Oxidized low-density lipoprotein-activated c-Jun NH2-terminal kinase regulates manganese superoxide dismutase ubiquitination: implication for mitochondrial redox status and apoptosis.
OBJECTIVE
Oxidized low-density lipoprotein (oxLDL) modulates intracellular redox status and induces apoptosis in endothelial cells. However, the signal pathways and molecular mechanism remain unknown. In this study, we investigated the role of manganese superoxide dismutase (Mn-SOD) on oxLDL-induced apoptosis via c-Jun NH2-terminal kinase (JNK)-mediated ubiquitin/proteasome pathway.


RESULTS
OxLDL induced JNK phosphorylation that peaked at 30 minutes in human aortic endothelial cells. Fluorescence-activated cell sorting analysis revealed that oxLDL increased mitochondrial superoxide production by 1.88+/-0.19-fold and mitochondrial membrane potential by 18%. JNK small interference RNA (siJNK) reduced oxLDL-induced mitochondrial superoxide production by 88.4% and mitochondrial membrane potential by 61.7%. OxLDL did not affect Mn-SOD mRNA expression, but it significantly reduced Mn-SOD protein level, which was restored by siJNK. Immunoprecipitation by ubiquitin antibody revealed that oxLDL increased ubiquitination of Mn-SOD, which was inhibited by siJNK. OxLDL-induced caspase-3 activities were also attenuated by siJNK but were enhanced by Mn-SOD small interfering RNA. Furthermore, overexpression of Mn-SOD abrogated oxLDL-induced caspase-3 activities.


CONCLUSIONS
OxLDL-induced JNK activation regulates mitochondrial redox status and Mn-SOD protein degradation via JNK-dependent ubiquitination, leading to endothelial cell apoptosis.
Takabe
Wakako
W
Department of Biomedical Engineering and Division of Cardiovascular Medicine, School of Medicine and School of Engineering, University of Southern California, 1042 Downey Way, Los Angeles, CA 90089, USA.
Li
Rongsong
R
Ai
Lisong
L
Yu
Fei
F
Berliner
Judith A
JA
Hsiai
Tzung K
TK
D001011:Aorta / Q000166:cytology / Q000378:metabolism; D017209:Apoptosis / Q000502:physiology*; D053148:Caspase 3 / Q000378:metabolism; D002478:Cells, Cultured; D004730:Endothelium, Vascular / Q000166:cytology / Q000378:metabolism*; D006801:Humans; D048031:JNK Mitogen-Activated Protein Kinases / Q000378:metabolism*; D008077:Lipoproteins, LDL / Q000378:metabolism*; D053078:Membrane Potential, Mitochondrial / Q000502:physiology; D008928:Mitochondria / Q000378:metabolism*; D010084:Oxidation-Reduction; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology; D013482:Superoxide Dismutase / Q000378:metabolism*; D054875:Ubiquitination / Q000502:physiology*
D008077:Lipoproteins, LDL; C099252:oxidized low density lipoprotein; D013482:Superoxide Dismutase; D048031:JNK Mitogen-Activated Protein Kinases; D053148:Caspase 3; D046988:Proteasome Endopeptidase Complex