title: HspB1 silences translation of PDZ-RhoGEF by enhancing miR-20a and miR-128 expression to promote neurite extension.
abstract: HspB1 is a small heat shock protein implicated in neuronal survival and neurite growth; mutations in HspB1 have been identified in hereditary motor neuronopathies and Charcot Marie Tooth Type 2 neuropathies. In cortical neurons we found that expression of HspB1 decreased RhoA activity and RhoA-GTP protein, and reversed the inhibition of neurite extension induced by NogoA. HspB1 decreased PDZ-RhoGEF, a RhoA specific guanine nucleotide exchange factor, while other regulators of RhoA activity were unchanged. The decrease in PDZ-RhoGEF was independent of proteasomal or lysosomal degradation pathways and was not associated with changes in PDZ-RhoGEF mRNA. We sequenced the 3'UTR of rat PDZ-RhoGEF and found binding sites for miRNAs miR-20a, miR-128 and miR-132. Expression of these microRNAs was substantially increased in cortical neurons transfected with HspB1. Co-transfection of HspB1 with specific inhibitors of miR-20a or miR-128 prevented the decrease in PDZ-RhoGEF and blocked the neurite growth promoting effects of HspB1. Using the 3'UTR of PDZ-RhoGEF mRNA in a luciferase reporter construct we observed that HspB1, miR-20a and miR-128 each inhibited luciferase expression. We conclude that HspB1 regulates RhoA activity through modulation of PDZ-RhoGEF levels achieved by translational control through enhanced expression of specific miRNAs (miR-20a and miR-128). Regulation of RhoA activity by translational silencing of PDZ-RhoGEF may be the mechanism through which HspB1 is involved in regulation of neurite growth. As RhoA-GTPase plays a regulatory role in the organization and stability of cytoskeletal networks through its downstream effectors, the results suggest a possible mechanism linking HspB1 mutations and axonal cytoskeletal pathology.
authors.affiliation: Department of Neurology, University of Michigan, Ann Arbor, MI 48109, USA; GRECC VA Ann Arbor Healthcare System, Ann Arbor, MI 48109, USA.
authors.forename: Xiankui
authors.initials: X
authors.lastname: Sun
authors.forename: Zhigang
authors.initials: Z
authors.lastname: Zhou
authors.forename: David J
authors.initials: DJ
authors.lastname: Fink
authors.forename: Marina
authors.initials: M
authors.lastname: Mata
mesh_terms: D020413:3' Untranslated Regions; D000818:Animals; D048708:Cell Growth Processes; D045744:Cell Line, Tumor; D002478:Cells, Cultured; D002540:Cerebral Cortex / Q000166:cytology; D020662:Guanine Nucleotide Exchange Factors / Q000235:genetics / Q000378:metabolism; D055551:HSP27 Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D035683:MicroRNAs / Q000235:genetics / Q000378:metabolism*; D016501:Neurites / Q000378:metabolism* / Q000502:physiology; D011485:Protein Binding; D014176:Protein Biosynthesis; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D020742:rhoA GTP-Binding Protein / Q000378:metabolism
chemical_list: D020413:3' Untranslated Regions; D020662:Guanine Nucleotide Exchange Factors; D055551:HSP27 Heat-Shock Proteins; C486114:Hspb1 protein, rat; C557010:MIRN128 microRNA, rat; C573236:MIRN20 microRNA, rat; D035683:MicroRNAs; C523071:PDZ-RhoGEF, rat; D012333:RNA, Messenger; D020742:rhoA GTP-Binding Protein
keywords: Guanine nucleotide exchange factor (GEF); Heat shock protein; MicroRNA; Neurite outgrowth; RhoA