Pancreatic and duodenal homeobox protein 1 (Pdx-1) maintains endoplasmic reticulum calcium levels through transcriptional regulation of sarco-endoplasmic reticulum calcium ATPase 2b (SERCA2b) in the islet β cell

J Biol Chem. 2014 Nov 21;289(47):32798-810. doi: 10.1074/jbc.M114.575191. Epub 2014 Sep 30.


Although the pancreatic duodenal homeobox 1 (Pdx-1) transcription factor is known to play an indispensable role in β cell development and secretory function, recent data also implicate Pdx-1 in the maintenance of endoplasmic reticulum (ER) health. The sarco-endoplasmic reticulum Ca(2+) ATPase 2b (SERCA2b) pump maintains a steep Ca(2+) gradient between the cytosol and ER lumen. In models of diabetes, our data demonstrated loss of β 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 Ca(2+), 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 Ca(2+) regulation in Pdx-1-deficient states.

Keywords: Calcium ATPase; Diabetes; Endoplasmic Reticulum Stress (ER Stress); Pancreatic And Duodenal Homeobox 1; Pancreatic Islet; Sarco-endoplasmic Reticulum Calcium ATPase; β Cell.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Animals
  • Calcium / metabolism*
  • Cell Line, Tumor
  • Diabetes Mellitus / genetics
  • Diabetes Mellitus / metabolism
  • Endoplasmic Reticulum / metabolism*
  • Gene Expression
  • Gene Expression Regulation
  • HEK293 Cells
  • Homeodomain Proteins / genetics*
  • Homeodomain Proteins / metabolism
  • Humans
  • Immunoblotting
  • Insulin-Secreting Cells / metabolism*
  • Mice
  • Mice, Inbred C57BL
  • Mice, Mutant Strains
  • Microscopy, Fluorescence / methods
  • NIH 3T3 Cells
  • RNA Interference
  • Reverse Transcriptase Polymerase Chain Reaction
  • Sarcoplasmic Reticulum Calcium-Transporting ATPases / genetics*
  • Sarcoplasmic Reticulum Calcium-Transporting ATPases / metabolism
  • Trans-Activators / genetics*
  • Trans-Activators / metabolism


  • Homeodomain Proteins
  • Trans-Activators
  • pancreatic and duodenal homeobox 1 protein
  • Sarcoplasmic Reticulum Calcium-Transporting ATPases
  • ATP2A2 protein, human
  • Atp2a2 protein, mouse
  • Calcium