title: Phosphorylated mitogen-activated protein kinase/extracellular signal-regulated kinase 1/2 may not always represent its kinase activity in a rat model of focal cerebral ischemia with or without ischemic preconditioning.
abstract: The extracellular signal-regulated kinase (ERK) 1/2 protein requires a dual phosphorylation at conserved threonine and tyrosine residues to be fully activated under normal physiological conditions. Thus, ERK1/2 kinase activity is often defined by the quantity of phosphorylated kinase. However, this may not accurately represent its true activity under certain pathological conditions. We investigated whether ERK1/2 kinase activity is proportional to its phosphorylation state in a rat focal ischemia model with and without rapid ischemic preconditioning. We showed that phosphorylated-ERK1/2 protein levels were increased 2.6±0.07-fold, and ERK1/2 kinase activity was increased 10.6±1.9-fold in animals receiving ischemic preconditioning alone without test ischemia compared with sham group (P<0.05, n=6/group), suggesting that phosphorylated-ERK1/2 protein levels represent its kinase activity under these conditions. However, preconditioning plus test ischemia robustly blocked ERK1/2 kinase activity, whereas it increased phosphorylated-ERK1/2 protein levels beyond those receiving test ischemia alone, suggesting that phosphorylated-ERK1/2 protein levels were not representative of actual kinase activity in this pathological condition. In conclusion, protein phosphorylation levels of ERK1/2 do not always correspond to kinase activity, thus, measuring the true kinase activity is essential.
authors.affiliation: Department of Neurosurgery and Stanford Stroke Center, Stanford University, Stanford, CA, USA.
authors.forename: T
authors.initials: T
authors.lastname: Takahashi
authors.forename: G K
authors.initials: GK
authors.lastname: Steinberg
authors.forename: H
authors.initials: H
authors.lastname: Zhao
mesh_terms: D000818:Animals; D015153:Blotting, Western; D002545:Brain Ischemia / Q000201:enzymology*; D004195:Disease Models, Animal; D004789:Enzyme Activation / Q000502:physiology; D019194:Ischemic Preconditioning; D008297:Male; D019950:Mitogen-Activated Protein Kinase 1 / Q000032:analysis / Q000378:metabolism*; D048052:Mitogen-Activated Protein Kinase 3 / Q000032:analysis / Q000378:metabolism*; D010766:Phosphorylation; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3