Apoptosis of insulin-secreting cells induced by endoplasmic reticulum stress is amplified by overexpression of group VIA calcium-independent phospholipase A2 (iPLA2 beta) and suppressed by inhibition of iPLA2 beta.
The death of insulin-secreting beta-cells that causes type I diabetes mellitus (DM) occurs in part by apoptosis, and apoptosis also contributes to progressive beta-cell dysfunction in type II DM. Recent reports indicate that ER stress-induced apoptosis contributes to beta-cell loss in diabetes. Agents that deplete ER calcium levels induce beta-cell apoptosis by a process that is independent of increases in [Ca(2+)](i). Here we report that the SERCA inhibitor thapsigargin induces apoptosis in INS-1 insulinoma cells and that this is inhibited by a bromoenol lactone (BEL) inhibitor of group VIA calcium-independent phospholipase A(2) (iPLA(2)beta). Overexpression of iPLA(2)beta amplifies thapsigargin-induced apoptosis of INS-1 cells, and this is also suppressed by BEL. The magnitude of thapsigargin-induced INS-1 cell apoptosis correlates with the level of iPLA(2)beta expression in various cell lines, and apoptosis is associated with stimulation of iPLA(2)beta activity, perinuclear accumulation of iPLA(2)beta protein and activity, and caspase-3-catalyzed cleavage of full-length 84 kDa iPLA(2)beta to a 62 kDa product that associates with nuclei. Thapsigargin also induces ceramide accumulation in INS-1 cells, and this response is amplified in cells that overexpress iPLA(2)beta. These findings indicate that iPLA(2)beta participates in ER stress-induced apoptosis, a pathway that promotes beta-cell death in diabetes.
Ramanadham
Sasanka
S
Mass Spectrometry Resource, Division of Endocrinology, Diabetes, and Metabolism, Department of Medicine, Washington University School of Medicine, Box 8127, 660 South Euclid Avenue, St. Louis, Missouri 63110, USA. sramanad@im.wustl.edu
Hsu
Fong-Fu
FF
Zhang
Sheng
S
Jin
Chun
C
Bohrer
Alan
A
Song
Haowei
H
Bao
Shunzhong
S
Ma
Zhongmin
Z
Turk
John
J
D000818:Animals; D017209:Apoptosis / Q000187:drug effects / Q000235:genetics; D045744:Cell Line, Tumor; D002518:Ceramides / Q000378:metabolism; D004121:Dimethyl Sulfoxide / Q000494:pharmacology; D004721:Endoplasmic Reticulum / Q000187:drug effects* / Q000201:enzymology / Q000502:physiology*; D019084:Fluorescent Antibody Technique, Indirect; D049452:Green Fluorescent Proteins; D054513:Group IV Phospholipases A2; D054522:Group VI Phospholipases A2; D015151:Immunoblotting; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D007527:Isoenzymes / Q000037:antagonists & inhibitors / Q000096:biosynthesis / Q000235:genetics; D008164:Luminescent Proteins / Q000096:biosynthesis / Q000737:chemistry / Q000235:genetics; D008970:Molecular Weight; D009281:Naphthalenes / Q000494:pharmacology; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology; D010741:Phospholipases A / Q000037:antagonists & inhibitors* / Q000096:biosynthesis* / Q000235:genetics; D054467:Phospholipases A2; D011753:Pyrones / Q000494:pharmacology; D051381:Rats; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis / Q000737:chemistry; D013347:Subcellular Fractions / Q000187:drug effects / Q000201:enzymology; D019284:Thapsigargin / Q000494:pharmacology; D014162:Transfection
D002518:Ceramides; D007328:Insulin; D007527:Isoenzymes; D008164:Luminescent Proteins; D009281:Naphthalenes; D010726:Phosphodiesterase Inhibitors; D011753:Pyrones; D011993:Recombinant Fusion Proteins; D049452:Green Fluorescent Proteins; D019284:Thapsigargin; C068314:6-(bromomethylene)tetrahydro-3-(1-naphthaleneyl)-2H-pyran-2-one; D010741:Phospholipases A; D054513:Group IV Phospholipases A2; D054522:Group VI Phospholipases A2; D054467:Phospholipases A2; D004121:Dimethyl Sulfoxide