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CANCER IS A GENETIC DISEASE

CANCER IS A GENETIC DISEASE. SUPPORTING EVIDENCE:. 1. Hereditary cancer. 2. Cancer-causing virus. 3. Alterations of cellular genes in cancer. 4. Clonal development of cancer. T1-1. A TYPICAL FAMILY TREE OF INHERITED CANCER SYNDROME. Individuals With Related Cancer. T1-2.

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CANCER IS A GENETIC DISEASE

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  1. CANCER IS A GENETIC DISEASE SUPPORTING EVIDENCE: 1. Hereditary cancer 2. Cancer-causing virus 3. Alterations of cellular genes in cancer 4. Clonal development of cancer T1-1

  2. A TYPICAL FAMILY TREE OF INHERITED CANCER SYNDROME Individuals With Related Cancer T1-2

  3. Inherited Cancer Syndrome: Sporadic Cancer: Germline mutation Somatic mutation Early onset Later in life More than one tumor Clonal tumor Rare One in four people T1-3

  4. CANCER IS A GENETIC DISEASE SUPPORTING EVIDENCE: 1. Hereditary cancer 2. Cancer-causing virus 3. Alterations of cellular genes in cancer 4. Clonal development of cancer T1-4

  5. Avian Sarcoma Virus Isolated by P. Rous in the early 1900’s 1. A retrovirus 2. Can be transmitted from chick to chick 3. Causes sarcoma, cancer of the connective tissue (fibroblasts) 4. Carries an “oncogene”, called src T1-4

  6. Viral Oncogene Originates in the virus. Viral oncogene product interacts with host proteins to cause trouble. Examples: T-antigen, E1A. Originates in the host. Viral transduction of altered host genes to cause trouble. Examples: v-Src, v-Ras, v-Myc, v-Abl. T1-6

  7. CANCER IS A GENETIC DISEASE SUPPORTING EVIDENCE: 1. Hereditary cancer 2. Cancer-causing virus 3. Alterations of cellular genes in cancer 4. Clonal development of cancer T1-7

  8. EXISTENCE OF GAIN OF FUNCTION GENETIC ALTERATIONS IN SPORADIC CANCER CELLS Method: Forcing DNA into Immortalized Mouse Cells (Transfection) Biological Assay: Transformation of immortalized mouse cells into tumorigenic mouse cells: • growth in soft agar • tumor formation in immune-deficient mice (nude mice) T1-8

  9. Experiment Prepare Total DNA from Human Bladder Cancer Cells (EJ) Transfection Immortalized Mouse Fibroblasts (3T3) Transformation Assay Isolate Transformed clones in soft agar Prepare DNA from these clones & transfect DNA again into T1-9

  10. Results • DNA from human bladder cancer cells can convert immortalized mouse cells into tumorigenic cells. • Repeated transfections allowed scientists to reduce the amount of human DNA in the tumorigenic mouse cells (purification of transforming DNA). • Human DNA contains signature repetitive sequences that are not in the mouse gnome. • Therefore, scientists were able to “isolate (clone)” the human DNA that caused tumorigenic conversion. Nucleotide sequencing identified this transforming gene to be a mutated Ras*! T1-10

  11. CANCER IS A GENETIC DISEASE SUPPORTING EVIDENCE: 1. Hereditary cancer 2. Cancer-causing virus 3. Alterations of cellular genes in cancer 4. Clonal development of cancer T1-11

  12. Clonal Development of Cancer Cancer of the B-lymphocytes (various forms of Leukemia or Lymphoma) can be shown to be monoclonal or oligoclonal by the analysis of immunoglobulin (Ig) genes, which undergo random rearrangement in B cells. Hence, the cancer cells are the Descendants of a few transformed B cells. Mixture of B cells: Ig genes in many different configurations due to random rearrangement A monoclonal population of B cells: Ig gene in one configuration. T1-12

  13. Clonal Development of Cancer Example: Abelson murine leukemia virus causes B-lymphoma that kills the mice in 3-6 weeks. The virus can infect almost every cell in the mouse, but, it only causes B-lymphoma which is monoclonal! T1-13

  14. CANCER CELLS DIFFER FROM NORMAL CELLS BECAUSE CANCER CELLS CONTAIN MULTIPLE GENETIC AND EPIGENETIC ALTERATIONS T1-14

  15. Cancer Development is Driven by Multiple Defects Evidence 1. Cancer rate increases with age. 2. A single mutation is not sufficient to cause cancer. Ras* does not transform normal cells, it only transforms “immortalized” mouse cells, which grow forever! Ras* actually causes primary cells to stop growing! 3. Clonality of cancer. T1-15

  16. HERITABLE ALTERATIONS IN CANCER CELLS •GAIN OF FUNCTIONS (NOT FOUND IN NORMAL CELLS) Creation of Oncogenes •LOSS OF FUNCTIONS (FOUND IN NORMAL CELLS) Destruction of Tumor Suppressor Genes T1-16

  17. WHY MULTIPLE ALTERATIONS? Cell proliferation is purposeful,and can respond to stress. Normal proliferation is coupled to Differentiation, Senescence, and Death by Suicide (Apoptosis). Deregulation of cell proliferation requires the uncoupling of these processes, hence, it requires a multitude of alterations. T1-17

  18. Normal Proliferation is Coupled to Multiple Choices Senescence Proliferation Stem cell Apoptosis Quiescence Differentiation Long-term survival death T1-18

  19. Cancer Proliferation is Uncoupled from the Normal Choices Senescence Proliferation Cancer cell Apoptosis Quiescence Differentiation T1-19

  20. Cancer Proliferation is Uncoupled from the Normal Choices More Cyclins Loss of p16 Senescence Proliferation Loss of Arf Reactivation of telomerase Cancer cell Gain of Ras Gain of growth factors Gain of Bcl2 Loss of p53 Apoptosis Gain of Myc Quiescence Loss of RB Differentiation T1-20

  21. TOPICS •DISCOVERY OF CANCER GENES •HOW CANCER GENES CONTRIBUTE TO CANCER CELL GROWTH •HOW CANCER GENES CONTRIBUTE TO CANCER GENETIC INSTABILITY •RATIONAL DESIGN OF CANCER THERAPY BASED ON CANCER GENES T1-21

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