Qm. Gong et al., Functional analysis of two promoters for the human mitochondrial glycerol phosphate dehydrogenase gene, J BIOL CHEM, 275(48), 2000, pp. 38012-38021
Mitochondrial glycerol phosphate dehydrogenase (mGPD) is abundant in the no
rmal pancreatic insulin cell, but its level is lowered 50% by diabetes. To
evaluate mGPD expression, we cloned and characterized the 5'-flanking regio
n of the human mGPD gene. The gene has two alternative first exons and two
promoters. The downstream promoter (B) is 10 times more active than the ups
tream promoter (A) in insulin secreting cells (INS-1) and HeLa cells. Promo
ter B has higher activity in INS-1 than in non-beta cells. Deletion and mut
ation analysis suggested that a NRF-2 binding site at -94 to -101 and an E2
F binding site at -208 to -215 are important regulatory cis elements in pro
moter B, Gel mobility shift assays indicated that the -94 to -101 region bi
nds the NRF-2 protein. When INS-1 cells were maintained in the presence of
high glucose (25 mM) for 7 days, mGPD was the only 1 of 6 enzyme activities
lowered (53%), mGPD promoter B activity was reduced by 60% in INS-1 cells
by the high glucose, but in HepG2 cells and HeLa cells, promoter B activity
was unchanged or slightly increased. Deletion analysis indicated the gluco
se responsiveness was distributed across the region from -340 to -260 in pr
omoter B. The results indicate that mGPD gene transcription in the beta cel
l is regulated differently from other cells and that decreased mGPD promote
r B transcription is at least in part the cause of the decreased beta cell
mGPD levels in diabetes.