Protein phosphatase 2A-negative regulation of the protective signaling pathway of Ca2+/CaM-dependent ERK activation in cerebral ischemia.
Extracellular-signal-regulated kinase (ERK) undergoes rapid inactivation following the intense activation evoked by cerebral ischemia and reperfusion. However, the precise mechanism of this inactivation has not been elucidated. To investigate how phosphatases regulate the ERK cascade following ischemia, the PP2A inhibitors cantharidin and okadaic acid were administrated to the CA1 subregion of the rat hippocampus. The resulting sustained ERK activity implies that PP2A is a major phosphatase contributing to the rapid inactivation, but not activation, of ERK following cerebral ischemia. The increase in PP2A activity induced by ceramide has a weak effect on the activation of Raf via dephosphorylation of Ser259 in response to ischemia. In contrast, ketamine (Keta) and cyclosporine A (CsA), two chemicals that block calcium signal in ischemia, decrease ERK activity by blocking Raf dephosphorylation of Ser259. We also observed that activation of an upstream protein, Ras-GRF, leads to calcium/calmodulin-dependent activation of the ERK signaling cascade in response to ischemic stimuli. In addition, the activity of cyclic AMP response element-binding protein (CREB) and estrogen receptor alpha (ER alpha), target proteins of ERK and protective elements against ischemic lesion, parallels the activity of ERK. These data indicate that PP2A plays a significant role in blocking the protective effect induced by the ERK kinase pathway and that fast inactivation of ERK is the result of cross talk between calcium/calmodulin-dependent, positively regulated signal cascades and a ceramide-dependent negative signaling pathway.
Zhao
Jie
J
Key Laboratory of Reproductive Medicine, Nanjing Medical University, Nanjing, People's Republic of China.
Wu
Hui-wen
HW
Chen
Yun-jiao
YJ
Tian
He-ping
HP
Li
Li-xin
LX
Han
Xiao
X
Guo
Jun
J
D000818:Animals; D002545:Brain Ischemia / Q000188:drug therapy / Q000201:enzymology*; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000037:antagonists & inhibitors* / Q000378:metabolism / Q000502:physiology; D002518:Ceramides / Q000494:pharmacology; D015536:Down-Regulation / Q000187:drug effects / Q000502:physiology*; D004789:Enzyme Activation / Q000187:drug effects / Q000502:physiology; D004791:Enzyme Inhibitors / Q000008:administration & dosage / Q000494:pharmacology / Q000627:therapeutic use; D048049:Extracellular Signal-Regulated MAP Kinases / Q000037:antagonists & inhibitors* / Q000378:metabolism / Q000502:physiology; D020935:MAP Kinase Signaling System / Q000187:drug effects / Q000502:physiology*; D008297:Male; D054648:Protein Phosphatase 2 / Q000037:antagonists & inhibitors / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology
D002518:Ceramides; D004791:Enzyme Inhibitors; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D048049:Extracellular Signal-Regulated MAP Kinases; D054648:Protein Phosphatase 2