Stimulation of insulin secretion and associated nuclear accumulation of iPLA(2)beta in INS-1 insulinoma cells.
Accumulating evidence suggests that the cytosolic calcium-independent phospholipase A(2) (iPLA(2)beta) manifests a signaling role in insulin-secreting (INS-1) beta-cells. Earlier, we reported that insulin-secretory responses to cAMP-elevating agents are amplified in iPLA(2)beta-overexpressing INS-1 cells (Ma Z, Ramanadham S, Bohrer A, Wohltmann M, Zhang S, and Turk J. J Biol Chem 276: 13198-13208, 2001). Here, immunofluorescence, immunoaffinity, and enzymatic activity analyses are used to examine distribution of iPLA(2)beta in stimulated INS-1 cells in greater detail. Overexpression of iPLA(2)beta in INS-1 cells leads to increased accumulation of iPLA(2)beta in the nuclear fraction. Increasing glucose concentrations alone results in modest increases in insulin secretion, relative to parental cells, and in nuclear accumulation of the iPLA(2)beta protein. In contrast, cAMP-elevating agents induce robust increases in insulin secretion and in time-dependent nuclear accumulation of iPLA(2)beta fluorescence, which is reflected by increases in nuclear iPLA(2)beta protein content and specific enzymatic activity. The stimulated effects are significantly attenuated in the presence of cell-permeable inhibitors of protein phosphorylation and glycosylation. These findings suggest that conditions that amplify insulin secretion promote translocation of beta-cell iPLA(2)beta to the nuclei, where it may serve a crucial signaling role.
Ma
Zhongmin
Z
Division of Experimental Diabetes and Aging, Mount Sinai School of Medicine, New York, New York 10029, USA.
Zhang
Sheng
S
Turk
John
J
Ramanadham
Sasanka
S
D015056:1-Methyl-3-isobutylxanthine / Q000494:pharmacology; D000818:Animals; D002467:Cell Nucleus / Q000201:enzymology*; D005576:Colforsin / Q000494:pharmacology; D017868:Cyclic AMP-Dependent Protein Kinases / Q000494:pharmacology; D005455:Fluorescent Antibody Technique; D015870:Gene Expression; D005947:Glucose / Q000494:pharmacology; D006031:Glycosylation; D054522:Group VI Phospholipases A2; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D007340:Insulinoma / Q000201:enzymology* / Q000378:metabolism / Q000648:ultrastructure; D007700:Kinetics; D010190:Pancreatic Neoplasms / Q000201:enzymology* / Q000378:metabolism / Q000648:ultrastructure; D010741:Phospholipases A / Q000032:analysis / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation; D051381:Rats; D015398:Signal Transduction; D014162:Transfection; D014407:Tumor Cells, Cultured
D007328:Insulin; D005576:Colforsin; D017868:Cyclic AMP-Dependent Protein Kinases; D010741:Phospholipases A; D054522:Group VI Phospholipases A2; D005947:Glucose; D015056:1-Methyl-3-isobutylxanthine