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Calcium-independent phospholipase A2 is required for lysozyme secretion in U937 promonocytes

María A Balboa1, Yolanda Sáez, Jesús Balsinde

  • 1Institute of Molecular Biology and Genetics, University of Valladolid School of Medicine, Valladolid, Spain.

Journal of Immunology (Baltimore, Md. : 1950)
|May 8, 2003
PubMed

Insights

Calcium-independent phospholipase A(2) (iPLA(2)) is crucial for lysozyme secretion in immune cells. This enzyme produces lysophosphatidylcholine (lysoPC), which restores lysozyme secretion when iPLA(2) is inhibited.

Area of Science:

  • Cell Biology
  • Immunology
  • Biochemistry

Background:

  • Monocytes/macrophages are key immune cells involved in pathogen surveillance.
  • These cells secrete lysozyme, a bactericidal enzyme, to combat infections.
  • The precise molecular mechanisms regulating lysozyme secretion are not fully understood.

Purpose of the Study:

  • To investigate the role of phospholipase A(2) enzymes in lysozyme secretion from U937 promonocytes.
  • To determine the specific contribution of calcium-independent phospholipase A(2) (iPLA(2)) and cytosolic phospholipase A(2) (cPLA(2)) in this process.

Main Methods:

  • U937 promonocytes were activated and treated with inhibitors of iPLA(2) (bromoenol lactone) and cPLA(2).
  • Antisense oligonucleotides were used to specifically inhibit iPLA(2) activity.
  • Levels of lysophosphatidylcholine (lysoPC) and arachidonic acid were measured.
  • Reconstitution experiments were performed using various lysophospholipids.

Main Results:

  • Inhibition of iPLA(2) significantly reduced lysozyme secretion.
  • iPLA(2) activity was essential for maintaining intracellular lysophosphatidylcholine (lysoPC) levels.
  • Lysophosphatidylcholine (lysoPC) addition restored lysozyme secretion in iPLA(2)-deficient cells.
  • Inhibition of cPLA(2) blocked arachidonic acid mobilization but did not affect lysozyme secretion.

Conclusions:

  • Calcium-independent phospholipase A(2) (iPLA(2)) is indispensable for lysozyme secretion in U937 cells.
  • iPLA(2)-mediated production of lysophosphatidylcholine (lysoPC) is a critical step in the lysozyme secretion pathway.
  • Cytosolic phospholipase A(2) (cPLA(2)) plays a distinct role in inflammatory signaling, separate from lysozyme secretion.

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