Akt and 14-3-3eta regulate Miz1 to control cell-cycle arrest after DNA damage

Epigallocatechin-3-gallate confers protection against myocardial ischemia/reperfusion injury by inhibiting ferroptosis, apoptosis, and autophagy via modulation of 14-3-3η

Previous studies have demonstrated that the underlying mechanisms of myocardial ischemia/reperfusion injury (MIRI) are complex and involve multiple types of regulatory cell death, including ferroptosis, apoptosis, and autophagy. Thus, we aimed to identify the mechanisms underlying MIRI and validate the protective role of epigallocatechin-3-gallate (EGCG) and its related mechanisms in MIRI. An in vivo and in vitro models of MIRI were constructed. The results showed that pretreatment with EGCG could attenuate MIRI, as indicated by increased cell viability, reduced lactate dehydrogenase (LDH) activity and apoptosis, inhibited iron overload, abnormal lipid metabolism, preserved mitochondrial function, decreased infarct size, maintained cardiac function, decreased reactive oxygen species (ROS) level, and reduced TUNEL-positive cells. Additionally, EGCG pretreatment could attenuate ferroptosis, apoptosis, and autophagy induced by MIRI via upregulating 14-3-3η protein levels. Furthermore, the protective effects of EGCG could be abolished with pAd/14-3-3η-shRNA or Compound C11 (a 14-3-3η inhibitor) but not pAd/NC-shRNA. In conclusion, EGCG pretreatment attenuated ferroptosis, apoptosis, and autophagy by mediating 14-3-3η and protected cardiomyocytes against MIRI.

Protein phosphatase 1 regulatory subunit 15 A promotes translation initiation and induces G2M phase arrest during cuproptosis in cancers

Copper ions play a crucial role as cofactors for essential enzymes in cellular processes. However, when the intracellular concentration of copper ions exceeds the homeostatic threshold, they become toxic to cells. In our study, we demonstrated that elesclomol, as a carrier of copper ions, caused an upregulation of protein phosphatase 1 regulatory subunit 15 A (PPP1R15A), which plays a role in regulating substrate selectivity of protein phosphatase 1 during cuproptosis. Mechanistically, we investigated that PPP1R15A activated translation initiation by dephosphorylating eukaryotic translation initiation factor 2 subunit alpha at the S51 residue through protein phosphatase 1 and phosphorylating eukaryotic translation initiation factor 4E binding protein 1 at the T70 residue. In addition, PPP1R15A reduced H3K4 methylation by altering the phosphorylation of histone methyltransferases, which led to the silencing of MYC and G2M phase arrest.

Interactions between 14-3-3 Proteins and Actin Cytoskeleton and Its Regulation by microRNAs and Long Non-Coding RNAs in Cancer

14-3-3s are a family of structurally similar proteins that bind to phosphoserine or phosphothreonine residues, forming the central signaling hub that coordinates or integrates various cellular functions, thereby controlling many pathways important in cancer, cell motility, cell death, cytoskeletal remodeling, neuro-degenerative disorders and many more. Their targets are present in all cellular compartments, and when they bind to proteins they alter their subcellular localization, stability, and molecular interactions with other proteins. Changes in environmental conditions that result in altered homeostasis trigger the interaction between 14-3-3 and other proteins to retrieve or rescue homeostasis. In circumstances where these regulatory proteins are dysregulated, it leads to pathological conditions. Therefore, deeper understanding is needed on how 14-3-3 proteins bind, and how these proteins are regulated or modified. This will help to detect disease in early stages or design inhibitors to block certain pathways. Recently, more research has been devoted to identifying the role of MicroRNAs, and long non-coding RNAs, which play an important role in regulating gene expression. Although there are many reviews on the role of 14-3-3 proteins in cancer, they do not provide a holistic view of the changes in the cell, which is the focus of this review. The unique feature of the review is that it not only focuses on how the 14-3-3 subunits associate and dissociate with their binding and regulatory proteins, but also includes the role of micro-RNAs and long non-coding RNAs and how they regulate 14-3-3 isoforms. The highlight of the review is that it focuses on the role of 14-3-3, actin, actin binding proteins and Rho GTPases in cancer, and how this complex is important for cell migration and invasion. Finally, the reader is provided with super-resolution high-clarity images of each subunit of the 14-3-3 protein family, further depicting their distribution in HeLa cells to illustrate their interactions in a cancer cell.

Suppression of Allergic Asthma by Loss of Function of Miz1-Mediated Th1 Skewing

Asthma is the most prevalent chronic respiratory disease worldwide. There is currently no cure, and it remains an important cause of morbidity and mortality. Here we report that lung-specific loss of function of the transcription factor c-Myc-interacting zinc finger protein-1 (Miz1) upregulates the pro-T helper 1 (Th1) cytokine interleukin 12 (IL-12). Upregulation of IL-12 in turn stimulates a Th1 response, thereby counteracting T helper 2 (Th2) response and preventing the allergic response in mouse models of house dust mite (HDM)- and ovalbumin (OVA)-induced asthma. Using transgenic mice expressing Cre under a cell-specific promoter, we demonstrate that Miz1 acts in lung epithelial cells and dendritic cells in asthma. Chromatin immunoprecipitation (ChIP) coupled with high-throughput DNA sequencing (ChIP-seq) or quantitative PCR (ChIP-qPCR) reveals the binding of Miz1 on the Il12 promoter indicating direct repression of IL-12 by Miz1. Additionally, histone deacetylase 1 (HDAC1) is recruited to the Il12 promoter in a Miz1-depdenent manner, suggesting epigenetic repression of Il12 by Miz1. Furthermore, Miz1 is upregulated in human asthmatic samples as well as in asthmatic mice. Our data together suggest that Miz1 is upregulated during asthma, which in turn promotes asthma pathogenesis by preventing Th1 skewing through the transcriptional repression of IL-12.

Deoxyelephantopin Induces Apoptosis and Enhances Chemosensitivity of Colon Cancer via miR-205/Bcl2 Axis

Colon cancer (CC) is one of the major causes of cancer death in humans. Despite recent advances in the management of CC, the prognosis is still poor and a new strategy for effective therapy is imperative. Deoxyelephantopin (DET), extracted from an important medicinal plant, Elephantopus scaber L., has been reported to exhibit excellent anti-inflammatory and -cancer activities, while the detailed anti-cancer mechanism remains unclear. Herein, we found that DET showed a significant CC inhibiting effect in vitro and in vivo without obvious organ toxicity. Mechanistically, DET inhibited CC cells and tumor growth by inducing G2/M phase arrest and subsequent apoptosis. DET-mediated cell cycle arrest was caused by severe DNA damage, and DET decreased the Bcl2 expression level in a dose-dependent manner to promote CC cell apoptosis, whereas restoring Bcl2 expression reduced apoptosis to a certain extent. Moreover, we identified a microRNA complementary to the 3'-UTR of Bcl2, miR-205, that responded to the DET treatment. An inhibitor of miR-205 could recover Bcl2 expression and promoted the survival of CC cells upon DET treatment. To further examine the potential value of the drug, we evaluated the combinative effects of DET and 5-Fluorouracil (5FU) through Jin's formula and revealed that DET acted synergistically with 5FU, resulting in enhancing the chemotherapeutic sensitivity of CC to 5FU. Our results consolidate DET as a potent drug for the treatment of CC when it is used alone or combined with 5FU, and elucidate the importance of the miR-205-Bcl2 axis in DET treatment.

The zinc finger protein Miz1 suppresses liver tumorigenesis by restricting hepatocyte-driven macrophage activation and inflammation

Chronic inflammation plays a central role in hepatocellular carcinoma (HCC), but the contribution of hepatocytes to tumor-associated inflammation is not clear. Here, we report that the zinc finger transcription factor Miz1 restricted hepatocyte-driven inflammation to suppress HCC, independently of its transcriptional activity. Miz1 was downregulated in HCC mouse models and a substantial fraction of HCC patients. Hepatocyte-specific Miz1 deletion in mice generated a distinct sub-group of hepatocytes that produced pro-inflammatory cytokines and chemokines, which skewed the polarization of the tumor-infiltrating macrophages toward pro-inflammatory phenotypes to promote HCC. Mechanistically, Miz1 sequestrated the oncoprotein metadherin (MTDH), preventing MTDH from promoting transcription factor nuclear factor κB (NF-κB) activation. A distinct sub-group of pro-inflammatory cytokine-producing hepatocytes was also seen in a subset of HCC patients. In addition, Miz1 expression inversely correated with disease recurrence and poor prognosis in HCC patients. Our findings identify Miz1 as a tumor suppressor that prevents hepatocytes from driving inflammation in HCC.

Target gene-independent functions of MYC oncoproteins

Oncoproteins of the MYC family are major drivers of human tumorigenesis. Since a large body of evidence indicates that MYC proteins are transcription factors, studying their function has focused on the biology of their target genes. Detailed studies of MYC-dependent changes in RNA levels have provided contrasting models of the oncogenic activity of MYC proteins through either enhancing or repressing the expression of specific target genes, or as global amplifiers of transcription. In this Review, we first summarize the biochemistry of MYC proteins and what is known (or is unclear) about the MYC target genes. We then discuss recent progress in defining the interactomes of MYC and MYCN and how this information affects central concepts of MYC biology, focusing on mechanisms by which MYC proteins modulate transcription. MYC proteins promote transcription termination upon stalling of RNA polymerase II, and we propose that this mechanism enhances the stress resilience of basal transcription. Furthermore, MYC proteins coordinate transcription elongation with DNA replication and cell cycle progression. Finally, we argue that the mechanism by which MYC proteins regulate the transcription machinery is likely to promote tumorigenesis independently of global or relative changes in the expression of their target genes.

Crosstalk between Phosphoinositide 3-kinase/Akt signaling pathway with DNA damage response and oxidative stress in cancer

The phosphatidylinositol 3-kinases (PI3K)/Akt signaling pathway is one of the well-characterized and most important signaling pathways activated in response to DNA damage. This review discusses the most recent discoveries on the involvement of PI3K/Akt signaling pathway in cancer development, as well as stimulation of some important signaling networks involved in the maintenance of cellular homeostasis upon DNA damage, with an exploration of how PI3K/Akt signaling pathway contributes to the regulation of modulators and effectors underlying DNA damage response, the intricate, protein-based signal transduction network, which decides between cell cycle arrest, DNA repair, and apoptosis, the elimination of irreparably damaged cells to maintain homeostasis. The review continues by looking at the interplay between cell cycle checkpoints, checking the repair of damage inflicted to the DNA before entering DNA replication to facilitate DNA synthesis, and PI3K/Akt signaling pathway. We then investigate the challenges the cells overcome to ameliorate damages induced by oxidative activities, for example, the recruitment of many pathways and factors to maintain integrity and hemostasis. Finally, the review provides a discussion of how cells use the PI3K/Akt signaling pathway to regulate the balance between these networks.

The functional significance of 14-3-3 proteins in cancer: focus on lung cancer

The 14-3-3 family proteins are phosphoserine/phosphothreonine binding proteins constituting a conserved class of proteins which are detected in all eukaryotic cells. In mammalians, 14-3-3 proteins have seven distinct isoforms (β, γ, ε, η, ζ, σ and τ/θ) which are involved in various cellular processes including signal transduction, cell cycle, cell proliferation, apoptosis, differentiation and survival. 14-3-3 proteins do not have a distinct catalytic activity and often regulate the activity, stability, subcellular localization and interactions of other proteins. The 14-3-3 family proteins function through interacting with their client proteins or facilitating the interaction of other proteins likely as adaptor proteins. The versatile functions of these proteins in the regulation of cell growth, cell division, cell death and cell migration make them candidate proteins for which an important role in cancer development could be envisioned. Indeed, analysis of cancer cell lines and tumor-derived tissues have indicated the differential abundance or post-translational modification of some 14-3-3 isoforms. In this review, we aimed to show how deregulation of 14-3-3 proteins contributes to initiation, establishment and progression of cancers with a particular emphasis on lung cancer. The role of these proteins in cancer-relevant processes including cell cycle, cell migration, cell-cell communication and programmed cell death will be discussed in detail.

Parasite Infection, Carcinogenesis and Human Malignancy

Cancer may be induced by many environmental and physiological conditions. Infections with viruses, bacteria and parasites have been recognized for years to be associated with human carcinogenicity. Here we review current concepts of carcinogenicity and its associations with parasitic infections. The helminth diseases schistosomiasis, opisthorchiasis, and clonorchiasis are highly carcinogenic while the protozoan Trypanosoma cruzi, the causing agent of Chagas disease, has a dual role in the development of cancer, including both carcinogenic and anticancer properties. Although malaria per se does not appear to be causative in carcinogenesis, it is strongly associated with the occurrence of endemic Burkitt lymphoma in areas holoendemic for malaria. The initiation of Plasmodium falciparum related endemic Burkitt lymphoma requires additional transforming events induced by the Epstein-Barr virus. Observations suggest that Strongyloides stercoralis may be a relevant co-factor in HTLV-1-related T cell lymphomas. This review provides an overview of the mechanisms of parasitic infection-induced carcinogenicity.

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The helminth diseases schistosomiasis, opisthorchiasis, and clonorchiasis are highly carcinogenic.

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Trypanosoma cruzi has a dual role in cancer development including both carcinogenic and anticancer properties.

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Initiation of Plasmodium falciparum related endemic Burkitt lymphoma requires additional transforming events induced by EBV.

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Strongyloides stercoralis may be a relevant co-factor in HTLV-1-related T cell lymphomas.

We searched MEDLINE database and PubMed for articles from 1970 through June 30, 2016. Search terms used in various combinations were “parasite infection”, “carcinogenesis”, “cancer”, “human malignancy”, “parasite and cancer”, “infection-associated cancer”, “parasite-associated cancer” “schistosomiasis”, “opisthorchiasis”, “malaria”, “Chagas disease”, and “strongyloidiasis”. Articles resulting from these searches and relevant references cited in those articles were selected based on their related topics and were reviewed. Abstracts and reports from meetings were also included. Articles published in English were included.

Liver fluke infection and cholangiocarcinoma: a review

Parasites are significant groups for carcinogenesis among which liver flukes, including Opisthorchis viverrini and Clonorchis sinensis, are typical representatives causing cholangiocarcinoma (CCA), the second most common primary hepatic malignancy with dismal prognosis. O. viverrini is prevalent in Southeast Asia, infecting 10 million people while C. sinensis has a wider distribution in East Asia and several Southeast Asian countries, affecting more than 35 million people's health. These two worms have some common characteristics and/or discrepancies in life cycle, genome, and transcriptome. As hot spots in recent years, genome and transcriptome research has extracted numerous novel fluke worm-derived proteins, which are excellent for carcinogenic exploration. However, just a handful of these studies have focused on the metabolic pathway. In this study, the main mechanisms of carcinogenesis of both worms, in terms of mechanical damage, metabolic products and immunopathology, and other possible pathways, will be discussed in detail. This review retrospectively describes the main traits of C. sinensis and O. viverrini, their molecular biology and core carcinogenic mechanisms in a contrast pattern.

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

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

Upregulation of 14-3-3 eta in chronic liver fluke infection is a potential diagnostic marker of cholangiocarcinoma

PURPOSE

To discover protein markers in chronic/advanced opisthorchiasis for the early detection of Opisthorchis viverrini (OV)-associated cholangiocarcinoma (CCA).

EXPERIMENTAL DESIGN

Liver tissues derived from normal hamsters and those with chronic/advanced opisthorchiasis (n = 5 per group) were subjected to 2DE and LC-MS/MS. Candidate protein expression was confirmed in hamster models and human CCA tissue microarray (TMA) using immunohistochemistry and Western blot.

RESULT

Proteomics analysis detected 14-3-3 eta only in infected hamsters, not in uninfected controls. Immunohistochemistry and Western blot analysis confirmed low expression of 14-3-3 eta in normal hamster livers and demonstrated increased expression through time in infected livers. This protein was also observed in parasite organs, especially during the chronic phase of opisthorchiasis. Moreover, increased expression of 14-3-3 eta, relative to normal hamster livers, was observed during the early stage of CCA induced by OV infection and administration of N-nitrosodimethylamine. Immunohistochemical analysis of human TMA revealed that 14-3-3 eta was highly expressed in CCA (84.23%, 187/222 cases) but was not found in hepatocellular carcinoma or healthy liver tissues.

CONCLUSIONS AND CLINICAL RELEVANCE

14-3-3 eta protein has potential as a screening and early diagnostic marker for CCA.

Integrate Omics Data and Molecular Dynamics Simulations toward Better Understanding of Human 14-3-3 Interactomes and Better Drugs for Cancer Therapy

The 14-3-3 protein family is among the most extensively studied, yet still largely mysterious protein families in mammals to date. As they are well recognized for their roles in apoptosis, cell cycle regulation, and proliferation in healthy cells, aberrant 14-3-3 expression has unsurprisingly emerged as instrumental in the development of many cancers and in prognosis. Interestingly, while the seven known 14-3-3 isoforms in humans have many similar functions across cell types, evidence of isoform-specific functions and localization has been observed in both healthy and diseased cells. The strikingly high similarity among 14-3-3 isoforms has made it difficult to delineate isoform-specific functions and for isoform-specific targeting. Here, we review our knowledge of 14-3-3 interactome(s) generated by high-throughput techniques, bioinformatics, structural genomics and chemical genomics and point out that integrating the information with molecular dynamics (MD) simulations may bring us new opportunity to the design of isoform-specific inhibitors, which can not only be used as powerful research tools for delineating distinct interactomes of individual 14-3-3 isoforms, but also can serve as potential new anti-cancer drugs that selectively target aberrant 14-3-3 isoform.

Syk-mediated tyrosine phosphorylation of mule promotes TNF-induced JNK activation and cell death

The transcription factor Miz1 negatively regulates TNF-induced JNK activation and cell death by suppressing TRAF2 K63-polyubiquitination; upon TNF stimulation, the suppression is relieved by Mule/ARF-BP1-mediated Miz1 ubiquitination and subsequent degradation. It is not known how Mule is activated by TNF. Here we report that TNF activates Mule by inducing the dissociation of Mule from its inhibitor ARF. ARF binds to and thereby inhibits the E3 ligase activity of Mule in the steady state. TNF induces tyrosine phosphorylation of Mule, which subsequently dissociates from ARF and becomes activated. Inhibition of Mule phosphorylation by silencing of the Spleen Tyrosine Kinase (Syk) prevents its dissociation from ARF, thereby inhibiting Mule E3 ligase activity and TNF-induced JNK activation and cell death. Our data provides a missing link in TNF signaling pathway that leads to JNK activation and cell death.

ZBTB17 (MIZ1) Is Important for the Cardiac Stress Response and a Novel Candidate Gene for Cardiomyopathy and Heart Failure

BACKGROUND

Mutations in sarcomeric and cytoskeletal proteins are a major cause of hereditary cardiomyopathies, but our knowledge remains incomplete as to how the genetic defects execute their effects.

METHODS AND RESULTS

We used cysteine and glycine-rich protein 3, a known cardiomyopathy gene, in a yeast 2-hybrid screen and identified zinc-finger and BTB domain-containing protein 17 (ZBTB17) as a novel interacting partner. ZBTB17 is a transcription factor that contains the peak association signal (rs10927875) at the replicated 1p36 cardiomyopathy locus. ZBTB17 expression protected cardiac myocytes from apoptosis in vitro and in a mouse model with cardiac myocyte-specific deletion of Zbtb17, which develops cardiomyopathy and fibrosis after biomechanical stress. ZBTB17 also regulated cardiac myocyte hypertrophy in vitro and in vivo in a calcineurin-dependent manner.

CONCLUSIONS

We revealed new functions for ZBTB17 in the heart, a transcription factor that may play a role as a novel cardiomyopathy gene.

Miz-1 regulates translation of Trp53 via ribosomal protein L22 in cells undergoing V(D)J recombination

To be effective, the adaptive immune response requires a large repertoire of antigen receptors, which are generated through V(D)J recombination in lymphoid precursors. These precursors must be protected from DNA damage-induced cell death, however, because V(D)J recombination generates double-strand breaks and may activate p53. Here we show that the BTB/POZ domain protein Miz-1 restricts p53-dependent induction of apoptosis in both pro-B and DN3a pre-T cells that actively rearrange antigen receptor genes. Miz-1 exerts this function by directly activating the gene for ribosomal protein L22 (Rpl22), which binds to p53 mRNA and negatively regulates its translation. This mechanism limits p53 expression levels and thus contains its apoptosis-inducing functions in lymphocytes, precisely at differentiation stages in which V(D)J recombination occurs.

Epstein-Barr virus nuclear antigen 3A protein regulates CDKN2B transcription via interaction with MIZ-1

The Epstein-Barr virus (EBV) nuclear antigen 3 family of protein is critical for the EBV-induced primary B-cell growth transformation process. Using a yeast two-hybrid screen we identified 22 novel cellular partners of the EBNA3s. Most importantly, among the newly identified partners, five are known to play direct and important roles in transcriptional regulation. Of these, the Myc-interacting zinc finger protein-1 (MIZ-1) is a transcription factor initially characterized as a binding partner of MYC. MIZ-1 activates the transcription of a number of target genes including the cell cycle inhibitor CDKN2B. Focusing on the EBNA3A/MIZ-1 interaction we demonstrate that binding occurs in EBV-infected cells expressing both proteins at endogenous physiological levels and that in the presence of EBNA3A, a significant fraction of MIZ-1 translocates from the cytoplasm to the nucleus. Moreover, we show that a trimeric complex composed of a MIZ-1 recognition DNA element, MIZ-1 and EBNA3A can be formed, and that interaction of MIZ-1 with nucleophosmin (NPM), one of its coactivator, is prevented by EBNA3A. Finally, we show that, in the presence of EBNA3A, expression of the MIZ-1 target gene, CDKN2B, is downregulated and repressive H3K27 marks are established on its promoter region suggesting that EBNA3A directly counteracts the growth inhibitory action of MIZ-1.

Nac1 interacts with the POZ-domain transcription factor, Miz1

Nac1 (nucleus accumbens 1) is a POZ (poxvirus and zinc finger)-domain transcriptional repressor that is expressed at high levels in ovarian serous carcinoma. Here we identify Nac1 as a novel interacting partner of the POZ-domain transcriptional activator, Miz1 (Myc-interacting zinc-finger protein 1), and using chemical crosslinking we show that this association is mediated by a heterodimeric interaction of the Nac1 and Miz1 POZ domains. Nac1 is found in discrete bodies within the nucleus of mammalian cells, and we demonstrate the relocalization of Miz1 to these structures in transfected HeLa cells. We show that siRNA (small interfering RNA)-mediated knockdown of Nac1 in ovarian cancer cells results in increased levels of the Miz1 target gene product, p21^Cip1. The interaction of Nac1 with Miz1 may thus be relevant to its mechanism of tumourigenesis in ovarian cancer.

Nac1 is a transcriptional repressor that has been implicated in ovarian serous carcinoma. Here we show that Nac1 interacts with the transcription factor Miz1, and suggest that this interaction may contribute to tumourigenesis.

Microtubule dynamics regulates Akt signaling via dynactin p150

Following activation at the plasma membrane, Akt is subsequently deactivated in the cytoplasm. Although activation and deactivation of Akt must sometimes be separated in order to elicit and control cellular responses, the exact details of the spatiotemporal organization of Akt signaling are incompletely understood. Here we show that microtubule dynamics specifically modulate the deactivation phase of Akt signaling. Localization of Akt to microtubules sustains its activity, while disruption of microtubules attenuates Akt signaling independent of its initial activation. Conversely, stabilization of microtubules elevates Akt signaling both in vitro and in muscle tissues in vivo. Localization of Akt to microtubules is mediated by the microtubule binding protein dynactin p150, which is shown to be a direct target of Akt. Finally, microtubule disruption-induced Akt deactivation contributes to delayed cell cycle progression and accelerated cell death. Taken together, we revealed that, after initiation, the overall intensity and duration of oncogenic Akt signaling are determined by microtubule dynamics, a mechanism that could be exploited for therapeutic purposes.

Ribonucleotide reductase M2B inhibits cell migration and spreading by early growth response protein 1-mediated phosphatase and tensin homolog/Akt1 pathway in hepatocellular carcinoma

Ribonucleotide reductase (RR)M2B is an enzyme belonging to the ribonucleotide reductase enzyme family, which is essential for DNA synthesis and repair. RRM2B plays an important role in tumor progression and metastasis; however, little is known about the expression and underlying molecular mechanisms of RRM2B in hepatocellular carcinoma (HCC). In the present study, we report that down-regulation of RRM2B in HCC is negatively associated with intrahepatic metastasis, regardless of p53 status. Moreover, the ectopic overexpression of RRM2B decreased HCC cell migration and invasion in vitro, whereas silencing RRM2B expression resulted in increased migration and invasion in vitro and intrahepatic and lung metastasis in vivo. Additionally, knockdown of RRM2B by short hairpin RNA (shRNA) in HCC cells was associated with epithelial-mesenchymal transition (EMT), including the down-regulation of E-cadherin, and the concomitant up-regulation of N-cadherin and slug. A further experiment showed that RRM2B inhibited cell migration and spreading through regulation of the early growth response protein 1 (Egr-1)/phosphatase and tensin homolog (PTEN)/Akt1 pathway. Consistently, we also detected a significant correlation between RRM2B and E-cadherin protein expression in HCC tissues. Furthermore, Egr-1 also directly bound to the RRM2B promoter and repressed RRM2B transcription, thereby establishing a negative regulatory feedback loop.

CONCLUSION

These findings indicate that RRM2B suppresses cell migration and spreading by way of modulation of the Egr-1/PTEN/Akt1 pathway.

Regulation of CDKN2B expression by interaction of Arnt with Miz-1--a basis for functional integration between the HIF and Myc gene regulatory pathways

Background

Hypoxia- and Myc-dependent transcriptional regulatory pathways are frequently deregulated in cancer cells. These pathways converge in many cellular responses, but the underlying molecular mechanisms are unclear.

Methods

The ability of Miz-1 and Arnt to interact was identified in a yeast two-hybrid screen. The mode of interaction and the functional consequences of complex formation were analyzed by diverse molecular biology methods, in vitro. Statistical analyses were performed by Student’s t-test and ANOVA.

Results

In the present study we demonstrate that the aryl hydrocarbon receptor nuclear translocator (Arnt), which is central in hypoxia-induced signaling, forms a complex with Miz-1, an important transcriptional regulator in Myc-mediated transcriptional repression. Overexpression of Arnt induced reporter gene activity driven by the proximal promoter of the cyclin-dependent kinase inhibitor 2B gene (CDKN2B), which is an established target for the Myc/Miz-1 complex. In contrast, mutated forms of Arnt, that were unable to interact with Miz-1, had reduced capability to activate transcription. Moreover, repression of Arnt reduced endogenous CDKN2B expression, and chromatin immunoprecipitation demonstrated that Arnt interacts with the CDKN2B promoter. The transcriptional activity of Arnt was counteracted by Myc, but not by a mutated variant of Myc that is unable to interact with Miz-1, suggesting mutually exclusive interaction of Arnt and Myc with Miz-1. Our results also establish CDKN2B as a hypoxia regulated gene, as endogenous CDKN2B mRNA and protein levels were reduced by hypoxic treatment of U2OS cells.

Conclusions

Our data reveal a novel mode of regulation by protein-protein interaction that directly ties together, at the transcriptional level, the Myc- and hypoxia-dependent signaling pathways and expands our understanding of the roles of hypoxia and cell cycle alterations during tumorigenesis.

Cystathionase mediates senescence evasion in melanocytes and melanoma cells

The development of malignant melanoma is a highly complex process, which is still poorly understood. A majority of human melanomas are found to express a few oncogenic proteins, such as mutant RAS and BRAF variants. However, these oncogenes are also found in nevi, and it is now a well-accepted fact that their expression alone leads to senescence. This renders the understanding of senescence escape mechanisms an important point to understand tumor development. Here, we approached the question of senescence evasion by expressing the transcription factor v-myc myelocytomatosis viral oncogene homolog (c-MYC), which is known to act synergistically with many oncogenes, in melanocytes. We observed that MYC drives the evasion of reactive-oxygen stress-induced melanocyte senescence, caused by activated receptor tyrosine kinase signaling. Conversely, MIZ1, the growth suppressing interaction partner of MYC, is involved in mediating melanocyte senescence. Both, MYC overexpression and Miz1 knockdown led to a strong reduction of endogenous reactive-oxygen species (ROS), DNA damage and senescence. We identified the cystathionase (CTH) gene product as mediator of the ROS-related MYC and MIZ1 effects. Blocking CTH enzymatic activity in MYC-overexpressing and Miz1 knockdown cells increased intracellular stress and senescence. Importantly, pharmacological inhibition of CTH in human melanoma cells also reconstituted senescence in the majority of cell lines, and CTH knockdown reduced tumorigenic effects such as proliferation, H2O2 resistance and soft agar growth. Thus, we identified CTH as new MYC target gene with an important function in senescence evasion.

The role of MIZ-1 in MYC-dependent tumorigenesis

A hallmark of MYC-transformed cells is their aberrant response to antimitogenic signals. Key examples include the inability of MYC-transformed cells to arrest proliferation in response to antimitogenic signals such as TGF-β or DNA damage and their inability to differentiate into adipocytes in response to hormonal stimuli. Given the plethora of antimitogenic signals to which a tumor cell is exposed, it is likely that the ability to confer resistance to these signals is central to the transforming properties of MYC in vivo. At the same time, the inability of MYC-transformed cells to halt cell-cycle progression on stress may establish a dependence on mutations that impair or disable apoptosis. We propose that the interaction of MYC with the zinc finger protein MIZ-1 mediates resistance to antimitogenic signals. In contrast to other interactions of MYC, there is currently little evidence that MIZ-1 associates with MYC in normal, unperturbed cells. The functional interaction of both proteins becomes apparent at oncogenic expression levels of MYC and association with MIZ-1 mediates both oncogenic functions of MYC as well as tumor-suppressive responses to oncogenic levels of MYC.

Suppression of inflammation and acute lung injury by Miz1 via repression of C/EBP-δ

Inflammation is essential for host defense but can cause tissue damage and organ failure if unchecked. How the inflammation is resolved remains elusive. Here we report that the transcription factor Miz1 was required for terminating lipopolysaccharide (LPS)-induced inflammation. Genetic disruption of the Miz1 POZ domain, which is essential for its transactivation or repression activity, resulted in hyper-inflammation, lung injury and increased mortality in LPS-treated mice while reduced bacterial load and mortality in mice with Pseudomonas aeruginosa pneumonia. Loss of the Miz1 POZ domain prolonged pro-inflammatory cytokine expression. Upon stimulation, Miz1 was phosphorylated at Ser178, which is required for recruiting histone deacetylase 1 to repress transcription of C/EBP-δ, an amplifier of inflammation. Our data provide a long-sought mechanism underlying resolution of LPS-induced inflammation.

The human papillomavirus type 16 E7 oncoprotein targets Myc-interacting zinc-finger protein-1

We demonstrate that HPV-16 E7 forms a complex with Miz-1. UV-induced expression of the CDK-inhibitor p21^Cip1 and subsequent cell cycle arrest depends upon endogenous Miz-1 in HPV-negative C33A cervical cancer cells containing mutated p53. Transient expression of E7 in C33A inhibits UV-induced expression of p21^Cip1 and overcomes Miz-1-induced G1-phase arrest. The C-terminal E7Δ79LEDLL83-mutant with reduced Miz-1-binding capacity was impaired in its capability to repress p21^Cip1 expression; whereas the pRB-binding-deficient E7C24G-mutant inhibited p21^Cip1 expression similar to wild-type E7. Using ChIP, we demonstrate that endogenous E7 is bound to the endogenous p21^Cip1 core-promoter in CaSki cells and RNAi-mediated knock down of Miz-1 abrogates E7-binding to the p21^Cip1 promoter. Co-expression of E7 with Miz-1 inhibited Miz-1-induced p21^Cip1 expression from the minimal-promoter via Miz-1 DNA-binding sites. Co-expression of E7Δ79LEDLL83 did not inhibit Miz-1-induced p21^Cip1 expression. E7C24G retained E7-wild-type capability to inhibit Miz-1-dependent transactivation. These findings suggest that HPV-16 E7 can repress Miz-1-induced p21^Cip1 gene expression.

The capture of phosphoproteins by 14-3-3 proteins mediates actions of insulin

How does signalling via PI3K-PKB (AKT)-mTORC1-p70S6K and ERK-p90RSK mediate wide-ranging physiological responses to insulin? Quantitative proteomics and biochemical experiments are revealing that these signalling pathways induce the phosphorylation of large and overlapping sets of proteins, which are then captured by phosphoprotein-binding proteins named 14-3-3s. The 14-3-3s are dimers that dock onto dual-phosphorylated sites in a configuration with special signalling and mechanical properties. They interact with the Rab GTPase-activating proteins AS160 and TBC1D1 to regulate glucose uptake into target tissues in response to insulin and energy stress. Dynamic patterns in the 14-3-3-binding phosphoproteome are providing new insights into how insulin triggers coherent shifts in metabolism that are integrated with other cellular response systems.

Brainstem deficiency of the 14-3-3 regulator of serotonin synthesis: a proteomics analysis in the sudden infant death syndrome

Impaired brainstem responses to homeostatic challenges during sleep may result in the sudden infant death syndrome (SIDS). Previously we reported a deficiency of serotonin (5-HT) and its key biosynthetic enzyme, tryptophan hydroxylase (TPH2), in SIDS infants in the medullary 5-HT system that modulates homeostatic responses during sleep. Yet, the underlying basis of the TPH2 and 5-HT deficiency is unknown. In this study, we tested the hypothesis that proteomics would uncover previously unrecognized abnormal levels of proteins related to TPH2 and 5-HT regulation in SIDS cases compared with controls, which could provide novel insight into the basis of their deficiency. We first performed a discovery proteomic analysis of the gigantocellularis of the medullary 5-HT system in the same data set with deficiencies of TPH2 and 5-HT levels. Analysis in 6 SIDS cases and 4 controls revealed a 42-75% reduction in abundance in 5 of the 6 isoforms identified of the 14-3-3 signal transduction family, which is known to influence TPH2 activity (p < 0.07). These findings were corroborated in an additional SIDS and control sample using an orthogonal MS(E)-based quantitative proteomic strategy. To confirm these proteomics results in a larger data set (38 SIDS, 11 controls), we applied Western blot analysis in the gigantocellularis and found that 4/7 14-3-3 isoforms identified were significantly reduced in SIDS cases (p ≤ 0.02), with a 43% reduction in all 14-3-3 isoforms combined (p < 0.001). Abnormalities in 5-HT and TPH2 levels and 5-HT(1A) receptor binding were associated with the 14-3-3 deficits in the same SIDS cases. These data suggest a potential molecular defect in SIDS related to TPH2 regulation, as 14-3-3 is critical in this process.

The role of protein disorder in the 14-3-3 interaction network

Disordered regions are segments of a protein that do not fold completely and thus remain flexible. These regions have key physiological roles, particularly in phospho-proteins, which are enriched in disorder-promoting residues surrounding their phosphorylation sites. 14-3-3 proteins are ordered hubs that interact with multiple and diverse intrinsically disordered phosphorylated targets. This provides 14-3-3 with the ability to participate in and to regulate multiple signalling networks. Here, I review the effect of structural disorder on the mechanism involved in 14-3-3 protein-protein interactions and how 14-3-3 impacts cell biology through disordered ligands. How 14-3-3 proteins constitute an advantageous system to identify novel classes of biological tools is discussed with a special emphasis on a particular-and innovative-use of small molecules to stabilize 14-3-3 protein complexes, useful to study gene expression, cancer signalling and neurodegenerative diseases.

Silver nanoparticles down-regulate Nrf2-mediated 8-oxoguanine DNA glycosylase 1 through inactivation of extracellular regulated kinase and protein kinase B in human Chang liver cells

Recently, we reported that silver nanoparticles (AgNPs) induced reactive oxygen species (ROS) generation and the resultant oxidative stress contributes to the cell damage associated with AgNPs. 8-Oxoguanine (8-oxoG) is sensitive marker of ROS-induced DNA damage. 8-Oxoguanine DNA glycosylase 1 (OGG1) is an important DNA repair enzyme that recognizes and excises 8-oxoG. The aim of the present study was to examine the effect of AgNPs-induced oxidative stress on OGG1 and to elucidate mechanisms underlying AgNPs toxicity. AgNPs decreased OGG1 mRNA and protein expression, resulting in decreased OGG1 activity. Decreased OGG1 activity in AgNPs-treated cells led to increased 8-oxoG levels. The transcription factor NF-E2-related factor 2 (Nrf2) is an important factor in the inducible regulation of OGG1. AgNPs treatment decreased nuclear Nrf2 expression, translocation into nucleus, and transcriptional activity of Nrf2. Extracellular regulated kinase (ERK) and protein kinase B (PKB, AKT), which are upstream of Nrf2, contribute to OGG1 expression. AgNPs attenuated both active forms of ERK and AKT protein expression, resulting in suppression of Nrf2 and decrease of OGG1 expression. These studies demonstrate that down-regulation of Nrf2-mediated OGG1 in exposure to AgNPs occurs through ERK and AKT inactivation.

SUMO pathway dependent recruitment of cellular repressors to herpes simplex virus type 1 genomes

Components of promyelocytic leukaemia (PML) nuclear bodies (ND10) are recruited to sites associated with herpes simplex virus type 1 (HSV-1) genomes soon after they enter the nucleus. This cellular response is linked to intrinsic antiviral resistance and is counteracted by viral regulatory protein ICP0. We report that the SUMO interaction motifs of PML, Sp100 and hDaxx are required for recruitment of these repressive proteins to HSV-1 induced foci, which also contain SUMO conjugates and PIAS2β, a SUMO E3 ligase. SUMO modification of PML and elements of its tripartite motif (TRIM) are also required for recruitment in cells lacking endogenous PML. Mutants of PML isoform I and hDaxx that are not recruited to virus induced foci are unable to reproduce the repression of ICP0 null mutant HSV-1 infection mediated by their wild type counterparts. We conclude that recruitment of ND10 components to sites associated with HSV-1 genomes reflects a cellular defence against invading pathogen DNA that is regulated through the SUMO modification pathway.

Regulation of the Aurora-A gene following topoisomerase I inhibition: implication of the Myc transcription factor

During the G2 phase of the cell cycle, the Aurora-A kinase plays an important role in centrosome maturation and progression to mitosis. In this study, we show in colorectal cell lines that Aurora-A expression is downregulated in response to topoisomerase I inhibition. Using chromatin immunoprecipitation assays, we have observed that the Myc transcription factor and its Max binding partner are associated with the Aurora-A promoter during the G2 phase of the cell cycle. RNA interference experiments indicated that Myc is involved in the regulation of the Aurora-A gene. Following topoisomerase I inhibition, the expression of Myc decreased whereas Mad was upregulated, and the association of Myc and Max with the promoter of the kinase was inhibited. In parallel, an increased association of Mad and Miz-1 was detected on DNA, associated with an inhibition of the recruitment of transcriptional coactivators. Interestingly, a gain of H3K9 trimethylation and HP1gamma recruitment was observed on the Aurora-A promoter following sn38 treatment, suggesting that this promoter is located within SAHF foci following genotoxic treatment. Since Aurora-A is involved in centrosome maturation, we observed as expected that topoisomerase I inhibition prevented centrosome separation but did not affect their duplication. As a consequence, this led to G2 arrest and senescence induction.These results suggest a model by which the Aurora-A gene is inactivated by the G2 checkpoint following topoisomerase I inhibition. We therefore propose the hypothesis that the coordinated overexpression of Myc and Aurora-A, together with a downregulation of Mad and Miz-1 should be tested as a prognosis signature of poor responses to topoisomerase I inhibitors.

E3 ubiquitin ligase Mule ubiquitinates Miz1 and is required for TNFalpha-induced JNK activation

The zinc finger transcription factor Miz1 is a negative regulator of TNFalpha-induced JNK activation and cell death through inhibition of TRAF2 K63-polyubiquitination in a transcription-independent manner. Upon TNFalpha stimulation, Miz1 undergoes K48-linked polyubiquitination and proteasomal degradation, thereby relieving its inhibition. However, the underling regulatory mechanism is not known. Here, we report that HECT-domain-containing Mule is the E3 ligase that catalyzes TNFalpha-induced Miz1 polyubiquitination. Mule is a Miz1-associated protein and catalyzes its K48-linked polyubiquitination. TNFalpha-induced polyubiquitination and degradation of Miz1 were inhibited by silencing of Mule and were promoted by ectopic expression of Mule. The interaction between Mule and Miz1 was promoted by TNFalpha independently of the pox virus and zinc finger domain of Miz1. Silencing of Mule stabilized Miz1, thereby suppressing TNFalpha-induced JNK activation and cell death. Thus, our study reveals a molecular mechanism by which Mule regulates TNFalpha-induced JNK activation and apoptosis by catalyzing the polyubiquitination of Miz1.

The expression of seven 14-3-3 isoforms in human meningioma

14-3-3 proteins comprise a large family of highly conserved, acidic polypeptides, expressed in all eukaryotic organisms, with highest concentration found in the brain. Multiple isoforms of 14-3-3 proteins have been shown to play an essential role in regulating differentiation, proliferation and transformation. In the previous study, the expression levels of all seven 14-3-3 isoforms were examined in astrocytoma. However, the expression of seven 14-3-3 isoforms in meningioma still remains unknown. This study is the first examination of 14-3-3 isoforms in three grades of meningioma by immunohistochemistry. 14-3-3epsilon, zeta and theta were specifically expressed in meningioma, and their expression levels increased with the increase of pathological grade of meningioma. The 14-3-3 eta, beta, gamma and sigma isoforms were negatively expressed in meningioma. In conclusion, The 14-3-3 epsilon, zeta and theta may be involved in tumorigenesis of meningioma and be efficient markers for predicting the degree of malignancy in meningioma.

Resistance to arginine deiminase treatment in melanoma cells is associated with induced argininosuccinate synthetase expression involving c-Myc/HIF-1alpha/Sp4

Arginine deiminase (ADI)-based arginine depletion is a novel strategy under clinical trials for the treatment of malignant melanoma with promising results. The sensitivity of melanoma to ADI treatment is based on its auxotrophy for arginine due to a lack of argininosuccinate synthetase (AS) expression, the rate-limiting enzyme for the de novo biosynthesis of arginine. We show here that AS expression can be transcriptionally induced by ADI in melanoma cell lines A2058 and SK-MEL-2 but not in A375 cells, and this inducibility was correlated with resistance to ADI treatment. The proximal region of the AS promoter contains an E-box that is recognized by c-Myc and HIF-1alpha and a GC-box by Sp4. Through ChIP assays, we showed that under noninduced conditions, the E-box was bound by HIF-1alpha in all the three melanoma cell lines. Under arginine depletion conditions, HIF-1alpha was replaced by c-Myc in A2058 and SK-MEL-2 cells but not in A375 cells. Sp4 was constitutively bound to the GC-box regardless of arginine availability in all three cell lines. Overexpressing c-Myc by transfection upregulated AS expression in A2058 and SK-MEL-2 cells, whereas cotransfection with HIF-1alpha suppressed c-Myc-induced AS expression. These results suggest that regulation of AS expression involves interplay among positive transcriptional regulators c-Myc and Sp4, and negative regulator HIF-1alpha that confers resistance to ADI treatment in A2058 and SK-MEL-2 cells. Inability of AS induction in A375 cells under arginine depletion conditions was correlated by the failure of c-Myc to interact with the AS promoter.

Identification of a suppressive mechanism for Hedgehog signaling through a novel interaction of Gli with 14-3-3

Gli transcription factors are central effectors of Hedgehog signaling in development and tumorigenesis. Using a tandem affinity purification (TAP) strategy and mass spectrometry, we have found that Gli1 interacts with 14-3-3epsilon, and that Gli2 and Gli3 also bind to 14-3-3epsilon through homologous sites. This interaction depends on their phosphorylation, and cAMP-dependent protein kinase (PKA), a known negative regulator of Hedgehog signaling serves as a responsible kinase. A Gli2 mutant engineered to eliminate this interaction exhibited increased transcriptional activity (2 approximately 3x). Transcriptional repression by 14-3-3 binding was also observed with Gli3, when its N-terminal repressor domain was deleted. The phosphorylation sites responsible for the binding to 14-3-3 are distinct from those required for proteolysis, the known mechanism for PKA-induced repression of Hh signaling. Our data propose a novel mechanism in which PKA down-regulates Hedgehog signaling by promoting the interaction between Gli and 14-3-3 as well as proteolysis. Given the certain neuronal or malignant disorders in human caused by the abnormality of 17p13 encompassing 14-3-3epsilon overlap with increased Hh signaling, the Gli-14-3-3 interaction may have pathological significance for those human diseases.

ARF antagonizes the ability of Miz-1 to inhibit p53-mediated transactivation

Although Myc-interacting zinc-finger protein-1 (Miz-1) is known to be a poxvirus and zinc-finger (POZ) transcription factor required for Myc transcriptional repression, additional regulatory function of Miz-1 is less well understood. Using a yeast two-hybrid screen, we identified human alternate reading frame (ARF) protein as a novel interaction partner of Miz-1. The zinc-finger domain of Miz-1 is involved in its binding to ARF. In addition, we found that Miz-1 was able to interact with p53 through its DNA-binding domain, thus to diminish the binding of p53 to its target promoter and inhibit p53-mediated gene transcription. Interestingly, the Miz-1-regulated p53 transcriptional suppression does not require the presence of ARF or Mdm2. Importantly, ARF and p53 were found to competitively bind to Miz-1 in regulating p53-mediated transcription, and this conclusion was verified by both in vitro binding assay and competitive chromatin immunoprecipitation assay using a bona fide p53 endogenous Bax and Puma promoters. Thus, our study reveals that Miz-1 acts as a p53 suppressor by interfering with p53 DNA-binding ability, and ARF is able to counteract the suppression of Miz-1 on p53 by direct binding to Miz-1, suggesting that Miz-1 is a novel mediator in the ARF-p53 pathway.

FOXO transcription factors enforce cell cycle checkpoints and promote survival of hematopoietic cells after DNA damage

The PI3K/AKT signaling pathway contributes to cell cycle progression of cytokine-dependent hematopoietic cells under normal conditions, and it is absolutely required to override DNA damage-induced cell cycle arrest checkpoints in these cells. Phosphatidylinositol-3-kinase (PI3K)/AKT activity also correlates with Cdk2 activity in hematopoietic cells, suggesting that Cdk2 activation may be a relevant end point for this signaling pathway. However, mediators downstream of AKT in this pathway have not been defined. The forkhead transcription factor O (FOXO) family are negatively regulated by AKT-dependent phosphorylation and are known regulators of genes affecting cell cycle progression. We show that enhanced FOXO activity replicates the effect of PI3K inhibitors in enforcing G(1) and G(2) phase arrest after DNA damage. Conversely, knockdown of endogenous FOXO proteins increased Cdk2 activity and overrode DNA damage checkpoints in cells lacking PI3K activity. Moreover, loss of FOXO activity caused an increase in sensitivity to cisplatin-induced cell death, which was associated with failure to arrest cell cycle progression in the face of DNA damage caused by this chemotherapeutic agent. These cell cycle arrests were dependent on p27 expression when mediated by FOXO3a alone, but also involve p27-independent mechanisms when promoted by endogenous FOXO proteins. Together, these observations show that FOXO proteins enforce DNA damage-induced cell cycle arrest in hematopoietic cells. Inhibition of FOXO activity by cytokine-induced PI3K/AKT signaling is sufficient to override these DNA damage-induced cell cycle checkpoints, but may negatively impact hematopoietic cell viability.

Differential 14-3-3 affinity capture reveals new downstream targets of phosphatidylinositol 3-kinase signaling

We devised a strategy of 14-3-3 affinity capture and release, isotope differential (d₀/d₄) dimethyl labeling of tryptic digests, and phosphopeptide characterization to identify novel targets of insulin/IGF1/phosphatidylinositol 3-kinase signaling. Notably four known insulin-regulated proteins (PFK-2, PRAS40, AS160, and MYO1C) had high d₀/d₄ values meaning that they were more highly represented among 14-3-3-binding proteins from insulin-stimulated than unstimulated cells. Among novel candidates, insulin receptor substrate 2, the proapoptotic CCDC6, E3 ubiquitin ligase ZNRF2, and signaling adapter SASH1 were confirmed to bind to 14-3-3s in response to IGF1/phosphatidylinositol 3-kinase signaling. Insulin receptor substrate 2, ZNRF2, and SASH1 were also regulated by phorbol ester via p90RSK, whereas CCDC6 and PRAS40 were not. In contrast, the actin-associated protein vasodilator-stimulated phosphoprotein and lipolysis-stimulated lipoprotein receptor, which had low d₀/d₄ scores, bound 14-3-3s irrespective of IGF1 and phorbol ester. Phosphorylated Ser¹⁹ of ZNRF2 (RTRAYpS¹⁹GS), phospho-Ser⁹⁰ of SASH1 (RKRRVpS⁹⁰QD), and phospho- Ser⁴⁹³ of lipolysis-stimulated lipoprotein receptor (RPRARpS⁴⁹³LD) provide one of the 14-3-3-binding sites on each of these proteins. Differential 14-3-3 capture provides a powerful approach to defining downstream regulatory mechanisms for specific signaling pathways.

Butin decreases oxidative stress-induced 8-hydroxy-2'-deoxyguanosine levels via activation of oxoguanine glycosylase 1

In response to oxidative DNA base damage, oxoguanine glycosylase 1 (OGG1), in a base-excision repair (BER) pathway in mammals, plays a vital role in the repair of 8-hydroxy-2'-deoxyguanosine (8-OHdG), which is a reliable marker of reactive oxygen species (ROS)-induced DNA base modification and contributes to the pathologic process of cancer. Recently, we have shown that butin (7,3',4'-trihydroxydihydroflavone) protects cells against hydrogen peroxide (H2O2)-induced damage of cellular components including DNA. In the present study, we examined the possible protective effect of butin on oxidative stress-induced DNA base modification, especially 8-OHdG. Hydrogen peroxide significantly increased the level of 8-OHdG, which was detected by 8-OHdG ELISA and confocal microscopy, but butin decreased this level. Suppression of 8-OHdG formation by butin was related to the enhanced mRNA and protein expression of OGG1, which was detected by RT-PCR and Western blot analysis. Butin also increased the transcriptional activity of OGG1, which was suppressed by H2O2 treatment; this transcriptional activity was detected by OGG1 promoter luciferase assay. Butin enhanced the expression of phosphorylated Akt (active form of Akt), a regulator of OGG1, which was decreased by H2O2 treatment. A PI3K-specific inhibitor, LY294002, abolished the phosphorylated Akt and OGG1 expressions induced by butin, suggesting that OGG1 induction by butin involves the PI3K/Akt pathway.

A structural rationale for selective stabilization of anti-tumor interactions of 14-3-3 proteins by cotylenin A

Cotylenin A, a fungal metabolite originally described as a cytokinin-like bioactive substance against plants shows differentiation-inducing and anti-tumor activity in certain human cancers. Here, we present the crystal structure of cotylenin A acting on a 14-3-3 regulatory protein complex. By comparison with the closely related, but non-anticancer agent fusicoccin A, a rationale for the activity of cotylenin A in human cancers is presented. This class of fusicoccane diterpenoids are possible general modulators of 14-3-3 protein-protein interactions. In this regard, specificities for individual 14-3-3/target protein complexes might be achieved by varying the substituent pattern of the diterpene ring system. As the different activities of fusicoccin A and cotylenin A in human cancers suggest, hydroxylation of C12 might be a sufficient determinant of structural specificity.

A ribosomal protein L23-nucleophosmin circuit coordinates Mizl function with cell growth

The Myc-associated zinc-finger protein, Miz1, is a negative regulator of cell proliferation and induces expression of the cell-cycle inhibitors p15(Ink4b) and p21(Cip1). Here we identify the ribosomal protein L23 as a negative regulator of Miz1-dependent transactivation. L23 exerts this function by retaining nucleophosmin, an essential co-activator of Miz1 required for Miz1-induced cell-cycle arrest, in the nucleolus. Mutant forms of nucleophosmin found in acute myeloid leukaemia fail to co-activate Miz1 and re-localize it to the cytosol. As L23 is encoded by a direct target gene of Myc, this regulatory circuit may provide a feedback mechanism that links translation of Myc target genes and cell growth to Miz1-dependent cell-cycle arrest.

Gfi-1 represses CDKN2B encoding p15INK4B through interaction with Miz-1

Gfi-1 is a nuclear zinc finger (ZF) transcriptional repressor that plays an important role in hematopoiesis and inner ear development, and has been implicated in lymphomagenesis. Gfi-1 represses transcription by directly binding to the consensus DNA sequence in the promoters of its target genes. We report here an alternative mechanism by which Gfi-1 represses CDKN2B encoding p15(INK4B). Gfi-1 does not directly bind to CDKN2B, but interacts with Miz-1 and, via Miz-1, is recruited to the core promoter of CDKN2B. Miz-1 is a POZ-ZF transcription factor that has been shown to mediate transcriptional repression by c-Myc. Like c-Myc, upon recruitment to the CDKN2B promoter, Gfi-1 represses transcriptional activation of CDKN2B by Miz-1 and in response to TGFbeta. Consistent with its role in repressing CDKN2B transcription, knockdown of Gfi-1 in human leukemic cells or deficiency of Gfi-1 in mouse bone marrow cells results in augmented expression of p15(INK4B). Notably, Gfi-1 and c-Myc are both recruited to the CDKN2B core promoter and act in collaboration to repress CDKN2B. Our data reveal a mechanism of transcriptional repression by Gfi-1 and may have important implications for understanding the roles of Gfi-1 in normal development and tumorigenesis.

Miz1 and HectH9 regulate the stability of the checkpoint protein, TopBP1

The Myc-associated zinc-finger protein, Miz1, activates transcription of the p21cip1 gene in response to UV irradiation. Miz1 associates with topoisomerase II binding protein1 (TopBP1), an essential activator of the Atr kinase. We show here that Miz1 is required for the recruitment of a fraction of TopBP1 to chromatin, for the protection of TopBP1 from proteasomal degradation and for Atr-dependent signal transduction. TopBP1 that is not bound to chromatin is degraded by the HectH9 (Mule, ARF-BP1 and HUWE1) ubiquitin ligase. Myc antagonizes the binding of TopBP1 to Miz1; as a result, expression of Myc leads to dissociation of TopBP1 from chromatin, reduces the amount of total TopBP1 and attenuates Atr-dependent signal transduction. Our data show that Miz1 and Myc affect the activity of the Atr checkpoint through their effect on TopBP1 chromatin association and stability.

Isoform-specific expression of 14-3-3 proteins in human astrocytoma

BACKGROUND

14-3-3 protein plays crucial roles in tumorigenesis, including the maintenance of cell cycle and DNA repair, the prevention of apoptosis, among others. In mammalian cells, seven 14-3-3 isoforms (beta, epsilon, zeta, eta, theta, gamma and sigma) have been identified and each of these seems to have distinct tissue localizations and isoform-specific functions. In the present study, the levels of all seven 14-3-3 isoforms were examined in astrocytoma.

METHODS

The expression of 14-3-3 isoforms and their protein expression levels were examined in five glioma cell lines by western blotting. Then in astrocytoma tissues, we investigated expression percentages of each isoform by immunohistochemistry. The protein and mRNA expression levels of each isoform were also detected by western blotting and RT-PCR, respectively.

RESULTS

14-3-3beta and eta were specifically expressed in astrocytoma, and their expression frequencies and levels increased with the increase of astrocytoma malignancy. The result from glioma cell lines was consistent with that from astrocytoma tissue.

CONCLUSIONS

In our study, we found two tumor-specific isoforms of 14-3-3 in astrocytoma. They might be involved in astrocytoma tumorigenesis and may be useful as targets for therapy.

Re-expression of transcription factor ATF5 in hepatocellular carcinoma induces G2-M arrest

Transcription factors represent an important class of genes that play key roles in controlling cellular proliferation, cell cycle modulation, and attractive targets for cancer therapy. Here, we report on the novel finding of common ATF5 down-regulations in hepatocellular carcinoma (HCC), a highly malignant tumor with a dismal clinical course. Array-based mapping in HCC highlighted a high and consistent incidence of transcription factor ATF5 repressions on regional chr.19q13. By quantitative reverse transcription-PCR, profound down-regulations of ATF5 were further suggested in 78% of HCC tumors (60 of 77 cases) compared to their adjacent nontumoral liver (P = 0.0004). Restoration of ATF5 expression in 3 nonexpressing HCC cell lines demonstrated a consistent growth inhibitory effect (P < 0.029) but minimal induction on cellular apoptosis. Subsequent flow cytometric investigations revealed a G(2)-M cell cycle arrest in HCC cells that were ectopically transfected with ATF5 (P < 0.002). The differential expressed genes from the functional effects of ATF5 were examined by array profiling. Over a hundred genes were identified, among which ID1 contains the ATF/CREB target binding sequences within its promoter region. An inverse relationship between ATF5 expressions with ID1 transcriptions was verified in HCC (P = 0.019), and a direct interaction of ATF5 on the promoter of ID1 was further demonstrated from electromobility shift assay. Examination of causal events underlying the silencing of ATF5 in HCC suggested copy number losses, promoter hypermethylation, histone deacetylation, and DNA mutations to be the likely inactivating mechanisms. In conclusion, our finding supports a tumor suppressive role for ATF5 in HCC, and highlighted ID1 as a potential downstream target.

Zbtb4 represses transcription of P21CIP1 and controls the cellular response to p53 activation

In response to stimuli that activate p53, cells can undergo either apoptosis or cell cycle arrest, depending on the precise pattern of p53 target genes that is activated. We show here that Zbtb4, a transcriptional repressor protein, associates with the Sin3/histone deacetylase co-repressor and represses expression of P21CIP1 as part of a heterodimeric complex with Miz1. In vivo, expression of ZBTB4 is downregulated in advanced stages of multiple human tumours. In cell culture, depletion of ZBTB4 promotes cell cycle arrest in response to activation of p53 and suppresses apoptosis through regulation of P21CIP1, thereby promoting long-term cell survival. Our data suggest that Zbtb4 is a critical determinant of the cellular response to p53 activation and reinforce the notion that p21Cip1 can provide an essential survival signal in cells with activated p53.

A vascular targeted pan phosphoinositide 3-kinase inhibitor prodrug, SF1126, with antitumor and antiangiogenic activity

PTEN and the pan phosphoinositide 3-kinase (PI3K) inhibitor 2-(4-morpholinyl)-8-phenyl-4H-1 benzopyran-4-one (LY294002) exert significant control over tumor-induced angiogenesis and tumor growth in vivo. The LY294002 compound is not a viable drug candidate due to poor pharmacologic variables of insolubility and short half-life. Herein, we describe the development and antitumor activity of a novel RGDS-conjugated LY294002 prodrug, termed SF1126, which is designed to exhibit increased solubility and bind to specific integrins within the tumor compartment, resulting in enhanced delivery of the active compound to the tumor vasculature and tumor. SF1126 is water soluble, has favorable pharmacokinetics, and is well tolerated in murine systems. The capacity of SF1126 to inhibit U87MG and PC3 tumor growth was enhanced by the RGDS integrin (alpha v beta 3/alpha 5 beta 1) binding component, exhibiting increased activity compared with a false RADS-targeted prodrug, SF1326. Antitumor activity of SF1126 was associated with the pharmacokinetic accumulation of SF1126 in tumor tissue and the pharmacodynamic knockdown of phosphorylated AKT in vivo. Furthermore, SF1126 seems to exhibit both antitumor and antiangiogenic activity. The results support SF1126 as a viable pan PI3K inhibitor for phase I clinical trials in cancer and provide support for a new paradigm, the application of pan PI3K inhibitory prodrugs for the treatment of cancer.

Identification of 14-3-3 protein isoforms in human astrocytoma by immunohistochemistry

The 14-3-3 proteins are highly conserved, ubiquitous molecules involved in a variety of biologic events, such as cell cycle control, and apoptosis. In our previous study, it has been proved that they are expressed in primary human nervous system tumors. However, the isoform-specific expression of 14-3-3 protein is still need to be identified. This study is the first detection of 14-3-3 isoforms' specific expression in human astrocytoma. In the normal brain tissues, all the seven 14-3-3 isoforms' immunoreactivity was localized mainly in the neurons, while only weak expression of epsilon, zeta and theta was found in some glial cells. However, beta, epsilon, zeta, eta and theta isoforms' immunoreactivity was seen in the majority of astrocytoma samples and its immunoreactivity score was increased markedly with an increase in the pathologic grade of human astrocytomas. These results indicate that the five isoforms may play an important role in tumorigenesis of human astrocytoma.