Regulation by Per-Arnt-Sim (PAS) kinase of pancreatic duodenal homeobox-1 nuclear import in pancreatic beta-cells.
The transcription factor PDX-1 (pancreatic duodenal homeobox-1) is required for normal pancreatic development and for the function of insulin-producing islet beta-cells in mammals. We have shown previously that glucose regulates insulin gene expression in part through the activation and translocation of PDX-1 from the nuclear periphery to the nucleoplasm. We have also found that PASK [PAS (Per-Arnt-Sim) kinase], a member of the nutrient-regulated family of protein kinases, is activated in response to glucose challenge in beta-cells and is involved in the regulation of expression of PDX-1. Purified PASK efficiently phosphorylated recombinant PDX-1 in vitro on a single site (Thr-152). To determine the impact of phosphorylation at this site, we generated wild-type and mutant (T152A, T152D and T152E) forms of PDX-1 and examined the distribution of each of these in clonal MIN6 beta-cells by immunocytochemical analysis. Unexpectedly, only the T152D mutation significantly affected subcellular distribution, increasing the ratio of nuclear/cytosolic labelling at low and high glucose concentrations, suggesting that phosphorylation at Thr-152 inhibits nuclear uptake in response to glucose. Based on these results, experiments to examine the contribution of Thr-152 to the overall phosphorylation of PDX-1 in intact cells will be undertaken.
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Henry Wellcome Signalling Laboratories and Department of Biochemistry, University of Bristol, Bristol BS8 ITD, UK.
da Silva Xavier
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Hao
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Semplici
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Rutter
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Rutter
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D002467:Cell Nucleus / Q000378:metabolism*; D004386:Duodenum / Q000502:physiology*; D018398:Homeodomain Proteins / Q000235:genetics / Q000378:metabolism* / Q000502:physiology*; D006706:Homeostasis; D006801:Humans; D050417:Insulin-Secreting Cells / Q000502:physiology*; D009154:Mutation; D010179:Pancreas / Q000502:physiology*; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D021381:Protein Transport; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism*
D018398:Homeodomain Proteins; D015534:Trans-Activators; C084010:pancreatic and duodenal homeobox 1 protein; C116037:PAS domain kinases; D017346:Protein Serine-Threonine Kinases