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Studies of insulin secretory responses and of arachidonic acid incorporation into phospholipids of stably transfected insulinoma cells that overexpress group VIA phospholipase A2 (iPLA2beta ) indicate a signaling rather than a housekeeping role for iPLA2beta.

Abstract
A cytosolic 84-kDa group VIA phospholipase A(2) (iPLA(2)beta) that does not require Ca(2+) for catalysis has been cloned from several sources, including rat and human pancreatic islet beta-cells and murine P388D1 cells. Many potential iPLA(2)beta functions have been proposed, including a signaling role in beta-cell insulin secretion and a role in generating lysophosphatidylcholine acceptors for arachidonic acid incorporation into P388D1 cell phosphatidylcholine (PC). Proposals for iPLA(2)beta function rest in part on effects of inhibiting iPLA(2)beta activity with a bromoenol lactone (BEL) suicide substrate, but BEL also inhibits phosphatidate phosphohydrolase-1 and a group VIB phospholipase A(2). Manipulation of iPLA(2)beta expression by molecular biologic means is an alternative approach to study iPLA(2)beta functions, and we have used a retroviral construct containing iPLA(2)beta cDNA to prepare two INS-1 insulinoma cell clonal lines that stably overexpress iPLA(2)beta. Compared with parental INS-1 cells or cells transfected with empty vector, both iPLA(2)beta-overexpressing lines exhibit amplified insulin secretory responses to glucose and cAMP-elevating agents, and BEL substantially attenuates stimulated secretion. Electrospray ionization mass spectrometric analyses of arachidonic acid incorporation into INS-1 cell PC indicate that neither overexpression nor inhibition of iPLA(2)beta affects the rate or extent of this process in INS-1 cells. Immunocytofluorescence studies with antibodies directed against iPLA(2)beta indicate that cAMP-elevating agents increase perinuclear fluorescence in INS-1 cells, suggesting that iPLA(2)beta associates with nuclei. These studies are more consistent with a signaling than with a housekeeping role for iPLA(2)beta in insulin-secreting beta-cells.
AuthorsZ Ma, S Ramanadham, M Wohltmann, A Bohrer, F F Hsu, J Turk
JournalThe Journal of biological chemistry (J Biol Chem) Vol. 276 Issue 16 Pg. 13198-208 (Apr 20 2001) ISSN: 0021-9258 [Print] United States
PMID11278673 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't, Research Support, U.S. Gov't, P.H.S.)
Chemical References
  • Enzyme Inhibitors
  • Insulin
  • Naphthalenes
  • Phosphatidylcholines
  • Phospholipids
  • Pyrones
  • Recombinant Proteins
  • Colforsin
  • Arachidonic Acid
  • 6-(bromomethylene)tetrahydro-3-(1-naphthaleneyl)-2H-pyran-2-one
  • Phospholipases A
  • Group VI Phospholipases A2
  • PLA2G6 protein, human
  • Phospholipases A2
  • Pla2g6 protein, mouse
  • Adenylyl Cyclases
  • Glucose
  • 1-Methyl-3-isobutylxanthine
Topics
  • 1-Methyl-3-isobutylxanthine (pharmacology)
  • Adenylyl Cyclases (metabolism)
  • Animals
  • Arachidonic Acid (metabolism)
  • Colforsin (pharmacology)
  • Enzyme Inhibitors (pharmacology)
  • Glucose (pharmacology)
  • Group VI Phospholipases A2
  • Humans
  • Insulin (metabolism)
  • Insulin Secretion
  • Insulinoma
  • Kinetics
  • Mice
  • Naphthalenes (pharmacology)
  • Pancreatic Neoplasms
  • Phosphatidylcholines (chemistry, metabolism)
  • Phospholipases A (genetics, metabolism)
  • Phospholipases A2
  • Phospholipids (biosynthesis)
  • Pyrones (pharmacology)
  • Rats
  • Recombinant Proteins (metabolism)
  • Signal Transduction (physiology)
  • Spectrometry, Mass, Electrospray Ionization
  • Substrate Specificity
  • Transfection
  • Tumor Cells, Cultured

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