Chromatin insulators are boundary elements between distinctly regulated, neighboring chromosomal domains, and they function by blocking the effects of nearby enhancers in a position-dependent manner. Here, we show that the SNF2-like chromodomain helicase protein CHD8 interacts with the insulator binding protein CTCF. Chromatin immunoprecipitation analysis revealed that CHD8 was present at known CTCF target sites, such as the differentially methylated region (DMR) of H19, the locus control region of beta-globin, and the promoter region of BRCA1 and c-myc genes. RNA interference-mediated knockdown of CHD8 significantly abolished the H19 DMR insulator activity that depends highly on CTCF, leading to reactivation of imprinted IGF2 from chromosome of maternal origin. Further, the lack of CHD8 affected CpG methylation and histone acetylation around the CTCF binding sites, adjacent to heterochromatin, of BRCA1 and c-myc genes. These findings provide insight into the role of CTCF-CHD8 complex in insulation and epigenetic regulation at active insulator sites.

Human-induced pluripotent stem cells (hiPSCs) are generated from somatic cells by ectopic expression of the 4 reprogramming factors (RFs) Oct-4, Sox2, Klf4, and c-Myc. To better define the stoichiometric requirements and dynamic expression patterns required for successful hiPSC induction, we generated 4 bicistronic lentiviral vectors encoding the 4 RFs co-expressed with discernable fluorescent proteins. Using this system, we define the optimal stoichiometry of RF expression to be highly sensitive to Oct4 dosage, and we demonstrate the impact that variations in the relative ratios of RF expression exert on the efficiency of hiPSC induction. Monitoring of expression of each individual RF in single cells during the course of reprogramming revealed that vector silencing follows acquisition of pluripotent cell markers. Pronounced lentiviral vector silencing was a characteristic of successfully reprogrammed hiPSC clones, but lack of complete silencing did not hinder hiPSC induction, maintenance, or directed differentiation. The vector system described here presents a powerful tool for mechanistic studies of reprogramming and the optimization of hiPSC generation.

PIK3CA gain-of-function mutations are a common oncogenic event in human malignancy, making phosphatidylinositol 3-kinase (PI3K) a target for cancer therapy. Despite the promise of targeted therapy, resistance often develops, leading to treatment failure. To elucidate mechanisms of resistance to PI3K-targeted therapy, we constructed a mouse model of breast cancer conditionally expressing human PIK3CA(H1047R). Notably, most PIK3CA(H1047R)-driven mammary tumors recurred after PIK3CA(H1047R) inactivation. Genomic analyses of recurrent tumors revealed multiple lesions, including focal amplification of Met or Myc (also known as c-Met and c-Myc, respectively). Whereas Met amplification led to tumor survival dependent on activation of endogenous PI3K, tumors with Myc amplification became independent of the PI3K pathway. Functional analyses showed that Myc contributed to oncogene independence and resistance to PI3K inhibition. Notably, PIK3CA mutations and c-MYC elevation co-occur in a substantial fraction of human breast tumors. Together, these data suggest that c-MYC elevation represents a potential mechanism by which tumors develop resistance to current PI3K-targeted therapies.

The calpains are a conserved family of cysteine proteinases that catalyse the controlled proteolysis of many specific substrates. Calpain activity is implicated in several fundamental physiological processes, including cytoskeletal remodelling, cellular signalling, apoptosis and cell survival. Calpain expression is altered during tumorigenesis, and the proteolysis of numerous substrates, such as inhibitors of nuclear factor-κB (IκB), focal adhesion proteins (including, focal adhesion kinase and talin) and proto-oncogenes (for example, MYC), has been implicated in tumour pathogenesis. Recent evidence indicates that the increased expression of certain family members might influence the response to cancer therapies, providing justification for the development of novel calpain inhibitors.

Disablement of cell death programs in cancer cells contributes to drug resistance and in some cases has been associated with altered translational control. As eukaryotic translation initiation factor 4E (eIF4E) cooperates with c-Myc during lymphomagenesis, induces drug resistance, and is a genetic modifier of the rapamycin response, we have investigated the effect of dysregulation of the ribosome recruitment phase of translation initiation on tumor progression and chemosensitivity. eIF4E is a subunit of eIF4F, a complex that stimulates ribosome recruitment during translation initiation by delivering the DEAD-box RNA helicase eIF4A to the 5' end of mRNAs. eIF4A is thought to prepare a ribosome landing pad on mRNA templates for incoming 40S ribosomes (and associated factors). Using small molecule screening, we found that cyclopenta[b]benzofuran flavaglines, a class of natural products, modulate eIF4A activity and inhibit translation initiation. One member of this class of compounds, silvestrol, was able to enhance chemosensitivity in a mouse lymphoma model in which carcinogenesis is driven by phosphatase and tensin homolog (PTEN) inactivation or elevated eIF4E levels. These results establish that targeting translation initiation can restore drug sensitivity in vivo and provide an approach to modulating chemosensitivity.

OBJECTIVE

Medulloblastoma is the most common malignant brain tumor in children. Current treatment decisions are based on clinical variables. Novel tumor-derived biomarkers may improve the risk stratification of medulloblastoma patients.

METHODS

A model for the molecular risk stratification was proposed from an array-based comparative genomic hybridization (array-CGH) screen (n = 80). Fluorescence in situ hybridization (FISH) analyses for chromosome arms 6q, 17p, and 17q and the MYC and MYCN loci were performed in an independent validation set (n = 260). Copy number aberrations were correlated with clinical, histologic, and survival data.

RESULTS

Gain of 6q and 17q and genomic amplification of MYC or MYCN were each associated with poor outcome in the array-CGH study (n = 80). In contrast, all patients with 6q-deleted tumors survived. Given these findings, the following hierarchical molecular staging system was defined: (1) MYC/MYCN amplification, (2) 6q gain, (3) 17q gain, (4) 6q and 17q balanced, and (5) 6q deletion. The prognostic value of this staging system was investigated by FISH analysis (n = 260). The addition of molecular markers to clinical risk factors resulted in the identification of a large proportion of patients (72 of 260 patients; 30%) at high risk for relapse and death who would be considered standard risk by application of clinical variables alone.

CONCLUSIONS

Genomic aberrations in medulloblastoma are powerful independent markers of disease progression and survival. By adding genomic markers to established clinical and histologic variables, outcome prediction can be substantially improved. Because the analyses can be conducted on routine paraffin-embedded material, it will be especially feasible to use this novel molecular staging system in large multicenter clinical trials.

We have examined the phosphorylation and the serine/threonine-specific kinase activity of the protooncogene product Raf-1 (formerly c-raf) in response to oncogenic transformation or growth-factor treatment of mouse 3T3 cells. Expression of the membrane-bound oncogene products encoded by v-fms, v-src, v-sis, polyoma virus middle-sized tumor antigen, and Ha-ras increased the apparent molecular weight and phosphorylation of the Raf-1 protein, while expression of the nuclear oncogene and protooncogene products encoded by v-fos and c-myc did not. Changes in electrophoretic mobility and phosphorylation occurred rapidly in response to treatment of cells with platelet-derived growth factor, acidic fibroblast growth factor, epidermal growth factor, and the protein kinase C activator phorbol 12-myristate 13-acetate, but not insulin. The phosphorylation of the Raf-1 protein occurred primarily on serine and threonine residues. However, a subpopulation of Raf-1 molecules was phosphorylated on tyrosine residues in cells transformed by v-src or stimulated with platelet-derived growth factor. Transformation by v-src, or treatment with platelet-derived growth factor or phorbol 12-myristate 13-acetate, activated the Raf-1-associated serine/kinase activity as measured in immune-complex kinase assays. These findings suggest that proliferative signals generated at the membrane result in the phosphorylation of the Raf-1 protein and the activation of its serine/threonine kinase activity. Raf-1 activation may thus serve to transduce signals from the membrane to the cytoplasm and perhaps on to the nucleus.

The early steps in the degradation of human c-myc mRNA were investigated, using a previously described cell-free mRNA decay system. The first detectable step was poly(A) shortening, which generated a pool of oligoadenylated mRNA molecules. In contrast, the poly(A) of a stable mRNA, gamma globin, was not excised, even after prolonged incubation. The second step, degradation of oligoadenylated c-myc mRNA, generated decay products whose 3' termini were located within the A+U-rich portion of the 3' untranslated region. These products disappeared soon after they were formed, consistent with rapid degradation of the 3' region. In contrast, the 5' region, corresponding approximately to c-myc exon 1, was stable in vitro. The data indicate a sequential degradation pathway in which 3' region cleavages occur only after most or all of the poly(A) is removed. To account for rapid deadenylation, we suggest that the c-myc poly(A)-poly(A)-binding protein complex is readily dissociated, generating a protein-depleted poly(A) tract that is no longer resistant to nucleases.

REST/NRSF (repressor-element-1-silencing transcription factor/neuron-restrictive silencing factor) negatively regulates the transcription of genes containing RE1 sites. REST is expressed in non-neuronal cells and stem/progenitor neuronal cells, in which it inhibits the expression of neuron-specific genes. Overexpression of REST is frequently found in human medulloblastomas and neuroblastomas, in which it is thought to maintain the stem character of tumour cells. Neural stem cells forced to express REST and c-Myc fail to differentiate and give rise to tumours in the mouse cerebellum. Expression of a splice variant of REST that lacks the carboxy terminus has been associated with neuronal tumours and small-cell lung carcinomas, and a frameshift mutant (REST-FS), which is also truncated at the C terminus, has oncogenic properties. Here we show, by using an unbiased screen, that REST is an interactor of the F-box protein beta-TrCP. REST is degraded by means of the ubiquitin ligase SCF(beta-TrCP) during the G2 phase of the cell cycle to allow transcriptional derepression of Mad2, an essential component of the spindle assembly checkpoint. The expression in cultured cells of a stable REST mutant, which is unable to bind beta-TrCP, inhibited Mad2 expression and resulted in a phenotype analogous to that observed in Mad2(+/-) cells. In particular, we observed defects that were consistent with faulty activation of the spindle checkpoint, such as shortened mitosis, premature sister-chromatid separation, chromosome bridges and mis-segregation in anaphase, tetraploidy, and faster mitotic slippage in the presence of a spindle inhibitor. An indistinguishable phenotype was observed by expressing the oncogenic REST-FS mutant, which does not bind beta-TrCP. Thus, SCF(beta-TrCP)-dependent degradation of REST during G2 permits the optimal activation of the spindle checkpoint, and consequently it is required for the fidelity of mitosis. The high levels of REST or its truncated variants found in certain human tumours may contribute to cellular transformation by promoting genomic instability.

Spinal cord injury causes secondary biochemical changes leading to neuronal cell death. To clarify the molecular basis of this delayed injury, we subjected rats to spinal cord injury and identified gene expression patterns by high-density oligonucleotide arrays (8,800 genes studied) at 30 minutes, 4 hours, 24 hours, or 7 days after injury (total of 26 U34A profiles). Detailed analyses were limited to 4,300 genes consistently expressed above background. Temporal clustering showed rapid expression of immediate early genes (30 minutes), followed by genes associated with inflammation, oxidative stress, DNA damage, and cell cycle (4 and 24 hours). Functional clustering showed a novel pattern of cell cycle mRNAs at 4 and 24 hours after trauma. Quantitative reverse transcription polymerase chain reaction verified mRNA changes in this group, which included gadd45a, c-myc, cyclin D1 and cdk4, pcna, cyclin G, Rb, and E2F5. Changes in their protein products were quantified by Western blot, and cell-specific expression was determined by immunocytochemistry. Cell cycle proteins showed an increased expression 24 hours after injury and were, in part, colocalized in neurons showing morphological evidence of apoptosis. These findings suggest that cell cycle-related genes, induced after spinal cord injury, are involved in neuronal damage and subsequent cell death.

Cyclin D1, a putative G1 cyclin, has been implicated in cell cycle control. The human cyclin D1 gene is located on chromosome 11q13 where DNA rearrangement and amplification have been detected in several types of human cancer. Previous studies demonstrated that the cyclin D1 gene is not only rearranged or amplified but also overexpressed in some of these human tumors and tumor-derived cell lines. To further address the roles of cyclin D1 in cell cycle control and tumorigenesis, we have stably overexpressed the human cyclin D1 cDNA in Rat6 embryo fibroblasts by using retrovirus mediated transduction. The cyclin D1 protein was overproduced about 10-fold and was localized predominately in the nucleus. Cyclin D1 overexpressing cells displayed a decrease in the duration of the G1 phase, decreased cell size, and induced tumors when injected into athymic (nude) mice. In addition, overexpression of cyclin D1 in Rat6 cells perturbed the expression of several cellular growth-related genes including c-myc, c-jun, and cyclin A, but not cyclin D3. Taken together, these results indicate that deregulated expression of the cyclin D1 gene can cause disturbances in cell cycle control and gene expression and also enhance tumorigenesis.

OBJECTIVE

Proliferation and migration of hepatic stellate cells (HSCs) and expression of chemokines are involved in the pathogenesis of liver inflammation and fibrogenesis. Peroxisome proliferator-activated receptor (PPAR)-gamma is a receptor transcription factor that controls growth and differentiation in different tissues. We explored the effects of PPAR-gamma agonists on the biological actions of cultured human HSCs.

METHODS

HSCs were isolated from normal human liver tissue and used in their myofibroblast-like phenotype or immediately after isolation. Activation of PPAR-gamma was induced with 15-deoxy-Delta(12, 14)-prostaglandin J(2) or with troglitazone.

RESULTS

PPAR-gamma agonists dose-dependently inhibited HSC proliferation and chemotaxis induced by platelet-derived growth factor. This effect was independent of changes in postreceptor signaling or expression of c-fos and c-myc and was associated with inhibition of cell cycle progression beyond the G(1) phase. Activation of PPAR-gamma also resulted in a complete inhibition of the expression of monocyte chemotactic protein 1 at the gene and protein levels. Comparison of quiescent and culture-activated HSCs revealed a marked decrease in PPAR-gamma expression in activated cells.

CONCLUSIONS

Activation of PPAR-gamma modulates profibrogenic and proinflammatory actions in HSCs. Reduced PPAR-gamma expression may contribute to confer an activated phenotype to HSCs.

Ever since Bishop and his co-workers discovered the c-myc gene in the late 1970s (Bishop 1982), voluminous literature has documented its central role in proliferation and malignant transformation of human and animal cells (Amati et al. 1998, Bouchard et al. 1998, Dang et al. 1999). Most, if not all, types of human malignancy have been reported to have amplification and/or overexpression of this gene, although the frequency of these alterations varies greatly among different reports (Nesbit et al. 1999). In 1992, researchers started to realize that aberrant expression of c-myc could cause apoptosis (Evan et al. 1992, Shi et al. 1992), although the phenomenon had actually been observed much earlier (Wurm et al. 1986). Studies in recent years have further shown that the c-myc gene regulates growth, both in the sense of cell size and in the context of tissue differentiation (Gandarillas & Watt 1997, Iritani & Eisenman 1999, Johnston et al. 1999, Schmidt 1999, Schuhmacher et al. 1999). Thus, it is now known that the c-myc gene participates in most aspects of cellular function, including replication, growth, metabolism, differentiation, and apoptosis (Packham & Cleveland 1995, Hoffman & Liebermann 1998, Dang 1999, Dang et al. 1999, Elend & Eilers 1999, Prendergast 1999). How the c-Myc protein may be specifically directed to perform one, but not the others, of these functions is still obscure, despite the fact that the relevant literature has been accumulating at a fast pace in the past two decades. This review focuses on the profound roles of c-Myc in breast cancer and in the actions of the hormones that are eitologically related to breast cancer.

Normal differentiated cells rely primarily on mitochondrial oxidative phosphorylation to produce adenosine triphosphate (ATP) to maintain their viability and functions by using three major bioenergetic fuels: glucose, glutamine and fatty acids. Many cancer cells, however, rely on aerobic glycolysis for their growth and survival, and recent studies indicate that some cancer cells depend on glutamine as well. This altered metabolism in cancers occurs through oncogene activation or loss of tumor suppressor genes in multiple signaling pathways, including the phosphoinositide 3-kinase and Myc pathways. Relatively little is known, however, about the role of fatty acids as a bioenergetic fuel in growth and survival of cancer cells. Here, we report that human glioblastoma SF188 cells oxidize fatty acids and that inhibition of fatty acid β-oxidation by etomoxir, a carnitine palmitoyltransferase 1 inhibitor, markedly reduces cellular ATP levels and viability. We also found that inhibition of fatty acid oxidation controls the NADPH level. In the presence of reactive oxygen species scavenger tiron, however, ATP depletion is prevented without restoring fatty acid oxidation. This suggests that oxidative stress may lead to bioenergetic failure and cell death. Our work provides evidence that mitochondrial fatty acid oxidation may provide NADPH for defense against oxidative stress and prevent ATP loss and cell death.

The control of cell proliferation by microRNAs (miRNAs) is well established and the alteration of these small, non-coding RNAs may contribute to tumor development by perturbing critical cell cycle regulators. Oncogenic miRNAs may facilitate cell cycle entry and progression by targeting CDK inhibitors or transcriptional repressors of the retinoblastoma family. On the other hand, tumor suppressor miRNAs induce cell cycle arrest by downregulating multiple components of the cell cycle machinery. Recent data also suggest that miRNAs act co-ordinately with transcriptional factors involved in cell cycle regulation such as c-MYC, E2F or p53. These miRNAs not only can potentiate the function of these factors but they may also limit the excessive translation of cell cycle proteins upon mitogenic or oncogenic stimuli to protect cells from replicative stress. The implications of these regulatory networks in cell proliferation and human disease are discussed.

Here, we report the identification of a new E1A binding protein complex that is essential for E1A-mediated transformation. Its core component is a SWI2/SNF2-related, 400 kDa protein (p400). Other components include the myc- and p/CAF-associated cofactor, TRRAP/PAF400, the DNA helicases TAP54alpha/beta, actin-like proteins, and the human homolog of the Drosophila Enhancer of Polycomb protein. An E1A mutant, defective in p400 binding, is also defective in transformation. Certain p400 fragments partially rescued this phenotype, underscoring the role of E1A-p400 complex formation in the E1A transforming process. Furthermore, E1A and c-myc each alter the subunit composition of p400 complexes, implying that physiological p400 complex formation contributes to transformation suppression.

Activation of telomerase is one of the rate-limiting steps in human cell immortalization and carcinogenesis Human telomerase is composed of at least two protein subunits and an RNA component. Regulation of expression of the catalytic subunit, human telomerase reverse transcriptase (hTERT), is suggested as the major determinant of the enzymatic activity. We report here the cloning and characterization of the 5'-regulatory region of the hTERT gene. The highly GC-rich content of the 5' end of the hTERT cDNA spans to the 5'-flanking region and intron 1, making a CpG island. A 1.7-kb DNA fragment encompassing the hTERT gene promoter was placed upstream of the luciferase reporter gene and transiently transfected into human cell lines of fibroblastic and epithelial origins that differed in their expression of the endogenous hTERT gene. Endogenous hTERT-expressing cells, but not nonexpressing cells, showed high levels of luciferase activity, suggesting that the regulation of hTERT gene expression occurs mainly at the transcriptional level. Additional luciferase assays using a series of constructs containing unidirectionally deleted fragments revealed that a 59-bp region (-208 to -150) is required for the maximal promoter activity. The region contains a potential Myc oncoprotein binding site (E-box), and cotransfection of a c-myc expression plasmid markedly enhanced the promoter activity, suggesting a role of the Myc protein in telomerase activation. Identification of the regulatory regions of the hTERT promoter sequence will be essential in understanding the molecular mechanisms of positive and negative regulation of telomerase.

Recently, genome-wide association studies have implicated the human LIN28B locus in regulating height and the timing of menarche. LIN28B and its homolog LIN28A are functionally redundant RNA-binding proteins that block biogenesis of let-7 microRNAs. lin-28 and let-7 were discovered in Caenorhabditis elegans as heterochronic regulators of larval and vulval development but have recently been implicated in cancer, stem cell aging and pluripotency. The let-7 targets Myc, Kras, Igf2bp1 and Hmga2 are known regulators of mammalian body size and metabolism. To explore the function of the Lin28-Let-7 pathway in vivo, we engineered transgenic mice to express Lin28a and observed in them increased body size, crown-rump length and delayed onset of puberty. Investigation of metabolic and endocrine mechanisms of overgrowth in these transgenic mice revealed increased glucose metabolism and insulin sensitivity. Here we report a mouse that models the human phenotypes associated with genetic variation in the Lin28-Let-7 pathway.

A considerable amount of knowledge has been produced during the last five years on the bioenergetics of cancer cells, leading to a better understanding of the regulation of energy metabolism during oncogenesis, or in adverse conditions of energy substrate intermittent deprivation. The general enhancement of the glycolytic machinery in various cancer cell lines is well described and recent analyses give a better view of the changes in mitochondrial oxidative phosphorylation during oncogenesis. While some studies demonstrate a reduction of oxidative phosphorylation (OXPHOS) capacity in different types of cancer cells, other investigations revealed contradictory modifications with the upregulation of OXPHOS components and a larger dependency of cancer cells on oxidative energy substrates for anabolism and energy production. This apparent conflictual picture is explained by differences in tumor size, hypoxia, and the sequence of oncogenes activated. The role of p53, C-MYC, Oct and RAS on the control of mitochondrial respiration and glutamine utilization has been explained recently on artificial models of tumorigenesis. Likewise, the generation of induced pluripotent stem cells from oncogene activation also showed the role of C-MYC and Oct in the regulation of mitochondrial biogenesis and ROS generation. In this review article we put emphasis on the description of various bioenergetic types of tumors, from exclusively glycolytic to mainly OXPHOS, and the modulation of both the metabolic apparatus and the modalities of energy substrate utilization according to tumor stage, serial oncogene activation and associated or not fluctuating microenvironmental substrate conditions. We conclude on the importance of a dynamic view of tumor bioenergetics.

Gene expression is modulated by the specific interactions of nuclear proteins with unique regulatory sequences in the genome. Proteins involved in transcriptional regulation seem to be either transcription factors or transcription modulators and their interactions are crucial in determining whether the expression of a specific gene is activated or repressed. Recently, the product of the proto-oncogene jun has been identified as the transcription factor AP-1, whereas nuclear oncoproteins fos and myc have been implicated in transcriptional transregulation of several promoters. Furthermore, the products of the fos and jun proto-oncogenes are associated in some transcription complexes. Although the nature of the association is unclear, the two proteins co-immunoprecipitate with fos antibodies in nuclear extracts. Here, we report studies that demonstrate that the fos protein directly modulates jun function by means of a heterodimer of fos and jun proteins. The fos 'leucine zipper' domain is necessary for the DNA binding of the heterodimer; a distinct domain, localized in the C-terminal region of the fos protein, is responsible for transcriptional regulation.

A meeting on the health effects of arsenic (As), its modes of action, and areas in need of future research was held in Hunt Valley, Maryland, on 22-24 September 1997. Exposure to As in drinking water has been associated with the development of skin and internal cancers and noncarcinogenic effects such as diabetes, peripheral neuropathy, and cardiovascular diseases. There is little data on specific mechanism(s) of action for As, but a great deal of information on possible modes of action. Although arsenite [As(III)] can inhibit more than 200 enzymes, events underlying the induction of the noncarcinogenic effects of As are not understood. With respect to carcinogenicity, As can affect DNA repair, methylation of DNA, and increase radical formation and activation of the protooncogene c-myc, but none of these potential pathways have widespread acceptance as the principal etiologic event. In addition, there are no accepted models for the study of As-induced carcinogenesis. At the final meeting session we considered research needs. Among the most important areas cited were a) As metabolism and its interaction with cellular constituents; b) possible bioaccumulation of As; c) interactions with other metals; d) effects of As on genetic material; e) development of animal models and cell systems to study effects of As; and f) a better characterization of human exposures as related to health risks. Some of the barriers to the advancement of As research included an apparent lack of interest in the United States on As research; lack of relevant animal models; difficulty with adoption of uniform methodologies; lack of accepted biomarkers; and the need for a central storage repository for stored specimens.

The nuclease hypersensitivity element III1 (NHE III1) upstream of the P1 and P2 promoters of c-MYC controls 80-90% of the transcriptional activity of this gene. The purine-rich strand in this region can form a G-quadruplex structure that is a critical part of the silencer element for this promoter. We have demonstrated that this G-quadruplex structure can form a mixture of four biologically relevant parallel-loop isomers, which upon interaction with the cationic porphyrin TMPyP4 are converted to mixed parallel/antiparallel G-quadruplex structures.

The locus for the cellular myc (c-myc) oncogene in humans is located on the region of chromosome 8 that is translocated to chromosome 14 in cells from most undifferentiated B-cell lymphomas. It is shown in this study that the c-myc locus is rearranged in 5 out of 15 cell lines from patients with undifferentiated B-cell lymphomas, and that the rearrangement involves a region at the 5' side of an apparently intact c-myc gene. In at least three patients, this rearranged region appears to contain immunoglobulin heavy chain mu sequences that are located on chromosome 14. The data indicate that this region contains the crossover point between chromosomes 8 and 14. The break point can occur at different positions on both chromosomes among individual cell lines.

Tumor cells increase the use of anabolic pathways to satisfy the metabolic requirements associated with a high growth rate. Transformed cells take up and metabolize nutrients such as glucose and glutamine at high levels that support anabolic growth. Oncogenic signaling through the PI3K/Akt and Myc pathways directly control glucose and glutamine uptake, respectively. In order to achieve elevated rates of nucleotide biosynthesis, neoplastic cells must divert carbon from PI3K/Akt-induced glycolytic flux into the nonoxidative branch of the pentose phosphate pathway to generate ribose-5-phosphate. This redirection of glucose catabolism appears to be regulated by cytoplasmic tyrosine kinases. Myc-induced glutamine metabolism also increases the abundance and activity of different rate-limiting enzymes that produce the molecular precursors required for de novo nucleotide synthesis. In this review, we will focus on recent progress in understanding how glucose and glutamine metabolism is redirected by oncogenes in order to support de novo nucleotide biosynthesis during proliferation and how metabolic reprogramming can be potentially exploited in the development of new cancer therapies.