Table of Contents

Volume 11, Issue 3

  February 1, 2012

  Pages 419 - 632

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EDITORIAL

Open Access Article

Letter from the Publisher

Ronald G. Landes
Page 419
http://dx.doi.org/10.4161/cc.11.3.19486
PDF




EDITORIALS: CELL CYCLE FEATURES

Spatial consequences of blocking mTOR/S6K: Relevance for therapy

Margit Rosner, Katharina Schipany and Markus Hengstschläger
Pages 420 - 421
http://dx.doi.org/10.4161/cc.11.3.19056
Abstract | PDF

Comment on: Rosner M, et al. Amino Acids 2011; In press.

Cell-autonomous hepatic circadian clock regulates polyamine synthesis

Ann Atwood and Steve A. Kay
Pages 422 - 423
http://dx.doi.org/10.4161/cc.11.3.19098
Abstract | PDF

Comment on: Atwood A, et al. Proc Natl Acad Sci U S A 2011; 108:18560-5.

Linking hematopoietic regeneration to developmental signaling pathways: A story of BMP and Wnt

Teresa V. Bowman, Eirini Trompouki and Leonard I. Zon
Pages 424 - 425
http://dx.doi.org/10.4161/cc.11.3.19161
Abstract | PDF

Comment on: Trompouki E, et al. Cell 2011; 147:577-89.

Direct interactions between intestinal immune cells and the diet

Marc Veldhoen
Pages 426 - 427
http://dx.doi.org/10.4161/cc.11.3.19163
Abstract | PDF

Comment on: Li Y, et al. Cell. 2011; 147:629-40.

Target of rapamcyin (TOR)-based therapeutics for cardiomyopathy: Insights from zebrafish genetics

Yonghe Ding, Xiaojing Sun, Margaret Redfield, Sudhir Kushwaha and Xiaolei Xu
Pages 428 - 429
http://dx.doi.org/10.4161/cc.11.3.19164
Abstract | PDF

Comment on: Ding Y, et al. Circ Res 2011; 109:658-69.

Murine models of ovarian cancer for preclinical testing of targeted therapeutics: Has their time arrived?

Kathleen R. Cho
Pages 430 - 431
http://dx.doi.org/10.4161/cc.11.3.19275
Abstract | PDF

Comment on: Wu R, et al. Clin Cancer Res 2011; 17:7359–72




CELL CYCLE NEWS & VIEWS

Open Access Article

Chemotherapy-induced p53-dependent and -independent DNA damage responses are enhanced by poly(ADP-ribose) polymerase (PARP) inhibition in BRCA-proficient cancer cells

Neil Johnson and Geoffrey I. Shapiro
Page 432
http://dx.doi.org/10.4161/cc.11.3.19167
Abstract | PDF

Comment on: Nguyen D, et al. Cell Cycle 2011; 10:4074-82.

Open Access Article

Myb: Getting involved in EMT

Robert Ramsay
Page 433
http://dx.doi.org/10.4161/cc.11.3.19168
Abstract | PDF

Comment on: Cesi V, et al. Cell Cycle 2011; 10:4149-61.

Open Access Article

BRAF mutation: A double-edged sword in epigenetic alterations?

Xiulong Xu
Page 434
http://dx.doi.org/10.4161/cc.11.3.19170
Abstract | PDF

Comment on: Hou P, et al. Cell Cycle 2012; 11:286-95.

Open Access Article

The proteasome activator PA28γ is a novel component of the DNA double-strand break response network

Shay Ben-Aroya
Page 435
http://dx.doi.org/10.4161/cc.11.3.19223
Abstract | PDF

Comment on: Levy-Barda A, et al. Cell Cycle 2011; 10:4300-10.

Open Access Article

Autophagy-dependent NFκB regulation

Valentina Cianfanelli and Francesco Cecconi
Pages 436 - 437
http://dx.doi.org/10.4161/cc.11.3.19224
Abstract | PDF

Comment on: Criollo A, et al. Cell Cycle 2012; 11:194-9.

Open Access Article

Polo-like kinase 2: A new exploitable target to undermine mutant p53-dependent chemoresistance

Marco Napoli, Javier E. Girardini and Giannino Del Sal
Page 438
http://dx.doi.org/10.4161/cc.11.3.19225
Abstract | PDF

Comment on: Valenti F, et al. Cell Cycle 2011; 10:4330-40.




EXTRA VIEWS

The Janus face of OSM-mediated cardiomyocyte dedifferentiation during cardiac repair and disease

Jochen Pöling, Praveen Gajawada, Holger Lörchner, Viktoria Polyakowa, Marten Szibor, Thomas Böttger, Henning Warnecke, Thomas Kubin and Thomas Braun
Pages 439 - 445
http://dx.doi.org/10.4161/cc.11.3.19024
Abstract | PDF

Dedifferentiation is a common phenomenon among plants but has only been found rarely in vertebrates where it is mostly associated with regenerative responses such as formation of blastemae in amphibians to initiate replacement of lost body parts. Relatively little attention has been paid to dedifferentiation processes in mammals although a decline of differentiated functions and acquisition of immature, "embryonic" properties is seen in various disease processes. Dedifferentiation of parenchymal cells in mammals might serve multiple purposes including (1) facilitation of tissue regeneration by generation of progenitor-like cells and (2) protection of cells from hypoxia by reduction of ATP consumption due to changes in energy metabolism and/or inactivation of energy-intensive "specialized" functions. We recently found that an inflammatory cytokine of the interleukin 6 family, oncostatin M (OSM), initiates dedifferentiation of cardiomyocytes both in vitro and in vivo. Interestingly, activation of the OSM signaling pathway protects the heart from acute myocardial ischemia but has a negative impact when continuously activated thereby promoting dilative cardiomyopathy. The strong presence of the OSM receptor on cardiomyocytes and the unique features of the OSM signaling circuit suggest a major role of OSM for cardiac protection and repair. We propose that continuous activation or malfunctions of the cellular dedifferentiation machinery might contribute to different disease conditions.

Does Δ133p53 isoform trigger inflammation and autoimmunity?

Hamish Campbell, Tania Slatter, Aaron Jeffs, Reena Mehta, Carina Rubio, Margaret Baird and Antony Braithwaite
Pages 446 - 450
http://dx.doi.org/10.4161/cc.11.3.19054
Abstract | PDF

Autoimmune diseases are characterized by the immune system mounting a response against self. The exact etiology of autoimmune diseases and autoimmunity remain unclear. Here, we demonstrate that Δ133p53, an isoform of the tumor suppressor protein p53, is involved in the development of autoimmunity. We have previously generated a mouse model of Δ133p53 (Δ122p53). Δ122p53 mice develop an autoimmune/ inflammation-like phenotype that includes the production of autoantibodies, elevated levels of pro-inflammatory cytokines and lymphocyte aggregations in various organs. Microarray analysis reveals that expression of Δ122p53 induces a number of pro-inflammatory genes, including the STAT1 pathway and interferon-related transcription profile. Comparative genetic signatures have been observed in human SLE (systemic lupus erythematosus) patients, and we show that Δ133p53 regulates STAT1 in human cells. Our findings provide the first evidence of a role for p53 isoforms in the development of autoimmune disease.

Mouse model for probing tumor suppressor activity of protein phosphatase 2A in diverse signaling pathways

Gernot Walter and Ralf Ruediger
Pages 451 - 459
http://dx.doi.org/10.4161/cc.11.3.19057
Abstract | PDF

Evidence that protein phosphatase 2A (PP2A) is a tumor suppressor in humans came from the discovery of mutations in the genes encoding the Aα and Aβ subunits of the PP2A trimeric holoenzymes, Aα-B-C and Aβ-B-C. One point mutation, Aα-E64D, was found in a human lung carcinoma. It renders Aα specifically defective in binding regulatory B’ subunits. Recently, we reported a knock-in mouse expressing Aα-E64D and an Aα knockout mouse. The mutant mice showed a 50–60% increase in the incidence of lung cancer induced by benzopyrene. Importantly, PP2A’s tumor suppressor activity depended on p53. These data provide the first direct evidence that PP2A is a tumor suppressor in mice. In addition, they suggest that PP2A is a tumor suppressor in humans. Here, we report that PP2A functions as a tumor suppressor in mice that develop lung cancer triggered by oncogenic K-ras. We discuss whether PP2A may function as a tumor suppressor in diverse tissues, with emphasis on endometrial and ovarian carcinomas, in which Aα mutations were detected at a high frequency. We propose suitable mouse models for examining whether PP2A functions as tumor suppressor in major growth-stimulatory signaling pathways, and we discuss the prospect of using the PP2A activator FTY720 as a drug against malignancies that are driven by these pathways.

Pick your poison: The Ripoptosome, a cell death platform regulating apoptosis and necroptosis

Maria Feoktistova, Peter Geserick, Diana Panayotova-Dimitrova and Martin Leverkus
Pages 460 - 467
http://dx.doi.org/10.4161/cc.11.3.19060
Abstract | PDF

At an unbelievable pace, recent evidence has emerged that demonstrates the importance of a programmed form of necrosis (necroptosis) in physiology, pathophysiology and embryonic development. It is clear that the understanding of the intracellular control of necroptosis as compared to caspase-dependent apoptosis is of paramount importance. Tumorigenesis, immune surveillance of cancer and pathogen-induced disease, to name only a few, appear to be affected by the mode of cell death in vivo. Here, we discuss the Ripoptosome, a newly defined 2 MDa intracellular signalling complex that can be formed upon genotoxic stress or loss of inhibitor-of apoptosis proteins (IAPs). The Ripoptosome is a signaling platform that can switch modes between apoptotic and necroptotic cell death. In this report, we extend our recent studies and further the notion that the stoichiometric balance between RIP1 and cIAPs is critical for Ripoptosome formation. Furthermore, we demonstrate the critical relevance of the balance of expression levels of short (cFLIPS) or viral (vFLIP) forms of FLIP and RIP3 kinase for the spontaneous execution of necroptosis whenever cIAPs are absent in the cells. Our study thus supports and extends the intriguing role of the Ripoptosome for the regulation of apoptosis and necroptosis.




PERSPECTIVE

MicroRNA/mRNA regulatory networks in the control of skin development and regeneration

Natalia Botchkareva
Pages 468 - 474
http://dx.doi.org/10.4161/cc.11.3.19058
Abstract | PDF

Skin development, postnatal growth and regeneration are governed by complex and well-balanced programs of gene activation and silencing. The crosstalk between small non-coding microRNAs (miRNAs) and mRNAs is highly important for steadiness of signal transduction and transcriptional activities as well as for maintenance of homeostasis in many organs, including the skin. Recent data demonstrated that the expression of many genes, including cell type-specific master transcription regulators implicated in the control of skin development and homeostasis, is regulated by miRNAs. In addition, individual miRNAs could mediate the effects of these signaling pathways through being their downstream components. In turn, the expression of a major constituent of the miRNA processing machinery, Dicer, can be controlled by cell type-specific transcription factors, which form negative feedback loop mechanisms essential for the proper execution of cell differentiation- associated gene expression programs and cell-cell communications during normal skin development and regeneration. This review summarizes the available data on how miRNA/mRNA regulatory networks are involved in the control of skin development, epidermal homeostasis, hair cycle-associated tissue remodeling and pigmentation. Understanding of the fundamental mechanisms that govern skin development and regeneration will contribute to the development of new therapeutic approaches for many pathological skin conditions by using miRNA-based interventions.




REVIEW

Autoregulation of kinase dephosphorylation by ATP binding in AGC protein kinases

Tung O. Chan, John Pascal, Roger Armen and Ulrich Rodeck
Pages 475 - 478
http://dx.doi.org/10.4161/cc.11.3.19059
Abstract | PDF

AGC kinases, including the three Akt (protein kinase B) isoforms, protein kinase A (PKA) and all protein kinase C (PKC) isoforms, require activation loop phosphorylation (threonine 308 in Akt1) as well as phosphorylation of a C-terminal residue (serine 473 in Akt1) for catalytic activity and phosphorylation of downstream targets. Conversely, phosphatases reverse these phosphorylations. Virtually all cellular processes are affected by AGC kinases, a circumstance that has led to intense scrutiny of the molecular mechanisms that regulate phosphorylation of these kinases. Here, we review a new layer of control of phosphorylation in Akt, PKA and PKC pointing to ATP binding pocket occupancy as a means to decelerate dephosphorylation of these and, potentially, other kinases. This additional level of kinase regulation opens the door to search for new functional motifs for the rational design of non- ATP-competitive kinase inhibitors that discriminate within and between protein kinase families.




REPORTS

Haploinsufficiency of SGO1 results in deregulated centrosome dynamics, enhanced chromosomal instability and colon tumorigenesis

Hiroshi Y. Yamada, Yixin Yao, Xiaoxing Wang, Yuting Zhang, Ying Huang, Wei Dai and Chinthalapally V. Rao
Pages 479 - 488
http://dx.doi.org/10.4161/cc.11.3.18994
Abstract | PDF

Chromosome instability (CIN) is found in 85% of colorectal cancers. Defects in mitotic processes are implicated in high CIN and may be critical events in colorectal tumorigenesis. Shugoshin-1 (SGO1) aids in the maintenance of chromosome cohesion and prevents premature chromosome separation and CIN. In addition, integrity of the centrosome may be compromised due to the deficiency of Cohesin and Sgo1 through the disengagement of centrioles. We report here the generation and characterization of SGO1-mutant mice and show that haploinsufficiency of SGO1 leads to enhanced colonic tumorigenesis. Complete disruption of SGO1 results in embryonic lethality, whereas SGO1^+/- mice are viable and fertile. Haploinsufficiency of SGO1 results in genomic instability manifested as missegregation of chromosomes and formation of extra centrosomal foci in both murine embryonic fibroblasts and adult bone marrow cells. Enhanced CIN observed in SGO1-deficient mice resulted in an increase in formation of aberrant crypt foci (ACF) and accelerated development of tumors after exposure to azoxymethane (AOM), a colon carcinogen. Together, these results suggest that haploinsufficiency of SGO1 causes enhanced CIN, colonic preneoplastic lesions and tumorigenesis in mice. SGO1 is essential for the suppression of CIN and tumor formation.

Aurora A is differentially expressed in gliomas, is associated with patient survival in glioblastoma and is a potential chemotherapeutic target in gliomas

Norman L. Lehman, James P. O'Donnell, Lisa J. Whiteley, Robert T. Stapp, Trang D. Lehman, Kathleen M. Roszka, Lonni R. Schultz, Caitlin J. Williams, Tom Mikkelsen, Stephen L. Brown, Jeffrey A. Ecsedy and Laila M. Poisson
Pages 489 - 502
http://dx.doi.org/10.4161/cc.11.3.18996
Abstract | PDF

Aurora A is critical for mitosis and is overexpressed in several neoplasms. Its overexpression transforms cultured cells, and both its overexpression and knockdown cause genomic instability. In transgenic mice, Aurora A haploinsufficiency, not overexpression, leads to increased malignant tumor formation. Aurora A thus appears to have both tumor-promoting and tumor-suppressor functions. Here, we report that Aurora A protein, measured by quantitative protein gel blotting, is differentially expressed in major glioma types in lineage-specific patterns. Aurora A protein levels in WHO grade II oligodendrogliomas (n = 16) and grade III anaplastic oligodendrogliomas (n = 16) are generally low, similar to control epilepsy cerebral tissue (n = 11). In contrast, pilocytic astrocytomas (n = 6) and ependymomas (n = 12) express high Aurora A levels. Among grade II to grade III astrocytomas (n = 7, n = 14, respectively) and grade IV glioblastomas (n = 31), Aurora A protein increases with increasing tumor grade. We also found that Aurora A expression is induced by hypoxia in cultured glioblastoma cells and is overexpressed in hypoxic regions of glioblastoma tumors. Retrospective Kaplan-Meier analysis revealed that both lower Aurora A protein measured by quantitative protein gel blot (n = 31) and Aurora A mRNA levels measured by real-time quantitative RT-PCR (n = 58) are significantly associated with poorer patient survival in glioblastoma. Furthermore, we report that the selective Aurora A inhibitor MLN8237 is potently cytotoxic to glioblastoma cells, and that MLN8237 cytotoxicty is potentiated by ionizing radiation. MLN8237 also appeared to induce senescence and differentiation of glioblastoma cells. Thus, in addition to being significantly associated with survival in glioblastoma, Aurora A is a potential new drug target for the treatment of glioblastoma and possibly other glial neoplasms.

Ribosomal stress induces L11- and p53-dependent apoptosis in mouse pluripotent stem cells

Lucia Morgado-Palacin, Susana Llanos and Manuel Serrano
Pages 503 - 510
http://dx.doi.org/10.4161/cc.11.3.19002
Abstract | PDF

Ribosome biogenesis is the most demanding energetic process in proliferating cells and it is emerging as a critical sensor of cellular homeostasis. Upon disturbance of ribosome biogenesis, specific free ribosomal proteins, most notably L11, bind and inhibit Mdm2, resulting in activation of the tumor suppressor p53. This pathway has been characterized in somatic and cancer cells, but its function in embryonic pluripotent cells has remained unexplored. Here, we show that treatment with low doses of Actinomycin D or depletion of ribosomal protein L37, two well-established inducers of ribosomal stress, activate p53 in an L11-dependent manner in mouse embryonic stem cells (ESCs) and in induced pluripotent stem cells (iPSCs). Activation of p53 results in transcriptional induction of p53 targets, including p21, Mdm2, Pidd, Puma, Noxa and Bax. Finally, ribosomal stress elicits L11- and p53-dependent apoptosis in ESCs/iPSCs. These results extend to pluripotent cells the functionality of the ribosomal stress pathway and we speculate that this could be a relevant cellular checkpoint during early embryogenesis.

TRIM8 modulates p53 activity to dictate cell cycle arrest

Mariano Francesco Caratozzolo, Lucia Micale, Maria Giuseppina Turturo, Silvia Cornacchia, Carmela Fusco, Flaviana Marzano, Bartolomeo Augello, Anna Maria D'Erchia, Luisa Guerrini, Graziano Pesole, Elisabetta Sbisà, Giuseppe Merla and Apollonia Tullo
Pages 511 - 523
http://dx.doi.org/10.4161/cc.11.3.19008
Abstract | PDF

p53 is a central hub in controlling cell proliferation. To maintain genome integrity in response to cellular stress, p53 directly regulates the transcription of genes involved in cell cycle arrest, DNA repair, apoptosis and/or senescence. An array of post-translational modifications and protein-protein interactions modulates its stability and activities in order to avoid malignant transformation. However, to date it is still not clear how cells decide their own fate in response to different types of stress. We described here that the human TRIM8 protein, a member of the TRIM family, is a new modulator of the p53-mediated tumor suppression mechanism. We showed that under stress conditions, such as UV exposure, p53 induced the expression of TRIM8, which in turn stabilized p53 leading to cell cycle arrest and reduction of cell proliferation through enhancement of CDKN1A (p21) and GADD45 expression. TRIM8 silencing reduced the capacity of p53 to activate genes involved in cell cycle arrest and DNA repair, in response to cellular stress. Concurrently, TRIM8 overexpression induced the degradation of the MDM2 protein, the principal regulator of p53 stability. Co-immunoprecipitation experiments showed that TRIM8 physically interacted with p53, impairing its interaction with MDM2. Altogether, our results reveal a previously unknown regulatory pathway controlling p53 activity and suggest TRIM8 as a novel therapeutic target to enhance p53 tumor suppressor activity.

Cdc6 is required for meiotic spindle assembly in Xenopus oocytes

Yadushyla Narasimhachar, Daniel R. Webster, David L. Gard and Martine Coué
Pages 524 - 531
http://dx.doi.org/10.4161/cc.11.3.19033
Abstract | PDF

During the maturation of Xenopus oocytes, Cdc6 expression is necessary to establish replication competence to support early embryonic DNA replication. However, Cdc6 is expressed before the completion of MI, at a time when its function as a replication factor is not required, suggesting additional roles for Cdc6 in meiosis. Confocal immunofluorescence microscopy revealed that Cdc6 protein was distributed around the spindle precursor at the time of germinal vesicle breakdown (GVBD), and localized to the margin of the nascent spindle early in prometaphase. Cdc6 subsequently localized to spindle poles in late prometaphase, where it remained until metaphase arrest. Microinjection of antisense oligonucleotides specific for Cdc6 mRNA disrupted spindle assembly, resulting in defects including delayed spindle assembly, misoriented and unattached anaphase spindles, monasters, multiple spindles, microtubule aggregates associated with condensed chromosomes, or the absence of recognizable spindle-like structures, depending on the level of residual Cdc6 expression. Furthermore, Cdc6 co-localized with γ-tubulin in centrosomes during interphase in all somatic cells analyzed, and associated with spindle poles in mitotic COS cells. Our data suggest a role for Cdc6 in spindle formation in addition to its role as a DNA replication factor.

GSK3β regulates Bcl2L12 and Bcl2L12A anti-apoptosis signaling in glioblastoma and is inhibited by LiCl

Chia-Hua Chou, An-Kuo Chou, Ching-Chih Lin, Wei-Jay Chen, Chih-Chang Wei, Ming-Chang Yang, Ching-Mei Hsu, For-Wey Lung, Joon-Khim Loh, Shen-Long Howng and Yi-Ren Hong
Pages 532 - 542
http://dx.doi.org/10.4161/cc.11.3.19051
Abstract | PDF

BCL2L12 has been reported to be involved in post-mitochondrial apoptotic events in glioblastoma, but the role of BCL2L12A, a splicing variant of BCL2L12, remains unknown. In this study, we showed that BCL2L12 and BCL2L12A were overexpressed in glioblastoma multiforme (GBM). Large-scale yeast two-hybrid screening showed that BCL2L12 was a GSK3b binding partner in a testis cDNA library. Our data demonstrated that GSK3b interacts with BCL2L12 but not BCL2L12A, whose C terminus lacks a binding region. We found that a BCL2L12_153–191 fragment located outside of the C-terminal BH2 motif is responsible for GSK3b binding. In contrast, no interaction was detected between BCL2L12A and GSK3b. In vitro kinase and l-phosphatase assays showed that GSK3b phosphorylates BCL2L12 at S156, while this site is absent on BCL2L12A. Moreover, our data also showed that the BCL2L12_153–191 fragment directly interrupted GSK3bmediated Tau phosphorylation in a dose-dependent manner. Ectopic expression of GFP-fused BCL2L12 or BCL2L12A in U87MG cells leads to repression of apoptotic markers and protects against staurosporine (STS) insults, indicating an antiapoptotic role for both BCL2L12 and BCL2L12A. In contrast, no anti-apoptotic ability was seen in BCL2L12(S156A). When BCL2L12-expressing U87MG cells were co-administrated with STS and LiCl, cells underwent apoptosis. This effect could be reversed by LiCl. In short, we established a model to demonstrate that GSK3b interacts with and phosphorylates BCL2L12 and might also affect BCL2L12A to modulate the apoptosis signaling pathway in glioblastoma. These findings suggest that LiCl may be a prospective therapeutic agent against GBM.

 p53 is not directly relevant to the response of Polo-like kinase 1 inhibitors

Mourad Sanhaji, Nina-Naomi Kreis, Brigitte Zimmer, Thorsten Berg, Frank Louwen and Juping Yuan
Pages 543 - 553
http://dx.doi.org/10.4161/cc.11.3.19076
Abstract | PDF

Polo-like kinase 1 (Plk1) is elementary for cell proliferation and its deregulation is involved in tumorigenesis. Plk1 has been established as one of the most attractive targets for molecular cancer therapy. In fact, multiple small molecule inhibitors targeting either the kinase domain or the Polo-box binding domain (PBD) of Plk1 have been identified and intensively investigated. Intriguingly, Plk1 depletion affects more cancer cells than normal cells. It is also reported that the cytotoxicity induced by Plk1 inhibition is elevated in cancer cells with defective p53. The data lead to the hypothesis that p53 might be a predictive marker for the response of Plk1 inhibition. In this study, we demonstrate that there is no obvious different cytotoxic response between cancer cells with and without functional p53, including the isogenic colon cancer cell lines HCT116p53(+/+) and HCT116p53(-/-), breast cancer cell line MCF7, lung cancer cell line A549 and cervical carcinoma cell line HeLa, after treatment with either siRNA against Plk1, the kinase domain inhibitors BI 2536 and BI 6727 or the PBD inhibitor Poloxin. We suggest that the p53 status is not a predictor for the response of Plk1 inhibition, at least not directly. Yet, the long-term outcomes of losing p53, such as genome instability, could be associated with the cytotoxicity of Plk1 inhibition. Further studies are required to investigate whether other circumstances of cancer cells, such as DNA replication/damage stress, mitotic stress, and metabolic stress, which make possibly the survival of cancer cells more dependent on Plk1 function, are responsible for the sensitivity of Plk1 inhibition.

Drosophila cyclin D/Cdk4 regulates mitochondrial biogenesis and aging and sensitizes animals to hypoxic stress

Amalia Icreverzi, Aida Flor de la Cruz, Wayne A. Van Voorhies and Bruce A. Edgar
Pages 554 - 568
http://dx.doi.org/10.4161/cc.11.3.19062
Abstract | PDF

Drosophila cyclinD (CycD) is the single fly ortholog of the mammalian cyclin D1 and promotes both cell cycle progression and cellular growth. However, little is known about how CycD promotes cell growth. We show here that CycD/Cdk4 hyperactivity leads to increased mitochondrial biogenesis (mitobiogenesis), mitochondrial mass, NRF-1 activity (Tfam transcript levels) and metabolic activity in Drosophila, whereas loss of CycD/Cdk4 activity has the opposite effects. Surprisingly, both CycD/Cdk4 addition and loss of function increase mitochondrial superoxide production and decrease lifespan, indicating that an imbalance in mitobiogenesis may lead to oxidative stress and aging. In addition, we provide multiple lines of evidence indicating that CycD/Cdk4 activity affects the hypoxic status of cells and sensitizes animals to hypoxia. Both mitochondrial and hypoxia-related effects can be detected at the global transcriptional level. We propose that mitobiogenesis and the hypoxic stress response have an antagonistic relationship, and that CycD/Cdk4 levels regulate mitobiogenesis contemporaneous to the cell cycle, such that only when cells are sufficiently oxygenated can they proliferate.

The metallophosphodiesterase Mpped2 impairs tumorigenesis in neuroblastoma

Lucia Liguori, Immacolata Andolfo, Paqualino De Antonellis, Veruska Aglio, Valeria di Dato, Natascia Marino, Nicola Ivan Orlotti, Daniela De Martino, Mario Capasso, Giuseppe Petrosino, Alexander Schramm, Luigi Navas, Gian Paolo Tonini, Angelika Eggert, Achille Iolascon and Massimo Zollo
Pages 569 - 581
http://dx.doi.org/10.4161/cc.11.3.19063
Abstract | PDF

Through microarray analyses, we identified the Mpped2 gene as differentially expressed in two neuroblastoma cell lines induced to differentiation with all-trans retinoic acid. Mpped2 codes for a new metallophosphodiesterase protein, the expression of which inhibits cell proliferation and soft agar colony formation in SH -SY5Y cells. This inhibition is concomitant to an increased proportion of the cells in G0/G1 phase and enhanced caspase 3 activation, effects not seen for the other phosphodiesterases. A Mpped2-null mutation (H67R) abrogates these functions, which indicates that the biochemical activity of Mpped2 is advantageous for cancer suppression. Expression analyses in the “Los Angeles” and “Essen” neuroblastoma gene-array data sets show that increased expression of Mpped2 is associated with good patient prognosis according to Kaplan-Meier analyses. Tumorigenic assays in mice show that overexpression of Mpped2 improves survival rate, substantially impairs tumor growth and induces neuronal differentiation. Altogether, these data show that Mpped2 expression impairs neuroblastoma tumorigenesis, and they establish a basis for future therapeutic applications.

Downregulation of Mdm2 and Mdm4 enhances viral gene expression during adenovirus infection

Heng Yang, Zhi Zheng, Lisa Zhao, Qiang Li and Daiqing Liao
Pages 582 - 593
http://dx.doi.org/10.4161/cc.11.3.19052
Abstract | PDF

Successful viral replication entails elimination or bypass of host antiviral mechanisms. Here, we show that shRNA-mediated knockdown of murine double minute (Mdm2) and its paralog Mdm4 enhanced the expression of early and late viral gene products during adenovirus (HAdV) infection. Remarkably, whereas the expression of HAdV genes was low in p53-deficient mouse embryonic fibroblasts (p53KO MEFs), the HAdV early gene products were efficiently expressed in Mdm2/p53 double-knockout (DKO) and Mdm4/p53 DKO MEFs, and viral capsid proteins were produced in Mdm2/p53 DKO MEFs. Thus, Mdm2 and Mdm4 seem to have potent antiviral property. In cells infected with wt HAdV or a mutant virus lacking the E1B-55K gene (dl1520), both Mdm2 and Mdm4 were rapidly depleted, whereas replication-deficient mutant viruses (Ad-GFP) or ΔpTP with deletions within the coding sequence of preterminal binding protein failed to induce their downregulation. Reduced expression of Mdm2 and Mdm4 was not due to general shutoff of host protein synthesis. Additionally, expression of a dominant-negative mutant of Cul5 did not affect Mdm2/Mdm4 downregulation. Thus, viral replication but not the presence of E1B-55K is required for Mdm2/Mdm4 degradation. Surprisingly, treatment of HAdV-infected cells with proteasome inhibitor MG132 only partially restored the protein levels of Mdm2 and Mdm4, suggesting that they may also be downregulated through an additional mechanism independent of proteasome. Interestingly, cyclin D1 and p21 appear to be downregulated similarly during HAdV infection. Collectively, our work provides the first biochemical evidence for antiviral function of Mdm2 and Mdm4 and that viruses employ efficient countermeasure to ensure viral replication.

mTOR-independent 4E-BP1 phosphorylation is associated with cancer resistance to mTOR kinase inhibitors

Yanjie Zhang and X.F. Steven Zheng
Pages 594 - 603
http://dx.doi.org/10.4161/cc.11.3.19096
Abstract | PDF

ATP -competitive mTO R kinase inhibitors (mTorKIs) are a new generation of mTO R-targeted agents with more potent anticancer activity than rapamycin in several tumor models. However, the sensitivity and resistance of cancer cells to mTorKIs remain poorly understood. In this study, we tested mTorKIs against a large panel of colorectal cancer (CRC) cell lines, and found that mTorKIs displayed broader anti-CRC activity than rapamycin, including CRC cells with K-Ras or B-Raf mutations, suggesting that these mTorKIs are particularly useful for CRCs resistant to EGFR inhibitors. Unexpectedly, we found that 40% CRC cell lines were intrinsically drug resistant. Moreover, we discovered an mTO R-independent 4E‑ BP1 phosphorylation that was correlated with mTorKI resistance. Altogether, our findings provide compelling preclinical support for testing mTorKIs in human CRC clinical trials. They further reveal the existence of significant intrinsic mTorKI drug resistance in cancer cells and suggest that 4E-BP1 phosphorylation is a predictive biomarker for mTorKI sensitivity and resistance.

Cyclin G-associated kinase regulates protein phosphatase 2A by phosphorylation of its B'γ subunit

Yoko Naito, Hiroyuki Shimizu, Takashi Kasama, Jun Sato, Hiroe Tabara, Ayumi Okamoto, Norikazu Yabuta and Hiroshi Nojima
Pages 604 - 616
http://dx.doi.org/10.4161/cc.11.3.19114
Abstract | PDF

Protein phosphatase 2A (PP2A) bearing the B’γ (= B’α/B56γ1/PR61γ) subunit is recruited to dephosphorylation targets by cyclin G. We demonstrate here that cyclin G-associated kinase (GAK), a component of the GAK/B’γ/cyclin G complex, directly phosphorylates the B’γ-Thr104 residue and regulates PP2A activity. Indeed, an anti-B’γ-pT104 antibody detected immunofluorescence signals at the chromosome and centrosome during mitosis; these signals were reduced by siRNA-mediated GAK knockdown. After DNA damage by γ-irradiation, the chromosome signals formed foci that colocalized with a DNA double-strand break (DSB) marker H2AX-pS139 (γH2AX) and CHK2-pT68. Moreover, B’γ-pT104 enhanced PP2A holoenzyme assembly and PP2A activity, as shown by the results of an in vitro phosphatase assay. These results suggest a novel role for GAK as a regulator of dephosphorylation events under the control of the PP2A B’γ subunit.

Brg1 regulates the transcription of human papillomavirus type 18 E6 and E7 genes

Hongpeng He and Yan Luo
Pages 617 - 627
http://dx.doi.org/10.4161/cc.11.3.19115
Abstract | PDF

Integrated high-risk human papillomavirus (HPV) DNA was frequently detected in the genomes of cervical carcinoma cells. The HPV E6 and E7 oncoproteins disrupt the functions of tumor suppressors p53 and Rb; thus, understanding the mechanism by which HPV E6 and E7 gene expression is regulated in cancer cells is highly relevant to cancer biology. Brg1 is a catalytic subunit of the SWI/SNF chromatin remodeling complexes that function in the transcriptional regulation of certain cellular genes. Here, we show that knockdown of Brg1 in HeLa cells leads to cell cycle arrest, p53 and Rb protein accumulation and, interestingly, downregulated expression of HPV18 E6 and E7 genes. Brg1 binds the HPV18 LCR in a JunB- and p300-dependent manner and is required for efficient recruitment of RNA polymerase II to the HPV18 LCR. The function of Brg1 in HPV18 gene regulation is unique given that its homolog Brm does not play a role in this regulatory pathway, and this may help design target-specific intervention strategies.

Inhibition and eradication of human glioma with tumor-targeting Salmonella typhimurium in an orthotopic nude-mouse model

Masashi Momiyama, Ming Zhao, Hiroaki Kimura, Benjamin Tran, Takashi Chishima, Michael Bouvet, Itaru Endo and Robert M. Hoffman
Pages 628 - 632
http://dx.doi.org/10.4161/cc.11.3.19116
Abstract | PDF

Malignant glioma tumors are the most common primary central nervous system tumors. Despite the multidisciplinary approach to treatment, prognosis remains poor. In this study, we demonstrated that the Salmonella typhimurium A1-R tumor-targeting strain can inhibit and eradicate human glioma in an orthotopic nude-mouse model. S. typhimurium A1-R was administered by injection through a craniotomy open-window or intravenously in nude mice. To establish the model, 2 x 105 U87-RFP human glioma cells were injected stereotactically into the mouse brain through the craniotomy open window. Two weeks after glioma-cell implantation, mice were treated with S. typhimurium A1-R [2 x 10⁷ CFU/200 μl intravenous injection (i.v.) or 1 x 10⁶ CFU/1 μl intracranial injection (i.c.)] once a week for 3 weeks. Brain tumors were observed by fluorescence imaging through the craniotomy open window over time. S. typhimurium A1-R, administered i.c., inhibited brain tumor growth 7.6-fold compared with untreated mice (p = 0.009) and improved survival 73% (p = 0.001). Two of ten mice appeared to have their tumors eradicated. Intravenous administration of S. typhimurium A1-R was not effective. The craniotomy open window enabled observation of tumor growth in the brain in real time in both treated and untreated mice. The results of the present study demonstrate that bacterial therapy of brain cancer is a novel, effective and safe treatment strategy in a highly treatment-resistance cancer.