Regulation and Cytoprotective Role of Hexokinase III

Abstract

BackgroundHexokinases (HKs) catalyze the first step in glucose metabolism. Of the three mammalian 100-kDa HK isoforms, HKI and II can bind to mitochondria and protect against cell death. HKIII does not bind mitochondria, and little is known about its regulation or cytoprotective effects. We studied the regulation of HKIII at the transcriptional and protein levels and investigated its role in cellular protection.Methodology/Principal FindingsWe show that like HKII, HKIII expression is regulated by hypoxia, but other factors that regulate HKII expression have no effect on HKIII levels. This transcriptional regulation is partially dependent on hypoxia-inducible factor (HIF) signaling. We also demonstrate regulation at the protein level, as mutations in putative N-terminal substrate binding residues altered C-terminal catalytic activity, suggesting that HKIII activity is governed, in part, by interactions between these two domains. Overexpression of HKIII reduced oxidant-induced cell death, increased ATP levels, decreased the production of reactive oxygen species (ROS), and preserved mitochondrial membrane potential. HKIII overexpression was also associated with higher levels of transcription factors that regulate mitochondrial biogenesis, and greater total mitochondrial DNA content. Attempts to target HKIII to the mitochondria by replacing its N-terminal 32-amino-acid sequence with the mitochondrial-targeting sequence of HKII led to protein aggregation, suggesting that this region is necessary to maintain proper protein folding and solubility.Conclusions/SignificanceThese results suggest that HKIII is regulated by hypoxia and there are functional interactions between its two halves. Furthermore, HKIII exerts protective effects against oxidative stress, perhaps by increasing ATP levels, reducing oxidant-induced ROS production, preserving mitochondrial membrane potential, and increasing mitochondrial biogenesis.

Low Oxygen Tension Enhances Hepatitis C Virus Replication

“…6A to C). Consistently, previous studies have directly implicated two glycolytic enzymes in the regulation of HCV replication (71,72), hexokinase III, which is transcriptionally activated by both HIF and MYC under hypoxia, and pyruvate kinase, which is enhanced in a HIF-independent manner (73)(74)(75). Thus, hypoxia-mediated upregulation of glycolysis represents an HCV replication-promoting metabolic modification.…”

Molecular mechanisms of neutrophil dysfunction in glycogen storage disease type Ib

“…The major HK isozyme in neutrophils is HK3, 36 which also plays the role of protecting cells from oxidant-induced cell death. 46 The expression of HK3 is upregulated by HIF-1a, 46 and consistent with this we observed that both HK3 mRNA and protein are increased 4-fold in G6PT-deficient neutrophils. In ER cycling, G6P enters the ER via G6PT, where it accumulates until it is hydrolyzed by G6Pase-b to glucose.…”

Correlation Between In Vivo 18F-FDG PET and Immunohistochemical Markers of Glucose Uptake and Metabolism in Pheochromocytoma and Paraganglioma

“…The upregulation of both GLUTs and HK is frequently associated with malignant transformation of cells (21). Furthermore, activity of HK-3 and monocarboxylate transporter type 4 (MCT-4), which facilitates the cellular lactate transport, possibly is regulated by hypoxia (10,22). In addition, hypoxia also promotes anaerobic glycolysis, and several studies have demonstrated that 18 F-FDG uptake is an indirect reflection of tumor hypoxia (23,24).…”