Molecular Biology of Cancer PDF

See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/206891569 Molecular Biology of Cancer Article · January 2003 DOI: 10.3109/9780203624340-2 CITATIONS READS 1...

See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/206891569 Molecular Biology of Cancer Article · January 2003 DOI: 10.3109/9780203624340-2 CITATIONS READS 17 22,182 5 authors, including: Jesse Martinez Kimberly Fultz University of Phoenix University of Alaska Fairbanks 72 PUBLICATIONS 2,539 CITATIONS 25 PUBLICATIONS 759 CITATIONS SEE PROFILE SEE PROFILE Natalia A Ignatenko Eugene Gerner University of Arizona University of Arizona 62 PUBLICATIONS 1,348 CITATIONS 276 PUBLICATIONS 12,139 CITATIONS SEE PROFILE SEE PROFILE All content following this page was uploaded by Eugene Gerner on 04 November 2017. The user has requested enhancement of the downloaded file. CHAPTER ONE Molecular Biology of Cancer JESSE D. MARTINEZ MICHELE TAYLOR PARKER KIMBERLY E. FULTZ NATALIA A. IGNATENKO EUGENE W. GERNER Departments of Radiation Oncology/Cancer Biology Section Molecular and Cellular Biology Biochemistry and Molecular Biophysics Cancer Biology Graduate Program The University of Arizona Tuscon, Arizona Contents 1 Introduction, 2 2 Tumorigenesis, 2 2.1 Normal-Precancer-Cancer Sequence, 2 2.2 Carcinogenesis, 3 2.3 Genetic Variability and Other Modifiers of Tumorigenesis, 5 2.3.1 Genetic Variability Affecting Cancer, 5 2.3.2 Genetic Variability in c-myc–Dependent Expression of Ornithine Decarboxylase, 7 2.4 Epigenetic Changes, 7 3 Molecular Basis of Cancer Phenotypes, 10 3.1 Immortality, 10 3.2 Decreased Dependence on Growth Factors to Support Proliferation, 11 3.3 Loss of Anchorage-Dependent Growth and Altered Cell Adhesion, 12 3.4 Cell Cycle and Loss of Cell Cycle Control, 14 3.5 Apoptosis and Reduced Sensitivity to Apoptosis, 16 3.6 Increased Genetic Instability, 19 3.7 Angiogenesis, 20 4 Cancer-Related Genes, 21 4.1 Oncogenes, 21 4.1.1 Growth Factors and Growth Factor Receptors, 21 4.1.2 G Proteins, 23 4.1.3 Serine/Threonine Kinases, 24 Burger’s Medicinal Chemistry and Drug Discovery 4.1.4 Nonreceptor Tyrosine Kinases, 24 Sixth Edition, Volume 5: Chemotherapeutic Agents 4.1.5 Transcription Factors as Oncogenes, Edited by Donald J. Abraham 25 ISBN 0-471-37031-2 © 2003 John Wiley & Sons, Inc. 4.1.6 Cytoplasmic Proteins, 26 1 2 Molecular Biology of Cancer 4.2 Tumor Suppressor Genes, 26 5.3.4 Limitations of Microarray 4.2.1 Retinoblastoma, 27 Technologies, 37 4.2.2 p53, 27 5.4 Modifying Cell Adhesion, 37 4.2.3 Adenomatous Polyposis Coli, 29 5.4.1 MMP Inhibitors, 37 4.2.4 Phosphatase and Tensin Homologue, 5.4.2 Anticoagulants, 38 30 5.4.3 Inhibitors of Angiogenesis, 38 4.2.5 Transforming Growth Factor-␤, 30 5.5 Prospects for Gene Therapy of Cancer, 39 4.2.6 Heritable Cancer Syndromes, 32 5.5.1 Gene Delivery Systems, 39 5 Interventions, 32 5.5.1.1 Viral Vectors, 40 5.1 Prevention Strategies, 32 5.5.1.2 Non-Viral Gene Delivery 5.2 Targets, 33 Systems, 42 5.2.1 Biochemical Targets, 33 5.6 Gene Therapy Approaches, 43 5.2.2 Cyclooxygenase-2 and Cancer, 33 5.6.1 Immunomodulation, 43 5.2.3 Other Targets, 35 5.6.2 Suicidal Gene Approach, 44 5.3 Therapy, 35 5.6.3 Targeting Loss of Tumor Suppressor 5.3.1 Importance of Studying Gene Function and Oncogene Expression, 35 Overexpression, 44 5.3.2 cDNA Microarray Technology, 35 5.6.4 Angiogenesis Control, 45 5.3.3 Discoveries from cDNA Microarray 5.6.5 Matrix Metalloproteinase, 45 Data, 37 6 Acknowledgments, 46 1 INTRODUCTION optosis, are now known to contribute to cer- tain types of cancer. Cancer is distinctive from Cancer is a major human health problem other tumor-forming processes because of its worldwide and is the second leading cause of ability to invade surrounding tissues. This death in the United States (1). Over the past chapter will address mechanisms regulating 30 years, significant progress has been the important cancer phenotypes of altered achieved in understanding the molecular basis cell proliferation, apoptosis, and invasiveness. of cancer. The accumulation of this basic Recently, it has become possible to exploit knowledge has established that cancer is a va- this basic information to develop mechanism- riety of distinct diseases and that defective based strategies for cancer prevention and genes cause these diseases. Further, gene de- treatment. The success of both public and pri- fects are diverse in nature and can involve ei- vate efforts to sequence genomes, including ther loss or gain of gene functions. A number human and other organisms, has contributed of inherited syndromes associated with in- to this effort. Several examples of mechanism- creased risk of cancer have been identified. based anti-cancer strategies will be discussed. This chapter will review our current under- Finally, potential strategies for gene therapy standing of the mechanisms of cancer develop- of cancer will also be addressed. ment, or carcinogenesis, and the genetic basis of cancer. The roles of gene defects in both 2 TUMORIGENESIS germline and somatic cells will be discussed as they relate to genetic and sporadic forms of 2.1 Normal-Precancer-Cancer Sequence cancer. Specific examples of oncogenes, or can- cer-causing genes, and tumor suppressor Insight into tumor development first came genes will be presented, along with descrip- from epidemiological studies that examined tions of the relevant pathways that signal nor- the relationship between age and cancer inci- mal and cancer phenotypes. dence that showed that cancer incidence in- While cancer is clearly associated with an creases with roughly the fifth power of elapsed increase in cell number, alterations in mecha- age (2). Hence, it was predicted that at least nisms regulating new cell birth, or cell prolif- five rate-limiting steps must be overcome be- eration, are only one facet of the mechanisms fore a clinically observable tumor could arise. of cancer. Decreased rates of cell death, or ap- It is now known that these rate-limiting steps 2 Tumorigenesis 3 are genetic mutations that dysregulate the ac- humans as the paradigm. They suggest that tivities of genes that control cell growth, reg- malignant colorectal tumors (carcinomas) ulate sensitivity to programmed cell death, evolve from preexisting benign tumors (ade- and maintain genetic stability. Hence, tumor- nomas) in a stepwise fashion with benign, less igenesis is a multistep process. aggressive lesions giving rise to more lethal Although the processes that occur during neoplasms. In their model, both genetic [e.g., tumorigenesis are only incompletely under- adenomatous polyposis coli (APC) mutations] stood, it is clear that the successive accumula- and epigenetic changes (e.g., DNA methyl- tion of mutations in key genes is the force that ation affecting gene expression) accumulate drives tumorigenesis. Each successive muta- over time, and it is the progressive accumula- tion is thought to provide the developing tu- tion of these changes that occur in a preferred, mor cell with important growth advantages but not invariable, order that are associated that allow cell clones to outgrow their more with the evolution of colonic neoplasms. Other normal neighboring cells. Hence, tumor devel- important features of this model are that at opment can be thought of as Darwinian evolu- least four to five mutations are required for tion on a microscopic scale with each succes- the formation of a malignant tumor, in agree- sive generation of tumor cell more adapted to ment with the epidemiological data, with overcoming the social rules that regulate the fewer changes giving rise to intermediate be- growth of normal cells. This is called clonal nign lesions, that tumors arise through the evolution (3). mutational activation of oncogenes and inac- Given that tumorigenesis is the result of tivation of tumor suppressor genes, and that it mutations in a select set of genes, much effort is the sum total of the effect of these mutations by cancer biologists has been focused on iden- on tumor cell physiology that is important tifying these genes and understanding how rather than the order in which they occur. they function to alter cell growth. Early efforts An important implication of the multistep in this area were lead by virologists studying model of tumorigenesis is that lethal neo- retrovirus-induced tumors in animal models. plasms are preceded by less aggressive inter- These studies led to cloning of the first onco- mediate steps with predictable genetic alter- genes and the realization that oncogenes, in- ations. This suggests that if the genetic defects deed all cancer-related genes, are aberrant which occur early in the process can be identi- forms of genes that have important functions fied, a strategy that interferes with their in regulating normal cell growth (4). In subse- function might prevent development of more quent studies, these newly identified onco- advanced tumors. Moreover, preventive screen- genes were introduced into normal cells in an ing methods that can detect cells with the effort to reproduce tumorigenesis in vitro. Im- early genetic mutations may help to identify portantly, it was found that no single onco- these lesions in their earliest and most curable gene could confer all of the physiological traits stages. Consequently, identification of the of a transformed cell to a normal cell. Rather genes that are mutated in cancers and eluci- this required that at least two oncogenes act- dation of their mechanism of action is impor- ing cooperatively to give rise to cells with the tant not only to explain the characteristic phe- fully transformed phenotype (5). This obser- notypes exhibited by tumor cells, but also to vation provides important insights into tu- provide targets for development of therapeu- morigenesis. First, the multistep nature of tu- tic agents. morigenesis can be rationalized as mutations 2.2 Carcinogenesis in different genes with each event providing a selective growth advantage. Second, oncogene Carcinogenesis is the process that leads to ge- cooperativity is likely to be cause by the re- netic mutations induced by physical or chem- quirement for dysregulation of cell growth at ical agents. Conceptually, this process can be multiple levels. divided into three distinct stages: initiation, Fearon and Vogelstein (6) have proposed a promotion, and progression (7). Initiation in- linear progression model (Fig. 1.1) to describe volves an irreversible genetic change, usually tumorigenesis using colon carcinogenesis in a mutation in a single gene. Promotion is gen- 4 Molecular Biology of Cancer DNA hypomethylation Mutation of Mutation of Other genetic APC K-ras Loss of DCC Loss of p53 alterations Normal Hyper- Early Intermediate Late colon Carcinoma Metastasis proliferation adenoma adenoma adenoma cell Figure 1.1. Adenoma-carcinoma sequence. Fearon and Vogelstein (6) proposed this classic model for the multistage progression of colorectal cancer. A mutation in the APC tumor suppressor gene is generally considered to be the initiation event. This is followed by the sequential accumulation of other epigenetic and genetic changes that eventually result in the progression from a normal cell to a metastatic tumor. erally associated with increased proliferation Promotion is a reversible process in which of initiated cells, which increases the popula- chemical agents stimulate proliferation of ini- tion of initiated cells. Progression is the accu- tiated cells. Typically, promoting agents are mulation of more genetic mutations that lead nongenotoxic, that is they are unable to form to the acquisition of the malignant or invasive DNA adducts or cause DNA damage but are phenotype. able to stimulate cell proliferation. Hence, ex- In the best-characterized model of chemical posure to tumor promoting agents results in carcinogenesis, the mouse skin model, initia- rapid growth of the initiated cells and the tion is an irreversible event that occurs when a eventual formation of non-invasive tumors. In genotoxic chemical, or its reactive metabolite, the mouse skin tumorigenesis model, applica- causes a DNA mutation in a critical growth tion of a single dose of an initiating agent does controlling gene such as Ha-ras (8). Out- not usually result in tumor formation. How- wardly, initiated cells seem normal. However, ever, when the initiation step is followed by they remain susceptible to promotion and fur- repeated applications of a tumor promoting ther neoplastic development indefinitely. agent, such as 12-O-tetradecanoyl-phorbol- DNA mutations that occur in initiated cells 13-acetate (TPA), numerous skin tumors arise can confer growth advantages, which allow and eventually result in invasive carcinomas. them to evolve and/or grow faster bypassing Consequently, tumor promoters are thought normal cellular growth controls. The different to function by fostering clonal selection of cells types of mutations that can occur include with a more malignant phenotype. Impor- point mutations, deletions, insertions, chro- tantly, tumor formation is dependent on re- mosomal translocations, and amplifications. peated exposure to the tumor promoter. Halt- Three important steps involved in initiation ing application of the tumor promoter are carcinogen metabolism, DNA repair, and prevents or reduces the frequency with which cell proliferation. Many chemical agents must tumors form. The sequence of exposure is im- be metabolically activated before they become portant because tumors do not develop in the carcinogenic. Most carcinogens, or their active absence of an initiating agent even if the tu- metabolites, are strong electrophiles and bind mor promoting agent is applied repeatedly. to DNA to form adducts that must be removed Therefore, the genetic mutation caused by the by DNA repair mechanisms (9). Hence, DNA initiating agent is essential for further neo- repair is essential to reverse adduct formation plastic development under the influence of the and to prevent DNA damage. Failure to repair promoting agent. chemical adducts, followed by cell prolifera- Progression refers to the process of acquir- tion, results in permanent alterations or mu- ing additional mutations that lead to malig- tation(s) in the genome that can lead to onco- nancy and metastasis. Many initiating agents gene activation or inactivation of tumor can also lead to tumor progression, strong sup- suppressor genes. port for the notion that further mutations are 2 Tumorigenesis 5 Metabolic activation Procarcinogen Carcinogen Detoxification DNA binding Excretion of Figure 1.2. Possible outcomes of metabolites carcinogen metabolic activation. Once a carcinogen is metabolically Formation of carcinogen-DNA adduct activated it can bind to DNA and form carcinogen-DNA adducts. These DNA repair adducts will ultimately lead to muta- Cell tions if they are not repaired. If DNA DNA replication death repair does not occur, the cell will ei- Normal cell ther undergo apoptosis or the DNA will be replicated, resulting in an ini- Initiated cell tiated cell. needed for cells to acquire the phenotypic play important roles in the metabolic activa- characteristics of malignant tumor cells. Some tion and detoxification of carcinogenic agents. of these agents include benzo(a)pyrene, The phase I enzymes include monooxygen- ␤ -napthylamine, 2-acetylaminofluorene, ases, dehydrogenases, esterases, reductases, aflatoxin B1, dimethylnitrosamine, 2-amino-3- and oxidases. These enzymes introduce func- methylimidazo(4,5-f)quinoline (IQ), benzi- tional groups on the substrate. The most im- dine, vinyl chloride, and 4-(methylnitros- portant superfamily of the phase I enzymes amino)-1-(3-pyridyl)-1-butanone (NNK) (10). are the cytochrome P450 monooxygenases, These chemicals are converted into positively which metabolize polyaromatic hydrocarbons, charged metabolites that bind to negatively aromatic amines, heterocyclic amines, and ni- charged groups on molecules like proteins and trosamines. Phase II metabolizing enzymes nucleic acids. This results in the formation of are important for the detoxification and excre- DNA adducts which, if not repaired, lead to tion of carcinogens. Some examples include mutations (9) (Fig. 1.2). The result of these epoxide hydrase, glutathione-S-transferase, mutations enables the tumors to grow, invade and uridine 5⬘-diphosphate (UDP) glucuro- surrounding tissue, and metastasize. nide transferase. There are also some direct Damage to DNA and the genetic mutations acting carcinogens that do not require meta- that can result from them are a central theme bolic activation. These include nitrogen mus- in carcinogenesis. Hence, the environmental tard, dimethylcarbamyl chloride, and ␤-pro- factors that cause DNA damage are of great piolactone. interest. Environmental agents that can cause DNA damage include ionizing radiation, ultra- 2.3 Genetic Variability and Other Modifiers violet (UV) light, and chemical agents (11). of Tumorigenesis Some of the DNA lesions that can result in- clude single-strand breaks, double-strand 2.3.1 Genetic Variability Affecting Cancer. breaks, base alterations, cross-links, insertion Different types of cancers, as well as their se- of incorrect bases, and addition/deletion of verity, seem to correlate with the type of mu- DNA sequences. Cells have evolved several tation acquired by a specific gene. Mutation different repair mechanisms that can reverse “hot spots” are regions of genes that are fre- the lesions caused by these agents, which has quently mutated compared with other regions been extensively reviewed elsewhere (12). within that gene. For example, observations The metabolic processing of environmental that the majority of colon adenomas are asso- carcinogens is also of key importance because ciated with alterations in the adenomatous this can determine the extent and duration to polyposis coli (APC) have been based on im- which an organism is exposed to a carcinogen. munohistochemical analysis of ␤-catenin lo- Phase I and phase II metabolizing enzymes calization and formation of less than full 6 Molecular Biology of Cancer Armadillo Mutation Drosophilia repeats cluster DLG binding 453 −766 region 2771− 2843 APC∆716 Min APC∆1638 Min 0 2843 Homodimerization Microtubule region binding 1−71 2143 − 2843 EB1 binding 2143 −2843 Murine models Intestinal tumor number ∆716 APC 200 − 600 Min (850 stopcodon) 60 − 80 APC∆1638