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

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-1 alpha (PGC-1 alpha) stimulates mouse G6pc-luciferase fusion gene expression through hepatocyte nuclear factor-4 alpha (HNF-4 alpha), 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-1 alpha. Methods PGC-1 alpha action was analysed by transient transfection and gel retardation assays. Results In H4IIE cells, PGC-1 alpha alone failed to stimulate human G6PC-luciferase fusion gene expression even though the sequence of the -76 to -64 HNF-4 alpha 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-1 alpha-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-1 alpha. 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-4 alpha binding to the half-site. Conclusions/interpretation These observations suggest that PGC-1 alpha may be more important in the control of mouse G6PC than human G6PC gene expression.