Proteins encoded by the human c-myc oncogene: differential expression in neoplastic cells

Exploring the dynamics and interactions of the N-myc transactivation domain through solution nuclear magnetic resonance spectroscopy

Myc proteins are transcription factors crucial for cell proliferation. They have a C-terminal domain that mediates Max and DNA binding, and an N-terminal disordered region culminating in the transactivation domain (TAD). The TAD participates in many protein-protein interactions, notably with kinases that promote stability (Aurora-A) or degradation (ERK1, GSK3) via the ubiquitin-proteasome system. We probed the structure, dynamics and interactions of N-myc TAD using nuclear magnetic resonance (NMR) spectroscopy following its complete backbone assignment. Chemical shift analysis revealed that N-myc has two regions with clear helical propensity: Trp77-Glu86 and Ala122-Glu132. These regions also have more restricted ps-ns motions than the rest of the TAD, and, along with the phosphodegron, have comparatively high transverse (R2) 15N relaxation rates, indicative of slower timescale dynamics and/or chemical exchange. Collectively these features suggest differential propensities for structure and interaction, either internal or with binding partners, across the TAD. Solution studies on the interaction between N-myc and Aurora-A revealed a previously uncharacterised binding site. The specificity and kinetics of sequential phosphorylation of N-myc by ERK1 and GSK3 were characterised using NMR and resulted in no significant structural changes outside the phosphodegron. When the phosphodegron was doubly phosphorylated, N-myc formed a robust interaction with the Fbxw7-Skp1 complex, but mapping the interaction by NMR suggests a more extensive interface. Our study provides foundational insights into N-myc TAD dynamics and a backbone assignment that will underpin future work on the structure, dynamics, interactions and regulatory post-translational modifications of this key oncoprotein.

Inhibition of WNK Kinases in NK Cells Disrupts Cellular Osmoregulation and Control of Tumor Metastasis

INTRODUCTION

The serine/threonine with-no-lysine (WNK) kinase family function in blood pressure control, electrolyte homeostasis, and cellular osmoregulation. These kinases and their downstream effectors are considered promising therapeutic targets in hypertension and stroke. However, the role of WNK kinases in immune cells remains poorly understood.

METHODS

Using the small-molecule WNK kinase inhibitors WNK463 and WNK-IN-11, we investigated how WNK kinase inhibition affects natural killer (NK) cell physiology.

RESULTS

WNK kinase inhibition with WNK463 or WNK-IN-11 significantly decreased IL-2-activated NK cell volume, motility, and cytolytic activity. Treatment of NK cells with these inhibitors induced autophagy by activating AMPK and inhibiting mTOR signaling. Moreover, WNK kinase inhibition increased phosphorylation of Akt and c-Myc by misaligning activity of activating kinases and inhibitory phosphatases. Treatment of tumor-bearing mice with WNK463 impaired tumor metastasis control by adoptively transferred NK cells.

CONCLUSION

The catalytic activity of WNK kinases has a critical role of multiple aspects of NK cell physiology and their pharmacologic inhibition negatively impacts NK cell function.

Regulation of Myc transcription by an enhancer cluster dedicated to pluripotency and early embryonic expression

MYC plays various roles in pluripotent stem cells, including the promotion of somatic cell reprogramming to pluripotency, the regulation of cell competition and the control of embryonic diapause. However, how Myc expression is regulated in this context remains unknown. The Myc gene lies within a ~ 3-megabase gene desert with multiple cis-regulatory elements. Here we use genomic rearrangements, transgenesis and targeted mutation to analyse Myc regulation in early mouse embryos and pluripotent stem cells. We identify a topologically-associated region that homes enhancers dedicated to Myc transcriptional regulation in stem cells of the pre-implantation and early post-implantation embryo. Within this region, we identify elements exclusively dedicated to Myc regulation in pluripotent cells, with distinct enhancers that sequentially activate during naive and formative pluripotency. Deletion of pluripotency-specific enhancers dampens embryonic stem cell competitive ability. These results identify a topologically defined enhancer cluster dedicated to early embryonic expression and uncover a modular mechanism for the regulation of Myc expression in different states of pluripotency.

The Role of NOTCH1, GATA3, and c-MYC in T Cell Non-Hodgkin Lymphomas

Lymphomas are heterogeneous malignant tumours of white blood cells characterised by the aberrant proliferation of mature lymphoid cells or their precursors. Lymphomas are classified into main types depending on the histopathologic evidence of biopsy taken from an enlarged lymph node, progress stages, treatment strategies, and outcomes: Hodgkin and non-Hodgkin lymphoma (NHL). Moreover, lymphomas can be further divided into subtypes depending on the cell origin, and immunophenotypic and genetic aberrations. Many factors play vital roles in the progression, pathogenicity, incidence, and mortality rate of lymphomas. Among NHLs, peripheral T cell lymphomas (PTCLs) are rare lymphoid malignancies, that have various cellular morphology and genetic mutations. The clinical presentations are usually observed at the advanced stage of the disease. Many recent studies have reported that the expressions of NOTCH1, GATA3, and c-MYC are associated with poorer prognosis in PTCL and are involved in downstream activities. However, questions have been raised about the pathological relationship between these factors in PTCLs. Therefore, in this review, we investigate the role and relationship of the NOTCH1 pathway, transcriptional factor GATA3 and proto-oncogene c-MYC in normal T cell development and malignant PTCL subtypes.

NSD3S stabilizes MYC through hindering its interaction with FBXW7

The MYC transcription factor plays a key role in cell growth control. Enhanced MYC protein stability has been found to promote tumorigenesis. Thus, understanding how MYC stability is controlled may have significant implications for revealing MYC-driven growth regulatory mechanisms in physiological and pathological processes. Our previous work identified the histone lysine methyltransferase nuclear receptor binding SET domain protein 3 (NSD3) as a MYC modulator. NSD3S, a noncatalytic isoform of NSD3 with oncogenic activity, appears to bind, stabilize, and activate the transcriptional activity of MYC. However, the mechanism by which NSD3S stabilizes MYC remains to be elucidated. To uncover the nature of the interaction and the underlying mechanism of MYC regulation by NSD3S, we characterized the binding interface between both proteins by narrowing the interface to a 15-amino acid region in NSD3S that is partially required for MYC regulation. Mechanistically, NSD3S binds to MYC and reduces the association of F-box and WD repeat domain containing 7 (FBXW7) with MYC, which results in suppression of FBXW7-mediated proteasomal degradation of MYC and an increase in MYC protein half-life. These results support a critical role for NSD3S in the regulation of MYC function and provide a novel mechanism for NSD3S oncogenic function through inhibition of FBXW7-mediated degradation of MYC.

Generation of anisotropic strain dysregulates wild-type cell division at the interface between host and oncogenic tissue

Epithelial tissues are highly sensitive to anisotropies in mechanical force, with cells altering fundamental behaviors, such as cell adhesion, migration, and cell division.1-5 It is well known that, in the later stages of carcinoma (epithelial cancer), the presence of tumors alters the mechanical properties of a host tissue and that these changes contribute to disease progression.6-9 However, in the earliest stages of carcinoma, when a clonal cluster of oncogene-expressing cells first establishes in the epithelium, the extent to which mechanical changes alter cell behavior in the tissue as a whole remains unclear. This is despite knowledge that many common oncogenes, such as oncogenic Ras, alter cell stiffness and contractility.10-13 Here, we investigate how mechanical changes at the cellular level of an oncogenic cluster can translate into the generation of anisotropic strain across an epithelium, altering cell behavior in neighboring host tissue. We generated clusters of oncogene-expressing cells within otherwise normal in vivo epithelium, using Xenopus laevis embryos. We find that cells in kRasV12, but not cMYC, clusters have increased contractility, which introduces radial stress in the tissue and deforms surrounding host cells. The strain imposed by kRasV12 clusters leads to increased cell division and altered division orientation in neighboring host tissue, effects that can be rescued by reducing actomyosin contractility specifically in the kRasV12 cells. Our findings indicate that some oncogenes can alter the mechanical and proliferative properties of host tissue from the earliest stages of cancer development, changes that have the potential to contribute to tumorigenesis.

The long journey to bring a Myc inhibitor to the clinic

The oncogene Myc is deregulated in the majority of human tumors and drives numerous hallmarks of cancer. Despite its indisputable role in cancer development and maintenance, Myc is still undrugged. Developing a clinical inhibitor for Myc has been particularly challenging owing to its intrinsically disordered nature and lack of a binding pocket, coupled with concerns regarding potentially deleterious side effects in normal proliferating tissues. However, major breakthroughs in the development of Myc inhibitors have arisen in the last couple of years. Notably, the direct Myc inhibitor that we developed has just entered clinical trials. Celebrating this milestone, with this Perspective, we pay homage to the different strategies developed so far against Myc and all of the researchers focused on developing treatments for a target long deemed undruggable.

Changes in Biomechanical Properties of A375 Cells Due to the Silencing of TMSB4X Expression Are Not Directly Correlated with Alterations in Their Stemness Features

Thymosin β4 (Tβ4) is a small, 44-amino acid polypeptide. It has been implicated in multiple processes, including cell movement, angiogenesis, and stemness. Previously, we reported that melanoma cell lines differ in Tβ4 levels. Studies on stable clones with silenced TMSB4X expression showed that Tβ4 impacted adhesion and epithelial-mesenchymal transition progression. Here, we show that the cells with silenced TMSB4X expression exhibited altered actin cytoskeleton’s organization and subcellular relocalization of two intermediate filament proteins: Nestin and Vimentin. The rearrangement of the cell cytoskeleton resulted in changes in the cells’ topology, height, and stiffness defined by Young’s modulus. Simultaneously, only for some A375 clones with a lowered Tβ4 level, we observed a decreased ability to initiate colony formation in soft agar, tumor formation in vivo, and alterations in Nanog’s expression level transcription factor regulating stemness. Thus, we show for the first time that in A375 cells, biomechanical properties are not directly coupled to stemness features, and this cell line is phenotypically heterogeneous.

Alternative approaches to target Myc for cancer treatment

The Myc proto-oncogene family consists of three members, C-MYC, MYCN, and MYCL, which encodes the transcription factor c-Myc (hereafter Myc), N-Myc, and L-Myc, respectively. Myc protein orchestrates diverse physiological processes, including cell proliferation, differentiation, survival, and apoptosis. Myc modulates about 15% of the global transcriptome, and its deregulation rewires the cellular signaling modules inside tumor cells, thereby acquiring selective advantages. The deregulation of Myc occurs in >70% of human cancers, and is related to poor prognosis; hence, hyperactivated Myc oncoprotein has been proposed as an ideal drug target for decades. Nevertheless, no specific drug is currently available to directly target Myc, mainly because of its "undruggable" properties: lack of enzymatic pocket for conventional small molecules to bind; inaccessibility for antibody due to the predominant nucleus localization of Myc. Although the topic of targeting Myc has actively been reviewed in the past decades, exciting new progresses in this field keep emerging. In this review, after a comprehensive summarization of valuable sources for potential druggable targets of Myc-driven cancer, we also peer into the promising future of utilizing macropinocytosis to deliver peptides like Omomyc or antibody agents to intracellular compartment for cancer treatment.

The Role of E3s in Regulating Pluripotency of Embryonic Stem Cells and Induced Pluripotent Stem Cells

Pluripotent embryonic stem cells (ESCs) are derived from early embryos and can differentiate into any type of cells in living organisms. Induced pluripotent stem cells (iPSCs) resemble ESCs, both of which serve as excellent sources to study early embryonic development and realize cell replacement therapies for age-related degenerative diseases and other cell dysfunction-related illnesses. To achieve these valuable applications, comprehensively understanding of the mechanisms underlying pluripotency maintenance and acquisition is critical. Ubiquitination modifies proteins with Ubiquitin (Ub) at the post-translational level to monitor protein stability and activity. It is extensively involved in pluripotency-specific regulatory networks in ESCs and iPSCs. Ubiquitination is achieved by sequential actions of the Ub-activating enzyme E1, Ub-conjugating enzyme E2, and Ub ligase E3. Compared with E1s and E2s, E3s are most abundant, responsible for substrate selectivity and functional diversity. In this review, we focus on E3 ligases to discuss recent progresses in understanding how they regulate pluripotency and somatic cell reprogramming through ubiquitinating core ESC regulators.

BRD4 prevents the accumulation of R-loops and protects against transcription-replication collision events and DNA damage

Proper chromatin function and maintenance of genomic stability depends on spatiotemporal coordination between the transcription and replication machinery. Loss of this coordination can lead to DNA damage from increased transcription-replication collision events. We report that deregulated transcription following BRD4 loss in cancer cells leads to the accumulation of RNA:DNA hybrids (R-loops) and collisions with the replication machinery causing replication stress and DNA damage. Whole genome BRD4 and γH2AX ChIP-Seq with R-loop IP qPCR reveals that BRD4 inhibition leads to accumulation of R-loops and DNA damage at a subset of known BDR4, JMJD6, and CHD4 co-regulated genes. Interference with BRD4 function causes transcriptional downregulation of the DNA damage response protein TopBP1, resulting in failure to activate the ATR-Chk1 pathway despite increased replication stress, leading to apoptotic cell death in S-phase and mitotic catastrophe. These findings demonstrate that inhibition of BRD4 induces transcription-replication conflicts, DNA damage, and cell death in oncogenic cells.

Structural and Biophysical Insights into the Function of the Intrinsically Disordered Myc Oncoprotein

Myc is a transcription factor driving growth and proliferation of cells and involved in the majority of human tumors. Despite a huge body of literature on this critical oncogene, our understanding of the exact molecular determinants and mechanisms that underlie its function is still surprisingly limited. Indubitably though, its crucial and non-redundant role in cancer biology makes it an attractive target. However, achieving successful clinical Myc inhibition has proven challenging so far, as this nuclear protein is an intrinsically disordered polypeptide devoid of any classical ligand binding pockets. Indeed, Myc only adopts a (partially) folded structure in some contexts and upon interacting with some protein partners, for instance when dimerizing with MAX to bind DNA. Here, we review the cumulative knowledge on Myc structure and biophysics and discuss the implications for its biological function and the development of improved Myc inhibitors. We focus this biophysical walkthrough mainly on the basic region helix-loop-helix leucine zipper motif (bHLHLZ), as it has been the principal target for inhibitory approaches so far.

Image-Based Analysis of Protein Stability

Short half-life proteins regulate many essential processes, including cell cycle, transcription, and apoptosis. However, few well-characterized protein-turnover pathways have been identified because traditional methods to measure protein half-life are time and labor intensive. To overcome this barrier, we developed a protein stability probe and high-content screening pipeline for novel regulators of short half-life proteins using automated image analysis. Our pilot probe consists of the short half-life protein c-MYC (MYC) fused to Venus fluorescent protein (MYC-Venus). This probe enables protein half-life to be scored as a function of fluorescence intensity and distribution. Rapid turnover prevents maximal fluorescence of the probe due to the relatively longer maturation time of the fluorescent protein. Cells expressing the MYC-Venus probe were analyzed using a pipeline in which automated confocal microscopy and image analyses were used to score MYC-Venus stability by two strategies: assaying the percentage of cells with Venus fluorescence above background, and phenotypic comparative analysis. To evaluate this high-content screening pipeline and our probe, a kinase inhibitor library was screened by confocal microscopy to identify known and novel kinases that regulate MYC stability. Compounds identified were shown to increase the half-life of both MYC-Venus and endogenous MYC, validating the probe and pipeline. Fusion of another short half-life protein, myeloid cell leukemia 1 (MCL1), with Venus also demonstrated an increase in percent Venus-positive cells after treatment with inhibitors known to stabilize MCL1. Together, the results validate the use of our automated microscopy and image analysis pipeline of stability probe-expressing cells to rapidly and quantitatively identify regulators of short half-life proteins. © 2019 The Authors. Cytometry Part A published by Wiley Periodicals, Inc. on behalf of International Society for Advancement of Cytometry.

Mission Possible: Advances in MYC Therapeutic Targeting in Cancer

MYC is a master transcriptional regulator that controls almost all cellular processes. Over the last several decades, researchers have strived to define the context-dependent transcriptional gene programs that are controlled by MYC, as well as the mechanisms that regulate MYC function, in an effort to better understand the contribution of this oncoprotein to cancer progression. There are a wealth of data indicating that deregulation of MYC activity occurs in a large number of cancers and significantly contributes to disease progression, metastatic potential, and therapeutic resistance. Although the therapeutic targeting of MYC in cancer is highly desirable, there remain substantial structural and functional challenges that have impeded direct MYC-targeted drug development and efficacy. While efforts to drug the ‘undruggable’ may seem futile given these challenges and considering the broad reach of MYC, significant strides have been made to identify points of regulation that can be exploited for therapeutic purposes. These include targeting the deregulation of MYC transcription in cancer through small-molecule inhibitors that induce epigenetic silencing or that regulate the G-quadruplex structures within the MYC promoter. Alternatively, compounds that disrupt the DNA-binding activities of MYC have been the long-standing focus of many research groups, since this method would prevent downstream MYC oncogenic activities regardless of upstream alterations. Finally, proteins involved in the post-translational regulation of MYC have been identified as important surrogate targets to reduce MYC activity downstream of aberrant cell stimulatory signals. Given the complex regulation of the MYC signaling pathway, a combination of these approaches may provide the most durable response, but this has yet to be shown. Here, we provide a comprehensive overview of the different therapeutic strategies being employed to target oncogenic MYC function, with a focus on post-translational mechanisms.

Max deletion destabilizes MYC protein and abrogates Eµ-Myc lymphomagenesis

Although MAX is regarded as an obligate dimerization partner for MYC, its function in normal development and neoplasia is poorly defined. We show that B-cell-specific deletion of Max has a modest effect on B-cell development but completely abrogates Eµ-Myc-driven lymphomagenesis. While Max loss affects only a few hundred genes in normal B cells, it leads to the global down-regulation of Myc-activated genes in premalignant Eµ-Myc cells. We show that the balance between MYC-MAX and MNT-MAX interactions in B cells shifts in premalignant B cells toward a MYC-driven transcriptional program. Moreover, we found that MAX loss leads to a significant reduction in MYC protein levels and down-regulation of direct transcriptional targets, including regulators of MYC stability. This phenomenon is also observed in multiple cell lines treated with MYC-MAX dimerization inhibitors. Our work uncovers a layer of Myc autoregulation critical for lymphomagenesis yet partly dispensable for normal development.

Pumilio directs deadenylation-associated translational repression of the cyclin-dependent kinase 1 activator RGC-32

Response gene to complement-32 (RGC-32) activates cyclin-dependent kinase 1, regulates the cell cycle and is deregulated in many human tumours. We previously showed that RGC-32 expression is upregulated by the cancer-associated Epstein-Barr virus (EBV) in latently infected B cells through the relief of translational repression. We now show that EBV infection of naïve primary B cells also induces RGC-32 protein translation. In EBV-immortalised cell lines, we found that RGC-32 depletion resulted in cell death, indicating a key role in B cell survival. Studying RGC-32 translational control in EBV-infected cells, we found that the RGC-32 3′untranslated region (3′UTR) mediates translational repression. Repression was dependent on a single Pumilio binding element (PBE) adjacent to the polyadenylation signal. Mutation of this PBE did not affect mRNA cleavage, but resulted in increased polyA tail length. Consistent with Pumilio-dependent recruitment of deadenylases, we found that depletion of Pumilio in EBV-infected cells increased RGC-32 protein expression and polyA tail length. The extent of Pumilio binding to the endogenous RGC-32 mRNA in EBV-infected cell lines also correlated with RGC-32 protein expression. Our data demonstrate the importance of RGC-32 for the survival of EBV-immortalised B cells and identify Pumilio as a key regulator of RGC-32 translation.

Expression of UPR effector proteins ATF6 and XBP1 reduce colorectal cancer cell proliferation and stemness by activating PERK signaling

The unfolded protein response (UPR) acts through its downstream branches, PERK-eIF2α signaling, IRE1α-XBP1 signaling and ATF6 signaling. In the intestine, activation of the UPR through the kinase PERK results in differentiation of intestinal epithelial stem cells and colon cancer stem cells, whereas deletion of XBP1 results in increased stemness and adenomagenesis. How downstream activation of XBP1 and ATF6 influences intestinal stemness and proliferation remains largely unknown. We generated colorectal cancer cells (LS174T) that harbor doxycycline inducible expression of the active forms of either XBP1(s) or ATF61-373. Activation of either XBP1 or ATF6 resulted in reduced cellular proliferation and reduced expression of markers of intestinal epithelial stemness. Moreover, XBP1 and ATF6 activation reduced global protein synthesis and lowered the threshold for UPR activation. XBP1-mediated loss of stemness and proliferation resulted from crossactivation of PERK-eIF2α signaling and could be rescued by constitutive expression of eIF2α phosphatase GADD34. We thus find that enforced activation of XBP1 and ATF6 results in reduction of stemness and proliferation. We expose a novel interaction between XBP1 and PERK-eIF2α signaling.

In silico modeling of phosphorylation dependent and independent c-Myc degradation

Background

c-Myc plays an important role in cell proliferation, cell growth and in differentiation, making it a key regulator for carcinogenesis and pluripotency. Tight control of c-myc turnover is required by ubiquitin-mediated degradation. This is achieved in the system by two F-box proteins Skp2 and FBXW7.

Results

Dynamic modelling technique was used to build two exclusive models for phosphorylation dependent degradation of Myc by FBXW7 (Model 1) and phosphorylation independent degradation by Skp2 (Model 2). Sensitivity analysis performed on these two models revealed that these models were corroborating experimental studies. It was also seen that Model 1 was more robust and perhaps more efficient in degrading c-Myc. These results questioned the existence of the two models in the system and to answer the question a combined model was hypothesised which had a decision making switch. The combined model had both Skp2 and FBXW7 mediated degradation where again the latter played a more important role. This model was able to achieve the lowest levels of ubiquitylated Myc and therefore functioned most efficiently in degradation of Myc.

Conclusion

In this report, c-Myc degradation by two F-box proteins was mathematically evaluated based on the importance of c-Myc turnover. The study was performed in a homeostatic system and therefore, prompts the exploration of c-Myc degradation in cancer state and in pluripotent state.

Electronic supplementary material

The online version of this article (10.1186/s12859-019-2846-x) contains supplementary material, which is available to authorized users.

Tracing MYC Expression for Small Molecule Discovery

Our inability to effectively "drug" targets such as MYC for therapeutic purposes requires the development of new approaches. We report on the implementation of a phenotype-based assay for monitoring MYC expression in multiple myeloma cells. The open reading frame (ORF) encoding an unstable variant of GFP was engineered immediately downstream of the MYC ORF using CRISPR/Cas9, resulting in co-expression of both proteins from the endogenous MYC locus. Using fluorescence readout as a surrogate for MYC expression, we implemented a pilot screen in which ∼10,000 compounds were prosecuted. Among known MYC expression inhibitors, we identified cardiac glycosides and cytoskeletal disruptors to be quite potent. We demonstrate the power of CRISPR/Cas9 engineering in establishing phenotype-based assays to identify gene expression modulators.

New MYC IHC Classifier Integrating Quantitative Architecture Parameters to Predict MYC Gene Translocation in Diffuse Large B-Cell Lymphoma

A new automated MYC IHC classifier based on bivariate logistic regression is presented. The predictor relies on image analysis developed with the open-source ImageJ platform. From a histologic section immunostained for MYC protein, 2 dimensionless quantitative variables are extracted: (a) relative distance between nuclei positive for MYC IHC based on euclidean minimum spanning tree graph and (b) coefficient of variation of the MYC IHC stain intensity among MYC IHC-positive nuclei. Distance between positive nuclei is suggested to inversely correlate MYC gene rearrangement status, whereas coefficient of variation is suggested to inversely correlate physiological regulation of MYC protein expression. The bivariate classifier was compared with 2 other MYC IHC classifiers (based on percentage of MYC IHC positive nuclei), all tested on 113 lymphomas including mostly diffuse large B-cell lymphomas with known MYC fluorescent in situ hybridization (FISH) status. The bivariate classifier strongly outperformed the “percentage of MYC IHC-positive nuclei” methods to predict MYC+ FISH status with 100% sensitivity (95% confidence interval, 94-100) associated with 80% specificity. The test is rapidly performed and might at a minimum provide primary IHC screening for MYC gene rearrangement status in diffuse large B-cell lymphomas. Furthermore, as this bivariate classifier actually predicts “permanent overexpressed MYC protein status,” it might identify nontranslocation-related chromosomal anomalies missed by FISH.

Genetic Drivers of Pancreatic Cancer Are Identical Between the Primary Tumor and a Secondary Lesion in a Long-Term (>5 Years) Survivor After a Whipple Procedure

Background: A new mass in the remnant pancreas of a patient with previously resected pancreatic ductal adenocarcinoma (PDA) typically represents either a recurrence of the initial primary tumor or a second primary tumor. Recent advances in next-generation sequencing (NGS) strategies allow us to compare the genetic makeup of primary and secondary lesions. Case presentation: A 50-year-old Caucasian female presented for a surgical evaluation of a new biopsy-proven PDA at the junction of the body and tail of the pancreas. Six years prior, in 2011, the patient was found to have a T3N0M0 PDA of the pancreatic head, which was surgically resected with a classic Whipple procedure and concurrent hemicolectomy. Pathology showed pancreatic intraepithelial neoplasia grade 2 and PDA with negative surgical margins, positive perineural spread, and negative lymphovascular spread, and the patient received adjuvant chemotherapy and local radiation. In 2017, she was diagnosed with a new PDA lesion in the remaining pancreatic body far from the previous anastomosis site and was taken to surgery for a completion pancreatectomy and revision of the gastrojejunostomy. NGS was performed on both specimens. Both lesions shared identical mutations in KRAS, TP53, and CDKN2A genes. Amplifications of MYC and mutant KRAS were identified in the 2017 tumor and an ACVR1B mutation was identified in the 2011 tumor, but was not found in the 2017 tumor. Conclusions: This case demonstrates the ability to evaluate similarities between key genetic drivers from a resected primary tumor and a PDA lesion that presented in the same patient 6 years later. Histological analysis and NGS can be used to understand potential differences and similarities between lesions and may be useful in future studies as predictive markers or to provide insight into resistance mechanisms (e.g., MYC amplification).

The impact of phosphatases on proliferative and survival signaling in cancer

The dynamic and stringent coordination of kinase and phosphatase activity controls a myriad of physiologic processes. Aberrations that disrupt the balance of this interplay represent the basis of numerous diseases. For a variety of reasons, early work in this area portrayed kinases as the dominant actors in these signaling events with phosphatases playing a secondary role. In oncology, these efforts led to breakthroughs that have dramatically altered the course of certain diseases and directed vast resources toward the development of additional kinase-targeted therapies. Yet, more recent scientific efforts have demonstrated a prominent and sometimes driving role for phosphatases across numerous malignancies. This maturation of the phosphatase field has brought with it the promise of further therapeutic advances in the field of oncology. In this review, we discuss the role of phosphatases in the regulation of cellular proliferation and survival signaling using the examples of the MAPK and PI3K/AKT pathways, c-Myc and the apoptosis machinery. Emphasis is placed on instances where these signaling networks are perturbed by dysregulation of specific phosphatases to favor growth and persistence of human cancer.

The MYC transcription factor network: balancing metabolism, proliferation and oncogenesis

Transcription factor networks have evolved in order to control, coordinate, and separate, the functions of distinct network modules spatially and temporally. In this review we focus on the MYC network (also known as the MAX-MLX Network), a highly conserved super-family of related basic-helix-loop-helix-zipper (bHLHZ) proteins that functions to integrate extracellular and intracellular signals and modulate global gene expression. Importantly the MYC network has been shown to be deeply involved in a broad spectrum of human and other animal cancers. Here we summarize molecular and biological properties of the network modules with emphasis on functional interactions among network members. We suggest that these network interactions serve to modulate growth and metabolism at the transcriptional level in order to balance nutrient demand with supply, to maintain growth homeostasis, and to influence cell fate. Moreover, oncogenic activation of MYC and/or loss of a MYC antagonist, results in an imbalance in the activity of the network as a whole, leading to tumor initiation, progression and maintenance.

Kinase inhibitors: the road ahead

Receptor tyrosine kinase signalling pathways have been successfully targeted to inhibit proliferation and angiogenesis for cancer therapy. However, kinase deregulation has been firmly demonstrated to play an essential role in virtually all major disease areas. Kinase inhibitor drug discovery programmes have recently broadened their focus to include an expanded range of kinase targets and therapeutic areas. In this Review, we provide an overview of the novel targets, biological processes and disease areas that kinase-targeting small molecules are being developed against, highlight the associated challenges and assess the strategies and technologies that are enabling efficient generation of highly optimized kinase inhibitors.

Network Features and Dynamical Landscape of Naive and Primed Pluripotency

Although the broad and unique differentiation potential of pluripotent stem cells relies on a complex transcriptional network centered around Oct4, Sox2, and Nanog, two well-distinct pluripotent states, called "naive" and "primed", have been described in vitro and markedly differ in their developmental potential, their expression profiles, their signaling requirements, and their reciprocal conversion. Aiming to determine the key features that segregate and coordinate these two states, data-driven optimization of network models is performed to identify relevant parameter regimes and reduce network complexity to its core structure. Decision dynamics of optimized networks is characterized by signal-dependent multistability and strongly asymmetric transitions among naive, primed, and nonpluripotent states. Further model perturbation and reduction approaches reveal that such a dynamical landscape of pluripotency involves a functional partitioning of the regulatory network. Specifically, two overlapping positive feedback modules, Klf4/Esrrb/Nanog and Oct4/Nanog, stabilize the naive or the primed state, respectively. In turn, their incoherent feedforward and negative feedback coupling mediated by the Erk/Gsk3 module is critical for robust segregation and sequential progression between naive and primed states before irreversible exit from pluripotency.

Non-AUG translation: a new start for protein synthesis in eukaryotes

This review by Kearse and Wilusz discusses the profound impact of non-AUG start codons in eukaryotic translation. It describes how misregulation of non-AUG initiation events contributes to multiple human diseases, including cancer and neurodegeneration, and how modulation of non-AUG usage may represent a novel therapeutic strategy.

Although it was long thought that eukaryotic translation almost always initiates at an AUG start codon, recent advancements in ribosome footprint mapping have revealed that non-AUG start codons are used at an astonishing frequency. These non-AUG initiation events are not simply errors but instead are used to generate or regulate proteins with key cellular functions; for example, during development or stress. Misregulation of non-AUG initiation events contributes to multiple human diseases, including cancer and neurodegeneration, and modulation of non-AUG usage may represent a novel therapeutic strategy. It is thus becoming increasingly clear that start codon selection is regulated by many trans-acting initiation factors as well as sequence/structural elements within messenger RNAs and that non-AUG translation has a profound impact on cellular states.

The Role of c-MYC in B-Cell Lymphomas: Diagnostic and Molecular Aspects

c-MYC is one of the most essential transcriptional factors, regulating a diverse array of cellular functions, including proliferation, growth, and apoptosis. Dysregulation of c-MYC is essential in the pathogenesis of a number of B-cell lymphomas, but is rarely reported in T-cell lymphomas. c-MYC dysregulation induces lymphomagenesis by loss of the tight control of c-MYC expression, leading to overexpression of intact c-MYC protein, in contrast to the somatic mutations or fusion proteins seen in many other oncogenes. Dysregulation of c-MYC in B-cell lymphomas occurs either as a primary event in Burkitt lymphoma, or secondarily in aggressive lymphomas such as diffuse large B-cell lymphoma, plasmablastic lymphoma, mantle cell lymphoma, or double-hit lymphoma. Secondary c-MYC changes include gene translocation and gene amplification, occurring against a background of complex karyotype, and most often confer aggressive clinical behavior, as evidenced in the double-hit lymphomas. In low-grade B-cell lymphomas, acquisition of c-MYC rearrangement usually results in transformation into highly aggressive lymphomas, with some exceptions. In this review, we discuss the role that c-MYC plays in the pathogenesis of B-cell lymphomas, the molecular alterations that lead to c-MYC dysregulation, and their effect on prognosis and diagnosis in specific types of B-cell lymphoma.

Immature Lymphocytes Inhibit Rag1 and Rag2 Transcription and V(D)J Recombination in Response to DNA Double-Strand Breaks

Mammalian cells have evolved a common DNA damage response (DDR) that sustains cellular function, maintains genomic integrity, and suppresses malignant transformation. In pre-B cells, DNA double-strand breaks (DSBs) induced at Igκ loci by the Rag1/Rag2 (RAG) endonuclease engage this DDR to modulate transcription of genes that regulate lymphocyte-specific processes. We previously reported that RAG DSBs induced at one Igκ allele signal through the ataxia telangiectasia mutated (ATM) kinase to feedback-inhibit RAG expression and RAG cleavage of the other Igκ allele. In this article, we show that DSBs induced by ionizing radiation, etoposide, or bleomycin suppress Rag1 and Rag2 mRNA levels in primary pre-B cells, pro-B cells, and pro-T cells, indicating that inhibition of Rag1 and Rag2 expression is a prevalent DSB response among immature lymphocytes. DSBs induced in pre-B cells signal rapid transcriptional repression of Rag1 and Rag2, causing downregulation of both Rag1 and Rag2 mRNA, but only Rag1 protein. This transcriptional inhibition requires the ATM kinase and the NF-κB essential modulator protein, implicating a role for ATM-mediated activation of canonical NF-κB transcription factors. Finally, we demonstrate that DSBs induced in pre-B cells by etoposide or bleomycin inhibit recombination of Igκ loci and a chromosomally integrated substrate. Our data indicate that immature lymphocytes exploit a common DDR signaling pathway to limit DSBs at multiple genomic locations within developmental stages wherein monoallelic Ag receptor locus recombination is enforced. We discuss the implications of our findings for mechanisms that orchestrate the differentiation of monospecific lymphocytes while suppressing oncogenic Ag receptor locus translocations.

Induction of endoplasmic reticulum stress by deletion of Grp78 depletes Apc mutant intestinal epithelial stem cells

Intestinal epithelial stem cells are highly sensitive to differentiation induced by endoplasmic reticulum (ER) stress. Colorectal cancer develops from mutated intestinal epithelial stem cells. The most frequent initiating mutation occurs in Apc, which results in hyperactivated Wnt signalling. This causes hyperproliferation and reduced sensitivity to chemotherapy, but whether these mutated stem cells are sensitive to ER stress induced differentiation remains unknown. Here we examined this by generating mice in which both Apc and ER stress repressor chaperone Grp78 can be conditionally deleted from the intestinal epithelium. For molecular studies, we used intestinal organoids derived from these mice. Homozygous loss of Apc alone resulted in crypt elongation, activation of the Wnt signature and accumulation of intestinal epithelial stem cells, as expected. This phenotype was however completely rescued on activation of ER stress by additional deletion of Grp78. In these Apc-Grp78 double mutant animals, stem cells were rapidly lost and repopulation occurred by non-mutant cells that had escaped recombination, suggesting that Apc-Grp78 double mutant stem cells had lost self-renewal capacity. Although in Apc-Grp78 double mutant mice the Wnt signature was lost, these intestines exhibited ubiquitous epithelial presence of nuclear β-catenin. This suggests that ER stress interferes with Wnt signalling downstream of nuclear β-catenin. In conclusion, our findings indicate that ER stress signalling results in loss of Apc mutated intestinal epithelial stem cells by interference with the Wnt signature. In contrast to many known inhibitors of Wnt signalling, ER stress acts downstream of β-catenin. Therefore, ER stress poses a promising target in colorectal cancers, which develop as a result of Wnt activating mutations.

Protective Effects of Gallic Acid Against NiSO4-Induced Toxicity Through Down-Regulation of the Ras/ERK Signaling Pathway in Beas-2B Cells

Background

This study aimed to explore the preventive effects of gallic acid (GA) on the toxicity induced by NiSO₄ in Beas-2B cells.

Material/Methods

Beas-2B cell viability was measured by MTT assay. The degree of oxidative stress was detected by measuring the levels of reactive oxygen species (ROS) and lipid peroxide (LPO). The rate of apoptosis was measured by flow cytometry. Ras/ERK-related protein levels were analyzed by Western blot analysis, which including Ras, ERK, c-Myc, PARP, and PARP cleavage.

Results

MTT assay showed that NiSO₄ induced cytotoxicity, while GA had a protective role against toxicity. Additionally, GA could reduce the apoptotic cell number and the level of ROS in Beas-2B cells induced by NiSO₄. Western blot analysis demonstrated that NiSO₄ could up-regulate the related protein in the Ras/ERK signaling pathway. Furthermore, we observed that GA could alleviate the toxicity of NiSO₄ through regulating protein changes in the Ras/ERK signaling pathway.

Conclusions

Preventive effects of GA on NiSO₄-induced cytotoxicity in Beas-2B cells may be through the Ras/ERK signaling pathways.

MYC-nick promotes cell migration by inducing fascin expression and Cdc42 activation

MYC-nick is a cytoplasmic, transcriptionally inactive member of the MYC oncoprotein family, generated by a proteolytic cleavage of full-length MYC. MYC-nick promotes migration and survival of cells in response to chemotherapeutic agents or withdrawal of glucose. Here we report that MYC-nick is abundant in colonic and intestinal tumors derived from mouse models with mutations in the Wnt, TGF-β, and PI3K pathways. Moreover, MYC-nick is elevated in colon cancer cells deleted for FBWX7, which encodes the major E3 ligase of full-length MYC frequently mutated in colorectal cancers. MYC-nick promotes the migration of colon cancer cells assayed in 3D cultures or grown as xenografts in a zebrafish metastasis model. MYC-nick accelerates migration by activating the Rho GTPase Cdc42 and inducing fascin expression. MYC-nick, fascin, and Cdc42 are frequently up-regulated in cells present at the invasive front of human colorectal tumors, suggesting a coordinated role for these proteins in tumor migration.

The Importance of Ubiquitination and Deubiquitination in Cellular Reprogramming

Ubiquitination of core stem cell transcription factors can directly affect stem cell maintenance and differentiation. Ubiquitination and deubiquitination must occur in a timely and well-coordinated manner to regulate the protein turnover of several stemness related proteins, resulting in optimal embryonic stem cell maintenance and differentiation. There are two switches: an E3 ubiquitin ligase enzyme that tags ubiquitin molecules to the target proteins for proteolysis and a second enzyme, the deubiquitinating enzyme (DUBs), that performs the opposite action, thereby preventing proteolysis. In order to maintain stemness and to allow for efficient differentiation, both ubiquitination and deubiquitination molecular switches must operate properly in a balanced manner. In this review, we have summarized the importance of the ubiquitination of core stem cell transcription factors, such as Oct3/4, c-Myc, Sox2, Klf4, Nanog, and LIN28, during cellular reprogramming. Furthermore, we emphasize the role of DUBs in regulating core stem cell transcriptional factors and their function in stem cell maintenance and differentiation. We also discuss the possibility of using DUBs, along with core transcription factors, to efficiently generate induced pluripotent stem cells. Our review provides a relatively new understanding regarding the importance of ubiquitination/deubiquitination of stem cell transcription factors for efficient cellular reprogramming.

MYC-driven aggressive B-cell lymphomas: biology, entity, differential diagnosis and clinical management

MYC, a potent oncogene located at chromosome locus 8q24.21, was identified initially by its involvement in Burkitt lymphoma with t(8;14)(q24;q32). MYC encodes a helix-loop-helix transcription factor that accentuates many cellular functions including proliferation, growth and apoptosis. MYC alterations also have been identified in other mature B-cell neoplasms and are associated with aggressive clinical behavior. There are several regulatory factors and dysregulated signaling that lead to MYC up-regulation in B-cell lymphomas. One typical example is the failure of physiological repressors such as Bcl6 or BLIMP1 to suppress MYC over-expression. In addition, MYC alterations are often developed concurrently with other genetic alterations that counteract the proapoptotic function of MYC. In this review, we discuss the physiologic function of MYC and the role that MYC likely plays in the pathogenesis of B-cell lymphomas. We also summarize the role MYC plays in the diagnosis, prognostication and various strategies to detect MYC rearrangement and expression.

ASK1 modulates the expression of microRNA Let7A in microglia under high glucose in vitro condition

Hyperglycemia results in oxidative stress and leads to neuronal apoptosis in the brain. Diabetes studies show that microglia participate in the progression of neuropathogenesis through their involvement in inflammation in vivo and in vitro. In high-glucose-induced inflammation, apoptosis signal regulating kinase 1 (ASK1) triggers the release of apoptosis cytokines and apoptotic gene expression. MicroRNA-Let7A (miR-Let7A) is reported to be a regulator of inflammation. In the present study, we investigated whether miR-Let7A regulates the function of microglia by controlling ASK1 in response to high-glucose-induced oxidative stress. We performed reverse transcription (RT) polymerase chain reaction, Taqman assay, real-time polymerase chain reaction, and immunocytochemistry to confirm the alteration of microglia function. Our results show that miR-Let7A is associated with the activation of ASK1 and the expression of anti-inflammatory cytokine (interleukin (IL)-10) and Mycs (c-Myc and N-Myc). Thus, the relationship between Let-7A and ASK1 could be a novel target for enhancing the beneficial function of microglia in central nervous system (CNS) disorders.

Targeting the eIF4F translation initiation complex: a critical nexus for cancer development

Elevated protein synthesis is an important feature of many cancer cells and often arises as a consequence of increased signaling flux channeled to eukaryotic initiation factor 4F (eIF4F), the key regulator of the mRNA-ribosome recruitment phase of translation initiation. In many cellular and preclinical models of cancer, eIF4F deregulation results in changes in translational efficiency of specific mRNA classes. Importantly, many of these mRNAs code for proteins that potently regulate critical cellular processes, such as cell growth and proliferation, enhanced cell survival and cell migration that ultimately impinge on several hallmarks of cancer, including increased angiogenesis, deregulated growth control, enhanced cellular survival, epithelial-to-mesenchymal transition, invasion, and metastasis. By being positioned as the molecular nexus downstream of key oncogenic signaling pathways (e.g., Ras, PI3K/AKT/TOR, and MYC), eIF4F serves as a direct link between important steps in cancer development and translation initiation. Identification of mRNAs particularly responsive to elevated eIF4F activity that typifies tumorigenesis underscores the critical role of eIF4F in cancer and raises the exciting possibility of developing new-in-class small molecules targeting translation initiation as antineoplastic agents.

MYC is an early response regulator of human adipogenesis in adipose stem cells

Adipose stem cell (ASC) differentiation is necessary for the proper maintenance and function of adipose tissue. The procurement and characterization of multipotent ASCs has enabled investigation into the molecular determinants driving human adipogenesis. Here, the transcription factor MYC was identified as a significant regulator of ASC differentiation. Expression of MYC transcript and protein was found to accumulate during the initial course of differentiation. Loss-of-function analysis using siRNA mediated knockdown of MYC demonstrated inhibition of hormonally stimulated adipogenesis. MYC exhibited an early and sustained expression pattern that preceded down regulation of key suppressor genes, as well as induction of transcriptional and functional effectors. Glucocorticoid stimulation was identified as a necessary component for MYC induction and was found to impact adipogenesis in a concentration-dependent manner. Global gene expression analysis of MYC knockdown in ASC enriched for functional pathways related to cell adhesion, cytoskeletal remodeling, and transcriptional components of adipogenesis. These results identify a functional role for MYC in promotion of multipotent ASC to the adipogenic lineage.

Functional characterization of the TERRA transcriptome at damaged telomeres

Telomere deprotection occurs during tumorigenesis and aging upon telomere shortening or loss of the telomeric shelterin component TRF2. Deprotected telomeres undergo changes in chromatin structure and elicit a DNA damage response (DDR) that leads to cellular senescence. The telomeric long noncoding RNA TERRA has been implicated in modulating the structure and processing of deprotected telomeres. Here, we characterize the human TERRA transcriptome at normal and TRF2-depleted telomeres and demonstrate that TERRA upregulation is occurring upon depletion of TRF2 at all transcribed telomeres. TRF2 represses TERRA transcription through its homodimerization domain, which was previously shown to induce chromatin compaction and to prevent the early steps of DDR activation. We show that TERRA associates with SUV39H1 H3K9 histone methyltransferase, which promotes accumulation of H3K9me3 at damaged telomeres and end-to-end fusions. Altogether our data elucidate the TERRA landscape and defines critical roles for this RNA in the telomeric DNA damage response.

MCL1 and BCL-xL levels in solid tumors are predictive of dinaciclib-induced apoptosis

Dinaciclib is a potent CDK1, 2, 5 and 9 inhibitor being developed for the treatment of cancer. Additional understanding of antitumor mechanisms and identification of predictive biomarkers are important for its clinical development. Here we demonstrate that while dinaciclib can effectively block cell cycle progression, in vitro and in vivo studies, coupled with mouse and human pharmacokinetics, support a model whereby induction of apoptosis is a main mechanism of dinaciclib's antitumor effect and relevant to the clinical duration of exposure. This was further underscored by kinetics of dinaciclib-induced downregulation of the antiapoptotic BCL2 family member MCL1 and correlation of sensitivity with the MCL1-to-BCL-xL mRNA ratio or MCL1 amplification in solid tumor models in vitro and in vivo. This MCL1-dependent apoptotic mechanism was additionally supported by synergy with the BCL2, BCL-xL and BCL-w inhibitor navitoclax (ABT-263). These results provide the rationale for investigating MCL1 and BCL-xL as predictive biomarkers for dinaciclib antitumor response and testing combinations with BCL2 family member inhibitors.

The long non-coding RNA GAS5 cooperates with the eukaryotic translation initiation factor 4E to regulate c-Myc translation

Long noncoding RNAs (lncRNAs) are important regulators of transcription; however, their involvement in protein translation is not well known. Here we explored whether the lncRNA GAS5 is associated with translation initiation machinery and regulates translation. GAS5 was enriched with eukaryotic translation initiation factor-4E (eIF4E) in an RNA-immunoprecipitation assay using lymphoma cell lines. We identified two RNA binding motifs within eIF4E protein and the deletion of each motif inhibited the binding of GAS5 with eIF4E. To confirm the role of GAS5 in translation regulation, GAS5 siRNA and in vitro transcribed GAS5 RNA were used to knock down or overexpress GAS5, respectively. GAS5 siRNA had no effect on global protein translation but did specifically increase c-Myc protein level without an effect on c-Myc mRNA. The mechanism of this increase in c-Myc protein was enhanced association of c-Myc mRNA with the polysome without any effect on protein stability. In contrast, overexpression of in vitro transcribed GAS5 RNA suppressed c-Myc protein without affecting c-Myc mRNA. Interestingly, GAS5 was found to be bound with c-Myc mRNA, suggesting that GAS5 regulates c-Myc translation through lncRNA-mRNA interaction. Our findings have uncovered a role of GAS5 lncRNA in translation regulation through its interactions with eIF4E and c-Myc mRNA.

Partition of Myc into immobile vs. mobile complexes within nuclei

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

MYC cofactors: molecular switches controlling diverse biological outcomes

The transcription factor MYC has fundamental roles in proliferation, apoptosis, tumorigenesis, and stem cell pluripotency. Over the last 30 years extensive information has been gathered on the numerous cofactors that interact with MYC and the target genes that are regulated by MYC as a means of understanding the molecular mechanisms controlling its diverse roles. Despite significant advances and perhaps because the amount of information learned about MYC is overwhelming, there has been little consensus on the molecular functions of MYC that mediate its critical biological roles. In this perspective, the major MYC cofactors that regulate the various transcriptional activities of MYC, including canonical and noncanonical transactivation and transcriptional repression, will be reviewed and a model of how these transcriptional mechanisms control MYC-mediated proliferation, apoptosis, and tumorigenesis will be presented. The basis of the model is that a variety of cofactors form dynamic MYC transcriptional complexes that can switch the molecular and biological functions of MYC to yield a diverse range of outcomes in a cell-type- and context-dependent fashion.

SUMOylation of Myc-family proteins

Myc-family proteins are key controllers of the metabolic and proliferative status of the cell, and are subjected to a complex network of regulatory events that guarantee their efficient and fast modulation by extracellular stimuli. Hence, unbalances in regulatory mechanisms leading to altered Myc levels or activities are often reported in cancer cells. Here we show that c- and N-Myc are conjugated to SUMO proteins at conserved lysines in their C-terminal domain. No obvious effects of SUMOylation were detected on bulk N-Myc stability or activities, including the regulation of transcription, proliferation or apoptosis. N-Myc SUMOylation could be induced by cellular stresses, such as heat shock and proteasome inhibition, and in all instances concerned a small fraction of the N-Myc protein. We surmise that, as shown for other substrates, SUMOylation may be part of a quality-control mechanism acting on misfolded Myc proteins.

Canine epidermal neural crest stem cells: characterization and potential as therapy candidate for a large animal model of spinal cord injury

The discovery of multipotent neural crest-derived stem cells, named epidermal neural crest stem cells (EPI-NCSC), that persist postnatally in an easy-to-access location-the bulge of hair follicles-opens a spectrum of novel opportunities for patient-specific therapies. We present a detailed characterization of canine EPI-NCSC (cEPI-NCSC) from multiple dog breeds and protocols for their isolation and ex vivo expansion. Furthermore, we provide novel tools for research in canines, which currently are still scarce. In analogy to human and mouse EPI-NCSC, the neural crest origin of cEPI-NCSC is shown by their expression of the neural crest stem cell molecular signature and other neural crest-characteristic genes. Similar to human EPI-NCSC, cEPI-NCSC also expressed pluripotency genes. We demonstrated that cEPI-NCSC can generate all major neural crest derivatives. In vitro clonal analyses established multipotency and self-renewal ability of cEPI-NCSC, establishing cEPI-NCSC as multipotent somatic stem cells. A critical analysis of the literature on canine spinal cord injury (SCI) showed the need for novel treatments and suggested that cEPI-NCSC represent viable candidates for cell-based therapies in dog SCI, particularly for chondrodystrophic dogs. This notion is supported by the close ontological relationship between neural crest stem cells and spinal cord stem cells. Thus, cEPI-NCSC promise to offer not only a potential treatment for canines but also an attractive and realistic large animal model for human SCI. Taken together, we provide the groundwork for the development of a novel cell-based therapy for a condition with extremely poor prognosis and no available effective treatment.

MYC degradation

The MYC oncoprotein is an essential transcription factor that regulates the expression of many genes involved in cell growth, proliferation, and metabolic pathways. Thus, it is important to keep MYC activity in check in normal cells in order to avoid unwanted oncogenic changes. Normal cells have adapted several ways to control MYC levels, and these mechanisms can be disrupted in cancer cells. One of the major ways in which MYC levels are controlled in cells is through targeted degradation by the ubiquitin-proteasome system (UPS). Here, we discuss the role of the UPS in the regulation of MYC protein levels and review some of the many proteins that have been shown to regulate MYC protein stability. In addition, we discuss how this relates to MYC transcriptional activity, human cancers, and therapeutic targeting.

Developments in Burkitt's lymphoma: novel cooperations in oncogenic MYC signaling

Burkitt's lymphoma (BL) is an aggressive disorder associated with extremely high rates of cell proliferation tempered by high levels of apoptosis. Despite the high levels of cell death, the net effect is one of rapid tumor growth. The tumor arises within the germinal centers of secondary lymphoid tissues and is identifiable by translocation of the c-MYC gene into the immunoglobulin gene loci, resulting in deregulation of the proto-oncogene. Many of the major players involved in determining the development of BL have been characterized in human BL cell lines or in mouse models of MYC-driven lymphomagenesis. Both systems have been useful so far in characterizing the role of tumor suppressor genes (for example, p53), prosurvival signaling pathways, and members of the B-cell lymphoma-2 family of apoptosis regulators in determining the fate of c-MYC overexpressing B-cells, and ultimately in regulating lymphoma development. Signaling through phosphoinositide (PI)3-kinase stands out as being critical for BL cell survival. Recurrent mutations in ID3 or TCF3 (E2A) that promote signaling through PI3-kinase have recently been identified in human BL samples, and new therapeutic strategies based on coordinately targeting both the prosurvival factor, B-cell lymphoma-XL, and the PI3-kinase/AKT/mammalian target of rapamycin (mTOR) signaling pathway to synergistically induced BL apoptosis have been proposed. Now, engineering both constitutive c-MYC expression and PI3-kinase activity, specifically in murine B-cells undergoing the germinal center reaction, has revealed that there is synergistic cooperation between c-MYC and PI3-kinase during BL development. The resulting tumors phenocopy the human malignancy, and acquire tertiary mutations also present in human tumors. This model may, therefore, prove useful in further studies to identify functionally relevant mutational events necessary for BL pathogenesis. This review discusses these cooperating interactions, the possible influence of BL tumor-associated viruses, and highlights potential new opportunities for therapeutic intervention.

An overview of MYC and its interactome

This review is intended to provide a broad outline of the biological and molecular functions of MYC as well as of the larger protein network within which MYC operates. We present a view of MYC as a sensor that integrates multiple cellular signals to mediate a broad transcriptional response controlling many aspects of cell behavior. We also describe the larger transcriptional network linked to MYC with emphasis on the MXD family of MYC antagonists. Last, we discuss evidence that the network has evolved for millions of years, dating back to the emergence of animals.

Deciphering the modulation of gene expression by type I and II interferons combining 4sU-tagging, translational arrest and in silico promoter analysis

Interferons (IFN) play a pivotal role in innate immunity, orchestrating a cell-intrinsic anti-pathogenic state and stimulating adaptive immune responses. The complex interplay between the primary response to IFNs and its modulation by positive and negative feedback loops is incompletely understood. Here, we implement the combination of high-resolution gene-expression profiling of nascent RNA with translational inhibition of secondary feedback by cycloheximide. Unexpectedly, this approach revealed a prominent role of negative feedback mechanisms during the immediate (≤60 min) IFNα response. In contrast, a more complex picture involving both negative and positive feedback loops was observed on IFNγ treatment. IFNγ-induced repression of genes associated with regulation of gene expression, cellular development, apoptosis and cell growth resulted from cycloheximide-resistant primary IFNγ signalling. In silico promoter analysis revealed significant overrepresentation of SP1/SP3-binding sites and/or GC-rich stretches. Although signal transducer and activator of transcription 1 (STAT1)-binding sites were not overrepresented, repression was lost in absence of STAT1. Interestingly, basal expression of the majority of these IFNγ-repressed genes was dependent on STAT1 in IFN-naïve fibroblasts. Finally, IFNγ-mediated repression was also found to be evident in primary murine macrophages. IFN-repressed genes include negative regulators of innate and stress response, and their decrease may thus aid the establishment of a signalling perceptive milieu.

MYC degradation under low O2 tension promotes survival by evading hypoxia-induced cell death

Cells encounter oxygen deprivation (hypoxia) in various physiological and pathological contexts. Adaptation to hypoxic stress occurs in part by suppressing MYC, a key regulator of cellular metabolism, proliferation, and survival. Hypoxia has been reported to inhibit MYC through multiple means, including disruption of MYC transcriptional complexes and decreased MYC protein abundance. Here we identify enhanced proteasomal degradation and cathepsin-mediated proteolysis as important mechanisms for hypoxic MYC inhibition in human colon carcinoma cells. MYC protein levels were similarly reduced in hypoxic primary keratinocytes. Increased MYC turnover at low O2 tension was dependent on the E3 ubiquitin ligases FBXW7 and DDB1, as well as hypoxic induction of cathepsins D and S. Reduced MYC protein levels coincided with hypoxic inhibition of RNA polymerase III-dependent MYC target genes, which MYC regulates independently of its binding partner MAX. Finally, MYC overexpression in hypoxic cells promoted cell cycle progression but also enhanced cell death via increased expression of the proapoptotic genes NOXA and PUMA. Collectively, these results indicate that hypoxic cells promote MYC degradation as an adaptive strategy to reduce proliferation, suppress biosynthetic processes, and promote cell survival under low O2 tension.

c-Myc and cancer metabolism

The processes of cellular growth regulation and cellular metabolism are closely interrelated. The c-Myc oncogene is a "master regulator" which controls many aspects of both of these processes. The metabolic changes which occur in transformed cells, many of which are driven by c-Myc overexpression, are necessary to support the increased need for nucleic acids, proteins, and lipids necessary for rapid cellular proliferation. At the same time, c-Myc overexpression results in coordinated changes in level of expression of gene families which result in increased cellular proliferation. This interesting duality of c-Myc effects places it in the mainstream of transformational changes and gives it a very important role in regulating the "transformed phenotype." The effects induced by c-Myc can occur either as a "primary oncogene" which is activated by amplification or translocation or as a downstream effect of other activated oncogenes. In either case, it appears that c-Myc plays a central role in sustaining the changes which occur with transformation. Although efforts to use c-Myc as a therapeutic target have been quite frustrating, it appears that this may change in the next few years.

Control of amino-acid transport by antigen receptors coordinates the metabolic reprogramming essential for T cell differentiation

T lymphocytes must regulate nutrient uptake to meet the metabolic demands of an immune response. Here we show that the intracellular supply of large neutral amino acids (LNAAs) in T cells was regulated by pathogens and the T cell antigen receptor (TCR). T cells responded to antigen by upregulating expression of many amino-acid transporters, but a single System L ('leucine-preferring system') transporter, Slc7a5, mediated uptake of LNAAs in activated T cells. Slc7a5-null T cells were unable to metabolically reprogram in response to antigen and did not undergo clonal expansion or effector differentiation. The metabolic catastrophe caused by loss of Slc7a5 reflected the requirement for sustained uptake of the LNAA leucine for activation of the serine-threonine kinase complex mTORC1 and for expression of the transcription factor c-Myc. Control of expression of the System L transporter by pathogens is thus a critical metabolic checkpoint for T cells.