期刊
JOURNAL OF BIOLOGICAL CHEMISTRY
卷 289, 期 47, 页码 -出版社
AMER SOC BIOCHEMISTRY MOLECULAR BIOLOGY INC
DOI: 10.1074/jbc.M114.575191
关键词
-
资金
- National Institutes of Health [R01 DK093954, RO1 DK46409, K01 DK101683]
- NIDDK, National Institutes of Health
- Veterans Affairs Merit Award [I01BX001733]
Although the pancreatic duodenal homeobox 1 (Pdx-1) transcription factor is known to play an indispensable role in beta cell development and secretory function, recent data also implicate Pdx-1 in the maintenance of endoplasmic reticulum (ER) health. The sarco-endoplasmic reticulum Ca2+ ATPase 2b (SERCA2b) pump maintains a steep Ca2+ gradient between the cytosol and ER lumen. In models of diabetes, our data demonstrated loss of beta cell Pdx-1 that occurs in parallel with altered SERCA2b expression, whereas in silico analysis of the SERCA2b promoter revealed multiple putative Pdx-1 binding sites. We hypothesized that Pdx-1 loss under inflammatory and diabetic conditions leads to decreased SERCA2b levels and activity with concomitant alterations in ER health. To test this, siRNA-mediated knockdown of Pdx-1 was performed in INS-1 cells. The results revealed reduced SERCA2b expression and decreased ER Ca2+, which was measured using fluorescence lifetime imaging microscopy. Cotransfection of human Pdx-1 with a reporter fused to the human SERCA2 promoter increased luciferase activity 3- to 4-fold relative to an empty vector control, and direct binding of Pdx-1 to the proximal SERCA2 promoter was confirmed by chromatin immunoprecipitation. To determine whether restoration of SERCA2b could rescue ER stress induced by Pdx-1 loss, Pdx1(+/-) mice were fed a high-fat diet. Isolated islets demonstrated an increased spliced-to-total Xbp1 ratio, whereas SERCA2b overexpression reduced the Xbp1 ratio to that of wild-type controls. Together, these results identify SERCA2b as a novel transcriptional target of Pdx-1 and define a role for altered ER Ca2+ regulation in Pdx-1-deficient states.
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