Table of Contents

Volume 10, Issue 13

  July 1, 2011

  Pages 2043 - 2234

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 Issue Catalogue (MARC XML)

EDITORIALS: CELL CYCLE FEATURES

Open Access Article

The Myc-ARF-Egr1 pathway: Unleashing the apoptotic power of c-Myc

David N. Boone and Stephen R. Hann
Pages 2043 - 2044
http://dx.doi.org/10.4161/cc.10.13.15711
Abstract | PDF

Comment on: Boone DN, et al. Proc Natl Acad Sci USA 2010; 108:632-7.

Open Access Article

MicroRNAs and lung cancer: From markers to targets

Gabriella Sozzi, Ugo Pastorino and Carlo M. Croce
Pages 2045 - 2046
http://dx.doi.org/10.4161/cc.10.13.15712
Abstract | PDF

Comment on: Boeri M, et al. Proc Natl Acad Sci USA 2011; 108:3713-8.

Open Access Article

Microparticulate systems for targeted drug delivery to phagocytes

Siddharth Jhunjhunwala and Steven R. Little
Pages 2047 - 2048
http://dx.doi.org/10.4161/cc.10.13.15713
Abstract | PDF

Comment on: Jhunjhunwala S, et al. J Control Release 2009;133:191-7.

Open Access Article

The complex roles of histone demethylases in vivo

Luisa Di Stefano and Nicholas Dyson
Pages 2049 - 2050
http://dx.doi.org/10.4161/cc.10.13.15758
Abstract | PDF

Comment on: Di Stefano L, et al. Genes Dev 2011; 25:17-28.

Open Access Article

An intimate connection between ubiquitination and compartmentalized cAMP signaling

Luca Lignitto, Maria Sepe, Annalisa Carlucci and Antonio Feliciello
Pages 2051 - 2052
http://dx.doi.org/10.4161/cc.10.13.15839
Abstract | PDF

Comment on: Lignitto L, et al. Nat Cell Biol 2011; 13:412-22.




CELL CYCLE NEWS & VIEWS

Open Access Article

Cohesin complexes get more complex: The novel kleisin RAD21L

Rolf Jessberger
Pages 2053 - 2058
http://dx.doi.org/10.4161/cc.10.13.15802
Abstract | PDF

Comment on: Gutiérrez-Caballero C, et al. Cell Cycle 2011; 10:1477-87.

Open Access Article

Gene profiling for assessment of cell-based therapies

David M. Engman

http://dx.doi.org/10.4161/cc.10.13.15804
Abstract | PDF

Comment on: Soares MBP, et al. Cell Cycle 2011; 10:1448-55.

Open Access Article

Division of labor of the replication fork protection complex subunits in sister chromatid cohesion and Chk1 activation

Eishi Noguchi

http://dx.doi.org/10.4161/cc.10.13.15805
Abstract | PDF

Comment on: Smith-Roe SL, et al. Cell Cycle 2011; 10:1618-24.

Open Access Article

Rae1: A new clue for nucleoporin leukemias

Tobias Stuwe and André Hoelz

http://dx.doi.org/10.4161/cc.10.13.15806
Abstract | PDF

Comment on: Funasaka T, et al. Cell Cycle 2011; 10:1456-67.

Open Access Article

A novel Rad18 ubiqitin ligase-mediated pathway for repair of camptothecin-induced DNA damage

Satoshi Tateishi

http://dx.doi.org/10.4161/cc.10.13.15840
Abstract | PDF

Comment on: Palle K, et al. Cell Cycle 2011; 10:1625–38.




EXTRA VIEWS

Open Access Article

Accelerated aging in the tumor microenvironment: Connecting aging, inflammation and cancer metabolism with personalized medicine

Michael P. Lisanti, Ubaldo E. Martinez-Outschoorn, Stephanos Pavlides, Diana Whitaker-Menezes, Richard G. Pestell, Anthony Howell and Federica Sotgia
Pages 2059 - 2063
http://dx.doi.org/10.4161/cc.10.13.16233
Abstract | PDF

Cancer is thought to be a disease associated with aging. Interestingly, normal aging is driven by the production of ROS and mitochondrial oxidative stress, resulting in the cumulative accumulation of DNA damage. Here, we discuss how ROS signaling, NFκB- and HIF1-activation in the tumor microenvironment induces a form of “accelerated aging,” which leads to stromal inflammation and changes in cancer cell metabolism. Thus, we present a unified model where aging (ROS), inflammation (NFκB) and cancer metabolism (HIF1), act as co-conspirators to drive autophagy (“self-eating”) in the tumor stroma. Then, autophagy in the tumor stroma provides high-energy “fuel” and the necessary chemical building blocks, for accelerated tumor growth and metastasis. Stromal ROS production acts as a “mutagenic motor” and allows cancer cells to buffer—at a distance—exactly how much of a mutagenic stimulus they receive, further driving tumor cell selection and evolution. Surviving cancer cells would be selected for the ability to induce ROS more effectively in stromal fibroblasts, so they could extract more nutrients from the stroma via autophagy. If lethal cancer is a disease of “accelerated host aging” in the tumor stroma, then cancer patients may benefit from therapy with powerful antioxidants. Antioxidant therapy should block the resulting DNA damage, and halt autophagy in the tumor stroma, effectively “cutting off the fuel supply” for cancer cells. These findings have important new implications for personalized cancer medicine, as they link aging, inflammation and cancer metabolism with novel strategies for more effective cancer diagnostics and therapeutics.

Open Access Article

A herpesvirus kinase that masquerades as Akt: You don’t have to look like Akt, to act like it

Uyanga Chuluunbaatar and Ian Mohr
Pages 2064 - 2068
http://dx.doi.org/10.4161/cc.10.13.16242
Abstract | PDF

The cellular protein synthesis machinery is tightly regulated and capable of rapid reaction to a variety of physiological inputs critical in stress-response, cell cycle control, cancer biology, and virus infection. One important strategy for stimulating protein synthesis involves the ser/thr kinase Akt, which subsequently triggers inactivation of the cap-dependent translational repressor 4E-BP1 by an mTOR-containing protein complex (mTORC1). A recent paper demonstrated that herpes simplex virus utilizes a remarkable tactic to activate mTOR in infected cells. Instead of using the cellular Akt, the virus produces a ser / thr kinase called Us3 that doesn’t look like Akt, but masquerades as Akt. By making the Akt-like protein unrecognizable, this disguise allows it to bypass the strict limits normally imposed on the real cellular Akt. Importantly, preventing the virus Akt-imposter from triggering mTORC1 inhibited viral growth, suggesting a new way to block herpes simplex virus. This study also raises the possibility that other Akt-impersonators may lurk hidden in our own genomes, possibly contributing to diseases ranging from diabetes to cancer.

Open Access Article

Biology using engineering tools: The negative feedback amplifier

Marc R. Birtwistle and Walter Kolch
Pages 2069 - 2076
http://dx.doi.org/10.4161/cc.10.13.16245
Abstract | PDF

Negative feedback is an ubiquitous feature of biological networks. Recent work from Sturm and colleaguespresents experimental evidence that biological negative feedback can serve the same function as it does for engineered systems: robustness to perturbations within the feedback loop. Such behavior has important implications for how to attack deregulated signaling networks containing negative feedback in diseases such as cancer.

Open Access Article

EAPP modulates the activity of p21 and Chk2

Peter Andorfer, Ludwig Schwarzmayr and Hans Rotheneder
Pages 2077 - 2082
http://dx.doi.org/10.4161/cc.10.13.16247
Abstract | PDF

Genomic instability is thought to be critical for the development of cancer. Among its causes microsatellite instability (MIN) and chromosomal instability (CIN) have attracted the most attention. Cell cycle checkpoints and DNA repair mechanisms are the first line of defense against DNA damage. Among the most dangerous DNA lesions are double-strand breaks. The response to DNA double strand breaks is regulated mainly by the serine/threonine kinases ATM and Chk2 and their downstream target the tumor suppressor p53, which in turn stimulates the expression of growth-inhibitory genes like p21 or pro-apoptotic genes like Bax. The balance between these gene products determines the fate of a cell. EAPP is a nuclear phosphoprotein that is frequently upregulated in human tumors. We have recently shown that EAPP levels are critical for cellular homeostasis. DNA damage elevates EAPP levels and its overexpression results in G1 arrest and impairs apoptosis in a p21-dependent manner. EAPP binds to the p21 promoter, stimulates its activity and seems to be essential for transcription initiation. In the present work we show that EAPP also regulates the phosphorylation status and thus the activity of Chk2. EAPP binding seems to trigger the dephosphorylation of P-Chk2 resulting in its inactivation. A newly described function of Chk2 in mitosis that secures genomic integrity might also be affected by EAPP overexpression. This might explain the abundance of EAPP in aneuploid tumor cells.

Open Access Article

Signaling at the gate: Phosphorylation of the mitochondrial protein import machinery

Sanjana Rao, Carolin Gerbeth, Angelika Harbauer, Despina Mikropoulou, Chris Meisinger and Oliver Schmidt
Pages 2083 - 2090
http://dx.doi.org/10.4161/cc.10.13.16054
Abstract | PDF

Protein import into mitochondria is an essential process in every eukaryotic organism. While most of the components of the import machinery have been identified and are mechanistically quite well understood, regulation of this process had been a largely neglected area of research in the past. Recently, we demonstrated for the first time that the translocase of the outer mitochondrial membrane (TOM) is phosphorylated and regulated by several cytosolic protein kinases. Among these, casein kinase 2 (CK2) governs the assembly of TOM complexes, while protein kinase A (PKA) controls translocase function. Here, we outline the current model of protein import regulation, together with additional mitochondrial functions of CK2 and PKA. We also reflect the data on mitochondria-associated protein kinases and phosphatases in the model organism baker's yeast.

Open Access Article

Mouse chimeras as a system to investigate development, cell and tissue function, disease mechanisms and organ regeneration

Sigrid Eckardt, K. John McLaughlin and Holger Willenbring
Pages 2091 - 2099
http://dx.doi.org/10.4161/cc.10.13.16360
Abstract | PDF

Chimeras are organisms composed of at least two genetically distinct cell lineages originating from different zygotes. In the laboratory, mouse chimeras can be produced experimentally; various techniques allow combining different early stage mouse embryos with each other or with pluripotent stem cells. Identification of the progeny of the different lineages in chimeras permits to follow cell fate and function, enabling correlation of genotype with phenotype. Mouse chimeras have become a tool to investigate critical developmental processes, including cell specification, differentiation, patterning, and the function of specific genes. In addition, chimeras can also be generated to address biological processes in the adult, including mechanisms underlying diseases or tissue repair and regeneration. This review summarizes the different types of chimeras and how they have been generated and provides examples of how mouse chimeras offer a unique and powerful system to investigate questions pertaining to cell and tissue function in the developing and adult organism.




PERSPECTIVE

Open Access Article

Is carcinogenesis a form of speciation?

Peter Duesberg, Daniele Mandrioli, Amanda McCormack and Joshua M. Nicholson
Pages 2100 - 2114
http://dx.doi.org/10.4161/cc.10.13.16352
Abstract | PDF

Since cancers have individual clonal karyotypes, are immortal and evolve from normal cells treated by carcinogens only after exceedingly long latencies of many months to decades—we deduce that carcinogenesis may be a form of speciation. This theory proposes that carcinogens initiate carcinogenesis by causing aneuploidy, i.e., losses or gains of chromosomes. Aneuploidy destabilizes the karyotype, because it unbalances thousands of collaborating genes including those that synthesize, segregate and repair chromosomes. Driven by this inherent instability aneuploid cells evolve ever-more random karyotypes automatically. Most of these perish, but a very small minority acquires reproductive autonomy—the primary characteristic of cancer cells and species. Selection for autonomy stabilizes new cancer species against the inherent instability of aneuploidy within specific margins of variation. The speciation theory explains five common characteristics of cancers: (1) species-specific autonomy; (2) karyotypic and phenotypic individuality; (3) flexibility by karyotypic variations within stable margins of autonomy; (4) immortality by replacing defective karyotypes from constitutive pools of competent variants or subspecies generated by this flexibility; and (5) long neoplastic latencies by the low probability that random karyotypic alterations generate new autonomous species. Moreover, the theory explains phylogenetic relations between cancers of the same tissue, because carcinogenesis is restricted by tissue-specific transcriptomes. The theory also solves paradoxes of other cancer theories. For example, “aneuploidy” of cancers is now said to be a “paradox” or “cancer’s fatal flaw,” because aneuploidy impairs normal growth and development. But if the “aneuploidies” of cancers are in effect the karyotypes of new species, this paradox is solved.




REVIEWS

Open Access Article

LKB1/AMPK/mTOR signaling pathway in hematological malignancies: From metabolism to cancer cell biology

Alexa S. Green, Nicolas Chapuis, Catherine Lacombe, Patrick Mayeux, Didier Bouscary and Jerome Tamburini
Pages 2115 - 2120
http://dx.doi.org/10.4161/cc.10.13.16244
Abstract | PDF

The link between cancer and metabolism has been suggested for a long time but further evidence of this hypothesis came from the recent molecular characterization of the LKB1/AMPK signaling pathway as a tumor suppressor axis. Besides the discovery of somatic mutations in the LKB1 gene in certain type of cancers, a critical emerging point was that the LKB1/AMPK axis remains generally functional and could be stimulated by pharmacological molecules such as metformin in cancer cells. Notably, most of experimental evidence of the anti-tumor activity of AMPK agonists comes from the study of solid tumors such as breast or prostate cancers and only few data are available in hematological malignancies, although recent works emphasized the potential therapeutic value of AMPK agonists in this setting. Further basic research work should be conducted to elucidate the molecular targets of LKB1/AMPK responsible for its anti-tumor activity in parallel of conducting clinical trials using metformin, AICAR or new AMPK activating agents to explore the potential of the LKB1/AMPK signaling pathway as a new target for anticancer drug development.

Open Access Article

Unleashing Chk1 in cancer therapy

Laura Carrassa and Giovanna Damia
Pages 2121 - 2128
http://dx.doi.org/10.4161/cc.10.13.16398
Abstract | PDF

The checkpoint kinase 1 (Chk1) is one of the major players in the signal transduction pathway set in motion in response to DNA damage which activates different cell cycle checkpoints including the G₁/S, the intra-S, G₂-M and the mitotic spindle checkpoint, contributing to the maintenance of genomic stability. Chk1 is considered a good molecular target to inhibit, in combination with other anticancer agents, to increase the sensitivity of treatment, especially in tumors with a defective G₁ checkpoint. Experimental evidence highlights the essential role of Chk1 in normal and cancer cells even under unstressed conditions, especially in controlling DNA replication and cell division. This review looks at the main functions of Chk1 and the data on Chk1 inhibitors at their preclinical and clinical development are reported. This information may suggest novel approaches for new treatments with Chk1 inhibitors in combination with anticancer agents or as single agents. The emergent synthetic lethality approach may help define the genetic background features where Chk1 inhibitors alone could be very effective.




REPORTS

Open Access Article

Zinc finger protein 521 antagonizes early B-cell factor 1 and modulates the B-lymphoid differentiation of primary hematopoietic progenitors

Tiziana Mega, Michela Lupia, Nicola Amodio, Sarah J. Horton, Maria Mesuraca, Daniela Pelaggi, Valter Agosti, Michele Grieco, Emanuela Chiarella, Raffaella Spina, Malcolm A.S. Moore, Jan Jacob Schuringa, Heather M. Bond and Giovanni Morrone
Pages 2129 - 2139
http://dx.doi.org/10.4161/cc.10.13.16045
Abstract | PDF

Zinc finger protein 521 (EHZF/ZNF521) is a multi-functional transcription co-factor containing 30 zinc fingers and an amino-terminal motif that binds to the nucleosome remodelling and histone deacetylase (NuRD) complex. ZNF521 is believed to be a relevant player in the regulation of the homeostasis of the hematopoietic stem/progenitor cell compartment, however the underlying molecular mechanisms are still largely unknown. Here, we show that this protein plays an important role in the control of B-cell development by inhibiting the activity of early B-cell factor-1 (EBF1), a master factor in B-lineage specification. In particular, our data demonstrate that: (1) ZNF521 binds to EBF1 via its carboxyl-terminal portion and this interaction is required for EBF1 inhibition; (2) NuRD complex recruitment by ZNF521 is not essential for the inhibition of transactivation of EBF1-dependent promoters; (3) ZNF521 represses EBF1 target genes in a human B-lymphoid molecular context; and (4) RNAi-mediated silencing of ZNF521/Zfp521 in primary human and murine hematopoietic progenitors strongly enhances the generation of B-lymphocytes in vitro. Taken together, our data indicate that ZNF521 can antagonize B-cell development and lend support to the notion that it may contribute to conserve the multipotency of primitive lympho-myeloid progenitors by preventing or delaying their EBF1-driven commitment toward the B-cell lineage.

Open Access Article

Scleroderma-like properties of skin from caveolin-1-deficient mice: Implications for new treatment strategies in patients with fibrosis and systemic sclerosis

Remedios Castello-Cros, Diana Whitaker-Menezes, Alex Molchansky, George Purkins, Louis J. Soslowsky, David P. Beason, Federica Sotgia, Renato V. Iozzo and Michael P. Lisanti
Pages 2140 - 2150
http://dx.doi.org/10.4161/cc.10.13.16227
Abstract | PDF

Caveolin-1 (Cav-1), the principal structural component of caveolae, participates in the pathogenesis of several fibrotic diseases, including systemic sclerosis (SSc). Interestingly, affected skin and lung samples from patients with SSc show reduced levels of Cav-1, as compared to normal skin. In addition, restoration of Cav-1 function in skin fibroblasts from SSc patients reversed their pro-fibrotic phenotype. Here, we further investigated whether Cav-1 mice are a useful pre-clinical model for studying the pathogenesis of SSc. For this purpose, we performed quantitative transmission electron microscopy, as well as biochemical and immuno-histochemical analysis, of the skin from Cav-1^–/– null mice. Using these complementary approaches, we now show that skin from Cav-1 null mice exhibits many of the same characteristics as SSc skin from patients, including a decrease in collagen fiber diameter, increased tensile strength, and stiffness, as well as mononuclear cell infiltration. Furthermore, an increase in autophagy/mitophagy was observed in the stromal cells of the dermis from Cav-1^–/– mice. These findings suggest that changes in cellular energy metabolism (e.g., a shift towards aerobic glycolysis) in these stromal cells may be a survival mechanism in this “hostile” or pro-inflammatory microenvironment. Taken together, our results demonstrate that Cav-1^–/– null mice are a valuable new pre-clinical model for studying scleroderma. Most importantly, our results suggest that inhibition of autophagy and/or aerobic glycolysis may represent a new promising therapeutic strategy for halting fibrosis in SSc patients. Finally, Cav-1^–/– null mice are also a pre-clinical model for a “lethal” tumor micro-environment, possibly explaining the link between fibrosis, tumor progression, and cancer metastasis.

Open Access Article

Caveolin-2-deficient mice show increased sensitivity to endotoxemia

Cecilia J. de Almeida, Agnieszka K. Witkiewicz, Jean-François Jasmin, Herbert B. Tanowitz, Federica Sotgia, Philippe G. Frank and Michael P. Lisanti
Pages 2151 - 2161
http://dx.doi.org/10.4161/cc.10.13.16234
Abstract | PDF

Caveolin proteins are structural components of caveolae and are involved in the regulation of many biological processes. Recent studies have shown that caveolin-1 modulates inflammatory responses and is important for sepsis development. In the present study, we show that caveolin-1 and caveolin-2 have opposite roles in lipopolysaccharide (LPS)-induced sepsis using caveolin-deficient (Cav-1^-/- and Cav-2^-/-) mice for each of these proteins. While Cav-1^-/- mice displayed delayed mortality following challenge with LPS, Cav-2^-/- mice were more sensitive to LPS compared to wild-type (WT). With Cav-2^-/- mice, this effect was associated with increased intestinal injury and increased intestinal permeability. This negative outcome was also correlated with enhanced expression of iNOS in epithelial intestinal cells, and enhanced production of nitric oxide (NO). By contrast, Cav-1^-/- mice demonstrated a decrease in iNOS expression with decreased NO production, but no alteration in intestinal permeability. The differential expression of iNOS was associated with a significant increase of STAT-1 activation in these mice. Intestinal cells of Cav-2^-/- mice showed increased phosphorylation of STAT-1 at tyrosine 701 compared to wild-type. However, Cav-1^-/- mice-derived intestinal cells showed decreased levels of phosphorylation of STAT-1 at tyrosine 701. Since caveolin-2 is almost completely absent in Cav-1^-/- mice, we conclude that it is not just the absence of caveolin-2 that is responsible for the observed effects, but that the balance between caveolin-1 and caveolin-2 is important for iNOS expression and ultimately for sepsis outcome.

Open Access Article

Cellular studies reveal mechanistic differences between taccalonolide A and paclitaxel

April L. Risinger and Susan L. Mooberry
Pages 2162 - 2171
http://dx.doi.org/10.4161/cc.10.13.16238
Abstract | PDF

Taccalonolide A is a microtubule stabilizer that has cellular effects almost identical to paclitaxel. However, biochemical studies show that, unlike paclitaxel, taccalonolide A does not enhance purified tubulin polymerization or bind tubulin/microtubules. Mechanistic studies aimed at understanding the nature of the differences between taccalonolide A and paclitaxel were conducted. Our results show that taccalonolide A causes bundling of interphase microtubules at concentrations that cause antiproliferative effects. In contrast, the concentration of paclitaxel that initiates microtubule bundling is 31-fold higher than its IC₅₀. Taccalonolide A’s effects are further differentiated from paclitaxel in that it is unable to enhance the polymerization of tubulin in cellular extracts. This finding extends previous biochemical results with purified brain tubulin to demonstrate that taccalonolide A requires more than tubulin and a full complement of cytosolic proteins to cause microtubule stabilization. Reversibility studies were conducted and show that the cellular effects of taccalonolide A persist after drug washout. In contrast, other microtubule stabilizers, including paclitaxel and laulimalide, demonstrate a much higher degree of cellular reversibility in both short-term proliferation and long-term clonogenic assays.   The propensity of taccalonolide A to alter interphase microtubules at antiproliferative concentrations as well as its high degree of cellular persistence may explain why taccalonolide A is more potent in vivo than would be expected from cellular studies. The close linkage between the microtubule bundling and antiproliferative effects of taccalonolide A is of interest given the recent hypothesis that the effects of microtubule targeting agents on interphase microtubules might play a prominent role in their clinical anticancer efficacy.

Open Access Article

MiRNA-27a controls FBW7/hCDC4-dependent cyclin E degradation and cell cycle progression

Mikael Lerner, Josefin Lundgren, Shahab Akhoondi, Angelina Jahn, Hwee-Fang Ng, Farhad Akbari Moqadam, Joachim A.F. Oude Vrielink, Reuven Agami, Monique L. Den Boer, Dan Grandér and Olle Sangfelt
Pages 2172 - 2183
http://dx.doi.org/10.4161/cc.10.13.16248
Abstract | PDF

The F-box protein FBW7/hCDC4 is a tumor suppressor that acts as the substrate recognition component of an SCF ubiquitin ligase that targets numerous oncoproteins for proteasomal degradation. In this study, we investigated whether FBW7 is regulated by microRNAs, using a screen combining bioinformatic analysis, luciferase reporters and microRNA libraries. The ubiquitous miR-27a was identified as a major suppressor of FBW7 and in line with this, miR-27a prohibited ubiquitylation and turnover of the key FBW7 substrate cyclin E. Notably, we found that miR-27a only suppresses FBW7 during specific cell cycle phases, relieving its negative impact at the G1 to S-phase transition, prior to cyclin E protein degradation. We also demonstrate that attenuation of FBW7 by miR-27a overexpression leads to improper cell cycle progression and DNA replication stress, consistent with dysregulation of cyclin E expression. Finally, in the context of human cancer, miR-27a was discovered to be generally overexpressed in pediatric B-ALL and its expression to be inversely correlated with that of FBW7 in hyperdiploid cases of B-ALL. These data provide evidence for microRNA-mediated regulation of FBW7, and highlight the role of miR-27a as a novel factor fine-tuning the periodic events regulating cell cycle progression.

Open Access Article

Kinetic profiling of the c-Myc transcriptome and bioinformatic analysis of repressed gene promoters

Chui-Sun Yap, Abigail L. Peterson, Gastone Castellani, John M. Sedivy and Nicola Neretti
Pages 2184 - 2196
http://dx.doi.org/10.4161/cc.10.13.16249
Abstract | PDF

Mammalian c-Myc is a member of a small family of three related proto-oncogenic transcription factors. c-Myc has an unusually broad array of regulatory functions, which include roles in cell cycle and apoptosis, a variety of metabolic functions, cell differentiation, senescence, and stem cell maintenance. c-Myc modulates the expression of a very large number of genes, but the magnitude of the majority of the regulatory effects is only 2-fold or less. c-Myc can both activate and repress the promoters of its target genes. Identification of genes directly regulated by c-Myc has been an enduring question in the field. We report here microarray expression profiling of a high resolution time course of c-Myc induction, using fibroblast cells in which c-Myc activity can be modulated from null to physiological. The c-Myc transcriptome dataset presented is the largest reported to date with 4,186 differentially regulated genes (1,826 upregulated, 2,360 downregulated, 1% FDR). The gene expression patterns fit well with the known biological functions of c-Myc. We describe several novel findings and present tools for further data mining. Although the mechanisms of transcriptional activation by c-Myc are well understood, how c-Myc represses an even greater number of genes remains incompletely described. One mechanism involves the binding of c-Myc to other, positively acting transcription factors, and interfering with their activities. We identified rapid-response genes likely to be direct c-Myc targets, and analyzed the promoters of the repressed genes to identify transcription factors that could be targets of c-Myc repression.

Open Access Article

Inhibition of the EGF receptor and ERK1/2 signaling pathways rescues the human epidermoid carcinoma A431 cells from IFNγ-induced apoptosis

Elena B. Burova, Irina S. Smirnova, Ilya V. Gonchar, Alla N. Shatrova and Nikolay N. Nikolsky
Pages 2197 - 2205
http://dx.doi.org/10.4161/cc.10.13.16055
Abstract | PDF

Interferon gamma (IFNγ) has been demonstrated to inhibit tumor growth in vivo as well as proliferation of multiple types of cultured transformed cells. In this study, we showed that IFNγ promoted progressive death in A431 cells, overexpressing EGF receptor (EGFR). Based on the data provided by evaluating cell morphology, MTT assay, FACS analysis, and cleaved caspase-3 staining we concluded that the major cause of IFNγ-induced A431 cell growth inhibition was not cell cycle arrest, but apoptosis. We investigated a role for the EGFR and ERK1/2 MAPK signaling pathways in IFNγ-induced apoptosis of A431 cells. IFNγ-induced cell death was accompanied by both an increase of the ERK1/2 MAPK activation and a simultaneous reduction of the EGFR activation. Activation of ERK1/2 was crucial for IFNγ-induced cell death because MEK1/2 inhibitors, PD0325901 and U0126 efficiently protected cells from apoptosis by suppressing caspase-3 activation. Even though EGFR tyrosine kinase inhibitor AG1478 also rescued A431 cells from IFNγ-induced apoptosis, unlike MEK1/2 inhibitors, it initiated G₁ arrest. Together, these results suggest that sustained inhibition of both EGFR and ERK1/2 leads to significant protection of the cells from IFNγ-induced apoptosis, indicating important roles for the EGFR tyrosine kinase and ERK1/2 MAP-kinases in regulating A431 cell death.

Open Access Article

Inhibition of Aurora-A kinase induces cell cycle arrest in epithelial ovarian cancer stem cells by affecting NFĸB pathway

Ilana Chefetz, Jennie C. Holmberg, Ayesha B. Alvero, Irene Visintin and Gil Mor
Pages 2206 - 2214
http://dx.doi.org/10.4161/cc.10.13.16348
Abstract | PDF

Recurrent ovarian cancer is resistant to conventional chemotherapy. A sub-population of ovarian cancer cells, the epithelial ovarian cancer stem cells (EOC stem cells) have stemness properties, constitutive NFκB activity, and represent the chemoresistant population. Currently, there is no effective treatment that targets these cells. Aurora-A kinase (Aurora-A) is associated with tumor initiation and progression and is overexpressed in numerous malignancies. The aim of this study is to determine the effect of Aurora-A inhibition in EOC stem cells. EOC stem cells were treated with the Aurora-A inhibitor, MK-5108. Cell growth was monitored by Incucyte real-time imaging system, cell viability was measured using the Celltiter 96 assay and cytokine levels were quantified using xMAP technology. The intracellular changes associated with MK-5108 treatment are: (1) polyploidy and cell cycle arrest; (2) inhibition of NFκB activity; (3) decreased cytokine production; and (4) nuclear accumulation of IκBα. Thus, inhibition of Aurora-A decreases cell proliferation in the EOC stem cells by inducing cell cycle arrest and affecting the NFκB pathway. As EOC stem cells represent a source of recurrence and chemoresistance, these results suggest that Aurora-A inhibition may effectively target the cancer stem cell population in ovarian cancer.

Open Access Article

Limited role of Sirt1 in cancer protection by dietary restriction

Daniel Herranz, Gema Iglesias, Maribel Muñoz-Martín and Manuel Serrano
Pages 2215 - 2217
http://dx.doi.org/10.4161/cc.10.13.16185
Abstract | PDF

Dietary restriction (DR) has multiple beneficial effects, the two most prominently studied being an increased longevity and an increased cancer protection. Mammalian Sirt1 is a protein deacetylase that has been linked to DR. To explore the relation between Sirt1 and DR, we have examined here DR-induced cancer protection in mice overexpressing Sirt1 (2-3 fold) under its own regulatory elements (Sirt1-tg mice). In particular, we have subjected p53‑deficient mice, carrying or not the Sirt1-tg allele, to every-other-day fasting (EOD), which is a type of DR that significantly delays cancer onset. As expected, EOD extended the survival of p53-heterozygous (p53^+/-) mice. However, the extension of survival of p53-heterozygous mice by EOD was the same in the presence or absence of the Sirt1-tg allele. These results suggest that Sirt1 has a limited role in mediating cancer protection by DR in mammals.

Open Access Article

MRE11 promotes AKT phosphorylation in direct response to DNA double-strand breaks

Michael Fraser, Shane M. Harding, Helen Zhao, Carla Coackley, Daniel Durocher and Robert G. Bristow
Pages 2218 - 2232
http://dx.doi.org/10.4161/cc.10.13.16305
Abstract | PDF

AKT is hyper-activated in many human cancers and promotes proliferation and cancer cell survival in response to DNA damaging agents. Ionizing radiation (IR) produces DNA double strand breaks (DSB) and activates AKT, however a direct mechanism linking intra-nuclear DSB and AKT signaling is lacking. Here we demonstrate that AKT is phosphorylated following IR in benign and malignant cells and, using colony-forming assays and in vitro rejoining assays, show that AKT promotes non-homologous end joining-mediated DSB repair and cell survival following IR. Further studies revealed that pAKT-S473, but not pAKT-T308 or total AKT, accumulates in the vicinity of IR-induced DSB and co-localizes with γH2AX and ATM-pSer1981. Based on whole-cell IR, nuclear UV microbeam, and endonuclease-induced DSB studies, we observed that pAKT-S473 is up-regulated by a DSB-induced signaling cascade, and this is dependent on the DSB sensor protein, MRE11. MRE11-dependent pAKT-S473 did not require the MRE11 endonuclease domain. The histone ubiquitin ligase RNF168 is also required for DSB-induced pAKT-S473, and DSB-induced pAKT-S473 is independent of DNA-PKcs, PI3K, and ATR. These data demonstrate that DSB activate a signaling cascade that directly promotes a PI3K-independent pathway of AKT phosphorylation that is dependent on MRE11-ATM-RNF168 signaling. Thus, these data directly link the presence of DNA breaks to AKT-mediated cell survival and support AKT as a target for cancer therapy.




LETTER TO THE EDITOR

Open Access Article

Loss of either hypoxia inducible factor 1 or 2 promotes lung cancer cell colonization

Qiyuan Zhou, Tianji Chen, Joyce C.F. Ibe, J. Usha Raj and Guofei Zhou
Pages 2233 - 2234
http://dx.doi.org/10.4161/cc.10.13.16307
PDF