title: Calcium/calmodulin-dependent serine protein kinase is involved in exendin-4-induced insulin secretion in INS-1 cells.
abstract: OBJECTIVE
  Exendin-4 (Ex-4) is an anti-diabetic drug that is a potent agonist of the glucagon-like peptide-1 (GLP-1) receptor. It has already been approved for the treatment of type 2 diabetes mellitus, but its underlying mechanisms of action are not fully understood. Calcium/calmodulin-dependent serine protein kinase (CASK), which plays a vital role in the transport and release of neurotransmitters in neurons, is expressed in pancreatic islet cells and β-cells. This study aimed to investigate whether CASK is involved in the insulin secretagogue action induced by Ex-4 in INS-1 cells.
  
  
  METHODS
  A glucose-stimulated insulin secretion (GSIS) assay was performed with or without siRNA treatment against CASK. The expression level and location of CASK were evaluated by real-time PCR, western blotting and immunofluorescence. With the use of a protein kinase A (PKA) inhibitor or an exchange protein directly activated by cAMP-2 (Epac2) agonist, immunoblotting was performed to establish the signaling pathway through which Ex-4 alters CASK expression.
  
  
  RESULTS
  Knock-down of CASK significantly attenuated the Ex-4-enhanced insulin release, and we showed that Ex-4 could increase transcription of CASK mRNA and expression of CASK protein but did not change the cellular location of CASK. A PKA inhibitor reduced the ability of Ex-4 to stimulate CASK expression, but an Epac2 agonist had no effect suggesting that regulation was mediated by the cAMP/PKA pathway.
  
  
  CONCLUSIONS
  Our study suggests that the stimulation of β-cell insulin secretion by Ex-4 is mediated, at least in part, by CASK via a novel signaling mechanism.
authors.affiliation: Department of Endocrinology, Zhongda Hospital, Institute of Diabetes, Southeast University, Nanjing 210009, PR China.
authors.forename: Zheng-Qiu
authors.initials: ZQ
authors.lastname: Zhu
authors.forename: Dong
authors.initials: D
authors.lastname: Wang
authors.forename: Dan
authors.initials: D
authors.lastname: Xiang
authors.forename: Yue-Xing
authors.initials: YX
authors.lastname: Yuan
authors.forename: Yao
authors.initials: Y
authors.lastname: Wang
mesh_terms: D000818:Animals; D015153:Blotting, Western; D045744:Cell Line, Tumor; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism*; D003924:Diabetes Mellitus, Type 2 / Q000188:drug therapy; D000077270:Exenatide; D055785:Gene Knockdown Techniques; D052216:Glucagon-Like Peptide 1 / Q000819:agonists; D051528:Guanylate Kinases / Q000235:genetics / Q000378:metabolism*; D007004:Hypoglycemic Agents / Q000494:pharmacology*; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D007340:Insulinoma / Q000201:enzymology / Q000378:metabolism*; D008856:Microscopy, Fluorescence; D010190:Pancreatic Neoplasms / Q000201:enzymology / Q000378:metabolism*; D010455:Peptides / Q000494:pharmacology*; D034741:RNA, Small Interfering / Q000378:metabolism; D051381:Rats; D060888:Real-Time Polymerase Chain Reaction; D015398:Signal Transduction; D014688:Venoms / Q000494:pharmacology*
chemical_list: D007004:Hypoglycemic Agents; D007328:Insulin; D010455:Peptides; D034741:RNA, Small Interfering; D014688:Venoms; D052216:Glucagon-Like Peptide 1; D000077270:Exenatide; C106868:CASK kinases; D017868:Cyclic AMP-Dependent Protein Kinases; D051528:Guanylate Kinases
keywords: 8-pCPT-2′-O-Me-cAMP-AM; CASK; ESCA-AM; Epac2; Ex-4; GLP-1; GSIS; H-89; N-[2-(p-bromocinnamylamino)ethyl]-5-isoquinolinesulfonamide; PKA; cAMP; calcium/calmodulin-dependent serine protein kinase; cyclic adenosine monophosphate; exchange protein directly activated by cAMP-2; exendin-4; glucagon-like peptide-1; glucose-stimulated insulin secretion; protein kinase A.