Promoter function of the human glucose-6-phosphate dehydrogenase gene depends on two 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 least nine GC boxes. By transient transfection of HeLa and HepG2 cells with constructs containing glucose-6-phosphate dehydrogenase gene regions linked to a reporter gene, we have now delineated the core promoter and have located upstream stimulatory and inhibitory sequences. By mutational analysis, we demonstrate that the activity of the core promoter requires two out of seven GC boxes. We show that stimulatory protein 1 (Sp1)-related factors and activator protein 2 (AP-2)-related proteins bind to these two boxes in band-shift experiments. One point mutation that affects the binding of only the Sp1-related factors to one or both boxes causes a marked decrease of promoter activity in HepG2 cells but not in HeLa cells. We conclude that (a) two out of many seemingly redundant GC boxes are necessary to drive a G+C-rich housekeeping promoter; (b) factors that bind to GC boxes may exert cell-type-specific regulation of housekeeping gene promoter activity; (c) point mutations in the promoter of the glucose-6-phosphate dehydrogenase gene can inhibit its transcription.