Molecular insights into the transcriptional regulation of the type II hexokinase gene in highly glycolytic hepatoma cells and hepatocytes

One of the most common biochemical phenotypes of highly malignant, rapidly growing tumors is their ability to utilize glucose at high rates dependent on hexokinase, the first enzyme of the glycolytic pathway. In such tumors, hexokinase is markedly elevated (>100 fold) and plays an essential role in sustaining the high glycolytic phenotype. Among the four mammalian hexokinase types (HK I–IV), type II (HKII) is predominantly overexpressed in such tumors. In contrast, HKII expression is nearly silent in many normal cells, e.g. hepatocytes. Molecular mechanisms involved in the differential regulation of the HKII gene have not been well understood. Using AS-30D hepatoma cells as a highly glycolytic cancer cell model, work described here has shown that the enhanced activity of the HKII promoter resides within a short segment (−281 to −35) of the proximal region and that the transcription factors Sp1, Sp2, Sp3, NF-Y, and CREB interact with sites in this region. In addition, the transcription factors Sp1, Sp2, Sp3, NF-Y, and CREB appear to reside together in a complex bound to the proximal promoter region thereby activating HKII expression. In contrast to hepatoma cells, the levels of transcription factors Sp1, Sp2, Sp3, NF-Y, and CREB are very low in primary hepatocytes and the binding of these factors to the HKII promoter is not detectable under the conditions of the assay employed. In summary, these studies provide novel insights into how the HKII gene may be differentially regulated in normal and cancer cells. Finally, in an independent but related study, it has been shown that the transcription factor Mnt/Rox is induced by a pH decrease in the medium.