Hypoxia induces hexokinase II gene expression in human lung cell line A549

Abstract

During adaptation to hypoxic and hyperoxic conditions, the genes involved in glucose metabolism are upregulated. To probe involvement of the transcription factor hypoxia-induced factor-1 (HIF-1) in hexokinase (HK) II expression in human pulmonary cells, A549 cells and small-airway epithelial cells (SAECs) were exposed to stimuli such as hypoxia, deferoxamine (DFO), and metal ions. The largest increase in HK-II (20-fold for mRNA and 2.5-fold for enzymatic activity) was observed in A549 cells when exposed to DFO. All stimuli selectively increased the 5.5-kb rather than 4-kb transcript in A549 cells. Cycloheximide and actinomycin D inhibited these responses. In addition, cells were transfected with luciferase reporter constructs driven by the full-length HK-II 5'-regulatory region (4.0 kb) or various deletions of that region. A549 cells transfected with the 4.0-kb construct and exposed to hypoxia or DFO increased their luciferase activity 7- and 10-fold, respectively, indicating that HK-II induction is, at least in part, due to increased gene transcription. Sixty percent of the inducible activity of the 4.0-kb construct was shown to reside within the proximal 0.5 kb. Additionally, cotransfection with a stable HIF-1 mutant and the 4.0-kb promoter construct resulted in increased luciferase activity under normoxic conditions. These results strongly suggest that HK-II is selectively regulated in pulmonary cells by a HIF-1-dependent mechanism.

Hexokinase II integrates energy metabolism and cellular protection: Akting on mitochondria and TORCing to autophagy

“…The α-subunit of HIF-1 (HIF-1α) is stabilized under hypoxic conditions, leading to the activation of a transcriptional program to adapt to the lack of oxygen. The HK-II promoter has a consensus motif for HIF-1 54,55 and HK-II expression is enhanced by hypoxia, [54][55][56][57] providing cellular protection 52,56 as well as a mechanism for elevated glycolysis in tumors. [58][59][60]61 HIF-1α expression is also under the control of the PI3K/Akt/ mTORC1 pathway, 53,[62][63][64][65] linking Akt/mTOR activation and HK-II upregulation.…”

Mitochondrial hexokinases, novel mediators of the antiapoptotic effects of growth factors and Akt

“…Some specialized functions of individual hexokinase isoforms have already been identified (Postic et al, 2001;Wilson, 2003), but the overarching rationale for the coexistence of multiple hexokinase isoforms within a single tissue, or within a given cell, remains incompletely defined (Wilson, 2003). Where examined, most mammalian tissues and cell types, including tumor cells, have been found to express multiple hexokinase isoforms (Katzen and Schimke, 1965;Wilson, 1985;Katzen and Soderman, 1988;Preller and Wilson, 1992;Shinohara et al, 1994;Allen et al, 1998;Riddle et al, 2000;Coy et al, 2002) (RB Robey, unpublished findings). Detailed information regarding isozymic composition, however, is notably lacking for many cell types, which has limited the ability to define unique roles for individual isoforms, as well as their relative biological contributions (Robey, 2003).…”

“…The ubiquitous HKI isoform appears to be constitutively expressed in most tissues. HKII, which represents the principal regulated isoform in many cell types (Osawa et al, 1995;Riddle et al, 2000;Shinohara et al, 2001;Bryson et al, 2002;Taneja et al, 2004) (RB Robey, unpublished findings), is also widely expressed and represents the major isoform in insulin-sensitive tissues such as muscle and adipose that account for the bulk of peripheral glucose utilization, as well as in many highly glycolytic cancers (Wilson, 1995;Pedersen et al, 2002). HKIII exhibits a similarly broad range of expression, but is not the predominant isoform in any tissue in which it has been examined, and the regulation of its expression has been largely unexplored (Wilson, 1985;Cardenas et al, 1998).…”

Genome-wide gene expression analysis of chemoresistant pulmonary carcinoid cells

“…In contrast to HK1, GAPDH is known to be induced by hypoxia or nickel. 23,24 Therefore, UMC-11 cells clearly showed signs of aerobic glycolysis and induction of hypoxia-induced genes under aerobic conditions. 25 Most cancers exhibit elevated protease levels that contribute to certain aspects of tumor behavior in regard to growth, metastasis, and angiogenesis.…”