title: Distribution, levels, and activation of MEK1 in Alzheimer's disease.
abstract: Extracellular-signal-regulated kinase (ERK) has been implicated in the pathogenesis of Alzheimer's disease (AD), but the upstream cascade leading to ERK activation has not been elucidated. In this study, we focused on one of the physiological activators of ERK, mitogen-activated protein kinase (MAPK)/ERK kinase 1 (MEK1). Although there was no significant difference in the level and distribution of total MEK1 between AD and age-matched control cases, increased levels of activated phospho-MEK1 were specifically localized to neuronal intracytoplasmic granular structures in severe AD (Braak stage V-VI). The considerable overlap between MEK1 and its downstream effector, phospho-ERK, suggests both a functional and mechanistic link. Nuclear localization of phospho-MEK1 was a prominent feature in both mild AD cases (Braak stage III-IV) and control cases with limited pathology (Braak stage I-II). Since MEK1 is normally cytoplasmic due to the active export from nucleus because of the presence of nuclear export signal in its amino-terminus, we suspect that the apparent nuclear accumulation of phospho-MEK1 in AD patients at early stages suggests that abnormal nuclear trafficking may contribute to the pathogenesis of AD. By immunoblot analyses, phospho-MEK1 was significantly increased in AD over control cases. Together, these findings lend further credence to the notion that the ERK pathway is dysregulated in AD and also indicate an active role for this pathway in disease pathogenesis.
authors.affiliation: Institute of Pathology, Case Western Reserve University, Cleveland, Ohio 44106, USA.
authors.forename: Xiongwei
authors.initials: X
authors.lastname: Zhu
authors.forename: Zheng
authors.initials: Z
authors.lastname: Sun
authors.forename: Hyoung-gon
authors.initials: HG
authors.lastname: Lee
authors.forename: Sandra L
authors.initials: SL
authors.lastname: Siedlak
authors.forename: George
authors.initials: G
authors.lastname: Perry
authors.forename: Mark A
authors.initials: MA
authors.lastname: Smith
mesh_terms: D021581:Active Transport, Cell Nucleus; D000368:Aged; D000369:Aged, 80 and over; D000544:Alzheimer Disease / Q000201:enzymology* / Q000473:pathology*; D002467:Cell Nucleus / Q000201:enzymology; D003594:Cytoplasmic Granules / Q000201:enzymology; D004789:Enzyme Activation / Q000502:physiology; D006801:Humans; D015151:Immunoblotting; D007150:Immunohistochemistry; D048369:MAP Kinase Kinase 1; D008875:Middle Aged; D020929:Mitogen-Activated Protein Kinase Kinases / Q000378:metabolism*; D009474:Neurons / Q000201:enzymology / Q000473:pathology; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*
chemical_list: D017346:Protein Serine-Threonine Kinases; D048369:MAP Kinase Kinase 1; C482125:MAP2K1 protein, human; D020929:Mitogen-Activated Protein Kinase Kinases