title: Exendin-4 regulates pancreatic ABCA1 transcription via CaMKK/CaMKIV pathway.
abstract: ATP-binding cassette transporter A1 (ABCA1) in pancreatic beta cells influences insulin secretion and glucose homeostasis. This study investigates whether the long-acting agonist of the glucagon-like peptide 1, namely exendin-4, which mediates stimulatory effects on ABCA1 gene expression, could interfere with the Ca(2+)/calmodulin (CaM)-dependent protein kinase (CaMK) cascade. ABCA1 promoter activity was examined by reporter gene assay in rat insulin-secreting INS-1 cells incubated with exendin-4. CaMKIV activity was assessed by detection of activation-loop phosphorylation (Thr(196)) of CaMKIV. We investigated the influence of the constitutively active form (CaMKIVc) or CaMKIV knockdown on ABCA1 expression. Increased abundance of ABCA1 protein was noted in response to rising concentrations of exendin-4 with maximum induction at 10 nM. Exendin-4 also stimulated ABCA1 promoter activity, but failed to do so in the presence of STO-609, a CaMKK inhibitor. Up-regulation of CaMKIV phosphorylation (at Thr(196)) peaked after 10 min. of exposure to exendin-4. CaMKIVc enhanced or up-regulated ABCA1 promoter activity in INS-1 cells. Furthermore, exendin-4 induction of ABCA1 protein expression was significantly suppressed in cells treated with CaMKIV-siRNA. Activation of the CaMKK/CaMKIV cascade by exendin-4 stimulated ABCA1 gene transcription, indicating that exendin-4 plays an important role in insulin secretion and cholesterol ester content in pancreatic beta cells.
authors.affiliation: Division of Endocrinology and Metabolism, Department of Internal Medicine, Faculty of Medicine, Kagawa University, Ikenobe Miki-CHO, Kita-gun, Kagawa, Japan.
authors.forename: Junhua
authors.initials: J
authors.lastname: Li
authors.forename: Koji
authors.initials: K
authors.lastname: Murao
authors.forename: Hitomi
authors.initials: H
authors.lastname: Imachi
authors.forename: Hisashi
authors.initials: H
authors.lastname: Masugata
authors.forename: Hisakazu
authors.initials: H
authors.lastname: Iwama
authors.forename: Satoshi
authors.initials: S
authors.lastname: Tada
authors.forename: Guo-Xing
authors.initials: GX
authors.lastname: Zhang
authors.forename: Ryoji
authors.initials: R
authors.lastname: Kobayashi
authors.forename: Toshihiko
authors.initials: T
authors.lastname: Ishida
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Tokumitsu
mesh_terms: D064286:ATP Binding Cassette Transporter 1; D018528:ATP-Binding Cassette Transporters / Q000235:genetics* / Q000378:metabolism; D000818:Animals; D054734:Calcium-Calmodulin-Dependent Protein Kinase Type 4 / Q000378:metabolism*; D000077270:Exenatide; D005786:Gene Expression Regulation / Q000187:drug effects; D010179:Pancreas / Q000187:drug effects* / Q000201:enzymology*; D010455:Peptides / Q000494:pharmacology*; D010766:Phosphorylation / Q000187:drug effects; D051381:Rats; D015398:Signal Transduction / Q000187:drug effects*; D014158:Transcription, Genetic / Q000187:drug effects*; D014688:Venoms / Q000494:pharmacology*
chemical_list: D064286:ATP Binding Cassette Transporter 1; D018528:ATP-Binding Cassette Transporters; D010455:Peptides; D014688:Venoms; D000077270:Exenatide; D054734:Calcium-Calmodulin-Dependent Protein Kinase Type 4; C517686:Camk4 protein, rat