Adrenodoxin (Adx) and CYP11A1 (P450scc) induce apoptosis by the generation of reactive oxygen species in mitochondria

Abstract

Mitochondrial cytochrome P450 systems are an indispensable component of mammalian steroid biosynthesis; they catalyze regio- and stereo-specific steroid hydroxylations and consist of three protein entities: adrenodoxin reductase (AdR), adrenodoxin (Adx), and a mitochondrial cytochrome P450 enzyme, e.g., CYP11A1 (P450 side chain cleavage, P450scc). It is known that the latter two are able to generate reactive oxygen species (ROS) in vitro . In this study, we investigated whether this ROS generation also occurs in vivo and, if so, whether it leads to the induction of apoptosis. We found that overexpression of either human or bovine Adx causes a significant loss of viability in 11 different cell lines. This loss of viability does not depend on the presence of the tumor suppressor protein p53. Transient overexpression of human Adx in HCT116 cells leads to ROS production, to a disruption of the mitochondrial transmembrane potential (DeltaPsi), to cytochrome c release from the mitochondria, and to caspase activation. In contrast, the effect of transient overexpression of human CYP11A1 on cell viability varies in different cell lines, with some being sensitive and others not. We conclude that mitochondrial cytochrome P450 systems are a source of mitochondrial ROS production and can play a role in the induction of mitochondrial apoptosis.

The variable expression of lectin-like oxidized low-density lipoprotein receptor (LOX-1) and signs of autophagy and apoptosis in freshly harvested human granulosa cells depend on gonadotropin dose, age, and body weight

“…Reactive oxygen species are normal byproducts of steroidogenesis due to electron leakage from the mitochondrial electron transport chain (17,18). Moderate amounts of ROS are compensated, for example, by catalase activity and the glutathione cycle, and, interestingly, are considered to be physiologically key molecules in oocyte maturation and fertilization.…”

ROS production by adrenodoxin does not cause apoptosis in fission yeast

“…Although the increase in mitochondrial ROS production after expression of Adx 1-108 in strain CAD48 was more than threefold in comparison to the background level, it did not cause cell death. For comparison, after transient expression of human Adx-WT in cell line HCT116 p53 -/-ROS formation increased merely by a factor of 1.6 (as measured by the same detection assay) but caused a drop in cell survival by more than 50% [20]. To the best of our knowledge, these findings provide the first example of strong ROS production being not linked to cell death in fission yeast.…”

“…We recently reported that transient overexpression of human or bovine Adx is sufficient to cause significant ROS formation in the mitochondria of mammalian cells, with an increase in mitochondrial ROS formation of about 60% above basal levels being sufficient to strongly induce apoptosis [20]. The aim of this study was to investigate the effects of Adx expression in the fission yeast S. pombe and to compare it to Adx-induced cell death in mammalian cells.…”

“…In mammalian cells, mitochondrial ROS are known to cause apoptosis and may be produced by the respiratory chain during oxidative phosphorylation or by mitochondrial cytochrome P450 systems [20]. In fission yeast, however, it remained unclear so far whether mitochondrial ROS are merely produced as a byproduct during apoptosis or whether they can actually cause apoptosis [21].…”

Temperature Derivative Spectroscopy To Monitor the Autoxidation Decay of Cytochromes P450

“…It is known that the autoxidation shunt accounts for a major fraction of reactive oxygen species (ROS) in mammalian P450 CYP11A1, both in vivo and in vitro 12 and this can lead to the induction of apoptosis in cells.…”