Reversion of transformed glycolysis to normal by inhibition of protein synthesis in rat kidney cells infected with temperature-sensitive mutant of Rous sarcoma virus

HIF-1 mediates metabolic responses to intratumoral hypoxia and oncogenic mutations

Hypoxia occurs frequently in human cancers and induces adaptive changes in cell metabolism that include a switch from oxidative phosphorylation to glycolysis, increased glycogen synthesis, and a switch from glucose to glutamine as the major substrate for fatty acid synthesis. This broad metabolic reprogramming is coordinated at the transcriptional level by HIF-1, which functions as a master regulator to balance oxygen supply and demand. HIF-1 is also activated in cancer cells by tumor suppressor (e.g., VHL) loss of function and oncogene gain of function (leading to PI3K/AKT/mTOR activity) and mediates metabolic alterations that drive cancer progression and resistance to therapy. Inhibitors of HIF-1 or metabolic enzymes may impair the metabolic flexibility of cancer cells and make them more sensitive to anticancer drugs.

Emerging roles of PKM2 in cell metabolism and cancer progression

Increased conversion of glucose to lactate is a key feature of many cancer cells that promotes rapid growth. Pyruvate kinase M2 (PKM2) expression is increased and facilitates lactate production in cancer cells. Modulation of PKM2 catalytic activity also regulates the synthesis of DNA and lipids that are required for cell proliferation, and of NADPH that is required for redox homeostasis. In addition to its role as a pyruvate kinase, PKM2 also functions as a protein kinase and as a transcriptional coactivator. These biochemical activities are controlled by allosteric regulators and post-translational modifications of PKM2 that include acetylation, oxidation, phosphorylation, prolyl hydroxylation, and sumoylation. Given its pleiotropic effects on cancer biology, PKM2 represents an attractive target for cancer therapy.

Peroxisome proliferator-activated receptor γ (PPARγ) mediates a Ski oncogene-induced shift from glycolysis to oxidative energy metabolism

Overexpression of the Ski oncogene induces oncogenic transformation of chicken embryo fibroblasts (CEFs). However, unlike most other oncogene-transformed cells, Ski-transformed CEFs (Ski-CEFs) do not display the classical Warburg effect. On the contrary, Ski transformation reduced lactate production and glucose utilization in CEFs. Compared with CEFs, Ski-CEFs exhibited enhanced TCA cycle activity, fatty acid catabolism through β-oxidation, glutamate oxidation, oxygen consumption, as well as increased numbers and mass of mitochondria. Interestingly, expression of PPARγ, a key transcription factor that regulates adipogenesis and lipid metabolism, was dramatically elevated at both the mRNA and protein levels in Ski-CEFs. Accordingly, PPARγ target genes that are involved in lipid uptake, transport, and oxidation were also markedly up-regulated by Ski. Knocking down PPARγ in Ski-CEFs by RNA interference reversed the elevated expression of these PPARγ target genes, as well as the shift to oxidative metabolism and the increased mitochondrial biogenesis. Moreover, we found that Ski co-immunoprecipitates with PPARγ and co-activates PPARγ-driven transcription.

Metabolic-flux analysis of hybridoma cells under oxidative and reductive stress using mass balances

Hybridoma cells were grown at steady state under both reductiveand oxidative stress and the intracellular fluxes weredetermined by mass-balancing techniques. By decreasing the dissolved oxygen pressure (pO(2)) in the bioreactor, the reduced formof nicotinamide adenine nucleotide (NADH) was enhanced relativeto the oxidized form (NAD(+)). Oxidative stress, as a resultof which the NAP(P)(+)/NAD(P)H-ratio increases, was generatedby both the enhancement of the pO(2) to 100% air saturationand by the addition of the artificial electron acceptorphenazine methosulphate (PMS) to the culture medium. It wasfound that fluxes of dehydrogenase reactions by which NAD(P)H isproduced decreased under hypoxic conditions. For example, thedegradation rates of arginine, isoleucine, lysine and theglutamate dehydrogenase flux were significantly lower at oxygenlimitation, and increased at higher pO(2) levels and when PMSwas added to the culture medium. In contrast, the prolinesynthesis reaction, which requires NADPH, decreased under PMSstress. The flux of the NADH-requiring lactate dehydrogenase reaction also strongly decreased from 19 to 3,4 pmol/cell/day,under oxygen limitation and under PMS stress, respectively. Thedata show that metabolic-flux balancing can be used to determinehow mammalian respond to oxidative and reduction stress.

HIF-1 mediates the Warburg effect in clear cell renal carcinoma

Hypoxia-inducible factor 1 (HIF-1) is a transcription factor that functions as a master regulator of oxygen homeostasis in all metazoan species. O(2)-dependent hydroxylation of two proline residues in the HIF-1alpha subunit is necessary for the binding of the von Hippel-Lindau (VHL) protein, which is a component of a ubiquitin protein ligase that ubiquitinates HIF-1alpha, leading to its degradation by the proteasome. In the majority of cases of the clear cell type of renal carcinoma, both VHL genes are inactivated by mutation or epigenetic silencing, leading to dysregulated HIF-1 transcriptional activity. VHL loss-of-function leads, under aerobic conditions, to a HIF-1-dependent reprogramming of glucose and energy metabolism that includes increased glucose uptake, glycolysis, and lactate production accompanied by a reciprocal decrease in respiration. These findings delineate for the first time the molecular mechanisms underlying the Warburg effect in a human cancer.

HIF-1 inhibits mitochondrial biogenesis and cellular respiration in VHL-deficient renal cell carcinoma by repression of C-MYC activity

Many cancer cells are characterized by increased glycolysis and decreased respiration, even under aerobic conditions. The molecular mechanisms underlying this metabolic reprogramming are unclear. Here we show that hypoxia-inducible factor 1 (HIF-1) negatively regulates mitochondrial biogenesis and O(2) consumption in renal carcinoma cells lacking the von Hippel-Lindau tumor suppressor (VHL). HIF-1 mediates these effects by inhibiting C-MYC activity via two mechanisms. First, HIF-1 binds to and activates transcription of the MXI1 gene, which encodes a repressor of C-MYC transcriptional activity. Second, HIF-1 promotes MXI-1-independent, proteasome-dependent degradation of C-MYC. We demonstrate that transcription of the gene encoding the coactivator PGC-1beta is C-MYC dependent and that loss of PGC-1beta expression is a major factor contributing to reduced respiration in VHL-deficient renal carcinoma cells.

Efficient RNase H-directed cleavage of RNA promoted by antisense DNA or 2'F-ANA constructs containing acyclic nucleotide inserts

The ability of modified antisense oligonucleotides (AONs) containing acyclic interresidue units to support RNase H-promoted cleavage of complementary RNA is described. Manipulation of the backbone and sugar geometries in these conformationally labile monomers shows great benefits in the enzymatic recognition of the nucleic acid hybrids, while highlighting the importance of local strand conformation on the hydrolytic efficiency of the enzyme more conclusively. Our results demonstrate that the duplexes support remarkably high levels of enzymatic degradation when treated with human RNase HII, making them efficient mimics of the native substrates. Furthermore, interesting linker-dependent modulation of enzymatic activity is observed during in vitro assays, suggesting a potential role for this AON class in an RNase H-dependent pathway of controlling RNA expression. Additionally, the butyl-modified 2'F-ANA AONs described in this work constitute the first examples of a nucleic acid species capable of eliciting high RNase H activity while possessing a highly flexible molecular architecture at predetermined sites along the AON.

Activated pp60c-Src leads to elevated hypoxia-inducible factor (HIF)-1alpha expression under normoxia

Hypoxia-inducible factor (HIF)-1 is a master transcription factor, which up-regulates glycolysis, erythropoiesis, and angiogenesis under hypoxia. HIF-1alpha accumulates in normoxic tumor cells, leading to glycolysis under aerobic conditions. This phenomenon, known as the "Warburg effect," is caused by a yet unknown mechanism. Here we show that transformed cells that express constitutively active pp60(c-Src) (Src) express HIF-1alpha protein under normoxia, which results in the expression of multiple HIF-1alpha target genes. We show that this occurrence is due to an enhanced rate of HIF-1alpha protein synthesis and not due to reduced HIF-1alpha degradation. Furthermore, we show that the Src-induced increase in protein synthesis is due to the global increase in the rate of cap-dependent translation and does not involve inhibition of HIF-1alpha degradation.

Hypoxia, clonal selection, and the role of HIF-1 in tumor progression

Tumor progression occurs as a result of the clonal selection of cells in which somatic mutations have activated oncogenes or inactivated tumor suppressor genes leading to increased proliferation and/or survival within the hypoxic tumor microenvironment. Hypoxia-inducible factor 1 (HIF-1) is a transcription factor that mediates adaptive responses to reduced O2 availability, including angiogenesis and glycolysis. Expression of the O2-regulated HIF-1alpha subunit and HIF-1 transcriptional activity are increased dramatically in hypoxic cells. Recent studies indicate that many common tumor-specific genetic alterations also lead to increased HIF-1alpha expression and/or activity. Thus, genetic and physiologic alterations within tumors act synergistically to increase HIF-1 transcriptional activity, which appears to play a critical role in the development of invasive and metastatic properties that define the lethal cancer phenotype.

Regulation of mammalian O2 homeostasis by hypoxia-inducible factor 1

Hypoxia-inducible factor 1 (HIF-1) is a heterodimeric basic-helix-loop-helix-PAS transcription factor consisting of HIF-1 alpha and HIF-1 beta subunits. HIF-1 alpha expression and HIF-1 transcriptional activity increase exponentially as cellular O2 concentration is decreased. Several dozen target genes that are transactivated by HIF-1 have been identified, including those encoding erythropoietin, glucose transporters, glycolytic enzymes, and vascular endothelial growth factor. The products of these genes either increase O2 delivery or allow metabolic adaptation to reduced O2 availability. HIF-1 is required for cardiac and vascular development and embryonic survival. In fetal and postnatal life, HIF-1 is required for a variety of physiological responses to chronic hypoxia. HIF-1 expression is increased in tumor cells by multiple mechanisms and may mediate adaptation to hypoxia that is critical for tumor progression. HIF-1 thus appears to function as a master regulator of O2 homeostasis that plays essential roles in cellular and systemic physiology, development, and pathophysiology.

Cellular and developmental control of O2 homeostasis by hypoxia-inducible factor 1 alpha

Hypoxia is an essential developmental and physiological stimulus that plays a key role in the pathophysiology of cancer, heart attack, stroke, and other major causes of mortality. Hypoxia-inducible factor 1 (HIF-1) is the only known mammalian transcription factor expressed uniquely in response to physiologically relevant levels of hypoxia. We now report that in Hif1a-/- embryonic stem cells that did not express the O2-regulated HIF-1alpha subunit, levels of mRNAs encoding glucose transporters and glycolytic enzymes were reduced, and cellular proliferation was impaired. Vascular endothelial growth factor mRNA expression was also markedly decreased in hypoxic Hif1a-/- embryonic stem cells and cystic embryoid bodies. Complete deficiency of HIF-1alpha resulted in developmental arrest and lethality by E11 of Hif1a-/- embryos that manifested neural tube defects, cardiovascular malformations, and marked cell death within the cephalic mesenchyme. In Hif1a+/+ embryos, HIF-1alpha expression increased between E8.5 and E9.5, coincident with the onset of developmental defects and cell death in Hif1a-/- embryos. These results demonstrate that HIF-1alpha is a master regulator of cellular and developmental O2 homeostasis.

A cis-acting element in Rous sarcoma virus long terminal repeat required for promoter repression by HeLa nuclear protein p21

HeLa cell basic nuclear protein (p21), which represses Rous sarcoma virus long terminal repeat (RSV LTR) promoter activity, diminished v-src expression and the appearance at permissive temperature of the transformed phenotype in tsRSVLA23 Rat-1, a cell line transformed with a temperature-sensitive mutant of RSV. Nuclear run-on analyses using COS-1 cells cotransfected with p21 cDNA and chloramphenicol acetyltransferase reporter indicated that p21 inhibits transcription initiation by targeting a region in the RSV LTR promoter between positions -108 and -85 upstream of the cap site. Insertion of this 24-base pair sequence in place of one of the 72-base pair enhancers in the SV40 early promoter rendered it sensitive to p21 repression. Electrophoretic mobility shift assays using a synthetic oligomer corresponding to the 24-base pair LTR promoter element revealed that p21 altered the pattern of protein.DNA complex formation apparently without binding DNA directly. Complex formation assayed by UV cross-linking and DNA affinity chromatography indicated further that a cellular factor which can interact with this element was decreased in cells transfected with p21 expression plasmid. The results indicate that p21 repression of RSV LTR is mediated by a cis-acting element and may occur by alteration of protein complexes formed on this promoter element.

A qualitative and quantitative protein database approach identifies individual and groups of functionally related proteins that are differentially regulated in simian virus 40 (SV40) transformed human keratinocytes: an overview of the functional changes associated with the transformed phenotype

A qualitative and quantitative two-dimensional (2-D) gel database approach has been used to identify individual and groups of proteins that are differentially regulated in simian virus 40 (SV40) transformed human keratinocytes (K14). Five hundred and sixty [35S]methionine-labeled proteins (462 isoelectric focusing, IEF; 98 nonequilibrium pH gradient electrophoresis, NEPHGE), out of the 3038 recorded in the master keratinocyte database, were excised from dry, silver-stained gels of normal proliferating primary keratinocytes and K14 cells and the radioactivity was determined by liquid scintillation counting. Two hundred and thirty five proteins were found to be either up- (177) or down-regulated (58) in the transformed cells by 50% or more, and of these, 115 corresponded to known proteins in the keratinocyte database (J.E. Celis et al., Electrophoresis 1993, 14, 1091-1198). The lowest abundance acidic protein quantitated was present in about 60,000 molecules per cell, assuming a value of 10(8) molecules per cell for total actin. The results identified individual, and groups of functionally related proteins that are differentially regulated in K14 keratinocytes and that play a role in a variety of cellular activities that include general metabolism, the cytoskeleton, DNA replication and cell proliferation, transcription and translation, protein folding, assembly, repair and turnover, membrane traffic, signal transduction, and differentiation. In addition, the results revealed several transformation sensitive proteins of unknown identity in the database as well as known proteins of yet undefined functions. Within the latter group, members of the S100 protein family--whose genes are clustered on human chromosome 1q21--were among the highest down-regulated proteins in K14 keratinocytes. Visual inspection of films exposed for different periods of time revealed only one new protein in the transformed K14 keratinocytes and this corresponded to keratin 18, a cytokeratin expressed mainly by simple epithelia. Besides providing with the first global overview of the functional changes associated with the transformed phenotype of human keratinocytes, the data strengthened previous evidence indicating that transformation results in the abnormal expression of normal genes rather than in the expression of new ones.

Steady-state physiological variations across a graded series of Na,K-ATPase-amplified cells

Measurements of internal ion concentrations, amino acid pools, and membrane potential were made across a series of HeLa subclones which are amplified for the genes for the sodium- and potassium-activated ATPase (Na,K-ATPase). These subclones expressed heterogeneous levels of ouabain-binding sites, allowing us to construct a graded amplification series. While [K+]i levels did not vary systematically across the series studied, [Na+]i ranged from 9 to 20 mM as a function of Na,K-ATPase expression. Steady-state accumulation of tetraphenylphosphonium in low versus high potassium was used to measure membrane potential. Values for [Na+]i and the membrane potential were used to calculate the sodium electrochemical potential, which was also found to be a function of Na,K-ATPase expression. Measurements of acid-soluble amino acid pools in cell lysates demonstrated that amino acids which are substrates for sodium-dependent transport systems, or which can potentially exchange through system L for a substrate of a sodium-dependent system, varied as a function of the sodium electrochemical potential. This confirmed our prediction of increased amino acid pool sizes in Na,K-ATPase-amplified lines based on observations of elevated flux through the sodium-independent system L. Finally, we measured lactate production and glycolytic potential in a subset of clones and found that both were reduced in subclones with elevated Na,K-ATPase.

Steady-state physiological variations across a graded series of Na,K-ATPase-amplified cells

Measurements of internal ion concentrations, amino acid pools, and membrane potential were made across a series of HeLa subclones which are amplified for the genes for the sodium- and potassium-activated ATPase (Na,K-ATPase). These subclones expressed heterogeneous levels of ouabain-binding sites, allowing us to construct a graded amplification series. While [K+]i levels did not vary systematically across the series studied, [Na+]i ranged from 9 to 20 mM as a function of Na,K-ATPase expression. Steady-state accumulation of tetraphenylphosphonium in low versus high potassium was used to measure membrane potential. Values for [Na+]i and the membrane potential were used to calculate the sodium electrochemical potential, which was also found to be a function of Na,K-ATPase expression. Measurements of acid-soluble amino acid pools in cell lysates demonstrated that amino acids which are substrates for sodium-dependent transport systems, or which can potentially exchange through system L for a substrate of a sodium-dependent system, varied as a function of the sodium electrochemical potential. This confirmed our prediction of increased amino acid pool sizes in Na,K-ATPase-amplified lines based on observations of elevated flux through the sodium-independent system L. Finally, we measured lactate production and glycolytic potential in a subset of clones and found that both were reduced in subclones with elevated Na,K-ATPase.

Pyruvate kinase type M2 is phosphorylated at tyrosine residues in cells transformed by Rous sarcoma virus

Chicken embryo cells (CECs) contain pyruvate kinase (PK) type M2 (M2-PK). Transformation of CECs by Rous sarcoma virus (RSV) leads to a reduction in the affinity of PK for the substrate phosphoenolpyruvate. In vitro, M2-PK can be phosphorylated at tyrosine residues by pp60v-src, the transforming protein of RSV. To study tyrosine phosphorylation of M2-PK in intact RSV-transformed cells, the protein was immunoprecipitated from 32P-labeled normal and RSV-SR-A-transformed CECs. Phosphoamino acid analysis of immunoprecipitated M2-PK revealed that M2-PK of both normal and transformed CECs contained phosphoserine and small amounts of phosphothreonine. Only M2-PK of transformed CECs contained phosphotyrosine in addition. For enzyme kinetic studies M2-PK was partially purified by chromatography upon DEAE-Sephacel and hydroxyapatite. A decreased affinity for phosphoenolpyruvate was observed 3 h after the onset of transformation using the temperature-sensitive mutant of RSV, ts-NY 68. The kinetic changes were correlated with tyrosine phosphorylation of M2-PK, but there is no direct evidence that they are caused by post-translational modification of the enzyme.

Transcription of proto-oncogenes in Rous sarcoma virus infected and transformed chicken embryo cells

To evaluate an effect of infection by RSV on the transcriptional activity of proto-oncogenes, we tested 19 cellular oncogenes and the beta-actin gene performing "nuclear run on transcription assays" using nuclei isolated from RSV infected or transformed chick embryo cells (CEC). A drastic increase in the transcriptional activity of the c-fgr proto-oncogene and a slight increase of c-fos and c-myc could be observed in uninfected compared to RSV infected CEC. To distinguish between infection- and transformation-dependent alterations we used the transformation-defective temperature-sensitive RSV mutant strain NY 68. Ts NY 68 infected CEC maintained at the permissive temperature of 36 degrees C and exhibiting a transformed phenotype, displayed no significant differences in the transcriptional activity of the 19 proto-oncogenes when compared to ts NY 68 infected CEC maintained at the nonpermissive temperature of 42 degrees C and exhibiting a normal phenotype. We conclude that the alterations observed were caused by the viral infection and are not due to the process of transformation. No significant changes in the transcription rate of the investigated genes could be observed after shifting ts NY 68 infected CEC from 42 degrees C to 36 degrees C. In contrast, a shift of ts NY 68 infected CEC from 36 degrees C to 42 degrees C results, after 2 hours, in a transient increase of the c-fos transcription.

Induction of mitochondrial mutations in human cells by methotrexate

Inhibition of dihydrofolate reductase by the folate analog, methotrexate (MTX) results in a depletion of tetrahydrofolate dependent one carbon transfer reactions in amino acid and nucleic acid biosynthesis. When human cells (either HeLa or normal skin fibroblasts) are exposed to MTX in a defined medium containing dialyzed fetal calf serum, essential and non-essential amino acids, and purine source, the thymidylate pools alone are depleted. Under these conditions exposure to 10(-6) M MTX induces mitochondrial mutagenesis, measured as an increase in the frequency of chloramphenicol resistant (CAPR) colonies, without altering the rate of nuclear mutation monitored by determining the frequency of 6-thioguanine resistance (TGr). The occurrence of CAPR mutations is time, and MTX concentration dependent and the frequency of CAPR can be decreased quantitatively by adding thymidine to the culture medium. This mitochondrial specific mutagenesis can also be achieved using the thymidylate synthetase inhibitor, 5-fluorodeoxyuridine further implicating thymidylate pools as the mediator of this effect. During the course of exposure to 10(-6) M MTX the thymidine kinase deficient HeLa BU25 cell line exhibits a progressive depletion and degradation of mitochondrial DNA suggesting that the mutagenesis and DNA degradation represent portions of a progressive process. The basis for the selective sensitivity of the mitochondrial genome to thymidylate depletion mutagenesis may be the consequence of its differences from the nuclear genome in mechanisms of DNA replication or repair.

The response of chicken embryo dermal fibroblasts to cytochalasin B is altered by Rous sarcoma virus-induced cell transformation

The drug cytochalasin B (CB), which disrupts the cellular microfilament network, allows the identification of as yet unclassified structural differences between normal and Rous sarcoma virus-transformed chicken embryo fibroblasts. When exposed to CB, normal chick fibroblasts attain an arborized or dendritic morphology. This results as the cytoplasm collapses upon the remaining structural and adhesive components of the cell. Rous sarcoma virus-transformed cells did not form or maintain these dendritic-like processes in the presence of CB and, as a result, rounded up but still remained attached to the substrate. With a temperature-sensitive mutant of Rous sarcoma virus, LA24A, it was possible to show that these effects are completely reversible and dependent on the expression of pp60src. The cytoskeleton in these CB-treated cells was examined by both immunofluorescence and electron microscopy. After exposure to CB, the microfilaments were found to be disrupted similarly throughout both the transformed and the nontransformed cells. In the nontransformed cells arborized by exposure to CB, the extended processes were found to contain intermediate filaments in an unusually high concentration and degree of organization. The distribution of these filaments in the central body of the arborized cells was random. This lower concentration and random distribution was similar to that seen throughout the transformed cells rounded up by exposure to CB. The failure of these transformed cells to arborize in CB indicates that the structural component(s) which is necessary for the formation or maintenance or both of the arborized state is altered by the expression of pp60src.

The response of chicken embryo dermal fibroblasts to cytochalasin B is altered by Rous sarcoma virus-induced cell transformation

The drug cytochalasin B (CB), which disrupts the cellular microfilament network, allows the identification of as yet unclassified structural differences between normal and Rous sarcoma virus-transformed chicken embryo fibroblasts. When exposed to CB, normal chick fibroblasts attain an arborized or dendritic morphology. This results as the cytoplasm collapses upon the remaining structural and adhesive components of the cell. Rous sarcoma virus-transformed cells did not form or maintain these dendritic-like processes in the presence of CB and, as a result, rounded up but still remained attached to the substrate. With a temperature-sensitive mutant of Rous sarcoma virus, LA24A, it was possible to show that these effects are completely reversible and dependent on the expression of pp60src. The cytoskeleton in these CB-treated cells was examined by both immunofluorescence and electron microscopy. After exposure to CB, the microfilaments were found to be disrupted similarly throughout both the transformed and the nontransformed cells. In the nontransformed cells arborized by exposure to CB, the extended processes were found to contain intermediate filaments in an unusually high concentration and degree of organization. The distribution of these filaments in the central body of the arborized cells was random. This lower concentration and random distribution was similar to that seen throughout the transformed cells rounded up by exposure to CB. The failure of these transformed cells to arborize in CB indicates that the structural component(s) which is necessary for the formation or maintenance or both of the arborized state is altered by the expression of pp60src.

Relationship between increased aerobic glycolysis and DNA synthesis initiation studied using glycolytic mutant fibroblasts

Reports from several laboratories have suggested increased rates of glycolysis play an essential part in the initiation of DNA synthesis. This is based on observations that aerobic glycolysis: (1) occurs at low rate in resting mammalian cells and at very high rate in tumour cells; (2) increases rapidly after DNA synthesis is initiated by addition of serum or purified growth factors, and (3) correlates with the expression of the transformed phenotype. Also, specific inhibitors of aerobic glycolysis prevent the initiation of DNA synthesis. To determine whether the rapid activation of phosphofructokinase--and therefore glycolysis--by purified growth factors is necessary for the initiation of cell proliferation, we have isolated and studied two classes of glycolytic mutants. The first, isolated from Chinese hamster fibroblasts, has a total block in the glycolytic pathway. The second, from hamster and Fisher rat fibroblasts maintains a permanent high rate of glycolysis. We have found that both classes of mutants retain normal control of DNA synthesis in response to serum. This dissociation indicates that growth-factor-stimulated glycolysis is not involved in the control of initiation of DNA synthesis and cell proliferation.

Isolation of a Chinese hamster fibroblast mutant defective in hexose transport and aerobic glycolysis: its use to dissect the malignant phenotype

A procedure is described for the selection of glucose uptake mutants based upon radiation suicide of Chinese hamster fibroblasts by 2-deoxy[3H]glucose. In one of these mutants, DS 7, the ability to transport either 2-deoxyglucose or 3-O-methylglucose was decreased to one-fifth to one-fourth. Besides this defect, DS7 produces 1/14th the lactic acid produced by the parent when grown on 5 mM glucose. This block in aerobic glycolysis is due to a mutation that affects the expression of the phosphoglucose isomerase gene because no isomerase activity is detected in cell extracts of DS7. This glycolytic block makes that cell line dependent exclusively on respiration for its energy requirement. Consequently, DS7 survives well after removal of glucose but dies quickly in the presence of oligomycin. The parental line O23 (subclone of CCl39) grows at low serum concentration, is anchorage-independent, and is tumorigenic in nude mice. The derived glycolytic mutant DS7 has retained both the in vitro transformed phenotype (low serum dependence and loss of anchorage dependence) and the tumor-forming capability. The tumor cells derived from the injection of DS7 cells have kept the original glycolytic defect. This finding suggests that the transformed properties (high hexose transport and aerobic glycolysis) that can be uncoupled from abnormal growth control are not necessary for the expression of the malignant phenotype in fibroblasts.