Table of Contents

Volume 7, Issue 23

  December 1, 2008

  Pages 3617 - 3783

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 Issue Catalogue (MARC XML)

NEWS

Open Access Article

Differential regulation of the PIKK kinase family by Tel2

Simon J. Boulton
Page 3617
http://dx.doi.org/10.4161/cc.7.23.7430
PDF




EXTRA VIEWS

Open Access Article

Working together and apart: The twisted relationship of the Mre11 complex and Chk2 in apoptosis and tumor suppression

Travis H. Stracker and John H.J. Petrini
Pages 3618 - 3621
http://dx.doi.org/10.4161/cc.7.23.7064
Abstract | PDF

Central to the DNA damage response (DDR) is the highly conserved Mre11 complex consisting of Mre11, Rad50, and Nbs1. The Mre11 complex acts as a sensor of DNA double-strand breaks (DSBs) and regulates the signal transduction cascades that are triggered following damage detection1. Rare human genetic instability syndromes such as Ataxia-telangiectasia (A-T) and Nijmegen Breakage Syndrome (NBS) have underscored the importance of the DSB response in the suppression of tumorigenesis, as well as other severe pathologies affecting the development of both the immune system and the central nervous system. Using murine models of the human diseases, we have investigated the role of the Mre11 complex, and other modulators of the DSB response, in tumor suppression2, 3. We found that the checkpoint kinase Chk2 is crucial for the suppression of a diverse array of tumor types in Mre11 complex mutants and uncovered multiple roles for the Mre11 complex in apoptotic signaling in parallel to Chk24, 5.

Open Access Article

Stemness, cancer, and cancer stem cells

David J. Wong, Eran Segal and Howard Y. Chang
Pages 3622 - 3624
http://dx.doi.org/10.4161/cc.7.23.7104
Abstract | PDF

The ability of cancers to grow indefinitely has fueled the idea that cancer and stem cells may have common underlying mechanisms. Detailed gene expression maps have now shown the diversity and distinctiveness in gene expression programs associated with stemness in embryonic and adult stem cells. These maps have further revealed a shared transcriptional program in embryonic stem cells (ESC) and cancer stem cells. Surprisingly, forced activation of an ESC-like gene expression program in adult epithelial cells can reprogram them into human cancer stem cells and achieve pathologic self-renewal. The ability to create induced cancer stem cells (iCSC) may provide opportunities to better define the biology of cancer stem cells in order to trace or eliminate them in human patients.

Open Access Article

Autophagy and T-cell education in the thymus: Eat yourself to know yourself

Jelena Nedjic, Martin Aichinger and Ludger Klein
Pages 3625 - 3628
http://dx.doi.org/10.4161/cc.7.23.7121
Abstract | PDF

During intrathymic generation of the T cell repertoire, a series of selection processes ensure that only self-MHC (Major Histocompatibility Complex) restricted and self-tolerant T cells are allowed to survive. Interactions with MHC ligands on the surface of thymic epithelial cells (TECs) play a pivotal role in the decision-making of developing thymocytes. A number of distinct cell-biological features of TECs have emerged that may predispose them to serve non-redundant functions in thymocyte “education”. Thus, cortical TECs express a rather unique set of proteolytic enzymes for antigen processing in the context of positive selection, whereas medullary TECs "ectopically" express a plethora of otherwise strictly tissue-restricted antigens (TRAs), a property that obviously has evolved to make these self-antigens "visible" to developing thymocytes for negative selection. One of the latest additions to this growing list of functional adaptations of TECs is their constitutively high rate of autophagy. Recently, we have provided evidence that autophagy in TECs shuttles cytoplasmic self-antigens into the MHC class II loading pathway for positive selection of T cells and tolerance induction.

Open Access Article

Cooperation of replication Protein A with the ubiquitin ligase Rad18 in DNA damage bypass

Diana Huttner and Helle D. Ulrich
Pages 3629 - 3633
http://dx.doi.org/10.4161/cc.7.23.7166
Abstract | PDF

Replicative DNA damage bypass promotes cell viability in the presence of genotoxic agents but at the same time may lead to mutations, thereby contributing to genomic instability. In eukaryotes, DNA damage bypass is mediated by damage-induced ubiquitylation of the replication clamp protein, proliferating cell nuclear antigen (PCNA). We have recently shown that replication protein A (RPA), a single-stranded (ss)DNA-binding protein essential for DNA replication, repair and recombination, is required for PCNA ubiquitylation in budding yeast. Both in yeast and in mammalian cells, RPA physically interacts with Rad18, the ubiquitin ligase responsible for PCNA mono-ubiquitylation. The association of Rad18 with chromatin correlates with that of RPA, and purified RPA can recruit the ligase to ssDNA in vitro. Here we have examined in more detail the interactions between Rad18, RPA and DNA and discuss their contribution to the activation of DNA damage bypass.




PERSPECTIVES

Open Access Article

Regulation of lymphocyte fate by Ras/ERK signals

Tomoharu Yasuda and Tomohiro Kurosaki
Pages 3634 - 3640
http://dx.doi.org/10.4161/cc.7.23.7103
Abstract | PDF

The Ras-ERK cascade is activated by countless external cues that stimulate diverse receptors. Therefore, the mechanisms by which distinct receptors dictate different cellular outcomes by activating the same signaling module has long fascinated many researchers. Initial clues came from observations that the duration of ERK activation is critical to cell-fate decisions. In classical experiments, PC12 cells proliferated after transient ERK activation by epidermal growth factor, but terminally differentiated after more sustained ERK activation by nerve growth factor. Subsequent studies suggested that the duration of ERK signaling is interpreted by cells through a network of immediate-early genes. Nevertheless, it remains ill-defined how the duration and strength of Ras-ERK signaling is established and what genes are differently regulated, thereby translating the response into different biological outcomes. Recent studies with lymphocytes have evoked a new idea that two types of interconnected mechanisms can contribute to the sensitivity and robustness of the ERK activity; 1) interplay between two types of Ras activators (Sos and RasGRP); 2) existence of two subcellular compartments for Ras activation (plasma membrane and Golgi). Moreover, candidate immediate early genes that regulate lymphocyte proliferation and differentiation have emerged.

Open Access Article

ARF in the mitochondria: The last frontier?

Koji Itahana, Hilary V. Clegg and Yanping Zhang
Pages 3641 - 3646
http://dx.doi.org/10.4161/cc.7.23.7105
Abstract | PDF

The tumor suppressor ARF carries out different functions in different cellular compartments. In the nucleus, ARF interacts physically and functionally with Mdm2 to inhibit cell cycle progression through activation of p53. In the nucleolus, ARF interacts with B23/NPM to inhibit ribosomal biogenesis through control of rRNA processing. Recent studies have expanded ARF's territory into the mitochondria. New data have shown that ARF interacts with the mitochondrial protein p32/C1QBP and that the interaction is critical in order for ARF to localize to the mitochondria and induce apoptosis. Remarkably, the ARF-p32 interaction, and hence ARF's pro-apoptotic function, can be interrupted by human cancer-derived mutations in exon2 of the p14ARF-p16INK4a gene locus. Here, we discuss the implications of these studies and their potential relevance to human cancer.

Open Access Article

Trim24 (Tif1α): An essential ‘brake’ for retinoic acid-induced transcription to prevent liver cancer

Konstantin Khetchoumian, Marius Teletin, Johan Tisserand, Benjamin Herquel, Khalid Ouararhni and Régine Losson
Pages 3647 - 3652
http://dx.doi.org/10.4161/cc.7.23.7123
Abstract | PDF

Retinoic acid (RA), the active derivative of vitamin A, is an important signaling molecule that controls various developmental processes and influence the proliferation and differentiation of a variety of cell types. RA exerts its biological functions primarily through binding to and activating nuclear RA receptors (RARs, which include the RARα, β and γ isotypes RARA, RARB and RARC). Aberrant expression or impaired function of these nuclear receptors has been linked to diverse types of cancer. RARs are RA-dependent transcription factors and regulate gene expression through the recruitment of different co-regulators (co-activators and co-repressors). TRIM24 (formerly known as TIF1α) was among the first co-regulators identified as interacting with RARs in a ligand-dependent fashion, and it was recently shown to function in mice as a potent liver-specific tumor suppressor by attenuating Rara-mediated transcription. The fact that Trim24-/-, but not Trim24-/-Rara+/-, mutant mice are highly predisposed to the development of hepatocellular carcinoma (HCC) has significant implications in cancer research. This result, along with the observation that in response to pharmacological inhibition of the RA signaling, hepatocytes lacking Trim24 loose their ability to proliferate, strongly implicates Rara as a proto-oncogene in HCC and demonstrates that overactivated RA signaling is deleterious to liver homeostasis.

Open Access Article

DNA lesions and DNA damage response: Even long lasting relationships need a "break"

Evi Soutoglou
Pages 3653 - 3658
http://dx.doi.org/10.4161/cc.7.23.7178
Abstract | PDF

The elucidation of the spatiotemporal map of the DNA damage response (DDR) has been critical to our understanding of how cells are protected against insults to genomic integrity. Recruitment and transient immobilization at DNA breaks is a typical characteristic of many DDR proteins. Here, I discuss evidence that stable association of DDR proteins with chromatin is sufficient to activate the DDR even in the absence of damage. These observations critically support the notion that nuclear repair compartments play a primary role in triggering and amplifying DDR.




REVIEWS

Open Access Article

Early origin of cancer metastases: Dissemination and evolution of premalignant cells

Stéphane Ansieau, George Hinkal, Clémence Thomas, Jérémy Bastid and Alain Puisieux
Pages 3659 - 3663
http://dx.doi.org/10.4161/cc.7.23.7049
Abstract | PDF

Metastasis is the main cause of death by cancer. Hence, establishing predictive markers constitutes a major clinical objective. The capacity for a tumor cell to migrate and survive from a primary tumor is often described as the ultimate step of Darwinian selection. These metastatic cells are believed to emerge from a subpopulation of cells present in a primary tumor. In line with this hypothesis, various gene "signatures" associated with poor prognosis and/or with tumors displaying high metastatic potential have been promoted. However, over the last few years, a growing body of evidence supports the idea that metastatic cells disseminate early from the primordial tumor and evolve independently of it. Herein, we propose to review to the data favoring this alternative model and discuss the interplay between metastatic mechanisms and failsafe mechanism pathways.

Open Access Article

Role of the cyclin-dependent kinase 9-related pathway in mammalian gene expression and human diseases

Gaetano Romano and Antonio Giordano
Pages 3664 - 3668
http://dx.doi.org/10.4161/cc.7.23.7122
Abstract | PDF

Cyclin-dependent kinase 9 (Cdk9) is a cdc2-like serine/threonine kinase. The so-called Cdk9-related pathway comprises two Cdk9 isoforms (Cdk9-42 and Cdk9-55), cyclin T1, cyclin T2a, cyclin T2b and cyclin K. The association between Cdk9 and one of its cyclin partners forms a heterodimer, which is the main component of the positive transcription elongation factor (P-TEFb). The latter stabilizes the elongation process of RNA polymerase II (polII) transcripts. Through the control of RNA polII-mediated gene expression, the Cdk9-related pathway performs an important role in several biological processes, such as cell growth, proliferation, protection from apoptosis and differentiation. Incidentally, the P-TEFb that contains the heterodimer Cdk9-cyclin T1 is also critical for HIV-1 and HIV-2 replication in human cells. A deregulation in the Cdk9-related pathway is associated with various types of human malignancies and cardiomyocytes hypertrophy. On these grounds, the characterization of Cdk9-related pathway deregulation might have a two-fold purpose: (1) the development of novel kinase inhibitors for the treatment of cancer, AIDS and cardiac hypertrophy and (2) a better understanding of the pathogenesis and progression of these maladies.

Open Access Article

Comparing and contrasting the roles of AMPK and SIRT1 in metabolic tissues

Marcella Fulco and Vittorio Sartorelli
Pages 3669 - 3679
http://dx.doi.org/10.4161/cc.7.23.7164
Abstract | PDF

The ability to adapt and respond to nutrients is an ancient cellular function, conserved from unicellular to the most complex multicellular organisms, including mammals. Mammals adapt to changes in nutritional status through the modulation of tissue-specific metabolic pathways so as to maintain energy homeostasis. At least two proteins are activated in response to reduced nutrient availability: AMP-activated protein kinase (AMPK) and NAD+-dependent deacetylase SIRT1. AMPK functions as a sensor of cellular energy status and as a master regulator of metabolism. When ATP levels decrease, AMPK is activated to boost ATP production and to inhibit ATP usage, thus restoring energy balance. Similarly, SIRT1 is activated in response to changes in the energy status to promote transcription of genes that mediate the metabolic response to stress, starvation, or calorie restriction. Several observations support a model where, in response to stress and reduced nutrients, a metabolic pathway is activated within which AMPK and SIRT1 concordantly function to ensure an appropriate cellular response and adaptation to environmental modifications. In this perspective, we compare and contrast the roles of SIRT1 and AMPK in several metabolic tissues and propose a working model of how the AMPK-SIRT1 axis may be regulated to control functions relevant to organismal physiology and pathophysiology.




REPORTS

Open Access Article

Disease phenocode analysis identifies SNP-guided microRNA maps (MirMaps) associated with human "master" disease genes

Gennadi Glinsky
Pages 3680 - 3694
http://dx.doi.org/10.4161/cc.7.23.7153
Abstract | PDF

Recently we reported the results of a genome-wide disease phenocode analysis interrogating the relationships between structural features and gene expression patterns of disease-linked SNPs, microRNAs, and mRNAs of protein-coding genes in association to phenotypes of 15 common human disorders (Cell Cycle 2008; 7: 2570-83). One of the main implications of this analysis is that transcriptionally co-regulated SNP sequence-bearing RNAs are more likely to exert a cumulative effect in trans on phenotypes. In this work, we test the validity of a disease phenocode concept within a genomic context of distinct continuously spaced sets of disease-linked SNPs and mRNAs of relevant protein-coding genes. We report a sequence homology profiling of two sets of disease-linked SNPs which are located within continuous genomic regions associated with individual protein-coding genetic loci (NLRP1 and STAT4) and are likely to exhibit common profiles of transcriptional activity. Most of microRNAs (15 of 19; 79%) homologous to the NLPRP1-associated disease-linked SNPs have potential protein-coding mRNA targets among the principal components of the nuclear import pathway (NIP) and/or inflammasome pathways, including KPNA1, NLRP1, and NLRP3 genes. We demonstrate that estimates of cumulative targeting effects of microRNAs on mRNAs within distinct allelic contexts of disease-linked SNPs are in agreement with microarray analysis-defined gene expression phenotypes associated with human genotypes of Crohn's disease (CD) and rheumatoid arthritis (RA) populations. Microarray experiments and disease phenocode analysis identify ten-gene expression signatures which seem to reflect the activated status of disease-linked SNPs/microRNAs/mRNAs axis in peripheral blood mononuclear cells (PBMC) of 66% CD patients and 80% RA patients. Comparisons of ten-gene signature expression profiles and NLRP3/NLRP1 mRNA expression ratios in PBMC of individual CD and RA patients and control subjects indicate that measurements of these markers may be useful for diagnostic applications. Our findings demonstrate that NLPRP1- and STAT4-associated disease-linked SNPs have common sequence-defined features which are recapitulating the essential phenotype-affecting features of genome-wide disease-linked SNPs, suggesting that NLRP1 (NALP1) and STAT4 genetic loci may constitute "master" disease genes. We conclude that both genome-wide SNP variations and SNP polymorphisms associated with "master" disease genes may cause similar genetically-defined malfunctions of the NIP and inflammasome/innate immunity pathways which are likely to contribute to pathogenesis of multiple common human disorders.

Open Access Article

Mec1 function in the DNA damage response does not require its interaction with Tel2

Carol M. Anderson and Elizabeth H. Blackburn
Pages 3695 - 3698
http://dx.doi.org/10.4161/cc.7.23.7154
Abstract | PDF

The essential, conserved Tel2 protein plays a role in the response to DNA damage and replication stress in a wide range of eukaryotes. Tel2 interacts physically with multiple members of the PI3-kinase related protein kinase (PIKK) family in mammalian cells and fission yeast. In mammalian cells, loss of Tel2 leads to destabilization of PIKKs. Our previous work in the yeast Saccharomyces cerevisiae showed that Tel2 interacts with the PIKK Tel1 (yeast ATM kinase), and that this interaction is abrogated by the only known non-lethal TEL2 mutation in S. cerevisiae, tel2-1. We showed that this mutation specifically disrupts the function of Tel1 and not the function of the closely related protein Mec1 (yeast ATR kinase) in DNA damage responses. Here we show that Tel2 and Mec1 interact in S. cerevisiae, and that surprisingly, this physical interaction is also disrupted by the tel2-1 mutation. Although the tel2-1 mutation leads to moderately lower Mec1 levels, the ability of Mec1 to localize to a site of DNA damage and to function in DNA damage signaling remains intact. These results suggest that the model of Tel2 as solely a global regulator of PIKK stability is insufficient. Rather, Tel2 can specifically and differentially regulate the function of individual PIKKs.

Open Access Article

A mitotic role for GSK-3β kinase in Drosophila

Edward J. Wojcik
Pages 3699 - 3708
http://dx.doi.org/10.4161/cc.7.23.7179
Abstract | PDF

Glycogen synthase kinase-3β (GSK-3β) is involved in a wide variety of cellular processes, and implicated in a growing list of human diseases. Recent drug inhibition studies have suggested a role for GSK-3β in mitosis in animals. Here, we take an alternative approach to understanding GSK-3β function in mitosis by genetic mutational analysis in Drosophila. GSK-3β function is well conserved between Drosophila (Zw3) and humans, frequently operating similarly in pathways, as diverse as the Wnt signaling and circadian rhythm pathways, and sharing a key role in the development of the neuromuscular junction. Unlike drug inhibitor studies, we find that loss of function mutations of zw3 result in markedly curved, or bent, metaphase spindles that exhibit metaphase delay. These defects do not routinely result in mitotic catastrophe, and argue that Zw3 plays a role in the maintenance of the mitotic spindle, rather than an essential role in spindle morphogenesis. Consistent with a mitotic function, we observe a complex and dynamic localization of Zw3 during cell division. These studies provide genetic data that validate and extend drug inhibition studies on a novel mitotic role for glycogen synthase kinase in the maintenance of the mitotic spindle.

Open Access Article

Experimental testing of predicted myristoylation targets involved in asymmetric cell division and calcium-dependent signalling

Wolfgang Benetka, Norbert Mehlmer, Sebastian Maurer-Stroh, Michaela Sammer, Manfred Koranda, Ralph Neumüller, Jörg Betschinger, Jürgen A. Knoblich, Markus Teige and Frank Eisenhaber
Pages 3709 - 3719
http://dx.doi.org/10.4161/cc.7.23.7176
Abstract | PDF

Evolutionary conservation of N-terminal N-myristoylation within protein families indicates significant functional impact of this lipid posttranslational modification for function. In the MYRbase study (Maurer-Stroh et al. (2004) Genome Biology 5, R21), protein families with relevance to asymmetric cell division in animals and the group of plant calcium-dependent protein kinases (CPKs) have surfaced with many predicted myristoylated members. Here, we describe experimental in vitro verification of predicted myristoylation and explore its impact on subcellular localization for these targets in vivo. Our results confirm that, indeed, Numb isoform A, Neuralized isoforms C and D from Drosophila melanogaster and two Neuralized-like homologues from Mus musculus have the capability for N-terminal myristoylation in vitro and in vivo (in fly tissue and in mouse 3T3 cells respectively) whereas other isoforms such as Neuralized A and B have not. The latter two cases are an example of different potential of various isoforms for posttranslational modifications. Additionally, the Arabidopsis thaliana CDPKs CPK6, CPK9 and CPK13 are shown to be substrates for myristoylation in vitro, which also affects their subcellular localization (in Arabidopsis protoplasts and tobacco leaves). At the same time, CPK6 and CPK13 do not appear to be substrates of a NMT1-like enzyme; the reasons for differing substrate specificities of NMT homologues in plants are derived from the evolutionary divergence of their N-myristoyl transferase sequences. As a methodical advance, we describe a fast and very sensitive technique (compared to traditional autoradiography) for in vitro testing of myristoylation based on thin layer chromatography read-out of the incorporated radioactive myristoyl anchor with subsequent Western blotting detection for protein yield determination using the same membrane.

Open Access Article

The fission yeast meiotic checkpoint kinase Mek1 regulates nuclear localization of Cdc25 by phosphorylation

Livia Pérez-Hidalgo, Sergio Moreno and Pedro A. San-Segundo
Pages 3720 - 3730
http://dx.doi.org/10.4161/cc.7.23.7177
Abstract | PDF

In eukaryotic cells, fidelity in transmission of genetic information during cell division is ensured by the action of cell cycle checkpoints. Checkpoints are surveillance mechanisms that arrest or delay cell cycle progression when critical cellular processes are defective or when the genome is damaged. During meiosis, the so-called meiotic recombination checkpoint blocks entry into meiosis I until recombination has been completed, thus avoiding aberrant chromosome segregation and the formation of aneuploid gametes. One of the key components of the meiotic recombination checkpoint is the meiosis-specific Mek1 kinase, which belongs to the family of Rad53/Cds1/Chk2 checkpoint kinases containing forkhead-associated domains. In fission yeast, several lines of evidence suggest that Mek1 targets the critical cell cycle regulator Cdc25 to delay meiotic cell cycle progression. Here, we investigate in more detail the molecular mechanism of action of the fission yeast Mek1 protein. We demonstrate that Mek1 acts independently of Cds1 to phosphorylate Cdc25, and this phosphorylation is required to trigger cell cycle arrest. Using ectopic overexpression of mek1+ as a tool to induce in vivo activation of Mek1, we find that Mek1 promotes cytoplasmic accumulation of Cdc25 and results in prolonged phosphorylation of Cdc2 at tyrosine 15. We propose that at least one of the mechanisms contributing to the cell cycle delay when the meiotic recombination checkpoint is activated in fission yeast is the nuclear exclusion of the Cdc25 phosphatase by Mek1-dependent phosphorylation.

Open Access Article

DNA damage-induced upregulation of miR-709 in the germline downregulates BORIS to counteract aberrant DNA hypomethylation

Jan Tamminga, Palak Kathiria, Igor Koturbash and Olga Kovalchuk
Pages 3731 - 3736
http://dx.doi.org/10.4161/cc.7.23.7186
Abstract | PDF

MicroRNAs as potent regulators of gene expression are involved in spermatogenesis, yet their role in response of germline to genotoxic stress is obscure. We studied the microRNAome profile of X-ray irradiated mouse testes using the microarray technique. We found that radiation exposure significantly affected microRNA expression in testes. Mir-709 was the most abundant in both control and irradiated testes, and a big difference in miR-709 levels was observed between the control and exposed group. We found that miR-709 targets the Brother of the Regulator of Imprinted Sites (BORIS), an important regulator of DNA methylation and imprinting. Here, we for the first time show that the DNA damage-induced and ATR/Rfx1-mediated increase of miR-709 expression in exposed testes may be a protective mechanism that effectively decreases a cellular level of BORIS to prevent massive aberrant erasure of DNA methylation after radiation exposure.

Open Access Article

Differential post-transcriptional regulation of two Ink4 proteins, p18Ink4c and p19Ink4d

Antoine Forget, Olivier Ayrault, Willem den Besten, Mei-Ling Kuo, Charles J. Sherr and Martine F. Roussel
Pages 3737 - 3746
http://dx.doi.org/10.4161/cc.7.23.7187
Abstract | PDF

Cyclin(-D-)-dependent kinase (Cdk) inhibitors of the Ink4 family specifically bind to Cdk4 and Cdk6, but not to other Cdks. Ink4c and Ink4d mRNAs are maximally and periodically expressed during the G2/M phase of the cell division cycle, but the abundance of their encoded proteins is regulated through distinct mechanisms. Both proteins undergo polyubiquitination, but the half life of p18Ink4c (~10 hours) is much longer than that of p19Ink4d (~2.5 hours). Lysines 46 and 112 are preferred sites of ubiquitin conjugation in p18Ink4c, although substitution of these and other lysine residues with arginine, particularly in combination, triggers protein misfolding and accelerates p18Ink4c degradation. When tethered to either catalytically active or inactive Cdk4 or Cdk6, polyubiquitination of p18Ink4c is inhibited, and the protein is further stabilized. Conversely, in competing with p18Ink4c for binding to Cdks, cyclin D1 accelerates p18Ink4c turnover. In direct contrast, polyubiquitination of p19Ink4d is induced by its association with Cdks, whereas cyclin D1 overexpression retards p19Ink4d degradation. Although it has been generally assumed that p18Ink4c and p19Ink4d are biochemically similar Cdk inhibitors, the major differences in their stability and turnover are likely key to understanding their distinct biological functions.

Open Access Article

Specific blockade of VEGF and HER2 pathways results in greater growth inhibition of breast cancer xenografts that overexpress HER2

Xiao-Feng Le, Weiqun Mao, Chunhua Lu, Angela Thornton, John V. Heymach, Anil K. Sood and Robert C. Bast, Jr.
Pages 3747 - 3758
http://dx.doi.org/10.4161/cc.7.23.7212
Abstract | PDF

We have previously reported that breast cancer cells which overexpress HER2 produce higher levels of VEGF than cells with low levels of HER2. This study tested the hypothesis that dual targeting of the VEGF (with VEGF-Trap) and HER2 (with trastuzumab) pathways would result in greater growth inhibition of HER2-overexpressing breast cancer xenografts than either agent alone. In this study we found that human and murine endothelial cells expressed high levels of VEGF receptors (VEGFR1, VEGFR2, & VEGFR3). VEGF-Trap decreased levels of secreted VEGF derived from both human and murine cells and effectively blocked VEGF-induced tyrosine phosphorylation of VEGFR2. VEGF-Trap as a single treatment inhibited tumor microvessel density (MVD), tumor vasculature, cell proliferation, and tumor growth of BT474 xenografts in a dose-dependent manner from 2.5 mg/kg to 25 mg/kg. VEGF-Trap decreased levels of both human VEGF and PlGF protein in vivo. Trastuzumab as a single agent effectively inhibited BT474 tumor growth in a dose-dependent manner, associated with a decrease in human VEGF, tumor MVD and tumor cell proliferation. Treatment with a combination of VEGF-Trap (2.5-10 mg/kg) and trastuzumab (1 mg/kg) produced significantly greater inhibition of BT474tumor growth than either individual agent, associated with greater inhibition of tumor MVD and tumor cell proliferation. Thus, VEGF-Trap in combination with trastuzumab produces superior growth inhibition of tumor xenografts which overexpress HER2, which may result from inhibition of both tumor angiogenesis and proliferation. Similar mechanisms may contribute to the clinical anti-tumor activity of trastuzumab in combination with inhibitors of VEGF signaling pathway in women with breast cancers which overexpress HER2.

Open Access Article

Hexamethylene Bisacetamide (HMBA) simultaneously targets AKT and MAPK pathway and represses NF-κB activity: Implications for cancer therapy

Anwesha Dey, Eetsin Wong, Nelly Kua, Hsiang Ling Teo, Vinay Tergaonkar and David Lane
Pages 3759 - 3767
http://dx.doi.org/10.4161/cc.7.23.7213
Abstract | PDF

Hexamethylene Bisacetamide (HMBA) is a hybrid polar compound originally developed as a differentiation inducing agent. We show in this study that HMBA can inhibit activation of several NF-κB target genes in both lung and breast cancer cell lines. Furthermore, consistent with its ability to inhibit NF-κB function, HMBA can also sensitize cells to apoptosis. We show that HMBA mediates inhibition of the Akt and ERK/MAPK cascade, both of which are critical for cell survival and proliferation and are well known regulators of NF-κB activation. We also show that PTEN negative breast cancer cells which have hyper activation of the PI3K/Akt pathway show increased sensitivity to growth inhibitory effects of combination of HMBA and TNFα. Furthermore, HMBA can decrease the kinase activity of the IKK complex leading to defective phosphorylation of IκBα and Ser536 of p65. This study gives mechanistic insight into the mechanism of action of HMBA, provides the rationale for the potential use of HMBA in combination with various existing kinase inhibitors in combination therapy and also suggests useful biomarkers for monitoring tumor response to HMBA.

Open Access Article

Differential regulation of cyclin D1 and D2 in protecting against cardiomyocyte proliferation

Mimi Tamamori-Adachi, Ikuko Goto, Kazuhiko Yamada and Shigetaka Kitajima
Pages 3768 - 3774
http://dx.doi.org/10.4161/cc.7.23.7239
Abstract | PDF

Cardiomyocytes withdraw from cell cycle after terminal differentiation due in part to impaired nuclear import of cyclin D1. Thus, we have previously shown that expression of nuclear localization signal-tagged cyclin D1 (D1NLS) and cyclin-dependent kinase 4 promotes cardiomyocyte proliferation both in vitro and in vivo. Here we show that cyclin D2 fails to stimulate cell cycle in cardiomocytes through a mechanism distinct from that of cyclin D1. We demonstrate that cyclin D2 can express in the nucleus much more efficiently than cyclin D1. Cyclin D2, however, was much less effective in activating CDK2 and cell proliferation than cyclin D1 when expressed transiently in the nucleus of cardiomyocytes using nuclear localization signals. Consistent with such an observation, CDK inhibitors p21cip1 and p27kip1 remained bound to CDK2 in cells expressing cyclin D2, whereas p21 and p27 were sequestered to cyclin D1 in cells expressing D1NLS. These data suggest that cyclin D2 has weaker affinities to the CDK inhibitors and therefore is less efficient in activating cell cycle than cyclin D1. According to such a notion, double knockdown of p21 and p27 in cells expressing D2NLS induced activation of CDK2/CDC2 and BrdU incorporation to levels similar to those in cells expressing D1NLS. Taken together, our data suggest that distinct mechanisms keep cyclin D1 and cyclin D2 from activating cell cycle in terminally differentiated cardiomyocytes.

Open Access Article

E2F3 plays an essential role in cardiac development and function

Jennifer C. King, Ivan P. G. Moskowitz, Patrick G. Burgon, Ferhaan Ahmad, James R. Stone, Jonathan G. Seidman and Jacqueline A. Lees
Pages 3775 - 3780
http://dx.doi.org/10.4161/cc.7.23.7240
Abstract | PDF

The E2F transcription factors are key downstream targets of the retinoblastoma protein tumor suppressor. They are known to regulate the expression of genes that control fundamental biological processes including cellular proliferation, apoptosis and differentiation. However, considerable questions remain about the precise roles of the individual E2F family members. This study shows that E2F3 is essential for normal cardiac development. E2F3-loss impairs the proliferative capacity of the embryonic myocardium and most E2f3-/- mice die in utero or perinatally with hypoplastic ventricular walls and/or severe atrial and ventricular septal defects. A small fraction of the E2f3-/- neonates have hearts that appear grossly normal and they initially survive. However, these animals display ultrastructural defects in the cardiac muscle and ultimately die as a result of congestive heart failure. These data demonstrate a clear role for E2F3 in myocardial and cardiac function during both development and adulthood.




LETTER TO THE EDITOR

Open Access Article

BRCA1 mutations contribute to cell motility and invasion by affecting its main regulators

Amber Yasmeen, Wenchao Liu, Hafedh Dekhil, Amal Kassab, Raquel Aloyz, William D. Foulkes and Ala-Eddin Al Moustafa
Pages 3781 - 3783
http://dx.doi.org/10.4161/cc.7.23.6993
Abstract | PDF

No abstract.