301
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Abstract
Knowledge about breast carcinogenesis has accumulated during the last decades but has barely been translated into strategies for early detection or prevention of this common disease. Changes in DNA methylation have been recognized as one of the most common molecular alterations in human neoplasia and hypermethylation of gene-promoter regions is being revealed as one of the most frequent mechanisms of loss of gene function. The heritability of methylation states and the secondary nature of the decision to attract or exclude methylation support the idea that DNA methylation is adapted for a specific cellular memory. According to Hanahan and Weinberg, there are six novel capabilities a cell has to acquire to become a cancer cell: limitless replicative potential, self-sufficiency in growth signals, insensitivity to growth-inhibitory signals, evasion of programmed cell death, sustained angiogenesis and tissue invasion and metastasis. This review highlights how DNA-methylation contributes to these features and offers suggestions about how these changes could be prevented, reverted or used as a 'tag' for early detection of breast cancer or, preferably, for detection of premalignant changes.
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Affiliation(s)
- Martin Widschwendter
- USC/Norris Comprehensive Cancer Center, Keck School of Medicine of the University of Southern California, 1441 Eastlake Avenue, MS 8302L, Los Angeles, California, CA 90089-9181, USA.
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302
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Rubio MA, Kim SH, Campisi J. Reversible manipulation of telomerase expression and telomere length. Implications for the ionizing radiation response and replicative senescence of human cells. J Biol Chem 2002; 277:28609-17. [PMID: 12034742 DOI: 10.1074/jbc.m203747200] [Citation(s) in RCA: 73] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Most human cells do not express telomerase and irreversibly arrest proliferation after a finite number of divisions (replicative senescence). Several lines of evidence suggest that replicative senescence is caused by short dysfunctional telomeres, which arise when DNA is replicated in the absence of adequate telomerase activity. We describe a method to reversibly bypass replicative senescence and generate mass cultures that have different average telomere lengths. A retrovirus carrying hTERT flanked by excision sites for Cre recombinase rendered normal human fibroblasts telomerase-positive and replicatively immortal. Superinfection with retroviruses carrying wild-type or mutant forms of TIN2, a negative regulator of telomere length, created telomerase-positive, immortal populations with varying average telomere lengths. Subsequent infection with a Cre-expressing retrovirus abolished telomerase activity, creating mortal cells with varying telomere lengths. Using these cell populations, we show that, after hTERT excision, cells senesce with shorter telomeres than parental cells. Moreover, long telomeres, but not telomerase, protected cells from the loss of division potential caused by ionizing radiation. Finally, although telomerase-negative cells with short telomeres senesced after fewer doublings than those with long telomeres, telomere length per se did not correlate with senescence. Our results support a role for telomere structure, rather than length, in replicative senescence.
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Affiliation(s)
- Miguel A Rubio
- Life Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
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303
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Kim H, Farris J, Christman SA, Kong BW, Foster LK, O'Grady SM, Foster DN. Events in the immortalizing process of primary human mammary epithelial cells by the catalytic subunit of human telomerase. Biochem J 2002; 365:765-72. [PMID: 11978176 PMCID: PMC1222721 DOI: 10.1042/bj20011848] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2001] [Revised: 04/12/2002] [Accepted: 04/29/2002] [Indexed: 11/17/2022]
Abstract
The in vitro immortalization of primary human mammary epithelial (HME) cells solely by the exogenous introduction of the catalytic subunit of human telomerase (hTERT) has been achieved. Early passage hTERT-transfected HME (T-HME) cells continuously decreased the length and density of telomeres even in the presence of telomerase activity, with a significant number of cells staining positive for senescence-associated beta-galactosidase (SA-beta-gal). Subsequently, with the increase in cell passages, the copy number of the exogenously transfected hTERT gene and the percentage of SA-beta-gal positive cells were found to decrease. Eventually, a single copy of the exogenous hTERT gene was observed in the relatively later passage T-HME cells in which telomere length was elongated and stabilized without obvious activation of endogenous hTERT and c-Myc expression. In T-HME cells, the expression of two p53 regulated genes p21(WAF) and HDM2 increased (as in primary senescent HME cells), and was found to be further elevated as the function of p53 was activated by treatment with DNA-damaging agents. p16(INK4a) was shown to be significantly higher in the primary senescent HME and the early passage T-HME cells when compared with the primary presenescent HME cells, with a dramatic repression of p16(INK4a) observed in the later passage T-HME cells. In addition, the expression of E2F1 and its transcription factor activity were found to be significantly higher in the later passage T-HME cells when compared with the earlier passage T-HME cells. Together, our results indicate that in vitro immortalization in HME cells may require the activation of the function of telomerase and other genetic alterations such as the spontaneous loss of p16(INK4a) expression.
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Affiliation(s)
- Hyunggee Kim
- Department of Animal Science, University of Minnesota, St. Paul, MN 55108, U.S.A
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304
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Abstract
Cancer is a disease of impaired genome stability. The molecular forces that maintain genome integrity and sense altered chromosome structure are invariably subverted in cancer cells. Here, we explore the contrasting contributions of telomeres in the initiation and suppression of cancer and review the evidence supporting a role for telomere dysfunction as a mechanism driving the radical chromosomal aberrations that typify cancer genomes. Recent work suggests that passage of cells through crisis in the setting of deactivated DNA damage checkpoints provides a mutational mechanism that can generate the diverse genetic alterations required for cancer initiation. A greater understanding of telomere-induced crisis and the cell's crisis management mechanisms should guide the rational development of new therapeutics for cancer and other disorders.
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Affiliation(s)
- Richard S Maser
- Department of Adult Oncology, Dana-Farber Cancer Institute, Harvard Medical School, 44 Binney Street, M413, Boston, MA 02115, USA
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305
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Abstract
Replicative aging is the process by which most normal human cells "count" the number of times they have divided, eventually undergoing a growth arrest termed cellular senescence. This process is dependent on the shortening of telomeres, repeated sequences at the ends of the chromosomes. The loss of telomeric sequences with each cell division eventually induces a growth arrest that has a similar phenotype to that of cells stressed by inadequate culture or other conditions. Experiments over the past several years have identified species in which replicative aging does not occur and many examples in which a failure to proliferate has been misinterpreted as replicative senescence. Insights from these studies now permit a reevaluation of much of the seemingly contradictory data concerning replicative aging. There are good theoretical reasons for believing a limited proliferative capacity contributes to declining tissue homeostasis with increasing age. Although the presence of telomere shortening provides strong circumstantial evidence that replicative aging is occurring in vivo, thus far there is only very limited direct evidence for actual physiological effects of replicative aging.
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Affiliation(s)
- Woodring E Wright
- Department of Cell Biology, University of Texas Southwestern Medical Center, Dallas, TX 75390-9039, USA.
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306
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Abstract
A long-standing controversy concerns the relevance of cellular senescence, defined and observed as a cell culture phenomenon, to tissue aging in vivo. Here the evidence on this topic is reviewed. The main conclusions are as follows. First, telomere shortening, the principal known mediator of cellular senescence, occurs in many human tissues in aging. Second, it is not clear whether this results in cellular senescence or in some other cell fate (e.g., crisis). Third, rodents probably are not appropriate experimental models for these questions, because of important differences in telomere biology between rodent cells and cells from long-lived mammals (e.g., human or bovine cells). Fourth, better and more comprehensive observations on aging human tissues are needed to answer the question of the occurrence of senescent cells in tissues, and new experimental approaches are needed to elucidate the consequences of telomere shortening in tissues in aging.
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Affiliation(s)
- Peter J Hornsby
- Department of Physiology and the Sam and Ann Barshop Center for Longevity and Aging Studies, University of Texas Health Science Center, San Antonio 78245, USA.
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307
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Dumont JE, Dremier S, Pirson I, Maenhaut C. Cross signaling, cell specificity, and physiology. Am J Physiol Cell Physiol 2002; 283:C2-28. [PMID: 12055068 DOI: 10.1152/ajpcell.00581.2001] [Citation(s) in RCA: 58] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
The literature on intracellular signal transduction presents a confusing picture: every regulatory factor appears to be regulated by all signal transduction cascades and to regulate all cell processes. This contrasts with the known exquisite specificity of action of extracellular signals in different cell types in vivo. The confusion of the in vitro literature is shown to arise from several causes: the inevitable artifacts inherent in reductionism, the arguments used to establish causal effect relationships, the use of less than adequate models (cell lines, transfections, acellular systems, etc.), and the implicit assumption that networks of regulations are universal whereas they are in fact cell and stage specific. Cell specificity results from the existence in any cell type of a unique set of proteins and their isoforms at each level of signal transduction cascades, from the space structure of their components, from their combinatorial logic at each level, from the presence of modulators of signal transduction proteins and of modulators of modulators, from the time structure of extracellular signals and of their transduction, and from quantitative differences of expression of similar sets of factors.
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Affiliation(s)
- J E Dumont
- Institute of Interdisciplinary Research, Free University of Brussels, Campus Erasme, B-1070 Brussels, Belgium.
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308
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Rheinwald JG, Hahn WC, Ramsey MR, Wu JY, Guo Z, Tsao H, De Luca M, Catricalà C, O'Toole KM. A two-stage, p16(INK4A)- and p53-dependent keratinocyte senescence mechanism that limits replicative potential independent of telomere status. Mol Cell Biol 2002; 22:5157-72. [PMID: 12077343 PMCID: PMC139780 DOI: 10.1128/mcb.22.14.5157-5172.2002] [Citation(s) in RCA: 259] [Impact Index Per Article: 11.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
With increasing frequency during serial passage in culture, primary human keratinocytes express p16(INK4A) (p16) and undergo senescence arrest. Keratinocytes engineered to express hTERT maintain long telomeres but typically are not immortalized unless, by mutation or other heritable event, they avoid or greatly reduce p16 expression. We have confirmed that keratinocytes undergo p16-related senescence during growth in culture, whether in the fibroblast feeder cell system or in the specialized K-sfm medium formulation, and that this mechanism can act as a barrier to immortalization following hTERT expression. We have characterized the p16-related arrest mechanism more precisely by interfering specifically with several regulators of cell cycle control. Epidermal, oral mucosal, corneal limbal, and conjunctival keratinocytes were transduced to express a p16-insensitive mutant cdk4 (cdk4(R24C)), to abolish p16 control, and/or a dominant negative mutant p53 (p53DD), to abolish p53 function. Expression of either cdk4(R24C) or p53DD alone had little effect on life span, but expression of both permitted cells to divide 25 to 43 population doublings (PD) beyond their normal limit. Keratinocytes from a p16(+/-) individual transduced to express p53DD alone displayed a 31-PD life span extension associated with selective growth of variants that had lost the wild-type p16 allele. Cells in which both p53 and p16 were nonfunctional divided rapidly during their extended life span but experienced telomere erosion and ultimately ceased growth with very short telomeres. Expression of hTERT in these cells immortalized them. Keratinocytes engineered to express cdk4(R24C) and hTERT but not p53DD did not exhibit an extended life span. Rare immortal variants exhibiting p53 pathway defects arose from them, however, indicating that the p53-dependent component of keratinocyte senescence is telomere independent. Mutational loss of p16 and p53 has been found to be a frequent early event in the development of squamous cell carcinoma. Our results suggest that such mutations endow keratinocytes with extended replicative potential which may serve to increase the probability of neoplastic progression.
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Affiliation(s)
- James G Rheinwald
- Department of Dermatology, Brigham and Women's Hospital, Harvard Medical School, 77 Avenue Louis Pasteur, Boston, MA 02115, USA.
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309
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Shimizu Y, Ishida T. Spontaneous establishment of a novel Japanese macaque cell line with epithelial cell phenotypes. In Vitro Cell Dev Biol Anim 2002; 38:311-3. [PMID: 12513117 DOI: 10.1290/1071-2690(2002)038<0311:seoanj>2.0.co;2] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
A novel macaque cell line (J3K) with epithelial phenotypes was spontaneously established from a kidney specimen of a Japanese macaque (Macaca fuscata). Its population doubling level reached more than 500, and it was regarded as an established permanent cell line. J3K cells have transformed cell phenotypes such as loss of contact inhibition and anchorage-independent cell growth. Unlike other monkey adherent cell lines, J3K had no SV40 large T antigen. After establishment, cells have constantly expressed telomerase activity, whereas telomere length has been maintained. No mutations in the coding regions of the p53 complementary deoxyribonucleic acid were detected in the late-passaged cells. J3K, a novel transformed epithelial cell line, will be useful material for the comparative study of human and other primate cellular aging as well as cancer cell biology.
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Affiliation(s)
- Yuko Shimizu
- Department of Biological Sciences, Graduate School of Science, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
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310
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Allsopp RC, Weissman IL. Replicative senescence of hematopoietic stem cells during serial transplantation: does telomere shortening play a role? Oncogene 2002; 21:3270-3. [PMID: 12032768 DOI: 10.1038/sj.onc.1205314] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Hematopoietic stem cells (HSC) have a finite proliferative lifespan, based upon the limited number of times they can be serially transplanted in mice. Telomeres have been shown to shorten during the division of many normal somatic cells in humans, and the attrition of telomeres has been shown to ultimately cause replicative senescence in vitro for a number of different human cell strains. Whereas most human cell types have little to no detectable levels of telomerase activity, hematopoietic cells, including HSC, express low to moderate levels of telomerase, and yet telomeres shorten considerably during replicative aging of these cells. Here we consider the role telomerase may play in the hematopoietic system as well as the effect that over-expression of telomerase reverse transcriptase may have on the replicative capacity of hematopoietic stem cells during transplantation.
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Affiliation(s)
- Richard C Allsopp
- Department of Pathology, Stanford University School of Medicine, Stanford, California, CA 94305, USA.
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311
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Kleer CG, Zhang Y, Pan Q, van Golen KL, Wu ZF, Livant D, Merajver SD. WISP3 is a novel tumor suppressor gene of inflammatory breast cancer. Oncogene 2002; 21:3172-80. [PMID: 12082632 DOI: 10.1038/sj.onc.1205462] [Citation(s) in RCA: 116] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2001] [Revised: 01/11/2002] [Accepted: 03/04/2002] [Indexed: 12/19/2022]
Abstract
Inflammatory breast cancer (IBC) is an aggressive form of breast cancer with a 5-year disease-free survival of less than 45%. Little is known about the genetic alterations that result in IBC. In our previous work, we found that WISP3 was specifically lost in human IBC tumors when compared to stage-matched, non-IBC tumors. We hypothesize that WISP3 has tumor suppressor function in the breast and that it may be a key genetic alteration that contributes to the unique IBC phenotype. The full-length WISP3 cDNA was sequenced and cloned into an expression vector. The resulting construct was introduced in to the SUM149 cell line that was derived from a patient with IBC and lacks WISP3 expression. In soft agar, stable WISP3 transfectants formed significantly fewer colonies than the controls. Stable WISP3 transfectants lost their ability to invade and had reduced angiogenic potential. WISP3 transfection was effective in suppressing in vivo tumor growth in nude mice. Mice bearing WISP3 expressing tumors had a significantly longer survival than those with vector-control transfectant tumors. Our data demonstrate that WISP3 acts as a tumor suppressor gene in the breast. Loss of WISP3 expression contributes to the phenotype of IBC by regulating tumor cell growth, invasion and angiogenesis.
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Affiliation(s)
- Celina G Kleer
- Department of Pathology, University of Michigan Comprehensive Cancer Center, 1500 East Medical Center Drive, Ann Arbor, MI 48109-0054, USA.
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312
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Abstract
Cancer arises from a stepwise accumulation of genetic changes that liberates neoplastic cells from the homeostatic mechanisms that govern normal cell proliferation. In humans, at least four to six mutations are required to reach this state, but fewer seem to be required in mice. By rationalizing the shared and unique elements of human and mouse models of cancer, we should be able to identify the molecular circuits that function differently in humans and mice, and use this knowledge to improve existing models of cancer.
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Affiliation(s)
- William C Hahn
- Whitehead Institute for Biomedical Research, Massachusetts 02142, USA.
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313
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McCaul JA, Gordon KE, Clark LJ, Parkinson EK. Telomerase inhibition and the future management of head-and-neck cancer. Lancet Oncol 2002; 3:280-8. [PMID: 12067805 DOI: 10.1016/s1470-2045(02)00729-5] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
Telomeres are tandem repeats of DNA associated with specific proteins. These structures cap eukaryotic chromosomes and maintain the integrity of the chromosome ends. In the germline, telomeres are maintained by the enzyme telomerase, but in normal somatic cells the enzyme's activity is low or undetectable. Human tumours, including squamous-cell carcinoma of the head and neck (SCCHN), need telomerase to maintain telomere function; inhibition of the enzyme can lead to apoptosis. Furthermore, because most tumour cells have very short telomeres, they are more likely to succumb to telomerase inhibition than normal cells. Telomerase is therefore a potential selective anticancer target. The telomere is also involved in the repair of DNA double strand breaks, and telomere dysfunction provokes radiosensitivity. In this review we consider whether manipulation of telomere function may selectively sensitise SCCHN to radiotherapy and discuss the possible pitfalls. We also assess how some conventional treatments may affect the subsequent use of telomerase inhibitors.
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Affiliation(s)
- James A McCaul
- Maxillofacial surgery, Beatson Institute for Cancer Research, Glasgow, UK.
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314
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Abstract
Multiple myeloma is a neoplasm of terminally differentiated B cells (plasma cells) in which chromosome translocations frequently place oncogenes under the control of immunoglobulin enhancers. Unlike most haematopoietic cancers, multiple myeloma often has complex chromosomal abnormalities that are reminiscent of epithelial tumours. What causes full-blown myeloma? And can our molecular understanding of this common haematological malignancy be used to develop effective preventive and treatment strategies?
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Affiliation(s)
- W Michael Kuehl
- Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda Naval Hospital, Maryland 20889-5105, USA.
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315
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Gao Y, Lu YJ, Xue SA, Chen H, Wedderburn N, Griffin BE. Hypothesis: a novel route for immortalization of epithelial cells by Epstein-Barr virus. Oncogene 2002; 21:825-35. [PMID: 11850810 DOI: 10.1038/sj.onc.1205130] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2001] [Revised: 10/30/2001] [Accepted: 10/31/2001] [Indexed: 11/09/2022]
Abstract
Transfection of primate tissue explants with a specific sub-fragment (p31) of EBV DNA results in epithelial (but no other) cells proliferating indefinitely (becoming 'immortalized') without evidence of a 'growth crisis'. Molecular evidence supports integration of viral information into the host chromosome, and an early genotypic alteration involving specific amplification of a sub-component (IR1) of p31 DNA, followed by apparent loss of viral DNA from chromosomes, consistent with a 'hit and run' mechanism. However, analysis at the individual cell level during long-term culture, by FISH techniques, reveals chromosomal alterations, and viral sequences surviving within double minute (DM) bodies. Changing growth patterns occurring at different stages during propagation (>a year in culture) may be explained by sporadic reintegration of surviving viral DNA into the host chromosome. Notably, throughout culture, telomere lengths in chromosomal DNAs do not alter but rather retain the length observed in the primary cell populations. Introduction of a growth stimulating function of EBV, BARF1, into the immortalized, non-clonable epithelial cells under conditions which permit overexpression, allows clonal populations to be derived. Based on the data, mechanisms of immortalization, in the absence of a proven viral oncogene in p31 DNA, and possible genes involved, are considered.
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Affiliation(s)
- Yanning Gao
- Viral Oncology Unit, Department of Medicine, Imperial College of Science, Technology and Medicine, Norfolk Place, London W2 1PG, UK
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316
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Abstract
The intent of this review is to describe what is known and unknown about telomerase in somatic cells of the human organism. First, we consider the telomerase enzyme. Human telomerase ribonucleoproteins undergo at least three stages of cellular biogenesis: accumulation, catalytic activation and recruitment to the telomere. Next, we describe the patterns of telomerase regulation in the human soma. Telomerase activation in some cell types appears to offset proliferation-dependent telomere shortening, delaying but not defeating the inherent mitotic clock. Finally, we elaborate the connection between telomerase misregulation and human disease, in the contexts of inappropriate telomerase activation and telomerase deficiency. We discuss how our current perspectives on telomerase function could be applied to improving human health.
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Affiliation(s)
- Kathleen Collins
- Department of Molecular and Cell Biology, University of California at Berkeley, Berkeley, California, CA 94720-3204, USA.
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317
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Sprenger CC, Vail ME, Evans K, Simurdak J, Plymate SR. Over-expression of insulin-like growth factor binding protein-related protein-1(IGFBP-rP1/mac25) in the M12 prostate cancer cell line alters tumor growth by a delay in G1 and cyclin A associated apoptosis. Oncogene 2002; 21:140-7. [PMID: 11791184 DOI: 10.1038/sj.onc.1205021] [Citation(s) in RCA: 60] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2001] [Revised: 09/12/2001] [Accepted: 10/02/2001] [Indexed: 11/09/2022]
Abstract
In the present study, we examined the effects of over-expression of the potential tumor suppressor gene IGFBP-rP1/mac25 on cell-cycle kinetics in prostate cancer cells. The majority of the high expressing IGFBP-rP1/mac25 cell population was located in the G1 and sub-G0/G1 peaks; synchronizing cells in G2/M with nocodazole demonstrated the high expressing IGFBP-rP1/mac25 clones were delayed in the G1 phase of the cell cycle. Unscheduled expression of cyclin A in the sub-G0/G1 peak occurred in the IGFBP-rP1/mac25 clones. Immunoblots showed decreased cyclin D1 and p21 and increased cyclin E, p16, and p27 in the high expressing IGFBP-rP1/mac25 clones compared to the control cells. Cyclin D1/cdk-4,6 and cyclin E/cdk-2 kinase activities decreased but cyclin A/cdk-2 kinase activity increased for the high expressing IGFBP-rP1/mac25 clones compared to control cells. A pRb immunoprecipitation demonstrated more binding of E2F-1 to pRb in the high expressing IGFBP-rP1/mac25 clones than in control cells. Finally, cell senescence, as assessed by senescence-associated beta-galactosidase, demonstrated significantly more staining in the IGFBP-rP1/mac25 cells than control cells. These results suggest that IGFBP-rP1/mac25 alters the cell cycle kinetics of the M12 prostate cell line by delaying the cells in the G1 phase of the cell cycle. In addition, the appearance of cyclin A in the sub-G0/G1 phase of the cell cycle and the increased kinase activity of cyclin A/cdk-2 in the IGFBP-rP1/mac25 clones suggests that cyclin A is associated with the apoptotic cells.
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Affiliation(s)
- Cynthia C Sprenger
- Geriatric Research Education and Clinical Center, VAPSHCS, Seattle/Tacoma, Washington, WA 98493, USA
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318
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Toouli CD, Huschtscha LI, Neumann AA, Noble JR, Colgin LM, Hukku B, Reddel RR. Comparison of human mammary epithelial cells immortalized by simian virus 40 T-Antigen or by the telomerase catalytic subunit. Oncogene 2002; 21:128-39. [PMID: 11791183 DOI: 10.1038/sj.onc.1205014] [Citation(s) in RCA: 91] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2001] [Revised: 09/29/2001] [Accepted: 10/01/2001] [Indexed: 12/17/2022]
Abstract
We directly compared two methods of immortalizing human mammary epithelial cells (HMECs). Cells were transfected with an expression plasmid either for hTERT, the catalytic subunit of telomerase, or for the simian virus 40 (SV40) early region genes. Under standard culture conditions, HMECs were not immortalized by hTERT unless they had spontaneously ceased expression of the p16(INK4a) tumor suppressor gene. Untransfected HMECs had low levels of telomerase expression, and immortalization by both methods was associated with an increase in telomerase activity and prevention of telomere shortening. SV40-induced immortalization was accompanied by aberrant differentiation, loss of DNA damage response, karyotypic instability and, in some cases, tumorigenicity. hTERT-immortalized cells had fewer karyotypic changes, but had intact DNA damage responses, and features of normal differentiation. Although SV40-immortalized cells are useful for studies of carcinogenesis, hTERT-immortalized cells retain more properties of normal cells.
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Affiliation(s)
- Christian D Toouli
- Children's Medical Research Institute, 214 Hawkesbury Road, Westmead 2145, Australia
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319
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Abstract
The tumor suppressor p53 controls numerous downstream targets that can result in variable outcomes, including apoptosis, transient growth arrest, and sustained growth arrest or senescence. The activation of p53, followed by its ability to play multiple roles in the control of genomic integrity or the elimination of damaged or tumorigenic cells, is performed by a complex process of cross-talk orchestrated to occur in the different compartments of the cell. Controlling performance of the many roles of p53 is a goal of many research groups and the focus of this review.
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Affiliation(s)
- Jill Bargonetti
- Institute for Biomolecular Structure and Function, Department of Biology, Hunter College and Graduate School, City University of New York, New York City 10021, USA.
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320
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Schwarze SR, Shi Y, Fu VX, Watson PA, Jarrard DF. Role of cyclin-dependent kinase inhibitors in the growth arrest at senescence in human prostate epithelial and uroepithelial cells. Oncogene 2001; 20:8184-92. [PMID: 11781834 DOI: 10.1038/sj.onc.1205049] [Citation(s) in RCA: 82] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2001] [Revised: 09/19/2001] [Accepted: 10/09/2001] [Indexed: 02/07/2023]
Abstract
Cellular senescence has been proposed to be an in vitro and in vivo block that cells must overcome in order to immortalize and become tumorigenic. To characterize these pathways, we focused on changes in the cyclin-dependent kinase inhibitors and their binding partners that underlie the cell cycle arrest at senescence. As a model, we utilized normal human prostate epithelial cell (HPEC) and human uroepithelial cell (HUC) cultures. After 30-40 population doublings cells became growth-arrested in G0/1 with a threefold decrease in Cdk2-associated activity, a point defined as pre-senescence. Temporally following this growth arrest, the cells develop a senescence morphology and express senescence-associated beta-galactosidase (SA-beta-gal). Levels of p16(INK4a) and p57(KIP2) rise in HUCs during progressive passages, whereas only p16 increases in HPEC cultures. The induced expression of p57, similar to p16, produces a senescent-like phenotype. pRB, cyclin D, p19(INK4d) and p27(KIP1) decrease in both cell types. We find that p53, p21(CIP1) and p15(INK4b) are transiently elevated in HPECs and HUCs at the pre-senescent growth arrest, then return to low proliferating levels at terminal senescence. Analysis of p53, p21(CIP1), p15(INK4b), p16(INK4a), and p57(KIP2) reveals altered expression in immortalized, non-tumorigenic HPV16 E6 and E7 prostate lines and in tumorigenic prostate cancer cells. These results indicate: (i) the existence of a subset of growth inhibiting genes elevated at the onset of the senescence, (ii) a distinct class of genes involved in the maintenance of senescence, and (iii) the frequent inactivation of these pathways during immortalization.
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Affiliation(s)
- S R Schwarze
- Department of Surgery, University of Wisconsin Comprehensive Cancer Center and the University of Wisconsin Medical School, Madison, WI 53972, USA
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321
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Abstract
Historically, the senescent state has been associated with, and was named after, the cell-cycle arrest that occurs after cells have undergone an intrinsically defined number of divisions in vitro. More recently, however, it has been shown that extrinsic factors, including those encountered in normal tissue-culture environments, can prematurely induce an indistinguishable senescent phenotype. In this review, we discuss the pathways of cell senescence, the mechanisms involved and the role that these pathways have in regulating the initiation and progression of cancer.
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Affiliation(s)
- N F Mathon
- Department of Biochemistry, University College London, UK
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322
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Speirs V. Normal mammary epithelial cells escape of senescence. Breast Cancer Res 2001. [DOI: 10.1186/bcr-2001-68444] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/03/2023] Open
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323
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Muyrers-Chen I, Paro R. Epigenetics: unforeseen regulators in cancer. BIOCHIMICA ET BIOPHYSICA ACTA 2001; 1552:15-26. [PMID: 11781112 DOI: 10.1016/s0304-419x(01)00032-4] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
The past several years have seen a tremendous advance in the understanding of the basic mechanisms of epigenetic regulation. A large number of studies have not only linked epigenetics with cell cycle regulation but also partially unravelled how epigenetics may regulate gene expression. The aim of this review is to provide an overview of the latest findings and current ideas on epigenetics with a focus on emphasizing the emerging influence epigenetics has on the onset and progression of cancer.
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Affiliation(s)
- I Muyrers-Chen
- ZMBH, University of Heidelberg, INF 282, D-69120 Heidelberg, Germany
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324
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Chou WC, Hawkins AL, Barrett JF, Griffin CA, Dang CV. Arsenic inhibition of telomerase transcription leads to genetic instability. J Clin Invest 2001; 108:1541-7. [PMID: 11714746 PMCID: PMC209426 DOI: 10.1172/jci14064] [Citation(s) in RCA: 85] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
Arsenic is effective in the treatment of acute promyelocytic leukemia. Paradoxically, it is also carcinogenic. In the process of elucidating a mechanism of arsenic resistance in a leukemia cell line, NB4, we discovered that arsenic exposure causes chromosomal abnormalities, with a preponderance of end-to-end fusions. These chromosomal end fusions suggested that telomerase activity may be inhibited by arsenic. We found that arsenic inhibits transcription of the hTERT gene, which encodes the reverse transcriptase subunit of human telomerase. This effect may in part be explained by decreased c-Myc and Sp1 transcription factor activities. Decreased telomerase activity leads to chromosomal end lesions, which promote either genomic instability and carcinogenesis or cancer cell death. These phenomena may explain the seemingly paradoxical carcinogenic and antitumor effects of arsenic.
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Affiliation(s)
- W C Chou
- Program in Human Genetics and Molecular Biology, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA
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325
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Abstract
Telomeres are the repetitive DNA sequences and specialized proteins that form the distinctive structure that caps the ends of linear chromosomes. Telomeres allow cells to distinguish the chromosome ends from double strand DNA breaks. The telomeric structure prevents the degradation or fusion of chromosome ends, and thus is essential for maintaining the integrity and stability of eukaryotic genomes. In addition, and perhaps less widely appreciated, telomeres may also indirectly influence gene expression. The length, structure and organization of telomeres are regulated by a host of telomere-associated proteins, and can be influenced by basic cellular processes such as cell proliferation, differentiation, and DNA damage. In mammalian cells, telomere length and/or telomere structure have been linked to both cancer and aging. Here, we briefly review what is known about mammalian telomeres and the proteins that associate with them, and discuss the cellular and organismal consequences of telomere dysfunction and the evidence that cells with dysfunctional telomeres can contribute to cancer and aging phenotypes.
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Affiliation(s)
- J Campisi
- Life Sciences Division, Lawrence Berkeley National Laboratory, Mailstop 84-171, 1 Cyclotron Road, Berkeley, CA 94720, USA.
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326
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Seewaldt VL, Mrózek K, Sigle R, Dietze EC, Heine K, Hockenbery DM, Hobbs KB, Caldwell LE. Suppression of p53 function in normal human mammary epithelial cells increases sensitivity to extracellular matrix-induced apoptosis. J Cell Biol 2001; 155:471-86. [PMID: 11673474 PMCID: PMC2150841 DOI: 10.1083/jcb.200011001] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
Little is known about the fate of normal human mammary epithelial cells (HMECs) that lose p53 function in the context of extracellular matrix (ECM)-derived growth and polarity signals. Retrovirally mediated expression of human papillomavirus type 16 (HPV-16) E6 and antisense oligodeoxynucleotides (ODNs) were used to suppress p53 function in HMECs as a model of early breast cancer. p53+ HMEC vector controls grew exponentially in reconstituted ECM (rECM) until day 6 and then underwent growth arrest on day 7. Ultrastructural examination of day 7 vector controls revealed acinus-like structures characteristic of normal mammary epithelium. In contrast, early passage p53- HMEC cells proliferated in rECM until day 6 but then underwent apoptosis on day 7. p53- HMEC-E6 passaged in non-rECM culture rapidly (8-10 passages), lost sensitivity to both rECM-induced growth arrest and polarity, and also developed resistance to rECM-induced apoptosis. Resistance was associated with altered expression of alpha3-integrin. Treatment of early passage p53- HMEC-E6 cells with either alpha3- or beta1-integrin function-blocking antibodies inhibited rECM-mediated growth arrest and induction of apoptosis. Our results indicate that suppression of p53 expression in HMECs by HPV-16 E6 and ODNs may sensitize cells to rECM-induced apoptosis and suggest a role for the alpha3/beta1-heterodimer in mediating apoptosis in HMECs grown in contact with rECM.
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Affiliation(s)
- V L Seewaldt
- Division of Medical Oncology, Duke University, Durham, NC 27710, USA.
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327
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Kameda T, Hatakeyama S, Terada K, Sugiyama T. Acceleration of the formation of cultured epithelium using the sonic hedgehog expressing feeder cells. TISSUE ENGINEERING 2001; 7:545-55. [PMID: 11694189 DOI: 10.1089/107632701753213174] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Sonic hedgehog (Shh) regulates the principal possesses in many developmental stages, including the epithelial-mesenchymal interaction. The extraordinary acceleration of signaling by Shh is responsible for the development of human basal cell carcinomas and trichoepitheliomas; they might originate from the very immature keratinocytes, including the stem cells. We tried to utilize the mitogenic effect of Shh to accelerate the formation of cultured epithelium, which is already used in the medical field practically. To this end, we transfected shh cDNA into a Swiss-3T3 cell line, widely used as a feeder for keratinocytes, and established a Shh expressing cell line. The lethally irradiated Shh expressing feeder cells remarkably accelerated the growth of keratinocyte colonies obtained from the human neonatal foreskin, and the formation of well-stratified cultured epithelium, which is rich in immature small keratinocytes, expressing cytokeratin 14. This acceleration was suppressed by the addition of cyclopamine, a specific inhibitor of Shh signaling. These data indicate that the Shh is a promising mitogen to improve the technology for cultured epithelium formation.
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Affiliation(s)
- T Kameda
- Department of Biochemistry, Akita University School of Medicine, Akita, Japan.
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328
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Abstract
The regenerative power of stem cells has raised issues about their relation to aging. We focus on the question of whether a decline in the function of stem cells may itself be a significant feature of aging. The question is implicitly two-fold: does functional depletion of stem cells affect the accumulation of aging-related deficits, and--whether or not depletion is significant--can activation of stem cells alleviate deficits? Two types of system are considered: 1) the exhaustible pool of ovarian follicles. The depletion of follicles leads to the aging-related phenomenon of menopause; and 2) the reserve of hematopoietic stem cells. Substantial numbers are sustained throughout life, but in mouse models, endogenous replicative activity has been shown to decline sharply with age. We discuss the possible implications of these observations for the rate of aging and the prospects for intervention.
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Affiliation(s)
- D Schlessinger
- Laboratory of Genetics, Gerontology Research Center, National Institute on Aging, NIH-NIA, 5600 Nathan Shock Drive, Baltimore, MD 21218, USA.
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329
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Abstract
This review describes the structure of telomeres, the protective DNA-protein complexes at eukaryotic chromosomal ends, and several molecular mechanisms involved in telomere functions. Also discussed are cellular responses to compromising the functions of telomeres and of telomerase, which synthesizes telomeric DNA.
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Affiliation(s)
- E H Blackburn
- Department of Biochemistry and Biophysics, University of California, San Francisco, 94143, USA.
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330
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Klekotka PA, Santoro SA, Ho A, Dowdy SF, Zutter MM. Mammary epithelial cell-cycle progression via the alpha(2)beta(1) integrin: unique and synergistic roles of the alpha(2) cytoplasmic domain. THE AMERICAN JOURNAL OF PATHOLOGY 2001; 159:983-92. [PMID: 11549591 PMCID: PMC1850465 DOI: 10.1016/s0002-9440(10)61774-9] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
The alpha(2)beta(1) integrin supports cell-cycle progression of mammary epithelial cells adherent to type I collagen matrices. Integrin collagen receptors containing the alpha(2) cytoplasmic domain stimulated expression of cyclin E and cyclin-dependent kinase (cdk)2, resulting in cyclin E/cdk2 activation in the absence of growth factors other than insulin. Integrin collagen receptors in which the alpha(2) cytoplasmic domain was replaced by the alpha(1) cytoplasmic domain or an alpha(2) subunit cytoplasmic domain truncated after the GFFKR sequence failed to stimulate cyclin E/cdk2 activation or entry into S phase in the absence of growth factors. Although overexpression of cyclins D or E or cdk2 in cells expressing the integrin collagen receptor with the alpha(1)-integrin cytoplasmic domain did not restore G(1) progression when mammary epithelial cells adhered to type I collagen, co-expression of cyclin E and cdk2 did rescue the ability of the transfectants to enter S phase. Activation of cyclin E/cdk2 complex by mammary epithelial cells required synergy between adhesion mediated by an integrin collagen receptor containing the alpha(2)-integrin subunit cytoplasmic domain and the insulin receptor.
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Affiliation(s)
- P A Klekotka
- Department of Pathology and Immunology, Washington University School of Medicine, St. Louis, Missouri 63110, USA
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331
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Abstract
The behavior of mammary epithelial cells during aging is dynamic and is likely to have significant implications in the pathogenesis of human breast cancer. The growth of epithelial cells over time was thought to parallel that of their underlying stroma, sequentially undergoing a defined period of growth, followed by senescence and, ultimately, cell crisis or rarely immortalization. Recent findings, however, suggest that the evolution of mammary epithelium at the proliferative and chromosomal levels is distinct from that of stroma, contributing to the neoplastic susceptibilities of epithelial cells.
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332
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Yaswen P, Stampfer MR. Epigenetic changes accompanying human mammary epithelial cell immortalization. J Mammary Gland Biol Neoplasia 2001; 6:223-34. [PMID: 11501582 DOI: 10.1023/a:1011364925259] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Acquisition of immortality may be an early and crucial step in malignant progression. We hypothesize that acquisition of unlimited growth potential in individual human mammary epithelial cells (HMEC) requires inactivation of several distinct negative growth constraints as well as reactivation of a mechanism to maintain telomeres on chromosomes. Some of the heritable changes that occur during HMEC immortalization, i.e., loss of expression of cyclin dependent kinase inhibitors p16INK4a and p57KIP2, loss of TGFbeta-mediated growth inhibition, and derepression of telomerase, appear to occur without identifiable mutations in the genes and pathways involved. The absence of mutations, combined with the fact that the changes are often incremental over several cell generations even in clonal populations indicates that some changes associated with immortalization can be epigenetic. We have used the term "conversion" to describe the gradual epigenetic process in chemical carcinogen-immortalized HMEC that leads to activation of telomerase, stabilization of telomere length, and ability to grow uniformly well in the presence or absence of TGFbeta. Characterization of the epigenetic mechanisms involved in immortalization may uncover additional factors that drive tumor progression, and that may be responsive to novel forms of intervention.
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Affiliation(s)
- P Yaswen
- Department of Cell and Molecular Biology, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.
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333
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Tlsty TD, Romanov SR, Kozakiewicz BK, Holst CR, Haupt LM, Crawford YG. Loss of chromosomal integrity in human mammary epithelial cells subsequent to escape from senescence. J Mammary Gland Biol Neoplasia 2001; 6:235-43. [PMID: 11501583 DOI: 10.1023/a:1011369026168] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
The genomic changes that foster cancer can be either genetic or epigenetic in nature. Early studies focused on genetic changes and how mutational events contribute to changes in gene expression. These point mutations, deletions and amplifications are known to activate oncogenes and inactivate tumor suppressor genes. More recently, multiple epigenetic changes that can have a profound effect on carcinogenesis have been identified. These epigenetic events, such as the methylation of promoter sequences in genes, are under active investigation. In this review we will describe a methylation event that occurs during the propagation of human mammary epithelial cells (HMEC) in culture and detail the accompanying genetic alterations that have been observed.
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Affiliation(s)
- T D Tlsty
- Department of Pathology, University of California at San Francisco, 94143-0506, USA.
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334
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Hulit J, Di Vizio D, Pestell RG. Inducible transgenics. New lessons on events governing the induction and commitment in mammary tumorigenesis. Breast Cancer Res 2001; 3:209-12. [PMID: 11434870 PMCID: PMC138683 DOI: 10.1186/bcr297] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/05/2001] [Revised: 04/11/2001] [Accepted: 04/23/2001] [Indexed: 12/29/2022] Open
Abstract
Breast cancer arises from multiple genetic events that together contribute to the established, irreversible malignant phenotype. The development of inducible tissue-specific transgenics has allowed a careful dissection of the events required for induction and subsequent maintenance of tumorigenesis. Mammary gland targeted expression of oncogenic Ras or c-Myc is sufficient for the induction of mammary gland tumorigenesis in the rodent, and when overexpressed together the rate of tumor onset is substantially enhanced. In an exciting recent finding, D'Cruz et al discovered tetracycline-regulated c-Myc overexpression in the mammary gland induced invasive mammary tumors that regressed upon withdrawal of c-Myc expression. Almost one-half of the c-Myc-induced tumors harbored K-ras or N-ras gene point mutations, correlating with tumor persistence on withdrawal of c-Myc transgene expression. These findings suggest maintenance of tumorigenesis may involve a second mutation within the Ras pathway.
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Affiliation(s)
- James Hulit
- The Albert Einstein Comprehensive Cancer Center, Division of Hormone-Responsive Cancers, Albert Einstein College of Medicine, Bronx, New York, USA
| | - Dolores Di Vizio
- The Albert Einstein Comprehensive Cancer Center, Division of Hormone-Responsive Cancers, Albert Einstein College of Medicine, Bronx, New York, USA
| | - Richard G Pestell
- The Albert Einstein Comprehensive Cancer Center, Division of Hormone-Responsive Cancers, Albert Einstein College of Medicine, Bronx, New York, USA
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335
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Stampfer MR, Yaswen P. Immortal transformation and telomerase reactivation of human mammary epithelial cells in culture. TELOMERASE, AGING AND DISEASE 2001. [DOI: 10.1016/s1566-3124(01)08006-3] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
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336
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Metzler DE, Metzler CM, Sauke DJ. Growth and Development. Biochemistry 2001. [DOI: 10.1016/b978-012492543-4/50035-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
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