PMID- 29875265 OWN - NLM STAT- MEDLINE DCOM- 20191025 LR - 20200306 IS - 1529-2401 (Electronic) IS - 0270-6474 (Print) IS - 0270-6474 (Linking) VI - 38 IP - 27 DP - 2018 Jul 4 TI - Activating Transcription Factor 4 (ATF4) Regulates Neuronal Activity by Controlling GABA(B)R Trafficking. PG - 6102-6113 LID - 10.1523/JNEUROSCI.3350-17.2018 [doi] AB - Activating Transcription Factor 4 (ATF4) has been postulated as a key regulator of learning and memory. We previously reported that specific hippocampal ATF4 downregulation causes deficits in synaptic plasticity and memory and reduction of glutamatergic functionality. Here we extend our studies to address ATF4's role in neuronal excitability. We find that long-term ATF4 knockdown in cultured rat hippocampal neurons significantly increases the frequency of spontaneous action potentials. This effect is associated with decreased functionality of metabotropic GABA(B) receptors (GABA(B)Rs). Knocking down ATF4 results in significant reduction of GABA(B)R-induced GIRK currents and increased mIPSC frequency. Furthermore, reducing ATF4 significantly decreases expression of membrane-exposed, but not total, GABA(B)R 1a and 1b subunits, indicating that ATF4 regulates GABA(B)R trafficking. In contrast, ATF4 knockdown has no effect on surface expression of GABA(B)R2s, several GABA(B)R-coupled ion channels or beta2 and gamma2 GABA(A)Rs. Pharmacologic manipulations confirmed the relationship between GABA(B)R functionality and action potential frequency in our cultures. Specifically, the effects of ATF4 downregulation cited above are fully rescued by transcriptionally active, but not by transcriptionally inactive, shRNA-resistant, ATF4. We previously reported that ATF4 promotes stabilization of the actin-regulatory protein Cdc42 by a transcription-dependent mechanism. To test the hypothesis that this action underlies the mechanism by which ATF4 loss affects neuronal firing rates and GABA(B)R trafficking, we downregulated Cdc42 and found that this phenocopies the effects of ATF4 knockdown on these properties. In conclusion, our data favor a model in which ATF4, by regulating Cdc42 expression, affects trafficking of GABA(B)Rs, which in turn modulates the excitability properties of neurons.SIGNIFICANCE STATEMENT GABA(B) receptors (GABA(B)Rs), the metabotropic receptors for the inhibitory neurotransmitter GABA, have crucial roles in controlling the firing rate of neurons. Deficits in trafficking/functionality of GABA(B)Rs have been linked to a variety of neurological and psychiatric conditions, including epilepsy, anxiety, depression, schizophrenia, addiction, and pain. Here we show that GABA(B)Rs trafficking is influenced by Activating Transcription Factor 4 (ATF4), a protein that has a pivotal role in hippocampal memory processes. We found that ATF4 downregulation in hippocampal neurons reduces membrane-bound GABA(B)R levels and thereby increases intrinsic excitability. These effects are mediated by loss of the small GTPase Cdc42 following ATF4 downregulation. These findings reveal a critical role for ATF4 in regulating the modulation of neuronal excitability by GABA(B)Rs. CI - Copyright (c) 2018 the authors 0270-6474/18/386102-12$15.00/0. FAU - Corona, Carlo AU - Corona C AUID- ORCID: 0000-0002-7462-3046 AD - Department of Pathology & Cell Biology and the Taub Institute for Research on Alzheimer's Disease and the Aging Brain, Columbia University Medical Center, New York, New York 10033. FAU - Pasini, Silvia AU - Pasini S AUID- ORCID: 0000-0002-2945-5573 AD - Department of Pathology & Cell Biology and the Taub Institute for Research on Alzheimer's Disease and the Aging Brain, Columbia University Medical Center, New York, New York 10033. FAU - Liu, Jin AU - Liu J AD - Department of Pathology & Cell Biology and the Taub Institute for Research on Alzheimer's Disease and the Aging Brain, Columbia University Medical Center, New York, New York 10033. FAU - Amar, Fatou AU - Amar F AUID- ORCID: 0000-0001-7735-1528 AD - Department of Pathology & Cell Biology and the Taub Institute for Research on Alzheimer's Disease and the Aging Brain, Columbia University Medical Center, New York, New York 10033. FAU - Greene, Lloyd A AU - Greene LA AUID- ORCID: 0000-0002-3225-5521 AD - Department of Pathology & Cell Biology and the Taub Institute for Research on Alzheimer's Disease and the Aging Brain, Columbia University Medical Center, New York, New York 10033. FAU - Shelanski, Michael L AU - Shelanski ML AUID- ORCID: 0000-0002-9806-1500 AD - Department of Pathology & Cell Biology and the Taub Institute for Research on Alzheimer's Disease and the Aging Brain, Columbia University Medical Center, New York, New York 10033 mls7@columbia.edu. LA - eng GR - R01 NS033689/NS/NINDS NIH HHS/United States GR - R01 NS072050/NS/NINDS NIH HHS/United States PT - Journal Article PT - Research Support, N.I.H., Extramural PT - Research Support, Non-U.S. Gov't DEP - 20180606 PL - United States TA - J Neurosci JT - The Journal of neuroscience : the official journal of the Society for Neuroscience JID - 8102140 RN - 0 (Atf4 protein, rat) RN - 0 (Receptors, GABA-B) RN - 145891-90-3 (Activating Transcription Factor 4) RN - EC 3.6.5.2 (cdc42 GTP-Binding Protein) SB - IM MH - Activating Transcription Factor 4/*metabolism MH - Animals MH - Female MH - Hippocampus/metabolism MH - Male MH - Neurons/metabolism MH - Protein Transport/physiology MH - Rats MH - Receptors, GABA-B/*metabolism MH - cdc42 GTP-Binding Protein/metabolism PMC - PMC6596153 OTO - NOTNLM OT - ATF4 OT - Cdc42 OT - GABAB receptors OT - GIRK channels OT - neuronal excitability EDAT- 2018/06/08 06:00 MHDA- 2019/10/28 06:00 PMCR- 2019/01/04 CRDT- 2018/06/08 06:00 PHST- 2017/11/27 00:00 [received] PHST- 2018/05/29 00:00 [revised] PHST- 2018/05/31 00:00 [accepted] PHST- 2018/06/08 06:00 [pubmed] PHST- 2019/10/28 06:00 [medline] PHST- 2018/06/08 06:00 [entrez] PHST- 2019/01/04 00:00 [pmc-release] AID - JNEUROSCI.3350-17.2018 [pii] AID - 3350-17 [pii] AID - 10.1523/JNEUROSCI.3350-17.2018 [doi] PST - ppublish SO - J Neurosci. 2018 Jul 4;38(27):6102-6113. doi: 10.1523/JNEUROSCI.3350-17.2018. Epub 2018 Jun 6.