title: Cyclic AMP and Polyamines Overcome Inhibition by Myelin-Associated Glycoprotein through eIF5A-Mediated Increases in p35 Expression and Activation of Cdk5.
abstract: Inhibitory molecules associated with CNS myelin, such as myelin-associated glycoprotein (MAG), represent major obstacles to axonal regeneration following CNS injury. Our laboratory has shown that elevating levels of intracellular cAMP, via application of the nonhydrolyzable analog dibutyryl cAMP (dbcAMP), can block the inhibitory effects of MAG and myelin. We have also shown that elevation of cAMP results in upregulation of arginase I and increased polyamine synthesis. Treatment with putrescine or spermidine blocks myelin-mediated inhibition of neurite outgrowth, but the mechanism underlying this effect has not yet been elucidated. Here we show that cyclin-dependent kinase 5 (Cdk5) is required for dbcAMP and putrescine to overcome MAG-mediated inhibition. The ability of dbcAMP and putrescine to overcome inhibition by MAG is abolished in the presence of roscovitine, a Cdk inhibitor that has greater selectivity for Cdk5, and expression of dominant negative Cdk5 abolishes the ability of dbcAMP or putrescine to enhance neurite outgrowth in the presence of MAG. Importantly, dbcAMP and putrescine increase expression of p35, the neuron-specific activator of Cdk5, and rat DRG neurons transduced with HSV overexpressing p35 can overcome inhibition by MAG. The upregulation of p35 by putrescine is also reflected in increased localization of p35 to neurites and growth cones. Last, we show that putrescine upregulates p35 expression by serving as a substrate for hypusine modification of eIF5A, and that this hypusination is necessary for putrescine's ability to overcome inhibition by MAG. Our findings reveal a previously unknown mechanism by which polyamines may encourage regeneration after CNS injury.
authors.affiliation: Department of Biological Sciences, Hunter College, City University of New York, New York, New York 10065.
authors.forename: Huifang
authors.initials: H
authors.lastname: He
authors.affiliation: Department of Biological Sciences, Hunter College, City University of New York, New York, New York 10065.
authors.forename: Kangwen
authors.initials: K
authors.lastname: Deng
authors.affiliation: Department of Biological Sciences, Hunter College, City University of New York, New York, New York 10065.
authors.forename: Mustafa M
authors.initials: MM
authors.lastname: Siddiq
authors.affiliation: Department of Biological Sciences, Hunter College, City University of New York, New York, New York 10065.
authors.forename: Aung
authors.initials: A
authors.lastname: Pyie
authors.affiliation: Department of Biological Sciences, Hunter College, City University of New York, New York, New York 10065.
authors.forename: Wilfredo
authors.identifier: http://orcid.org/0000-0003-4665-5961
authors.initials: W
authors.lastname: Mellado
authors.affiliation: Department of Biological Sciences, Hunter College, City University of New York, New York, New York 10065 sari.hannila@umanitoba.ca.
authors.forename: Sari S
authors.identifier: http://orcid.org/0000-0002-5750-7852
authors.initials: SS
authors.lastname: Hannila
authors.affiliation: Department of Biological Sciences, Hunter College, City University of New York, New York, New York 10065.
authors.forename: Marie T
authors.initials: MT
authors.lastname: Filbin
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D001921:Brain / Q000166:cytology; D003994:Bucladesine / Q000494:pharmacology; D016466:CHO Cells; D002478:Cells, Cultured; D003412:Cricetulus; D000242:Cyclic AMP / Q000378:metabolism*; D051360:Cyclin-Dependent Kinase 5 / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000378:metabolism*; D020536:Enzyme Activators / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005786:Gene Expression Regulation / Q000187:drug effects / Q000235:genetics; D018992:Myelin-Associated Glycoprotein / Q000378:metabolism*; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000378:metabolism*; D016501:Neurites / Q000187:drug effects / Q000378:metabolism; D009474:Neurons / Q000187:drug effects; D011073:Polyamines / Q000378:metabolism* / Q000494:pharmacology; D051381:Rats; D020318:Rats, Long-Evans; D014157:Transcription Factors / Q000378:metabolism*; D015854:Up-Regulation / Q000187:drug effects* / Q000235:genetics
chemical_list: D004268:DNA-Binding Proteins; C500759:Elf5 protein, mouse; D020536:Enzyme Activators; D004791:Enzyme Inhibitors; D018992:Myelin-Associated Glycoprotein; D009419:Nerve Tissue Proteins; D011073:Polyamines; D014157:Transcription Factors; C089495:neuronal Cdk5 activator (p25-p35); D003994:Bucladesine; D000242:Cyclic AMP; D051360:Cyclin-Dependent Kinase 5
keywords: Cdk5; MAG; eIF5A; neurite; p35; putrescine