title: Regulation of AMP-activated protein kinase signaling by AFF4 protein, member of AF4 (ALL1-fused gene from chromosome 4) family of transcription factors, in hypothalamic neurons.
abstract: In the hypothalamus, fasting induces a member of the AF4 family of transcription factors, AFF4, which was originally identified as a fusion partner of the mixed-lineage leukemia gene in infant acute lymphoblastic leukemia. However, the roles of AFF4 in the hypothalamus remain unclear. We show herein that expression of AFF4 increased upon addition of ghrelin and fasting in the growth hormone secretagogue receptor-expressing neurons of the hypothalamus. In the growth hormone secretagogue receptor-expressing hypothalamic neuronal cell line GT1-7, ghrelin markedly induced expression of AFF4 in a time- and dose-dependent manner. Overexpression of AFF4 in GT1-7 cells specifically induced expression of the AMP-activated protein kinase (AMPK) α2 subunit but failed to induce other AMPK subunits and AMPK upstream kinases. The promoter activity of the AMPKα2 gene increased upon addition of AFF4, suggesting that AFF4 regulates transcription of the AMPKα2 gene. Additionally, AFF4 also increased the phosphorylation of acetyl-CoA carboxylase α (ACCα), a downstream target of AMPK. In GT1-7 cells, ghrelin phosphorylated ACCα through AMPKα phosphorylation in the early phase (15 min) of the activation. However, ghrelin-induced expression of AMPKα2 and phosphorylation of ACCα in the late phase (2 h) of the activation were independent of AMPKα phosphorylation. Attenuation of expression of AFF4 by its siRNA in GT1-7 cells decreased ghrelin-induced AMPKα2 expression and ACCα phosphorylation in the late phase of the activation. AFF4 may therefore help to maintain activation of AMPK downstream signaling under conditions of prolonged stimulation with ghrelin, such as during fasting.
authors.affiliation: Department of Anatomy and Neurobiology, Wakayama Medical University, 811-1 Kimiidera, Wakayama 641-8509, Japan.
authors.forename: Tadasuke
authors.initials: T
authors.lastname: Komori
authors.forename: Asako
authors.initials: A
authors.lastname: Doi
authors.forename: Tetsuya
authors.initials: T
authors.lastname: Nosaka
authors.forename: Hiroto
authors.initials: H
authors.lastname: Furuta
authors.forename: Takashi
authors.initials: T
authors.lastname: Akamizu
authors.forename: Toshio
authors.initials: T
authors.lastname: Kitamura
authors.forename: Emiko
authors.initials: E
authors.lastname: Senba
authors.forename: Yoshihiro
authors.initials: Y
authors.lastname: Morikawa
mesh_terms: D055372:AMP-Activated Protein Kinases / Q000378:metabolism*; D000103:Acetyl-CoA Carboxylase / Q000096:biosynthesis / Q000235:genetics; D000818:Animals; D002460:Cell Line; D005215:Fasting / Q000378:metabolism*; D005786:Gene Expression Regulation / Q000502:physiology*; D054439:Ghrelin / Q000494:pharmacology; D007031:Hypothalamus / Q000166:cytology / Q000378:metabolism*; D051379:Mice; D009419:Nerve Tissue Proteins / Q000378:metabolism*; D009474:Neurons / Q000166:cytology / Q000378:metabolism*; D010766:Phosphorylation / Q000187:drug effects / Q000502:physiology; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology*; D014157:Transcription Factors / Q000096:biosynthesis*; D014158:Transcription, Genetic / Q000187:drug effects / Q000502:physiology*; D035602:Transcriptional Elongation Factors
chemical_list: C503581:Aff4 protein, mouse; D054439:Ghrelin; D009419:Nerve Tissue Proteins; D014157:Transcription Factors; D035602:Transcriptional Elongation Factors; C534978:Prkaa2 protein, mouse; D055372:AMP-Activated Protein Kinases; D000103:Acetyl-CoA Carboxylase