Endoplasmic reticulum stress induces Wfs1 gene expression in pancreatic beta-cells via transcriptional activation.
OBJECTIVE
The WFS1 gene encodes an endoplasmic reticulum (ER) membrane-embedded protein. Homozygous WFS1 gene mutations cause Wolfram syndrome, characterized by insulin-deficient diabetes mellitus and optic atropy. Pancreatic beta-cells are selectively lost from the patient's islets. ER localization suggests that WFS1 protein has physiological functions in membrane trafficking, secretion, processing and/or regulation of ER calcium homeostasis. Disturbances or overloading of these functions induces ER stress responses, including apoptosis. We speculated that WFS1 protein might be involved in these ER stress responses.


METHODS
Islet expression of the Wfs1 protein was analyzed immunohistochemically. Induction of Wfs1 upon ER stress was examined by Northern and Western blot analyses using three different models: human skin fibroblasts, mouse pancreatic beta-cell-derived MIN6 cells, and Akita mouse-derived Ins2 (96Y/Y) insulinoma cells. The human WFS1 gene promoter-luciferase reporter analysis was also conducted.


RESULTS
Islet beta-cells were the major site of Wfs1 expression. This expression was also found in delta-cells, but not in alpha-cells. WFS1 expression was transcriptionally up-regulated by ER stress-inducing chemical insults. Treatment of fibroblasts and MIN6 cells with thapsigargin or tunicamycin increased WFS1 mRNA. WFS1 protein also increased in response to thapsigargin treatment in these cells. WFS1 gene expression was also increased in Ins2 (96Y/Y) insulinoma cells. In these cells, ER stress was intrinsically induced by mutant insulin expression. The WFS1 gene promoter-luciferase reporter system revealed that the human WFS1 promoter was activated by chemically induced ER stress in MIN6 cells, and that the promoter was more active in Ins2 (96Y/Y) cells than Ins2 (wild/wild) cells.


CONCLUSIONS
Wfs1 expression, which is localized to beta- and delta-cells in pancreatic islets, increases in response to ER stress, suggesting a functional link between Wfs1 and ER stress.
Ueda
Kohei
K
Health Service Center, Organization for University Education, Yamaguchi University, Yamaguchi, Japan.
Kawano
June
J
Takeda
Komei
K
Yujiri
Toshiaki
T
Tanabe
Katsuya
K
Anno
Takatoshi
T
Akiyama
Masaru
M
Nozaki
Junichi
J
Yoshinaga
Takeo
T
Koizumi
Akio
A
Shinoda
Koh
K
Oka
Yoshitomo
Y
Tanizawa
Yukio
Y
D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D045744:Cell Line, Tumor; D004721:Endoplasmic Reticulum / Q000502:physiology*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005347:Fibroblasts / Q000166:cytology; D015870:Gene Expression / Q000187:drug effects / Q000502:physiology; D006801:Humans; D007340:Insulinoma; D007476:Ionophores / Q000494:pharmacology; D007515:Islets of Langerhans / Q000166:cytology / Q000502:physiology*; D008565:Membrane Proteins / Q000235:genetics*; D051379:Mice; D010190:Pancreatic Neoplasms; D011401:Promoter Regions, Genetic / Q000502:physiology; D013268:Stimulation, Chemical; D019284:Thapsigargin / Q000494:pharmacology; D015533:Transcriptional Activation / Q000187:drug effects / Q000502:physiology*; D014415:Tunicamycin / Q000494:pharmacology; D015854:Up-Regulation / Q000187:drug effects / Q000502:physiology
D000900:Anti-Bacterial Agents; D004791:Enzyme Inhibitors; D007476:Ionophores; D008565:Membrane Proteins; C114987:wolframin protein; D014415:Tunicamycin; D019284:Thapsigargin