ARS | Publication request: Over-expression of ZnT7 increases insulin synthesis and secretion in pancreatic beta-cells by promoting insulin gene transcription

Submitted to: Experimental Cell Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 22, 2010
Publication Date: July 1, 2010
Repository URL: http://www.sciencedirect.com/science?_ob=MImg&_imagekey=B6WFC-50F3V8N-2-10&_cdi=6791&_user=4421&_pii=S0014482710003265&_origin=search&_coverDate=10%2F01%2F2010&_sk=996839983&view=c&wchp=dGLzVlz-zSkzV&md5=69fc7b09cd86f43d57cc1a9554359492&ie=/sdarticle.pdf
Citation: Huang, L., Mi, Y., Kirschke, C.P. 2010. Over-expression of ZnT7 increases insulin synthesis and secretion in pancreatic beta-cells by promoting insulin gene transcription. Experimental Cell Research. 2010 Volume 316, Issue 16 2630-2643

Interpretive Summary: The pancreas is a gland organ containing an endocrine gland producing hormones, such as insulin from beta-cells, glucagon from alpha-cells, and somatostatin from delta-cells, and an exocrine gland producing pancreatic digestive enzymes helping breakdown of the carbohydrates, protein, and fat in the small intestine. Impaired insulin synthesis and insulin secretion and perturbed proinsulin processing are hallmarks of beta-cell dysfunction in diabetes. Connections between zinc homeostasis and diabetes remain largely unknown. The zinc content in the pancreatic beta-cells is known to be among the highest in the body. Regulation of cellular zinc homeostasis in pancreatic beta-cells is still unknown. ZnT7 resides in the Golgi apparatus and plays a role in delivery of zinc into it. In this study, we demonstrated that zinc transporter 7 (ZnT7, Slc30a7) was co-expressed with insulin in the islet of Langerhans in the mouse pancreas. In RIN5mF cells (rat insulinoma cells), ZnT7 was found mainly residing in the perinuclear region of the cell, which is consistent with its Golgi apparatus localization. Over-expression of ZnT7 in RIN5mF cells increased total cellular insulin content leading to a high basal insulin secretion. Furthermore, glucose-induced insulin secretion was not altered in RIN5mF cells over-expressing ZnT7. Quantitative RT-PCR and 35S metabolic labeling analysis demonstrated that over-expression of ZnT7 in RIN5mF cells led to an increase of insulin mRNA expression and subsequent insulin protein synthesis in the cell. Metal-responsive elements (MREs) were identified in the promoter regions of the Ins1 and Ins2 genes. Mtf1, a metal-responsive transcription factor, was shown to specifically bind to the MRE in the Ins genes and activated the insulin gene transcription. Together, the data strongly suggest that ZnT7 plays an important role in regulating insulin expression by modulating Mtf1 transcriptional activity.

Technical Abstract: The mechanism by which zinc regulates insulin synthesis and secretion in pancreatic beta-cells is still unclear. Cellular zinc homeostasis is largely maintained by zinc transporters and intracellular zinc binding proteins. In this study, we demonstrated that zinc transporter 7 (ZnT7, Slc30a7) was co-expressed with insulin in the islet of Langerhans in the mouse pancreas. In RIN5mF cells (rat insulinoma cells), ZnT7 was found mainly residing in the perinuclear region of the cell, which is consistent with its Golgi apparatus localization. Over-expression of ZnT7 in RIN5mF cells increased total cellular insulin content leading to a high basal insulin secretion. Furthermore, glucose-induced insulin secretion was not altered in RIN5mF cells over-expressing ZnT7. Quantitative RT-PCR and 35S metabolic labeling analysis demonstrated that over-expression of ZnT7 in RIN5mF cells led to an increase of insulin mRNA expression and subsequent insulin protein synthesis in the cell. Metal-responsive elements (MREs) were identified in the promoter regions of the Ins1 and Ins2 genes. Mtf1, a metal-responsive transcription factor, was shown to specifically bind to the MRE in the Ins genes and activated the insulin gene transcription. Together, the data strongly suggest that ZnT7 plays an important role in regulating insulin expression by modulating Mtf1 transcriptional activity.