Ch. 20 Genetics

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Cencer cells share two fundamental properties:

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- unregulated cell proliferation
- metastatic spread

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genomic alteration associated with cancer:

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- single-nucleotide substitutions
- large scale chromosomal rearrangements
- amplifications
- deletions

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clonal

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tumors originated from a common ancestral cel that accumulated numerous specific mutations

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SLIDE 8

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do this one!

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tumorigenesis

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each step is the result of one or more genetic alterations that progressively release the cell from the normal controls on cell growth and proliferation.

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mutator phenotype

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high level of genomic instability in cancer cells

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cancer cells show higher than normal rates of :

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- mutation
- chromosomal abnormalities
- genomc instability

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genomic instability can cause:

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- translocations
- aneuploidy
- chromosome loss
- DNA amplification
- chromosomal deletions

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Epigenetics

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the study of factors that cause DNA modifications in a heritable way without affecting he nucleotide sequence of the DNA.

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G0

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cells that stop proliferating enter this stage in which they do not grow or divide but are metabolically active.

CANCER CELL ARE UNABLE TO ENTER G0

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Signal Transduction

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initiates a program of gene expression that propels the cell out of G0 and back into the cell cycle.

CANCER CELLS OFTEN HAVE DEFECTS IN SIGNAL TRANSDUCTION PATHWAYS

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G1/S, G2/M, and M checkpoints

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this is where cells decide whether to proceed to the next stage of the cell cycle.

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Cyclins

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mediates regulation of cell cycle

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Cyclin-dependent Kinases (CDKs)

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regulate synthesis and destruction of cyclin proteins

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Cells halt progress through the cell cycle if ______ are abberant/

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DNA replication, repair, or chromosome assembly

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apoptosis

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programmed cell death; if DNA damage is so sever that repair is impossible the cell may initiate this.

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caspases

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a series of proteases responsible for initiating apoptosis and for digesting intracellular components

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Bcl2-BAX

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heterodimer thta joins together the homodimers Bcl2 and BAX and is an active complex

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Bcl2 homodimer

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blocks apoptosis

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BAX

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promotes apoptosis

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Proto-oncogenes

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genes whose products promote cell growth and division

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Proto-oncogenes encode:

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- transcription factors that stimulate expression of other genes
- signal transduction molecules that stimulate cell division
- cell-cycle regulators that move through the cell cycle

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In cancer cells one or more proto-oncogenes...

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are altered in such a way that their activities cannot be controlled normally.

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oncogene

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a proto-oncogene that i mutated or aberrantly expressed and contributes to the development of cancer.

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tumor suppressor genes

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normally regulate cell cycle checkpoints and initiate the process of apoptosis.

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when tumor suppressor genes are mutated or inactivated

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cells are unable to undergo apoptosis if DNA damage is extensive.

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ras genes

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encode signal transduction molecules that regulate cell growth division.

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Mutations that convert the ras proto-oncogene to an oncogene...

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freeze the ras protein into its active conformation, constantly stimulating the cell to divide.

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Cyclins

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form complexes with CDKs that are importnat regulators of each phase of the cell

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Cyclin D1 and Cyclin E are...

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proto-oncogenes

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p53 tumor suppressor gne

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encodes a nuclear protein that acts as a transcription factor that represses or stimulates transcription of more than 50 different genes.

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cells lacking p53

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are unable to arrest the cell cycle at checkpoints or enter apoptosis in response to DNA damage.

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RB1 tumor supressor gene

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contributes to the development of many cancers due to unregulated progression through the cell cycle

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familial retinoblastoma

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a mutated RB1 is inherited

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Sporadic retinoblastoma

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requires two independent mutational events of RB1 within the same cell

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retinblastoma protein

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a tumor supressor protein that controls the G1/S cell cycle checkpoint.

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metastasize

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the primary tumor cells must digest components of the extracellular matrix and basal lamina that normally inhibit migration of cells.

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proteolytic enzymes

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present at higher than normal levels in highly malignant tumors and are not susceptible to the normal controls conferred by regulatory molecules.

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familial adenomatous polyposis

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an example of the necessity of mutation in other genes to fully express the cancer phenotype.

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Most animal viruses that casue cancer are

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retroviruses.

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acute transforming retroviruses

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viruses that cause cancer in animals because they transform normal cells into cancer cells

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carcinogenic

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any substance or event that damages DNA causing mutations to occur in proto-oncogenes or tumor suppressor genes

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carcinogens can be:

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chemicals, radiation, some viruses, and chronic infections