Hepatocyte nuclear factor-4alpha mediates the stimulatory effect of peroxisome proliferator-activated receptor gamma co-activator-1alpha (PGC-1alpha) on glucose-6-phosphatase catalytic subunit gene transcription in H4IIE cells

Abstract

It has recently been shown that adenoviral-mediated expression of peroxisome proliferator-activated receptor gamma co-activator-1 alpha (PGC-1 alpha) in hepatocytes stimulates glucose-6-phosphatase catalytic subunit (G6Pase) gene expression. A combination of fusion gene, gel retardation and chromatin immunoprecipitation assays revealed that, in H4IIE cells, PGC-1 alpha mediates this stimulation through an evolutionarily conserved region of the G6Pase promoter that binds hepatocyte nuclear factor-4 alpha.

Sequence variation between the mouse and human glucose-6-phosphatase catalytic subunit gene promoters results in differential activation by peroxisome proliferator activated receptor gamma coactivator-1α

“…Since PGC-1α markedly induces G6PC expression and HGP [7], we next compared the ability of PGC-1α to stimulate mouse G6pc-and human G6PC-luciferase fusion gene expression in rat H4IIE hepatoma cells. As previously reported [21], co-transfection of H4IIE cells with an expression vector encoding PGC-1α robustly induces the expression of a mouse G6pc−luciferase fusion gene containing promoter sequence between −484 and +66 (Fig. 2a).…”

“…3). The previously identified mouse HNF-4α binding site [21] is Dexamethasone stimulates mouse G6pc-and human G6PC-luciferase fusion gene expression. H4IIE cells were transiently cotransfected, as described in the Methods section, with the indicated mouse G6pc-or human G6PC−luciferase fusion genes (15 μg) and expression vectors encoding Renilla luciferase (0.15 μg) and the glucocorticoid receptor (5 μg).…”

“…The effect of PGC-1α on mouse G6pc−luciferase fusion gene expression was previously mapped to the promoter region between −85 and +66 and was shown to require an HNF-4α binding site located between −76 and −64 [21]. The 5′ untranslated regions (5′ UTRs) of the mouse and human genes contain numerous sequence variations, whereas the mouse promoter sequence between −85 and +1 and the equivalent human sequence between −83 and +1 are highly conserved (Fig.…”

“…Expression vectors encoding the rat glucocorticoid receptor (pRSV-GR) [23], rat HNF-4α (pSG5-HNF4α) [24]) and human forkhead box O1 (FOXO1; pcDNA3-FKHR) [25] [26] minus amino acids 476 to 487 has been previously described [21]. A fulllength pBJ5-PGC-1α expression vector was constructed by inserting the missing PGC-1α sequence, which was isolated from I.M.A.G.E.…”

“…We have previously shown that in rat H4IIE hepatoma cells the activation of mouse G6pc expression by PGC-1α was mediated through an HNF-4α binding site located between −76 and −64 [21], whereas Rhee et al [20] showed in immortalised mouse hepatocytes that the activation of human G6PC expression by PGC-1α was mainly mediated through two HNF-4α binding sites located between −296 and −284, and −256 and −244. Because these latter sites are poorly conserved in the mouse G6pc promoter, this observation appeared to explain the differences between the reported results.…”