MEK and ERK protect hypoxic cortical neurons via phosphorylation of Bad.
We investigated the role of mitogen-activated protein kinase (MAPK) pathways in hypoxic neuronal injury using primary cultures from murine cerebral cortex. Hypoxia caused the death of approximately 50% of neurons at 16 h and approximately 65% of neurons at 24 h. This was associated with phospho-activation of the MAPK/extracellular signal-regulated kinase (ERK) kinase MEK1/2 and its downstream target ERK1/2, but not p38 MAPK or c-Jun N-terminal kinase (JNK), as detected by western blotting. The MEK1/2 inhibitor, PD98059, increased neuronal death in hypoxic cultures, suggesting that MEK1/2 promotes neuronal survival, whereas the p38 inhibitors, SB202190 and SB203580, had no effect. To identify downstream effects of ERK1/2 that might regulate hypoxic neuronal death, we measured hypoxia-induced phosphorylation of three ERK1/2 targets: the 90-kDa ribosomal protein S6 kinase (RSK), the transcription factor ELK1, and the pro-apoptotic Bcl-2 family protein Bad. We observed increased abundance of inactivated (phospho-)Bad, but no change in phospho-RSK or phospho-ELK1. Moreover, the MEK inhibitor PD98059 reduced phospho-inactivation of Bad in hypoxic cultures. These findings suggest that a cell-survival program involving phospho-activation of MEK1/2 and ERK1/2 and inactivation of Bad is mobilized in hypoxic neurons, and may help to regulate neuronal fate following hypoxic-ischemic injury.
Jin
Kunlin
K
Buck Institute for Age Research, Novato, California 94945, USA. kjin@buckinstitute.org
Mao
Xiao Ou
XO
Zhu
Yonghua
Y
Greenberg
David A
DA
D000818:Animals; D001927:Brain Diseases / Q000473:pathology / Q000503:physiopathology*; D002352:Carrier Proteins / Q000378:metabolism*; D002470:Cell Survival / Q000187:drug effects / Q000502:physiology; D002478:Cells, Cultured; D002540:Cerebral Cortex / Q000473:pathology / Q000503:physiopathology; D004622:Embryo, Mammalian; D004791:Enzyme Inhibitors; D005419:Flavonoids / Q000494:pharmacology; D000860:Hypoxia / Q000473:pathology / Q000503:physiopathology*; D051379:Mice; D008815:Mice, Inbred Strains; D020928:Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors / Q000502:physiology*; D009474:Neurons / Q000473:pathology / Q000502:physiology; D018696:Neuroprotective Agents; D010766:Phosphorylation; D051025:bcl-Associated Death Protein
C494820:Bad protein, mouse; D002352:Carrier Proteins; D004791:Enzyme Inhibitors; D005419:Flavonoids; D018696:Neuroprotective Agents; D051025:bcl-Associated Death Protein; D020928:Mitogen-Activated Protein Kinases; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one