Table of Contents

Volume 11, Issue 21

  November 1, 2012

  Pages 3903 - 4095

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 Issue Catalogue (MARC XML)

EDITORIALS: CELL CYCLE FEATURES

Open Access Article

The transformative promise of aging science

David Stipp
Pages 3903 - 3904
http://dx.doi.org/10.4161/cc.22211
Abstract | Full Text | PDF

Adapted from a whitepaper written for the Healthspan Campaign, sponsored by the Alliance for Aging Research.

Open Access Article

Human embryonic stem cells: Living on the edge

Vivian Gama and Mohanish Deshmukh
Pages 3905 - 3906
http://dx.doi.org/10.4161/cc.22233
Full Text | PDF

Open Access Article

Dynamic nature of heterochromatin highlighted by a HP1^Swi6-dependent gene silencing mechanism

Marc Bühler and Sebastian Hiller
Pages 3907 - 3908
http://dx.doi.org/10.4161/cc.22234
Full Text | PDF

Open Access Article

An expanded role of the tumor suppressor TSC1 in T cell tolerance

Xiao-Ping Zhong
Pages 3909 - 3910
http://dx.doi.org/10.4161/cc.22235
Full Text | PDF

Open Access Article

“Remembering” tissue-specific transcription patterns through mitosis

Stephan Kadauke and Gerd A. Blobel
Pages 3911 - 3912
http://dx.doi.org/10.4161/cc.22237
Full Text | PDF




CELL CYCLE NEWS & VIEWS

Open Access Article

Cyclin-dependent kinase 4/6 inhibition in cancer therapy

Neil Johnson and Geoffrey I. Shapiro
Page 3913
http://dx.doi.org/10.4161/cc.22390
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Open Access Article

ORCA is regulated by ubiquitin-mediated degradation to control Orc2 function

Amy E. Ikui
Page 3914
http://dx.doi.org/10.4161/cc.22391
Full Text | PDF

Open Access Article

New functions for ecotropic viral integration site 1 (EVI1), an oncogene causing aggressive malignant disease

Rotraud Wieser
Page 3915
http://dx.doi.org/10.4161/cc.22392
Full Text | PDF

Open Access Article

Addicted to PAR?: A closer look at PARP inhibitor sensitivity

Matthias Altmeyer
Page 3916
http://dx.doi.org/10.4161/cc.22393
Full Text | PDF

Open Access Article

UnCHKed DNA replication: A stressful matter

Jennifer L. Gryp and Gustavo J. Gutierrez
Pages 3917 - 3918
http://dx.doi.org/10.4161/cc.22394
Full Text | PDF




EXTRA VIEWS

Open Access Article

Glucose—a sweet way to die: Metabolic switching modulates tumor cell death

Marion MacFarlane, Gemma L. Robinson and Kelvin Cain
Pages 3919 - 3925
http://dx.doi.org/10.4161/cc.21804
Abstract | Full Text | PDF

TRAIL, a putative anticancer cytokine, induces extrinsic cell death by activating the caspase cascade directly (Type I cells) via the death-inducing signaling complex (DISC) or indirectly (Type II cells) by caspase-8 cleavage of Bid and activation of the mitochondrial cell death pathway. Cancer cells are characterized by their dependence on aerobic glycolysis, which, although inefficient in terms of ATP production, facilitates tumor metabolism. Our studies show that TRAIL-induced cell death is significantly affected by the metabolic status of the cell. Inhibiting glycolysis with 2-deoxyglucose potentiates TRAIL-induced cell death, whereas glucose deprivation can paradoxically inhibit apoptosis. These conflicting responses to glycolysis inhibition are modulated by the balance between the Akt and AMPK pathways and their subsequent downstream regulation of mTORC1. This results in marked changes in protein translation, in which the equilibrium between anti- and pro-apoptotic Bcl-2 family member proteins is decided by their individual degradation rates. This regulates the mitochondrial cell death pathway and alters its sensitivity not only to TRAIL, but to ABT-737, a Bcl-2 inhibitor. Taken together, our studies show that the sensitivity of cancer cells to apoptosis can be modulated by targeting their unique metabolism in order to enhance sensitivity to apoptotic agents.

Open Access Article

Hypoxia and gerosuppression: The mTOR saga continues

Olga V. Leontieva and Mikhail V. Blagosklonny
Pages 3926 - 3931
http://dx.doi.org/10.4161/cc.21908
Abstract | Full Text | PDF

Growth-promoting and nutrient/mitogen-sensing pathways such as mTOR convert p21- and p16-induced arrest into senescence (geroconversion). We have recently demonstrated that hypoxia, especially near-anoxia, suppresses geroconversion. This gerosuppressive effect of hypoxia correlated with inhibition of the mTOR/S6K pathway but not with modulation of the LKB1/AMPK/eEF2 pathway. Here we further show that mTOR inhibition is required for gerosuppression by hypoxia, at least in some cellular models, because depletion of TSC2 abolished mTOR inhibition and gerosupression by hypoxia. Also, in two cancer cell lines resistant to inhibition of mTOR by both p53 and hypoxia, hypoxia did not suppress geroconversion. Therefore, the effects of hypoxia on the oxygen-sensing mTOR pathway and geroconversion are cell type-specific. We also briefly discuss replicative senescence, organismal aging and free radical theory.




PERSPECTIVES

The real face of HIF1α in the tumor process

Matthias Kappler, Helge Taubert, Johannes Schubert, Dirk Vordermark and Alexander W. Eckert
Pages 3932 - 3936
http://dx.doi.org/10.4161/cc.21854
Abstract | Full Text | PDF

It is well known that the hypoxia-inducible factor 1 α (HIF1α) is detectable as adaptive metabolic response to hypoxia. However, HIF1/HIF1α is detectable even under normoxic conditions, if the metabolism is altered, e.g., high proliferation index. Importantly, both hypoxic metabolism and the Warburg effect have in common a decrease of the intracellular pH value.

In our interpretation, HIF1α is not directly accumulated by hypoxia, but by a process which occurs always under hypoxic conditions, a decrease of the intracellular pH value because of metabolic imbalances. We assume that HIF1α is a sensitive controller of the intracellular pH value independently of the oxygen concentration. Moreover, HIF1α has its major role in activating genes to eliminate toxic metabolic waste products (e.g., NH₃/NH₄+) generated by the tumor-specific metabolism called glutaminolysis, which occur during hypoxia, or the Warburg effect. For that reason, HIF1α appears as a potential target for tumor therapy to disturb the pH balance and to inhibit the elimination of toxic metabolic waste products in the tumor cells.

Understanding the origins of UV-induced recombination through manipulation of sister chromatid cohesion

Shay Covo, Wenjian Ma, James W. Westmoreland, Dmitry A. Gordenin and Michael A. Resnick
Pages 3937 - 3944
http://dx.doi.org/10.4161/cc.21945
Abstract | Full Text | PDF

Ultraviolet light (UV) can provoke genome instability, partly through its ability to induce homologous recombination (HR). However, the mechanism(s) of UV-induced recombination is poorly understood. Although double-strand breaks (DSBs) have been invoked, there is little evidence for their generation by UV. Alternatively, single-strand DNA lesions that stall replication forks could provoke recombination. Recent findings suggest efficient initiation of UV-induced recombination in G₁ through processing of closely spaced single-strand lesions to DSBs. However, other scenarios are possible, since the recombination initiated in G₁ can be completed in the following stages of the cell cycle. We developed a system that could address UV-induced recombination events that start and finish in G₂ by manipulating the activity of the sister chromatid cohesion complex. Here we show that sister-chromatid cohesion suppresses UV-induced recombination events that are initiated and resolved in G₂. By comparing recombination frequencies and survival between UV and ionizing radiation, we conclude that a substantial portion of UV-induced recombination occurs through DSBs. This notion is supported by a direct physical observation of UV-induced DSBs that are dependent on nucleotide excision repair. However, a significant role of nonDSB intermediates in UV-induced recombination cannot be excluded.




REVIEW

Open Access Article

Local and global functions of Timeless and Tipin in replication fork protection

Adam R. Leman and Eishi Noguchi
Pages 3945 - 3955
http://dx.doi.org/10.4161/cc.21989
Abstract | Full Text | PDF

The eukaryotic cell replicates its chromosomal DNA with almost absolute fidelity in the course of every cell cycle. This accomplishment is remarkable considering that the conditions for DNA replication are rarely ideal. The replication machinery encounters a variety of obstacles on the chromosome, including damaged template DNA. In addition, a number of chromosome regions are considered to be difficult to replicate owing to DNA secondary structures and DNA binding proteins required for various transactions on the chromosome. Under these conditions, replication forks stall or break, posing grave threats to genomic integrity. How does the cell combat such stressful conditions during DNA replication? The replication fork protection complex (FPC) may help answer this question. Recent studies have demonstrated that the FPC is required for the smooth passage of replication forks at difficult-to-replicate genomic regions and plays a critical role in coordinating multiple genome maintenance processes at the replication fork.




REPORTS

Ketone bodies and two-compartment tumor metabolism: Stromal ketone production fuels mitochondrial biogenesis in epithelial cancer cells

Ubaldo E. Martinez-Outschoorn, Zhao Lin, Diana Whitaker-Menezes, Anthony Howell, Michael P. Lisanti and Federica Sotgia
Pages 3956 - 3963
http://dx.doi.org/10.4161/cc.22136
Abstract | Full Text | PDF

We have previously suggested that ketone body metabolism is critical for tumor progression and metastasis. Here, using a co-culture system employing human breast cancer cells (MCF7) and hTERT-immortalized fibroblasts, we provide new evidence to directly support this hypothesis. More specifically, we show that the enzymes required for ketone body production are highly upregulated within cancer-associated fibroblasts. This appears to be mechanistically controlled by the stromal expression of caveolin-1 (Cav-1) and/or serum starvation. In addition, treatment with ketone bodies (such as 3-hydroxy-butyrate, and/or butanediol) is sufficient to drive mitochondrial biogenesis in human breast cancer cells. This observation was also validated by unbiased proteomic analysis. Interestingly, an MCT1 inhibitor was sufficient to block the onset of mitochondrial biogenesis in human breast cancer cells, suggesting a possible avenue for anticancer therapy. Finally, using human breast cancer tumor samples, we directly confirmed that the enzymes associated with ketone body production (HMGCS2, HMGCL and BDH1) were preferentially expressed in the tumor stroma. Conversely, enzymes associated with ketone re-utilization (ACAT1) and mitochondrial biogenesis (HSP60) were selectively associated with the epithelial tumor cell compartment. Our current findings are consistent with the “two-compartment tumor metabolism” model. Furthermore, they suggest that we should target ketone body metabolism as a new area for drug discovery, for the prevention and treatment of human cancers.

Featured Article - FREE

Ketone body utilization drives tumor growth and metastasis

Ubaldo E. Martinez-Outschoorn, Zhao Lin, Diana Whitaker-Menezes, Anthony Howell, Federica Sotgia and Michael P. Lisanti
Pages 3964 - 3971
http://dx.doi.org/10.4161/cc.22137
Abstract | Full Text | PDF

We have previously proposed that catabolic fibroblasts generate mitochondrial fuels (such as ketone bodies) to promote the anabolic growth of human cancer cells and their metastasic dissemination. We have termed this new paradigm “two-compartment tumor metabolism.” Here, we further tested this hypothesis by using a genetic approach. For this purpose, we generated hTERT-immortalized fibroblasts overexpressing the rate-limiting enzymes that promote ketone body production, namely BDH1 and HMGCS2. Similarly, we generated MDA-MB-231 human breast cancer cells overexpressing the key enzyme(s) that allow ketone body re-utilization, OXCT1/2 and ACAT1/2. Interestingly, our results directly show that ketogenic fibroblasts are catabolic and undergo autophagy, with a loss of caveolin-1 (Cav-1) protein expression. Moreover, ketogenic fibroblasts increase the mitochondrial mass and growth of adjacent breast cancer cells. However, most importantly, ketogenic fibroblasts also effectively promote tumor growth, without a significant increase in tumor angiogenesis. Finally, MDA-MB-231 cells overexpressing the enzyme(s) required for ketone re-utilization show dramatic increases in tumor growth and metastatic capacity. Our data provide the necessary genetic evidence that ketone body production and re-utilization drive tumor progression and metastasis. As such, ketone inhibitors should be designed as novel therapeutics to effectively treat advanced cancer patients, with tumor recurrence and metastatic disease. In summary, ketone bodies behave as onco-metabolites, and we directly show that the enzymes HMGCS2, ACAT1/2 and OXCT1/2 are bona fide metabolic oncogenes.

The milk protein α-casein functions as a tumor suppressor via activation of STAT1 signaling, effectively preventing breast cancer tumor growth and metastasis

Gloria Bonuccelli, Remedios Castello-Cros, Franco Capozza, Ubaldo E. Martinez-Outschoorn, Zhao Lin, Aristotelis Tsirigos, Jiao Xuanmao, Diana Whitaker-Menezes, Anthony Howell, Michael P. Lisanti and Federica Sotgia
Pages 3972 - 3982
http://dx.doi.org/10.4161/cc.22227
Abstract | Full Text | PDF

Here, we identified the milk protein α-casein as a novel suppressor of tumor growth and metastasis. Briefly, Met-1 mammary tumor cells expressing α-casein showed a ~5-fold reduction in tumor growth and a near 10-fold decrease in experimental metastasis. To identify the molecular mechanism(s), we performed genome-wide transcriptional profiling. Interestingly, our results show that α-casein upregulates gene transcripts associated with interferon/STAT1 signaling and downregulates genes associated with “stemness.” These findings were validated by immunoblot and FACS analysis, which showed the upregulation and hyperactivation of STAT1 and a decrease in the number of CD44(+) “cancer stem cells.” These gene signatures were also able to predict clinical outcome in human breast cancer patients. Thus, we conclude that a lactation-based therapeutic strategy using recombinant α-casein would provide a more natural and non-toxic approach to the development of novel anticancer therapies.

Open Access Article

DNA2 and EXO1 in replication-coupled, homology-directed repair and in the interplay between HDR and the FA/BRCA network

Kenneth K. Karanja, Stephanie W. Cox, Julien P. Duxin, Sheila A. Stewart and Judith L. Campbell
Pages 3983 - 3996
http://dx.doi.org/10.4161/cc.22215
Abstract | Full Text | PDF

During DNA replication, stalled replication forks and DSBs arise when the replication fork encounters ICLs (interstrand crosslinks), covalent protein/DNA intermediates or other discontinuities in the template. Recently, homologous recombination proteins have been shown to function in replication-coupled repair of ICLs in conjunction with the Fanconi anemia (FA) regulatory factors FANCD2-FANCI, and, conversely, the FA gene products have been shown to play roles in stalled replication fork rescue even in the absence of ICLs, suggesting a broader role for the FA network than previously appreciated. Here we show that DNA2 helicase/nuclease participates in resection during replication-coupled repair of ICLs and other replication fork stresses. DNA2 knockdowns are deficient in HDR (homology-directed repair) and the S phase checkpoint and exhibit genome instability and sensitivity to agents that cause replication stress. DNA2 is partially redundant with EXO1 in these roles. DNA2 interacts with FANCD2, and cisplatin induces FANCD2 ubiquitylation even in the absence of DNA2. DNA2 and EXO1 deficiency leads to ICL sensitivity but does not increase ICL sensitivity in the absence of FANCD2. This is the first demonstration of the redundancy of human resection nucleases in the HDR step in replication-coupled repair, and suggests that DNA2 may represent a new mediator of the interplay between HDR and the FA/BRCA pathway.

Cyclosporin A inhibits colon cancer cell growth independently of the calcineurin pathway

Miriam B.F. Werneck, Eugênio Hottz, Patrícia T. Bozza and João P.B. Viola
Pages 3997 - 4008
http://dx.doi.org/10.4161/cc.22222
Abstract | Full Text | PDF

Chronic inflammation is a risk factor for the development of colon cancer, providing genotoxic insults, growth and pro-angiogenic factors that can promote tumorigenesis and tumor growth. Immunomodulatory agents can interfere with the inflammation that feeds cancer, but their impact on the transformed cell is poorly understood. The calcium/calcineurin signaling pathway, through activation of NFAT, is essential for effective immune responses, and its inhibitors cyclosporin A (CsA) and FK506 are used in the clinics to suppress immunity. Moreover, the kinases GSK3β and mTOR, modulated by PI-3K/Akt, can inhibit NFAT activity, suggesting a cross-talk between the calcium and growth factor signaling pathways. Both NFAT and mTOR activity have been associated with tumorigenesis. We therefore investigated the impact of calcineurin and PI-3K/mTOR inhibition in growth of human colon carcinoma cells. We show that despite the efficient inhibition of NFAT1 activity, FK506 promotes tumor growth, whereas CsA inhibits it due to a delay in cell cycle progression and induction of necroptosis. We found NFκB activation and mTORC1 activity not to be altered by CsA or FK506. Similarly, changes to mitochondrial homeostasis were equivalent upon treatment with these drugs. We further show that, in our model, NFAT1 activation is not modulated by PI3K/mTOR. We conclude that CsA slows cell cycle progression and induces necroptosis of human carcinoma cell lines in a TGFβ-, NFAT-, NFκB- and PI3K/mTOR-independent fashion. Nevertheless, our data suggest that CsA, in addition to its anti-inflammatory capacity, may target transformed colon and esophagus carcinoma cells without affecting non-transformed cells, promoting beneficial tumoristatic effects.

cIAP2 represses IKKα/β-mediated activation of MDM2 to prevent p53 degradation

Rosanna Lau, Min Ying Niu and M.A. Christine Pratt
Pages 4009 - 4019
http://dx.doi.org/10.4161/cc.22223
Abstract | Full Text | PDF

Cellular inhibitor of apoptosis proteins (cIAP1 and cIAP2) function to prevent apoptosis and are often overexpressed in various cancers. However, mutations in cIAP1/2 can activate the alternative NFκB pathway through IκBα-kinase-α (IKKα) and are associated with hematopoetic malignancies. In the current study, we found that knockdown of cIAP2 in human mammary epithelial cells resulted in activation of MDM2 through increased SUMOylation and profound reduction of the pool of MDM2 not phosphorylated at Ser166. cIAP2 siRNA markedly decreased p53 levels, which were rescued by addition of the MDM2 inhibitor, Nutlin3a. An IAP antagonist, which induces cIAP degradation, transiently increased MDM2 mRNA. Simultaneous transfection of siRNA for cIAP2 and IKKα reduced MDM2 protein, while expression of a kinase-dead IKKβ strongly increased non-Ser166 P-MDM2. Inhibition of either IKKα or -β partially rescued p53 levels, while concomitant IKKα/β inhibition fully rescued p53 after cIAP2 knockdown. Surprisingly, IKKα knockdown alone increased SUMO-MDM2, suggesting that in the absence of activation, IKKα can prevent MDM2 SUMOylation. cIAP2 knockdown disrupted the interaction between the MDM2 SUMO ligase, PIAS1 and IKKα. Partial knockdown of cIAP2 cooperated with ^V12H-ras-transfected mammary epithelial cells to enhance colony formation. In summary, our data identify a novel role for cIAP2 in maintaining wild-type p53 levels by preventing both an NFκB-mediated increase and IKKα/-β-dependent transcriptional and post-translational modifications of MDM2. Thus, mutations or reductions in cIAP2 could contribute to cancer promotion, in part, through downregulation of p53.

Epithelial-to-mesenchymal transition (EMT) confers primary resistance to trastuzumab (Herceptin)

Cristina Oliveras-Ferraros, Bruna Corominas-Faja, Sílvia Cufí, Alejandro Vazquez-Martin, Begoña Martin-Castillo, Juan Manuel Iglesias, Eugeni López-Bonet, Ángel G. Martin and Javier A. Menendez
Pages 4020 - 4032
http://dx.doi.org/10.4161/cc.22225
Abstract | Full Text | PDF

The rate of inherent resistance to single-agent trastuzumab in HER2-overexpressing metastatic breast carcinomas is impressive at above 70%. Unfortunately, little is known regarding the distinctive genetic signatures that could predict trastuzumab refractoriness ab initio. The epithelial-to-mesenchymal transition (EMT) molecular features, HER2 expression status and primary responses to trastuzumab were explored in the public Lawrence Berkeley Laboratory (LBL) Breast Cancer Collection. Lentivirus-delivered small hairpin RNAs were employed to reduce specifically and stably the expression of EMT transcription factors in trastuzumab-refractory basal/HER2⁺ cells. Cell proliferation assays and pre-clinical nude mice xenograft-based studies were performed to assess the contribution of specific EMT transcription factors to inherent trastuzumab resistance. Primary sensitivity to trastuzumab was restricted to the SLUG/SNAIL2-negative subset of luminal/HER2⁺ cell lines, whereas all of the SLUG/SNAIL2-positive basal/HER2⁺ cell lines exhibited an inherent resistance to trastuzumab. The specific knockdown of SLUG/SNAIL2 suppressed the stem-related CD44⁺CD24^-/low mesenchymal immunophenotype by transcriptionally upregulating the luminal epithelial marker CD24 in basal/HER2⁺ cells. Basal/HER2⁺ cells gained sensitivity to the growth-inhibitory effects of trastuzumab following SLUG/SNAIL2 gene depletion, which induced the expression of the mesenchymal-to-epithelial transition (MET) genes involved in promoting an epithelial phenotype. The isolation of CD44⁺CD24^-/low mesenchymal cells by magnetic-activated cell sorting (MACS) confirmed their intrinsic unresponsiveness to trastuzumab. A reduction in tumor growth and dramatic gain in sensitivity to trastuzumab in vivo were confirmed when the SLUG/SNAIL2 knockdown basal/HER2⁺ cells were injected into nude mice. HER2 overexpression in a basal, rather than in a luminal molecular background, results in a basal/HER2⁺ breast cancer subtype that is intrinsically resistant to trastuzumab. EMT transcription factors might induce an enhanced phenotypic plasticity that would allow basal/HER2⁺ breast cancer cells to “enter” into and “exit” dynamically from trastuzumab-responsive stem cell-like states. The systematic determination of SLUG/SNAIL2 as a stem/CD44⁺CD24^-/low cell-associated protein may improve the therapeutic management of HER2⁺ breast carcinomas.

p53 mutation alters the effect of the esophageal tumor suppressor KLF5 on keratinocyte proliferation

Yizeng Yang, Rohinton S. Tarapore, Melissa H. Jarmel, Marie-Pier Tetreault and Jonathan P. Katz
Pages 4033 - 4039
http://dx.doi.org/10.4161/cc.22265
Abstract | Full Text | PDF

Krüppel-like factor 5 (KLF5) is a key transcriptional regulator that is typically pro-proliferative in non-transformed epithelial cells but inhibits proliferation in transformed epithelial cells. However, the underlying mechanisms for this context-dependent function are not known. KLF5 is epigenetically silenced and exhibits a tumor suppressive function in esophageal squamous cell cancer (ESCC). Since p53 mutation is the most common genetic alteration in ESCC, as in other human epithelial cancers, we hypothesized that the context-dependent functions of KLF5 in cell proliferation were dependent on p53 status. In fact, in non-transformed human primary esophageal keratinocytes, when p53 was wild-type, KLF5 was pro-proliferative; however, KLF5 became anti-proliferative when p53 was mutated. KLF5 loss in human primary keratinocytes harboring p53 mutation accelerated the cell cycle and decreased expression of p21^Waf1/Cip1; similar effects were also seen in ESCC cells with established p53 mutations. Further, p21^Waf1/Cip1 was directly and differentially bound and regulated by KLF5 in the presence or absence of mutant p53, and suppression of p21^Waf1/Cip1 reversed the antiproliferative effects of KLF5 in the presence of p53 mutation. Thus, KLF5 is a critical brake on an aberrant cell cycle, with important tumor suppressive functions in esophageal squamous cell and potentially other epithelial cancers.

Open Access Article

CDK inhibitors R-roscovitine and S-CR8 effectively block renal and hepatic cystogenesis in an orthologous model of ADPKD

Nikolay O. Bukanov, Sarah E. Moreno, Thomas A. Natoli, Kelly A. Rogers, Laurie A. Smith, Steven R. Ledbetter, Nassima Oumata, Hervé Galons, Laurent Meijer and Oxana Ibraghimov-Beskrovnaya
Pages 4040 - 4046
http://dx.doi.org/10.4161/cc.22375
Abstract | Full Text | PDF

Autosomal dominant polycystic kidney disease (ADPKD) and other forms of PKD are associated with dysregulated cell cycle and proliferation. Although no effective therapy for the treatment of PKD is currently available, possible mechanism-based approaches are beginning to emerge. A therapeutic intervention targeting aberrant cilia-cell cycle connection using CDK-inhibitor R-roscovitine showed effective arrest of PKD in jck and cpk models that are not orthologous to human ADPKD. To evaluate whether CDK inhibition approach will translate into efficacy in an orthologous model of ADPKD, we tested R-roscovitine and its derivative S-CR8 in a model with a conditionally inactivated Pkd1 gene (Pkd1 cKO). Similar to ADPKD, Pkd1 cKO mice developed renal and hepatic cysts. Treatment of Pkd1 cKO mice with R-roscovitine and its more potent and selective analog S-CR8 significantly reduced renal and hepatic cystogenesis and attenuated kidney function decline. Mechanism of action studies demonstrated effective blockade of cell cycle and proliferation and reduction of apoptosis. Together, these data validate CDK inhibition as a novel and effective approach for the treatment of ADPKD.

B-Myb promotes S-phase independently of its sequence-specific DNA binding activity and interacts with polymerase delta-interacting protein 1 (Pdip1)

Eugen Werwein, Thore Schmedt, Heiko Hoffmann, Clemens Usadel, Nora Obermann, Jeffrey D. Singer and Karl-Heinz Klempnauer
Pages 4047 - 4058
http://dx.doi.org/10.4161/cc.22386
Abstract | Full Text | PDF

B-Myb is a highly conserved member of the Myb transcription factor family, which plays an essential role in cell cycle progression by regulating the transcription of genes at the G₂/M-phase boundary. The role of B-Myb in other parts of the cell cycle is less well-understood. By employing siRNA-mediated silencing of B-Myb expression, we found that B-Myb is required for efficient entry into S-phase. Surprisingly, a B-Myb mutant that lacks sequence-specific DNA-binding activity and is unable to activate transcription of B-Myb target genes is able to rescue the S-phase defect observed after B-Myb knockdown. Moreover, we have identified polymerase delta-interacting protein 1 (Pdip1), a BTB domain protein known to bind to the DNA replication and repair factor PCNA as a novel B-Myb interaction partner. We have shown that Pdip1 is able to interact with B-Myb and PCNA simultaneously. In addition, we found that a fraction of endogenous B-Myb can be co-precipitated via PCNA, suggesting that B-Myb might be involved in processes related to DNA replication or repair. Taken together, our work suggests a novel role for B-Myb in S-phase that appears to be independent of its sequence-specific DNA-binding activity and its ability to stimulate the expression of bona fide B-Myb target genes.

FBXW7 is involved in Aurora B degradation

Chieh-Lin Teng, Yun-Chi Hsieh, Liem Phan, Jihyun Shin, Chris Gully, Guermarie Velazquez-Torres, Stephen Skerl, Sai-Ching J. Yeung, Shih-Lan Hsu and Mong-Hong Lee
Pages 4059 - 4068
http://dx.doi.org/10.4161/cc.22381
Abstract | Full Text | PDF

FBXW7, a component of E3 ubiquitin ligase, plays an important role in mitotic checkpoint, but its role remains unclear. Aurora B is a mitotic checkpoint kinase that plays a pivotal role in mitosis by ensuring correct chromosome segregation and normal progression through mitosis. Whether Aurora B and FBXW7 are coordinately regulated during mitosis is not known. Here, we show that FBXW7 is a negative regulator for Aurora B. Ectopic expression of FBXW7 can suppress the expression of Aurora B. Accordingly, FBXW7 deficiency leads to Aurora B elevation. Mechanistic studies show that all FBXW7 isoforms are negative regulators of Aurora B expression through ubiquitination-mediated protein degradation. Aurora B interacts with R465 and R505 residues of WD 40 domain of FBXW7. Significantly, inverse correlation between FBXW7 and Aurora B elevation is translated into the deregulation of mitosis. FBWX7 expression mitigates Aurora B-mediated cell growth and mitotic deregulation. In addition, FBXW7 reduces the percentage of multinucleated cells caused by Aurora B overexpression. These data suggest that FBXW7 is an important negative regulator of Aurora B, and that the loss or mutation of FBXW7 as seen in many types of cancer could lead to an abnormal elevation of Aurora B and result in deregulated mitosis, which accelerates cancer cell growth.

Open Access Article

The PERK-eIF2α phosphorylation arm is a pro-survival pathway of BCR-ABL signaling and confers resistance to imatinib treatment in chronic myeloid leukemia cells

Monika Kusio-Kobialka, Paulina Podszywalow-Bartnicka, Philippos Peidis, Eliza Glodkowska-Mrowka, Kamila Wolanin, Grzegorz Leszak, Ilona Seferynska, Tomasz Stoklosa, Antonis E. Koromilas and Katarzyna Piwocka
Pages 4069 - 4078
http://dx.doi.org/10.4161/cc.22387
Abstract | Full Text | PDF

Activation of adaptive mechanisms plays a crucial role in cancer progression and drug resistance by allowing cell survival under stressful conditions. Therefore, inhibition of the adaptive response is considered as a prospective therapeutic strategy. The PERK-eIF2α phosphorylation pathway is an important arm of the unfolded protein response (UPR), which is induced under conditions of endoplasmic reticulum (ER) stress. Our previous work showed that ER stress is induced in chronic myeloid leukemia (CML) cells. Herein, we demonstrate that the PERK-eIF2α phosphorylation pathway is upregulated in CML cell lines and CD34⁺ cells from CML patients and is associated with CML progression and imatinib resistance. We also show that induction of apoptosis by imatinib results in the downregulation of the PERK-eIF2α phosphorylation arm. Furthermore, we demonstrate that inactivation of the PERK-eIF2α phosphorylation arm decreases the clonogenic and proliferative capacities of CML cells and sensitizes them to death by imatinib. These findings provide evidence for a pro-survival role of PERK-eIF2α phosphorylation arm that contributes to CML progression and development of imatinib resistance. Thus, the PERK-eIF2α phosphorylation arm may represent a suitable target for therapeutic intervention for CML disease.

Featured Article - FREE

Erlotinib antagonizes ABC transporters in acute myeloid leukemia

Elodie Lainey, Marie Sébert, Sylvain Thépot, Marie Scoazec, Cyrielle Bouteloup, Carole Leroy, Stéphane De Botton, Lorenzo Galluzzi, Pierre Fenaux and Guido Kroemer
Pages 4079 - 4092
http://dx.doi.org/10.4161/cc.22382
Abstract | Full Text | PDF

Erlotinib was originally developed as an epidermal growth factor receptor (EGFR)-specific inhibitor for the treatment of solid malignancies, yet also exerts significant EGFR-independent antileukemic effects in vitro and in vivo. The molecular mechanisms underlying the clinical antileukemic activity of erlotinib as a standalone agent have not yet been precisely elucidated. Conversely, in preclinical settings, erlotinib has been shown to inhibit the constitutive activation of SRC kinases and mTOR, as well as to synergize with the DNA methyltransferase inhibitor azacytidine (a reference therapeutic for a subset of leukemia patients) by promoting its intracellular accumulation. Here, we show that both erlotinib and gefitinib (another EGFR inhibitor) inhibit transmembrane transporters of the ATP-binding cassette (ABC) family, including P-glycoprotein (P-gp), multidrug resistance-associated proteins (MRPs) and breast cancer resistance protein (BCRP), also in acute myeloid leukemia (AML) cells that do not overexpress these pumps. Thus, inhibition of drug efflux by erlotinib and gefitinib selectively exacerbated (in a synergistic or additive fashion) the cytotoxic response of KG-1 cells to chemotherapeutic agents that are normally extruded by ABC transporters (e.g., doxorubicin and etoposide). Erlotinib limited drug export via ABC transporters by multiple mechanisms, including the downregulation of surface-exposed pumps and the modulation of their ATPase activity. The effects of erlotinib on drug efflux and its chemosensitization profile persisted in patient-derived CD34⁺ cells, suggesting that erlotinib might be particularly efficient in antagonizing leukemic (stem cell) subpopulations, irrespective of whether they exhibit or not increased drug efflux via ABC transporters.




LETTER TO THE EDITOR

Level of cdk5 expression predicts the survival of relapsed multiple myeloma patients

Zachary Levacque, Jesusa L. Rosales and Ki-Young Lee
Pages 4093 - 4095
http://dx.doi.org/10.4161/cc.21886
Full Text | PDF