GLUCOSE-DEPENDENT TRANSLOCATION OF INSULIN PROMOTER FACTOR-I (IPF-1) BETWEEN THE NUCLEAR PERIPHERY AND THE NUCLEOPLASM OF SINGLE MIN6 BETA-CELLS

Using laser-scanning confocal microscopy, we have monitored glucose-in duced changes in the subcellular localization of insulin promoter fact or-1 (IPF-1) labeled with a c-myc epitope tag. This construct trans-ac tivated the insulin promoter in single living MIN6-beta-cells as asses sed by luciferase-based promoter analysis. IPF-1.c-myc expression also enhanced the response of the insulin promoter to elevations in extrac ellular glucose concentration. In the majority (148/235, 63%) of cells maintained at low (3 mM) extracellular glucose concentration, IPF-1.c -myc immunoreactivity was confined to the nuclear periphery. Incubatio n of cells at stimulatory (30 mM) glucose concentrations caused a rapi d redistribution of the chimera to the nucleoplasm (775/958, 81% of ce lls). By contrast, the irrelevant transcription factor c-Fos, tagged w ith either c-myc or as a chimera with luciferase, was localized exclus ively to the nucleoplasm irrespective of the glucose concentration. Fu rthermore, IPF-1 extended with the bulky (27 kDa) enhanced green fluor escent protein (EGFP) group was confined largely to the nucleoplasm at all glucose concentrations tested and did not support trans-activatio n of the insulin promoter by glucose. Movement of endogenous IPF-1 fro m the nuclear periphery to the nucleoplasm may therefore increase the trans-activational capacity of this factor in native beta-cells expose d to high extracellular glucose concentrations.