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

Abstract

Aims/hypothesis: The glucose-6-phosphatase catalytic subunit (G6PC) plays a key role in hepatic glucose production by catalysing the final step in gluconeogenesis and glycogenolysis. Peroxisome proliferator activated receptor gamma coactivator-1α (PGC-1α) stimulates mouse G6pc-luciferase fusion gene expression through hepatocyte nuclear factor-4α (HNF-4α), which binds an element located between -76 and -64 in the promoter. The aim of this study was to compare the regulation of mouse G6pc and human G6PC gene expression by PGC-1α. Methods: PGC-1α action was analysed by transient transfection and gel retardation assays. Results: In H4IIE cells, PGC-1α alone failed to stimulate human G6PC-luciferase fusion gene expression even though the sequence of the -76 to -64 HNF-4α binding site is perfectly conserved in the human promoter. This difference could be explained, in part, by a 3 bp sequence variation between the mouse and human promoters. Introducing the human sequence into the mouse G6pc promoter reduced PGC-1α-stimulated fusion gene expression, whereas the inverse experiment, in which the mouse sequence was introduced into the human G6PC promoter, resulted in the generation of a G6PC-luciferase fusion gene that was now induced by PGC-1α. This critical 3 bp region is located immediately adjacent to a consensus nuclear hormone receptor half-site that is perfectly conserved between the mouse G6pc and human G6PC promoters. Gel retardation experiments revealed that this 3 bp region influences the affinity of HNF-4α binding to the half-site. Conclusions/interpretation: These observations suggest that PGC-1α may be more important in the control of mouse G6pc than human G6PC gene expression. © 2008 Springer-Verlag.