Bax is translocated into the mitochondrial membrane and oligomerized therein to initiate mitochon-drial apoptotic signaling. Our previous study indicated that reactive oxygen species (ROS)-mediated activation of mitogen-activated protein kinase (MAPK) and caspase is critically involved in 6-hydroxydopamine (6-OHDA)-mediated neurodegeneration. Here, we specifically attempted to examine whether and how these death signaling pathways may be linked to Bax translocation and oligomerization. We found that 6-OHDA treatment triggered translocation and oligomerization of Bax onto the mitochondria in MN9D dopaminergic neuronal cells. These events preceded cyto-chrome c release into the cytosol. Cross-linking assay revealed that co-treatment with a ROS scavenger or a pan-caspase inhibitor inhibited 6-OHDA-induced Bax oligo-merization. Among several candidates of ROS-activated MAPKs and caspases, we found that co-treatment with PD169316 or VDVAD specifically inhibited 6-OHDA-induced Bax oligomerization, suggesting critical involvement of p38 MAPK and caspase-2. Consequently, overexpression of a dominant negative form of p38 MAPK or a shRNA-mediated knockdown of caspase-2 indeed inhibited 6-OHDA-induced Bax oligomerization. However, activation of p38 MAPK and caspase-2 was independently linked to oligomerization of Bax. This specificity was largely confirmed with a Bax 6A7 antibody known to detect activated forms of Bax on the mitochondria. Taken together, our data suggest that there is an independent amplification loop of Bax translocation and oligomerization via caspase-2 and p38 MAPK during ROS-mediated dopaminergic neurodegeneration.
Bibliographical noteFunding Information:
Acknowledgments This work was supported by a grant of the Korea Healthcare Technology R&D Project from the Ministry for Health, Welfare & Family Affairs (A090063), and in part by a grant from the Ministry of Science and Technology through the Brain Research Center (Infra-2), KOSEF (SRC, R11-20080036-00000-0) and WCU (R33-2008-10014).
All Science Journal Classification (ASJC) codes
- Pharmaceutical Science
- Clinical Biochemistry
- Cell Biology
- Biochemistry, medical
- Cancer Research