Article

Sumoylation of Pdx1 is associated with its nuclear localization and insulin gene activation.

Departments of Medicine and Anatomy, Shiga University of Medical Science, Seta, Otsu, Shiga 520-2192 Japan.
AJP Endocrinology and Metabolism (impact factor: 4.75). 05/2003; 284(4):E830-40. DOI:10.1152/ajpendo.00390.2002 pp.E830-40
Source: PubMed

ABSTRACT Pancreatic duodenal homeobox-1 (Pdx1) is a transcription factor, and its phosphorylation is thought to be essential for activation of insulin gene expression. This phosphorylation is related to a concomitant shift in molecular mass from 31 to 46 kDa. However, we found that Pdx1 was modified by SUMO-1 (small ubiquitin-related modifier 1) in beta-TC-6 and COS-7 cells, which were transfected with Pdx1 cDNA. This modification contributed to the increase in molecular mass of Pdx1 from 31 to 46 kDa. Additionally, sumoylated Pdx1 localized in the nucleus. The reduction of SUMO-1 protein by use of RNA interference (SUMO-iRNAs) resulted in a significant decrease in Pdx1 protein in the nucleus. A 34-kDa form of Pdx1 was detected by the cells exposed to SUMO-iRNAs in the presence of lactacystin, a proteasome inhibitor. Furthermore, the reduced nuclear sumoylated Pdx1 content was associated with significant lower transcriptional activity of the insulin gene. These findings indicate that SUMO-1 modification is associated with both the localization and stability of Pdx1 as well as its effect on insulin gene activation.

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Keywords

COS-7 cells
 
insulin gene
 
insulin gene activation
 
insulin gene expression
 
Pancreatic duodenal homeobox-1
 
Pdx1
 
Pdx1 cDNA
 
Pdx1 protein
 
proteasome inhibitor
 
reduced nuclear sumoylated Pdx1 content
 
RNA interference
 
significant decrease
 
significant lower transcriptional activity
 
small ubiquitin-related modifier 1
 
SUMO-1
 
SUMO-1 modification
 
SUMO-1 protein
 
SUMO-iRNAs
 
sumoylated Pdx1 localized
 
transcription factor