Biochemistry _ Cell Growth
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This document discusses cell growth and carcinogenesis. It begins by describing the natural limits to cell growth, including the increasing stress on DNA and difficulty transporting nutrients/wastes as cell volume increases faster than surface area. It then describes the cell cycle and its regulation to maintain healthy cell division. Disruptions can lead to uncontrolled growth and cancer. Cancer results from genetic changes that affect cell cycle controls, like mutations in tumor suppressor genes like p53. Various environmental and genetic factors can increase cancer risk by damaging DNA or interfering with cell cycle regulation. Precise control of cell division and DNA replication is essential to prevent multistage carcinogenesis.
![THOUSANDS OF KNOWN CARCINOGENIC
AGENTS ARE IN THE ENVIRONMENT
• Organic molecules (aromatic amines)
• Inorganic molecules (vinyl chloride)
• Heavy metals (lead, arsenic, chromium[VI])
• Viruses (HBV, HCV, HPV, HIV)
• Radiation (gamma, X-ray, high energy beta)
• Inert substances (asbestos)](https://image.slidesharecdn.com/otq4nzxrr9afaxcbaahc-signature-091447bade647bc70325d98b994f7c3a3901d946a34a4516654ab9d79d1d0b85-poli-141026005448-conversion-gate02/85/Biochemistry-_-Cell-Growth-37-320.jpg)
Biochemistry _ Cell Growth
- 1. Lecture 27 Cell growth and carcinogenesis
- 2. • Limits to growth Cell Growth – Stress on DNA – Difficulty moving nutrients/wastes across membrane • Ratio of surface area to volume • Volume increases at a faster rate than surface area
- 3. Cell Division • Before a cell becomes too large, it divides, producing 2 daughter cells – Each daughter cell is an exact replica of the parent cell • Before the cell divides, the DNA is replicated, so each new cell will have the same genetic information as the parent cell • 2 stages (eukaryotes) – Mitosis- division of the cell nucleus – Cytokinesis- division of the cytoplasm
- 4. The Cell Cycle • 2 major phases – Interphase – Mitosis
- 5. Interphase • 3 phases – G1 phase= cells do most of their growing • Increase in size and synthesize new proteins and organelles – S phase= chromosomes are replicated and the synthesis and DNA molecules takes place • Usually if a cell enters S phase and begins replication, it completes the rest of the cycle – G2 phase= many of the organelles and molecules required for cell division are produced • Shortest of the 3 phases of interphase
- 6. Mitosis • Divided into 4 phases – Prophase – Metaphase – Anaphase – Telophase • Followed with Cytokinesis • Depending on cell- may last a few minutes to several days
- 8. Cell cycle regulation is necessary for healthy growth.
- 9. Regulating Cell Growth • Cyclins- proteins that regulate the timing of the cell cycle in eukaryotic cells – Internal regulators: proteins that respond to events inside the cell • i.e. make sure all chromosomes have been replicated; make sure all chromosomes are attached to the spindle before entering anaphase – External regulators: proteins that respond to events outside the cell • i.e. embryonic development; wound healing
- 10. Cell cycle control Animal cells have built-in “stop” signals that halt the cell cycle at checkpoints until overridden by “go” signals To function properly checkpoint signals have to percept “reports” from crucial cellular processes: have it been completed correctly and should the cell cycle proceed. Checkpoint also register signals from outside the cell
- 11. Cell cycle control The most important decision to make is: to continue the cell division after the exit from M phase or not. Cells that do not receive the “go” signal at the G1 checkpoint, switch into a nondividing state called the G0 phase.
- 12. Cyclins and cyclin-dependent kinases (Cdks) Regulatory molecules of the cycle transition are proteins of two main types: protein kinases and cyclins. Protein kinases are proteins that regulate the activity of the others by phosphorylating them.
- 13. Cyclins and cyclin-dependent kinases (Cdks) “Go” signal at the G1 and G2 checkpoints is regulated by particular protein kinases. To be active, such a kinase must be attached to a cyclin, a protein that gets its name from its cyclically fluctuating concentration in the cell This kinases are called cyclin-dependent kinases – Cdks.
- 14. Control at the G2 checkpoint The stepwise processes of the cell cycle are timed by rhythmic fluctuations in the activity of protein kinases. There is a direct correlation between cyclin accumulation and the three major cell cycle checkpoints.
- 15. Control at the G2 checkpoint Cdk-cyclin complex called MPF (maturation promotion factor), acts at the G2 checkpoint to trigger mitosis. MPF activity fluctuates with the level of cyclin in the cell. The cyclin level rises throughout interphase (G1, S, and G2 phases), then falls abruptly during mitosis (M phase). The Cdk itself is present at a constant level.
- 16. Cdc2 (cdk1) is phosphorylated by Cyclin B at 3 regulatory positions MPF promotes mitosis by phosphorylating various proteins One effect of MPF is to the breakdown of its own cyclin. The Cdk component of MPF is recycled. Its kinase activity will be restored by association with new cyclin.
- 19. Internal regulation Internal signals Anaphase, the separation of sister chromatids, does not begin until all the chromosomes are properly attached to the spindle at the metaphase plate. Certain associated proteins trigger a signalling pathway that keeps an anaphase promoting complex (APC) in an inactive state. M-phase checkpoint is the gatekeeper. Only when all the kinetochores are attached to the spindle does the “wait” signal cease.
- 20. External regulation External signals: growth factors. Most of mammalian cells divide in culture only if the growth medium includes specific growth factors. PDGF – platelet-derived growth factor – is required for the division of fibroblasts.
- 21. External regulation Density-dependent inhibition of cell division, a phenomenon in which crowded cells stop dividing. Cultured cells normally divide until they form a single layer of cells on the inner surface of the culture container.
- 22. Density-dependent inhibition • Effects of controlled cell growth can be seen by placing some cells in a petri dish containing nutrient broth • Cells grow until they form a thin layer covering the bottom of the dish • Cells stop growing when they come into contact with other cells • If cells are removed, the remaining cells will begin dividing again
- 23. Uncontrolled Cell Growth • Cancer- disorder in which some of the body’s own cells lose the ability to control growth • Cancer cells do not respond to the signals that regulate the growth of most cells • P53 gene halts the cell cycle until all chromosomes have been properly replicated – A damaged or defective p53 gene causes the cells to lose the information needed to respond to signals that would normally control their growth
- 24. Cancer results from genetic changes that affect cell cycle control • The gene regulation systems that go wrong during cancer are the very same systems involved in embryonic development
- 25. Cancer Cancer is not a single disease but rather a name applied to a great variety of malignant tumor that are formed by the same basic process of uncontrolled growth. Cancer is one of the most common and severe problem of clinical medicine. Cancer has emerged as a major public health problem in developing countries for the first time, matching its effect in industrialized nations. This is a global problem.
- 26. Cancer Cancer may affect people at all ages, even fetuses but risk for the more common varieties tends to increase with age. Early diagnosis and early treatment are vital, and identification of persons at increased risk of cancer before its development is an important objective of cancer research.
- 27. Benign Tumors Self-limited in their growth. Do not invade or metastasize (although some benign tumor types are capable of becoming malignant).
- 28. Malignant N ( eoplasm or Tumors (Cancer Excessive growth and division without respect to normal limit, Invasive, invade and destroy adjacent tissues, and sometime, Distant metastasis spread to other locations in the body.
- 29. Risk Factors Old age Unhealthy lifestyle (Western lifestyle), Poor diet, lack of physical activity, or being overweight. Environmental factors, defined broadly to include tobacco use, diet, sunlight and infectious diseases. Occupational carcinogens Radiation Family history of cancer (Genetic susceptibility) Alcohol Chemicals and other substance
- 30. Risk Factor/ Cancer Type Cancer Type Risk Factor Lung Cancer Tobacco smoke Asbestos and other substances Air pollution Breast Radiation Genetic changes (Inherited mutation) Colorectal Genetic alteration Diet Cigarette smoking Ulcerative colitis or chon's disease Prostate Diet Certain prostate changes Race Africans Americans
- 31. Risk Factor/ Cancer Type Cancer Type Risk Factor Liver Hepatitis viruses (HCV.HBV) Pancreas Smoking Diabetes Being male Chronic pancreatitis Kidney Tobacco smoking High blood pressure Von-Hippel-Lindau syndrome (VHL) Leukemia Radiation Chemotherapy Certain disease (Down syndrome) Human T cell leukemia virus Myelodysplatic syndrome
- 32. Risk Factor/ Cancer Type Cancer Type Risk Factor Bladder Occupation Certain infection Tobacco smoking Race Twice as often as Africans Americans Treatment with cyclophosphamide or arsenic Uterine Endometrial hyperplasia Race Africans Americans Hormonal replacement therapy Obesity Melanoma Dysplastic nevi Fair skin Weakened immune system Sever blistering/Sunburn UV irradiation
- 33. Certain viruses or bacteria may increase the risk of developing cancer Microorganism Cancer Human papilloma virus Cervical cancer Helicobacter pylori Stomach cancer Hepatitis B and hepatitis C viruses Liver cancer Human T-cell leukemia/lymphoma virus Lymphoma and leukemia Human immunodeficiency virus Lymphoma and a rare cancer called Kaposi's sarcoma Epstein-Barr virus Lymphoma Human herpes virus 8 Kaposi's sarcoma
- 34. Etiology The etiology of cancer is multifactorial, with genetic, environmental, medical, and lifestyle factors interacting to produce a given malignancy. Agents (molecules, radiation or viruses) that cause cancer are called carcinogens. This causal process is called carcinogenesis. In humans, it is generally accepted that most epithelial cancers are caused by environmental exposure to certain kinds of chemicals. However, carcinogenesis is clearly influenced by large numbers of genes and non-carcinogenic environmental factors (notably diet, and underlying inflammation).
- 35. Etiology •New perceptions of previously known carcinogens: •Combined effects of multiple exposures Most cancer is caused by genetic mutations often, by a series of mutations.
- 36. CCeellll RReepplliiccaattiioonn iiss EEsssseennttiiaall ffoorr MMuullttiissttaaggee CCaarrcciinnooggeenneessiiss Decreases time available ffoorr DDNNAA rreeppaaiirr CCoonnvveerrttss rreeppaaiirraabbllee DDNNAA ddaammaaggee iinnttoo nnoonn--rreeppaaiirraabbllee mmuuttaattiioonnss NNeecceessssaarryy ffoorr cchhrroommoossoommaall aabbeerrrraattiioonnss,, iinnsseerrttiioonnss,, ddeelleettiioonnss aanndd ggeennee aammpplliiffiiccaattiioonn CClloonnaallllyy eexxppaannddss eexxiissttiinngg cceellll ppooppuullaattiioonnss
- 37. THOUSANDS OF KNOWN CARCINOGENIC AGENTS ARE IN THE ENVIRONMENT • Organic molecules (aromatic amines) • Inorganic molecules (vinyl chloride) • Heavy metals (lead, arsenic, chromium[VI]) • Viruses (HBV, HCV, HPV, HIV) • Radiation (gamma, X-ray, high energy beta) • Inert substances (asbestos)
- 38. o Proportion off cchheemmiiccaallss eevvaalluuaatteedd aass ccaarrcciinnooggeenniicc Proportion Percentage Chemicals tested in both rats and mice 350/590 59% Naturally occurring chemicals 79/139 57% Synthetic chemicals 271/451 60% Chemicals tested in rats and/or mice Chem. in Carcinogen. Potency Database 702/1348 52% Natural pesticides 37/71 52% Mold toxins 14/23 61% Chemicals in roasted coffee 21/30 70% Physician’s desk reference Drugs with reported cancer tests 117/241 49% FDA database of drug submissions 125/282 44% AAmmeess aanndd GGoolldd MMuuttaatt RReess 444477::33--1133,, 22000000
- 39. Classification of Carcinogens AAccccoorrddiinngg ttoo tthhee MMooddee ooff AAccttiioonn GGEENNOOTTOOXXIICC NNOONN-- GGEENNOOTTOOXXIICC GGEENNOOTTOOXXIICC:: DDNNAA--rreeaaccttiivvee oorr DDNNAA--rreeaaccttiivvee mmeettaabboolliitteess DDiirreecctt iinntteerraaccttiioonn ttoo aalltteerr cchhrroommoossoommaall nnuummbbeerr//iinntteeggrriittyy MMaayy bbee mmuuttaaggeenniicc oorr ccyyttoottooxxiicc UUssuuaallllyy ccaauussee mmuuttaattiioonnss iinn ssiimmppllee ssyysstteemmss DDNNAA AAdddduucctt MMuuttaattiioonn CCaanncceerr
- 40. Mechanism ooff CCaarrcciinnooggeenneessiiss:: GGeennoottooxxiicc CCaarrcciinnooggeennss 1.. CCaarrcciinnooggeenn aaccttiivvaattiioonn 22.. DDNNAA bbiinnddiinngg 4.. GGeennee mmuuttaattiioonn CYP450s Chemical "Activated“ carcinogen 33.. CCeellll pprroolliiffeerraattiioonn ((ffiixx mmuuttaattiioonn)) “inactivated“ carcinogen DNA Repair APOPTOSIS
- 41. the mechanism of causing cancer by exposure to polycyclic aarroommaattiicc hhyyddrrooccaarrbboonnss
- 42. Classification of Carcinogens According ttoo tthhee MMooddee ooff AAccttiioonn NNOONN--GGEENNOOTTOOXXIICC:: Do not directly cause DNA mutation Mechanism of action is not completely understood Difficult to detect - requires rodent carcinogen bioassay ?? MMuuttaattiioonn CCaanncceerr
- 43. Mechanisms ooff NNoonn--GGeennoottooxxiicc CCaarrcciinnooggeenneessiiss ““bbllaacckk bbooxx”” IInnccrreeaasseedd cceellll pprroolliiffeerraattiioonn DDeeccrreeaasseedd aappooppttoossiiss CChhaannggeess iinn ggeennee eexxpprreessssiioonn IInndduuccttiioonn ooff mmeettaabboolliizziinngg eennzzyymmeess AAccttiivvaattiioonn ooff rreecceeppttoorrss ((ssiiggnnaalliinngg)) OOxxiiddaattiivvee ssttrreessss ??????
- 44. OOxxiiddaattiivvee SSttrreessss IInnddiirreecctt DDNNAA ddaammaaggee IInndduuccttiioonn ooff cceellll pprroolliiffeerraattiioonn//aappooppttoossiiss ssiiggnnaalliinngg ccaassccaaddeess
- 45. Non-Genotoxic CCaarrcciinnooggeennss 11)) MMiittooggeennss:: • ssttiimmuullaattiioonn ooff pprroolliiffeerraattiioonn • mmuuttaattiioonnss mmaayy ooccccuurr sseeccoonnddaarriillyy ttoo cceellll pprroolliiffeerraattiioonn • mmaayy ccaauussee pprreeffeerreennttiiaall ggrroowwtthh ooff pprreenneeooppllaassttiicc cceellllss 22)) CCyyttoottooxxiiccaannttss:: • ccyyttoolleetthhaall • iinndduuccee rreeggeenneerraattiivvee ggrroowwtthh • mmuuttaattiioonnss mmaayy ooccccuurr sseeccoonnddaarriillyy ttoo cceellll pprroolliiffeerraattiioonn
- 46. Mechanism of Carcinogenesis: Non-Genotoxic Carcinogens Cell proliferation (to fix ““ssppoonnttaanneeoouuss”” mmuuttaattiioonn)) APOPTOSIS CANCER X
- 47. Apoptosis • Apoptosis is a tightly regulated form of cell death, also called the programmed cell death. • Morphologically, it is characterized by chromatin condensation and cell shrinkage in the early stage. Then the nucleus and cytoplasm fragment, forming membrane-bound apoptotic bodies which can be engulfed by phagocytes. • In contrast, cells undergo another form of cell death, necrosis, swell and rupture. The released intracellular contents can damage surrounding cells and often cause inflammation.
- 49. Cancer: Pathogenesis • GGeenneerraall mmeecchhaanniissmmss:: – AAccqquuiirreedd ccaappaabbiilliittiieess ((SSeellff--mmaaiinnttaaiinneedd rreepplliiccaattiioonn,, lloonnggeerr ssuurrvviivvaall,, ggeenneettiicc iinnssttaabbiilliittyy,, nneeooaannggiiooggeenneessiiss,, iinnvvaassiioonn aanndd mmeettaassttaassiiss)) – AAccttiivvaattiioonn ooff oonnccooggeenneess,, iinnaaccttiivvaattiioonn ooff ttuummoorr-- ssuupppprreessssoorr ggeenneess,, nnoonn--eeffffeeccttiivvee DDNNAA rreeppaaiirr – CCaarreettaakkeerr aanndd ggaatteekkeeeeppeerr ppaatthhwwaayyss
- 50. • Caretaker genes encode products that stabilize the genome. Mutations in caretaker genes lead to genomic instability. • Gatekeeper genes encode gene products that act to prevent growth of potential cancer cells and prevent accumulation of mutations that directly lead to increased cellular proliferation.
- 52. Abnormalities i : n the genetic material due to Error in DNA replication (randomly acquired). Effects of carcinogens, such as tobacco smoke, radiation, chemicals, or infectious agents. Inheritance, and thus present in all cells from birth.
- 53. Series Mutation can Lead to Cancer
- 54. The Multistep Model of Cancer Development • Multiple mutations are generally needed for full-fledged cancer; thus the incidence increases with age • At the DNA level, a cancerous cell is usually characterized by at least one active oncogene and the mutation of several tumor-suppressor genes
- 55. Colon Normal colon epithelial cells 1 Loss of tumor-suppressor gene APC (or other) 2 3 4 5 Colon wall Small benign growth (polyp) Activation of ras oncogene Loss of tumor-suppressor gene DCC Loss of tumor-suppressor gene p53 Additional mutations Malignant tumor (carcinoma) Larger benign growth (adenoma)
- 56. Initiating Event SSttaaggeess ooff CCaarrcciinnooggeenneessiiss Cell Proliferation (clonal expansion) Progression Cell Proliferation Cell Proliferation Malignancy Se cond M uta ting E ve nt "N " M uta ting E ve nt Initiation Promotion
- 57. Cellular and Molecular Mechanisms in Multistage Carcinogenesis: INITIATION Initiating event involves cellular genome – MUTATIONS Target genes: - oncogenes/tumor suppressor genes - signal transduction - cell cycle/apoptosis regulators “Simple” genetic changes
- 58. SSOOUURRCCEESS OOFF MMUUTTAATTIIOONNSS EENNDDOOGGEENNOOUUSS DDNNAA DDAAMMAAGGEE EEXXOOGGEENNOOUUSS DDNNAA DDAAMMAAGGEE DDeeppuurriinnaattiioonn DDNNAA RREEPPAAIIRR MMUUTTAATTIIOONN LLiiffee SSttyylleess EEnnvviirroonnmmeennttaall AAggeennttss FFrreeee RRaaddiiccaallss PPoollyymmeerraassee EErrrroorrss CCEELLLL RREEPPLLIICCAATTIIOONN
- 59. CChheemmiiccaall EExxppoossuurree ((aaiirr,, wwaatteerr,, ffoooodd,, eettcc..)) IInntteerrnnaall EExxppoossuurree MMeettaabboolliicc AAccttiivvaattiioonn MMaaccrroommoolleeccuullaarr BBiinnddiinngg DDeettooxxiiccaattiioonn DDNNAA RRNNAA PPrrootteeiinn BBiioollooggiiccaallllyy EEffffeeccttiivvee DDoossee XX EEffffiicciieennccyy ooff MMiissppaaiirriinngg XX CCeellll PPrroolliiffeerraattiioonn IInniittiiaattiioonn ((BBiioommaarrkkeerr))
- 60. EPIGENETICS Epigenetic alterations – changes induced in cells that alter the expression of the information on transcriptional, translational, or post-translational levels without changes in DNA sequence Methylation of DNA DNMT1 DNMT3a DNMT3b SAM SAH Modifications of histones RNA-mediated modifications • RNA-directed DNA methylation • RNA-mediated chromatin remodeling • RNAi, siRNA, miRNA … - acetylation - methylation - phosphorylation - ubiquitination A Me P U P U Me A
- 61. GENETIC AND EPIGENETIC MODELS OF THE CANCER INITIATION Normal cells Epigenetically reprogrammed cells Mutator phenotype cells Endogenous EEnnvviirroonnmmeennttaall ALTERATIONS IN CELLULAR EPIGENOME Cancer cells Normal cells Clonal selection and expression of initiated cells Mutator phenotype cells Endogenous EEnnvviirroonnmmeennttaall ACQUISITION OF ADDITIONAL RANDOM MUTATIONS Cancer cells
- 62. Cellular and Molecular Mechanisms in Multistage Carcinogenesis: PROMOTION Reversible enhancement/repression of gene expression: - increased cell proliferation - inhibition of apoptosis No direct structural alteration in DNA by agent or its metabolites
- 63. Cellular and Molecular Mechanisms in Multistage Carcinogenesis: PROGRESSION • Irreversible enhancement/repression of gene expression • Complex genetic alterations (chromosomal translocations, deletions, gene amplifications, recombinations, etc.) • Selection of neoplastic cells for optimal growth genotype/ phenotype in response to the cellular environment “Complex” genetic changes
- 64. Phenotypic characteristics of cancer cells: • Immortalization • Transformation • Loss of contact growth inhibition • Autonomy of proliferation • Avoidance of apoptosis • Aberrant differentiation • Induction of angiogenesis
- 65. Tumor Cells and the Onset of Cancer
- 66. Hallmarks of Cancer Cells • Self-maintained replication • Longer survival • Genetic instability • Capable of inducing neoangiogenesis • Capable of invasion and metastasis – Apoptosis down-regulation – Lack of response to inhibitory factors – Self-sustained proliferation
- 67. Hallmarks of Cancer Cells • Self-maintained replication • Longer survival • Genetic instability • Capable of inducing neoangiogenesis • Capable of invasion and metastasis –Apoptosis down-regulation –Telomerase reactivation
- 68. Hallmarks of Cancer Cells • Self-maintained replication • Longer survival • Genetic instability • Capable of inducing neoangiogenesis • Capable of invasion and metastasis –Cooperative genetic damage –Mutagenic agents –Defective repair systems
- 69. Hallmarks of Cancer Cells • Self-maintained replication • Longer survival • Genetic instability • Capable of inducing neoangiogenesis • Capable of invasion and metastasis
- 71. Stages of tumour development Malignant cell Proliferation Angiogenesis Dissemination of other organs Invasion Neovascular endothelial maintenance Invasion Cytotoxics Endocrine EGFR inhibitors HER2 antibodies Anti-angiogenics Vascular targeting agents Novel Novel agents agents Metastatic Cancer of other organs
- 72. Types of Genes Associated with Cancer • Cancer can be caused by mutations to genes that regulate cell growth and division • Tumor viruses can cause cancer in animals including humans
- 73. AAlltteerraattiioonn ooff GGeennee EExxpprreessssiioonn NNuucclleeaarr ((hhoorrmmoonnee--lliikkee)) rreecceeppttoorrss KKiinnaassee ccaassccaaddeess CCaallcciiuumm--,, nniittrriicc ooxxiiddee--mmeeddiiaatteedd ssiiggnnaalliinngg TTrraannssccrriippttiioonn ffaaccttoorrss GGeennee mmeetthhyyllaattiioonn ssttaattuuss ((hhyyppoo -->> eennhhaanncceedd ggeennee eexxpprreessssiioonn;; hhyyppeerr -->> ggeennee ssiilleenncciinngg))
- 74. What types of genes get mutated in cancer? • Oncogenes are activated – Normal function: cell growth, gene transcription • Tumor suppressor genes are inactivated – Normal function: DNA repair, cell cycle control, cell death
- 75. • Oncogenes are cancer-causing genes • Proto-oncogenes are the corresponding normal cellular genes that are responsible for normal cell growth and division • Conversion of a proto-oncogene to an oncogene can lead to abnormal stimulation of the cell cycle
- 76. • Proto-oncogenes can be converted to oncogenes by – Movement of DNA within the genome: if it ends up near an active promoter, transcription may increase – Amplification of a proto-oncogene: increases the number of copies of the gene – Point mutations in the proto-oncogene or its control elements: cause an increase in gene expression
- 77. Proto-oncogene DNA Translocation or transposition: gene moved to new locus, under new controls Gene amplification: multiple copies of the gene New promoter Normal growth-stimulating protein in excess Normal growth-stimulating protein in excess Point mutation: within a control element within the gene Oncogene Oncogene Normal growth-stimulating protein in excess Hyperactive or degradation-resistant protein
- 78. Tumor-Suppressor Genes • Tumor-suppressor genes help prevent uncontrolled cell growth • Mutations that decrease protein products of tumor-suppressor genes may contribute to cancer onset • Tumor-suppressor proteins – Repair damaged DNA – Control cell adhesion – Inhibit the cell cycle in the cell-signaling pathway
- 79. Interference with Normal Cell-Signaling Pathways • Mutations in the ras proto-oncogene and p53 tumor-suppressor gene are common in human cancers • Mutations in the ras gene can lead to production of a hyperactive Ras protein and increased cell division
- 81. TUMOR SUPPRESSOR GENES Disorders in which gene is affected Gene (locus) Function Familial Sporadic DCC (18q) cell surface unknown colorectal interactions cancer WT1 (11p) transcription Wilm’s tumor lung cancer Rb1 (13q) transcription retinoblastoma small-cell lung carcinoma p53 (17p) transcription Li-Fraumeni breast, colon, syndrome & lung cancer BRCA1(17q) transcriptional breast cancer breast/ovarian tumors BRCA2 (13q) regulator/DNA repair
- 82. Inherited Predisposition and Other Factors Contributing to Cancer • Individuals can inherit oncogenes or mutant alleles of tumor-suppressor genes • Inherited mutations in the tumor-suppressor gene adenomatous polyposis coli （APC）are common in individuals with colorectal cancer • Mutations in the BRCA1 or BRCA2 gene are found in at least half of inherited breast cancers, and tests using DNA sequencing can detect these mutations
- 83. Multiple Stages of Human Colon Cancer • It is estimated that by age 70, 50% of the population at large have acquired pre-cancerous adenomas in the colon; 10% of this group will progress to malignancy in the following 10 years. • Familial Adenomatous Polyposis (FAP) is linked to the APC gene whose protein is involved in ß-catenin signaling. The gene acts as a tumor suppressor, and the loss of function mutation causes development of hundreds to thousands of adenomas, with a consequent high risk of progression to malignancy.
- 84. Multiple Stages of Human Colon Cancer APC protein (Adenomatous Polyposis Coli) is normally expressed in colorectal epithelial cells, a site of relatively high natural proliferation rates. The epithelium is convoluted into deep recesses called crypts and projections called villi. Crypts contain stem cells for tissue replacement, and the base of the crypt is a site of high mitotic activity. As cells age, they progress up the villus to the tip. Polyps Adenomas Progression to cancer Germline APC+/– FAP >90% by age 20 >90% by age 30 50% by age 40 Germline APC+/+ normal 50% by age 70 5% Cell accumulation and dysplasia hyperplasia, aneuploidy proliferating, anti-apoptotic, metastatic, angiogenic
- 85. Growth factor 1 2 3 4 5 1 2 Receptor G protein P Protein kinases (phosphorylation cascade) Hyperactive Ras protein (product of oncogene) issues signals on its own. NUCLEUS Transcription factor (activator) DNA Gene expression Protein that stimulates the cell cycle (a) Cell cycle–stimulating pathway MUTATION Ras Ras GTP GTP P P P P P Protein kinases UV light DNA damage in genome Active form of p53 DNA Protein that inhibits the cell cycle (b) Cell cycle–inhibiting pathway MUTATION Defective or missing transcription factor, such as p53, cannot activate transcription. EFFECTS OF MUTATIONS Protein overexpressed Cell cycle overstimulated (c) Effects of mutations Increased cell division Protein absent Cell cycle not inhibited 3
- 86. • Suppression of the cell cycle can be important in the case of damage to a cell’s DNA; p53 prevents a cell from passing on mutations due to DNA damage • Mutations in the p53 gene prevent suppression of the cell cycle
- 87. p53 in apoptosis Following DNA damage, e.g. by radiation, p53 levels rise, and proliferating cells arrest in G1. This allows time for DNA repair prior to the next round of replication. This arrest is mediated by stimulation of expression of p21CIP1, the cyclin kinase inhibitor. Very high p53 levels, or susceptible cell types, e.g. lymphocytes, are triggered to undergo apoptosis. Bcl-2 acts between p53 and the caspase.
- 88. P53 as a transcription factor which exerts its effect by regulating other genes P53 can bind to DNA DNA p53
- 89. Induce DNA repair enzymes Allow cells time to repair the damaged DNA Li-Fraumeni Syndrome (hereditary p53 mutation) High risk of getting mutation of the second copy of the gene DNA damaging chemicals and radiation Tobacco---Lung cells UVB --- Skin cells p53 upregulated modulator of apoptosis
- 90. P53 and the cell cycle P53 arrests the cell cycle primarily by upregulating p21 (Cip1/Waf-1), which inactivates CDK/cyclin P53 can also activate apoptosis P21 is a kinase inhibitor
- 91. Inhibition of p53 functions
- 92. Genetic Instability in Tumors • (+) Oncogenes • (-) Tumor suppressor genes • Telomere shortening • Mismatch repair (MMR) genes • Chromosomal Instability • Microsatellite Instability
- 93. Aneuploidy in Human Hepatocellular Carcinoma Cell Line Hsr = homogeneously staining region due to endoreduplication of chromosomal segments resulting in gene amplification
- 94. Fluorescent in situ hybridization (FISH) of normal metaphase human chromosomes using chromosome specific DNA probes with different fluorescent dyes Figure 1.11b The Biology of Cancer (© Garland Science 2007)
- 95. Aneuploid karyotype of human breast cancer cell. Note “scrambling” of colors demonstrating chromosomal reciprocal translocations
- 96. Intra-chromosonal inversion by M-band fluorescent in situ hybridization (mFISH)
- 97. Telomeres and Cell Senescence
- 98. 1800 Human Genes mRNA’s From 142 different human tumors Red = elevated expression Green = diminished expression Gene Expression DNA Array Analysis
- 99. Tumor Immunity • General Principles – Tumors not entirely self • Express non-self proteins – Immune-mediated recognition of tumor cells may be “positive mechanism of eliminating transformed cells • Immune surveillance
- 100. Tumor Antigens • Tumor Specific Antigens – Present only on Tumor cells – Recognized by cytotoxic T cells • Bound by class I MHC – Several antigens in humans found that are not unique for tumor, however are generally not expressed by normal tissue • Melanoma-associated antigen-1 (MAGE-1): – Embryonal protein normally expressed in testis » Melanomas, breast ca, lung ca
- 101. Tumor Antigens • Tumor Associated Antigens – Not unique to tumors, shared by normal cells • Differentiation- specific antigens – CALLA (CD10) in early B cells – Prostate specific antigen PSA
- 102. Antitumor Effector Mechanisms • Cytotoxic T-cells – MHC restricted CD-8 cells (viruses) • NK cells – Destroying tumor cells without prior sensitization • Macrophages – Ifn-gamma • Humoral Mechanisms – Via complement and NK cells
- 103. Antitumor Effector Mechanisms Cytotoxic T-cell NK cell Humoral Macrophage Mechanisms
- 104. IMMUNOSURVAILLANCE • Argument for: – Increased cancer in immunodeficient hosts • 200x increase in immunodeficiencies (lymphoma) – X-linked lymphoproliferative disorder (XLP » EBV related • Escape Mechanism Theories – Selective outgrowth of antigen-negative variants – Loss or reduction of HLA (escape T-cells) – Immunosuppression (Tumors secrete factors TGF-b)
- 105. IMMUNOTHERAPY • Replace suppressed components of immune system or stimulate endogenous responses – Adoptive Cellular Therapy • Incubation of lymphocytes with IL-2 to generate lymphokine activated killer (LAK) cells with potent antitumor activity – Enriched tumor specific cytotoxic T cells » Tumor infiltrating lymphocytes (TIL)
- 106. Cytokine Therapy – Activate specific and nonspecific (inflammatory) host defenses. • Interferon-a, TNF-a, Il-2, IFN-g – IFN-a activates NK cells, increase MHC expression on tumor cells » Used for hairy cell leukemia
- 107. Antibody-Based Therapy – Antibodies as targeting agents – Direct use of antibodies to activate host immune system • Her-2/neu in advance breast cancer
- 110. Sample questions • The event(s) which does not occur during interphase, is/are • A. Chromatin condenses • B. Protein Synthesis • C. Organelles replication • D. DNA replication
- 111. • At the center of the cell cycle control system is Cdk, a protein that • A. is phosphorylated to become active • B. binds to different cyclins • C. is only active during mitosis • D. manufactures growth factors
- 112. Sample questions • An oncogene is • A. a viral gene with no relation to the host cell's genes. • B. a mutated form of a proto-oncogene. • C. a bacterial gene that causes cancer in the host. • D. a gene that turns off cellular reproduction.
Editor's Notes
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- #56: <number> A multistep model for the development of colorectal cancer.
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- #78: <number> Genetic changes that can turn proto-oncogenes into oncogenes.
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- #86: <number> Signaling pathways that regulate cell division.
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- #94: <number> Chromosome number, structure of individual defined numbered chromosomes, and fine structure as shown by banding patterns are grossly abnormal in advanced cancers. (Compare to the previous slide of normal chromosomal structures.).
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- #96: <number> Note intermixing of chromosomal components between and among chromosomes. What are the chances that this cell will express normal behavior if it is viable?
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