Transcriptional regulation and transformation by Myc proteins

Myc mediates cancer stem-like cells and EMT changes in triple negative breast cancers cells

Women with triple negative breast cancer (TNBC) have poor prognosis compared to other breast cancer subtypes. There were several reports indicating racial disparity in breast cancer outcomes between African American (AA) and European American (EA) women. For example, the mortality rates of AA breast cancer patients were three times higher than of EA patients, even though, the incidence is lower in AA women. Our in vitro studies indicate that cancer stem-like cells (CSCs) derived from AA TNBC cell lines have significantly higher self-renewal potential (mammosphere formation) than CSCs derived from EA cell lines. TNBC tumors express high levels of Myc compared to luminal A or HER2 expressing breast cancers. We studied the effects of c-Myc overexpression on CSCs and chemotherapy in AA, and EA derived TNBC cell line(s). Overexpression of c-Myc in AA derived MDA-MB-468 (Myc/MDA-468) cells resulted in a significant increase in CSCs and with minimal changes in epithelial-to-mesenchymal transition (EMT) compared to the control group. In contrast, overexpression of c-Myc in EA derived MDA-MB-231(Myc/MDA-231) cells led to increased epithelial-to-mesenchymal transition (EMT), with a minimal increase in CSCs compared to the control group. Myc/MDA-468 cells were resistant to standard chemotherapeutic treatments such as iniparib (PARP inhibitor) plus cisplatin, / iniparib, cisplatin, paclitaxel and docetaxel. However, Myc/MDA-231 cells, which showed EMT changes responded to iniparib with cisplatin, but were resistant to other drugs, such as iniparib, cisplatin, paclitaxel and docetaxel. Collectively, our results indicate that intrinsic differences in the tumor biology may contribute to the breast cancer disparities.

Sulforaphane inhibits cancer stem-like cell properties and cisplatin resistance through miR-214-mediated downregulation of c-MYC in non-small cell lung cancer

We herein report that sulforaphane (SFN), a potent anti-cancer and well-tolerated dietary compound, inhibits cancer stem-like cell (CSC) properties and enhances therapeutic efficacy of cisplatin in human non-small cell lung cancer (NSCLC). SFN exerted these functions through upregulation of miR-214, which in turn targets the coding region of c-MYC. This finding was further corroborated by our observations that plasmid or lentiviral vector-mediated expression of 3'UTR-less c-MYC cDNA and cisplatin- or doxorubicin-induced endogenous c-MYC accumulation was similarly suppressed by either SFN or miR-214. Further, we showed that the reported inhibitory effects of SFN on β-catenin are also mediated by miR-214. SFN/miR-214 signaling inhibited CSC properties and enhanced the cytotoxicity of chemotherapeutic drugs in vitro. Experiments with nude mice carrying xenograft tumors showed that SFN sensitized NSCLC cells to cisplatin's efficacy, which is accompanied by inhibition of cisplatin-induced c-MYC accumulation in tumor tissues. Our results provided strong evidence and mechanisms to support consideration of SFN or synthetic derivatives as a therapeutic agent in combination with cisplatin for the treatment of patients with NSCLC and, potentially, other types of c-MYC-addicted tumors.

The emerging role and targetability of the TCA cycle in cancer metabolism

The tricarboxylic acid (TCA) cycle is a central route for oxidative phosphorylation in cells, and fulfills their bioenergetic, biosynthetic, and redox balance requirements. Despite early dogma that cancer cells bypass the TCA cycle and primarily utilize aerobic glycolysis, emerging evidence demonstrates that certain cancer cells, especially those with deregulated oncogene and tumor suppressor expression, rely heavily on the TCA cycle for energy production and macromolecule synthesis. As the field progresses, the importance of aberrant TCA cycle function in tumorigenesis and the potentials of applying small molecule inhibitors to perturb the enhanced cycle function for cancer treatment start to evolve. In this review, we summarize current knowledge about the fuels feeding the cycle, effects of oncogenes and tumor suppressors on fuel and cycle usage, common genetic alterations and deregulation of cycle enzymes, and potential therapeutic opportunities for targeting the TCA cycle in cancer cells. With the application of advanced technology and in vivo model organism studies, it is our hope that studies of this previously overlooked biochemical hub will provide fresh insights into cancer metabolism and tumorigenesis, subsequently revealing vulnerabilities for therapeutic interventions in various cancer types.

BNIP3L-dependent mitophagy accounts for mitochondrial clearance during 3 factors-induced somatic cell reprogramming

Induced pluripotent stem cells (iPSCs) have fewer and immature mitochondria than somatic cells and mainly rely on glycolysis for energy source. During somatic cell reprogramming, somatic mitochondria and other organelles get remodeled. However, events of organelle remodeling and interaction during somatic cell reprogramming have not been extensively explored. We show that both SKP/SKO (Sox2, Klf4, Pou5f1/Oct4) and SKPM/SKOM (SKP/SKO plus Myc/c-Myc) reprogramming lead to decreased mitochondrial mass but with different kinetics and by divergent pathways. Rapid, MYC/c-MYC-induced cell proliferation may function as the main driver of mitochondrial decrease in SKPM/SKOM reprogramming. In SKP/SKO reprogramming, however, mitochondrial mass initially increases and subsequently decreases via mitophagy. This mitophagy is dependent on the mitochondrial outer membrane receptor BNIP3L/NIX but not on mitochondrial membrane potential (ΔΨ_m) dissipation, and this SKP/SKO-induced mitophagy functions in an important role during the reprogramming process. Furthermore, endosome-related RAB5 is involved in mitophagosome formation in SKP/SKO reprogramming. These results reveal a novel role of mitophagy in reprogramming that entails the interaction between mitochondria, macroautophagy/autophagy and endosomes.

The overexpression and prognostic role of DCAF13 in hepatocellular carcinoma

DDB1 and CUL4 associated factor 13 (DCAF13) is a protein coding gene located on chromosome 8q22.3, which is a hotspot amplified in various cancers. DCAF13 has been reported to be frequently amplified in breast cancer patients. However, the genetic alteration and potential role of DCAF13 in other cancers, including hepatocellular carcinoma, have not been investigated yet. In this study, we found that DCAF13 was amplified in 14.7% of the cases and its expression was upregulated (p < 0.001) in hepatocellular carcinoma samples in The Cancer Genome Atlas dataset. Increased expression of DCAF13 was also noticed in 40 paired hepatocellular carcinoma and adjacent non-tumor tissues both at messenger RNA and protein levels (p = 0.0002 and 0.0016, respectively). A positive relationship was observed between augmented DCAF13 levels and poorer tumor grade (p = 0.005), and we also found that hepatocellular carcinoma patients with increased DCAF13 expression in their tumors had significantly poorer survival compared with those with decreased DCAF13 expression (median survival time: 45.73 and 70.53 months, respectively). Multivariate Cox regression analysis showed that DCAF13 was an independent prognostic predictor of survival in hepatocellular carcinoma patients. Gene ontology and Kyoto Encyclopedia of Genes and genomes analysis indicated the potential role of DCAF13 as a crucial cell cycle regulator. Collectively, our findings revealed that the overexpression of DCAF13 in hepatocellular carcinoma was significantly associated with poor survival and may participate in the regulation of cell cycle progression.

Inhibition of c-Myc expression accounts for an increase in the number of multinucleated cells in human cervical epithelial cells

The present study aimed to explore the mechanisms by which c-Myc is involved in mitotic catastrophe. HeLa-630 is a cell line stably silenced for c-Myc expression that was established in the laboratory of the School of Radiation Medicine and Protection. Multinucleated cells were observed in this line, and gene expression analysis was utilized to examine differences in gene expression in these cells compared with in the control cells transfected with the control plasmid. Gene ontology analysis was performed for differentially expressed genes. Expression profile analyses revealed that cells with silenced c-Myc exhibited abnormal expression patterns of genes involved in various functions, including the regulation of microtubule nucleation, centrosome duplication, the formation of pericentriolar material, DNA synthesis and metabolism, protein metabolism and the regulation of ion concentrations. Pathway analyses of differentially expressed genes demonstrated that these genes were primarily involved in diverse signal transduction pathways, including not only the adherens junction pathway, the transforming growth factor-β signaling pathway and the Wnt signaling pathway, among others, but also signaling pathways with roles in cytokine and immune regulation. The proportion of multinucleated cells with multipolar spindles was significantly higher in silenced c-Myc cells as compared with the control cells, and this discrepancy became more pronounced following cell irradiation. The inhibition of c-Myc in tumors may account for the radiosensitization of certain tumor cell types.

Clinicopathological significance of c-MYC in esophageal squamous cell carcinoma

Esophageal squamous cell carcinoma is one of the most common malignant tumors. The oncogene c-MYC is thought to be important in the initiation, promotion, and therapy resistance of cancer. In this study, we aim to investigate the clinicopathologic roles of c-MYC in esophageal squamous cell carcinoma tissue. This study is aimed at discovering and analyzing c-MYC expression in a series of human esophageal tissues. A total of 95 esophageal squamous cell carcinoma samples were analyzed by the western blotting and immunohistochemistry techniques. Then, correlation of c-MYC expression with clinicopathological features of esophageal squamous cell carcinoma patients was statistically analyzed. In most esophageal squamous cell carcinoma cases, the c-MYC expression was positive in tumor tissues. The positive rate of c-MYC expression in tumor tissues was 61.05%, obviously higher than the adjacent normal tissues (8.42%, 8/92) and atypical hyperplasia tissues (19.75%, 16/95). There was a statistical difference among adjacent normal tissues, atypical hyperplasia tissues, and tumor tissues. Overexpression of the c-MYC was detected in 61.05% (58/95) esophageal squamous cell carcinomas, which was significantly correlated with the degree of differentiation (p = 0.004). The positive rate of c-MYC expression was 40.0% in well-differentiated esophageal tissues, with a significantly statistical difference (p = 0.004). The positive rate of c-MYC was 41.5% in T1 + T2 esophageal tissues and 74.1% in T3 + T4 esophageal tissues, with a significantly statistical difference (p = 0.001). The positive rate of c-MYC was 45.0% in I + II esophageal tissues and 72.2% in III + IV esophageal tissues, with a significantly statistical difference (p = 0.011). The c-MYC expression strongly correlated with clinical staging (p = 0.011), differentiation degree (p = 0.004), lymph node metastasis (p = 0.003), and invasion depth (p = 0.001) of patients with esophageal squamous cell carcinoma. The c-MYC was differentially expressed in a series of human esophageal tissues, and the aberrant c-MYC expression could be a potential factor in carcinogenesis and progression of esophageal squamous cell carcinoma. There was a statistical signification for c-MYC in esophageal squamous cell carcinoma patients to analyze clinicopathological features. It possibly becomes a new diagnostic indicator of esophageal squamous cell carcinoma.

Arginine methylation regulates c-Myc-dependent transcription by altering promoter recruitment of the acetyltransferase p300

Protein arginine methyltransferase 1 (PRMT1) is an essential enzyme controlling about 85% of the total cellular arginine methylation in proteins. We have shown previously that PRMT1 is an important regulator of innate immune responses and that it is required for M2 macrophage differentiation. c-Myc is a transcription factor that is critical in regulating cell proliferation and also regulates the M2 transcriptional program in macrophages. Here, we sought to determine whether c-Myc in myeloid cells is regulated by PRMT1-dependent arginine methylation. We found that PRMT1 activity was necessary for c-Myc binding to the acetyltransferase p300. PRMT1 inhibition decreased p300 recruitment to c-Myc target promoters and increased histone deacetylase 1 (HDAC1) recruitment, thereby decreasing transcription at these sites. Moreover, PRMT1 inhibition blocked c-Myc-mediated induction of several of its target genes, including peroxisome proliferator-activated receptor γ (PPARG) and mannose receptor C-type 1 (MRC1), suggesting that PRMT1 is necessary for c-Myc function in M2 macrophage differentiation. Of note, in primary human blood monocytes, p300-c-Myc binding was strongly correlated with PRMT1 expression, and in liver sections, PRMT1, c-Myc, and M2 macrophage levels were strongly correlated with each other. Both PRMT1 levels and M2 macrophage numbers were significantly lower in livers from individuals with a history of spontaneous bacterial peritonitis, known to have defective cellular immunity. In conclusion, our findings demonstrate that PRMT1 is an important regulator of c-Myc function in myeloid cells. PRMT1 loss in individuals with cirrhosis may contribute to their immune defects.

OncoPPi-informed discovery of mitogen-activated protein kinase kinase 3 as a novel binding partner of c-Myc

Mitogen-activated protein kinase kinase 3 (MKK3) is a dual threonine/tyrosine protein kinase that regulates inflammation, proliferation and apoptosis through specific phosphorylation and activation of the p38 MAPK. However, the role of MKK3 beyond p38-signaling remains elusive. Recently, we reported a protein-protein interaction (PPI) network of cancer-associated genes, termed OncoPPi, as a resource for the scientific community to generate new biological models. Analysis of the OncoPPi connectivity identified MKK3 as one of the major hub proteins in the network. Here, we show that MKK3 interacts with a large number of proteins critical for cell growth and metabolism, including the major oncogenic driver MYC. Multiple complementary approaches were employed to demonstrate the direct interaction of MKK3 with MYC in vitro and in vivo. Computational modeling and experimental studies mapped the interaction interface to the MYC helix-loop-helix domain and a novel 15-residue MYC-binding motif in MKK3 (MBM). The MBM in MKK3 is distinct from the known binding sites for p38 or upstream kinases. Functionally, MKK3 stabilized MYC protein, enhanced its transcriptional activity and increased expression of MYC-regulated genes. The defined MBM peptide mimicked the MKK3 effect in promoting MYC activity. Together, the exploration of OncoPPi led to a new biological model in which MKK3 operates by two distinct mechanisms in cellular regulation through its phosphorylation of p38 and its activation of MYC through protein-protein interaction.

MYC and hsa‑miRNA‑423‑5p as biomarkers in nasopharyngeal carcinoma revealed by miRNA‑mRNA‑pathway network integrated analysis

The present study was performed to identify the dysregulated microRNAs (miRNAs/miRs) and mRNAs, and enriched pathways involved in nasopharyngeal carcinoma (NPC) through the establishment of an miRNA-mRNA-pathways network. mRNA and miRNA expression profiles were collected from the European Molecular Biology Laboratory-European Bioinformatics Institute. Differentially expressed genes and differentially expressed miRNA were selectively screened using the metaDE package. Following prediction of the risk genes and pathway pairs involved in NPC, an miRNA-mRNA-pathway network was constructed by merging the miRNA-mRNA pairs, the mRNA-pathway pairs and the mRNA-mRNA pairs. The miRNA and mRNA biomarkers, as well as the functional pathway pairs, were identified in the network analysis, based on the topological properties of nodes in the network. Additionally, 10-fold cross-validation was performed to evaluate the performance of the selected risk genes and their corresponding miRNA in NPC by calculating the area under the curve (AUC). In total, 99 upregulated and 841 downregulated genes, and 192 upregulated and 26 downregulated miRNAs were identified. The miRNA-mRNA-pathway network was established using 403 miRNA-mRNA pairs, including 40 miRNAs and 302 risk genes, as well as 22 prominent pathway pairs. Network analysis demonstrated that v-myc avian myelocytomatosis viral oncogene homolog (MYC) and hsa-miR-423-5p were the mRNA and miRNA signatures for NPC, respectively. The AUC of these biomarkers for NPC was 0.7568 and 0.7798, respectively. Additionally, the focal adhesion pair pathway in cancer was identified to be associated with NPC. MYC and hsa-miR-423-5p have been identified to be critical biomarkers in NPC as revealed by miRNA-mRNA-pathway network integrated analysis, suggesting a direction for further research into the diagnosis and treatment of NPC.

MYC-Master Regulator of the Cancer Epigenome and Transcriptome

Overexpression of MYC is a hallmark of many human cancers. The MYC oncogene has long been thought to execute its neoplastic functions by acting as a classic transcription factor, deregulating the expression of a large number of specific target genes. However, MYC’s influence on many of these target genes is rather modest and there is little overlap between MYC regulated genes in different cell types, leaving many mechanistic questions unanswered. Recent advances in the field challenge the dogma further, revealing a role for MYC that extends beyond the traditional concept of a sequence-specific transcription factor. In this article, we review MYC’s function as a regulator of the cancer epigenome and transcriptome. We outline our current understanding of how MYC regulates chromatin structure in both a site-specific and genome-wide fashion, and highlight the implications for therapeutic strategies for cancers with high MYC expression.

Critical role of Myc activation in mouse hepatocarcinogenesis induced by the activation of AKT and RAS pathways

MYC activation at modest levels has been frequently found in hepatocellular carcinoma. However, its significance in hepatocarcinogenesis has remained obscure. Here we examined the role of Myc activation in mouse liver tumours induced by hepatocytic expression of myristoylated AKT (AKT) and/or mutant HRAS^V12 (HRAS) via transposon-mediated gene integration. AKT or HRAS alone required 5 months to induce liver tumours, whereas their combination generated hepatocellular carcinoma within 8 weeks. Co-introduction of AKT and HRAS induced lipid-laden preneoplastic cells that grew into nodules composed of tumour cells with or without intracytoplasmic lipid, with the latter being more proliferative and associated with spontaneous Myc expression. AKT/HRAS-induced tumorigenesis was almost completely abolished when MadMyc, a competitive Myc inhibitor, was expressed simultaneously. The Tet-On induction of MadMyc in preneoplastic cells significantly inhibited the progression of AKT/HRAS-induced tumours; its induction in transformed cells suppressed their proliferative activity with alterations in lipid metabolism and protein translation. Transposon-mediated Myc overexpression facilitated tumorigenesis by AKT or HRAS, and when it was co-introduced with AKT and HRAS, diffusely infiltrating tumours without lipid accumulation developed as early as 2 weeks. Examination of the dose-responses of Myc in the enhancement of AKT/HRAS-induced tumorigenesis revealed that a reduction to one-third retained enhancing effect but three-times greater introduction damped the process with increased apoptosis. Myc overexpression suppressed the mRNA expression of proteins involved in the synthesis of fatty acids, and when combined with HRAS introduction, it also suppressed the mRNA expression of proteins involved in their degradation. Finally, the MYC-positive human hepatocellular carcinoma was characterized by the cytoplasm devoid of lipid accumulation, prominent nucleoli and a higher proliferative activity. Our results demonstrate that in hepatocarcinogenesis induced by both activated AKT and HRAS, activation of endogenous Myc is an enhancing factor and adequate levels of Myc deregulation further facilitate the process with alterations in cellular metabolism.

Deubiquitinating enzyme USP22 positively regulates c-Myc stability and tumorigenic activity in mammalian and breast cancer cells

The proto-oncogene c-Myc has a pivotal function in growth control, differentiation, and apoptosis and is frequently affected in human cancer, including breast cancer. Ubiquitin-specific protease 22 (USP22), a member of the USP family of deubiquitinating enzymes (DUBs), mediates deubiquitination of target proteins, including histone H2B and H2A, telomeric repeat binding factor 1, and cyclin B1. USP22 is also a component of the mammalian SAGA transcriptional co-activating complex. In this study, we explored the functional role of USP22 in modulating c-Myc stability and its physiological relevance in breast cancer progression. We found that USP22 promotes deubiquitination of c-Myc in several breast cancer cell lines, resulting in increased levels of c-Myc. Consistent with this, USP22 knockdown reduces c-Myc levels. Furthermore, overexpression of USP22 stimulates breast cancer cell growth and colony formation, and increases c-Myc tumorigenic activity. In conclusion, the present study reveals that USP22 in breast cancer cell lines increases c-Myc stability through c-Myc deubiquitination, which is closely correlated with breast cancer progression.

Didymin: an orally active citrus flavonoid for targeting neuroblastoma

Neuroblastoma, a rapidly growing yet treatment responsive cancer, is the third most common cancer of children and the most common solid tumor in infants. Unfortunately, neuroblastoma that has lost p53 function often has a highly treatment-resistant phenotype leading to tragic outcomes. In the context of neuroblastoma, the functions of p53 and MYCN (which is amplified in ~25% of neuroblastomas) are integrally linked because they are mutually transcriptionally regulated, and because they together regulate the catalytic activity of RNA polymerases. Didymin is a citrus-derived natural compound that kills p53 wild-type as well as drug-resistant p53-mutant neuroblastoma cells in culture. In addition, orally administered didymin causes regression of neuroblastoma xenografts in mouse models, without toxicity to non-malignant cells, neural tissues, or neural stem cells. RKIP is a Raf-inhibitory protein that regulates MYCN activation, is transcriptionally upregulated by didymin, and appears to play a key role in the anti-neuroblastoma actions of didymin. In this review, we discuss how didymin overcomes drug-resistance in p53-mutant neuroblastoma through RKIP-mediated inhibition of MYCN and its effects on GRK2, PKCs, Let-7 micro-RNA, and clathrin-dependent endocytosis by Raf-dependent and -independent mechanisms. In addition, we will discuss studies supporting potential clinical impact and translation of didymin as a low cost, safe, and effective oral agent that could change the current treatment paradigm for refractory neuroblastoma.

Biophysical characterization of the b-HLH-LZ of ΔMax, an alternatively spliced isoform of Max found in tumor cells: Towards the validation of a tumor suppressor role for the Max homodimers

It is classically recognized that the physiological and oncogenic functions of Myc proteins depend on specific DNA binding enabled by the dimerization of its C-terminal basic-region-Helix-Loop-Helix-Leucine Zipper (b-HLH-LZ) domain with that of Max. However, a new paradigm is emerging, where the binding of the c-Myc/Max heterodimer to non-specific sequences in enhancers and promoters drives the transcription of genes involved in diverse oncogenic programs. Importantly, Max can form a stable homodimer even in the presence of c-Myc and bind DNA (specific and non-specific) with comparable affinity to the c-Myc/Max heterodimer. Intriguingly, alterations in the Max gene by germline and somatic mutations or changes in the gene product by alternative splicing (e.g. ΔMax) were recently associated with pheochromocytoma and glioblastoma, respectively. This has led to the proposition that Max is, by itself, a tumor suppressor. However, the actual mechanism through which it exerts such an activity remains to be elucidated. Here, we show that contrary to the WT motif, the b-HLH-LZ of ΔMax does not homodimerize in the absence of DNA. In addition, although ΔMax can still bind the E-box sequence as a homodimer, it cannot bind non-specific DNA in that form, while it can heterodimerize with c-Myc and bind E-box and non-specific DNA as a heterodimer with high affinity. Taken together, our results suggest that the WT Max homodimer is important for attenuating the binding of c-Myc to specific and non-specific DNA, whereas ΔMax is unable to do so. Conversely, the splicing of Max into ΔMax could provoke an increase in overall chromatin bound c-Myc. According to the new emerging paradigm, the splicing event and the stark reduction in homodimer stability and DNA binding should promote tumorigenesis impairing the tumor suppressor activity of the WT homodimer of Max.

Therapeutic Interventions of Cancers Using Intrinsically Disordered Proteins as Drug Targets: c-Myc as Model System

The concept of protein intrinsic disorder has taken the driving seat to understand regulatory proteins in general. Reports suggest that in mammals nearly 75% of signalling proteins contain long disordered regions with greater than 30 amino acid residues. Therefore, intrinsically disordered proteins (IDPs) have been implicated in several human diseases and should be considered as potential novel drug targets. Moreover, intrinsic disorder provides a huge multifunctional capability to hub proteins such as c-Myc and p53. c-Myc is the hot spot for understanding and developing therapeutics against cancers and cancer stem cells. Our past understanding is mainly based on in vitro and in vivo experiments conducted using c-Myc as whole protein. Using the reductionist approach, c-Myc oncoprotein has been divided into structured and disordered domains. A wealth of data is available dealing with the structured perspectives of c-Myc, but understanding c-Myc in terms of disordered domains has just begun. Disorderness provides enormous flexibility to proteins in general for binding to numerous partners. Here, we have reviewed the current progress on understanding c-Myc using the emerging concept of IDPs.

miR-19a promotes colorectal cancer proliferation and migration by targeting TIA1

BACKGROUND

Colorectal cancer (CRC) is a major worldwide health problem due to its high prevalence and mortality rate. T-cell intracellular antigen 1 (TIA1) is an important tumor suppressor involved in many aspects of carcinogenesis and cancer development. How TIA1 expression is regulated during CRC development remains to be carefully elucidated.

METHODS

In CRC tissue sample pairs, TIA1 protein and mRNA levels were monitored by Western blot and qRT-PCR, respectively. Combining meta-analysis and miRNA target prediction software, we could predict microRNAs that targeted TIA1. Next, three CRC cell lines (SW480, Caco2 and HT29) were used to demonstrate the direct targeting of TIA1 by miR-19a. In addition, we investigated the biological effects of TIA1 inhibition by miR-19a both in vitro by CCK-8, EdU, Transwell, Ki67 immunofluorescence and Colony formation assays and in vivo by a xenograft mice model.

RESULTS

In colorectal cancer (CRC), we found that TIA1 protein, but not its mRNA, was downregulated. We predicted that TIA1 was a target of miR-19a and validated that miR-19a binded directly to the 3'-UTR of TIA1 mRNA. miR-19a could promote cell proliferation and migration in CRC cells and accelerated tumor growth in xenograft mice by targeting TIA1.

CONCLUSIONS

This study highlights an oncomiR role for miR-19a in regulating TIA1 in CRC and suggests that miR-19a may be a novel molecular therapeutic target for CRC.

Chaperone-mediated autophagy prevents cellular transformation by regulating MYC proteasomal degradation

Chaperone-mediated autophagy (CMA), a selective form of protein lysosomal degradation, is maximally activated in stress situations to ensure maintenance of cellular homeostasis. CMA activity decreases with age and in several human chronic disorders, but in contrast, in most cancer cells, CMA is upregulated and required for tumor growth. However, the role of CMA in malignant transformation remains unknown. In this study, we demonstrate that CMA inhibition in fibroblasts augments the efficiency of MYC/c-Myc-driven cellular transformation. CMA blockage contributes to the increase of total and nuclear MYC, leading to enhancement of cell proliferation and colony formation. Impaired CMA functionality accentuates tumorigenesis-related metabolic changes observed upon MYC-transformation. Although not a direct CMA substrate, we have found that CMA regulates cellular MYC levels by controlling its proteasomal degradation. CMA promotes MYC ubiquitination and degradation by regulating the degradation of C330027C09Rik/KIAA1524/CIP2A (referred to hereafter as CIP2A), responsible for MYC stabilization. Ubiquitination and proteasomal degradation of MYC requires dephosphorylation at Ser62, and CIP2A inhibits the phosphatase responsible for this dephosphorylation. Failure to degrade CIP2A upon CMA blockage leads to increased levels of phosphorylated MYC (Ser62) and to stabilization of this oncogene. We demonstrate that this phosphorylation is essential for the CMA-mediated effect, since specific mutation of this site (Ser62 to Ala62) is enough to normalize MYC levels in CMA-incompetent cells. Altogether these data demonstrate that CMA mitigates MYC oncogenic activity by promoting its proteasomal degradation and reveal a novel tumor suppressive role for CMA in nontumorigenic cells.

Stabilization of HIF-1α and HIF-2α, up-regulation of MYCC and accumulation of stabilized p53 constitute hallmarks of CNS-PNET animal model

Recently, we described a new animal model of CNS primitive neuroectodermal tumors (CNS-PNET), which was generated by orthotopic transplantation of human Radial Glial (RG) cells into NOD-SCID mice's brain sub-ventricular zone. In the current study we conducted comprehensive RNA-Seq analyses to gain insights on the mechanisms underlying tumorigenesis in this mouse model of CNS-PNET. Here we show that the RNA-Seq profiles derived from these tumors cluster with those reported for patients' PNETs. Moreover, we found that (i) stabilization of HIF-1α and HIF-2α, which are involved in mediation of the hypoxic responses in the majority of cell types, (ii) up-regulation of MYCC, a key onco-protein whose dysregulation occurs in ~70% of human tumors, and (iii) accumulation of stabilized p53, which is commonly altered in human cancers, constitute hallmarks of our tumor model, and might represent the basis for CNS-PNET tumorigenesis in this model. We discuss the possibility that these three events might be interconnected. These results indicate that our model may prove invaluable to uncover the molecular events leading to MYCC and TP53 alterations, which would be of broader interest considering their relevance to many human malignancies. Lastly, this mouse model might prove useful for drug screening targeting MYCC and related members of its protein interaction network.

Interplay between cancer cell cycle and metabolism: Challenges, targets and therapeutic opportunities

A growing interest has emerged in the field of studying the cross-talk between cancer cell cycle and metabolism. In this review, we aimed to present how metabolism and cell cycle are correlated and how cancer cells get energy to drive cell cycle. Cell proliferation and cell death largely depend on the metabolic activity of the cell. Cell cycle proteins, e.g. cyclin D, cyclin dependent kinase (CDK), some pro-apoptotic and anti-apoptotic proteins, and P53 have been shown to be regulated by metabolic crosstalk. Dysregulation of this cross-talk between metabolism and cell cycle leads to degenerative disorder(s) and cancer. It is not fully understood the actual reason of aberration between metabolism and cell cycle, but it is a hallmark of cancer research. Herein, we discussed the role of some regulatory molecules relative of cell cycle and metabolism and highlight how they control the function of each other. We also pointed out, current therapeutic opportunities and some additional crucial therapeutic targets on these fields that could be a breakthrough in cancer research.

miRNA-320a inhibits tumor proliferation and invasion by targeting c-Myc in human hepatocellular carcinoma

BACKGROUND

Downregulated expression levels of microRNA-320a (miR-320a) were found in primary breast cancers and colorectal cancer. Previous findings indicated that miRNA-320a may involve in the cancer development. In this study, we explored the roles of miR-320a by targeting c-Myc in the tumor growth of hepatocellular carcinoma (HCC).

METHODS

Quantitative reverse-transcription polymerase chain reaction (qRT-PCR) was performed to detect the expression of miR-320a in 50 HCC tissues and four HCC cells. Luciferase reporter assay was conducted to confirm the direct downstream target of miR-320a in HEK-293 cells. The effect of miR-320a on endogenous c-Myc expression was investigated by transfecting miR-320a mimics into HepG2 and QGY-7703 cell lines. The c-Myc and miR-320a expressions were analyzed by immunohistochemistry (IHC) and qRT-PCR in the same HCC tissues. Furthermore, the biological functional correlation of miR-320a with c-Myc was determined by studying the effect of miR-320a mimics or c-Myc small interfering RNA (siRNA) on HCC cell proliferation and invasion.

RESULTS

The expression of miR-320a was downregulated in 50 HCC tissues and 4 HCC cells. Luciferase assay revealed that c-Myc is a direct target of miR-320a. IHC and Western blot analysis showed that the c-Myc expression was inhibited by miR-320a in HCC tissues and cell lines. Upregulation of miR-320a suppressed the HCC cell proliferation and invasion capacity induced by inhibiting c-Myc, and the results were consistent with the effects of c-Myc siRNA on tumor suppression. These results revealed that miRNA-320a inhibits tumor proliferation and invasion by targeting c-Myc in HCC cells.

CONCLUSION

Our results showed that miR-320a functions as a tumor suppressor in HCC. By targeting c-Myc directly, miR-320a inhibits the HCC cell growth. Our studies provide evidence of miR-320a as a potentially target for HCC treatment.

Oncogenic KRAS and the EGFR loop in pancreatic carcinogenesis-A connection to licensing nodes

EGFR signaling has a critical role in oncogenic KRAS-driven tumorigenesis of the pancreas, whereas it is dispensable in other organs. The complex signaling network engaged by oncogenic KRAS and its modulation by EGFR signaling, remains incompletely understood. In order to study early signaling events activated by oncogenic KRAS in the pancreas, we recently developed a novel model system based on murine primary pancreatic epithelial cells enabling the time-specific expression of mutant Kras^G12D from its endogenous promoter. Here, we discuss our findings of a Kras^G12D-induced autocrine EGFR loop, how this loop is integrated by the MYC oncogene, and point to possible translational implications.

Combined proteomic and metallomic analyses in Scrobicularia plana clams to assess environmental pollution of estuarine ecosystems

Estuaries are very important ecosystems with great ecological and economic value, but usually highly impacted by anthropogenic pressure. Thus, the assessment of pollution levels in these habitats is critical in order to evaluate their environmental quality. In this work, we combined complementary metallomic and proteomic approaches with the aim to monitor the effects of environmental pollution on Scrobicularia plana clams captured in three estuarine systems from the south coast of Portugal; Arade estuary, Ria Formosa and Guadiana estuary. Multi-elemental profiling of digestive glands was carried out to evaluate the differential pollution levels in the three study areas. Then, proteomic analysis by means of two-dimensional gel electrophoresis and mass spectrometry revealed twenty-one differential proteins, which could be associated with multiple toxicological mechanisms induced in environmentally stressed organisms. Accordingly, it could be concluded that the combination of different omic approaches presents a great potential in environmental research.

Structural basis of N-Myc binding by Aurora-A and its destabilization by kinase inhibitors

Myc family proteins promote cancer by inducing widespread changes in gene expression. Their rapid turnover by the ubiquitin-proteasome pathway is regulated through phosphorylation of Myc Box I and ubiquitination by the E3 ubiquitin ligase SCFFbxW7 However, N-Myc protein (the product of the MYCN oncogene) is stabilized in neuroblastoma by the protein kinase Aurora-A in a manner that is sensitive to certain Aurora-A-selective inhibitors. Here we identify a direct interaction between the catalytic domain of Aurora-A and a site flanking Myc Box I that also binds SCFFbxW7 We determined the crystal structure of the complex between Aurora-A and this region of N-Myc to 1.72-Å resolution. The structure indicates that the conformation of Aurora-A induced by compounds such as alisertib and CD532 is not compatible with the binding of N-Myc, explaining the activity of these compounds in neuroblastoma cells and providing a rational basis for the design of cancer therapeutics optimized for destabilization of the complex. We also propose a model for the stabilization mechanism in which binding to Aurora-A alters how N-Myc interacts with SCFFbxW7 to disfavor the generation of Lys48-linked polyubiquitin chains.

Polo-like Kinase-1 Regulates Myc Stabilization and Activates a Feedforward Circuit Promoting Tumor Cell Survival

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

Rapid Conversion of Mutant IDH1 from Driver to Passenger in a Model of Human Gliomagenesis

Missense mutations in the active site of isocitrate dehydrogenase 1 (IDH1) biologically and diagnostically distinguish low-grade gliomas and secondary glioblastomas from primary glioblastomas. IDH1 mutations lead to the formation of the oncometabolite 2-hydroxyglutarate (2-HG) from the reduction of α-ketoglutarate (α-KG), which in turn facilitates tumorigenesis by modifying DNA and histone methylation as well blocking differentiation processes. Although mutant IDH1 expression is thought to drive the gliomagenesis process, the extent to which it remains a viable therapeutic target remains unknown. To address this question, we exposed immortalized (p53/pRb deficient), untransformed human astrocytes to the mutant IDH1 inhibitor AGI-5198 prior to, concomitant with, or at intervals after, introduction of transforming mutant IDH1, then measured effects on 2-HG levels, histone methylation (H3K4me3, H3K9me2, H3K9me3, or H3K27me3), and growth in soft agar. Addition of AGI-5198 prior to, or concomitant with, introduction of mutant IDH1 blocked all mutant IDH1-driven changes, including cellular transformation. Addition at time intervals as short as 4 days following introduction of mutant IDH1 also suppressed 2-HG levels, but had minimal effects on histone methylation, and lost the ability to suppress clonogenicity in a time-dependent manner. Furthermore, in two different models of mutant IDH1-driven gliomagenesis, AGI-5198 exposures that abolished production of 2-HG also failed to decrease histone methylation, adherent cell growth, or anchorage-independent growth in soft agar over a prolonged period. These studies show although mutant IDH1 expression drives gliomagenesis, mutant IDH1 itself rapidly converts from driver to passenger.

IMPLICATIONS

Agents that target mutant IDH may be effective for a narrow time and may require further optimization or additional therapeutics in glioma. Mol Cancer Res; 14(10); 976-83. ©2016 AACR.

Clinical significance of high c-MYC and low MYCBP2 expression and their association with Ikaros dysfunction in adult acute lymphoblastic leukemia

Increased expression of c-MYC is observed in both Acute Myeloid Leukemia (AML) and T- cell Acute Lymphoblastic Leukemia (T-ALL). MYC binding protein 2 (MYCBP2) is a probable E3 ubiquitin ligase and its function in leukemia is unknown. IKZF1 deletion is associated with the development and poor outcome of ALL. Here, we observed significant high c-MYC expression and low MYCBP2 expression in adult ALL patients. Patients with high c-MYC expression and/or low MYCBP2 expression had higher WBC counts and a higher percentage of CD34+ or CD33+ cells, as well as splenomegaly, liver infiltration, higher BM blasts, and lower CR rate. Ikaros bound to the regulatory regions of c-MYC and MYCBP2, suppressed c-MYC and increased MYCBP2 expression in ALL cells. Expression of c-MYC mRNA was significantly higher in patients with IKZF1 deletion; conversely MYCBP2 mRNA expression was significantly lower in those patients. A CK2 inhibitor, which acts as an Ikaros activator, also suppressed c-MYC and increased MYCBP2 expression in an Ikaros (IKZF1) dependent manner in the ALL cells. In summary, our data indicated the correlation of high c-MYC expression, low MYCBP2 expression and high c-MYC plus low MYCBP2 expression with high-risk factors and proliferation markers in adult ALL patients. Our data also revealed an oncogenic role for an Ikaros/MYCBP2/c-MYC axis in adult ALL, providing a mechanism of target therapies that activate Ikaros in adult ALL.

Deubiquitinating c-Myc: USP36 steps up in the nucleolus

Ubiquitination plays a key and complex role in the regulation of c-Myc stability, transactivation, and oncogenic activity. c-Myc is ubiquitinated by a number of ubiquitin ligases (E3s), such as SCF(Fbw7) and SCF(Skp2). Depending on the E3s, ubiquitination can either positively or negatively regulate c-Myc levels and activity. Meanwhile, c-Myc ubiquitination can be reversed by deubiquitination. An early study showed that USP28 deubiquitinates c-Myc via interacting with Fbw7α whereas a recent study reveals that USP37 deubiquitinates c-Myc independently of Fbw7 and c-Myc phosphorylation. Consequently, both USP28 and USP37 stabilize c-Myc and enhance its activity. We recently found the nucleolar USP36 as a novel c-Myc deubiquitinase that controls the end-point of c-Myc degradation pathway in the nucleolus. Here we briefly review the current understanding of ubiquitination and deubiquitination regulation of c-Myc and further discuss the USP36-c-Myc regulatory pathway.

Transcriptional Repression of IFN Regulatory Factor 7 by MYC Is Critical for Type I IFN Production in Human Plasmacytoid Dendritic Cells

Type I IFNs are crucial mediators of human innate and adaptive immunity and are massively produced from plasmacytoid dendritic cells (pDCs). IFN regulatory factor (IRF)7 is a critical regulator of type I IFN production when pathogens are detected by TLR 7/9 in pDC. However, hyperactivation of pDC can cause life-threatening autoimmune diseases. To avoid the deleterious effects of aberrant pDC activation, tight regulation of IRF7 is required. Nonetheless, the detailed mechanisms of how IRF7 transcription is regulated in pDC are still elusive. MYC is a well-known highly pleiotropic transcription factor; however, the role of MYC in pDC function is not well defined yet. To identify the role of transcription factor MYC in human pDC, we employed a knockdown technique using human pDC cell line, GEN2.2. When we knocked down MYC in the pDC cell line, production of IFN-stimulated genes was dramatically increased and was further enhanced by the TLR9 agonist CpGB. Interestingly, MYC is shown to be recruited to the IRF7 promoter region through interaction with nuclear receptor corepressor 2/histone deacetylase 3 for its repression. In addition, activation of TLR9-mediated NF-κB and MAPK and nuclear translocation of IRF7 were greatly enhanced by MYC depletion. Pharmaceutical inhibition of MYC recovered IRF7 expression, further confirming the negative role of MYC in the antiviral response by pDC. Therefore, our results identify the novel immunomodulatory role of MYC in human pDC and may add to our understanding of aberrant pDC function in cancer and autoimmune disease.

MYU, a Target lncRNA for Wnt/c-Myc Signaling, Mediates Induction of CDK6 to Promote Cell Cycle Progression

Aberrant activation of Wnt/β-catenin signaling is a major driving force in colon cancer. Wnt/β-catenin signaling induces the expression of the transcription factor c-Myc, leading to cell proliferation and tumorigenesis. c-Myc regulates multiple biological processes through its ability to directly modulate gene expression. Here, we identify a direct target of c-Myc, termed MYU, and show that MYU is upregulated in most colon cancers and required for the tumorigenicity of colon cancer cells. Furthermore, we demonstrate that MYU associates with the RNA binding protein hnRNP-K to stabilize CDK6 expression and thereby promotes the G1-S transition of the cell cycle. These results suggest that the MYU/hnRNP-K/CDK6 pathway functions downstream of Wnt/c-Myc signaling and plays a critical role in the proliferation and tumorigenicity of colon cancer cells.

Discovery of a Family of Genomic Sequences Which Interact Specifically with the c-MYC Promoter to Regulate c-MYC Expression

G-quadruplex forming sequences are particularly enriched in the promoter regions of eukaryotic genes, especially of oncogenes. One of the most well studied G-quadruplex forming sequences is located in the nuclease hypersensitive element (NHE) III₁ of the c-MYC promoter region. The oncoprotein c-MYC regulates a large array of genes which play important roles in growth regulation and metabolism. It is dysregulated in >70% of human cancers. The silencer NHEIII₁ located upstream of the P1 promoter regulates up-to 80% of c-MYC transcription and includes a G-quadruplex structure (Pu27) that is required for promoter inhibition. We have identified, for the first time, a family of seventeen G-quadruplex-forming motifs with >90% identity with Pu27, located on different chromosomes throughout the human genome, some found near or within genes involved in stem cell maintenance or neural cell development. Notably, all members of the Pu27 family interact specifically with NHEIII₁ sequence, in vitro. Crosslinking studies demonstrate that Pu27 oligonucleotide binds specifically to the C-rich strand of the NHEIII₁ resulting in the G-quadruplex structure stabilization. Pu27 homologous sequences (Pu27-HS) significantly inhibit leukemic cell lines proliferation in culture. Exposure of U937 cells to the Pu27-HS induces cell growth inhibition associated with cell cycle arrest that is most likely due to downregulation of c-MYC expression at the RNA and/or protein levels. Expression of SOX2, another gene containing a Pu27-HS, was affected by Pu27-HS treatment as well. Our data suggest that the oligonucleotides encoding the Pu27 family target complementary DNA sequences in the genome, including those of the c-MYC and SOX2 promoters. This effect is most likely cell type and cell growth condition dependent. The presence of genomic G-quadruplex-forming sequences homologous to Pu27 of c-MYC silencer and the fact that they interact specifically with the parent sequence suggest a common regulatory mechanism for genes whose promoters contain these sequences.

Relationship of Amplification and Expression of the C-MYC Gene with Survival among Gastric Cancer Patients

BACKGROUND

During the past decades, the incidence and mortality rate of stomach cancer has demonstrated a great decrease in the world, but it is still one of the most common and fatal cancers especially among men worldwide, including Iran. The MYC proto-oncogene, which is located at 8q24.1, regulates 15% of genes and is activated in 20% of all human tumors. MYC amplification and overexpression of its protein product has been reported in 15-30% of gastric neoplasias. The aim of this investigation was to find the relative efficacy of CISH (chromogenic in situ hybridization) or IHC (immunohistochemistry) in diagnosis and prognosis of gastric cancer, as well as the relationship of amplification and expression of C-MYC gene with patient survival.

MATERIALS AND METHODS

In this cross-sectional study, 102 samples of gastric cancer were collected from patients who had undergone primary surgical resection at the Cancer Institute Hospital, Tehran University of Medical Sciences, from July 2009 to March 2014. All samples were randomly selected from those who were diagnosed with gastric adenocarcinomas. CISH and IHC methods were performed on all of them.

RESULTS

Patients were classified into two groups. The first consisted of stage I and II cases, and the second of stage III and IV. Survival tests for both groups was carried out with referrnce to CISH test reults. Group II (stage III and IV) with CISH+ featured lower survival than those with CISH- (p=0.233), but group I (stage I and II) patients demonstrated no significant variation with CISH+ or CISH- (p=0.630). Kaplan-Meier for both groups was carried out with IHC test findings and showed similar results. This data revealed that both diffuse and intestinal types of gastric cancer occurred significantly more in men than women. Our data also showed that CISH+ patients (43%) were more frequent in comparison with IHC+ patients (14.7%).

CONCLUSIONS

For planning treatment of gastric cancer patients, by focusing on expanding tumors, which is the greatest concern of the surgeons and patients, CISH is a better and more feasible test than IHC, in regard to sensitivity and specificity. Therefore, CISH can be used as a feasible test for tumor growth and prognosis in stage III and IV lesions. This study also indicated that C-MYC amplification in gastric cancer is correlated with survival in advanced stages.

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

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

Influence of selected anti-cancer drugs on the induction of DNA double-strand breaks and changes in gene expression in human hepatoma HepG2 cells

In chemotherapy, various anti-cancer drugs with different mechanisms of action are used and may represent different risk of undesirable delayed side effects in treated patients as well as in occupationally exposed populations. The aim of the present study was to evaluate genotoxic potential of four widely used anti-cancer drugs with different mechanisms of action: 5-fluorouracil (5-FU), cisplatin (CDDP) and etoposide (ET) that cause cell death by targeting DNA function and imatinib mesylate (IM) that inhibits targeted protein kinases in cancer cells in an experimental model with human hepatoma HepG2 cells. After 24 h of exposure all four anti-cancer drugs at non-cytotoxic concentrations induced significant increase in formation of DNA double strand breaks (DSBs), with IM being the least effective. The analysis of the changes in the expression of genes involved in the response to DNA damage (CDKN1A, GADD45A, MDM2), apoptosis (BAX, BCL2) and oncogenesis (MYC, JUN) showed that 5-FU, CDDP and ET upregulated the genes involved in DNA damage response, while the anti-apoptotic gene BCL2 and oncogene MYC were downregulated. On the contrary, IM did not change the mRNA level of the studied genes, showing different mechanism of action that probably does not involve direct interaction with DNA processing. Genotoxic effects of the tested anti-cancer drugs were observed at their therapeutic concentrations that may consequently lead to increased risk for development of delayed adverse effects in patients. In addition, considering the genotoxic mechanism of action of 5-FU, CDDP and ET an increased risk can also not be excluded in occupationally exposed populations. The results also indicate that exposure to 5-FU, CDDP and ET represent a higher risk for delayed effects such as cancer, reproductive effects and heritable disease than exposure to IM.

The proto-oncogene Myc drives expression of the NK cell-activating NKp30 ligand B7-H6 in tumor cells

Natural Killer (NK) cells are innate effector cells that are able to recognize and eliminate tumor cells through engagement of their surface receptors. NKp30 is a potent activating NK cell receptor that elicits efficient NK cell-mediated target cell killing. Recently, B7-H6 was identified as tumor cell surface expressed ligand for NKp30. Enhanced B7-H6 mRNA levels are frequently detected in tumor compared to healthy tissues. To gain insight in the regulation of expression of B7-H6 in tumors, we investigated transcriptional mechanisms driving B7-H6 expression by promoter analyses. Using luciferase reporter assays and chromatin immunoprecipitation we mapped a functional binding site for Myc, a proto-oncogene overexpressed in certain tumors, in the B7-H6 promoter. Pharmacological inhibition or siRNA/shRNA-mediated knock-down of c-Myc or N-Myc significantly decreased B7-H6 expression on a variety of tumor cells including melanoma, pancreatic carcinoma and neuroblastoma cell lines. In tumor cell lines from different origin and primary tumor tissues of hepatocellular carcinoma (HCC), lymphoma and neuroblastoma, mRNA levels of c-Myc positively correlated with B7-H6 expression. Most importantly, upon inhibition or knock-down of c-Myc in tumor cells impaired NKp30-mediated degranulation of NK cells was observed. Thus, our data imply that Myc driven tumors could be targets for cancer immunotherapy exploiting the NKp30/B7-H6 axis.

Generation of Induced Pluripotent Stem Cells with Substitutes for Yamanaka's Four Transcription Factors

Induced pluripotent stem cells (iPSCs) share many characteristics with embryonic stem cells, but lack ethical controversy. They provide vast opportunities for disease modeling, pathogenesis understanding, therapeutic drug development, toxicology, organ synthesis, and treatment of degenerative disease. However, this procedure also has many potential challenges, including a slow generation time, low efficiency, partially reprogrammed colonies, as well as somatic coding mutations in the genome. Pioneered by Shinya Yamanaka's team in 2006, iPSCs were first generated by introducing four transcription factors: Oct 4, Sox 2, Klf 4, and c-Myc (OSKM). Of those factors, Klf 4 and c-Myc are oncogenes, which are potentially a tumor risk. Therefore, to avoid problems such as tumorigenesis and low throughput, one of the key strategies has been to use other methods, including members of the same subgroup of transcription factors, activators or inhibitors of signaling pathways, microRNAs, epigenetic modifiers, or even differentiation-associated factors, to functionally replace the reprogramming transcription factors. In this study, we will mainly focus on the advances in the generation of iPSCs with substitutes for OSKM. The identification and combination of novel proteins or chemicals, particularly small molecules, to induce pluripotency will provide useful tools to discover the molecular mechanisms governing reprogramming and ultimately lead to the development of new iPSC-based therapeutics for future clinical applications.

Therapeutic implication of concomitant chromosomal aberrations in patients with aggressive B-cell lymphomas

A subset of diffuse large B-cell lymphomas (DLBCL) harbors concomitant rearrangements of MYC, BCL2 and BCL6 and is characterized by clinical aggressiveness and intrinsic refractoriness to standard chemo-immunotherapy. Commonly identified as "double or triple hit" lymphomas, these diseases represent a therapeutic challenge to chemotherapy-based regimens and likely require a more targeted approach. Herein we summarize the unique biological behavior of double and triple hit lymphomas focusing on the coordinated network of pathways that enable cancer cells to tolerate the oncogenic stress imposed by the co-expression of MYC, BCL2 and BCL6. We discuss how these enabling pathways contribute to the chemo-refractoriness of these tumors. We propose to exploit lymphoma cells' addiction to these oncogenic networks to design combinatorial treatments for this aggressive disease based on the modulation of epigenetically-silenced pathways and decreasing expression and activity of these oncogenic drivers.

Induction of micronuclei and alteration of gene expression by an organomodified clay in HepG2 cells

Clay2 is an organomodified montmorillonite developed by the Technological Institute of Packaging, Transport and Logistic (ITENE) in order to improve polymeric materials used in food packaging. There is not much known on Clay2 toxic potential, particularly at DNA level, therefore it is mandatory to assess its toxicity prior to its commercialization. In the present study the human hepatoma cell line (HepG2) was exposed to non-cytotoxic concentrations of Clay2 and the genomic stability was studied with the Cytokinesis block micronucleus cytome assay, by determining the formation of micronuclei (MN), nucleoplasmic bridges (NPBs) and nuclear buds (NBUDs). Moreover, the expression of various genes involved in the mechanisms of its action using the real-time quantitative PCR was studied. The results obtained provide the evidence that Clay2 is potentially genotoxic as it increased the frequency of micronuclei. In addition it deregulated genes involved in the metabolism, immediate-early response/signaling, DNA damage and oxidative stress showing new valuable information on the cellular response to Clay2. Nonetheless, further studies are highly needed to elucidate the molecular mechanisms of clays toxicity.

Btg2 is a Negative Regulator of Cardiomyocyte Hypertrophy through a Decrease in Cytosolic RNA

Under hypertrophic stimulation, cardiomyocytes enter a hypermetabolic state and accelerate biomass accumulation. Although the molecular pathways that regulate protein levels are well-studied, the functional implications of RNA accumulation and its regulatory mechanisms in cardiomyocytes remain elusive. Here, we have elucidated the quantitative kinetics of RNA in cardiomyocytes through single cell imaging and c-Myc (Myc)-mediated hypermetabolic analytical model using cultured cardiomyocytes. Nascent RNA labeling combined with single cell imaging demonstrated that Myc protein significantly increased the amount of global RNA production per cardiomyocyte. Chromatin immunoprecipitation with high-throughput sequencing clarified that overexpressed Myc bound to a specific set of genes and recruits RNA polymerase II. Among these genes, we identified Btg2 as a novel target of Myc. Btg2 overexpression significantly reduced cardiomyocyte surface area. Conversely, shRNA-mediated knockdown of Btg2 accelerated adrenergic stimulus-induced hypertrophy. Using mass spectrometry analysis, we determined that Btg2 binds a series of proteins that comprise mRNA deadenylation complexes. Intriguingly, Btg2 specifically suppresses cytosolic, but not nuclear, RNA levels. Btg2 knockdown further enhances cytosolic RNA accumulation in cardiomyocytes under adrenergic stimulation, suggesting that Btg2 negatively regulates reactive hypertrophy by negatively regulating RNA accumulation. Our findings provide insight into the functional significance of the mechanisms regulating RNA levels in cardiomyocytes.

MYC/MIZ1-dependent gene repression inversely coordinates the circadian clock with cell cycle and proliferation

The circadian clock and the cell cycle are major cellular systems that organize global physiology in temporal fashion. It seems conceivable that the potentially conflicting programs are coordinated. We show here that overexpression of MYC in U2OS cells attenuates the clock and conversely promotes cell proliferation while downregulation of MYC strengthens the clock and reduces proliferation. Inhibition of the circadian clock is crucially dependent on the formation of repressive complexes of MYC with MIZ1 and subsequent downregulation of the core clock genes BMAL1 (ARNTL), CLOCK and NPAS2. We show furthermore that BMAL1 expression levels correlate inversely with MYC levels in 102 human lymphomas. Our data suggest that MYC acts as a master coordinator that inversely modulates the impact of cell cycle and circadian clock on gene expression.

The circadian clock and the cell cycle systems coordinate global physiology. Here the authors show that MYC represses the clock genes, together with MIZ1, and induces proliferation, suggesting that MYC inversely modulates cell cycle and circadian clock genes.

Analysis of the transcriptional regulation of cancer-related genes by aberrant DNA methylation of the cis-regulation sites in the promoter region during hepatocyte carcinogenesis caused by arsenic

Liver is the major organ for arsenic methylation metabolism and may be the potential target of arsenic-induced cancer. In this study, normal human liver cell was treated with arsenic trioxide, and detected using DNA methylation microarray. Some oncogenes, tumor suppressor genes, transcription factors (TF), and tumor-associated genes (TAG) that have aberrant DNA methylation have been identified. However, simple functional studies of genes adjacent to aberrant methylation sites cannot well reflect the regulatory relationship between DNA methylation and gene transcription during the pathogenesis of arsenic-induced liver cancer, whereas a further analysis of the cis-regulatory elements and their trans-acting factors adjacent to DNA methylation can more precisely reflect the relationship between them. MYC and MAX (MYC associated factor X) were found to participating cell cycle through a bioinformatics analysis. Additionally, it was found that the hypomethylation of cis-regulatory sites in the MYC promoter region and the hypermethylation of cis-regulatory sites in the MAX promoter region result in the up-regulation of MYC mRNA expression and the down-regulation of MAX mRNA, which increased the hepatocyte carcinogenesis tendency.

Regulation of tumorigenesis in oral epithelial cells by defined reprogramming factors Oct4 and Sox2

Oct4 and Sox2 are pluripotent stem cell factors but the interplay between them in tumorigenesis is unclear. The aim of the present study was to investigate the roles of Oct4 and Sox2 in the reprogramming of oral cancer stem cells. One or both Oct4 and Sox2 were overexpressed in immortalized oral epithelial (hTERT+-OME) cells by lentivirus transduction. In addition, Oct4 and Sox2 proteins in two oral squamous cell carcinoma cell (OSCC) lines (Cal27 and primary cultured OSCC from a T2N2M0 patient) were individually or combinedly knocked down by shRNA. The results showed that the doubly transduced (Oct4+Sox2+) cells could trigger neoplasms in immunodeficient mice after lentivirus transduction, but single transduced (Oct4+ or Sox2+) cells had no tumor formation ability. The knockdown Sox2low and knockdown Oct4lowSox2low cells resulted in decreased tumor size in the immunodeficient mice but the single knockdown Oct4low cancer cells acquired more aggressive xenografts. Our findings suggest that Oct4+Sox2+ cells may be reprogrammed cancer stem cells inducing oral carcinogenesis.

The Quest for Targets Executing MYC-Dependent Cell Transformation

MYC represents a transcription factor with oncogenic potential converting multiple cellular signals into a broad transcriptional response, thereby controlling the expression of numerous protein-coding and non-coding RNAs important for cell proliferation, metabolism, differentiation, and apoptosis. Constitutive activation of MYC leads to neoplastic cell transformation, and deregulated MYC alleles are frequently observed in many human cancer cell types. Multiple approaches have been performed to isolate genes differentially expressed in cells containing aberrantly activated MYC proteins leading to the identification of thousands of putative targets. Functional analyses of genes differentially expressed in MYC-transformed cells had revealed that so far more than 40 upregulated or downregulated MYC targets are actively involved in cell transformation or tumorigenesis. However, further systematic and selective approaches are required for determination of the known or yet unidentified targets responsible for processing the oncogenic MYC program. The search for critical targets in MYC-dependent tumor cells is exacerbated by the fact that during tumor development, cancer cells progressively evolve in a multistep process, thereby acquiring their characteristic features in an additive manner. Functional expression cloning, combinatorial gene expression, and appropriate in vivo tests could represent adequate tools for dissecting the complex scenario of MYC-specified cell transformation. In this context, the central goal is to identify a minimal set of targets that suffices to phenocopy oncogenic MYC. Recently developed genomic editing tools could be employed to confirm the requirement of crucial transformation-associated targets. Knowledge about essential MYC-regulated genes is beneficial to expedite the development of specific inhibitors to interfere with growth and viability of human tumor cells in which MYC is aberrantly activated. Approaches based on the principle of synthetic lethality using MYC-overexpressing cancer cells and chemical or RNAi libraries have been employed to search for novel anticancer drugs, also leading to the identification of several druggable targets. Targeting oncogenic MYC effector genes instead of MYC may lead to compounds with higher specificities and less side effects. This class of drugs could also display a wider pharmaceutical window because physiological functions of MYC, which are important for normal cell growth, proliferation, and differentiation would be less impaired.

Down-Regulation of Ribosomal S6 kinase RPS6KA6 in Acute Myeloid Leukemia Patients

Objective

Signaling pathways such as extracellular regulated kinase/mitogen activated protein kinase (ERK/MAPK) have increased activity in leukemia. Ribosomal 6 kinase (RSK4) is a factor downstream of the MAPK/ERK pathway and an important tumor suppressor which inhibits ERK trafficking. Decrease in RSK4 expression has been reported in some malignancies, which leads to an increase in growth and proliferation and eventually poor prognosis. In this study we measured RSK4 expression rate in acute myeloid leukemia (AML).

Materials and Methods

This cross-sectional study was undertaken in 2013-2014 at Ghaem Hospital in Mashhad, Iran, on 40 AML patients and 10 non-AML patients as the control group. The expression rate was measured by real-time polymerase change reaction (PCR) and employing the ΔΔCT method. Data were analyzed using Mann-Whitney and Spearman tests using SPSS (version 11.5).

Results

Expression rate of RSK4 was significantly decreased in the AML group in comparison with the non-AML group (P<0.001). There was also a significant decrease in RSK4 expression in AML with t(15;17) in comparison to other translocations (P=0.004).

Conclusion

We detected a down-regulation of RSK4 in AML patients. This may lead to an increase in the activity of the ERK/MPAK pathway and exacerbate leukemogenesis or the prognosis of the patients.

Common genetic variation in ETV6 is associated with colorectal cancer susceptibility

Genome-wide association studies (GWASs) have identified multiple susceptibility loci for colorectal cancer, but much of heritability remains unexplained. To identify additional susceptibility loci for colorectal cancer, here we perform a GWAS in 1,023 cases and 1,306 controls and replicate the findings in seven independent samples from China, comprising 5,317 cases and 6,887 controls. We find a variant at 12p13.2 associated with colorectal cancer risk (rs2238126 in ETV6, P=2.67 × 10(-10)). We replicate this association in an additional 1,046 cases and 1,076 controls of European ancestry (P=0.034). The G allele of rs2238126 confers earlier age at onset of colorectal cancer (P=1.98 × 10(-6)) and reduces the binding affinity of transcriptional enhancer MAX. The mRNA level of ETV6 is significantly lower in colorectal tumours than in paired normal tissues. Our findings highlight the potential importance of genetic variation in ETV6 conferring susceptibility to colorectal cancer.

The cytoskeleton adaptor protein ankyrin-1 is upregulated by p53 following DNA damage and alters cell migration

The integrity of the genome is maintained by a host of surveillance and repair mechanisms that are pivotal for cellular function. The tumour suppressor protein p53 is a major component of the DNA damage response pathway and plays a vital role in the maintenance of cell-cycle checkpoints. Here we show that a microRNA, miR-486, and its host gene ankyrin-1 (ANK1) are induced by p53 following DNA damage. Strikingly, the cytoskeleton adaptor protein ankyrin-1 was induced over 80-fold following DNA damage. ANK1 is upregulated in response to a variety of DNA damage agents in a range of cell types. We demonstrate that miR-486-5p is involved in controlling G1/S transition following DNA damage, whereas the induction of the ankyrin-1 protein alters the structure of the actin cytoskeleton and sustains limited cell migration during DNA damage. Importantly, we found that higher ANK1 expression correlates with decreased survival in cancer patients. Thus, these observations highlight ANK1 as an important effector downstream of the p53 pathway.