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Diabetes 53:S186-S189, 2004
© 2004 by the American Diabetes Association, Inc.

Section IV: Lipid Modulators of Islet Function

ß-Cell Calcium-Independent Group VIA Phospholipase A2 (iPLA2ß)

Tracking iPLA2ß Movements in Response to Stimulation With Insulin Secretagogues in INS-1 Cells

Shunzhong Bao1, Chun Jin1, Sheng Zhang1, John Turk1, Zhongmin Ma2, and Sasanka Ramanadham1

1 Mass Spectrometry Resource, Division of Endocrinology, Diabetes, and Metabolism, Department of Medicine, Washington University School of Medicine, St. Louis, Missouri
2 Division of Experimental Diabetes and Aging, Mount Sinai School of Medicine, New York, New York

Evidence that group VIA cytosolic calcium-independent phospholipase A2 (iPLA2ß) participates in ß-cell signal transduction includes the observations that inhibition of iPLA2ß with the bromoenol lactone suicide substrate suppresses glucose-stimulated insulin secretion and that overexpression of iPLA2ß amplifies insulin secretory responses in INS-1 insulinoma cells. Immunofluorescence analyses also reveal that iPLA2ß accumulates in the perinuclear region of INS-1 cells stimulated with glucose and forskolin. To characterize this phenomenon further, iPLA2ß was expressed as a fusion protein with enhanced green fluorescent protein (EGFP) in INS-1 cells so that movements of iPLA2ß are reflected by changes in the subcellular distribution of green fluorescence. Stimulation of INS-1 cells overexpressing iPLA2ß-EGFP induced greater insulin secretion and punctate accumulation of iPLA2ß-EGFP fluorescence in the perinuclear region. To determine the identity of organelles with which iPLA2ß might associate, colocalization of green fluorescence with fluorophores associated with specific trackers targeted to different subcellular organelles was examined. Such analyses reveal association of iPLA2ß-EGFP fluorescence with the ER and Golgi compartments. Arachidonate-containing plasmenylethanolamine phospholipid species are abundant in ß-cell endoplasmic reticulum (ER) and are excellent substrates for iPLA2ß. Arachidonic acid produced by iPLA2ß-catalyzed hydrolysis of their substrates induces release of Ca2+ from ER stores—an event thought to participate in glucose-stimulated insulin secretion.

Address correspondence and reprint requests to Sasanka Ramanadham, Washington University School of Medicine, Department of Medicine, Box 8127, 660 S. Euclid Ave., St. Louis, MO 63110. E-mail: sramanad{at}im.wustl.edu


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Diabetes Diabetes Care Clinical Diabetes Diabetes Spectrum
Copyright © 2004 by the American Diabetes Association.