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Articles in PresS, published online ahead of print November 27, 2001
Am J Physiol Endocrinol Metab, 10.1152/ajpendo.00165.2001
Submitted on April 10, 2001
Accepted on November 16, 2001
1 Division of Experimental Diabetes and Aging, Mount Sinai School of Medicine, New York, NY, USA
* To whom correspondence should be addressed. E-mail: sramanad{at}im.wustl.edu.
Accumulating evidence suggests that the cytosolic calcium independent phospholipase A2 (iPLA2ß) manifests a signaling role in insulin secreting ß-cells. Earlier, we reported that insulin secretory responses to cAMP-elevating agents are amplified in iPLA2ß overexpressing INS-1 cells (Ma et al., J. Biol. Chem. 276:13198-13208, 2001). Here, immunofluorescence, immunoaffinity, and enzymatic activity analyses are used to examine distribution of iPLA2ß in stimulated INS-1 cells in greater detail. Overexpression of iPLA2ß in INS-1 cells leads to increased accumulation of iPLA2ß 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 iPLA2ß protein. In contrast, cAMP-elevating agents induce robust increases in insulin secretion and in time-dependent nuclear accumulation of iPLA2ß fluorescence, that is reflected by increases in nuclear iPLA2ß 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 ß-cell iPLA2ß to the nuclei where it may serve a crucial signaling role.
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