Glucose catabolism in cancer cells - Identification and characterization of a marked activation response of the type II hexokinase gene to hypoxic conditions

One of the most common signatures of highly malignant tumors is their capac ity to metabolize more glucose to lactic acid than their tissues of origin. Hepatomas exhibiting this phenotype are dependent on the high expression o f type Il hexokinase, which supplies such tumors with abundant amounts of g lucose 6-phosphate, a significant carbon and energy source especially under hypoxic conditions. Here we report that the distal region of the hepatoma. type Il hexokinase promoter displays consensus motifs for hypoxia-inducibl e factor (HIF-1) that overlap E-box sequences known to be related in other gene promoters to glucose response. Moreover, we show that subjecting trans fected hepatoma cells to hypoxic conditions activates the type II hexokinas e promoter almost 3-fold, a value that approaches 7-fold in the presence of glucose. Consistent with these findings is the induction under hypoxic con ditions of the HIF-1 protein. Reporter gene analyses with a series of neste d deletion mutants of the hepatoma type II hexokinase promoter show that a significant fraction of the total activation observed under hypoxic conditi ons localizes to the distal region where the overlapping HIF-1/E-box sequen ces are located. Finally, DNase I footprint analysis with a segment of the promoter containing these elements reveals the binding of several nuclear p roteins. In summary, these novel studies identify and characterize a marked glucose-modulated activation response of the type II hexokinase gene to hy poxic conditions within highly glycolytic hepatoma cells, a property that m ay help assure that such cells exhibit a growth and survival advantage over their parental cells of origin.