title: MEK5 and ERK5 are localized in the nuclei of resting as well as stimulated cells, while MEKK2 translocates from the cytosol to the nucleus upon stimulation.
abstract: The ERK5 signaling cascade acts through sequential activation of MEKK2/3, MEK5 and ERK5 and transmits signals to a variety of stress and mitogenic related targets. In this study we examined the subcellular localization of the components of the ERK5 cascade and found that in resting, as well as in EGF-stimulated HeLa and Rat-1 cells, endogenous ERK5 is localized mainly in the nucleus. This location is different from the previously described location of exogenous ERK5, in the cytosol of resting cells, which is confirmed in this study. The reason for the different localization could be a saturation of anchoring moieties by the endogenous ERK5. Indeed, in situ detergent extraction analysis using Nonidet P-40, revealed that ERK5 is bound to detergent resistant moieties in the nucleus, while the exogenous protein fails to interact with those anchors. The upstream activator MEK5 is also localized in the nucleus both before and after EGF stimulation and is resistant to NP-40 extraction in resting cells. ERK5 remains bound to these nuclear moieties even after stimulation, while MEK5 is detached from the anchors but remains localized in the nucleus. Unlike ERK5 and MEK5, their upstream activator MEKK2 is localized mainly in the cytosol of resting cells, and translocates into the nucleus upon EGF stimulation, allowing transmission of signals to the nuclear MEK5. The nuclear localization of MEK5 and ERK5 is different from that of ERK1/2 and MEK1/2 in resting cells, indicating that each MAPK cascade uses distinct mechanisms to transmit extracellular signals to their nuclear targets.
authors.affiliation: Department of Biological Regulation, The Weizmann Institute of Science, Rehovot 76100, Israel.
authors.forename: Ziv
authors.initials: Z
authors.lastname: Raviv
authors.forename: Eyal
authors.initials: E
authors.lastname: Kalie
authors.forename: Rony
authors.initials: R
authors.lastname: Seger
mesh_terms: D000818:Animals; D002453:Cell Cycle / Q000187:drug effects*; D002460:Cell Line; D002467:Cell Nucleus / Q000187:drug effects / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism; D003902:Detergents / Q000494:pharmacology; D004815:Epidermal Growth Factor / Q000494:pharmacology; D006801:Humans; D048369:MAP Kinase Kinase 1 / Q000378:metabolism; D048370:MAP Kinase Kinase 2 / Q000378:metabolism; D048671:MAP Kinase Kinase 5 / Q000235:genetics / Q000378:metabolism*; D048730:MAP Kinase Kinase Kinase 2 / Q000378:metabolism*; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism; D048054:Mitogen-Activated Protein Kinase 7 / Q000235:genetics / Q000378:metabolism*; D017830:Octoxynol; D011092:Polyethylene Glycols / Q000494:pharmacology; D021381:Protein Transport / Q000187:drug effects; D051381:Rats; D015398:Signal Transduction / Q000187:drug effects; D014162:Transfection
chemical_list: D003902:Detergents; D011092:Polyethylene Glycols; D004815:Epidermal Growth Factor; D017830:Octoxynol; C010615:Nonidet P-40; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D048054:Mitogen-Activated Protein Kinase 7; D048730:MAP Kinase Kinase Kinase 2; D048369:MAP Kinase Kinase 1; D048370:MAP Kinase Kinase 2; D048671:MAP Kinase Kinase 5; C482565:Map2k5 protein, rat