Table of Contents

Volume 1, Issue 6

  November/December 2002

  Pages 360 - 437

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PORTRAIT OF AN EDITORIAL BOARD MEMBER

Open Access Article

Carlo M. Croce: Seeking Truth and Beauty

Kay Huebner
Pages 360 - 361
http://dx.doi.org/10.4161/cc.1.6.256
Abstract | PDF

Believe it or not, as a boy Carlo Croce liked to hang out in art museums, to his mother’s chagrin. There are a lot of art museums in Italy, so his mother started dropping him off and going off to the coffee bar to find more interesting company. He bought his first painting, an old master, at age 12 and that used all his savings. He didn't resume his old master collection until he was in his 30s and had saved some money from his job at the Wistar Institute in Philadelphia. He now has an exciting and growing collection. In the meantime, he received his MD degree from the University of Rome “La Sapienza” while reading textbooks and journals in English to supplement the old style medical education. He planned to join Karl Habel at Scripps Clinic in 1970 for a research fellowship just as Dr. Habel was struck in his prime by a monkey B virus infection, so Carlo was diverted from California to Philadelphia to join Hilary Koprowski's internationally known Wistar Institute of Anatomy and Biology. I was a Ph.D. student at Wistar at the time and witnessed the arrival of the quiet 25 yr. old Italian who was too shy to try out his textbook English. He began his work in somatic cell genetics and virology in a large laboratory where a number of us worked on related projects, including Barbara Knowles (now Associate Director for Research at Jackson Laboratory) and Davor Solter (now Director of Developmental Biology, Max Planck Institute, Freiburg, Germany). One of his first accomplishments was to map the very first viral integration site on chromosome 7q in an SV40 transformed fibroblast cell line, using human-mouse somatic cell hybrids that retained human chromosome 7, the SV40 T-antigen and the SV40 genome. Very recently, one of his hybrid clones was used by others to clone the SV40 genome integration site and to show that the SV40 genome had integrated into a common fragile site. Still using somatic cell hybrids, Carlo Croce and his laboratory began in the late 70s and early 80s to map genes important in cancer, such as the immunoglobulin genes that are rearranged in lymphomas, along with the MYC and BCL2 genes among others. These experiments took advantage of the leukemia/lymphoma specific translocation to walk from immunoglobulin loci, and later TCR loci, into the oncogene loci juxtaposed by translocation, the beginning of positional cloning of translocation breakpoints. These studies involved collaborations with valued colleagues, including Peter Nowell, the co-discoverer with David Hungerford, of the Philadelphia chromosome, the first reported cancer specific chromosome alteration. In the exciting decode of the 1980s, the Croce laboratory published 23 reports in Science, including the discovery of the BCL2 gene with Yoshiide Tsujimoto (now University of Osaka). They also observed that mistakes by immunoglobulin family rearrangement/recombination machinery was responsible for the type of chromosome translocations that involved the IG and TCR genes. Carlo Croce has been not only an outstanding laboratory scientist with numerous important discoveries to his credit; he has also been the Director of an NCI designated Cancer Center, first at the Fels Institute for Cancer Research, where he built a first class basic cancer research faculty from the ground up. In 1991, he moved his cancer research faculty to Jefferson Medical College, where it took the name of its benefactor, Sidney Kimmel, and became the Kimmel Cancer Center. At KCI the Croce laboratory continued to find and study genes involved in cancer development: oncogenes activated by translocation such as ALL1, involved in biphenotypic leukemias, discovered with another important collaborator, Eli Canaani and TCL1 (with Gianni Russo’s lab) activated by translocation to the TCRa locus in lymphomas of ataxia telangiectasia patients; or tumor suppressor genes, lost usually through deletions in epithelial cancers, such as FEZ1/LZTS1 at 8p22 lost in prostate, breast and other cancers and the FHIT gene at the 3p14.2 common fragile site (discovered in a collaboration with my laboratory), confirming a long held hypothesis that genes at chromosome fragile sites could contribute to cancer development through frequent chromosomal rearrangements. At the same time, Carlo Croce was living the nearly always tumultuous life of a Director of a Cancer Center, involving recruitment of faculty, constant bargaining with Deans, department chairman, University administrators, but he still manages to fit in a few skiing meetings, gossip sessions with colleagues like Web Cavenee, visits for good coffee, good food and TV appearances in his beloved Italy and most of all, he still manages to study, examine, buy, transport, restore, reframe and admire his old master paintings. I think he loves it as much as science because discovering a beautiful but misattributed painting at an obscure or even well known auction house, buying it and then proving that it is actually a painting by a Gentileschi or a Cavallino is as thrilling and elegant as discovering the connection between a specific gene alteration and its cancer.




REVIEW: SPOTLIGHT ON CANCER THERAPY

Open Access Article

Therapeutic Exploitation of Checkpoint Defects in Cancer Cells Lacking p53 Function

Helen Dixon and Chris J. Norbury
Pages 362 - 368
http://dx.doi.org/10.4161/cc.1.6.257
Abstract | PDF

Cytotoxic agents form the basis of most cancer therapies. These agents primarily affect rapidly proliferating cells, so their use incurs morbidity associated with damage to tissues such as bone marrow and gastrointestinal mucosa. Clinical outcome would be improved if it were possible to develop therapeutics with more specific activity against p53-deficient cancers, which account for over 50% of all cases. p53 deficiency alters the cellular response to DNA damage in that it leaves cells with attenuated DNA damage checkpoint controls and a reduced propensity for apoptotic cell death. Thus, the DNA repair capacity of these cells is reduced but survival is increased. This promotes genomic instability and contributes to the resistance of p53-deficient cells to cytotoxic agents. Disabling the residual G2 checkpoint function of p53-deficient cells may favour cell death following DNA damage. Several potential strategies for G2 checkpoint abrogation show promise for the specific sensitization of cancer cells. Here we detail how the G2 DNA damage checkpoint is influenced by p53 status and how the loss of p53 function in cancer cells can be exploited to enhance the cytotoxicity of anti-cancer agents.

Open Access Article

Cell Cycle Phase-Specific CHemotherapy: Computation Methods for Guiding Treatment

Shea N. Gardner
Pages 369 - 374
http://dx.doi.org/10.4161/cc.1.6.258
Abstract | PDF

Computational models of cancer chemotherapy enhance the understanding of in vitro, in vivo, and clinical trial data and have the potential to contribute to the design of rational treatment regimens. In particular, mechanistic, predictive models are superior to statistical, phenomenological descriptions of data. Mechanistic models based on functional data from tumor biopsies will enable the response to treatment to be predicted for a specific patient, in contrast to statistical models in which the probability of response for a given patient may differ substantially from the population average. This review summarizes mathematical models developed to improve the design of treatment regimens using cell-cycle phase-specific chemotherapy. It starts with simple models of dose response, then moves to more complex models of scheduling cell-cycle phase-specific drugs, and finally discusses mechanistic models that incorporate both genetic drug resistance and cell cycle-mediated drug resistance. This last class of models will be most useful in designing treatment regimens tailored for individual patients.

Key words

Cell-cycle phase-specific drugs, Mathematical models, Cell kinetic, Drug resistance, Chemotherapy, Tumor heterogeneity

Open Access Article

Cyclotherapy: Protection of Normal Cells and Unshielding of Cancer Cells

Mikhail V. Blagosklonny and Zbigniew Darzynkiewicz
Pages 375 - 382
http://dx.doi.org/10.4161/cc.1.6.259
Abstract | PDF

Avoidance of apoptosis and mitogen-independent growth are hallmarks of cancer. Mitogen-activated kinases (for example, ErbB1, Raf-1, MEK, PI-3-K, mTOR) can suppress chemotherapy-induced apoptosis in cancer cells. While kinase inhibitors restore susceptibility of cancer cells to apoptosis, they do not necessarily cause growth arrest in cancer cells harboring additional mutations in downstream signaling pathways such as inactivation of Rb and overexpression of c-myc. This article provides a conceptual basis for a novel use of inhibitors of mitogenic kinases. While arresting growth of normal cells, kinase inhibitors may not arrest cancer cells but instead can sensitize them to apoptosis. Following pretreatment with low doses of kinase inhibitors, the chemotherapy that predominantly induces apoptosis in cycling cells (cyclotherapy) will kill cancer cells while sparing normal cells.

Key words

Cancer, Kinase inhibitors, Chemotherapy

Open Access Article

Conversion of Drug-Induced Differentiation to Apoptosis by Pharmacologic Cyclin-Dependent Kinase Inhibitors

Steven Grant and Paul Dent
Pages 383 - 388
http://dx.doi.org/10.4161/cc.1.6.260
Abstract | PDF

Recently, considerable attention has focused on the clinical development of novel anticancer agents which are intended to induce differentiation (i.e., protein kinase C activators and histone deacetylase inhibitors) or to inhibit cyclin-dependent kinases (CDKs) (i.e., flavopiridol and UCN-01). Because the differentiation process requires cell cycle arrest (e.g., in G1), the possibility arises that CDK inhibitors might potentiate the maturation response of neoplastic cells to various differentiation-inducing agents. However, recent findings indicate that contrary to expectations, pharmacologic CDK inhibitors fail to promote differentiation, at least in human leukemia cells; instead, they antagonize the maturation process and induce dysregulation of various cell cycle and apoptotic regulatory proteins that culminate in mitochondrial injury and apoptosis. A brief summary of the events that might contribute to these phenomena in human leukemia cells follows below. A better understanding of interactions between putative differentiation-inducers and cell cycle inhibitors may provide the foundation for the future development of novel chemotherapeutic strategies in hematopoietic and possibly non-hematopoietic malignancies.




FOCUS ON P27

Open Access Article

Keeping p27^Kip1 in the Cytoplasm: A Second Front in Cancer's War on p27

Steven I. Reed
Pages 389 - 390
http://dx.doi.org/10.4161/cc.1.6.261
Abstract | PDF

no abstract available

Open Access Article

Are p27 and p21 Cytoplasmic Oncoproteins?

Mikhail V. Blagosklonny
Pages 391 - 393
http://dx.doi.org/10.4161/cc.1.6.262
Abstract | PDF

By causing cytoplasmic mislocation of p27 and p21, the Akt oncogenic kinase functionally inactivates these nuclear tumor suppressor proteins. Is cytoplasmic localization of p27 and p21 simply equivalent to loss of their function or are new functions acquired in the cytoplasm? Indeed, several lines of evidence suggest that cytoplasmic p27 and p21 may be oncoproteins with antiapoptotic activities.

Open Access Article

Understanding p27^kip1 Deregulation in Cancer: Downregulation or Mislocalizaiton?

Giuseppe Viglietto, Maria Letizia Motti and Alfredo Fresco
Pages 394 - 400
http://dx.doi.org/10.4161/cc.1.6.263
Abstract | PDF

There is considerable evidence that the inactivation of the cyclin-dependent kinase inhibitor p27kip1 is a fundamental step for the development of human malignancies. In particular, reduced expression of p27kip1, due to increased protein degradation, correlates with poor prognosis of patients affected by various types of cancer. The purpose of this mini-review is to present an overview of the current understanding of the alteration of p27kip1 function in human cancer and to describe the different mechanisms that contributes to it. Particular emphasis is placed on the novel finding of p27kip1 mislocalization in tumor cells and on the biochemical pathways responsible for p27kip1 cytosolic accumulation. Finally, we review the possible clinical implications of these observations with respect to prognosis and novel anticancer therapies.




VIEWS AND COMMENTARIES

Open Access Article

CHK2: A Tumor Suppressor or Not?

Clare H. McGowan
Pages 401 - 403
http://dx.doi.org/10.4161/cc.1.6.264
Abstract | PDF

no absract available

Open Access Article

Open Heart Surgery of PI-3 Kinase Signaling

James R. Woodgett
Pages 404 - 405
http://dx.doi.org/10.4161/cc.1.6.265
Abstract | PDF

no absract available

Open Access Article

Empty Pockets Yield More Telomere Change

William C. Hahn
Pages 406 - 407
http://dx.doi.org/10.4161/cc.1.6.266
Abstract | PDF

no absract available

Open Access Article

Chk2 Meets Plk3 in Damage Control

Chris R. Herzog
Pages 408 - 409
http://dx.doi.org/10.4161/cc.1.6.268
Abstract | PDF

no absract available




EXPERIMENTAL PAPERS

Open Access Article

Derivatives of Vitamins D₂ and D₃ Activate Three MAPK Pathways and Upregulate pRb Expression in Differentiating HL60 Cells

Yen Ji, Andrzg Kutner, Annemieke Verstuyf, Lieve Verlinden and George P. Studzinski
Pages 410 - 415
http://dx.doi.org/10.4161/cc.1.6.269
Abstract | PDF

Analogs of vitamin D have been synthesized which have reduced calcemic activities yet increased anti-proliferative and differentiation-inducing properties, raising expectations that they will be useful for treatment of human neoplastic diseases. In the present study we compared the abilities of three such analogs, 24a, 24b-dihomo-1,25-dihydroxyvitamin D₃ (PRI-1890), 24-ene-1,25-dihydroxyvitamin D₂(PRI-1906) and (24R)-1,24-dihydroxy-vitamin D₃ (PRI-2191) to induce markers (CD14, CD11b and MSE) of differentiation, G₁ phase block, and associated molecular events in human promyeloblastic leukemia cells HL60. We found that the potencies of the analogs to induce differentiation paralleled their activation of Erk, JNK and p38 mitogen-activated protein kinase (MAPK) pathways, and the anti-proliferative activity closely correlated with the extent of hypophosphorylation of retinoblastoma protein (pRb). Interestingly, low concentrations of derivatives of vitamin D, which were insufficient to induce any detectable changes in the cell cycle traverse, markedly increased the levels of total pRb, which was highly phosphorylated. These results suggest that pRb may have an unsuspected role in monocytic differentiation, perhaps to increase the sensitivity of the G₁ checkpoint, by increasing the amount of substrate for cyclin-dependent kinases.

Open Access Article

DNMT1 is a Component of a Multiprotein DNA Replication Complex

Paula M. Vertino, Jennifer A. Sekowski, Jennifer M. Coll, Nancy Applegreen, Suhua Han, Robert J. Hickey and Linda H. Malkas
Pages 416 - 423
http://dx.doi.org/10.4161/cc.1.6.270
Abstract | PDF

DNA methylation is a major determinant of epigenetic inheritance and plays an important role in genome stability. The accurate propagation of DNA methylation patterns with cell division requires that methylation be closely coupled to DNA replication, however the precise molecular determinants of this interaction have not been defined. In the present study, we show that the predominant DNA methyltransferase species in somatic cells, DNMT1, is a component of a multiprotein DNA replication complex termed the DNA synthesome that fully supports semi-conservative DNA replication in a cell-free system. DNMT1 protein and activity were found to co-purify with the human DNA synthesome through a series of subcellular fractionation and chromatography steps, resulting in an enrichment of methyltransferase specific activity from two human cell lines. DNA methyltransferase activity co-eluted with in vitro replication activity and DNA polymerase a activity on sucrose density gradients suggesting that DNMT1 is a tightly bound, core component of the replication complex. The synthesome-associated pool of DNA methyltransferase exhibited both maintenance and de novo methyltransferase activity and the ratio of the two was similar to that observed in whole cell lysates and for recombinant DNMT1. These data indicate that interactions within the synthesome complex do not influence the intrinsic preference of DNMT1 for hemimethylated DNA, but suggest that newly replicated DNA may be subject to low level de novo methylation. The data indicate that DNA methylation is tightly coupled to replication through physical interaction of DNMT1 and core components of the replication machinery. The definition of the molecular interactions between DNMT1 and other proteins in the replication complex in normal and neoplastic cells will provide further insight into the regulation of DNA methylation and the mechanisms underlying the alteration of DNA methylation patterns during carcinogenesis.

Open Access Article

Genotoxic Stress-Induced Activation of Plk3 is Partly Mediated by Chk2

Suqing Xie, Huiyun Wu, Qi Wang, Jan Kunicki, Raymond O. thomas, Robert E. Hollingsworth, John Cogswell and Wei Dai
Pages 424 - 429
http://dx.doi.org/10.4161/cc.1.6.271
Abstract | PDF

Polo-like kinase 3 (Plk3, alternatively termed Prk) is involved in the regulation of DNA damage checkpoint as well as in M-phase function. Plk3 physically interacts with p53 and phosphorylates this tumor suppressor protein on serine-20, suggesting that the role of Plk3 in cell cycle progression is mediated, at least in part, through direct regulation of p53. Here we show that Plk3 is rapidly activated by reactive oxygen species in normal diploid fibroblast cells (WI-38), correlating with a subsequent increase in p53 protein level. Plk3 physically interacts with Chk2 and the interaction is enhanced upon DNA damage. In addition, Chk2 immunoprecipitated from cell lysates of Daudi (which expressed little Plk3) is capable of stimulating the kinase activity of purified recombinant Plk3 in vitro, and this stimulation is more pronounced when Plk3 is supplemented with Chk2 immunoprecipitated from Daudi after DNA damage. Furthermore, ectopic expression Chk2 activates cellular Plk3. Together, our studies suggest Chk2 may mediate direct activation of Plk3 in response to genotoxic stresses.

Open Access Article

Farnesylated RhoB Prevents Cell Cycle Arrest and Actin Cytoskeleton Disruption Caused by the Geranylgeranyltransferase I Inhibitor GGTI-298

Cuider Allal, Anne Pradines, Andrew D. Hamilton, Said M. Sebti and Gilles FAVRE
Pages 430 - 437
http://dx.doi.org/10.4161/cc.1.6.272
Abstract | PDF

Here we demonstrate that the geranylgeranyltransferase-I inhibitor GGTI-298 inhibits the RhoB pathway and disrupts stress fiber and focal adhesion formation in NIH-3T3 cells. Farnesylated V14RhoB-CAIM (resistant to GGTI-298), but not geranylgeranylated V14RhoB (-CLLL), prevented inhibition of actin stress fiber and focal adhesion formation, underlining the critical role of RhoB. In contrast, farnesylated, V14RhoA (-CVLS) was unable to prevent effects of GGTI 298 on cytoskeleton organization. Furthermore, the ability of GGTI-298 to induce p21WAF and to block cells in the G0/G1 phase of the cell cycle was also prevented by farnesylated V14RhoB but not by farnesylated V14RhoA. Moreover, treatment with GGTI-298 of cells expressing farnesylated RhoB results in accumulation of these cells in the G2/M phase. Therefore, the RhoB pathway is a critical target of GGTI-298.