Integrated control of cell proliferation and cell death by the c-myc oncogene

MYC: there is more to it than cancer

MYC is a pleiotropic transcription factor involved in multiple cellular processes. While its mechanism of action and targets are not completely elucidated, it has a fundamental role in cellular proliferation, differentiation, metabolism, ribogenesis, and bone and vascular development. Over 4 decades of research and some 10,000 publications linking it to tumorigenesis (by searching PubMed for "MYC oncogene") have led to MYC becoming a most-wanted target for the treatment of cancer, where many of MYC's physiological functions become co-opted for tumour initiation and maintenance. In this context, an abundance of reviews describes strategies for potentially targeting MYC in the oncology field. However, its multiple roles in different aspects of cellular biology suggest that it may also play a role in many additional diseases, and other publications are indeed linking MYC to pathologies beyond cancer. Here, we review these physiological functions and the current literature linking MYC to non-oncological diseases. The intense efforts towards developing MYC inhibitors as a cancer therapy will potentially have huge implications for the treatment of other diseases. In addition, with a complementary approach, we discuss some diseases and conditions where MYC appears to play a protective role and hence its increased expression or activation could be therapeutic.

Hsa_circ_0001479 accelerates tumorigenesis of gastric cancer and mediates immune escape

Gastric cancer (GC) is a common fatal malignant tumor of the digestive tract, particularly in Asia. Circular RNA (circRNA) has been proved to regulate malignancy progression and immunotherapeutic efficacy in multiple tumors, including GC. Notably, the function of circRNAs in GC has not been completely revealed. Therefore, exploration of more GC related circRNAs may provide potential strategies for GC treatment. In the study, it was observed that hsa_circ_0001479 exhibited a high level of expression in GC and was subsequently found to be associated with the depth of invasion, lymph node metastasis, and TNM stage. Functionally, the overexpression of hsa_circ_0001479 was found to enhance the proliferation and migration of GC cells, as evidenced by various experiments such as CCK-8, EdU, colony forming and transwell. Dual-luciferase reporter assay verified that hsa_circ_0001479 upregulated DEK expression by sponge targeting miR-133a-5p. Further investigations indicated DEK affected the entry of β-catenin into the nucleus by activating Wnt/β-catenin signaling pathway to promote accumulation of downstream c-Myc. As a transcription factor, c-Myc combined with the promoter of hsa_circ_0001479 parent gene to stimulate hsa_circ_0001479 generation. Besides, hsa_circ_0001479 inhibited theinfiltration with CD8+T cells in GC and associated with immune checkpoints. In summary, hsa_circ_0001479 accelerated the development and metastasis of GC and mediates immune escape of CD8+T cells. Targeting it may provide a novel immunotherapy to better locally treat GC and reduce the incidence of metastases.

MiR-138-5p suppresses the progression of lung cancer by targeting SNIP1

BACKGROUND

MicroRNAs (miRNAs) play crucial roles in the development of various cancers. Here, we aimed to evaluate the roles of miR-138-5p in lung cancer progression and the value of miR-138-5p in lung cancer diagnosis.

METHODS

Quantitative real-time PCR was performed to examine the expressions of miR-138-5p and smad nuclear interacting protein 1 (SNIP1) mRNA. The diagnostic value of miR-138-5p was analyzed using receiver operating characteristic (ROC) curve analysis, sensitivity, and specificity. We explored the effect of miR-138-5p on cell proliferation and metastasis by CCK-8, colony formation, wound healing and transwell assays. Western blot was employed to detect the protein expression of SNIP1 and related genes. Lung cancer cell growth was evaluated in vivo using xenograft tumor assay.

RESULTS

MiR-138-5p was decreased in the serum of patients with non-small cell lung cancer (NSCLC) and in NSCLC cells and tissues. The area under the ROC curve of serum miR-138-5p in the diagnosis of NSCLC was 0.922. This finding indicates the high diagnostic efficiency for lung cancer. MiR-138-5p suppressed but its inhibitor promoted cell proliferation and migration compared with control treatment in vitro and in vivo. MiR-138-5p directly binds to the 3'-untranslated region of SNIP1 and negatively regulated the expression of SNIP1, thereby inhibiting the expression of cyclin D1 and c-Myc. Moreover, overexpression of SNIP1 rescues the miR-138-5p-mediated inhibition in NSCLC cells.

CONCLUSIONS

The results suggested that miR-138-5p suppressed lung cancer cell proliferation and migration by targeting SNIP1. Serum miR-138-5p is a novel and valuable biomarker for NSCLC diagnosis.

Stabilization of c-Myc by the atypical cell cycle regulator, Spy1, decreases efficacy of breast cancer treatments

PURPOSE

c-Myc is frequently upregulated in breast cancers, however, targeting c-Myc has proven to be a challenge. Targeting of downstream mediators of c-Myc, such as the 'cyclin-like' cell cycle regulator Spy1, may be a viable therapeutic option in a subset of breast cancer subtypes.

METHODS

Mouse mammary tumor cells isolated from MMTV-Myc mice and human breast cancer cell lines were used to manipulate Spy1 levels followed by tamoxifen or chemotherapeutic treatment with a variety of endpoints. Patient samples from TNBC patients were obtained and constructed into a TMA and stained for c-Myc and Spy1 protein levels.

RESULTS

Over time, MMTV-Myc cells show a decreased response to tamoxifen treatment with increasing levels of Spy1 in the tamoxifen-resistant cells. shRNA against Spy1 re-establishes tamoxifen sensitivity. Spy1 was found to be highly elevated in human TNBC cell and patient samples, correlating to c-Myc protein levels. c-Myc was found to be stabilized by Spy1 and knocking down Spy1 in TNBC cells shows a significant increase in response to chemotherapy treatments.

CONCLUSION

Understanding the interplay between protein expression level and response to treatment is a critical factor in developing novel treatment options for breast cancer patients. These data have shown a connection between Spy1 and c-Myc protein levels in more aggressive breast cancer cells and patient samples. Furthermore, targeting c-Myc has proven difficult, these data suggest targeting Spy1 even when c-Myc is elevated can confer an advantage to current chemotherapies.

Roles of diencephalon/mesencephalon homeobox 1 in the development and prognosis of hepatocellular carcinoma

INTRODUCTION AND OBJECTIVES

The oncogene diencephalon/mesencephalon homeobox 1 (DMBX1) is widely overexpressed in a variety of human cancers. The present study aimed to analyze the expression and clinical importance of DMBX1 in nonneoplastic tissues and tumor tissues from patients with hepatocellular carcinoma (HCC).

MATERIALS AND METHODS

DMBX1 expression in HCC and adjacent nontumor tissues was analyzed using immunohistochemical staining. Chi-square tests were applied to compare DMBX1 expression between the tumors and the adjacent normal tissues. We explored the correlation of DMBX1 expression with clinicopathological factors and its effect on the prognosis of HCC. Finally, we investigated the role of DMBX1 in HCC via knockdown experiments, which analyzed changes in cell invasion, cell proliferation and epithelial-mesenchymal transition (EMT) biomarkers (E-cadherin, N-cadherin, vimentin). The mRNAs that were coexpressed with DMBX1 in HCC, based on the TCGA cohort (n = 366), were obtained from the cBioPortal database.

RESULTS

The average score for DMBX1 expression was significantly different (P < 0.001) between HCC and paired adjacent nontumor tissues, and DMBX1 expression correlated with hepatitis B virus (HBV) infection, tumor size, metastasis, and tumor node metastasis (TNM) stage (P < 0.05). A multivariate Cox regression analysis identified significant correlations of DMBX1 expression with tumor metastasis, TNM stage, and tumor capsule. Moreover, Kaplan-Meier survival analysis revealed an association between DMBX1 overexpression and shorter overall survival of patients with HCC (P < 0.05). In HCC cell lines, silencing DMBX1 markedly inhibited migration, proliferation and EMT markers. The mRNAs that were negatively (R ≤ -0.25, n = 1094) or positively (R ≥ 0.25, n = 2906) coexpressed with DMBX1 mRNA were selected for further Gene Ontology enrichment analysis, and the results revealed that the predicted functions of DMBX1 in HCC support the in vitro experimental results.

CONCLUSIONS

Our data provide evidence that DMBX1 overexpression is associated with HCC metastasis and poor prognosis, suggesting that DMBX1 represents a therapeutic target in HCC.

Uncovering emergent phenotypes in endothelial cells by clustering of surrogates of cardiovascular risk factors

Endothelial dysfunction (ED) is a hallmark of atherosclerosis and is influenced by well-defined risk factors, including hypoxia, dyslipidemia, inflammation, and oscillatory flow. However, the individual and combined contributions to the molecular underpinnings of ED remain elusive. We used global gene expression in human coronary artery endothelial cells to identify gene pathways and cellular processes in response to chemical hypoxia, oxidized lipids, IL-1β induced inflammation, oscillatory flow, and these combined stimuli. We found that clustering of the surrogate risk factors differed from the sum of the individual insults that gave rise to emergent phenotypes such as cell proliferation. We validated these observations in samples of human coronary artery atherosclerotic plaques analyzed using single-cell RNA sequencing. Our findings suggest a hierarchical interaction between surrogates of CV risk factors and the advent of emergent phenotypes in response to combined stimulation in endothelial cells that may influence ED.

Verdinexor, a Selective Inhibitor of Nuclear Exportin 1, Inhibits the Proliferation and Migration of Esophageal Cancer via XPO1/c-Myc/FOSL1 Axis

Esophageal carcinoma (EC) ranks sixth among cancers in mortality worldwide and effective drugs to reduce EC incidence and mortality are lacking. To explore potential anti-esophageal cancer drugs, we conducted drug screening and discovered that verdinexor, a selective inhibitor of nuclear exportin 1 (XPO1/CRM1), has anti-esophageal cancer effects both in vivo and in vitro. However, the mechanism and role of verdinexor in esophageal cancer remain unknown. In the present study, we observed that verdinexor inhibited the proliferation and migration of EC cells in vitro and suppressed tumor growth in vivo. Additionally, we found that verdinexor induced cleavage of PARP and downregulated XPO1, c-Myc, and FOSL1 expression. RNA-sequence analysis and protein-protein interaction (PPI) analysis revealed that verdinexor regulated the XPO1/c-Myc/FOSL1 axis. The results of immunoprecipitation and proximity ligation assays confirmed that verdinexor disrupted the interaction between XPO1 and c-Myc. Overexpression of c-Myc rescued the inhibition of cell proliferation and cell migration caused by verdinexor. Overexpressed FOSL1 restored the inhibited migration by verdinexor. Taken together, verdinexor inhibited cell proliferation and migration of esophageal cancer via XPO1/c-Myc/FOSL1 axis. Our findings provide a new option for the development of anti-esophageal cancer drugs.

A nonautophagic role of ATG5 in regulating cell growth by targeting c-Myc for proteasome-mediated degradation

Autophagy is a conserved biological process that maintains cell homeostasis by targeting macromolecules for lysosome-mediated degradation. The levels of autophagy are relatively lower under normal conditions than under stress conditions (e.g., starvation), as autophagy is usually stimulated after multiple stresses. However, many autophagy-related regulators are still expressed under normal conditions. Although these regulators have been studied deeply in autophagy regulation, the nonautophagic roles of these regulators under normal conditions remain incompletely understood. Here, we found that autophagy-related 5 (ATG5), which is a key regulator of autophagy, regulates c-Myc protein degradation under normal conditions through the ubiquitin-proteasome pathway. We also found that ATG5 binds c-Myc and recruits the E3 ubiquitin-protein ligase FBW7 to promote c-Myc degradation. Moreover, ATG5-mediated degradation of c-Myc limits cell growth under normal conditions and is essential for embryonic stem cell differentiation. Therefore, this study reveals a nonautophagic role of ATG5 in regulating of c-Myc protein degradation.

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ATG5 differentially regulates cell growth between normal and starvation conditions

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ATG5 recruits FBW7 to regulate c-Myc protein degradation under normal conditions

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ATG5-mediated degradation of c-Myc limits cell growth under normal conditions

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ATG5 negatively regulates the protein level of c-Myc during ESC differentiation

Selective targeting of MYC mRNA by stabilized antisense oligonucleotides

MYC is a prolific proto-oncogene driving the malignant behaviors of numerous common cancers, yet potent and selective cell-permeable inhibitors of MYC remain elusive. In order to ultimately realize the goal of therapeutic MYC inhibition in cancer, we have initiated discovery chemistry efforts aimed at inhibiting MYC translation. Here we describe a series of conformationally stabilized synthetic antisense oligonucleotides designed to target MYC mRNA (MYCASOs). To support bioactivity, we designed and synthesized this focused library of MYCASOs incorporating locked nucleic acid (LNA) bases at the 5'- and 3'-ends, a phosphorothioate backbone, and internal DNA bases. Treatment of MYC-expressing cancer cells with MYCASOs leads to a potent decrease in MYC mRNA and protein levels. Cleaved MYC mRNA in MYCASO-treated cells is detected with a sensitive 5' Rapid Amplification of cDNA Ends (RACE) assay. MYCASO treatment of cancer cell lines leads to significant inhibition of cellular proliferation while specifically perturbing MYC-driven gene expression signatures. In a MYC-induced model of hepatocellular carcinoma, MYCASO treatment decreases MYC protein levels within tumors, decreases tumor burden, and improves overall survival. MYCASOs represent a new chemical tool for in vitro and in vivo modulation of MYC activity, and promising therapeutic agents for MYC-addicted tumors.

Mathematical model of STAT signalling pathways in cancer development and optimal control approaches

In various diseases, the STAT family display various cellular controls over various challenges faced by the immune system and cell death programs. In this study, we investigate how an intracellular signalling network (STAT1, STAT3, Bcl-2 and BAX) regulates important cellular states, either anti-apoptosis or apoptosis of cancer cells. We adapt a mathematical framework to illustrate how the signalling network can generate a bi-stability condition so that it will induce either apoptosis or anti-apoptosis status of tumour cells. Then, we use this model to develop several anti-tumour strategies including IFN-β infusion. The roles of JAK-STATs signalling in regulation of the cell death program in cancer cells and tumour growth are poorly understood. The mathematical model unveils the structure and functions of the intracellular signalling and cellular outcomes of the anti-tumour drugs in the presence of IFN-β and JAK stimuli. We identify the best injection order of IFN-β and DDP among many possible combinations, which may suggest better infusion strategies of multiple anti-cancer agents at clinics. We finally use an optimal control theory in order to maximize anti-tumour efficacy and minimize administrative costs. In particular, we minimize tumour volume and maximize the apoptotic potential by minimizing the Bcl-2 concentration and maximizing the BAX level while minimizing total injection amount of both IFN-β and JAK2 inhibitors (DDP).

Methionine restriction breaks obligatory coupling of cell proliferation and death by an oncogene Src in Drosophila

Oncogenes often promote cell death as well as proliferation. How oncogenes drive these diametrically opposed phenomena remains to be solved. A key question is whether cell death occurs as a response to aberrant proliferation signals or through a proliferation-independent mechanism. Here, we reveal that Src, the first identified oncogene, simultaneously drives cell proliferation and death in an obligatorily coupled manner through parallel MAPK pathways. The two MAPK pathways diverge from a lynchpin protein Slpr. A MAPK p38 drives proliferation whereas another MAPK JNK drives apoptosis independently of proliferation signals. Src-p38-induced proliferation is regulated by methionine-mediated Tor signaling. Reduction of dietary methionine uncouples the obligatory coupling of cell proliferation and death, suppressing tumorigenesis and tumor-induced lethality. Our findings provide an insight into how cells evolved to have a fail-safe mechanism that thwarts tumorigenesis by the oncogene Src. We also exemplify a diet-based approach to circumvent oncogenesis by exploiting the fail-safe mechanism.

A high-content screen identifies the vulnerability of MYC-overexpressing cells to dimethylfasudil

A synthetic lethal effect arises when a cancer-associated change introduces a unique vulnerability to cancer cells that makes them unusually susceptible to a drug’s inhibitory activity. The synthetic lethal approach is attractive because it enables targeting of cancers harboring specific genomic or epigenomic alterations, the products of which may have proven refractory to direct targeting. An example is cancer driven by overexpression of MYC. Here, we conducted a high-content screen for compounds that are synthetic lethal to elevated MYC using a small-molecule library to identify compounds that are closely related to, or are themselves, regulatory-approved drugs. The screen identified dimethylfasudil, a potent and reversible inhibitor of Rho-associated kinases, ROCK1 and ROCK2. Close analogs of dimethylfasudil are used clinically to treat neurologic and cardiovascular disorders. The synthetic lethal interaction was conserved in rodent and human cell lines and could be observed with activation of either MYC or its paralog MYCN. The synthetic lethality seems specific to MYC overexpressing cells as it could not be substituted by a variety of oncogenic manipulations and synthetic lethality was diminished by RNAi-mediated depletion of MYC in human cancer cell lines. Collectively, these data support investigation of the use of dimethylfasudil as a drug that is synthetic lethal for malignancies that specifically overexpress MYC.

miR-29a-3p directly targets Smad nuclear interacting protein 1 and inhibits the migration and proliferation of cervical cancer HeLa cells

Smad nuclear interacting protein 1 (SNIP1) is a nuclear protein and involved in essential biological processes. MicroRNAs are effective regulators of tumorigenesis and cancer progression via targeting multiple genes. In present study, we aimed to investigate the function of SNIP1 and identify novel miRNA-SNIP1 axis in the development of cervical cancer. The results showed for the first time that silencing of the SNIP1 gene inhibited the migration and proliferation in HeLa cells significantly. Bioinformatics analysis and dual luciferase reporter assay demonstrated that miR-29a-3p could target 3' UTR of SNIP1 directly. The mRNA and protein expression levels of SNIP1 were negative regulated by miR-29a-3p according to the RT-qPCR and Western blot analysis, respectively. Furthermore, functional studies showed that over-expression of miR-29a-3p restrained HeLa cells migration and proliferation, and the mRNA expression of SNIP1 downstream genes (HSP27, c-Myc, and cyclin D1) were down-regulated by miR-29a-3p. Together, we concluded that miR-29a-3p suppressed the migration and proliferation in HeLa cells by directly targeting SNIP1. The newly identified miR-29a-3p/SNIP1 axis could provide new insight into the development of cervical cancer.

Resolution of Complex Issues in Genome Regulation and Cancer Requires Non-Linear and Network-Based Thermodynamics

The apparent lack of success in curing cancer that was evidenced in the last four decades of molecular medicine indicates the need for a global re-thinking both its nature and the biological approaches that we are taking in its solution. The reductionist, one gene/one protein method that has served us well until now, and that still dominates in biomedicine, requires complementation with a more systemic/holistic approach, to address the huge problem of cross-talk between more than 20,000 protein-coding genes, about 100,000 protein types, and the multiple layers of biological organization. In this perspective, the relationship between the chromatin network organization and gene expression regulation plays a fundamental role. The elucidation of such a relationship requires a non-linear thermodynamics approach to these biological systems. This change of perspective is a necessary step for developing successful 'tumour-reversion' therapeutic strategies.

Network analysis of microRNAs, transcription factors, and target genes involved in axon regeneration

Axon regeneration is crucial for recovery from neurological diseases. Numerous studies have identified several genes, microRNAs (miRNAs), and transcription factors (TFs) that influence axon regeneration. However, the regulatory networks involved have not been fully elucidated. In the present study, we analyzed a regulatory network of 51 miRNAs, 27 TFs, and 59 target genes, which is involved in axon regeneration. We identified 359 pairs of feed-forward loops (FFLs), seven important genes (Nap1l1, Arhgef12, Sema6d, Akt3, Trim2, Rab11fip2, and Rps6ka3), six important miRNAs (hsa-miR-204-5p, hsa-miR-124-3p, hsa-miR-26a-5p, hsa-miR-16-5p, hsa-miR-17-5p, and hsa-miR-15b-5p), and eight important TFs (Smada2, Fli1, Wt1, Sp6, Sp3, Smad4, Smad5, and Creb1), which appear to play an important role in axon regeneration. Functional enrichment analysis revealed that axon-associated genes are involved mainly in the regulation of cellular component organization, axonogenesis, and cell morphogenesis during neuronal differentiation. However, these findings need to be validated by further studies.

The MYC oncogene is a global regulator of the immune response

The MYC proto-oncogene is a gene product that coordinates the transcriptional regulation of a multitude of genes that are essential to cellular programs required for normal as well as neoplastic cellular growth and proliferation, including cell cycle, self-renewal, survival, cell growth, metabolism, protein and ribosomal biogenesis, and differentiation. Here, we propose that MYC regulates these programs in a manner that is coordinated with a global influence on the host immune response. MYC had been presumed to contribute to tumorigenesis through tumor cell-intrinsic influences. More recently, MYC expression in tumor cells has been shown to regulate the tumor microenvironment through effects on both innate and adaptive immune effector cells and immune regulatory cytokines. Then, MYC was shown to regulate the expression of the immune checkpoint gene products CD47 and programmed death-ligand 1. Similarly, other oncogenes, which are known to modulate MYC, have been shown to regulate immune checkpoints. Hence, MYC may generally prevent highly proliferative cells from eliciting an immune response. MYC-driven neoplastic cells have coopted this mechanism to bypass immune detection. Thus, MYC inactivation can restore the immune response against a tumor. MYC-induced tumors may be particularly sensitive to immuno-oncology therapeutic interventions.

Glycolysis promotes caspase-3 activation in lipid rafts in T cells

Resting T cells undergo a rapid metabolic shift to glycolysis upon activation in the presence of interleukin (IL)-2, in contrast to oxidative mitochondrial respiration with IL-15. Paralleling these different metabolic states are striking differences in susceptibility to restimulation-induced cell death (RICD); glycolytic effector T cells are highly sensitive to RICD, whereas non-glycolytic T cells are resistant. It is unclear whether the metabolic state of a T cell is linked to its susceptibility to RICD. Our findings reveal that IL-2-driven glycolysis promotes caspase-3 activity and increases sensitivity to RICD. Neither caspase-7, caspase-8, nor caspase-9 activity is affected by these metabolic differences. Inhibition of glycolysis with 2-deoxyglucose reduces caspase-3 activity as well as sensitivity to RICD. By contrast, IL-15-driven oxidative phosphorylation actively inhibits caspase-3 activity through its glutathionylation. We further observe active caspase-3 in the lipid rafts of glycolytic but not non-glycolytic T cells, suggesting a proximity-induced model of self-activation. Finally, we observe that effector T cells during influenza infection manifest higher levels of active caspase-3 than naive T cells. Collectively, our findings demonstrate that glycolysis drives caspase-3 activity and susceptibility to cell death in effector T cells independently of upstream caspases. Linking metabolism, caspase-3 activity, and cell death provides an intrinsic mechanism for T cells to limit the duration of effector function.

Differentially expressed proteins in the human esophageal cancer cell line Eca‑109, in the presence and absence of gemcitabine

The present study aimed to screen and study the roles of differentially expressed proteins in the human esophageal cancer cell line Eca‑109, in the presence and absence of gemcitabine (GEM). The 3‑(4,5)‑dimethylthiahiazo (-z-y1)-3,5-di-phenytetrazoliumromide (MTT) method was used to assay the vitality of the Eca‑109 cells following treatment with GEM (1‑16 µg/ml). The cell apoptosis was measured by using fluorescence activated cell sorting. The proteins in the treated Eca‑109 cells were extracted, validated, and assayed via two‑dimensional gel electrophoresis combined with matrix‑assisted laser desorption/ionization time of flight mass spectrometry (MALDI‑TOF‑MS). The differentially expressed proteins were then determined by western blotting. Furthermore, alterations in mitochondrial ultrastructure of the treated cells were observed under a transmission electron microscope. GEM significantly inhibited the growth of the Eca‑109 cells in a concentration‑ and time‑dependent manner, and the 50% inhibition concentration (IC50) value was 3.87 µg/ml. The MALDI‑TOF‑MS analysis revealed that there were three differentially expressed proteins following the GEM treatment, compared with the control. The differential proteins were verified to be B cell lymphoma‑2 associated X, apoptosis regulator (Bax)‑α, apoptosis‑associated speck‑like protein containing a CARD (ASC) and myeloid cell leukemia sequence (Mcl)‑1. Western blotting revealed that the expression levels of ASC and Bax‑α proteins in the treated cancer cells were significantly upregulated, whereas the Mcl‑1 protein expression was markedly downregulated compared with the control. Furthermore, the GEM treatment destroyed the mitochondrial ultrastructure of the cancer cells, leaving swelled mitochondria, a fading matrix and destroyed the mitochondrial cristae. GEM significantly inhibits the growth and promotes apoptosis of the Eca‑109 cells, due to the alterations in the expression levels of the differential proteins, including ASC, Mcl‑1 and Bax‑α.

Expression analysis of genes encoding double B-box zinc finger proteins in maize

The B-box proteins play key roles in plant development. The double B-box (DBB) family is one of the subfamily of the B-box family, with two B-box domains and without a CCT domain. In this study, 12 maize double B-box genes (ZmDBBs) were identified through a genome-wide survey. Phylogenetic analysis of DBB proteins from maize, rice, Sorghum bicolor, Arabidopsis, and poplar classified them into five major clades. Gene duplication analysis indicated that segmental duplications made a large contribution to the expansion of ZmDBBs. Furthermore, a large number of cis-acting regulatory elements related to plant development, response to light and phytohormone were identified in the promoter regions of the ZmDBB genes. The expression patterns of the ZmDBB genes in various tissues and different developmental stages demonstrated that ZmDBBs might play essential roles in plant development, and some ZmDBB genes might have unique function in specific developmental stages. In addition, several ZmDBB genes showed diurnal expression pattern. The expression levels of some ZmDBB genes changed significantly under light/dark treatment conditions and phytohormone treatments, implying that they might participate in light signaling pathway and hormone signaling. Our results will provide new information to better understand the complexity of the DBB gene family in maize.

MYC: Master Regulator of Immune Privilege

Cancers are often initiated by genetic events that activate proto-oncogenes or inactivate tumor-suppressor genes. These events are also crucial for sustained tumor cell proliferation and survival, a phenomenon described as oncogene addiction. In addition to this cell-intrinsic role, recent evidence indicates that oncogenes also directly regulate immune responses, leading to immunosuppression. Expression of many oncogenes or loss of tumor suppressors induces the expression of immune checkpoints that regulate the immune response, such as PD-L1. We discuss here how oncogenes, and in particular MYC, suppress immune surveillance, and how oncogene-targeted therapies may restore the immune response against tumors.

Mapping and analysis of Caenorhabditis elegans transcription factor sequence specificities

Caenorhabditis elegans is a powerful model for studying gene regulation, as it has a compact genome and a wealth of genomic tools. However, identification of regulatory elements has been limited, as DNA-binding motifs are known for only 71 of the estimated 763 sequence-specific transcription factors (TFs). To address this problem, we performed protein binding microarray experiments on representatives of canonical TF families in C. elegans, obtaining motifs for 129 TFs. Additionally, we predict motifs for many TFs that have DNA-binding domains similar to those already characterized, increasing coverage of binding specificities to 292 C. elegans TFs (∼40%). These data highlight the diversification of binding motifs for the nuclear hormone receptor and C2H2 zinc finger families and reveal unexpected diversity of motifs for T-box and DM families. Motif enrichment in promoters of functionally related genes is consistent with known biology and also identifies putative regulatory roles for unstudied TFs.

DOI:http://dx.doi.org/10.7554/eLife.06967.001

Many scientists use ‘model’ species—such as the fruit fly or a nematode worm called Caenorhabditis elegans—in their research because these organisms have useful features that make it easier to carry out many experiments. For example, C. elegans has a smaller genome compared to many other animals, which is useful for studying the roles of individual genes or stretches of DNA.

Transcription factors are a type of protein that can bind to specific stretches of DNA and help to switch certain genes on or off. These ‘motifs’ may be close to the gene or further away in the genome, and therefore, must stand out amongst the rest of the DNA, like lights on a landing strip. However, the motifs for only 10% of the estimated 763 transcription factors in C. elegans have been identified so far.

In this study, Narasimhan, Lambert, Yang et al. used a technique called a ‘protein binding microarray’ to identify the motifs for many more of the C. elegans transcription factors. These findings were then used to predict motifs for other transcription factors. Together, these methods increased the proportion of C. elegans transcription factors with known DNA-binding motifs from 10% to around 40%.

Now that more DNA motifs have been identified, it is possible to look for similarities and differences between them. For example, Narasimhan, Lambert, Yang et al. found that transcription factors with similar sequences can bind to very varied motifs. On the other hand, some transcription factors that are very different are able to recognize very similar motifs. The experiments also indicate that motifs found very close to genes—in sequences known as ‘promoters’—may be able to interact with many proteins to influence the activity of genes.

Narasimhan, Lambert, Yang et al.'s findings increase the number of C. elegans transcription factors with a motif, bringing the knowledge of these proteins more in line with the better-studied transcription factors of humans and fruit flies. The next challenge is to identify DNA motifs for the remaining 60% of transcription factors.

DOI:http://dx.doi.org/10.7554/eLife.06967.002

REGULATOR: a database of metazoan transcription factors and maternal factors for developmental studies

BACKGROUND

Genes encoding transcription factors that constitute gene-regulatory networks and maternal factors accumulating in egg cytoplasm are two classes of essential genes that play crucial roles in developmental processes. Transcription factors control the expression of their downstream target genes by interacting with cis-regulatory elements. Maternal factors initiate embryonic developmental programs by regulating the expression of zygotic genes and various other events during early embryogenesis.

RESULTS

This article documents the transcription factors of 77 metazoan species as well as human and mouse maternal factors. We improved the previous method using a statistical approach adding Gene Ontology information to Pfam based identification of transcription factors. This method detects previously un-discovered transcription factors. The novel features of this database are: (1) It includes both transcription factors and maternal factors, although the number of species, in which maternal factors are listed, is limited at the moment. (2) Ontological representation at the cell, tissue, organ, and system levels has been specially designed to facilitate development studies. This is the unique feature in our database and is not available in other transcription factor databases.

CONCLUSIONS

A user-friendly web interface, REGULATOR ( http://www.bioinformatics.org/regulator/ ), which can help researchers to efficiently identify, validate, and visualize the data analyzed in this study, are provided. Using this web interface, users can browse, search, and download detailed information on species of interest, genes, transcription factor families, or developmental ontology terms.

Migfilin sensitizes cisplatin-induced apoptosis in human glioma cells in vitro

AIM

Filamin binding LIM protein 1, also known as migfilin, is a skeleton organization protein that binds to mitogen-inducible gene 2 at cell-extracellular matrix adhesions. The aim of this study was to investigate the role of migfilin in cisplatin-induced apoptosis in human glioma cells, to determine the functional domains of migfilin, and to elucidate the molecular mechanisms underlying the regulation of cisplatin-related chemosensitivity.

METHODS

The human glioma cell lines Hs683, H4, and U-87 MG were transfected with pEGFP-C2-migfilin to elevate the expression level of migfilin. RNA interference was used to reduce the expression of migfilin. To determine the functional domains of migfilin, U-87 MG cells were transfected with plasmids of migfilin deletion mutants. After treatment with cisplatin (40 μmol/L) for 24 h, the cell viability was assessed using the MTS assay, and the cell apoptotic was examined using the DAPI staining assay and TUNEL analysis. Expression levels of apoptosis-related proteins were detected by Western blot analysis.

RESULTS

Overexpression of migfilin significantly enhanced cisplatin-induced apoptosis in Hs683, H4, and U-87 MG cells, whereas downregulation of migfilin expression inhibited the chemosensitivity of these cell lines. The N-terminal region of migfilin alone was able to enhance the cisplatin-induced apoptosis. However, despite the existence of the N-terminal region, mutants of migfilin with any one of three LIM domains deleted led to a function loss. Furthermore, apoptotic proteins (PARP and caspase-3) and the anti-apoptotic protein Bcl-xL were modulated by the expression level of migfilin in combination with cisplatin.

CONCLUSION

The LIM1-3 domains of migfilin play a key role in sensitizing glioma cells to cisplatin-induced apoptosis through regulation of apoptosis-related proteins.

Genome-wide transcription factor gene prediction and their expressional tissue-specificities in maize

Transcription factors (TFs) are important regulators of gene expression. To better understand TF-encoding genes in maize (Zea mays L.), a genome-wide TF prediction was performed using the updated B73 reference genome. A total of 2298 TF genes were identified, which can be classified into 56 families. The largest family, known as the MYB superfamily, comprises 322 MYB and MYB-related TF genes. The expression patterns of 2 014 (87.64%) TF genes were examined using RNA-seq data, which resulted in the identification of a subset of TFs that are specifically expressed in particular tissues (including root, shoot, leaf, ear, tassel and kernel). Similarly, 98 kernel-specific TF genes were further analyzed, and it was observed that 29 of the kernel-specific genes were preferentially expressed in the early kernel developmental stage, while 69 of the genes were expressed in the late kernel developmental stage. Identification of these TFs, particularly the tissue-specific ones, provides important information for the understanding of development and transcriptional regulation of maize.

Apoptotic caspases regulate induction of iPSCs from human fibroblasts

The molecular mechanisms involved in the derivation of induced pluripotent stem cells (iPSCs) from differentiated cells are poorly understood. Here we report that caspases 3 and 8, two proteases associated with apoptotic cell death, play critical roles in induction of iPSCs from human fibroblasts. Activation of caspases 3 and 8 occurs soon after transduction of iPSC-inducing transcription factors. Oct-4, a key iPSC transcription factor, is responsible for the activation. Inhibition of caspase 3 or 8 in human fibroblast cells partially or completely (respectively) prevents the induction of iPSCs. Furthermore, retinoblastoma susceptibility (Rb) protein appears to be one of the factors that act downstream of the caspases. We propose that caspases are key facilitators of nuclear reprogramming in iPSC induction.

The effect of raloxifene on Bax protein expression in breast carcinomas of postmenopausal women

The actual role of Bax protein as a prognostic biomarker that predicts response to therapy remains unclear. The objective of this study was to evaluate the effect of raloxifene on Bax protein expression in breast carcinomas of postmenopausal women. Twenty postmenopausal patients with operable stage II, estrogen receptor-positive, infiltrating ductal breast carcinoma were treated with oral raloxifene at a dose of 60 mg/day for a period of 28 days before definitive surgery. Tumor samples were obtained by incisional biopsy at the time of diagnosis and again at the time of definitive surgical treatment. Immunohistochemical evaluation of Bax expression was assessed semiquantitatively based on the fraction of stained tumor cells and intensity of staining. McNemar's test was used to analyze data (P < 0.05). Eleven of the 20 (55%) patients were classified as positive for Bax expression before raloxifene treatment, whereas 9(45%) were classified as positive after raloxifene treatment (P = 0.479). In conclusion, raloxifene did not alter Bax expression significantly in estrogen receptor-positive breast carcinomas of postmenopausal women.

Kaposi sarcoma-associated herpesvirus-encoded viral FLICE inhibitory protein (vFLIP) K13 cooperates with Myc to promote lymphoma in mice

Primary effusion lymphoma (PEL) is an aggressive form of lymphoma that is associated with infection by Kaposi's sarcoma-associated herpesvirus (KSHV). One of the KSHV genes expressed in PEL cells is K13, a potent activator of the NF-κB pathway. K13 transgenic mice develop lymphomas, but after a long period of latency. A possible candidate that could cooperate with K13 in the development of PEL is c-Myc, whose expression is frequently dysregulated in PEL cells. To study the cooperative interaction between K13 and c-Myc in the pathogenesis of PEL, we crossed the K13 transgenic mice to iMyc(Eμ) transgenic mice that overexpress Myc. We report that lymphomas in the K13/iMyc(Eμ) double transgenic mice developed with shorter latency and were histologically distinct from those observed in the iMyc(Eμ) mice. Lymphomas in the K13/iMyc(Eμ) mice also lacked the expression of B- and T-cell markers, thus resembling the immunophenotype of PEL. The accelerated development of lymphoma in the K13/iMyc(Eμ) mice was associated with increased expression of K13, elevated NF-κB activity and decrease in apoptosis. Taken collectively, our results demonstrate a cooperative interaction between the NF-κB and Myc pathways in lymphomagenesis.

Evaluation of Ki-67 and Bcl-2 antigen expression in breast carcinomas of women treated with raloxifene

OBJECTIVES

To evaluate the effect of raloxifene on Ki-67 and Bcl-2 antigen expression in operable, stage II, oestrogen-receptor-positive invasive ductal breast carcinomas.

MATERIALS AND METHODS

Twenty post-menopausal women who had taken 60 mg of raloxifene daily for 28 days prior to definitive surgery were enrolled in the investigation. Two tumour samples were obtained by incisional biopsy during the study, one at the time of confirmation of diagnosis of invasive ductal carcinoma and evaluation of oestrogen receptor status, and the other 29 days later, at the time of definitive surgery. Immunohistochemistry was performed on tumour samples, prior to and after raloxifene treatment, to evaluate Ki-67 and Bcl-2 expression. Friedman and McNemar tests were used for statistical analysis of the data, significance being established at 5%.

RESULTS

Mean percentage of Ki-67-stained nuclei was 24.86 +/- 2.95 prior to raloxifene treatment and 13.33 +/- 1.52 after treatment (P < 0.001). Prior to raloxifene treatment, only 9/20 cases (45%) were classified as Bcl-2-positive, whereas after treatment, 17/20 (85%) were classified as Bcl-2-positive (P < 0.013).

CONCLUSIONS

Raloxifene treatment significantly reduced Ki-67 antigen expression and increased Bcl-2 expression in breast carcinomas of post-menopausal women.

The ups and downs of Myc biology

The basic helix-loop-helix protein Myc is a renowned transcription factor controlling disparate aspects of cell physiology that, together, allow efficient proliferation of somatic cells. This ability, together with the observation that its deregulated expression occurs in the majority of human cancers, suggests that Myc could be a good therapeutic target. However, several aspects of Myc biology remain elusive: what is the major difference between oncogenic and physiological Myc? How does oncogenic Myc evade the intrinsic tumor surveillance pathways provided by evolution? If Myc inhibition were even possible, what would be the consequences for the homeostasis of normal proliferating tissues versus the fate of cancer cells? Here we summarize the latest works addressing these issues.

The apoptotic paradox in retinoblastoma

The purpose of this study was to investigate the clinicopathological features and the expression of proteins involved in cell proliferation and the different pathways of apoptosis in retinoblastoma. Nineteen retinoblastoma patients were included, and mitotic index (MI) and apoptotic index (AI) were assessed. The expression of MIB-1, p53, caspase-3, Bcl-2, and Fas protein was assessed by immunohistochemistry. Mann-Whitney U test and Fisher's exact test were used for statistical comparison. High MI (mean 16.84, range 0-66) and high MIB-1 expression (mean 57.89, range 0-90) were found. The MI was significantly related to MIB-1 expression (P= 0.01). The tumors showed a high apoptotic index (mean 40.26, range 1-110), and the AI was associated with the mitotic index (P= 0.02). The caspase-3 expression was positively related to the AI (P= 0.03), although a small number of tumors with no significant or very low caspase-3 staining showed a high number of apoptotic cells, suggestive of a caspase-3-independent apoptosis pathway. Bcl-2 expression was not significantly related to AI (P= 0.07). No striking relationship was found in expression patterns of p53, Bcl-2, caspase-3, and Fas. In conclusion, we found that (1) cell proliferation and apoptosis are linked in retinoblastoma; (2) activation of effector caspase-3 induces apoptosis in retinoblastoma, but Bcl-2 overexpression does not prevent apoptosis in many tumors; (3) there is a p53-independent pathway in approximately one-quarter of cases; (4) the findings suggesting a caspase-3-independent pathway might lead to apoptosis in retinoblastoma; and, finally, we found no consistent pattern of expression of apoptotic and antiapoptotic molecules, suggesting that in retinoblastoma there is no preference for any single pathway of apoptosis. Confirmation of the results in a large set of tumors would be useful.

The fascia of the limbs and back--a review

Although fasciae have long interested clinicians in a multitude of different clinical and paramedical disciplines, there have been few attempts to unite the ensuing diverse literature into a single review. The current article gives an anatomical perspective that extends from the gross to the molecular level. For expediency, it deals only with fascia in the limbs and back. Particular focus is directed towards deep fascia and thus consideration is given to structures such as the fascia lata, thoracolumbar fascia, plantar and palmar fascia, along with regional specializations of deep fascia such as retinacula and fibrous pulleys. However, equal emphasis is placed on general aspects of fascial structure and function, including its innervation and cellular composition. Among the many functions of fascia considered in detail are its ectoskeletal role (as a soft tissue skeleton for muscle attachments), its importance for creating osteofascial compartments for muscles, encouraging venous return in the lower limb, dissipating stress concentration at entheses and acting as a protective sheet for underlying structures. Emphasis is placed on recognizing the continuity of fascia between regions and appreciating its key role in coordinating muscular activity and acting as a body-wide proprioceptive organ. Such considerations far outweigh the significance of viewing fascia in a regional context alone.

Gfi1 integrates progenitor versus granulocytic transcriptional programming

In patients with severe congenital neutropenia (SCN) and mice with growth factor independent-1 (Gfi1) loss of function, arrested myeloid progenitors accumulate, whereas terminal granulopoiesis is blocked. One might assume that Gfi-null progenitors accumulate because they lack the ability to differentiate. Instead, our data indicate that Gfi1 loss of function deregulates 2 separable transcriptional programs, one of which controls the accumulation and lineage specification of myeloid progenitors, but not terminal granulopoiesis. We demonstrate that Gfi1 directly represses HoxA9, Pbx1, and Meis1 during normal myelopoiesis. Gfi1-/- progenitors exhibit elevated levels of HoxA9, Pbx1 and Meis1, exaggerated HoxA9-Pbx1-Meis1 activity, and progenitor transformation in collaboration with oncogenic K-Ras. Limiting HoxA9 alleles corrects, in a dose-dependent manner, in vivo and in vitro phenotypes observed with loss of Gfi1 in myeloid progenitor cells but did not rescue Gfi1-/- blocked granulopoiesis. Thus, Gfi1 integrates 2 events during normal myeloid differentiation; the suppression of a HoxA9-Pbx1-Meis1 progenitor program and the induction of a granulopoietic transcription program.

c-Myc and caspase-2 are involved in activating Bax during cytotoxic drug-induced apoptosis

Activation of Bax following diverse cytotoxic stress has been shown to be an essential gateway to mitochondrial dysfunction and activation of the intrinsic apoptotic pathway characterized by cytochrome c release with caspase-9/-3 activation. Interestingly, c-Myc has been reported to promote apoptosis by destabilizing mitochondrial integrity in a Bax-dependent manner. Stress-induced activation of caspase-2 may also induce permeabilization of mitochondria with activation of the intrinsic death pathway. To test whether c-Myc and caspase-2 cooperate to activate Bax and thereby mediate intrinsic apoptosis, small interfering RNA was used to efficiently knock down the expression of c-Myc, caspase-2, and Apaf-1, an activating component in the apoptosome, in two human cancer cell lines, lung adenocarcinoma A-549 and osteosarcoma U2-OS cells. Under conditions when the expression of endogenous c-Myc, caspase-2, or Apaf-1 is reduced 80-90%, cisplatin (or etoposide)-induced apoptosis is significantly decreased. Biochemical studies reveal that the expression of c-Myc and caspase-2 is crucial for cytochrome c release from mitochondria during cytotoxic stress and that Apaf-1 is only required following cytochrome c release to activate caspases-9/-3. Although knockdown of c-Myc or caspase-2 does not affect Bax expression, caspase-2 is important for cytosolic Bax to integrate into the outer mitochondrial membrane, and c-Myc is critical for oligomerization of Bax once integrated into the membrane.

Oncogene addiction: setting the stage for molecularly targeted cancer therapy

In pugilistic parlance, the one-two punch is a devastating combination of blows, with the first punch setting the stage and the second delivering the knock-out. This analogy can be extended to molecularly targeted cancer therapies, with oncogene addiction serving to set the stage for tumor cell killing by a targeted therapeutic agent. While in vitro and in vivo examples abound documenting the existence of this phenomenon, the mechanistic underpinnings that govern oncogene addiction are just beginning to emerge. Our current inability to fully exploit this weakness of cancer cells stems from an incomplete understanding of oncogene addiction, which nonetheless represents one of the rare chinks in the formidable armor of cancer cells.

Profilin 1 obtained by proteomic analysis in all-trans retinoic acid-treated hepatocarcinoma cell lines is involved in inhibition of cell proliferation and migration

Previous studies have shown that all-trans retinoic acid (ATRA) suppresses growth of hepatocarcinoma cell in vitro. To understand the underlying mechanisms, we investigated the protein expression profiles by 2-DE in hepatocarcinoma cell line SMMC-7721 treated with ATRA. Our results reveal that six proteins were differently expressed in response to ATRA. Using MS and database searching, they were identified as profilin 1, phosphoglycerate kinase 1, RuvB-like 1, alpha-enolase, pyridoxal kinase and F-actin capping protein. We selected the up-regulated protein, profilin 1 (PFN1), for further studies. The PFN1 expression was increased in response to ATRA in a dose- and time-dependent manner. The PFN1 expression was reduced dramatically in four hepatoma cell lines compared to L02 cell line of non-tumor origin. The PFN1 expression was also examined in 4 cases of primary hepatocarcinoma tissues by Western blot and 30 cases by tissues microarray. It was found that the protein level of PFN1 was lower in hepatocarcinoma tissues compared to that in the adjacent tissues. Similar to ATRA, overexpression of PFN1 led to inhibition of cell proliferation and migration. Furthermore, RNAi-based PFN1 knockdown could rescue the inhibitory effect of ATRA on cell proliferation and migration. In conclusion, ATRA inhibited cell proliferation and migration through up-regulation of PFN1.

miRNAs and apoptosis: RNAs to die for

MicroRNAs (miRNAs) are small non-coding RNAs of about 18-24 nucleotides in length that negatively regulate gene expression. Discovered only recently, it has become clear that they are involved in many biological processes such as developmental timing, differentiation and cell death. Data that connect miRNAs to various kinds of diseases, particularly cancer, are accumulating. miRNAs can influence cancer development in many ways, including the regulation of cell proliferation, cell transformation, and cell death. In this review, we focus on miRNAs that have been shown to play a role in the regulation of apoptosis. We first describe in detail how Drosophila has been utilized as a model organism to connect several miRNAs with the cell death machinery. We discuss the genetic approaches that led to the identification of those miRNAs and subsequent work that helped to establish their function. In the second part of the review article, we focus on the involvement of miRNAs in apoptosis regulation in mammals. Intriguingly, many of the miRNAs that regulate apoptosis have been shown to affect cancer development. In the end, we discuss a virally encoded miRNA that influences the cell death response in the mammalian host cell. In summary, the data gathered over the recent years clearly show the potential and important role of miRNAs to regulate apoptosis at various levels and in several organisms.

Regulation of reactive oxygen species, DNA damage, and c-Myc function by peroxiredoxin 1

Overexpression of c-Myc results in transformation and multiple other phenotypes, and is accompanied by the deregulation of a large number of target genes. We previously demonstrated that peroxiredoxin 1 (Prdx1), a scavenger of reactive oxygen species (ROS), interacts with a region of the c-Myc transcriptional regulatory domain that is essential for transformation. This results either in the suppression or enhancement of some c-Myc functions and in the altered expression of select target genes. Most notably, c-Myc-mediated transformation is inhibited, implying a tumor suppressor role for Prdx1. Consistent with this, prdx1-/- mice develop age-dependent hemolytic anemias and/or malignancies. We now show that erythrocytes and embryonic fibroblasts from these animals contain higher levels of ROS, and that the latter cells show evidence of c-Myc activation, including the ability to be transformed by a ras oncogene alone. In contrast, other primary cells from prdx1-/- mice do not have elevated ROS, but nonetheless show increased oxidative DNA damage. This apparent paradox can be explained by the fact that ROS localize primarily to the cytoplasm of prdx1+/+ cells, whereas in prdx1-/- cells, much higher levels of nuclear ROS are seen. We suggest that increased DNA damage and tumor susceptibility in prdx1-/- animals results from this shift in intracellular ROS. prdx1-/- mice should be useful in studying the role of oxidative DNA damage in the causation of cancer and its prevention by antioxidants. They should also help in studying the relationship between oncogenes such as c-Myc and DNA damage.

Short-Term Changes in Ki-67 during Neoadjuvant Treatment of Primary Breast Cancer with Anastrozole or Tamoxifen Alone or Combined Correlate with Recurrence-Free Survival

Purpose: Neoadjuvant (preoperative) therapy for breast cancer may allow for the development of intermediate markers of treatment benefit, thereby circumventing the need for efficacy trials of adjuvant therapy, which require much larger patient numbers and longer follow-up. The aim of this study—as part of the Immediate Preoperative “Arimidex” (anastrozole), Tamoxifen, or Arimidex Combined with Tamoxifen (IMPACT) trial (n = 330)—was to test the hypotheses that changes in Ki-67 after 2 weeks and/or 12 weeks: (i) differed between treatments, (ii) predicted clinical tumor response, and/or (iii) may predict long-term outcome differences between treatments in adjuvant therapy.

Experimental Design: The Arimidex, Tamoxifen, Alone or in Combination (ATAC) trial compared these same agents in the adjuvant setting. Biomarkers were measured in biopsy specimens taken before and after 2 and 12 weeks of treatment.

Results: Suppression of the proliferation marker Ki-67 after 2 and 12 weeks was significantly greater with anastrozole than with tamoxifen (P = 0.004 and P &lt; 0.001) but was similar between tamoxifen and the combination (P = 0.600 and P = 0.912). This result closely parallels that seen for the relative recurrence-free survival with the treatments after a median follow-up of 31 months in the ATAC trial in 9,366 patients. Against expectations, apoptosis was not increased in any of the treatment arms.

Conclusions: The data indicate that short-term changes in proliferation in the neoadjuvant setting may be able to predict outcome during adjuvant use of the same treatments. If this can be confirmed, these findings could lead to a profound change in approaches to drug development in breast cancer. The data indicate that estrogen is not an important survival factor for human breast cancer cells.

Ionizing radiation induces a stress response in primary cultures of rainbow trout skin

Fish skin is very vulnerable to damage from physical and chemical pollutants because it is in direct contact with the aquatic environment. In this study, the effect of gamma radiation on primary cultures of rainbow trout skin was investigated. Primary cultures containing two cell types, epidermal cells and goblet mucous cells, were exposed to doses ranging from 0.5-15 Gy 60Co gamma radiation. Expression of PCNA, c-myc and BCL2 was investigated as well as growth and levels of apoptosis and necrosis. Morphological and functional changes were also studied. The irradiated cultures showed evidence of a dose-dependent increase in necrosis and enhanced proliferation as well as morphological damage. In addition, mucous cell area was found to decrease significantly after irradiation. The study shows the value of these primary cultures as in vitro models for studying radiation effects. They provide an effective alternative to whole-animal exposures for radiation risk assessment.

Critical prosurvival roles for C/EBP beta and insulin-like growth factor I in macrophage tumor cells

One of the hallmarks of leukemic cells is their ability to proliferate and survive in the absence of exogenous growth factors (GFs). However, the molecular mechanisms used by myeloid tumor cells to escape apoptosis are not fully understood. Here we report that Myc/Raf-transformed macrophages require the transcription factor C/EBP beta to prevent cell death. In contrast to wild-type cells, C/EBP beta(-/-) macrophages were completely dependent on macrophage colony-stimulating factor or granulocyte-macrophage colony-stimulating factor for survival and displayed impaired tumorigenicity in vivo. Microarray analysis revealed that C/EBP beta-deficient cells expressed significantly reduced levels of the prosurvival factor insulin-like growth factor I (IGF-I). Overexpression of C/EBP beta stimulated transcription from the IGF-I promoter, indicating that IGF-I is a direct transcriptional target of C/EBP beta. Serological neutralization of IGF-I in C/EBP beta(+/+) tumor cell cultures induced apoptosis, showing that IGF-I functions as an autocrine survival factor in these cells. Macrophage tumor cells derived from IGF-I(-/-) mice were GF dependent, similar to C/EBP beta-deficient cells. Forced expression of either C/EBP beta or IGF-I in C/EBP beta(-/-) bone marrow cells restored Myc/Raf-induced transformation and permitted neoplastic growth without exogenous GFs. Thus, our findings demonstrate that C/EBP beta is essential for oncogenic transformation of macrophages and functions at least in part by regulating expression of the survival factor IGF-I.

The Drosophila sterile-20 kinase slik controls cell proliferation and apoptosis during imaginal disc development

Cell proliferation and programmed cell death are closely controlled during animal development. Proliferative stimuli generally also induce apoptosis, and anti-apoptotic factors are required to allow net cell proliferation. Genetic studies in Drosophila have led to identification of a number of genes that control both processes, providing new insights into the mechanisms that coordinate cell growth, proliferation, and death during development and that fail to do so in diseases of cell proliferation. We present evidence that the Drosophila Sterile-20 kinase Slik promotes cell proliferation and controls cell survival. At normal levels, Slik provides survival cues that prevent apoptosis. Cells deprived of Slik activity can grow, divide, and differentiate, but have an intrinsic survival defect and undergo apoptosis even under conditions in which they are not competing with normal cells for survival cues. Like some oncogenes, excess Slik activity stimulates cell proliferation, but this is compensated for by increased cell death. Tumor-like tissue overgrowth results when apoptosis is prevented. We present evidence that Slik acts via Raf, but not via the canonical ERK pathway. Activation of Raf can compensate for the lack of Slik and support cell survival, but activation of ERK cannot. We suggest that Slik mediates growth and survival cues to promote cell proliferation and control cell survival during Drosophila development.

Identification and characterization of Slik as a new regulator of cell growth and survival based on loss-of-function and overexpression analysis

The human herpes virus 8-encoded viral FLICE-inhibitory protein induces cellular transformation via NF-kappaB activation

Infection with human herpes virus 8 (HHV8) has been associated with Kaposi's sarcoma, primary effusion lymphoma, and multicentric Castleman's disease. HHV8 encodes for a viral FLICE-inhibitory protein (vFLIP), designated K13, which resembles the prodomain of caspase-8 in structure and has been shown to protect cells against death receptor-induced apoptosis in vitro and in vivo. In this report, we present evidence that HHV8 vFLIP also possesses the unique ability of transforming Rat-1 and Balb/3T3 fibroblast cells, which is not shared by other vFLIPs. Rat-1 cells expressing HHV8 vFLIP form colonies in soft agar and form tumors in nude mice. The transforming ability of HHV8 vFLIP is associated with the activation of the NF-kappaB pathway and is blocked by molecular and chemical inhibitors of this pathway. Our results suggest that vFLIP K13 has activity beyond its role as an inhibitor of death receptor signaling and may play a causative role in the pathogenesis of HHV8-associated malignancies. Furthermore, inhibitors of the NF-kappaB pathway may have a role in the treatment of malignancies linked to HHV8 infection.

Regulation and critical role of potassium homeostasis in apoptosis

Programmed cell death or apoptosis is broadly responsible for the normal homeostatic removal of cells and has been increasingly implicated in mediating pathological cell loss in many disease states. As the molecular mechanisms of apoptosis have been extensively investigated a critical role for ionic homeostasis in apoptosis has been recently endorsed. In contrast to the ionic mechanism of necrosis that involves Ca(2+) influx and intracellular Ca(2+) accumulation, compelling evidence now indicates that excessive K(+) efflux and intracellular K(+) depletion are key early steps in apoptosis. Physiological concentration of intracellular K(+) acts as a repressor of apoptotic effectors. A huge loss of cellular K(+), likely a common event in apoptosis of many cell types, may serve as a disaster signal allowing the execution of the suicide program by activating key events in the apoptotic cascade including caspase cleavage, cytochrome c release, and endonuclease activation. The pro-apoptotic disruption of K(+) homeostasis can be mediated by over-activated K(+) channels or ionotropic glutamate receptor channels, and most likely, accompanied by reduced K(+) uptake due to dysfunction of Na(+), K(+)-ATPase. Recent studies indicate that, in addition to the K(+) channels in the plasma membrane, mitochondrial K(+) channels and K(+) homeostasis also play important roles in apoptosis. Investigations on the K(+) regulation of apoptosis have provided a more comprehensive understanding of the apoptotic mechanism and may afford novel therapeutic strategies for apoptosis-related diseases.

miRNAs: micro managers of programmed cell death

Genomes encode numerous small RNAs, but the function of these molecules has been elusive. Recent studies show that two distinct microRNAs regulate programmed cell death, and provide new mechanisms for the regulation of animal development.

bantam encodes a developmentally regulated microRNA that controls cell proliferation and regulates the proapoptotic gene hid in Drosophila

Cell proliferation, cell death, and pattern formation are coordinated in animal development. Although many proteins that control cell proliferation and apoptosis have been identified, the means by which these effectors are linked to the patterning machinery remain poorly understood. Here, we report that the bantam gene of Drosophila encodes a 21 nucleotide microRNA that promotes tissue growth. bantam expression is temporally and spatially regulated in response to patterning cues. bantam microRNA simultaneously stimulates cell proliferation and prevents apoptosis. We identify the pro-apoptotic gene hid as a target for regulation by bantam miRNA, providing an explanation for bantam's anti-apoptotic activity.

Chemically modified tetracyclines induce cytotoxic effects against J774 tumour cell line by activating the apoptotic pathway

Here, we have studied the effects of chemically modified tetracyclines (CMTs) on apoptosis both at the level of the cytoplasmic proteolytic caspase cascade, and on Bcl-2 and c-myc mRNA expression in the J774 macrophage cell line. The results indicate that CMTs induce morphological changes consistent with apoptotic events, as clearly demonstrated both by the acridine orange and ethidium bromide staining, and by TUNEL and fragmentation ELISA assays. Furthermore, the analysis of the cell cycle by flow cytometry shows an evident apoptotic sub-G0G1 peak, without important modifications in the cell cycle distribution. CMTs induce programmed cell death (PCD) in a dose-dependent manner and CMT-8 is the strongest among them. CMT-1 and CMT-8 activate mainly caspase-8 as attested by the inhibitory effects of Z-VAD-fmk and Z-IEDT-fmk on CMT-induced apoptosis. Part of CMT-induced PCD is due to the activation of caspase-9, since it is reduced by the specific caspase-9 inhibitor, Z-LEHD-fmk. Besides, CMTs increase Bcl-2 and c-myc mRNA expression. Collectively, these data indicate that CMTs are potentially anti-tumour agents, since they strongly trigger apoptosis both activating the proteolytic system of the caspase family and modulating genes involved in PCD regulation.

Impaired postnatal hepatocyte proliferation and liver regeneration in mice lacking c-jun in the liver

Mice lacking the AP-1 transcription factor c-jun die at mid-gestation showing heart defects and impaired hepatogenesis. To inactivate c-jun in hepatocytes, mice carrying a floxed c-jun allele were generated. Perinatal liver-specific c-jun deletion caused reduced hepatocyte proliferation and decreased body size. After partial hepatectomy, half of the mutants died and liver regeneration was impaired. This phenotype was not present in mice lacking the N-terminal phosphorylation sites of c-Jun. The failure to regenerate was accompanied by increased cell death and lipid accumulation in hepatocytes. Moreover, cyclin-dependent kinases and several cell cycle regulators were affected, resulting in inefficient G(1)-S phase progression. These studies identify c-Jun as a critical regulator of hepatocyte proliferation and survival during liver development and regeneration.