show a profound proinflammatory phenotype having increased serum concentrations of interleukin-6 and other proinflammatory cytokines and lymphocyte aggregates in the lung and liver as well as other pathologies. Based on these observations, we propose that human Δ133p53 also functions to promote cell proliferation and inflammation, one or both of which contribute to tumor development.

Illicit survival of cancer cells during polyploidization and depolyploidization

Tetraploidy and the depolyploidization of tetraploid cells may contribute to oncogenesis. Several mechanisms have evolved to avoid the generation, survival, proliferation and depolyploidization of tetraploids. Cells that illicitly survive these checkpoints are prone to chromosomal instability and aneuploidization. Along with their replication, tetraploids constantly undergo chromosomal rearrangements that eventually lead to pseudodiploidy by two non-exclusive mechanisms: (i) multipolar divisions and (ii) illicit bipolar divisions in the presence of improper microtubule-kinetochore attachments. Here, we describe the regulation and the molecular mechanisms that underlie such a 'polyploidization-depolyploidization' cascade, while focusing on the role of oncogenes and tumor suppressor genes in tetraploidy-driven tumorigenesis. We speculate that the identification of signaling/metabolic cascades that are required for the survival of tetraploid or aneuploid (but not diploid) cancer cells may pave the way for the development of novel broad-spectrum anticancer agents.

Point mutations in c-Myc uncouple neoplastic transformation from multiple other phenotypes in rat fibroblasts

Deregulation of c-Myc (Myc) occurs in many cancers. In addition to transforming various cell types, Myc also influences additional transformation-associated cellular phenotypes including proliferation, survival, genomic instability, reactive oxygen species production, and metabolism. Although Myc is wild type in most cancers (wtMyc), it occasionally acquires point mutations in certain lymphomas. Some of these mutations confer a survival advantage despite partially attenuating proliferation and transformation. Here, we have evaluated four naturally-occurring or synthetic point mutations of Myc for their ability to affect these phenotypes, as well as to promote genomic instability, to generate reactive oxygen species and to up-regulate aerobic glycolysis and oxidative phosphorylation. Our findings indicate that many of these phenotypes are genetically and functionally independent of one another and are not necessary for transformation. Specifically, the higher rate of glucose metabolism known to be associated with wtMyc deregulation was found to be independent of transformation. One mutation (Q131R) was greatly impaired for nearly all of the studied Myc phenotypes, yet was able to retain some ability to transform. These findings indicate that, while the Myc phenotypes examined here make additive contributions to transformation, none, with the possible exception of increased reliance on extracellular glutamine for survival, are necessary for achieving this state.

The c-Myc target glycoprotein1balpha links cytokinesis failure to oncogenic signal transduction pathways in cultured human cells

An increase in chromosome number, or polyploidization, is associated with a variety of biological changes including breeding of cereal crops and flowers, terminal differentiation of specialized cells such as megakaryocytes, cellular stress and oncogenic transformation. Yet it remains unclear how cells tolerate the major changes in gene expression, chromatin organization and chromosome segregation that invariably accompany polyploidization. We show here that cancer cells can initiate increases in chromosome number by inhibiting cell division through activation of glycoprotein1b alpha (GpIbalpha), a component of the c-Myc signaling pathway. We are able to recapitulate cytokinesis failure in primary cells by overexpression of GpIbalpha in a p53-deficient background. GpIbalpha was found to localize to the cleavage furrow by microscopy analysis and, when overexpressed, to interfere with assembly of the cellular cortical contraction apparatus and normal division. These results indicate that cytokinesis failure and tetraploidy in cancer cells are directly linked to cellular hyperproliferation via c-Myc induced overexpression of GpIbalpha.

Multipolar mitosis of tetraploid cells: inhibition by p53 and dependency on Mos

Tetraploidy can constitute a metastable intermediate between normal diploidy and oncogenic aneuploidy. Here, we show that the absence of p53 is not only permissive for the survival but also for multipolar asymmetric divisions of tetraploid cells, which lead to the generation of aneuploid cells with a near-to-diploid chromosome content. Multipolar mitoses (which reduce the tetraploid genome to a sub-tetraploid state) are more frequent when p53 is downregulated and the product of the Mos oncogene is upregulated. Mos inhibits the coalescence of supernumerary centrosomes that allow for normal bipolar mitoses of tetraploid cells. In the absence of p53, Mos knockdown prevents multipolar mitoses and exerts genome-stabilizing effects. These results elucidate the mechanisms through which asymmetric cell division drives chromosomal instability in tetraploid cells.

Widespread genomic instability mediated by a pathway involving glycoprotein Ib alpha and Aurora B kinase

c-Myc (Myc) oncoprotein induction of genomic instability (GI) contributes to its initial transforming function and subsequent tumor cell evolution. We describe here a pathway by which Myc, via its target protein glycoprotein Ibalpha (GpIb alpha), mediates GI. Proteomic profiling revealed that the serine/threonine kinase Aurora B is down-regulated by GpIb alpha in p53-deficient primary human fibroblasts. The phenotypes of Aurora B deficiency are strikingly reminiscent of Myc or GpIb alpha overexpression and include double-stranded DNA breaks, altered nuclear size and morphology, chromatin bridges, cleavage furrow regression, and tetraploidy. During mitosis, GpIb alpha and Aurora B redistribute to the cleavage furrow along with other cleavage furrow proteins. GpIb alpha overexpression at levels comparable with those seen in some tumor cells causes the dispersal of these proteins but not Aurora B, resulting in furrow regression and cytokinesis failure. Aurora B normalization redirects the mislocalized furrow proteins to their proper location, corrects the cleavage furrow abnormalities, and restores genomic stability. Aurora B thus appears necessary for a previously unrecognized function in guiding and positioning a number of key proteins, including GpIb alpha to the cleavage furrow. These findings underscore the importance of maintaining a delicate balance among cleavage furrow-associated proteins during mitosis. Suppression of Aurora B via GpIb alpha provides a unifying and mechanistic explanation for several types of Myc-mediated GI.

Prognostic relevance of c-MYC gene amplification and polysomy for chromosome 8 in suboptimally-resected, advanced stage epithelial ovarian cancers: a Gynecologic Oncology Group study

OBJECTIVE

The Gynecologic Oncology Group (GOG) examined the prognostic relevance of c-MYC amplification and polysomy 8 in epithelial ovarian cancer (EOC).

METHODS

Women with suboptimally-resected, advanced stage EOC who participated in GOG-111, a multicenter randomized phase III trial of cyclophosphamide+cisplatin vs. paclitaxel+cisplatin, and who provided a tumor block through GOG-9404 were eligible. Fluorescence in situ hybridization (FISH) with probes for c-MYC and the centromere of chromosome 8 (CEP8) was used to examine c-MYC amplification (> or =2 copies c-MYC/CEP8) and polysomy 8 (> or =4 CEP8 copies).

RESULTS

c-MYC amplification, defined as > or =2 copies c-MYC/CEP8, was observed in 29% (28/97) of EOCs and levels were ranged from 2.0-3.3 copies of c-MYC/CEP8. c-MYC amplification was not associated with patient age, race, GOG performance status, stage, cell type, grade, measurable disease status following surgery, tumor response or disease status following platinum-based combination chemotherapy. Women with vs. without c-MYC amplification did not have an increased risk of disease progression (hazard ratio [HR]=1.03; 95% confidence interval [CI]=0.65-1.64; p=0.884) or death (HR=1.08; 95% CI=0.68-1.72; p=0.745). c-MYC amplification was not an independent prognostic factor for progression-free survival (HR=1.03, 95% CI=0.57-1.85; p=0.922) or overall survival (HR=1.01, 95% CI=0.56-1.80; p=0.982). Similar insignificant results were obtained for c-MYC amplification categorized as > or =1.5 copies c-MYC/CEP8. Polysomy 8 was observed in 22 patients without c-MYC amplification and 3 with c-MYC amplification, and was associated with age and measurable disease status, but not other clinical covariates or outcomes.

CONCLUSIONS

c-MYC amplification and polysomy 8 have limited predictive or prognostic value in suboptimally-resected, advanced stage EOC treated with platinum-based combination chemotherapy.

Reflecting on 25 years with MYC

Just over 25 years ago, MYC, the human homologue of a retroviral oncogene, was identified. Since that time, MYC research has been intense and the advances impressive. On reflection, it is astonishing how each incremental insight into MYC regulation and function has also had an impact on numerous biological disciplines, including our understanding of molecular oncogenesis in general. Here we chronicle the major advances in our understanding of MYC biology, and peer into the future of MYC research.

Modularity of the oncoprotein-like properties of platelet glycoprotein Ibalpha

Glycoprotein Ib alpha (GpIbalpha), a trans-membrane glycoprotein, is expressed on the surface of megakaryocytes and platelets, where, in association with glycoprotein Ib beta, glycoprotein V, and glycoprotein IX, it normally forms the von Willebrand factor receptor (vWFR). A fully functional vWFR is necessary for platelet attachment, aggregation, and activation and has also been shown to regulate megakaryocyte ploidy. We have recently shown that the gene encoding GpIbalpha is a transcriptional target for the c-Myc oncoprotein and is more widely expressed than previously thought, with particularly high levels occurring in transformed cells. Indeed, GpIbalpha can substitute for c-Myc in promoting growth, transformation, and genomic instability. In the current work, we have demonstrated that, despite the promiscuous expression of GpIbalpha, other vWFR subunits remain largely restricted to megakaryocytes. We have characterized a panel of GpIbalpha mutants and shown that some regions of the protein essential for vWFR activity are not necessary for c-Myc-like functions. Specifically, the six C-terminal amino acids of the cytoplasmic domain, which mediate vWFR signaling, are entirely dispensible for the c-Myc-like functions of GpIbalpha. Instead, these require a more membrane-proximal filamin-binding domain. Also important is the GpIbalpha signal peptide, which, in the absence of other vWFR subunits, directs GpIbalpha to the endoplasmic reticulum rather than the membrane. Together, these results provide strong evidence that the domains of GpIbalpha mediating c-Myc-like functions are modular, genetically distinct, and independent of those involved in vWFR signaling.

A role for polyploidy in the tumorigenicity of Pim-1-expressing human prostate and mammary epithelial cells

Background

Polyploidy is a prominent feature of many human cancers, and it has long been hypothesized that polyploidy may contribute to tumorigenesis by promoting genomic instability. In this study, we investigated whether polyploidy per se induced by a relevant oncogene can promote genomic instability and tumorigenicity in human epithelial cells.

Principal Findings

When the oncogenic serine-threonine kinase Pim-1 is overexpressed in immortalized, non-tumorigenic human prostate and mammary epithelial cells, these cells gradually converted to polyploidy and became tumorigenic. To assess the contribution of polyploidy to tumorigenicity, we obtained sorted, matched populations of diploid and polyploid cells expressing equivalent levels of the Pim-1 protein. Spectral karyotyping revealed evidence of emerging numerical and structural chromosomal abnormalities in polyploid cells, supporting the proposition that polyploidy promotes chromosomal instability. Polyploid cells displayed an intact p53/p21 pathway, indicating that the viability of polyploid cells in this system is not dependent on the inactivation of the p53 signaling pathway. Remarkably, only the sorted polyploid cells were tumorigenic in vitro and in vivo.

Conclusions

Our results support the notion that polyploidy can promote chromosomal instability and the initiation of tumorigenesis in human epithelial cells.

Transformation, genomic instability and senescence mediated by platelet/megakaryocyte glycoprotein Ibalpha

GpIbalpha, a subunit of the von Willebrand factor receptor, functions during blood clotting to promote platelet adhesion and activation. GpIbalpha is widely expressed, is positively regulated by c-Myc and is essential for the promotion of c-Myc-mediated chromosomal instability. We now show that GpIbalpha is also a classical oncoprotein in which its deregulated expression leads to transformation, reduced growth factor requirements, increased resistance to apoptosis, and, in primary cells, p53-dependent senescence. Finally, GpIbalpha also promotes double-stranded DNA breaks, and induces profound nuclear dysmorphology, indicating that, in addition to its direct transforming function, it displays genotoxicity at several distinct levels. These findings identify novel functions for GpIbalpha and pathways through which c-Myc mediates transformation and global genomic destabilization.

c-Myc-mediated genomic instability proceeds via a megakaryocytic endomitosis pathway involving Gp1balpha

Genomic instability (GI) is essential for the initiation and evolution of many cancers and often precedes frank neoplastic conversion. Although GI can occur at several levels, the most conspicuous examples involve gains or losses of entire chromosomes (aneuploidy), the antecedent of which may be whole genome duplication (tetraploidy). Through largely undefined mechanisms, the c-Myc oncoprotein and its downstream target, MTMC1, promote tetraploidy and other forms of GI. In myeloid cells, c-Myc and MTMC1 also regulate a common, small subset of c-Myc target genes including GP1Balpha, which encodes a subunit of the von Willebrand's factor receptor complex that mediates platelet adhesion and aggregation. Gp1balpha also participates in megakaryocyte endomitosis, a form of controlled and precise whole-genome amplification. In this article, we show that both c-Myc and MTMC1 strongly up-regulate Gp1balpha concurrent with their promotion of tetraploidy. shRNA-mediated inhibition of Gp1balpha prevents tetraploidy by both c-Myc and MTMC1, whereas Gp1balpha overexpression alone is sufficient to induce tetraploidy in established and primary cells. Once acquired, tetraploidy persists in most cases examined. Our results indicate that chromosome-level GI, induced by c-Myc overexpression, proceeds by means of the sequential up-regulation of MTMC1 and Gp1balpha and further suggest that the pathways leading to megakaryocytic endomitosis and c-Myc-induced tetraploidy are mechanistically linked by their reliance on Gp1balpha.