Hydrogen peroxide stimulates nuclear import of the POU homeodomain protein Oct-1 and its repressive effect on the expression of Cdx-2.
BACKGROUND
The ubiquitously expressed POU homeodomain protein Oct-1 serves as a sensor for stress induced by irradiation. We found recently that in pancreatic and intestinal endocrine cells, Oct-1 also functions as a sensor for cyclic AMP (cAMP). The caudal homeobox gene Cdx-2 is a transactivator of proglucagon (gcg) and pro-insulin genes. Oct-1 binds to Cdx-2 promoter and represses its expression. cAMP elevation leads to increased nuclear exclusion of Oct-1, associated with reduced recruitment of nuclear co-repressors to the Cdx-2 promoter and increased Cdx-2 expression.


RESULTS
We show in this study that inducing oxidative stress by hydrogen peroxide (H2O2) increased nuclear Oct-1 content in both pancreatic alpha and beta cell lines, as well as in a battery of other cells. This increase was then attributed to accelerated nuclear import of Oct-1, assessed by Fluorescence Recovery After Photobleaching (FRAP) using green fluorescence protein (EGFP) tagged Oct-1 molecule. H2O2 treatment was then shown to stimulate the activities of DNA-dependent protein kinase (DNA-PK) and c-jun N-terminal kinase (JNK). Finally, increased Oct-1 nuclear content upon H2O2 treatment in a pancreatic alpha cell line was associated with reduced Cdx-2 and gcg mRNA expression.


CONCLUSIONS
These observations suggest that Oct-1 functions as a sensor for both metabolic and stress/survival signaling pathways via altering its nuclear-cytoplasmic shuttling.
Wang
Peixiang
P
Div of Cell and Molecular Biology, Toronto General Research Institute, University Health Network, 10-354 Toronto Medical Discovery Tower, The MaRS Building, 101 College St, Toronto, Ontario M5G 1L7, Canada.
Jin
Tianru
T
D021581:Active Transport, Cell Nucleus / Q000187:drug effects; D000818:Animals; D000071616:CDX2 Transcription Factor; D019556:COS Cells; D018938:Caco-2 Cells; D002467:Cell Nucleus / Q000378:metabolism*; D002522:Chlorocebus aethiops; D006224:Cricetinae; D018398:Homeodomain Proteins / Q000096:biosynthesis* / Q000235:genetics; D006801:Humans; D006861:Hydrogen Peroxide / Q000494:pharmacology; D051379:Mice; D050811:Octamer Transcription Factor-1 / Q000235:genetics / Q000378:metabolism*; D018384:Oxidative Stress; D010179:Pancreas / Q000187:drug effects / Q000378:metabolism* / Q000473:pathology; D051381:Rats; D015534:Trans-Activators / Q000096:biosynthesis* / Q000235:genetics
D000071616:CDX2 Transcription Factor; D018398:Homeodomain Proteins; D050811:Octamer Transcription Factor-1; D015534:Trans-Activators; D006861:Hydrogen Peroxide