Cancer biol lecture - Tumor formation requires a large...

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Tumor formation requires a large number of cell divisions Cancer cells have unlimited proliferative potential: i.e they are immortal
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Limits to proliferation Precancerous lesions are quite common Cells have gained the capacity to overcome growth barriers but lesions never develop into tumors. Why? The cell environment limits cell division (i) Apoptosis (ii) Senescence after a limited number of population doublings Overcome via changes in signaling pathways (cell cycle, growth factor etc) Precancerous lesions
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Many cells undergo apoptosis Limits increase in cell number/rate of tumor growth Greatly increases number of population doublings (PD) required to form A tumor Tunnel staining
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Human primary cells become senescent after a limited number of PD. Hayflick phenomenon 1. Cells become large & flat, stain with β galactosidase 2. Cells do not incorporate BrdU (i.e no DNA replication) Replicative Senescence (post mitotic senescence: aging in non-dividing cells due to accumlated damage)
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Reasons for replicative senescence 1. Poor growth conditions: CO2, media, growth surface 2. Mitotic clock: No cell divisions is limited even with ideal culture conditions: Can overcome by expressing SV40 large T antigen Cell division is limited by telomere length
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G-overhang binding protein Double-strand binding proteins Telomeres are the protective DNA-protein caps at the ends of chromosomes REPEATED SEQUENCE DNA 10-20 kb T 2 AG 3 in Humans and Chickens 300 bp G 4 T 2 in Tetrahymena and S. cerevisiae 3’ 5’ Nucleosomes
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Telomeres and the end replication problem 5’ 3’ + 5’ 3’ 5’ 3’ Loss of telomeric DNA Short telomeres are recognized as DNA damage The damage response causes cells to stop dividing Cancer cells express telomerase , an enzyme that adds back telomeric DNA
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Hande et al. J. Cell Biol.
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This note was uploaded on 08/17/2009 for the course 26CB 880 taught by Professor Khan during the Spring '07 term at University of Cincinnati.

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Cancer biol lecture - Tumor formation requires a large...

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