Overexpression of bcl-2 results in reduction of cytochrome c content and inhibition of complex I activity.

ABSTRACT

Bcl-2 has been shown to exert its antiapoptotic activity predominantly at the level of mitochondria by preventing cytochrome c release. Whether Bcl-2 is involved in the regulation of mitochondrial function prior to an apoptotic stimulus remains elusive. Using functional and spectrophotometric measurements in an inducible PC12-Tet-on-bcl-2 cell line we demonstrate that induction of Bcl-2 overexpression rapidly reduced cytochrome b and c levels as well as complex I activity. To confirm that these changes were specific for Bcl-2 we generated a bcl-2 antisense construct under the control of the tetracycline responsive promotor. Transient transfection with this antisense plasmid prevented both the decrease of cytochrome b and c levels and the loss of complex I activity. The decrease of cytochrome b levels was paralleled by a decrease of cytochrome b mRNA levels while Northern blot analysis of cytochrome c mRNA expression did not reveal any overt changes in Bcl-2 cells. We propose that the antiapoptotic properties of Bcl-2 are related to the reduction of mitochondrial complex I activity and lowered mitochondrial cytochrome b and c levels.