title: Intracellular nucleotides act as critical prosurvival factors by binding to cytochrome C and inhibiting apoptosome.
abstract: Cytochrome c (CC)-initiated Apaf-1 apoptosome formation represents a key initiating event in apoptosis. This process can be reconstituted in vitro with the addition of CC and ATP or dATP to cell lysates. How physiological levels of nucleotides, normally at high mM concentrations, affect apoptosome activation remains unclear. Here we show that physiological levels of nucleotides inhibit the CC-initiated apoptosome formation and caspase-9 activation by directly binding to CC on several key lysine residues and thus preventing CC interaction with Apaf-1. We show that in various apoptotic systems caspase activation is preceded or accompanied by decreases in overall intracellular NTP pools. Microinjection of nucleotides inhibits whereas experimentally reducing NTP pools enhances both CC and apoptotic stimuli-induced cell death. Our results thus suggest that the intracellular nucleotides represent critical prosurvival factors by functioning as natural inhibitors of apoptosome formation and a barrier that cells must overcome the nucleotide barrier to undergo apoptosis cell death.
authors.affiliation: Department of Carcinogenesis, University of Texas MD Anderson Cancer Center, Science Park-Research Division, Smithville, TX 78957, USA. dhchandra@mdanderson.org
authors.forename: Dhyan
authors.initials: D
authors.lastname: Chandra
authors.forename: Shawn B
authors.initials: SB
authors.lastname: Bratton
authors.forename: Maria D
authors.initials: MD
authors.lastname: Person
authors.forename: Yanan
authors.initials: Y
authors.lastname: Tian
authors.forename: Angel G
authors.initials: AG
authors.lastname: Martin
authors.forename: Mary
authors.initials: M
authors.lastname: Ayres
authors.forename: Howard O
authors.initials: HO
authors.lastname: Fearnhead
authors.forename: Varsha
authors.initials: V
authors.lastname: Gandhi
authors.forename: Dean G
authors.initials: DG
authors.lastname: Tang
mesh_terms: D017209:Apoptosis / Q000502:physiology*; D053477:Apoptotic Protease-Activating Factor 1; D001665:Binding Sites; D053453:Caspase 9; D020169:Caspases / Q000378:metabolism; D002460:Cell Line; D002470:Cell Survival / Q000502:physiology; D002474:Cell-Free System; D045304:Cytochromes c / Q000737:chemistry / Q000378:metabolism*; D004789:Enzyme Activation; D006801:Humans; D066298:In Vitro Techniques; D047908:Intracellular Signaling Peptides and Proteins / Q000737:chemistry / Q000378:metabolism; D008239:Lysine / Q000737:chemistry; D008958:Models, Molecular; D046912:Multiprotein Complexes; D009711:Nucleotides / Q000378:metabolism*; D011487:Protein Conformation; D020836:Protein Structure, Quaternary; D011506:Proteins / Q000737:chemistry / Q000378:metabolism
chemical_list: C506592:APAF1 protein, human; D053477:Apoptotic Protease-Activating Factor 1; D047908:Intracellular Signaling Peptides and Proteins; D046912:Multiprotein Complexes; D009711:Nucleotides; D011506:Proteins; D045304:Cytochromes c; C506433:CASP9 protein, human; D053453:Caspase 9; D020169:Caspases; D008239:Lysine