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The Journal of Neuroscience, October 8, 2008, 28(41):10245-10256; doi:10.1523/JNEUROSCI.2139-08.2008

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Development/Plasticity/Repair
The Ubiquitin–Proteasome System Is Necessary for Long-Term Synaptic Depression in Aplysia

Diasinou Fioravante, Rong-Yu Liu, and John H. Byrne

Department of Neurobiology and Anatomy, W. M. Keck Center for the Neurobiology of Learning and Memory, The University of Texas Medical School at Houston, Houston, Texas 77030

Correspondence should be addressed to Dr. John H. Byrne, Department of Neurobiology and Anatomy, W. M. Keck Center for the Neurobiology of Learning and Memory, The University of Texas Medical School at Houston, P.O. Box 20708, Houston, TX 77225. Email: john.h.byrne{at}uth.tmc.edu

The neuropeptide Phe-Met-Arg-Phe-NH₂ (FMRFa) can induce transcription-dependent long-term synaptic depression (LTD) in Aplysia sensorimotor synapses. We investigated the role of the ubiquitin–proteasome system and the regulation of one of its components, ubiquitin C-terminal hydrolase (ap-uch), in LTD. LTD was sensitive to presynaptic inhibition of the proteasome and was associated with upregulation of ap-uch mRNA and protein. This upregulation appeared to be mediated by CREB2, which is generally regarded as a transcription repressor. Binding of CREB2 to the promoter region of ap-uch was accompanied by histone hyperacetylation, suggesting that CREB2 cannot only inhibit but also promote gene expression. CREB2 was phosphorylated after FMRFa, and blocking phospho-CREB2 blocked LTD. In addition to changes in the expression of ap-uch, the synaptic vesicle-associated protein synapsin was downregulated in LTD in a proteasome-dependent manner. These results suggest that proteasome-mediated protein degradation is engaged in LTD and that CREB2 may act as a transcription activator under certain conditions.

Key words: p38 kinase; lactacystin; ubiquitin C-terminal hydrolase; CREB2; histone acetylation; synapsin

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Received May 9, 2008; revised July 20, 2008; accepted Aug. 5, 2008.

Correspondence should be addressed to Dr. John H. Byrne, Department of Neurobiology and Anatomy, W. M. Keck Center for the Neurobiology of Learning and Memory, The University of Texas Medical School at Houston, P.O. Box 20708, Houston, TX 77225. Email: john.h.byrne{at}uth.tmc.edu

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