Characterization of an ATP-Stimulatable Ca2+-Independent Phospholipase A2 from Clonal Insulin-Secreting HIT Cells and Rat Pancreatic Islets: A Possible Molecular Component of the β-Cell Fuel Sensor

Academic Article

Abstract

  • Isolated pancreatic islets from rats and humans express a plasmalogen-preferring ATP-stimulatable, Ca2+-independent phospholipase A2 (ASCI-PLA2) enzyme which participates in the glucose-stimulated hydrolysis of arachidonate from membrane phospholipids and in insulin secretion. Here we report that clonal insulin-secreting HIT β-cells contain substantial amounts of endogenous plasmalogens and express a similar ASCI-PLA2 activity with the following properties: (1) Enzymatic activity as well as glucose-induced eicosanoid release and insulin secretion are inhibited by a mechanism-based suicide substrate directed towards ASCI-PLA2. (2) HIT cell ASCI-PLA2 is selectively activated and protected against thermal denaturation by ATP. (3) The magnitude of ASCI-PLA2 activation by the nonhydrolyzable ATP analog AMP-PCP is similar to that by ATP. (4) The ATP concentrations required to activate ASCI-PLA2 fall within physiologic ranges in the presence of Mg2+. (5) ADP induces a concentration-dependent attenuation of the activation of ASCI-PLA2 by ATP. HIT cell ASCI-PLA2 exhibited an apparent isoelectric point of 7.5 on chromatofocusing analysis and was quantitatively adsorbed to an ATP-agarose matrix and selectively desorbed from this column by ATP. Mono-Q anion-exchange analysis of the active ATP-agarose eluant yielded a peak of ASCI-PLA2 activity associated with a single protein band with an apparent molecular mass of 40 kDa. Similar chromatographic behavior of the rat pancreatic islet ASCI-PLA2 activity was observed during sequential ATP-agarose and Mono-Q anion-exchange steps. These results indicate that HIT cells express an ASCI-PLA2 similar to the analogous islet enzyme and suggest that expression of this enzyme and of its preferred plasmalogen substrates may be a general property of insulin-secreting β-cells. © 1994, American Chemical Society. All rights reserved.
  • Published In

  • Biochemistry  Journal
  • Digital Object Identifier (doi)

    Author List

  • Ramanadham S; Jett PA; Turk J; Wolf MJ; Gross RW
  • Start Page

  • 7442
  • End Page

  • 7452
  • Volume

  • 33
  • Issue

  • 23