title: Activation of caspase-9 is required for UV-induced apoptosis of human keratinocytes.
abstract: UV radiation from the sun activates both the membrane death receptor and the intrinsic or mitochondrial apoptotic signaling pathways in epidermal keratinocytes, triggering apoptosis and affording protection against skin cancer formation. We have investigated the involvement of caspase-9 in the UV death effector pathway in human keratinocytes, since this is the initiating caspase in the mitochondrial pathway required for UV-induced apoptosis in some, but not all, cell types. UV radiation triggered activation of caspase-3, caspase-9, and caspase-8 with similar kinetics, although the rank order of activation was caspase-3 > caspase-9 > caspase-8. Inhibition of caspase-9 with either the peptide inhibitor benzyloxycarbonyl-Leu-Glu(OCH(3))-His-Asp(OCH(3))-fluoromethyl ketone, or expression of a catalytically inactive caspase-9 by retroviral transduction, protected normal keratinocytes from UV-induced apoptosis. HaCaT keratinocytes harboring mutant p53 alleles were also protected from UV-induced apoptosis by the dominant negative caspase-9. The dominant negative caspase-9 blocked UV-induced activation of caspase-3, caspase-9, and caspase-8, and also protected cells from the loss of mitochondrial membrane potential. In contrast, the dominant negative caspase-9 did not protect from anti-Fas-induced apoptosis or caspase activation. These results identify caspase-9 as the critical upstream caspase initiating apoptosis by UV radiation in human keratinocytes, the relevant cell type for this important environmental carcinogen.
authors.affiliation: Department of Pathology and the Cardinal Bernardin Cancer Center, Skin Cancer Research Program, Loyola University Medical Center, Maywood, Illinois 60153, USA.
authors.forename: Leonid A
authors.initials: LA
authors.lastname: Sitailo
authors.forename: Shalini S
authors.initials: SS
authors.lastname: Tibudan
authors.forename: Mitchell F
authors.initials: MF
authors.lastname: Denning
mesh_terms: D000483:Alleles; D017209:Apoptosis; D015153:Blotting, Western; D053181:Caspase 8; D053453:Caspase 9; D020169:Caspases / Q000378:metabolism*; D002478:Cells, Cultured; D018076:DNA, Complementary / Q000378:metabolism; D004789:Enzyme Activation; D004792:Enzyme Precursors / Q000378:metabolism; D005434:Flow Cytometry; D016158:Genes, p53; D006801:Humans; D015603:Keratinocytes / Q000473:pathology* / Q000528:radiation effects*; D007700:Kinetics; D008856:Microscopy, Fluorescence; D008928:Mitochondria / Q000378:metabolism; D008954:Models, Biological; D009154:Mutation; D011994:Recombinant Proteins / Q000378:metabolism; D012190:Retroviridae / Q000235:genetics; D013997:Time Factors; D014466:Ultraviolet Rays; D019014:fas Receptor / Q000378:metabolism
chemical_list: D018076:DNA, Complementary; D004792:Enzyme Precursors; D011994:Recombinant Proteins; D019014:fas Receptor; C505530:CASP8 protein, human; C506433:CASP9 protein, human; D053181:Caspase 8; D053453:Caspase 9; D020169:Caspases