The zinc transporter ZNT3 co-localizes with insulin in INS-1E pancreatic beta cells and influences cell survival, insulin secretion capacity, and ZNT8 expression
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Zinc trafficking in pancreatic beta cells is tightly regulated by zinc transporting (ZNTs) proteins. The role of different ZNTs in the beta cells is currently being clarified. ZNT8 transports zinc into insulin granules and is critical for a correct insulin crystallization and storage in the granules whereas ZNT3 knockout negatively affects beta cell function and survival. Here, we describe for the first time the sub-cellular localization of ZNT3 by immuno-gold electron microscopy and supplement previous data from knockout experiments with investigations of the effect of ZNT3 in a pancreatic beta cell line, INS-1E overexpressing ZNT3. In INS-1E cells, we found that ZNT3 was abundant in insulin containing granules located close to the plasma membrane. The level of ZNT8 mRNA was significantly decreased upon over-expression of ZNT3 at different glucose concentrations (5, 11 and 21 mM glucose). ZNT3 over-expression decreased insulin content and insulin secretion whereas ZNT3 over-expression improved the cell survival after 24 h at varying glucose concentrations (5, 11 and 21 mM). Our data suggest that ZNT3 and ZNT8 (known to regulate insulin secretion) have opposite effects on insulin synthesis and secretion possibly by a transcriptional co-regulation since mRNA expression of ZNT3 was inversely correlated to ZNT8 and ZNT3 over-expression reduced insulin synthesis and secretion in INS-1E cells. ZNT3 over-expression improved cell survival.
KeywordsZNT3 SLC30A3 ZNT8 Localization Insulin secretion Beta cell survival
INS-1E cells were kindly provided by Professor Emeritus Claes Wollheim and Professor Pierre Maechler, University of Geneva, Switzerland. We want to thank laboratory technician Elin Carstensen for help with the insulin assay, Else-Merete Løcke for assistance in electron microscopy and immunofluorescence, and laboratory technician Helle Zibrandtsen for help with the immunoblotting analysis. The study was supported by AP Møller and wife Chastine Mc-Kinney Møller Foundation and Desirée and Niels Ydes Foundation. Preliminary reports of these findings have previously been published in abstract form (Smidt et al. 2013) and reported at the 49th EASD Annual Meeting in Barcelona in 2013.
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Conflict of interest
The authors declare that they have no conflict of interest.
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