The role of MIZ-1 in MYC-dependent tumorigenesis

MYC Induces Oncogenic Stress through RNA Decay and Ribonucleotide Catabolism in Breast Cancer

Upregulation of MYC is a hallmark of cancer, wherein MYC drives oncogenic gene expression and elevates total RNA synthesis across cancer cell transcriptomes. Although this transcriptional anabolism fuels cancer growth and survival, the consequences and metabolic stresses induced by excess cellular RNA are poorly understood. Herein, we discover that RNA degradation and downstream ribonucleotide catabolism is a novel mechanism of MYC-induced cancer cell death. Combining genetics and metabolomics, we find that MYC increases RNA decay through the cytoplasmic exosome, resulting in the accumulation of cytotoxic RNA catabolites and reactive oxygen species. Notably, tumor-derived exosome mutations abrogate MYC-induced cell death, suggesting excess RNA decay may be toxic to human cancers. In agreement, purine salvage acts as a compensatory pathway that mitigates MYC-induced ribonucleotide catabolism, and inhibitors of purine salvage impair MYC+ tumor progression. Together, these data suggest that MYC-induced RNA decay is an oncogenic stress that can be exploited therapeutically. Significance: MYC is the most common oncogenic driver of poor-prognosis cancers but has been recalcitrant to therapeutic inhibition. We discovered a new vulnerability in MYC+ cancer where MYC induces cell death through excess RNA decay. Therapeutics that exacerbate downstream ribonucleotide catabolism provide a therapeutically tractable approach to TNBC (Triple-negative Breast Cancer) and other MYC-driven cancers.

Low NDRG2, regulated by the MYC/MIZ-1 complex and methylation, predicts poor outcomes in DLBCL patients

Diffuse large B-cell lymphoma (DLBCL) represents the most common tumor in non-Hodgkin's lymphoma. N-Myc downstream-regulated gene 2 (NDRG2) is a tumor suppressor highly expressed in healthy tissues but downregulated in many cancers. Although cell proliferation-related metabolism rewiring has been well characterized, less is known about the mechanism of metabolic changes with DLBCL. Herein, we investigated the expressions of NDRG2, MYC and Myc-interacting zinc finger protein 1 (MIZ-1) in seven human lymphoma (mostly DLBCLs) cell lines. NDRG2 expression was inversely correlated with the expressions of MYC and MIZ-1. Further, we explored the regulatory mechanism and biological functions underlying the lymphomagenesis involving NDRG2, MYC and MIZ-1. MYC and MIZ-1 promoted DLBCL cell proliferation, while NDRG2 induced apoptosis in LY8 cells. Moreover, NDRG2 methylation was reversed by the 5-Aza-2'-deoxycytidine (5-Aza-CDR) treatment, triggering the downregulation of MYC and inhibiting DLBCL cell survival. MYC interacts with NDRG2 to regulate energy metabolism associated with mTOR. Remarkably, supporting the biological significance, the converse correlation between NDRG2 and MYC was observed in human DLBCL tumor tissues (R = -0.557). Bioinformatics analysis further validated the association among NDRG2, MYC, MIZ-1, mTOR, and related metabolism genes. Additionally, NDRG2 (P = 0.001) and MYC (P < 0.001) were identified as promising prognostic biomarkers in DLBCL patients through survival analysis. Together, our data demonstrate that the MYC/MIZ-1 complex interplays with NDRG2 to influence the proliferation and apoptosis of DLBCL cells and show the characterizations of NDRG2, MYC and MIZ-1 for metabolism features and prediction prognosis in DLBCL.

Immune evasion: An imperative and consequence of MYC deregulation

MYC has been implicated in the pathogenesis of a wide range of human tumors and has been described for many years as a transcription factor that regulates genes with pleiotropic functions to promote tumorigenic growth. However, despite extensive efforts to identify specific target genes of MYC that alone could be responsible for promoting tumorigenesis, the field is yet to reach a consensus whether this is the crucial function of MYC. Recent work shifts the view on MYC's function from being a gene-specific transcription factor to an essential stress resilience factor. In highly proliferating cells, MYC preserves cell integrity by promoting DNA repair at core promoters, protecting stalled replication forks, and/or preventing transcription-replication conflicts. Furthermore, an increasing body of evidence demonstrates that MYC not only promotes tumorigenesis by driving cell-autonomous growth, but also enables tumors to evade the host's immune system. In this review, we summarize our current understanding of how MYC impairs antitumor immunity and why this function is evolutionarily hard-wired to the biology of the MYC protein family. We show why the cell-autonomous and immune evasive functions of MYC are mutually dependent and discuss ways to target MYC proteins in cancer therapy.

Regulation of BCR-mediated Ca2+ mobilization by MIZ1-TMBIM4 safeguards IgG1+ GC B cell-positive selection

The transition from immunoglobulin M (IgM) to affinity-matured IgG antibodies is vital for effective humoral immunity. This is facilitated by germinal centers (GCs) through affinity maturation and preferential maintenance of IgG+ B cells over IgM+ B cells. However, it is not known whether the positive selection of the different Ig isotypes within GCs is dependent on specific transcriptional mechanisms. Here, we explored IgG1+ GC B cell transcription factor dependency using a CRISPR-Cas9 screen and conditional mouse genetics. We found that MIZ1 was specifically required for IgG1+ GC B cell survival during positive selection, whereas IgM+ GC B cells were largely independent. Mechanistically, MIZ1 induced TMBIM4, an ancestral anti-apoptotic protein that regulated inositol trisphosphate receptor (IP3R)-mediated calcium (Ca2+) mobilization downstream of B cell receptor (BCR) signaling in IgG1+ B cells. The MIZ1-TMBIM4 axis prevented mitochondrial dysfunction-induced IgG1+ GC cell death caused by excessive Ca2+ accumulation. This study uncovers a unique Ig isotype-specific dependency on a hitherto unidentified mechanism in GC-positive selection.

MYC Oncogene: A Druggable Target for Treating Cancers with Natural Products

Various diseases, including cancers, age-associated disorders, and acute liver failure, have been linked to the oncogene, MYC. Animal testing and clinical trials have shown that sustained tumor volume reduction can be achieved when MYC is inactivated, and different combinations of therapeutic agents including MYC inhibitors are currently being developed. In this review, we first provide a summary of the multiple biological functions of the MYC oncoprotein in cancer treatment, highlighting that the equilibrium points of the MYC/MAX, MIZ1/MYC/MAX, and MAD (MNT)/MAX complexes have further potential in cancer treatment that could be used to restrain MYC oncogene expression and its functions in tumorigenesis. We also discuss the multifunctional capacity of MYC in various cellular cancer processes, including its influences on immune response, metabolism, cell cycle, apoptosis, autophagy, pyroptosis, metastasis, angiogenesis, multidrug resistance, and intestinal flora. Moreover, we summarize the MYC therapy patent landscape and emphasize the potential of MYC as a druggable target, using herbal medicine modulators. Finally, we describe pending challenges and future perspectives in biomedical research, involving the development of therapeutic approaches to modulate MYC or its targeted genes. Patients with cancers driven by MYC signaling may benefit from therapies targeting these pathways, which could delay cancerous growth and recover antitumor immune responses.

Manipulating Myc for reparative regeneration

The Myc family of proto-oncogenes is a key node for the signal transduction of external pro-proliferative signals to the cellular processes required for development, tissue homoeostasis maintenance, and regeneration across evolution. The tight regulation of Myc synthesis and activity is essential for restricting its oncogenic potential. In this review, we highlight the central role that Myc plays in regeneration across the animal kingdom (from Cnidaria to echinoderms to Chordata) and how Myc could be employed to unlock the regenerative potential of non-regenerative tissues in humans for therapeutic purposes. Mastering the fine balance of harnessing the ability of Myc to promote transcription without triggering oncogenesis may open the door to many exciting opportunities for therapeutic development across a wide array of diseases.

MYC function and regulation in physiological perspective

MYC, a key member of the Myc-proto-oncogene family, is a universal transcription amplifier that regulates almost every physiological process in a cell including cell cycle, proliferation, metabolism, differentiation, and apoptosis. MYC interacts with several cofactors, chromatin modifiers, and regulators to direct gene expression. MYC levels are tightly regulated, and deregulation of MYC has been associated with numerous diseases including cancer. Understanding the comprehensive biology of MYC under physiological conditions is an utmost necessity to demark biological functions of MYC from its pathological functions. Here we review the recent advances in biological mechanisms, functions, and regulation of MYC. We also emphasize the role of MYC as a global transcription amplifier.

NPM1 mutation reprograms leukemic transcription network via reshaping TAD topology

C-terminal mutation of Nucleophosmin 1 (NPM1C+) was thought to be a primary driving event in acute myeloid leukemia (AML) that reprograms leukemic-associated transcription programs to transform hematopoietic stem and progenitor cells (HSPCs). However, molecular mechanisms underlying NPM1C+-driven leukemogenesis remain elusive. Here, we report that NPM1C+ activates signature HOX genes and reprograms cell cycle regulators by altering CTCF-driven topologically associated domains (TADs). Hematopoietic-specific NPM1C+ knock-in alters TAD topology leading to disrupted regulation of the cell cycle as well as aberrant chromatin accessibility and homeotic gene expression, which results in myeloid differentiation block. Restoration of NPM1 within the nucleus re-establishes differentiation programs by reorganizing TADs critical for myeloid TFs and cell cycle regulators that switch the oncogenic MIZ1/MYC regulatory axis in favor of interacting with coactivator NPM1/p300, and prevents NPM1C+-driven leukemogenesis. In sum, our data reveal that NPM1C+ reshapes CTCF-defined TAD topology to reprogram signature leukemic transcription programs required for cell cycle progression and leukemic transformation.

RUNX3 inactivates oncogenic MYC through disruption of MYC/MAX complex and subsequent recruitment of GSK3β-FBXW7 cascade

MYC is one of the most commonly dysregulated proto-oncogenes in cancer. MYC promotes cancer initiation and maintenance by regulating multiple biological processes, such as proliferation and stem cell function. Here, we show that developmental regulator RUNX3 targets MYC protein for rapid degradation through the glycogen synthase kinase-3 beta-F-box/WD repeat-containing protein 7 (GSK3β-FBXW7) proteolytic pathway. The evolutionarily conserved Runt domain of RUNX3 interacts directly with the basic helix-loop-helix leucine zipper of MYC, resulting in the disruption of MYC/MAX and MYC/MIZ-1 interactions, enhanced GSK3β-mediated phosphorylation of MYC protein at threonine-58 and its subsequent degradation via the ubiquitin-proteasomal pathway. We therefore uncover a previously unknown mode of MYC destabilization by RUNX3 and provide an explanation as to why RUNX3 inhibits early-stage cancer development in gastrointestinal and lung mouse cancer models.

NIPSNAP1 directs dual mechanisms to restrain senescence in cancer cells

BACKGROUND

Although the executive pathways of senescence are known, the underlying control mechanisms are diverse and not fully understood, particularly how cancer cells avoid triggering senescence despite experiencing exacerbated stress conditions within the tumor microenvironment.

METHODS

Mass spectrometry (MS)-based proteomic screening was used to identify differentially regulated genes in serum-starved hepatocellular carcinoma cells and RNAi employed to determine knockdown phenotypes of prioritized genes. Thereafter, gene function was investigated using cell proliferation assays (colony-formation, CCK-8, Edu incorporation and cell cycle) together with cellular senescence assays (SA-β-gal, SAHF and SASP). Gene overexpression and knockdown techniques were applied to examine mRNA and protein regulation in combination with luciferase reporter and proteasome degradation assays, respectively. Flow cytometry was applied to detect changes in cellular reactive oxygen species (ROS) and in vivo gene function examined using a xenograft model.

RESULTS

Among the genes induced by serum deprivation, NIPSNAP1 was selected for investigation. Subsequent experiments revealed that NIPSNAP1 promotes cancer cell proliferation and inhibits P27-dependent induction of senescence via dual mechanisms. Firstly, NIPSNAP1 maintains the levels of c-Myc by sequestering the E3 ubiquitin ligase FBXL14 to prevent the proteasome-mediated turnover of c-Myc. Intriguingly, NIPSNAP1 levels are restrained by transcriptional repression mediated by c-Myc-Miz1, with repression lifted in response to serum withdrawal, thus identifying feedback regulation between NIPSNAP1 and c-Myc. Secondly, NIPSNAP1 was shown to modulate ROS levels by promoting interactions between the deacetylase SIRT3 and superoxide dismutase 2 (SOD2). Consequent activation of SOD2 serves to maintain cellular ROS levels below the critical levels required to induce cell cycle arrest and senescence. Importantly, the actions of NIPSNAP1 in promoting cancer cell proliferation and preventing senescence were recapitulated in vivo using xenograft models.

CONCLUSIONS

Together, these findings reveal NIPSNAP1 as an important mediator of c-Myc function and a negative regulator of cellular senescence. These findings also provide a theoretical basis for cancer therapy where targeting NIPSNAP1 invokes cellular senescence.

The Roles of Zinc Finger Proteins in Colorectal Cancer

Despite colorectal cancer remaining a leading worldwide cause of cancer-related death, there remains a paucity of effective treatments for advanced disease. The molecular mechanisms underlying the development of colorectal cancer include altered cell signaling and cell cycle regulation that may result from epigenetic modifications of gene expression and function. Acting as important transcriptional regulators of normal biological processes, zinc finger proteins also play key roles in regulating the cellular mechanisms underlying colorectal neoplasia. These actions impact cell differentiation and proliferation, epithelial-mesenchymal transition, apoptosis, homeostasis, senescence, and maintenance of stemness. With the goal of highlighting promising points of therapeutic intervention, we review the oncogenic and tumor suppressor roles of zinc finger proteins with respect to colorectal cancer tumorigenesis and progression.

Disruption of Multiple Overlapping Functions Following Stepwise Inactivation of the Extended Myc Network

Myc, a member of the "Myc Network" of bHLH-ZIP transcription factors, supervises proliferation, metabolism, and translation. It also engages in crosstalk with the related "Mlx Network" to co-regulate overlapping genes and functions. We investigated the consequences of stepwise conditional inactivation of Myc and Mlx in primary and SV40 T-antigen-immortalized murine embryonic fibroblasts (MEFs). Myc-knockout (MycKO) and Myc × Mlx "double KO" (DKO)-but not MlxKO-primary MEFs showed rapid growth arrest and displayed features of accelerated aging and senescence. However, DKO MEFs soon resumed proliferating, indicating that durable growth arrest requires an intact Mlx network. All three KO MEF groups deregulated multiple genes and functions pertaining to aging, senescence, and DNA damage recognition/repair. Immortalized KO MEFs proliferated in Myc's absence while demonstrating variable degrees of widespread genomic instability and sensitivity to genotoxic agents. Finally, compared to primary MycKO MEFs, DKO MEFs selectively downregulated numerous gene sets associated with the p53 and retinoblastoma (Rb) pathways and G2/M arrest. Thus, the reversal of primary MycKO MEF growth arrest by either Mlx loss or SV40 T-antigen immortalization appears to involve inactivation of the p53 and/or Rb pathways.

Reversible Myc hypomorphism identifies a key Myc-dependency in early cancer evolution

Germ-line hypomorphism of the pleiotropic transcription factor Myc in mice, either through Myc gene haploinsufficiency or deletion of Myc enhancers, delays onset of various cancers while mice remain viable and exhibit only relatively mild pathologies. Using a genetically engineered mouse model in which Myc expression may be systemically and reversibly hypomorphed at will, we asked whether this resistance to tumour progression is also emplaced when Myc hypomorphism is acutely imposed in adult mice. Indeed, adult Myc hypomorphism profoundly blocked KRasG12D-driven lung and pancreatic cancers, arresting their evolution at the early transition from indolent pre-tumour to invasive cancer. We show that such arrest is due to the incapacity of hypomorphic levels of Myc to drive release of signals that instruct the microenvironmental remodelling necessary to support invasive cancer. The cancer protection afforded by long-term adult imposition of Myc hypomorphism is accompanied by only mild collateral side effects, principally in haematopoiesis, but even these are circumvented if Myc hypomorphism is imposed metronomically whereas potent cancer protection is retained.

Molecular mimicry: HUWE1 binds an atypical site in MIZ1 by adopting a typical BTB fold

In this issue of Structure, Orth et al. describe an exposed binding site in the MIZ1 BTB domain due to an atypical flexible region within the BTB core. This site allows HECT-type ubiquitin ligase 1 to bind the MIZ1 homodimer by forming β strands and completing the canonical BTB fold.

Targeting cancer stem cells in medulloblastoma by inhibiting AMBRA1 dual function in autophagy and STAT3 signalling

Medulloblastoma (MB) is a childhood malignant brain tumour comprising four main subgroups characterized by different genetic alterations and rate of mortality. Among MB subgroups, patients with enhanced levels of the c-MYC oncogene (MB_Group3) have the poorest prognosis. Here we identify a previously unrecognized role of the pro-autophagy factor AMBRA1 in regulating MB. We demonstrate that AMBRA1 expression depends on c-MYC levels and correlates with Group 3 patient poor prognosis; also, knockdown of AMBRA1 reduces MB stem potential, growth and migration of MB_Group3 stem cells. At a molecular level, AMBRA1 mediates these effects by suppressing SOCS3, an inhibitor of STAT3 activation. Importantly, pharmacological inhibition of autophagy profoundly affects both stem and invasion potential of MB_Group3 stem cells, and a combined anti-autophagy and anti-STAT3 approach impacts the MB_Group3 outcome. Taken together, our data support the c-MYC/AMBRA1/STAT3 axis as a strong oncogenic signalling pathway with significance for both patient stratification strategies and targeted treatments of MB_Group3.

Metabolic convergence on lipogenesis in RAS, BCR-ABL, and MYC-driven lymphoid malignancies

BACKGROUND

Metabolic reprogramming is a central feature in many cancer subtypes and a hallmark of cancer. Many therapeutic strategies attempt to exploit this feature, often having unintended side effects on normal metabolic programs and limited efficacy due to integrative nature of metabolic substrate sourcing. Although the initiating oncogenic lesion may vary, tumor cells in lymphoid malignancies often share similar environments and potentially similar metabolic profiles. We examined cells from mouse models of MYC-, RAS-, and BCR-ABL-driven lymphoid malignancies and find a convergence on de novo lipogenesis. We explore the potential role of MYC in mediating lipogenesis by 13C glucose tracing and untargeted metabolic profiling. Inhibition of lipogenesis leads to cell death both in vitro and in vivo and does not induce cell death of normal splenocytes.

METHODS

We analyzed RNA-seq data sets for common metabolic convergence in lymphoma and leukemia. Using in vitro cell lines derived in from conditional MYC, RAS, and BCR-ABL transgenic murine models and oncogene-driven human cell lines, we determined gene regulation, metabolic profiles, and sensitivity to inhibition of lipogenesis in lymphoid malignancies. We utilize preclinical murine models and transgenic primary model of T-ALL to determine the effect of lipogenesis blockade across BCR-ABL-, RAS-, and c-MYC-driven lymphoid malignancies. Statistical significance was calculated using unpaired t-tests and one-way ANOVA.

RESULTS

This study illustrates that de novo lipid biogenesis is a shared feature of several lymphoma subtypes. Using cell lines derived from conditional MYC, RAS, and BCR-ABL transgenic murine models, we demonstrate shared responses to inhibition of lipogenesis by the acetyl-coA carboxylase inhibitor 5-(tetradecloxy)-2-furic acid (TOFA), and other lipogenesis inhibitors. We performed metabolic tracing studies to confirm the influence of c-MYC and TOFA on lipogenesis. We identify specific cell death responses to TOFA in vitro and in vivo and demonstrate delayed engraftment and progression in vivo in transplanted lymphoma cell lines. We also observe delayed progression of T-ALL in a primary transgenic mouse model upon TOFA administration. In a panel of human cell lines, we demonstrate sensitivity to TOFA treatment as a metabolic liability due to the general convergence on de novo lipogenesis in lymphoid malignancies driven by MYC, RAS, or BCR-ABL. Importantly, cell death was not significantly observed in non-malignant cells in vivo.

CONCLUSIONS

These studies suggest that de novo lipogenesis may be a common survival strategy for many lymphoid malignancies and may be a clinically exploitable metabolic liability.

TRIAL REGISTRATION

This study does not include any clinical interventions on human subjects.

MYC: a multipurpose oncogene with prognostic and therapeutic implications in blood malignancies

MYC oncogene is a transcription factor with a wide array of functions affecting cellular activities such as cell cycle, apoptosis, DNA damage response, and hematopoiesis. Due to the multi-functionality of MYC, its expression is regulated at multiple levels. Deregulation of this oncogene can give rise to a variety of cancers. In this review, MYC regulation and the mechanisms by which MYC adjusts cellular functions and its implication in hematologic malignancies are summarized. Further, we also discuss potential inhibitors of MYC that could be beneficial for treating hematologic malignancies.

MYC- and MIZ1-Dependent Vesicular Transport of Double-Strand RNA Controls Immune Evasion in Pancreatic Ductal Adenocarcinoma

Deregulated expression of the MYC oncoprotein enables tumor cells to evade immune surveillance, but the mechanisms underlying this surveillance are poorly understood. We show here that endogenous MYC protects pancreatic ductal adenocarcinoma (PDAC) driven by KRAS^G12D and TP53^R172H from eradication by the immune system. Deletion of TANK-binding kinase 1 (TBK1) bypassed the requirement for high MYC expression. TBK1 was active due to the accumulation of double-stranded RNA (dsRNA), which was derived from inverted repetitive elements localized in introns of nuclear genes. Nuclear-derived dsRNA is packaged into extracellular vesicles and subsequently recognized by toll-like receptor 3 (TLR3) to activate TBK1 and downstream MHC class I expression in an autocrine or paracrine manner before being degraded in lysosomes. MYC suppressed loading of dsRNA onto TLR3 and its subsequent degradation via association with MIZ1. Collectively, these findings suggest that MYC and MIZ1 suppress a surveillance pathway that signals perturbances in mRNA processing to the immune system, which facilitates immune evasion in PDAC. SIGNIFICANCE: This study identifies a TBK1-dependent pathway that links dsRNA metabolism to antitumor immunity and shows that suppression of TBK1 is a critical function of MYC in pancreatic ductal adenocarcinoma.

lncRNAs as Potential Targets in Small Cell Lung Cancer: MYC -dependent Regulation

BACKGROUND

Small Cell Lung Cancer (SCLC) is a highly aggressive malignancy. MYC family oncogenes are amplified and overexpressed in 20% of SCLCs, showing that MYC oncogenes and MYC regulated genes are strong candidates as therapeutic targets for SCLC. c-MYC plays a fundamental role in cancer stem cell properties and malignant transformation. Several targets have been identified by the activation/repression of MYC. Deregulated expression levels of lncRNAs have also been observed in many cancers.

OBJECTIVE

The aim of the present study is to investigate the lncRNA profiles which depend on MYC expression levels in SCLC.

METHODS

Firstly, we constructed lentiviral vectors for MYC overexpression/inhibition. MYC expression is suppressed by lentiviral shRNA vector in MYC amplified H82 and N417 cells, and overexpressed by lentiviral inducible overexpression vector in MYC non-amplified H345 cells. LncRNA cDNA is transcribed from total RNA samples, and 91 lncRNAs are evaluated by qRT-PCR.

RESULTS

We observed that N417, H82 and H345 cells require MYC for their growth. Besides, MYC is not only found to regulate the expressions of genes related to invasion, stem cell properties, apoptosis and cell cycle (p21, Bcl2, cyclinD1, Sox2, Aldh1a1, and N-Cadherin), but also found to regulate lncRNAs. With this respect, expressions of AK23948, ANRIL, E2F4AS, GAS5, MEG3, H19, L1PA16, SFMBT2, ZEB2NAT, HOTAIR, Sox2OT, PVT1, and BC200 were observed to be in parallel with MYC expression, whereas expressions of Malat1, PTENP1, Neat1, UCA1, SNHG3, and SNHG6 were inversely correlated.

CONCLUSION

Targeting MYC-regulated genes as a therapeutic strategy can be important for SCLC therapy. This study indicated the importance of identifying MYC-regulated lncRNAs and that these can be utilized to develop a therapeutic strategy for SCLC.

Positive Selection in the Light Zone of Germinal Centers

Germinal centers (GCs) are essential sites for the production of high-affinity antibody secreting plasma cells (PCs) and memory-B cells (MBCs), which form the framework of vaccination. Affinity maturation and permissive selection in GCs are key for the production of PCs and MBCs, respectively. For these purposes, GCs positively select “fit” cells in the light zone of the GC and instructs them for one of three known B cell fates: PCs, MBCs and persistent GC-B cells as dark zone entrants. In this review, we provide an overview of the positive selection process and discuss its mechanisms and how B cell fates are instructed.

Transcriptome Analysis Identifies Novel Mechanisms Associated with the Antitumor Effect of Chitosan-Stabilized Selenium Nanoparticles

Selenium nanoparticles (SeNPs) have been receiving special attention in recent years due to their antioxidant capacity and antitumor properties. However, the mechanisms associated with these properties remain to be elucidated. For this reason, a global transcriptome analysis has been designed in this work and it was carried out using human hepatocarcinoma cells and chitosan-stabilized SeNPs (Ch-SeNPs) to identify new targets and pathways related to the antitumor mechanisms associated with Ch-SeNPs. The results obtained confirm the alteration of the cell cycle and the effect of Ch-SeNPs on different tumor suppressors and other molecules involved in key mechanisms related to cancer progression. Furthermore, we demonstrated the antioxidant properties of these nanoparticles and their capacity to induce senescence, which was further confirmed through the measurement of β-galactosidase activity.

MYC and TFEB Control DNA Methylation and Differentiation in AML

Although the MYC transcription factor has been consistently implicated in acute myeloid leukemia (AML), its gene targets and precise role in leukemogenesis remain unknown. In this issue of Blood Cancer Discovery, Yun and colleagues provide evidence that MYC directly suppresses the expression of TFEB, an mTORC1-regulated transcription factor. They show that, in the context of the myelocytic/granulocytic lineage, TFEB acts as a tumor suppressor by inducing the IDH1/2-TET pathway, which in turn, leads to altered DNA methylation and increased expression of genes involved in myeloid differentiation and apoptosis. Therefore, high levels of MYC suppress an epigenetic pathway that should normally act to attenuate leukemic progression. Identification of the components of this pathway is likely to inform new therapeutic tactics for AML and possibly other cancers. See related article by Yun et al., p. 162.

Taking the Myc out of cancer: toward therapeutic strategies to directly inhibit c-Myc

c-Myc is a transcription factor that is constitutively and aberrantly expressed in over 70% of human cancers. Its direct inhibition has been shown to trigger rapid tumor regression in mice with only mild and fully reversible side effects, suggesting this to be a viable therapeutic strategy. Here we reassess the challenges of directly targeting c-Myc, evaluate lessons learned from current inhibitors, and explore how future strategies such as miniaturisation of Omomyc and targeting E-box binding could facilitate translation of c-Myc inhibitors into the clinic.

Targeting MYC: From understanding its biology to drug discovery

The MYC oncogene is considered to be a high priority target for clinical intervention in cancer patients due to its aberrant activation in more than 50% of human cancers. Direct small molecule inhibition of MYC has traditionally been hampered by its intrinsically disordered nature and lack of both binding site and enzymatic activity. In recent years, however, a number of strategies for indirectly targeting MYC have emerged, guided by the advent of protein structural information and the growing set of computational tools that can be used to accelerate the hit to lead process in medicinal chemistry. In this review, we provide an overview of small molecules developed for clinical applications of these strategies, which include stabilization of the MYC guanine quadruplex, inhibition of BET factor BRD4, and disruption of the MYC:MAX heterodimer. The recent identification of novel targets for indirect MYC inhibition at the protein level is also discussed.

Identification of the transcription factor Miz1 as an essential regulator of diphthamide biosynthesis using a CRISPR-mediated genome-wide screen

Diphthamide is a unique post-translationally modified histidine residue (His⁷¹⁵ in all mammals) found only in eukaryotic elongation factor-2 (eEF-2). The biosynthesis of diphthamide represents one of the most complex modifications, executed by protein factors conserved from yeast to humans. Diphthamide is not only essential for normal physiology (such as ensuring fidelity of mRNA translation), but is also exploited by bacterial ADP-ribosylating toxins (e.g., diphtheria toxin) as their molecular target in pathogenesis. Taking advantage of the observation that cells defective in diphthamide biosynthesis are resistant to ADP-ribosylating toxins, in the past four decades, seven essential genes (Dph1 to Dph7) have been identified for diphthamide biosynthesis. These technically unsaturated screens raise the question as to whether additional genes are required for diphthamide biosynthesis. In this study, we performed two independent, saturating, genome-wide CRISPR knockout screens in human cells. These screens identified all previously known Dph genes, as well as further identifying the BTB/POZ domain-containing transcription factor Miz1. We found that Miz1 is absolutely required for diphthamide biosynthesis via its role in the transcriptional regulation of Dph1 expression. Mechanistically, Miz1 binds to the Dph1 proximal promoter via an evolutionarily conserved consensus binding site to activate Dph1 transcription. Therefore, this work demonstrates that Dph1-7, along with the newly identified Miz1 transcription factor, are likely to represent the essential protein factors required for diphthamide modification on eEF2.

Diphthamide is a unique post-translationally modified histidine residue (His⁶⁹⁹ in yeast, His⁷¹⁵ in all mammals) found only in eukaryotic elongation factor-2 (eEF-2). Mice that are deficient in diphthamide biosynthesis are embryonic lethal, attesting to the importance of diphthamide in normal physiology. It has taken four decades to identify the seven non-redundant genes in diphthamide biosynthesis, but whether additional factors are required and how the pathway is regulated remained elusive. To address these issues, we performed two saturating, independent, and unbiased genome-wide CRISPR knockout screens. The screens concluded independently that Dph1-Dph7 and additionally transcription factor Miz1 are the key factors required for diphthamide biosynthesis. Mechanistically, Miz1 binds to the Dph1 proximal promoter via an evolutionarily conserved consensus binding site to activate Dph1 transcription. While diphthamide biosynthesis machinery (Dph1-Dph7) exists across eukaryotes, Miz1 orthologues do not exist in lower species such as yeast, C. elegans, and Drosophila, indicating that the regulation of diphthamide modification by Miz1 emerged much later in evolution. The work opens a new avenue for understanding the role that diphthamide modification plays in normal physiology and bacterial toxin pathogenesis.

Dissecting transcriptional amplification by MYC

Supraphysiological MYC levels are oncogenic. Originally considered a typical transcription factor recruited to E-boxes (CACGTG), another theory posits MYC a global amplifier increasing output at all active promoters. Both models rest on large-scale genome-wide "-omics'. Because the assumptions, statistical parameter and model choice dictates the '-omic' results, whether MYC is a general or specific transcription factor remains controversial. Therefore, an orthogonal series of experiments interrogated MYC's effect on the expression of synthetic reporters. Dose-dependently, MYC increased output at minimal promoters with or without an E-box. Driving minimal promoters with exogenous (glucocorticoid receptor) or synthetic transcription factors made expression more MYC-responsive, effectively increasing MYC-amplifier gain. Mutations of conserved MYC-Box regions I and II impaired amplification, whereas MYC-box III mutations delivered higher reporter output indicating that MBIII limits over-amplification. Kinetic theory and experiments indicate that MYC activates at least two steps in the transcription-cycle to explain the non-linear amplification of transcription that is essential for global, supraphysiological transcription in cancer.

Restriction of memory B cell differentiation at the germinal center B cell positive selection stage

Memory B cells (MBCs) are key for protection from reinfection. However, it is mechanistically unclear how germinal center (GC) B cells differentiate into MBCs. MYC is transiently induced in cells fated for GC expansion and plasma cell (PC) formation, so-called positively selected GC B cells. We found that these cells coexpressed MYC and MIZ1 (MYC-interacting zinc-finger protein 1 [ZBTB17]). MYC and MIZ1 are transcriptional activators; however, they form a transcriptional repressor complex that represses MIZ1 target genes. Mice lacking MYC-MIZ1 complexes displayed impaired cell cycle entry of positively selected GC B cells and reduced GC B cell expansion and PC formation. Notably, absence of MYC-MIZ1 complexes in positively selected GC B cells led to a gene expression profile alike that of MBCs and increased MBC differentiation. Thus, at the GC positive selection stage, MYC-MIZ1 complexes are required for effective GC expansion and PC formation and to restrict MBC differentiation. We propose that MYC and MIZ1 form a module that regulates GC B cell fate.

"B" aware: Memory lane access is restricted!

Understanding the molecular mechanisms that govern the differentiation of high-affinity germinal center (GC) B cells into memory B cells versus plasma cells is a major quest of adaptive immunity. In this issue, Toboso-Navasa et al. (https://doi.org/10.1084/jem.20191933) provide evidence that the MYC-MIZ1 transcriptional repressor complex restricts the differentiation of GC B cells into MBCs.

MYC and the unfolded protein response in cancer: synthetic lethal partners in crime?

The transcription factors of the MYC family play pivotal roles in the initiation and progression of human cancers. High oncogenic level of MYC invades low‐affinity sites and enhancer sequences, which subsequently alters the transcriptome, causes metabolic imbalance, and induces stress response. The endoplasmic reticulum (ER) not only plays a central role in maintaining proteostasis, but also contributes to other key biological processes, including Ca²⁺ metabolism and the synthesis of lipids and glucose. Stress conditions, such as shortage in glucose or oxygen and disruption of Ca²⁺ homeostasis, may perturb proteostasis and induce the unfolded protein response (UPR), which either restores homeostasis or triggers cell death. Crucial roles of ER stress and UPR signaling have been implicated in various cancers, from oncogenesis to treatment response. Here, we summarize the current knowledge on the interaction between MYC and UPR signaling, and its contribution to cancer development. We also discuss the potential of targeting key UPR signaling nodes as novel synthetic lethal strategies in MYC‐driven cancers.

Myc-Miz1 signaling promotes self-renewal of leukemia stem cells by repressing Cebpα and Cebpδ

c-Myc (Myc hereafter) is found to be deregulated and/or amplified in most acute myeloid leukemias (AMLs). Almost all AML cells are dependent upon Myc for their proliferation and survival. Thus, Myc has been proposed as a critical anti-AML target. Myc has Max-mediated transactivational and Myc-interacting zinc finger protein 1 (Miz1)-mediated transrepressional activities. The role of Myc-Max-mediated transactivation in the pathogenesis of AML has been well studied; however, the role of Myc-Miz1-mediated transrepression in AML is still somewhat obscure. Myc protein harboring a V394D mutation (MycV394D) is a mutant form of Myc that lacks transrepressional activity due to a defect in its ability to interact with Miz1. We found that, compared with Myc, the oncogenic function of MycV394D is significantly impaired. The AML/myeloproliferative disorder that develops in mice receiving MycV394D-transduced hematopoietic stem/progenitor cells (HSPCs) is significantly delayed compared with mice receiving Myc-transduced HSPCs. Using a murine MLL-AF9 AML model, we found that AML cells expressing MycV394D (intrinsic Myc deleted) are partially differentiated and show reductions in both colony-forming ability in vitro and leukemogenic capacity in vivo. The reduced frequency of leukemia stem cells (LSCs) among MycV394D-AML cells and their reduced leukemogenic capacity during serial transplantation suggest that Myc-Miz1 interaction is required for the self-renewal of LSCs. In addition, we found that MycV394D-AML cells are more sensitive to chemotherapy than are Myc-AML cells. Mechanistically, we found that Myc represses Miz1-mediated expression of CCAAT/enhancer-binding protein α (Cebpα) and Cebpδ, thus playing an important role in the pathogenesis of AML by maintaining the undifferentiated state and self-renewal capacity of LSCs.

MYC-Associated Factor MAX is a Regulator of the Circadian Clock

The circadian transcriptional network is based on a competition between transcriptional activator and repressor complexes regulating the rhythmic expression of clock-controlled genes. We show here that the MYC-associated factor X, MAX, plays a repressive role in this network and operates through a MYC-independent binding to E-box-containing regulatory regions within the promoters of circadian BMAL1 targets. We further show that this "clock" function of MAX is required for maintaining a proper circadian rhythm and that MAX and BMAL1 contribute to two temporally alternating transcriptional complexes on clock-regulated promoters. We also identified MAX network transcriptional repressor, MNT, as a fundamental partner of MAX-mediated circadian regulation. Collectively, our data indicate that MAX regulates clock gene expression and contributes to keeping the balance between positive and negative elements of the molecular clock machinery.

The CARM1-p300-c-Myc-Max (CPCM) transcriptional complex regulates the expression of CUL4A/4B and affects the stability of CRL4 E3 ligases in colorectal cancer

The transcription factor c-Myc and two cullin family members CUL4A/4B function as oncogenes in colorectal cancer. Our recent publication reveals that c-Myc specifically activates the expression of CUL4A/4B through binding to their promoters. However, the underlying mechanism of how c-Myc actions in this process is still unknown. Using mass spectrometry and immunoprecipitation assays, we identified c-Myc formed a transcriptional complex with its partner Max (Myc-associated factor X), a histone acetyltransferase p300 and a coactivator associated arginine methyltransferase 1 (CARM1) in the present study. Knockdown or overexpression of the components of CARM1-p300-c-Myc-Max (CPCM) complex resulted in a decrease or increase of CUL4A/4B levels, respectively. Individual knockdown or inhibition of CPCM components decreased cell proliferation, colony formation, and cell invasion. Biochemically, knockdown or inhibition of CPCM components decreased their occupancies on the promoters of CUL4A/4B and resulted in their downregulation. Importantly, inhibition of CPCM components also caused a decrease of CRL4 E3 ligase activities and eventually led to an accumulation of ST7 (suppression of tumorigenicity 7), the specific substrate of CRL4 E3 ligases in colorectal cancer. Moreover, the in vivo tumor formation results indicated that knockdown or inhibition of CPCM components significantly decreased the tumor volumes. Together, our results suggest that the CPCM complex mediates explicitly the expression of CUL4A/4B, and thus affects the stability of CRL4 E3 ligases and the ubiquitination of ST7. These results provide more options by targeting the CPCM components to inhibit tumor growth in the therapy of colorectal cancer.

INHBB Is a Novel Prognostic Biomarker Associated with Cancer-Promoting Pathways in Colorectal Cancer

BACKGROUND

Inhibin subunit beta B (INHBB) is a protein-coding gene that participated in the synthesis of the transforming growth factor-β (TGF-β) family members. The study is aimed at exploring the clinical significance of INHBB in patients with colorectal cancer (CRC) by bioinformatics analysis.

METHODS

Real-time PCR and analyses of Oncomine, Gene Expression Omnibus (GEO), and The Cancer Genome Atlas (TCGA) databases were utilized to evaluate the INHBB gene transcription level of colorectal cancer (CRC) tissue. We evaluated the INHBB methylation level and the relationship between expression and methylation levels of CpG islands in CRC tissue. The corresponding clinical data were obtained to further explore the association of INHBB with clinical and survival features. In addition, Gene Set Enrichment Analysis (GSEA) was performed to explore the gene ontology and signaling pathways of INHBB involved.

RESULTS

INHBB expression was elevated in CRC tissue. Although the promoter of INHBB was hypermethylated in CRC, methylation did not ultimately correlate with the expression of INHBB. Overexpression of INHBB was significantly and positively associated with invasion depth, distant metastasis, and TNM stage. Cox regression analyses and Kaplan-Meier survival analysis indicated that high expression of INHBB was correlated with worse overall survival (OS) and disease-free survival (DFS). GSEA showed that INHBB was closely correlated with 5 cancer-promoting signaling pathways including the Hedgehog signaling pathway, ECM receptor interaction, TGF-β signaling pathway, focal adhesion, and pathway in cancer. INHBB expression significantly promoted macrophage infiltration and inhibited memory T cell, mast cell, and dendritic cell infiltration. INHBB expression was positively correlated with stromal and immune scores of CRC samples.

CONCLUSION

INHBB might be a potential prognostic biomarker and a novel therapeutic target for CRC.

Omomyc Reveals New Mechanisms To Inhibit the MYC Oncogene

The MYC oncogene is upregulated in human cancers by translocation, amplification, and mutation of cellular pathways that regulate Myc. Myc/Max heterodimers bind to E box sequences in the promoter regions of genes and activate transcription.

The MYC oncogene is upregulated in human cancers by translocation, amplification, and mutation of cellular pathways that regulate Myc. Myc/Max heterodimers bind to E box sequences in the promoter regions of genes and activate transcription. The MYC inhibitor Omomyc can reduce the ability of MYC to bind specific box sequences in promoters of MYC target genes by binding directly to E box sequences as demonstrated by chromatin immunoprecipitation (CHIP). Here, we demonstrate by both a proximity ligation assay (PLA) and double chromatin immunoprecipitation (ReCHIP) that Omomyc preferentially binds to Max, not Myc, to mediate inhibition of MYC-mediated transcription by replacing MYC/MAX heterodimers with Omomyc/MAX heterodimers. The formation of Myc/Max and Omomyc/Max heterodimers occurs cotranslationally; Myc, Max, and Omomyc can interact with ribosomes and Max RNA under conditions in which ribosomes are intact. Taken together, our data suggest that the mechanism of action of Omomyc is to bind DNA as either a homodimer or a heterodimer with Max that is formed cotranslationally, revealing a novel mechanism to inhibit the MYC oncogene. We find that in vivo, Omomyc distributes quickly to kidneys and liver and has a short effective half-life in plasma, which could limit its use in vivo.

ChEA3: transcription factor enrichment analysis by orthogonal omics integration

Identifying the transcription factors (TFs) responsible for observed changes in gene expression is an important step in understanding gene regulatory networks. ChIP-X Enrichment Analysis 3 (ChEA3) is a transcription factor enrichment analysis tool that ranks TFs associated with user-submitted gene sets. The ChEA3 background database contains a collection of gene set libraries generated from multiple sources including TF-gene co-expression from RNA-seq studies, TF-target associations from ChIP-seq experiments, and TF-gene co-occurrence computed from crowd-submitted gene lists. Enrichment results from these distinct sources are integrated to generate a composite rank that improves the prediction of the correct upstream TF compared to ranks produced by individual libraries. We compare ChEA3 with existing TF prediction tools and show that ChEA3 performs better. By integrating the ChEA3 libraries, we illuminate general transcription factor properties such as whether the TF behaves as an activator or a repressor. The ChEA3 web-server is available from https://amp.pharm.mssm.edu/ChEA3.

Transcriptional suppression of the miR-15/16 family by c-Myc in malignant pleural mesothelioma

MicroRNA downregulation is frequent in malignant pleural mesothelioma (MPM), but the mechanisms responsible for loss of miR-15/16 and miR-193a are yet to be elucidated and were investigated in this study. Copy Number Variation (CNV) of microRNA-coding genes was analyzed in MPM cells by digital droplet PCR (ddPCR) and revealed heterozygous loss of miR-193a and miR-15a/16-1, but no change in miR-15b/16-2. Epigenetic control of microRNA expression was inferred following decitabine and Trichostatin A (TSA) treatment which did not substantially affect microRNA expression. Knockdown of c-Myc expression led to upregulation of SMC4, miR-15b and 16, and to a lesser extent DLEU2 and miR-15a, whereas c-Myc overexpression repressed microRNA expression. Chromatin immunoprecipitation (ChIP) assays confirmed the interaction of c-Myc with the DLEU2 and SMC4 promoters. Tumor microRNA expression was determined in samples from MPM patients, with samples of pleura from cardiac surgery patients used as controls. In tumor samples, a strong correlation was observed between the expression of miR-15b and 16 (R²=0.793), but not miR-15a and 16. Our data suggest that in MPM, the downregulation of miR-15/16 is due to transcriptional repression by c-Myc, primarily via control of the miR-15b/16-2 locus, while miR-193a-3p loss is due to genomic deletion.

A targeted proteomics approach reveals a serum protein signature as diagnostic biomarker for resectable gastric cancer

BACKGROUND

Gastric cancer (GC) is the third leading cause of cancer death. Early detection is a key factor to reduce its mortality.

METHODS

We retrospectively collected pre- and postoperative serum samples as well as tumour tissues and adjacent normal tissues from 100 GC patients. Serum samples from non-cancerous patients were served as controls (n = 50). A high-throughput protein detection technology, multiplex proximity extension assays (PEA), was applied to measure levels of over 300 proteins. Alteration of each protein was analysed by univariate analysis. Elastic-net logistic regression was performed to select serum proteins into the diagnostic model.

FINDINGS

We identified 19 serum proteins (CEACAM5, CA9, MSLN, CCL20, SCF, TGF-alpha, MMP-1, MMP-10, IGF-1, CDCP1, PPIA, DDAH-1, HMOX-1, FLI1, IL-7, ZBTB-17, APBB1IP, KAZALD-1, and ADAMTS-15) that together distinguish GC cases from controls with a diagnostic sensitivity of 93%, specificity of 100%, and area under receiver operating characteristic curve (AUC) of 0·99 (95% CI: 0·98-1). Moreover, the 19-serum protein signature provided an increased diagnostic capacity in patients at TNM I-II stage (sensitivity 89%, specificity 100%, AUC 0·99) and in patients with high microsatellite instability (MSI) (91%, 98%, and 0·99) compared to individual proteins. These promising results will inspire a large-scale independent cohort study to be pursued for validating the proposed protein signature.

INTERPRETATION

Based on targeted proteomics and elastic-net logistic regression, we identified a 19-serum protein signature which could contribute to clinical GC diagnosis, especially for patients at early stage and those with high MSI. FUND: This study was supported by a European H2020-Marie Skłodowska-Curie Innovative Training Networks grant (316,929, GastricGlycoExplorer). Funder had no influence on trial design, data evaluation, and interpretation.

MYC Oncogene Contributions to Release of Cell Cycle Brakes

Promotion of the cell cycle is a major oncogenic mechanism of the oncogene c-MYC (MYC). MYC promotes the cell cycle by not only activating or inducing cyclins and CDKs but also through the downregulation or the impairment of the activity of a set of proteins that act as cell-cycle brakes. This review is focused on the role of MYC as a cell-cycle brake releaser i.e., how MYC stimulates the cell cycle mainly through the functional inactivation of cell cycle inhibitors. MYC antagonizes the activities and/or the expression levels of p15, ARF, p21, and p27. The mechanism involved differs for each protein. p15 (encoded by CDKN2B) and p21 (CDKN1A) are repressed by MYC at the transcriptional level. In contrast, MYC activates ARF, which contributes to the apoptosis induced by high MYC levels. At least in some cells types, MYC inhibits the transcription of the p27 gene (CDKN1B) but also enhances p27's degradation through the upregulation of components of ubiquitin ligases complexes. The effect of MYC on cell-cycle brakes also opens the possibility of antitumoral therapies based on synthetic lethal interactions involving MYC and CDKs, for which a series of inhibitors are being developed and tested in clinical trials.

Dancing from bottoms up - Roles of the POZ-ZF transcription factor Kaiso in Cancer

The POZ-ZF transcription factor Kaiso was discovered two decades ago as a binding partner for p120^ctn. Since its discovery, roles for Kaiso in diverse biological processes (epithelial-to-mesenchymal transition, apoptosis, inflammation) and several signalling pathways (Wnt/β-catenin, TGFβ, EGFR, Notch) have emerged. While Kaiso's biological role in normal tissues has yet to be fully elucidated, Kaiso has been increasingly implicated in multiple human cancers including colon, prostate, ovarian, lung, breast and chronic myeloid leukemia. In the majority of human cancers investigated to date, high Kaiso expression correlates with aggressive tumor characteristics including proliferation and metastasis, and/or poor prognosis. More recently, interest in Kaiso stems from its apparent correlation with racial disparities in breast and prostate cancer incidence and survival outcomes in people of African Ancestry. This review discusses Kaiso's role in various cancers, and Kaiso's potential for driving racial disparities in incidence and/or outcomes in people of African ancestry.

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.

Merkel cell polyomavirus recruits MYCL to the EP400 complex to promote oncogenesis

Merkel cell carcinoma (MCC) frequently contains integrated copies of Merkel cell polyomavirus DNA that express a truncated form of Large T antigen (LT) and an intact Small T antigen (ST). While LT binds RB and inactivates its tumor suppressor function, it is less clear how ST contributes to MCC tumorigenesis. Here we show that ST binds specifically to the MYC homolog MYCL (L-MYC) and recruits it to the 15-component EP400 histone acetyltransferase and chromatin remodeling complex. We performed a large-scale immunoprecipitation for ST and identified co-precipitating proteins by mass spectrometry. In addition to protein phosphatase 2A (PP2A) subunits, we identified MYCL and its heterodimeric partner MAX plus the EP400 complex. Immunoprecipitation for MAX and EP400 complex components confirmed their association with ST. We determined that the ST-MYCL-EP400 complex binds together to specific gene promoters and activates their expression by integrating chromatin immunoprecipitation with sequencing (ChIP-seq) and RNA-seq. MYCL and EP400 were required for maintenance of cell viability and cooperated with ST to promote gene expression in MCC cell lines. A genome-wide CRISPR-Cas9 screen confirmed the requirement for MYCL and EP400 in MCPyV-positive MCC cell lines. We demonstrate that ST can activate gene expression in a EP400 and MYCL dependent manner and this activity contributes to cellular transformation and generation of induced pluripotent stem cells.

RLIM suppresses hepatocellular carcinogenesis by up-regulating p15 and p21

Hepatocellular carcinogenesis results from dysregulation of oncogenes and tumor suppressors that influence cellular proliferation, differentiation and apoptosis. p15 and p21 are cyclin-dependent kinase inhibitors, which arrest cell proliferation and serve as critical tumor suppressors. Here we report that the E3 ubiquitin ligase RLIM expression is downregulated in hepatocellular carcinoma patients, and correlated with p15 and p21 expression in clinical progression. In addition, we showed that RLIM overexpression suppresses the cell growth and arrests cell cycle progression of hepatocellular carcinoma. Mechanistically, we found that RLIM directly binds to MIZ1, disrupting the interaction between c-MYC and MIZ1, and enhancing p15 and p21 transcription. Our results demonstrate that RLIM is an important suppressor in hepatocellular carcinogenesis.

Ribosomal protein L23 negatively regulates cellular apoptosis via the RPL23/Miz-1/c-Myc circuit in higher-risk myelodysplastic syndrome

Ribosomal protein (RP) L23 is a negative regulator of cellular apoptosis, and RPL23 overexpression is associated with abnormal apoptotic resistance in CD34+ cells derived from patients with higher-risk myelodysplastic syndrome (MDS). However, the mechanism underlying RPL23-induced apoptotic resistance in higher-risk MDS patients is poorly understood. In this study, we showed that reduced RPL23 expression led to suppressed cellular viability, increased apoptosis and G1-S cell cycle arrest. Gene microarray analysis comparing RPL23-knockdown and control cells identified an array of differentially expressed genes, of which, Miz-1, was upregulated with transactivation of the cell cycle inhibitors p15^Ink4b and p21^Cip1, and Miz-1’s functional repressor, c-Myc, was downregulated. Cells derived from higher-risk MDS patients demonstrated consistently increased expression of RPL23 and c-Myc and decreased Miz-1 expression compared with cells from lower-risk patients. In conclusion, Miz-1-dependent induction of p15^Ink4b and p21^Cip1 was depressed with decreased Miz-1 and increased c-Myc expression under conditions of elevated RPL23 expression, leading to apoptotic resistance in higher-risk MDS patients. Because RPL23 is encoded by a target gene of c-Myc, the RPL23/Miz-1/c-Myc regulatory circuit provides a feedback loop that links efficient RPL23 expression with c-Myc’s function to suppress Miz-1-induced Cdk inhibitors and thereby leads to apoptotic resistance in higher-risk MDS patients.

Modeling and Targeting MYC Genes in Childhood Brain Tumors

Brain tumors are the second most common group of childhood cancers, accounting for about 20%–25% of all pediatric tumors. Deregulated expression of the MYC family of transcription factors, particularly c-MYC and MYCN genes, has been found in many of these neoplasms, and their expression levels are often correlated with poor prognosis. Elevated c-MYC/MYCN initiates and drives tumorigenesis in many in vivo model systems of pediatric brain tumors. Therefore, inhibition of their oncogenic function is an attractive therapeutic target. In this review, we explore the roles of MYC oncoproteins and their molecular targets during the formation, maintenance, and recurrence of childhood brain tumors. We also briefly summarize recent progress in the development of therapeutic approaches for pharmacological inhibition of MYC activity in these tumors.

Structural Insights into c-Myc-interacting Zinc Finger Protein-1 (Miz-1) Delineate Domains Required for DNA Scanning and Sequence-specific Binding

c-Myc-interacting zinc finger protein-1 (Miz-1) is a poly-Cys2His2 zinc finger (ZF) transcriptional regulator of many cell cycle genes. A Miz-1 DNA sequence consensus has recently been identified and has also unveiled Miz-1 functions in other cellular processes, underscoring its importance in the cell. Miz-1 contains 13 ZFs, but it is unknown why Miz-1 has so many ZFs and whether they recognize and bind DNA sequences in a typical fashion. Here, we used NMR to deduce the role of Miz-1 ZFs 1-4 in detecting the Miz-1 consensus sequence and preventing nonspecific DNA binding. In the construct containing the first 4 ZFs, we observed that ZFs 3 and 4 form an unusual compact and stable structure that restricts their motions. Disruption of this compact structure by an electrostatically mismatched A86K mutation profoundly affected the DNA binding properties of the WT construct. On the one hand, Miz1-4^WT was found to bind the Miz-1 DNA consensus sequence weakly and through ZFs 1-3 only. On the other hand, the four ZFs in the structurally destabilized Miz1-4^A86K mutant bound to the DNA consensus with a 30-fold increase in affinity (100 nm). The formation of such a thermodynamically stable but nonspecific complex is expected to slow down the rate of DNA scanning by Miz-1 during the search for its consensus sequence. Interestingly, we found that the motif stabilizing the compact structure between ZFs 3 and 4 is conserved and enriched in other long poly-ZF proteins. As discussed in detail, our findings support a general role of compact inter-ZF structures in minimizing the formation of off-target DNA complexes.