APOPTOSIS-ASSOCIATED DERANGEMENT OF MITOCHONDRIAL-FUNCTION IN CELLS LACKING MITOCHONDRIAL-DNA

U937 cells lacking mitochondrial DNA (rho degrees cells) are auxotroph ic for uridine and pyruvate, hypersensitive to hypoglycemic conditions , and resistant to antimycin A-induced apoptosis, In spite of their ob vious metabolic defects, rho degrees cells possess a normal mitochondr ial transmembrane potential, as well as a near-normal capacity to gene rate superoxide anion after menadione treatment, Similarly to rho(+) c ontrols, rho degrees cells undergo apoptosis in response to tumor necr osis factor-alpha plus cycloheximide, Detailed comparison of the apopt otic process in rho(+) and rho degrees cells reveals essentially the s ame sequence of events, In response to tumor necrosis factor/cyclohexi mide, cells first lose their mitochondrial transmembrane potential (De lta psi(m)) and then manifest late apoptotic alterations, such as gene ration of reactive oxygen species and DNA fragmentation, Experiments i nvolving isolated mitochondria from rho(+) and rho degrees cells confi rm that rho degrees mitochondria can be induced to undergo permeabilit y transition, a process thought to account for the pre-apoptotic Delta psi(m) disruption in cells, Like rho(+) mitochondria, p degrees mitoc hondria contain a pre-formed soluble factor that is capable of inducin g chromatin condensation in isolated nuclei in vitro, This factor is r eleased from mitochondria upon induction of permeability transition by calcium or the specific ligand of the adenine nucleotide translocator atractyloside, In conclusion, it appears that all structures involved in the maintenance and pre-apoptotic disruption of the Delta psi(m), as well as a mitochondrial apoptotic factor(s), are present in rho deg rees cells and thus are controlled by the nuclear rather than by the m itochondrial genome, These findings underline the contribution of mito chondria to the apoptotic process.