PROMOTER FUNCTION OF THE HUMAN GLUCOSE-6-PHOSPHATE-DEHYDROGENASE GENEDEPENDS ON 2 GC BOXES THAT ARE CELL SPECIFICALLY CONTROLLED

Human glucose-6-phosphate dehydrogenase is expressed in all cells by a housekeeping gene whose regulatory 5'-flanking sequence includes at l east nine GC boxes. By transient transfection of HeLa and HepG2 cells with constructs containing glucose-6-phosphate dehydrogenase gene regi ons linked to a reporter gene, we have now delineated the core promote r and have located upstream stimulatory and inhibitory sequences. By m utational analysis, we demonstrate that the activity of the core promo ter requires two out of seven GC boxes. We show that stimulatory prote in 1 (Sp1)-related factors and activator protein 2 (AP-2)-related prot eins bind to these two boxes in band-shift experiments. One point muta tion that affects the binding of only the Sp1-related factors to one o r both boxes causes a marked decrease of promoter activity in HepG2 ce lls but not in HeLa cells. We conclude that (a) two out of many seemin gly redundant GC boxes are necessary to drive a G+C-rich housekeeping promoter; (b) factors that bind to GC boxes may exert cell-type-specif ic regulation of housekeeping gene promoter activity; (c) point mutati ons in the promoter of the glucose-6-phosphate dehydrogenase gene can inhibit its transcription.