title: UV-induced apoptosis is mediated independent of caspase-9 in MCF-7 cells: a model for cytochrome c resistance.
abstract: The importance of the mitochondria in UV-induced apoptosis has become increasingly apparent. Following DNA damage cytochrome c and other pro-apoptotic factors are released from the mitochondria, allowing for formation of the apoptosome and subsequent cleavage and activation of caspase-9. Active caspase-9 then activates downstream caspases-3 and/or -7, which in turn cleave poly(ADP)-ribose polymerase (PARP) and other down-stream targets, resulting in apoptosis. In an effort to understand the mechanisms of Akt-mediated cell survival in breast cancer, we studied the effects of insulin-like growth factor (IGF)-I treatment on UV-treated MCF-7 human breast cancer cells. Apoptosis was induced in MCF-7 cells after UV treatment, as measured by caspase-7 and PARP cleavage, and IGF-I co-treatment protected against this response. Surprisingly caspase-9 cleavage was unchanged with UV and/or IGF-I treatment. Using MCF-7 cells overexpressing caspase-3 we have shown that resistance of caspase-9 to cleavage was not altered by the expression of caspase-3. Furthermore, overexpression of caspase-9 did not enhance PARP or caspase-7 cleavage after UV treatment. Because caspase-8 was activated with UV treatment alone, we believe that UV-induced apoptosis in MCF-7 cells occurs independently of cytochrome c and caspase-9, supporting the existence of a cytoplasmic inhibitor of cytochrome c in MCF-7 cells. We anticipate that such inhibitors may be overexpressed in cancer cells, allowing for treatment resistance.
authors.affiliation: School of Pharmacy, University of Colorado Health Sciences Center, Denver, Colorado 80262, USA.
authors.forename: Heather A
authors.initials: HA
authors.lastname: Ferguson
authors.forename: Peter M
authors.initials: PM
authors.lastname: Marietta
authors.forename: Carla L
authors.initials: CL
authors.lastname: Van Den Berg
mesh_terms: D017209:Apoptosis; D015153:Blotting, Western; D001943:Breast Neoplasms / Q000378:metabolism; D053148:Caspase 3; D053179:Caspase 7; D053453:Caspase 9; D020169:Caspases / Q000378:metabolism / Q000502:physiology*; D002460:Cell Line; D045744:Cell Line, Tumor; D002470:Cell Survival; D045304:Cytochromes c / Q000378:metabolism*; D004789:Enzyme Activation; D006801:Humans; D007334:Insulin-Like Growth Factor I / Q000378:metabolism; D008856:Microscopy, Fluorescence; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D011065:Poly(ADP-ribose) Polymerases / Q000378:metabolism; D011233:Precipitin Tests; D011506:Proteins / Q000378:metabolism; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism; D012313:RNA / Q000378:metabolism; D013997:Time Factors; D014162:Transfection; D014466:Ultraviolet Rays; D051636:X-Linked Inhibitor of Apoptosis Protein
chemical_list: D011506:Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D051636:X-Linked Inhibitor of Apoptosis Protein; C496866:XIAP protein, human; D012313:RNA; D007334:Insulin-Like Growth Factor I; D045304:Cytochromes c; D011065:Poly(ADP-ribose) Polymerases; D019869:Phosphatidylinositol 3-Kinases; C505407:CASP3 protein, human; C505520:CASP7 protein, human; C506433:CASP9 protein, human; D053148:Caspase 3; D053179:Caspase 7; D053453:Caspase 9; D020169:Caspases