title: Par-4 is a synaptic protein that regulates neurite outgrowth by altering calcium homeostasis and transcription factor AP-1 activation.
abstract: Although Par-4 (prostate apoptosis response-4) is involved in initiation of neurodegenerative cascades associated with certain neurodegenerative disorders, normal physiological roles of Par-4 in neurons have remained elusive. It was recently reported that Par-4 protein levels could be regulated at translational level in synaptic terminals following apoptotic insults, suggesting that Par-4 might play a role in synaptic function. We report that Par-4 is a synaptic protein preferably localized in postsynaptic density (PSD). The expression of Par-4 in synaptosome preparations and PSDs are developmentally and regionally regulated. Synaptic Par-4 is enriched in the cerebral cortex and the hippocampus, but not in the cerebellum. In vitro as well as in vivo experiments demonstrate that the levels of synaptic Par-4 increase as the neurons mature. Overexpression of Par-4 in transfected PC12 cells inhibits nerve growth factor (NGF)-induced cellular differentiation and neurite outgrowth by a mechanism involving aberrant elevation of intracellular calcium levels and suppression of activation of the transcription factor AP-1. The actions of Par-4 were consistently blocked by co-expression of the dominant negative regulator of Par-4 activity (the leucine zipper domain of Par-4). Since the leucine zipper domain of Par-4 (Leu.zip) may mediate protein--protein interactions, the results indicate that the actions of Par-4 require its interaction with other protein(s) or dimerization with itself. These results suggest that Par-4 may play an important role in postsynaptic signal transduction and regulation of cellular pathways associated with cellular differentiation and neurite outgrowth. Identification of Par-4 as a novel synaptic protein may have significant implications in understanding the mechanisms of synaptic functions in physiological and pathological settings.
authors.affiliation: Department of Neurobiology and Pharmacology, Northeastern Ohio Universities College of Medicine, 4209 State Route 44, PO Box 95, Rootstown, OH 44272-0095, USA. qguo@neuocom.edu
authors.forename: Q
authors.initials: Q
authors.lastname: Guo
authors.forename: J
authors.initials: J
authors.lastname: Xie
authors.forename: X
authors.initials: X
authors.lastname: Chang
authors.forename: X
authors.initials: X
authors.lastname: Zhang
authors.forename: H
authors.initials: H
authors.lastname: Du
mesh_terms: D000818:Animals; D000906:Antibodies; D051017:Apoptosis Regulatory Proteins; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling / Q000502:physiology*; D002352:Carrier Proteins / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D002451:Cell Compartmentation / Q000502:physiology; D002540:Cerebral Cortex / Q000166:cytology; D015870:Gene Expression / Q000502:physiology; D006624:Hippocampus / Q000166:cytology; D006706:Homeostasis / Q000502:physiology; D047908:Intracellular Signaling Peptides and Proteins; D051379:Mice; D008810:Mice, Inbred C57BL; D020932:Nerve Growth Factor / Q000494:pharmacology; D016501:Neurites / Q000378:metabolism*; D009474:Neurons / Q000378:metabolism / Q000648:ultrastructure; D016716:PC12 Cells; D051381:Rats; D013574:Synaptosomes / Q000378:metabolism; D018808:Transcription Factor AP-1 / Q000378:metabolism*; D015533:Transcriptional Activation / Q000187:drug effects / Q000502:physiology; D014162:Transfection
chemical_list: D000906:Antibodies; D051017:Apoptosis Regulatory Proteins; D002352:Carrier Proteins; D047908:Intracellular Signaling Peptides and Proteins; D018808:Transcription Factor AP-1; C101296:prostate apoptosis response-4 protein; D020932:Nerve Growth Factor; D002118:Calcium