Table of Contents

Volume 1, Issue 3

  May/June 2002

  Pages 155 - 224

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 Issue Catalogue (MARC XML)

REVIEWS

Open Access Article

Phytochemicals as Cell Cycle Modulators A Less Toxic Approach in Halting Human Cancers

Rana P. Singh, Sivanandhan Dhanalakshmi and Rajesh Agarwal
Pages 155 - 160
http://dx.doi.org/10.4161/cc.1.3.117
Abstract | PDF

The multistep nature of cancer development provides a rationale for cancer prevention. Activation of oncogenes, inactivation of tumor suppressor genes and modulation of mitogenic signal transduction pathways are critical in cancer progression and present attractive targets for cancer prevention/intervention. In this respect, cell cycle regulation and its modulation by various natural (plant-derived) and synthetic agents are gaining widespread attention in recent years. A number of phytochemicals inhibit cell cycle progression in cancer cells, yet their clinical applications are still in infancy. The present review is focused on the modulatory effects of phytochemicals on critical cell cycle molecules, and discusses how they inhibit proliferation and/or induce apoptotic death in cancer cells.

Key Words:

Cell cycle, Cyclins, Growth factors, Oncogenes

Open Access Article

Linking DNA Damage to Cell Cycle Checkpoints

Temesgen Samuel, H. Oliver Weber and Jens Oliver Funk
Pages 161 - 167
http://dx.doi.org/10.4161/cc.1.3.118
Abstract | PDF

Cell cycle checkpoints constitute a network of signal transduction mechanisms to monitor DNA damage and replication and thereby regulate progression through the cell cycle. A series of events is triggered in cells upon DNA damage. Here we describe a framework for the understanding of the functions of the core components involved in the cell cycle response to DNA damage and the relevance to the origin of cancer.

Key Words:

Checkpoint, Tumor suppressor, CDK inhibitor, Genetic instability

Open Access Article

Cold-Shock and the Mammalian Cell Cycle

Conly L. Rieder and Richard W. Cole
Pages 168 - 174
http://dx.doi.org/10.4161/cc.1.3.119
Abstract | PDF

Progression through the cell cycle is temperature sensitive, but the relationship is not straightforward. In culture, many types of mammalian cells fail to undergo the G2/M transition after cooling from 37?C to 16-20?C (moderate hypothermia). However, progression through G1 and S is not blocked at these temperatures, nor is progression through mitosis in cells cooled after they have become committed to the division process. Thus, at least one pathway is present during G2-—but not during G1, S or mitosis—that is selectively disrupted at or below a critical temperature. As a result, a prolonged (24-48 hr) exposure to moderate hypothermia can be used to enrich cultures for G2 cells. A brief (1 hr) exposure to severe hypothermia (4-10?C) is also reported to induce a high degree of mitotic synchrony (up to 80%) in some mammalian cultures. Although the mechanism behind this synchronization remains vague, it may involve a cell cycle checkpoint, triggered in response to the cold shock, that transiently inhibits the G1/S transition.

Key Words:

Mitosis, G2 arrest, G1 arrest, Cell cycle synchronization, Antephase




VIEWS AND COMMENTARIES

Open Access Article

Cell Cycle in Plants: Decatenation Checkpoint is Conserved Across the

William K. Kaufmann
Pages 175 - 176
http://dx.doi.org/10.4161/cc.1.3.120
Abstract | PDF

No Abstract Available

Key Words:

Checkpoints, Decatenation, Topoisomerase II

Open Access Article

BRCA1 and Chk1 in G2/M Checkpoint: A New Order of Regulation

Eva Y.-H. P. Lee
Pages 177 - 179
http://dx.doi.org/10.4161/cc.1.3.121
Abstract | PDF

No Abstract Available

Key Words:

DNA damage, Checkpoints, BRCA1, Chk1

Open Access Article

When Duplicated Centrosomes Won’t Split

Wei Dai
Pages 180 - 182
http://dx.doi.org/10.4161/cc.1.3.122
Abstract | PDF

No Abstract Available

Key Words:

Centrosome duplication, Cdc14, Microtubule organization center, Phosphatase, Kinase

Open Access Article

Arsenic Trioxide: Still a Mystery

Tito Fojo and Susan Bates
Pages 183 - 185
http://dx.doi.org/10.4161/cc.1.3.123
Abstract | PDF

No Abstract Available

Key Words:

APL (acute promyelocyctic leukemia), As2O3, PML (promyelocytic leukemia) gene, PML/RARa fusion protein, HDAC (histone deacetylase inhibitor)




EXPERIMENTAL PAPERS

Open Access Article

A Topoisomerase II-Dependent Checkpoint in G2-Phase Plant Cells Can Be Bypassed by Ectopic Expression of Mitotic Cyclin B2

Juan F. Gimenez-Abian, Magdalena Weingartner, Pavla Binarova, Duncan J. Clarke, Richard G. Anthony, Ornella Calderini, Erwin Heberle-Bors, Susana Moreno, Díaz de la Espina, László Bögre and Consuelo de la Torre
Pages 186 - 191
http://dx.doi.org/10.4161/cc.1.3.124
Abstract | PDF

DNA topoisomerase II is required for mitotic chromosome condensation and segregation. Here we characterize the effects of inhibiting DNA topoisomerase II activity in plant cells using the non-DNA damaging topoisomerase II inhibitor ICRF-193. We report that ICRF-193 abrogated chromosome condensation in cultured alfalfa (Medicago sativa L.) and tobacco (Nicotiana tabaccum L.) mitoses and led to bridged chromosomes at anaphase. Moreover, ICRF-193 treatment delayed entry into mitosis, increasing the frequency of cells having a pre-prophase band of microtubules, a marker of late G2 and prophase, and delaying the activation of cyclin-dependent kinase. These data suggest the existence of a late G2 checkpoint in plant cells that is activated in the absence of topoisomerase II activity. To determine whether the checkpoint-induced delay was a result of reduced cyclin-dependent kinase activity, mitotic cyclin B2 was ectopically expressed. Cyclin B2 bypassed the ICRF-193-induced delay before mitosis, and correspondingly, reduced the frequency of interphase cells with a pre-prophase band. These data provide evidence that plant cells possess a topoisomerase II-dependent G2 cell cycle checkpoint that transiently inhibits mitotic CDK activation and entry into mitosis, and that is overridden by raising the level of CDK activity through the ectopic expression of a plant mitotic cyclin.

Key Words:

Plant cyclin B2, Topoisomerase II, ICRF-193, G2 checkpoint, Microtubules

Open Access Article

Radiation Dose-Dependent Maintenance of G2 Arrest Requires Retinoblastoma Protein

Soheil Naderi, Irina C. Hunton and Jean Y.J. Wang
Pages 192 - 199
http://dx.doi.org/10.4161/cc.1.3.125
Abstract | PDF

In response to ionizing radiation (IR), cell cycle checkpoints are activated to provide time for DNA repair. Several different checkpoint mechanisms have been elucidated. However, mechanisms that regulate the duration of cell cycle arrest are not understood. Previous studies have shown that the retinoblastoma tumor suppressor protein (RB) is required for radiation-induced G1 arrest. Working with primary fibroblasts derived from Rb+/+ and Rb-/- mouse embryos, we show that RB also regulates the duration of G2 arrest. The initial G2 checkpoint response is enhanced in Rb-/- cells due to a defect in G1 arrest. However, the permanent arrest in G2 induced by higher doses of IR does not occur in Rb-/- cells. Rb-/- cells either resumed proliferation or underwent apoptosis at IR doses that caused the majority of Rb+/+ cells to arrest permanently in G2. The prolongation of G2 arrest in Rb+/+ cells correlated with a gradual accumulation of hypophosphorylated RB. Thus, regulation of the RB function may be an important aspect in the maintenance of cell cycle checkpoints in DNA damage response.

Key Words:

RB phosphorylation, Ionizing radiation, DNA damage, G2 checkpoint, Mouse embryo fibroblasts

Open Access Article

Arsenic Trioxide Arrests Cells Early in Mitosis Leading to Apoptosis

H. Dorota Halicka, Piotr Smolewski, Zbigniew Darzynkiewicz, Wei Dai and Frank Traganos
Pages 200 - 208
http://dx.doi.org/10.4161/cc.1.3.126
Abstract | PDF

Arsenic trioxide (As2O3) is highly effective in the treatment of acute promyelocytic leukemias that express the promyelocytic leukemia-retinoic acid receptor-a (PML-RARa) fusion protein. However, evidence has accumulated that As2O3 induces apoptosis regardless of PML-RARa status. Here we show that, at clinically relevant concentrations, As2O3 causes S and G2M phase arrest of both PML-RARa-positive and -negative leukemia cell lines, thus inhibiting their growth. Apoptotic cells are generated predominately from the G2M fraction. Using several independent methods, we demonstrate that the cells accumulated in the G2M peak consist primarily of cells arrested in the early stages of mitosis, prophase, prometaphase and metaphase. In mitotic cells, there was significant activation of caspases, PARP cleavage, and morphological changes characteristic of apoptosis. Unlike microtubule-active drugs that arrest cells in metaphase, arsenic trioxide did not affect the architecture of microtubules. Our data suggest that the antileukemic activities of arsenic may be a result of mitotic arrest which culminates in apoptosis.

Key Words:

PML nuclear bodies (NB), Phosphorylated histone H3

Open Access Article

Degradation of ATM-Independent Decatenation Checkpoint Function in Human Cells is Secondary to Inactivation of p53 and Correlated with Chromosomal Destabilization

William K. Kaufmann, Christine B. Campbell, Dennis A. Simpson, Paula B. Deming, Leonid Filatov, Denise A. Galloway, Xiu J. Zhao, Andrew M. Creighton and C. Stephen Downes
Pages 209 - 217
http://dx.doi.org/10.4161/cc.1.3.127
Abstract | PDF

DNA topoisomerase II is required in the cell cycle to decatenate intertwined daughter chromatids prior to mitosis. To study the mechanisms that cells use to accomplish timely chromatid decatenation, the activity of a catenation-responsive checkpoint was monitored in human skin fibroblasts with inherited or acquired defects in the DNA damage G2 checkpoint. G2 delay was quantified shortly after a brief incubation with ICRF-193, which blocks the ability of topoisomerase II to decatenate chromatids, or treatment with ionizing radiation (IR), which damages DNA. Both treatments induced G2 delay in normal human fibroblasts. Ataxia telangiectasia fibroblasts with defective G2 checkpoint response to IR displayed normal G2 delay after treatment with ICRF-193, demonstrating that ATM kinase was not required for signaling when chromatid decatenation was blocked. The G2 delay induced by ICRF-193 was reversed by caffeine, indicating that active checkpoint signaling was involved. ICRF-193-induced G2 delay also was independent of p53 function, being evident in cells expressing HPV16E6 to inactivate p53. However, as fibroblasts expressing HPV16E6 aged in culture, they lost the ability to delay entry to mitosis, both after DNA damage and when decatenation was blocked. This age-related loss of G2 delay in response to ICRF-193 and IR in E6-expressing cells was blocked by induction of telomerase. Expression of telomerase also prevented chromosomal destabilization in aging E6-expressing cells. These observations lead to a new model of genetic instability, in which attenuation of G2 decatenatory checkpoint function permits cells to enter mitosis with insufficiently decatenated chromatids, leading to aneuploidy and polyploidy.

Key Words:

Checkpoints, DNA damage, Decatenation, Topoisomerase II, ICRF-193, Radiation

Open Access Article

Raf-Induced Cell Cycle Progression in Human TF-1 Hematopoietic Cells

Fumin Chang, Linda S. Steelman and James A. McCubrey
Pages 218 - 224
http://dx.doi.org/10.4161/cc.1.3.128
Abstract | PDF

Ras/Raf/MEK/ERK is a crucial pathway regulating cell cycle progression, apoptosis, and drug resistance. The Ras oncogene is frequently mutated in human cancer, which can result in the activation of the downstream Raf/MEK/ERK cascade leading to cell cycle progression in the absence of a growth stimulus. Raf-induced proliferation has been observed in hematopoietic cells. However, the mechanisms by which Raf affects cell cycle progression are not well described. To investigate the importance of Raf/MEK/ERK signaling in human hematopoietic cell growth, the effects of three different Raf genes, A-Raf, B-Raf and Raf-1, on cell cycle progression and regulatory gene expression were examined in TF-1 cells transformed to grow in response to b-estradiol-regulated DRaf:ER genes. Raf activation increased the expression of cyclin A, cyclin D, cyclin E, and p21Cip1, which are associated with G1 progression. Activated DRaf-1:ER and DA-Raf:ER but not DB-Raf:ER increased Cdk2 and Cdk4 kinase activity. The regulatory role of p16Ink4a, a potent Cdk4 kinase inhibitor, on the kinase activity of Cdk2 and Cdk4 was also examined. Raf induced p16Ink4a suppressor but this did not eliminate Cdk4 kinase activity. These results indicate that human hematopoietic cells transformed to grow in response to activated Raf can be used to elucidate the mechanisms by which various cell cycle regulatory molecules effect cell cycle progression. Furthermore, the differences that the various Raf isoforms have on Cdk4 activity and other cell cycle regulatory molecules can be determined in these cells.

Key Words:

Cell cycle, Raf, p21Cip1, p27Kip1, Cyclins, Cdks, Hematopoietic cells