Perturbation of the Bcl-2 network and an induced Noxa/Bcl-xL interaction trigger mitochondrial dysfunction after DNA damage.
How most apoptotic stimuli trigger mitochondrial dysfunction remains to be resolved. We screened the entire Bcl-2 network for its involvement in DNA damage-induced apoptosis in HeLa cells. Although the anti-apoptotic member Bcl-xL served as a major suppressor, apoptosis initiated only when both Mcl-1 and Bcl-xL were eliminated. The pro-apoptotic members Bak, Bad, Bim, and Noxa were required for apoptosis induced by DNA damaging agents camptothecin and UV. We, therefore, used a His-tagged Bcl-xL expression system to capture the relevant BH3-only proteins that bind to Bcl-xL in response to DNA damage. Surprisingly, unlike Bad and Bim, which bound Bcl-xL constitutively, Noxa became "Mcl-1-free" and interacted with Bcl-xL after DNA damage but not after death receptor engagement. Similar observations were also made in A431 cells. Importantly, this induced interaction caused cytochrome c release and apoptosis and was directly inhibited by Mcl-1, a protein eliminated or inactivated after DNA damage. These results suggest that the loss/inactivation of Mcl-1 in conjunction with an induced Noxa/Bcl-xL interaction may serve as a trigger for mitochondrial dysfunction during DNA damage-induced apoptosis.
Eppley Institute for Research in Cancer and Allied Diseases, University of Nebraska Medical Center, Omaha, Nebraska 68198-7696.
Hernando
H
Lopez
Eppley Institute for Research in Cancer and Allied Diseases, University of Nebraska Medical Center, Omaha, Nebraska 68198-7696.
Liqiang
L
Zhang
Eppley Institute for Research in Cancer and Allied Diseases, University of Nebraska Medical Center, Omaha, Nebraska 68198-7696.
Nicholas M
NM
George
Eppley Institute for Research in Cancer and Allied Diseases, University of Nebraska Medical Center, Omaha, Nebraska 68198-7696.
Xiaoqiong
X
Liu
Eppley Institute for Research in Cancer and Allied Diseases, University of Nebraska Medical Center, Omaha, Nebraska 68198-7696.
Xiaming
X
Pang
Eppley Institute for Research in Cancer and Allied Diseases, University of Nebraska Medical Center, Omaha, Nebraska 68198-7696.
Jacquelynn J D
JJD
Evans
Eppley Institute for Research in Cancer and Allied Diseases, University of Nebraska Medical Center, Omaha, Nebraska 68198-7696.
Natalie M
NM
Targy
Eppley Institute for Research in Cancer and Allied Diseases, University of Nebraska Medical Center, Omaha, Nebraska 68198-7696. Electronic address: xuluo@unmc.edu.
Xu
X
Luo
D017209:Apoptosis / Q000187:drug effects; D002166:Camptothecin / Q000494:pharmacology; D002460:Cell Line; D045304:Cytochromes c / Q000378:metabolism; D004249:DNA Damage; D006367:HeLa Cells; D006801:Humans; D008928:Mitochondria / Q000502:physiology*; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D051020:bcl-X Protein / Q000378:metabolism*
C498702:PMAIP1 protein, human; D019253:Proto-Oncogene Proteins c-bcl-2; D051020:bcl-X Protein; D045304:Cytochromes c; D002166:Camptothecin