Table of Contents

Volume 5, Issue 23

  December 1, 2006

  Pages 2697 - 2826

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 Issue Catalogue (MARC XML)

EXTRA VIEWS

Open Access Article

Senescence, Wound Healing, and Cancer: the PAI-1 Connection

Roderik M. Kortlever and Rene Bernards
Pages 2697 - 2703
http://dx.doi.org/10.4161/cc.5.23.3510
Abstract | PDF

Prolonged propagation of primary diploid fibroblasts in culture activates an ageing process known as replicative senescence, which is considered to provide a barrier against oncogenic transformation. Remarkably, both cell autonomous tumor-suppressive and cell non-autonomous tumor-promoting effects of senescent cells have been reported. Recently, we described that the p53 target gene plasminogen activator inhibitor-1 (PAI-1) is an essential mediator of replicative senescence. PAI-1 antagonizes the protease urokinase-type plasminogen activator (uPA). Both are secreted factors and involved in heterotypic signaling processes such as wound healing, angiogenesis and metastasis. Both uPA and PAI-1 are expressed in senescent cells and their relative abundance controls proliferation downstream of p53. Here, we present data that the effects of PAI- 1 and uPA in the senescence response are not strictly cell autonomous. We discuss these findings in the context of the emerging roles of PAI-1 and uPA in heterotypic cellular signaling in senescence, wound healing and metastasis.

Open Access Article

Notch and Minichromosome Maintenance (MCM) Proteins: Integration of Two Ancestral Pathways in Cell Cycle Control

Michela Noseda and Aly Karsan
Pages 2704 - 2709
http://dx.doi.org/10.4161/cc.5.23.3515
Abstract | PDF

Notch transmembrane receptors govern a highly evolutionarily conserved intercellular signaling mechanism activated by the engagement of Notch receptors by their cognate ligands expressed on neighboring cells. The subsequently cleaved intracellular domain of Notch receptors translocates to the nucleus where it interacts with the transcriptional regulator CSL, thereby regulating expression of target genes. The Notch pathway controls cell fate by regulating proliferation, differentiation, and apoptosis. Mini-chromosome maintenance (MCM) proteins are components of the pre-replicative complex (pre-RC) that are essential for DNA replication. It has recently been shown that activated Notch downregulates mini-chromosome-maintenance (MCM) proteins MCM2 and MCM6 by a CSL-dependent mechanism. Here, we review the canonical pathway mediated by Notch receptors and discuss recent findings connecting the Notch pathway with the ancestral MCM complex during cell cycle progression.

Open Access Article

Genome Maintenance and Mutagenesis in Embryonic Stem Cells

Qing Lin, Sarah L Donahue and H Earl Ruley
Pages 2710 - 2714
http://dx.doi.org/10.4161/cc.5.23.3517
Abstract | PDF

Widespread loss of heterozygosity (LOH) in cancer cells is often thought to result from chromosomal instability caused by mutations affecting DNA repair/genome maintenance; however, the origin of LOH in most tumors is unknown. In a recent study, we examined the ability of carcinogenic agents to induce LOH in diploid mouse embryo-derived stem (ES) cells. Brief exposures to non-toxic levels of several carcinogens stimulated genome-wide LOH, with maximum per-gene frequencies approaching one percent. These results suggest that LOH contributes significantly to the carcinogenicity of a variety of mutagens, and that genome-wide LOH may result from prior exposure to genotoxic agents rather than from a state of chromosomal instability during the carcinogenic process. Mechanisms in stem cells that influence carcinogen-induced LOH are likely to play central roles in the etiology of non-hereditary cancers that often arise after extensive carcinogen exposures.

Open Access Article

Applications of Fluorescence for Detecting Rare Sequence Rearrangements In Vivo

Dominika M Wiktor-Brown, Carrie A Hendricks, Werner Olipitz, Arlin Rogers and Bevin Engelward
Pages 2715 - 2719
http://dx.doi.org/10.4161/cc.5.23.3527
Abstract | PDF

Homologous recombination (HR) is an important pathway for the accurate repair of potentially cytotoxic or mutagenic double strand breaks (DSBs), as well as double strand ends that arise due to replication fork breakdown. Thus, measuring HR events can provide information on conditions that induce DSB formation and replicative stress. To study HR events in vivo, we previously developed Fluorescent Yellow Direct Repeat (FYDR) mice in which a recombination event at an integrated transgene yields a fluorescent signal. Recently, we published an application of these mice demonstrating that fluorescent recombinant cells can be directly detected within intact pancreatic tissue. Here, we show that in situ imaging is a more sensitive method for detecting exposure-induced recombinant cells, yielding statistical significance with smaller cohorts. In addition, we show inter-mouse and gender-dependent variation in transgene expression, examine its impact on data interpretation, and discuss solutions to overcoming the effects of such variation. Finally, we also present data on EYFP expression, showing that several tissues, in addition to the pancreas, may be amenable for in situ detection of recombinant cells in the FYDR mice. The FYDR mice provide a unique tool for identifying genetic conditions and environmental exposures that induce genotoxic stress in a variety of tissues.

Open Access Article

Degradation of the Hypoxia-Inducible Factor 1α, Where Does it Happen?

Teresa Pereira, Xiaowei Zheng and Lorenz Poellinger
Pages 2720 - 2722
http://dx.doi.org/10.4161/cc.5.23.3536
Abstract | PDF

Adaptive responses to hypoxia are essential for the survival of all organisms. Under hypoxic conditions, the transcription of a large group of genes relevant for oxygen homeostasis is induced by the hypoxia-inducible factor-1 (HIF-1). These genes encode proteins that enable the cells to adapt to limiting oxygen levels by increasing oxygen delivery through induction of angiogenesis or erythopoiesis and producing ATP under anerobic conditions. The stability of HIF-1α protein is also target of O₂ regulation. At normoxia HIF-1α is hydroxylated at specific proline residues by a recently identified family of prolyl hydroxyalses. Hydroxylated HIF-1α is recognized by the Von Hippel-Lindau tumor suppressor gene product (pVHL) as an ubiquitylation substrate that leads to proteasomal-dependent degradation of HIF-1α. We have recently demonstrated that the major subcellular compartment where degradation of HIF-1α occurs is dependent on the levels of proteosomal activity and on the localization of HIF-1α. Furthermore we have shown that the localization of HIF-1α degradation is a cell type-characteristic parameter. These observations indicate new levels of complexity in the regulation of HIF-1α degradation.




PERSPECTIVES

Open Access Article

FGFR3 Mutations in Benign Skin Tumors

Christian Hafner, Thomas Vogt and Arndt Hartmann
Pages 2723 - 2728
http://dx.doi.org/10.4161/cc.5.23.3509
Abstract | PDF

Activating FGFR3 germline mutations cause skeletal dysplasia and craniosynostosis syndromes. Somatic FGFR3 mutations have been identified in several cancer entities such as urothelial carcinoma and multiple myeloma. Recently, the same FGFR3 mutations known from skeletal dysplasia syndromes and urothelial carcinoma have been shown to cause benign human skin tumors such as seborrheic keratoses and epidermal nevi. The underlying mechanisms for the somatic FGFR3 mutations in the epidermis are unknown so far, as well as details of the involved signaling pathways in the mutant keratinocytes leading to the formation of acanthotic skin tumors. Herein we discuss potential mechanisms and functional consequences of activating FGFR3 mutations in human skin. Further studies are required to provide insights in the pathogenesis of benign skin tumors caused by FGFR3 mutations. These studies will add to new non-invasive therapeutical strategies for benign acanthotic skin tumors in dermatology.

Open Access Article

The Association of Tap42-Phosphatase Complexes with TORC1 — Another Level of Regulation in Tor Signaling

Charles J Di Como and Yu Jiang
Pages 2729 - 2732
http://dx.doi.org/10.4161/cc.5.23.3516
Abstract | PDF

In the budding yeast Saccharomyces cerevisiae, rapamycin has been known to induce a rapid dephosphorylation of many downstream targets of Tor. The key components mediating this dephosphorylation process are the Tap42-associated phosphatases, which become active upon rapamycin treatment. However, the mechanism by which rapamycin rapidly activates phosphatases is unclear. A recent report has provided evidence demonstrating a physical association of the Tap42-phosphatase complexes with TORC1, which is sensitive to rapamycin treatment or nutrient starvation. This association adds another level of regulation in Tor signaling, and explains why rapamycin or nutrient availability is able to initiate a rapid and robust response in the cell.

Open Access Article

Motors and Their Tethers: The Role of Secondary Binding Sites in Processive Motility

Margaret M Kincaid and Stephen J King
Pages 2733 - 2737
http://dx.doi.org/10.4161/cc.5.23.3521
Abstract | PDF

Cytoskeletal motors convert the energy from binding and hydrolyzing ATP into conformational changes that direct movement along a cytoskeletal polymer substrate. These enzymes utilize different mechanisms to generate long-range motion on the order of a micron or more that is required for functions ranging from muscle contraction to transport of growth factors along a nerve axon. Several of the individual cytoskeletal motors are processive, meaning that they have the ability to take sequential steps along their polymer substrate without dissociating from the polymer. This ability to maintain contact with the polymer allows individual motors to move cargos quickly from one cellular location to another. Many of the processive motors have now been found to utilize secondary binding sites that aid in motor processivity.

Open Access Article

Depletion of Histone Deacetylase I Protein: A Common Consequence of Inflammatory Cytokine Signaling?

Y.N. Vashisht Gopal and Michael Van Dyke
Pages 2738 - 2743
http://dx.doi.org/10.4161/cc.5.23.3522
Abstract | PDF

The dynamics of histone acetylation and deacetylation have long been known to influence gene expression by cellular signaling pathways. However, the mechanisms that regulate histone acetyl transferases (HATs) and histone deacetylases (HDACs) by these pathways have only recently become the focus of scientific investigation, spurred by increasing knowledge that HDACs can promote cancer growth. We recently reported that pro-inflammatory signals such as tumor necrosis factor α (TNFα) induce HDAC1 ubiquitination and proteasomal degradation through the IκB kinase IKKβ. The resulting depletion of cellular HDAC1 levels lead to a consequent depletion of HDAC1 associated with the CDKN1A gene promoter and increased expression of its protein product, p^21WAF1/CIP1. This phenomenon heralds a unique mechanism of HDAC regulation that modulates the pro-inflammatory activity of TNFα and other cytokines at the level of gene expression. Here we discuss the current knowledge of pro-inflammatory cytokine-induced regulation of gene expression, emphasizing the involvement of HDAC1, and its possible implications in inflammation, cancer, and their therapy.

Open Access Article

Mapping Cellular Routes of Ras: A Ubiquitin Trail

Natalia Jura and Dafna Bar-Sagi
Pages 2744 - 2747
http://dx.doi.org/10.4161/cc.5.23.3532
Abstract | PDF

The three mammalian Ras isoforms: HRas, NRas and KRas have been widely implicated in the control of cell proliferation, survival, motility and transformation. Although nearly identical with respect to their catalytic and effector-binding properties, HRas, NRas and KRas lead to different biological outcomes in development, cell growth and cancer. This functional distinction is believed to result at least in part from the differential membrane compartmentalization of Ras isoforms. The different distribution of Ras proteins in cellular membranes dictates unique spatio-temporal patterns of activation of effector pathways. This perspective focuses on the factors that control membrane compartmentalization of Ras with an emphasis on a recently discovered novel posttranslational modification of Ras—ubiquitination. The properties of Ras ubiquitination, its contribution to the regulation of Ras intracellular trafficking and finally the influence of Ras ubiquitination on its signaling potential are discussed.

Open Access Article

Molecular Imaging of Human Embryonic Stem Cells: Keeping an Eye on Differentiation, Tumorigenicity and Immunogenicity

Koen E.A. van der Bogt, Rutger-Jan Swijnenburg, Feng Cao and Joseph C. Wu
Pages 2748 - 2752
http://dx.doi.org/10.4161/cc.5.23.3533
Abstract | PDF

Human embryonic stem cells (hESCs) are capable of differentiation into every cell type of the human being. They are under extensive investigation for their regenerative potential in a variety of debilitating diseases. However, the field of hESC research is still in its infancy, as there are several critical issues that need to be resolved before clinical translation. Two major concerns are the ability of undifferentiated hESCs to form teratomas and the possibility of a provoked immune reaction after transplantation of hESCs into a new host. Therefore, it is imperative to develop non-invasive imaging modalities that allow for longitudinal, repetitive, and quantitative assessment of transplanted cell survival, proliferation, and migration in vivo. Reporter gene-based molecular imaging offers these characteristics and has great potential in the field of stem cell therapy. Moreover, it has recently been shown that reporter gene imaging can be combined with therapeutic strategies. Here, we provide an outline of the current status of hESC research and discuss the concerns of tumorigenicity and immunogenicity. Furthermore, we describe how molecular imaging can be utilized to follow and resolve these issues.




REPORTS

Open Access Article

Expression of EWS-ETS Fusions in NIH3T3 Cells Reveals Significant Differences to Ewing’s Sarcoma

Chi L. Braunreiter, Jeffery D Hancock, Cheryl Coffin, Kenneth M Boucher and Stephen L. Lessnick
Pages 2753 - 2759
http://dx.doi.org/10.4161/cc.5.23.3505
Abstract | PDF

Ewing’s sarcomas contain specific chromosomal translocations that fuse EWS to ETS family members, including FLI, ERG, FEV, ETV1 and ETV4. Prior work has suggested that functional differences exist between some of these EWS-ETS fusions. However, as the cell of origin of Ewing’s sarcoma is unknown, this prior work was conducted in NIH3T3 cells, which have not been validated as an appropriate model for the study of EWS-ETS fusions. To determine if NIH3T3 cells are a good model for Ewing’s sarcoma, we introduced all five EWS-ETS fusions into these cells, and analyzed their phenotypes and gene expression patterns. EWS-FLI, EWS-ERG, and EWS-FEV caused NIH3T3 cells to exhibit anchorage independent growth whereas EWS-ETV1 and EWS-ETV4 did not. In contrast, all the EWS-ETS fusions induced tumor formation in a xenograft model. We defined the core transcriptional profile of the EWS-ETS fusions using cDNA microarrays, and compared these to data derived from patient-derived Ewing’s sarcoma cell lines. The NIH3T3 model did not recapitulate the gene expression pattern of bona fide Ewing’s sarcoma. Based on these results, we conclude that while there may be functional differences between the various EWS-ETS fusions, the NIH3T3 cell model is inadequate to study the gene expression pattern induced by EWS-ETS proteins in Ewing’s sarcoma. Thus, data derived from the NIH3T3 model system needs to be appropriately validated before they can be accepted as relevant to the human disease.

Open Access Article

Structural Basis for the Modulation of CDK-Dependent/Independent Activity of Cyclin D1

Jean-Luc Ferrer, Jerome Dupuy, Franck Borel, Lilian Jacquamet, Joseph P. Noel and Vjekoslav Dulic
Pages 2760 - 2768
http://dx.doi.org/10.4161/cc.5.23.3506
Abstract | PDF

D-type cyclins are key regulators of the cell division cycle. In association with Cyclin Dependent Kinases (CDK) 2/4/6, they control the G1/S-phase transition in part by phosphorylation and inactivation of tumor suppressor of retinoblastoma family. Defective regulation of the G1/S transition is a well-known cause of cancer, making the cyclin D1-CDK4/6 complex a promising therapeutic target. Our objective is to develop inhibitors that would block the formation or the activation of the cyclin D1-CDK4/6 complex, using in silico docking experiments on a structural homology model of the cyclin D1-CDK4/6 complex. To this end we focused on the cyclin subunit in three different ways: (i) targeting the part of the cyclin D1 facing the N-terminal domain of CDK4/6, in order to prevent the dimer formation; (ii) targeting the part of the cyclin D1 facing the C-terminal domain of CDK4/6, in order to prevent the activation of CDK4/6 by blocking the T-loop in an inactive conformation, and also to destabilize the dimer; (iii) targeting the groove of cyclin D1 where p21 binds, in order to mimic its inhibition mode by preventing binding of cyclin D1-CDK4/6 complex to its targets. Our strategy, and the tools we developed, will provide a computational basis to design lead compounds for novel cancer therapeutics, targeting a broad range of proteins involved in the regulation of the cell cycle.

Open Access Article

Studying The Right Cell In Acute Myelogenous Leukemia: Dynamic Changes Of Apoptosis And Signal Transduction Pathway Protein Expression In Chemotherapy Resistant Ex-Vivo Selected “Survivor Cells”

Steven M. Kornblau, Yi Hua Qiu, BN Bekele, Jenny Straka Cade, Xiao Zhou, David Harris, Ellen Jackson, Zeev Estrov and Michael Andreeff
Pages 2769 - 2777
http://dx.doi.org/10.4161/cc.5.23.3507
Abstract | PDF

We hypothesized that studying protein expression in cells surviving in vitro chemotherapy (“survivor cells”, SV), could provide more important insight into the biology of drug-resistant AML cells than analysis of the bulk population of leukemic cells. Leukemia-enriched samples from 79 patients with new or relapsed AML were cultured for 4 days ± cytarabine (5-10 μM). Early apoptotic cells were removed to yield purified SV. Expression of BCL2, bax, PKCα, ERK2, and pERK2 proteins was measured using laser scanning cytometry. The SV population was enriched for CD34+ stem cells. Protein expression patterns in SV differed considerably from those in controls; culture and reanalysis of protein expression revealed stability, reversion, or new patterns of change. Patterns of pairs or triads of proteins were nonrandomly distributed and appeared at statistically unlikely frequencies, suggesting preferential adoption of certain patterns. The patterns of change were highly predictive of remission attainment, relapse, and survival in univariate and multivariate analysis. We conclude that in vitro SV cells have protein expression patterns distinct from those of the bulk population of leukemic cells and that these patterns are predictive of outcome. Analysis of SV cells may be more informative than analysis of the bulk population of leukemia cells.

Open Access Article

Concomitant Inhibition of MDM2 and Bcl-2 Protein Function Synergistically Induce Mitochondrial Apoptosis in AML

Kensuke Kojima, Marina Konopleva, Ismael J Samudio, Wendy D Schober, William Bornmann and Michael Andreeff
Pages 2778 - 2786
http://dx.doi.org/10.4161/cc.5.23.3520
Abstract | PDF

Disruption of Mdm2-p53 interaction activates p53 signaling, disrupts the balance of antiapoptotic and proapoptotic Bcl-2 family proteins and induces apoptosis in acute myeloid leukemia (AML). Overexpression of Bcl-2 may inhibit this effect. Thus, functional inactivation of antiapoptotic Bcl-2 proteins may enhance apoptogenic effects of Mdm2 inhibition. We here investigate the potential therapeutic utility of combined targeting of Mdm2 by Nutlin-3a and Bcl-2 by ABT-737, recently developed inhibitors of protein-protein interactions. Nutlin-3a and ABT-737 induced Bax conformational change and mitochondrial apoptosis in AML cells in a strikingly synergistic fashion. Nutlin-3a induced p53-mediated apoptosis predominantly in S and G₂/M cells, while cells in G₁ were protected through induction of p21. In contrast, ABT-737 induced apoptosis predominantly in G₁ , the cell cycle phase with the lowest Bcl-2 protein levels and Bcl-2/Bax ratios. In addition, Bcl-2 phosphorylation on Ser⁷⁰ was absent in G₁ but detectable in G₂/M, thus lower Bcl-2 levels and absence of Bcl-2 phosphorylation appeared to facilitate ABT-737-induced apoptosis of G₁ cells. The complementary effects of Nutlin-3a and ABT-737 in different cell cycle phases could, in part, account for their synergistic activity. Our data suggest that combined targeting of Mdm2 and Bcl-2 proteins could offer considerable therapeutic promise in AML.

Open Access Article

TGFβ1-Induced Activation of ATM and p53 Mediates Apoptosis in a Smad7-Dependent Manner

Shouting Zhang, Maria Ekman, Noopur Thakur, Shizhong Bu, Padideh Davoodpour, Susanne Grimsby, Seicchi Tagami, Carl-Henrik Heldin and Marene Landström
Pages 2787 - 2795
http://dx.doi.org/10.4161/cc.5.23.3523
Abstract | PDF

ATM, a DNA-damage sensitive kinase and p53, are frequently inactivated in a variety of cancers as they together with γH2AX are critical guardians against DNA damage. Here, we report of a functional cross-talk between the cytokine TGFβ and p53, leading to apoptosis of epithelial cells, involving Smad7, a TGF-β target gene, p38 MAP kinase, and ATM. Using ectopic expression of p53, siRNA for Smad7, p38α -/- deficient cells and specific inhibitors, we show that TGF-β induces apoptosis via ATM and p53 in epithelial cells. Intriguingly, Smad7 act as a scaffold protein to promote functional interactions between p38, ATM and p53 upon TGFβ treatment, facilitating their activation. Smad7 colocalizes with γH2AX in DNA damage foci and was required for proper cell cycle checkpoints to prevent genetic instability. Our data imply that Smad7 plays a crucial role upstream of ATM and p53 to protect the genome from insults evoked by extracellular stress.

Open Access Article

Human PIF Helicase is Cell Cycle Regulated and Associates with Telomerase

Maria K Mateyak and Virginia A Zakian
Pages 2796 - 2804
http://dx.doi.org/10.4161/cc.5.23.3524
Abstract | PDF

The evolutionarily conserved PIF1 DNA helicase family is important for the maintenance of genome stability in the yeast, Saccharomyces cerevisiae. There are two PIF1 family helicases in S. cerevisiae, Pif1p and Rrm3p that both possess 5’→3’ DNA helicase activity but maintain unique functions in telomerase regulation and semi-conservative DNA replication. Database analysis shows that the PIF1 helicase family is represented by a single homologue in higher eukaryotes. To analyze the function of PIF1 homologues in mammals, we cloned the full length human PIF (hPIF) cDNA. Comparison of hPIF with its S. cerevisiae homologues showed that human PIF is equally similar to Pif1p and Rrm3p. Human PIF1 was expressed at low levels in a variety of tissues and immunofluorescence analysis showed that ectopic hPIF1 was localized to nuclear foci. hPIF was expressed in late S/G2 phase of the cell cycle and this cell cycle regulated abundance was conferred by both cell cycle regulated mRNA accumulation and ubiquitin-mediated degradation. Furthermore, hPIF is likely a target of the anaphase promoting complex/cyclosome as its abundance was decreased when an activator of the APC/C was over-expressed. Finally, antibodies against hPIF immunoprecipitated telomerase activity from human cell lines, and we have observed a physical interaction between hPIF and the catalytic subunit of telomerase, hTERT. Our data suggest that human PIF, like S. cerevisiae Pif1p, plays a role in telomerase regulation.

Open Access Article

Identification of New p63 Targets in Human Keratinocytes

Barbara Testoni, Serena Borrelli, Elena Tenedini, Daniela Alotto, Carlotta Castagnoli, Stefano Piccolo, Enrico Tagliafico, Sergio Ferrari, M Alessandra Viganò and Roberto Mantovani
Pages 2805 - 2811
http://dx.doi.org/10.4161/cc.5.23.3525
Abstract | PDF

p63 is a transcription factor involved in the development of ectodermal tissues, including limb, skin and, in general, multilayered epithelia. We identified both activated and repressed genes in human keratinocytes via gene expression profiling of p63-depleted cells and validated 21 new primary targets by RT-PCR and ChIP location analysis. The p63 isoforms differentially activate or repress selected promoters. ChIPs in primary keratinocytes indicate that p63 targets are generally shared with p53, but some are p63-specific. Several growth suppressors are among repressed genes. The newly identified genes belong to pathways of growth and differentiation and are regulated in HaCaT differentiation and in stratification of human skin.

Open Access Article

Ser46 Phosphorylation Regulates p53-Dependent Apoptosis and Replicative Senescence

Lijin Feng, Monica Hollstein and Yang Xu
Pages 2812 - 2819
http://dx.doi.org/10.4161/cc.5.23.3526
Abstract | PDF

Posttranslational modification such as phosphorylation of p53 plays important roles in activating p53 responses to various cellular and genotoxic stresses. Cell line studies have shown that phosphorylation of Ser46 is correlated with the activation of p53 apoptotic activity. To address the physiological roles of Ser46 phosphorylation, we employed homologous recombination and LoxP/Cre-mediated deletion to introduce Ser46 to Ala missense mutation into the human p53 knock-in (HUPKI) allele in mice (p53hki^S46A). p53 stabilization in response to various types of DNA damage is modestly reduced in p53hki^S46A embryonic stem (ES) cells, mouse embryonic fibroblasts (MEFs) and thymocytes. In addition, p53-dependent apoptosis is partially impaired in p53hki^S46A thymocytes and E1A/Ras-expressing mouse embryonic fibroblasts (MEFs) after DNA damage. Consistent with this finding, transcription of p53 target apoptotic genes is preferentially affected by S46A mutation after DNA damage. p53hki^S46A MEFs proliferate and reach senescence normally but can be spontaneously immortalized more easily than wild type MEFs. In addition, p53hki^S46A MEFs more readily escapes from Ras-induced senescence. Therefore, Ser46 phosphorylation activates p53-dependent apoptosis induced by DNA damage and cellular senescence induced by oncogenic stress.

Open Access Article

EGF Induces Cell Motility and Multi-Drug Resistance Gene Expression in Breast Cancer Cells

Ruben Garcia, Richard A. Franklin and James A. McCubrey
Pages 2820 - 2826
http://dx.doi.org/10.4161/cc.5.23.3535
Abstract | PDF

The epidermal growth factor receptor (EGFR) is important for normal development, differentiation, and cell proliferation. Deregulation of EGFR has been observed in breast cancer. EGFR and signal pathways activated by these receptors have been associated with an advanced tumor stage and a poor clinical prognosis in breast cancer, however, the precise mechanisms responsible for this process are still not known. Here we show that treatment of MCF-7 breast cancer cells with EGF activated Akt and ERK, induced morphological changes, and increased cell motility. In addition, the constitutive expression of Raf-1 and the use of a MEK inhibitor demonstrated the participation of the Raf/MEK/ERK pathway in these processes. Importantly we detected that EGF induced MRP-1, 3, 5 and 7 gene expression and an increase in MRP1 promoter activity. In conclusion, treatment of MCF-7 breast cancer cells with EGF, in the absence of other growth factors, resulted in activation of EGFR signal transduction pathways; which were related with cell motility and drug resistance.