Developmental expression of hexokinase 1 in the rat

Pacritinib inhibits glucose consumption in squamous cell lung cancer cells by targeting FLT3

Squamous cell lung cancer maintains its growth through elevated glucose consumption, but selective glucose consumption inhibitors are lacking. Here, we discovered using a high-throughput screen new compounds that block glucose consumption in three squamous cell lung cancer cell lines and identified 79 compounds that block glucose consumption in one or more of these cell lines. Based on its ability to block glucose consumption in all three cell lines, pacritinib, an inhibitor of FMS Related Receptor Tyrosine Kinase 3 (FLT3) and Janus Kinase 2 (JAK2), was further studied. Pacritinib decreased glucose consumption in squamous cell lung cancer cells in cell culture and in vivo without affecting glucose consumption in healthy tissues. Pacritinib blocked hexokinase activity, and Hexokinase 1 and 2 mRNA and protein expression. Overexpression of Hexokinase 1 blocked the ability of pacritinib to inhibit glucose consumption in squamous cell lung cancer cells. Overexpression of FLT3 but not JAK2 significantly increased glucose consumption and blocked the ability of pacritinib to inhibit glucose consumption in squamous cell lung cancer cells. Additional FLT3 inhibitors blocked glucose consumption in squamous cell lung cancer cells. Our study identifies FLT3 inhibitors as a new class of inhibitors that can block glucose consumption in squamous cell lung cancer.

Hexokinase domain-containing protein-1 in metabolic diseases and beyond

Glucose phosphorylation by hexokinases (HKs) traps glucose in cells and facilitates its usage in metabolic processes dependent on cellular needs. HK domain-containing protein-1 (HKDC1) is a recently discovered protein with wide expression containing HK activity, first noted through a genome-wide association study (GWAS) to be linked with gestational glucose homeostasis during pregnancy. Since then, HKDC1 has been observed to be expressed in many human tissues. Moreover, studies have shown that HKDC1 plays a role in glucose homeostasis by which it may affect the progression of many pathophysiological conditions such as gestational diabetes mellitus (GDM), nonalcoholic steatohepatitis (NASH), and cancer. Here, we review the key studies contributing to our current understanding of the roles of HKDC1 in human pathophysiological conditions and potential therapeutic interventions.

LncRNA LncHrt preserves cardiac metabolic homeostasis and heart function by modulating the LKB1-AMPK signaling pathway

Metabolic modulation is a promising therapeutic approach to prevent adverse remodeling of the ischemic heart. Because little is known about the involvement of long non-coding RNAs (lncRNAs) in regulating cardiac metabolism, we used unbiased transcriptome profiling in a mouse model of myocardial infarction (MI). We identified a novel cardiomyocyte-enriched lncRNA, called LncHrt, which regulates metabolism and the pathophysiological processes that lead to heart failure. AAV-based LncHrt overexpression protects the heart from MI as demonstrated by improved contractile function, preserved metabolic homeostasis, and attenuated maladaptive remodeling responses. RNA-pull down followed by mass spectrometry and RNA immunoprecipitation (RIP) identified SIRT2 as a LncHrt-interacting protein involved in cardiac metabolic regulation. Mechanistically, we established that LncHrt interacts with SIRT2 to preserve SIRT2 deacetylase activity by interfering with the CDK5 and SIRT2 interaction. This increases downstream LKB1-AMPK kinase signaling, which ameliorates functional and metabolic deficits. Importantly, we found the expression of the human homolog of mouse LncHrt was decreased in patients with dilated cardiomyopathy. Together, these studies identify LncHrt as a cardiac metabolic regulator that plays an essential role in preserving heart function by regulating downstream metabolic signaling pathways. Consequently, LncHrt is a potentially novel RNA-based therapeutic target for ischemic heart disease.

TMT-based proteomics analysis to screen potential biomarkers of acute-phase TBI in rats

AIMS

Traumatic brain injury (TBI) is a common nervous system injury. However, the detailed mechanisms about functional dysregulation and dignostic biomarkers post-TBI are still unclear. So we aimed to identify potential differentially expressed proteins and genes in TBI for clinical diagnosis and therapeutic purposes.

MAIN METHODS

Rat TBI model was established by the weight-drop method. First, through TMT-proteomics, we screened for the change in the proteins expression profile acute phase post-TBI. The DAVID and Reactome databases were used to analyze and visualize the dysregulation proteins. Then, using publicly available microarray datasets GSE45997, differentially expressed genes (DGEs) were identified for the 24 h post-TBI stage. Also, the proteomic data were compared with microarray data to analyze the similarity.

KEY FINDINGS

We found significant proteomics and transcriptomic changes in post-TBI samples. 989, 881, 832, 1057 proteins were quantitated at 1 h, 6 h, 24 h, and 3 d post-injury correspondingly. Concerning proteomics findings, oxygen transport, acute-phase response, and negative regulation of endopeptidase activity were influenced throughout the acute phrase of TBI. Also, pathways related to scavenging of heme from plasma, binding, and uptake of ligands by scavenger receptors were highly enriched in all time-points of TBI samples.

SIGNIFICANCE

We noticed that the interaction-networks trend to get complicated with more node connections following the progression of TBI. We inferred that Hk-1, PRKAR2A, and MBP could be novel candidate biomarkers related to time-injury in acute-phase TBI. Also, Ceruloplasmin and Complement C3 were found to be important proteins and genes are involved in the TBI.

Antidiabetic and antioxidative efficacy of the constituents present in the fraction solvents of Curcuma amada rhizomes: An experimental study on the diabetic rat model

All over the world, the prevalence of diabetes mellitus is increasing. The main goal of this experiment was to identify the most effective fraction of aqueous-methanol extract of Curcuma amada rhizome for its antidiabetic and antioxidative properties. The fractions (n-hexane or chloroform or ethyl-acetate or n-butanol) of aqueous-methanol extract were administered to the streptozotocin-induced diabetic groups at a dose of 10 mg/100 g body weight/day for 4 weeks. The antidiabetic and antioxidative efficacies of the fractions on glycemic, enzymatic, genomic, and histological sensors and pancreatic β-cells population and general toxicity were assessed. After the fraction treatment, out of the fraction used, the significant recovery in most sensors was noted at the ethyl-acetate fraction in glycemic, enzymatic, genomic, β cells population, diameter of the pancreatic islet and toxicity level. In conclusion, it may be stated that the ethyl-acetate fraction of C. amada was the most effective solvent in this study. PRACTICAL APPLICATIONS: The ethyl-acetate fraction of aqueous-methanol extract of Curcuma amada has antidiabetic property, it gives a clue to the herbal medicine manufacturing company to produce phytotherapeutic drugs to cure the complication related to diabetes.

Phytoecdysteroids from Ajuga iva act as potential antidiabetic agent against alloxan-induced diabetic male albino rats

The present study investigated the protective effect of phytoecdysteroids extracted from the Ajuga iva plant on body weight changes, blood glucose, insulin total protein, blood urea nitrogen (BUN), creatinine, triglycerides (TG), cholesterol, lipid peroxidation, antioxidant enzymes, pancreatic histopathology and hexokinase-I expression in the alloxan-induced diabetic rats. Experimental diabetes was induced following 15day intraperitoneal administration of alloxan. The rats were divided into four groups. Group I served as a sham group, and group II served as the diabetic control. Group III served as a treatment for phytoecdysteroids (10mg/kg), and group IV served as a treatment for phytoecdysteroids (20mg/kg). Phytoecdysteroids restored body weight loss to its antihyperglycemic effect. Blood glucose was reduced 19.2 and 52.9% in group III and IV respectively. Blood insulin (54.9 and 105.88%) and total protein (25 and 72.2%) was increased in group III and IV respectively. BUN, creatinine, TG, cholesterol and lipid peroxidation was significantly reduced following treatment. Catalase, superoxide dismutase (SOD), and glutathione peroxidase activity were significantly increased following treatment. Islet β-cells are lost in alloxan-induced diabetic rats. Regeneration of islets and reduced atrophy of acinar cells were noted. The number of insulin-secreting cells was tremendously reduced in alloxan-induced diabetic rats. Insulin-secreting cells were increased 48 and 61% in group III and IV respectively. Hexokinase-I mRNA (28.3 & 93.5%) and protein (27.9 and 55.3%) expression were significantly increased following treatment. Taking all these data together, it is suggested that the phytoecdysteroid could be a potential therapeutic agent against experimental diabetes.

Fatty acids in energy metabolism of the central nervous system

In this review, we analyze the current hypotheses regarding energy metabolism in the neurons and astroglia. Recently, it was shown that up to 20% of the total brain's energy is provided by mitochondrial oxidation of fatty acids. However, the existing hypotheses consider glucose, or its derivative lactate, as the only main energy substrate for the brain. Astroglia metabolically supports the neurons by providing lactate as a substrate for neuronal mitochondria. In addition, a significant amount of neuromediators, glutamate and GABA, is transported into neurons and also serves as substrates for mitochondria. Thus, neuronal mitochondria may simultaneously oxidize several substrates. Astrocytes have to replenish the pool of neuromediators by synthesis de novo, which requires large amounts of energy. In this review, we made an attempt to reconcile β-oxidation of fatty acids by astrocytic mitochondria with the existing hypothesis on regulation of aerobic glycolysis. We suggest that, under condition of neuronal excitation, both metabolic pathways may exist simultaneously. We provide experimental evidence that isolated neuronal mitochondria may oxidize palmitoyl carnitine in the presence of other mitochondrial substrates. We also suggest that variations in the brain mitochondrial metabolic phenotype may be associated with different mtDNA haplogroups.

Identification, expression and bioactivity of hexokinase in amphioxus: insights into evolution of vertebrate hexokinase genes

Hexokinase family includes hexokinases I, II, III and IV, that catalyze the phosphorylation of glucose to produce glucose 6-phosphate. Hexokinase IV, also known as glucokinase, is only half size of the other types of hexokinases that contain two hexokinase domains. Despite the enormous progress in the study of hexokinases, the evolutionary relationship between glucokinase and other hexokinases is still uncertain, and the molecular processes leading to the emergence of hexokinases in vertebrates remain controversial. Here we clearly demonstrated the presence of a single hexokinase-like gene in the amphioxus Branchiostoma japonicum, Bjhk, which shows a tissue-specific expression pattern, with the most abundant expression in the hepatic caecum, testis and ovary. The phylogenetic and synteny analyses both reveal that BjHK is the archetype of vertebrate hexokinases IV, i.e. glucokinases. We also found for the first time that recombinant BjHK showed functional enzyme activity resembling vertebrate hexokinases I, II, III and IV. In addition, a native glucokinase activity was detected in the hepatic caecum. Finally, glucokinase activity in the hepatic caecum was markedly reduced by fasting, whereas it was considerably increased by feeding. Altogether, these suggest that Bjhk represents the archetype of glucokinases, from which vertebrate hexokinase gene family was evolved by gene duplication, and that the hepatic caecum plays a role in the control of glucose homeostasis in amphioxus, in favor of the notion that the hepatic caecum is a tissue homologous to liver.

Diffusion of D-glucose measured in the cytosol of a single astrocyte

Astrocytes interact with neurons and endothelial cells and may mediate exchange of metabolites between capillaries and nerve terminals. In the present study, we investigated intracellular glucose diffusion in purified astrocytes after local glucose uptake. We used a fluorescence resonance energy transfer (FRET)-based nano sensor to monitor the time dependence of the intracellular glucose concentration at specific positions within the cell. We observed a delay in onset and kinetics in regions away from the glucose uptake compared with the region where we locally super-fused astrocytes with the D-glucose-rich solution. We propose a mathematical model of glucose diffusion in astrocytes. The analysis showed that after gradual uptake of glucose, the locally increased intracellular glucose concentration is rapidly spread throughout the cytosol with an apparent diffusion coefficient (D app) of (2.38 ± 0.41) × 10(-10) m(2) s(-1) (at 22-24 °C). Considering that the diffusion coefficient of D-glucose in water is D = 6.7 × 10(-10) m(2) s(-1) (at 24 °C), D app determined in astrocytes indicates that the cytosolic tortuosity, which hinders glucose molecules, is approximately three times higher than in aqueous solution. We conclude that the value of D app for glucose measured in purified rat astrocytes is consistent with the view that cytosolic diffusion may allow glucose and glucose metabolites to traverse from the endothelial cells at the blood-brain barrier to neurons and neighboring astrocytes.

Aspects of astrocyte energy metabolism, amino acid neurotransmitter homoeostasis and metabolic compartmentation

Astrocytes are key players in brain function; they are intimately involved in neuronal signalling processes and their metabolism is tightly coupled to that of neurons. In the present review, we will be concerned with a discussion of aspects of astrocyte metabolism, including energy-generating pathways and amino acid homoeostasis. A discussion of the impact that uptake of neurotransmitter glutamate may have on these pathways is included along with a section on metabolic compartmentation.

Glial cells in (patho)physiology

Neuroglial cells define brain homeostasis and mount defense against pathological insults. Astroglia regulate neurogenesis and development of brain circuits. In the adult brain, astrocytes enter into intimate dynamic relationship with neurons, especially at synaptic sites where they functionally form the tripartite synapse. At these sites, astrocytes regulate ion and neurotransmitter homeostasis, metabolically support neurons and monitor synaptic activity; one of the readouts of the latter manifests in astrocytic intracellular Ca(2+) signals. This form of astrocytic excitability can lead to release of chemical transmitters via Ca(2+) -dependent exocytosis. Once in the extracellular space, gliotransmitters can modulate synaptic plasticity and cause changes in behavior. Besides these physiological tasks, astrocytes are fundamental for progression and outcome of neurological diseases. In Alzheimer's disease, for example, astrocytes may contribute to the etiology of this disorder. Highly lethal glial-derived tumors use signaling trickery to coerce normal brain cells to assist tumor invasiveness. This review not only sheds new light on the brain operation in health and disease, but also points to many unknowns.

Astrocytes and energy metabolism

Astrocytes are glial cells, which play a significant role in a number of processes, including the brain energy metabolism. Their anatomical position between blood vessels and neurons make them an interface for effective glucose uptake from blood. After entering astrocytes, glucose can be involved in different metabolic pathways, e.g. in glycogen production. Glycogen in the brain is localized mainly in astrocytes and is an important energy source in hypoxic conditions and normal brain functioning. The portion of glucose metabolized into glycogen molecules in astrocytes is as high as 40%. It is thought that the release of gliotransmitters (such as glutamate, neuroactive peptides and ATP) into the extracellular space by regulated exocytosis supports a significant part of communication between astrocytes and neurons. On the other hand, neurotransmitter action on astrocytes has a significant role in brain energy metabolism. Therefore, understanding the astrocytes energy metabolism may help understanding neuron-astrocyte interactions.

Changes in cytosolic glucose level in ATP stimulated live astrocytes

Astrocytes which lie between brain capillaries and neuronal terminals are the primary site of glucose uptake and have a key role in coupling synaptic activity to glucose utilization in the central nervous system (CNS). We used a fluorescence resonance energy transfer (FRET) based approach to monitor cytosolic glucose in astrocytes. We determined the effect of increasing extracellular glucose concentrations on FRET ratio as a measure of increased cytosolic glucose in astrocytes. By briefly raising extracellular glucose concentration, astrocytes responded promptly by increased cytosolic glucose levels, which was manifested by decreased time-dependent FRET ratio. The FRET ratio fall-time recorded at low extracellular D-glucose concentration change (from 0 to 0.5 mM) was 53 s, whereas 17 s was recorded by raising extracellular concentration of D-glucose from 0 to 10 mM, which is likely due to facilitated d-glucose entry along the increased D-glucose gradient across the plasmalemma. The relationship between the extracellular glucose concentration and the FRET ratio change is limited to the maximal ratio change, where the D-glucose plasma membrane permeability is balanced by the cytosolic utilization. We measured the effect of extracellular ATP, an important extracellular messenger for astrocyte-to-astrocyte communication, on intracellular glucose concentration. The results show that stimulation of astrocytes with ATP (1 mM) decreases cytosolic glucose concentration with a time constant of ∼145 s. The mechanism of this change is discussed.

Induction of hexokinase I expression in normal and diabetic rats by a brassinosteroid isoform

This study aimed to investigate the effect of the plant growth regulator 28-homobrassinolide (HB) on the hexokinase I (HK I) enzyme gene expression in the tissues of normal and streptozotocin-induced diabetic rats. Normal and diabetic rats were administered 50 microg of HB for 15 consecutive days. The tissues level of HK I mRNA expression was quantitated by PCR and densitometry analysis, HK I protein expression was quantitated by Western blot and densitometry analysis, localization of HK I was done by immunohistochemistry and HK enzyme activity was determined by coupled enzyme assay. Subchronic treatment of rats with HB enhanced HK I enzyme expression in diabetic rat compared to the control rat. From these experimental evidences, we came to the conclusion that HK I played a vital role in the regulation of blood sugar in streptozotocin-induced diabetic rats. A direct role for hexokinase enzyme activity in the control of diabetes is presented.

Molecular evolution of the vertebrate hexokinase gene family: Identification of a conserved fifth vertebrate hexokinase gene

Hexokinases (HK) phosphorylate sugar immediately upon its entry into cells allowing these sugars to be metabolized. A total of four hexokinases have been characterized in a diversity of vertebrates-HKI, HKII, HKIII, and HKIV. HKIV is often called glucokinase (GCK) and has half the molecular weight of the other hexokinases, as it only has one hexokinase domain, while other vertebrate HKs have two. Differing hypothesis has been proposed to explain the diversification of the hexokinase gene family. We used a genomic approach to characterize hexokinase genes in a diverse array of vertebrate species and close relatives. Surprisingly we identified a fifth hexokinase-like gene, HKDC1 that exists and is expressed in diverse vertebrates. Analysis of the amino acid sequence of HKDC1 suggests that it may function as a hexokinase. To understand the evolution of the vertebrate hexokinase gene family we established a phylogeny of the hexokinase domain in all of the vertebrate hexokinase genes, as well as hexokinase genes from close relatives of the vertebrates. Our phylogeny demonstrates that duplication of the hexokinase domain, yielding a HK with two hexokinase domains, occurred prior to the diversification of the hexokinase gene family. We also establish that GCK evolved from a two hexokinase domain-containing gene, but has lost its N-terminal hexokinase domain. We also show that parallel changes in enzymatic function of HKI and HKIII have occurred.

Glucose metabolism and proliferation in glia: role of astrocytic gap junctions

Astrocytes play a well-established role in brain metabolism, being a key element in the capture of energetic compounds from the circulation and in their delivery to active neurons. Their metabolic status is affected in many pathological situations, such as gliomas, which are the most common brain tumors. This proliferative dysfunction is associated with changes in gap junctional communication, a property strongly developed in normal astrocytes studied both in vitro and in vivo. Here, we summarize and discuss the findings that have lead to the identification of a link between gap junctions, glucose uptake, and proliferation. Indeed, the inhibition of gap junctional communication is associated with an increase in glucose uptake due to a rapid change in the localization of both GLUT-1 and type I hexokinase. This effect persists due to the up-regulation of GLUT-1 and type I hexokinase and to the induction of GLUT-3 and type II hexokinase. In addition, cyclins D1 and D3 have been found to act as sensors of the inhibition of gap junctions and have been proposed to play the role of mediators in the mitogenic effect observed. Conversely, in C6 glioma cells, characterized by a low level of intercellular communication, an increase in gap junctional communication reduces glucose uptake by releasing type I and type II hexokinases from the mitochondria and decreases the exacerbated rate of proliferation due to the up-regulation of the Cdk inhibitors p21 and p27. Identification of the molecular actors involved in these pathways should allow the determination of potential therapeutic targets that could lead to the testing of alternative strategies to prevent, or at least slow down, the proliferation of glioma cells.

Endothelin-1 stimulates the translocation and upregulation of both glucose transporter and hexokinase in astrocytes: relationship with gap junctional communication

We have previously shown that endothelin-1 increases glucose uptake in astrocytes. In the present work we investigate the mechanism through which endothelin-1 (ET-1) increases glucose uptake. Our results show that ET-1 activates a short-term and a long-term mechanism. Thus, ET-1 induced a rapid change in the localization of both GLUT-1 and type I hexokinase. These changes are probably aimed at rapidly increasing the entry and phosphorylation of glucose. In addition, ET-1 upregulated GLUT-1 and type I hexokinase and induced the expression of isoforms not normally expressed in astrocytes, such as GLUT-3 and type II hexokinase. These changes provide astrocytes with the machinery required to sustain a high rate of glucose uptake for a longer period of time. Our previous work had suggested that the effect of ET-1 on glucose uptake was associated with the inhibition of gap junctions. In this work, we compare the effect of ET-1 with that of carbenoxolone, a classical inhibitor of gap junction communication. Carbenoxolone increased glucose uptake to the same extent as ET-1 following the same mechanisms. Thus, carbenoxolone induced a rapid change in the localization of both GLUT-1 and type I hexokinase, upregulated GLUT-1 and type I hexokinase and induced the expression of GLUT-3 and type II hexokinase. When the inhibition of gap junction was prevented by tolbutamide, neither ET-1 nor carbenoxolone were able to increase the levels of GLUT-1, GLUT-3, type I hexokinase or type II hexokinase, indicating that these events are closely related to gap junctions.

Glucose transporters, hexokinase, and phosphofructokinase in brain of rats with perinatal asphyxia

Transport by glucose transporters from blood to the brain during hypoxic-ischemic conditions is well studied. However, the recent availability of a clinically related animal model of perinatal asphyxia and the fact that no concomitant determination of glucose transporters, parameters for glucose utilization, brain glucose, and cerebral blood flow (CBF) have been reported and the early phase of perinatal asphyxia has never been studied led us to perform the following study. Cesarean section was performed on full-term pregnant rats. The obtained pups within patent uterus horns were placed into a water bath at 37 degrees C from which they were subsequently removed after 5-20 min of graded asphyxia. Brain pH, brain tissue glucose, CBF, mRNA and activity of hexokinase and phosphofructokinase, and mRNA and protein of the glucose transporters GLUTI and GLUT3 were determined. Brain pH decreased and brain tissue glucose and CBF increased with the length of the asphyctic period; hexokinase and phosphofructokinase mRNA and activity were unchanged during the observation period. The mRNA and protein of both glucose transporters were comparable between normoxic and asphyctic groups. We show that glucose transport and utilization are unchanged in the early phase of perinatal asphyxia at a time point when CBF and brain glucose are already significantly increased and severe acidosis is present.

Hexokinase II-deficient mice. Prenatal death of homozygotes without disturbances in glucose tolerance in heterozygotes

Type 2 diabetes is characterized by decreased rates of insulin-stimulated glucose uptake and utilization, reduced hexokinase II mRNA and enzyme production, and low basal levels of glucose 6-phosphate in insulin-sensitive skeletal muscle and adipose tissues. Hexokinase II is primarily expressed in muscle and adipose tissues where it catalyzes the phosphorylation of glucose to glucose 6-phosphate, a possible rate-limiting step for glucose disposal. To investigate the role of hexokinase II in insulin action and in glucose homeostasis as well as in mouse development, we generated a hexokinase II knock-out mouse. Mice homozygous for hexokinase II deficiency (HKII(-/-)) died at approximately 7.5 days post-fertilization, indicating that hexokinase II is vital for mouse embryogenesis after implantation and before organogenesis. HKII(+/-) mice were viable, fertile, and grew normally. Surprisingly, even though HKII(+/-) mice had significantly reduced (by 50%) hexokinase II mRNA and activity levels in skeletal muscle, heart, and adipose tissue, they did not exhibit impaired insulin action or glucose tolerance even when challenged with a high-fat diet.

Differences in expression and intracellular distribution of hexokinase isoenzymes in rat liver cells of different transformation stages

The activity, intracellular distribution and mRNA expression of hexokinase isoenzymes were studied in normal rat liver, and in epithelial liver cells at different stages of neoplastic transformation, including non-tumorigenic and tumorigenic cell lines. In contrast to liver, all transformed cells exhibited only hexokinase I and II, which both showed significantly increased activity, hexokinase II being the more abundant form. In parallel, the mRNA expression of the two isoenzymes was elevated, indicating transcriptional control of gene expression. Hexokinase I and II were found in the cytosol and bound to mitochondrial membranes; the percentage of membrane-bound enzyme activity increased with the grade of transformation from 32% of total activity in normal liver up to 69% in dedifferentiated tumor cells. The ratio of hexokinase I/II was higher in the membrane fraction than in the cytosol. In all tissues studied hexokinase II could be resolved in two subtypes IIa and IIb by hydrophobic interaction chromatography. The relative proportion of cytosolic IIa and IIb varied significantly between normal liver (1:1) and transformed cells, and among cells of different transformation stages (4:1 to 1:10). IIa demonstrated the main activity in the more differentiated, IIb in the less differentiated cell lines. IIa-activity showed a good correlation with the intracellular glucose 6-phosphate concentration of the cells. The data indicate that neoplastic cell transformation is accompanied by progressive alterations in the proportion and subcellular distribution of hexokinase isoenzymes I and II.

Microheterogeneity of cytosolic and membrane-bound hexokinase II in Morris hepatoma 3924A

Phosphorylation of glucose by hexokinase is the key step in glucose and energy metabolism of the cell. In the Morris hepatoma 3924A, hexokinase II is the predominant hexokinase isoenzyme and occurs in the cytosol as well as bound to membranes. Hexokinase II was isolated by DEAE-cellulose chromatography from both the cytosolic and the mitochondria-enriched fractions and further resolved by hydrophobic-interaction chromatography on phenyl-Sepharose into two components designated hexokinase IIa and IIb. In both the soluble and the mitochondria-enriched fractions, type IIb was the predominant form, but the IIb/IIa ratio was higher in the particulate (6-8) as compared with the cytosolic fraction (1.5-2.0). Binding of the isolated forms of the enzyme to rat liver mitochondria resulted in a 2-10-fold activation of both subtypes. Biochemical characterization showed that both subtypes are closely related to the isoenzyme commonly referred to as hexokinase II, and that the microheterogeneity was not a consequence of contamination with hexokinase I or III. Both subtypes had a molecular mass of 110 kDa, they were inhibited by Pi at concentrations higher than 5 mM, and activated by the detergent CHAPS. The two subtypes differed in electrophoretic mobility (IIa > IIb), in Km values for glucose (IIa, 0.109 mM; IIb, 0.216 mM), in Ki values for glucose 6-phosphate (IIa, 25 microM; IIb, 0.106 mM), and in Ki values for glucose 1,6-biphosphate (IIa, 12.2 microM; IIb, 5.5 microM). An artificial proteolytic cleavage as cause of the hexokinase II microheterogeneity can be excluded, since both subtypes show the same molecular mass and the ability to bind to mitochondria and phenyl-Sepharose. In addition, the relative proportions of the two subtypes did not vary markedly between several enzyme preparations. Northern-blot analysis with a hexokinase II-specific cDNA probe revealed two distinct mRNA transcripts of 5.2 and 6.3 kb in length, which offers the possibility that hexokinase II microheterogeneity is due to differential RNA transcription and/or processing.

Development and regulation of glucose transporter and hexokinase expression in rat

The ontogenesis of the glucose transporters GLUT-1, GLUT-2, and GLUT-4 and the hexokinases HK-I, HK-II, and HK-IV (glucokinase) was studied in rat tissues. In brown adipose tissue, high levels of GLUT-4 and HK-II were observed during fetal life; both decreased at birth and then increased throughout development. At birth, cold exposure increased GLUT-4 and HK-II expression in brown adipose tissue, whereas fasting decreased it. GLUT-1 and HK-I were present in fetal muscle, but GLUT-4 and HK-II were absent. The coordinate appearance of GLUT-4 and HK-II in skeletal muscle was concomitant with the acquisition of insulin sensitivity after weaning. In the heart, the glucose transporter isoform switched from GLUT-1 to GLUT-4 during the suckling period. The coordinate expression of GLUT-4 and HK-II in heart was observed after weaning. GLUT-2, detected in fetal liver, increased throughout development. GLUT-1 and HK-I were detectable in fetal liver, whereas glucokinase appeared after weaning. Consumption of a high-carbohydrate diet after weaning increased GLUT-4 and HK-II in muscle and GLUT-2 in liver, whereas consumption of a high-fat diet prevented these changes. These results showed that 1) GLUT-1 and HK-I are abundant in most fetal rat tissues, 2) GLUT-4 and HK-II expression is associated with the appearance of tissue insulin sensitivity, and 3) GLUT-2 is expressed early in liver, before the appearance of glucokinase.

Analysis of pyruvate dehydrogenase expression in embryonic mouse brain: localization and developmental regulation

Brain malformations and neurological dysfunctions are often seen in pyruvate dehydrogenase (PDH) deficient patients. To understand these clinical presentations, we have analyzed the localization and developmental expression of PDH in the embryonic mouse nervous system. Immunostaining was performed to localize PDH E1 alpha protein. PDH activities were measured before and after activation. PDH E1 alpha mRNA levels were quantitated by reverse transcriptase-polymerase chain reaction. Abundant PDH E1 alpha protein was localized in the central nervous system and other neural tissues in embryos at embryonic day (E) 11 onwards. The PDH activity was very low in E9 brain and it increased continuously until the end of gestation. The proportion of active form of PDH increased significantly in E15 brain. Analysis of the PDH E1 alpha mRNA showed that only the X-linked form of the gene was transcribed. The overall mRNA level of E9 brain was approximately 93% of the adult value. It decreased gradually during embryogenesis. A large increase took place at the end of gestation. The mRNA level of PDH was approximately 100 times higher than that of the acetoacetyl-CoA thiolase gene. These results suggest that PDH E1 alpha transcripts of E9 brain are not translated at a high level. The appearance of PDH activity and its increase during E11 and E15 are mainly due to increased levels of translation and activation of PDH. Increased PDH activity at the end of gestation is attributed to an increase in transcription. Our data to a large extent explain pathological presentations in PDH E1 alpha deficient patients with congenital brain disorders.

Characterization of human genomic yeast artificial chromosome inserts containing hexokinase 1 coding information on chromosome 10

Hexokinase 1 (HK1) is one of four mammalian HK isoenzymes and maps to human chromosome 10. Two yeast artificial chromosomes (YACs) were identified in the Washington University human YAC library using polymerase chain reaction (PCR) primers designed with knowledge of the human HK1 cDNA sequence. YAC B129B12 is 120 kb in length and maps entirely to chromosome 10. YAC A159D5 is 400 kb in length and appears to have resulted from a recombination of chromosome 10 with non-chromosome 10 material. We report these YACs as potential resources for those interested in HK1 gene organization and mapping, as well as those desiring additional genomic information and markers on chromosome 10.