title: Regulation of apoptosis signal-regulating kinase 1 (ASK1) by polyamine levels via protein phosphatase 5.
abstract: Recent evidence has implicated the protein phosphatase PP5 in a variety of signaling pathways. Whereas several proteins have been identified that interact with PP5 and regulate its activity, a possibility of its regulation by second messengers remains speculative. Activation of PP5 in vitro by polyunsaturated fatty acids (e.g. arachidonic acid) and fatty acyl-CoA esters (e.g. arachidonoyl-CoA) has been reported. We report here that PP5 is strongly inhibited by micromolar concentrations of a natural polyamine spermine. This inhibition was observed both in assays with a low molecular weight substrate p-nitrophenyl phosphate as well as phosphocasein and apoptosis signal-regulating kinase 1 (ASK1), thought to be a physiological substrate of PP5. Furthermore, a decrease in polyamine levels in COS-7 cells induced by alpha-difluoromethylornithine (DFMO), an inhibitor of ornithine decarboxylase, led to accelerated dephosphorylation of oxidative stress-activated ASK1. This effect was suppressed by okadaic acid and by siRNA-mediated PP5 depletion, indicating that the effect of polyamine levels on ASK1 dephosphorylation was mediated by PP5. In line with the decreased ASK1 activation, polyamine depletion in COS-7 cells abrogated oxidative stress-induced activation of caspase-3, which executes ASK1-induced apoptosis, as well as caspase-3 activation induced by ASK1 overexpression, but had no effect on basal caspase-3 activity. These results implicate polyamines, emerging intracellular signaling molecules, as potential physiological regulators of PP5. Our findings also suggest a novel mechanism of the anti-apoptotic action of a decrease in polyamine levels via de-inhibition of PP5 and accelerated dephosphorylation and deactivation of ASK1.
authors.affiliation: Department of Pharmacology, College of Medicine, University of Illinois at Chicago, Chicago, Illinois 60612, USA.
authors.forename: Mikhail A
authors.initials: MA
authors.lastname: Kutuzov
authors.forename: Alexandra V
authors.initials: AV
authors.lastname: Andreeva
authors.forename: Tatyana A
authors.initials: TA
authors.lastname: Voyno-Yasenetskaya
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000502:physiology*; D019556:COS Cells; D002522:Chlorocebus aethiops; D004789:Enzyme Activation / Q000502:physiology; D048848:MAP Kinase Kinase Kinase 5 / Q000378:metabolism*; D009687:Nuclear Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D018384:Oxidative Stress / Q000502:physiology; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation; D034741:RNA, Small Interfering; D015398:Signal Transduction / Q000502:physiology; D013096:Spermine / Q000378:metabolism*; D013379:Substrate Specificity
chemical_list: D009687:Nuclear Proteins; D034741:RNA, Small Interfering; D013096:Spermine; D048848:MAP Kinase Kinase Kinase 5; D010749:Phosphoprotein Phosphatases; C089641:protein phosphatase 5