Bcl-2 potentiates the maximal calcium uptake capacity of neural cell mitochondria.

Abstract

Expression of the human protooncogene bcl-2 protects neural cells from death induced by many forms of stress, including conditions that greatly elevate intracellular Ca2 . Considering that Bcl-2 is partially localized to mitochondrial membranes and that excessive mitochondrial Ca2+ uptake can impair electron transport and oxidative phosphorylation, the present study tested the hypothesis that mitochondria from Bcl-2-expressing cells have a higher capacity for energy-dependent Ca2+ uptake and a greater resistance to Ca2+-induced respiratory injury than mitochondria from cells that do not express this protein. The overexpression of bcl-2 enhanced the mitochondrial Ca2+ uptake capacity using either digitonin-permeabilized GT1-7 neural cells or isolated GT1-7 mitochondria by 1.7 and 3.9 fold, respectively, when glutamate and malate were used as respiratory substrates. This difference was less apparent when respiration was driven by the oxidation of succinate in the presence of the respiratory complex I inhibitor rotenone. Mitochondria from Bcl-2 expressors were also much more resistant to inhibition of NADH-dependent respiration caused by sequestration of large Ca2+ loads. The enhanced ability of mitochondria within Bcl-2-expressing cells to sequester large quantities of Ca2+ without undergoing profound respiratory impairment provides a plausible mechanism by which Bcl-2 inhibits certain forms of delayed cell death, including neuronal death associated with ischemia and excitotoxicity.

Inhibition of mitochondrial respiratory chain complex I by TNF results in cytochrome c release, membrane permeability transition, and apoptosis

“…Interestingly, Bcl-2 can inhibit complex I damage by a Ca 2+ overload and an increase in Ca 2+ uptake capacity when the electron is transferred through complexes I, III and IV (Murphy et al, 1996). Therefore, it is very possible that Bcl-2 can regulate the activity of MRC complex I through unknown mechanisms, and thus regulate apoptosis.…”

Protection against hydrogen peroxide cytotoxicity in Rat-1 fibroblasts provided by the oncoprotein Bcl-2: maintenance of calcium homoeostasis is secondary to the effect of Bcl-2 on cellular glutathione

“…The observation that Bcl-2 does not directly regulate cellular Ca# + compartmentation and fluxes but modulates sensitivity to Ca# + -dependent injurious processes through the intermediary glutathione may also help to explain the contradictory results reported for the action of Bcl-2 on cellular Ca# + homoeostasis and on Ca# + -mediated cell death [5][6][7][8][9][10][11][12]. According to the results obtained here with Rat-1 fibroblasts, Bcl-2 should only affect those Ca# + -mediated processes that are triggered by alterations in cellular glutathione homoeostasis, but should leave nonglutathione-dependent processes unaffected.…”

“…In some of these injurious processes, disruption of cellular Ca# + homoeostasis, especially elevations of cytosolic Ca# + concentration, is considered to play a decisive intermediary role [4]. Accordingly, effects of Bcl-2 on Ca# + homoeostasis and on Ca# + -mediated cell death have been studied in a number of experimental models [5][6][7][8][9][10][11][12]. These studies, however, led to contradictory results and no clear picture emerged as to how Bcl-2 may affect Ca# + -mediated cell-injurious processes.…”

Bcl-2 prevents topoisomerase II inhibitor GL331-induced apoptosis is mediated by down-regulation of poly(ADP-ribose)polymerase activity

“…The precise biochemical mechanisms by which Bcl-2 proteins in¯uence cell life and death, however, remain unclear. This is despite the fact that several theories have been advanced, including regulation of organellar Ca 2+ homeostasis (Murph et al, 1996), reactive oxygen species production (Kane et al, 1993), cysteine protease activation (Ibrado et al, 1996), and mitochondrial permeability transition (PT) (Marchetti et al, 1996). To prevent cell death induced by DNAdamaging drugs, Bcl-2 does not reduce drugs-induced damage to DNA, increase rates of DNA repair, inhibit drug-induced alterations in nucleotide pools, or change cell cycle kinetics (Fairbarn et al, 1994;Eymin et al, 1997).…”