Repression of the human immunodeficiency virus type-1 long terminal repeat by the c-Myc oncoprotein

The effect of trans-acting factors on cis-acting DNA elements on the HIV-1 promoter are the principal determinant regulating transcriptional activation and repression. Host factors that limit viral replication can contribute to the emergence and maintenance of proviral reservoirs. The current paradigm is that this sub-population of latently infected cells confers a biological advantage to the virus by facilitating evasion of immunologic responses and therapeutic strategies resulting in life-long and persistent infection. In this report, we show that ectopic expression of the nuclear phosphoprotein, c-Myc can inhibit HIV-1 gene expression and virus production in CD4+ T-lymphocytes. The effect exerted does not appear to involve other known functions of c-Myc such as proliferation, or apoptosis. The mechanism does implicate c-Myc in a direct role. We have found evidence that c-Myc can specifically recognize the HIV-1 initiator element surrounding the start site of transcription and linker scanning mutagenesis experiments confirmed a loss of c-Myc-mediated repression in the absence of this region. Moreover, we show that c-Myc can interact with the initiator binding proteins YY-1 and LBP-1 and can cooperate with these factors to synergistically repress HIV-1 LTR transcription. Taken together, these results indicate that c-Myc is an important regulator of HIV-1 transcription that potentially contributes to the latent proviral state.

The long-term effects of anti-retroviral protease inhibitors on sugar transport in L6 cells

The objective of this study was to investigate the long-term effects of anti-retroviral protease inhibitors (PIs) on 2-deoxy-d -glucose (2-DG) transport in L6 cells in vitro. Exposure of L6 cells to saquinavir, ritonavir, indinavir and amprenavir resulted in significant increases in 2-DG transport using PI concentrations of 1-10 microM with continual exposure to PI. After removal of the PI for up to 48 h, 2-DG transport increases did not change and remained at pre-reversal levels. These changes in 2-DG transport were not related to stress-induced sugar transport or to apoptosis. The examination of glucose transporter (GLUT) 1, 3 or 4 translocation with subcellular fractionation indicated that insulin (i.e. 67 nM) could induce the translocation of all the GLUTs to the plasma membrane. Also, ritonavir (10 microM), which leads to a 2-fold increase in 2-DG transport, demonstrated increased GLUT (i.e. 1, 3 or 4) presence in the plasma membrane fraction, in the presence or absence of insulin. This increased 2-DG transport involved transporter presence in plasma membrane preparations and did not affect the ability of insulin to stimulate 2-DG transport with continual PI exposure. The mechanism(s) involved indicates ready reversibility of PI effects on transporters. The mechanism(s) why reversibility of PI-induced 2-DG transport was similar plus or minus PI was not apparent.

Indinavir uncovers different contributions of GLUT4 and GLUT1 towards glucose uptake in muscle and fat cells and tissues

AIMS/HYPOTHESIS

Insulin-dependent glucose influx in skeletal muscle and adipocytes is believed to rely largely on GLUT4, but this has not been confirmed directly. We assessed the relative functional contribution of GLUT4 in experimental models of skeletal muscle and adipocytes using the HIV-1 protease inhibitor indinavir.

METHODS

Indinavir (up to 100 micro mol/l) was added to the glucose transport solution after insulin stimulation of wild-type L6 muscle cells, L6 cells over-expressing either GLUT4myc or GLUT1myc, 3T3-L1 adipocytes, isolated mouse brown or white adipocytes, and isolated mouse muscle preparations.

RESULTS

100 micro mol/l indinavir inhibited 80% of both basal and insulin-stimulated 2-deoxyglucose uptake in L6GLUT4myc myotubes and myoblasts, but only 25% in L6GLUT1myc cells. Cell-surface density of glucose transporters was not affected. In isolated soleus and extensor digitorum longus muscles, primary white and brown adipocytes, insulin-stimulated glucose uptake was inhibited 70 to 80% by indinavir. The effect of indinavir on glucose uptake was variable in 3T3-L1 adipocytes, averaging 45% and 67% inhibition of basal and maximally insulin-stimulated glucose uptake, respectively. In this cell, fractional inhibition of glucose uptake by indinavir correlated positively with the fold-stimulation of glucose uptake by insulin, and was higher with sub-maximal insulin concentrations. The latter finding coincided with an increase only in GLUT4, but not GLUT1, in plasma membrane lawns.

CONCLUSION/INTERPRETATION

Indinavir is a useful tool to assess different functional contributions of GLUT4 to glucose uptake in common models of skeletal muscle and adipocytes.

Sugar transport regulation: comparative characterization of the effect of NADH CoQ reductase deficiency in two cell culture systems

In this report, we have characterized the upregulation of glucose transport in two different respiration-deficient fibroblast cell cultures. We have demonstrated that glucose transport increases in respiration-deficient cells as measured by 2 deoxy D-glucose transport and is readily observed in both the WG750 human and G14 Chinese hamster fibroblast respiration-deficient cell lines when compared with the MCH55 normal human and V79 parental Chinese hamster cell lines, respectively. Using subcellular fractionation techniques, the GLUT 1 glucose transporter was found located predominantly in the plasma membrane-enriched fraction of the human and hamster cell lines. In human cells, the expression of the GLUT 1 glucose transporter was elevated three-fold in the plasma membrane-enriched fraction of the WG750 respiration-deficient mutant cells. In the Chinese hamster cell lines, the respiration-deficient G14 cells exhibited no such GLUT 1 glucose transporter elevation in the plasma membrane-enriched fraction, yet expressed a >2-fold increase in glucose transport. Furthermore, the G14 cells had a similar content of GLUT 1 glucose transporter in the plasma membrane fraction when compared with the V79 parental cell line. Using Western blot analysis, the GLUT 1 glucose transporter in G14 cells exhibited a different mobility on a polyacrylamide gel when compared with the mobility of the GLUT 1 glucose transporter of the V79 cell line. This differential mobility of the glucose transporters in the hamster cells appeared to be related to glycosylation differences of the glucose transporters. Although normal human and hamster cell lines exhibited significant increases in insulin-stimulated sugar transport (P < 0.05), the two respective respiration-deficient cell lines exhibited no significant increases in insulin-stimulated sugar transport (P > 0.05). Additionally, the expression of the GLUT 1 mRNA in the human WG750 mutant cells was elevated when compared with GLUT 1 mRNA in normal cells. Insulin exposure significantly increased GLUT 1 mRNA in human cells (P < 0.05). No differences in the GLUT 1 mRNA were observed between both hamster cell lines. Thus, both respiration-deficient cell lines are insulin resistant (i.e., regarding their insulin-stimulated sugar transport). The respiration-deficient mutation results in an increased sugar transport in the human and hamster cells; however, the human cells adapt to the mutation by increasing their levels of GLUT 1 mRNA and eventually membrane-located glucose transporters. On the other hand, the hamster cells adapt by apparently modifying their glucose transporters' intrinsic activity via glycosylation. We feel that these cell systems can be effective models to study the multiple factors involved in sugar transport regulation in vertebrate cells.

Effect of insulin-like growth factor I on HIV type 1 long terminal repeat-driven chloramphenicol acetyltransferase expression

In this study, we have investigated the ability of insulin-like growth factor I (IGF-I) to inhibit HIV long terminal repeat (LTR)-driven gene expression. Using COS 7 cells cotransfected with tat and an HIV LTR linked to a chloramphenicol acetyltransferase (CAT) reporter, we observed that physiological levels of IGF-I (10(-9) M) significantly inhibited CAT expression in a concentration- and time-dependent manner. IGF-I did not inhibit CAT expression in COS 7 cells transfected with pSVCAT, and did not affect CAT expression in the absence of cotransfection with tat. Transfection of HIV-1 proviral DNA into COS 7 cells +/- IGF-I resulted in a significant decrease (p < 0.05) in infectious virion production. Both IGF-I and Ro24-7429 inhibited LTR-driven CAT expression, while TNF-alpha-enhanced CAT expression was not affected by IGF-I. On the other hand, a plasmid encoding parathyroid hormone-related peptide exhibited dramatic additivity of inhibition of CAT expression in COS 7 cells. Finally, we show that in Jurkat or U937 cells cotransfected with HIVLTRCAT/tat, IGF-I significantly inhibited CAT expression. Further, interleukin 4 showed in U937 cells inhibition of CAT expression that was not additive to IGF-I induced inhibition. Our data demonstrate that IGF-I can specifically inhibit HIVLTRCAT expression. This inhibition may occur at the level of the tat/TAR interaction. Finally, this IGF-I effect is seen in target cell lines and similar paths of inhibition may be involved in the various cell types employed.

Sugar transport and glut transporter expression in a variety of human immunodeficiency virus-1 (HIV-1) chronically infected target cell lines

In this study, sugar transport and the cellular content of the human Glut 1 and 3 glucose transporters were ascertained in uninfected and chronically HIV-infected Jurkat and H9 cell lines (T-cell lines) and U937 cells (a promonocytic cell line). Sugar transport was determined by monitoring 2-deoxy glucose uptake (2DG) and glut transporter content was determined by Western analysis. Although 'acute' HIV infection of H9 cells led to increased cellular transport activity and Glut 3 transporter content, chronic HIV infection exhibited no significant differences in sugar transport in any of the cell types investigated whether log or stationary phase cultures were employed. When uninfected and chronically HIV-infected cell lines were compared, all cell lines expressed the Glut 1 transporter, however, significant differences in Glut 1 transporter content were not observed. The Glut 3 transporter which could only be detected in the H9 cell line exhibited no differences in Glut 3 content in uninfected or chronically HIV-infected cells (2.1 +/- 0.6 versus 3.8 +/- 2.1 x 10(-3) arbitrary units/microgram protein). A trend towards lower amino acid uptake was seen in the chronically HIV-infected cells but this was not significantly different from uninfected cell cultures. The data indicate that: (1) glucose transport and the Glut 1 and 3 transporters are not increased in cells chronically infected with HIV-1 and (2) the expression of the Glut 3 sugar transporters is not the same in all target cells.

Acylation-stimulating protein (ASP) regulates glucose transport in the rat L6 muscle cell line

Acylation-stimulating protein (ASP), a human plasma protein, is a potent stimulator of triglyceride synthesis and glucose transport in both human adipocytes and fibroblasts. The purpose of the present in vitro study was to examine the effect of ASP on glucose transport in muscle cells. ASP stimulated 2-deoxy-glucose transport (2-DG) in differentiated rat L6 myotubes in a time (30 min to 24 h) and concentration dependent manner (97% increase). The magnitude of the ASP effect on glucose transport was comparable to the time- and concentration-dependent effects seen with insulin (125% increase), but was additive to insulin, pointing to involvement of differential signalling pathways. ASP stimulation was dependent on cell differentiation in that glucose transport increased by only 12% in myoblasts, comparable to the effect of insulin in myoblasts (15% increase) demonstrating selective responsiveness of the differentiated myotubes to ASP and insulin. The mechanism for the ASP induced increase in glucose transport was also examined. ASP increased the Vmax for 2-DG transport by 183% (4.02 vs. 1.42 nmol/mg cell protein/30 s; ASP vs. Control, respectively). This could be explained by an increased translocation of glucose transporters (GLUT 1, GLUT 4 and GLUT 3) to the plasma membrane surface as demonstrated by Western analysis (+43% P < 0.05, +30% P < 0.05, and +49% P < 0.05, respectively). The effects of ASP were equal to those of insulin (+47%, +26% and +53% for GLUT 1, GLUT 4 and GLUT 3, respectively) and in all cases were paralleled by comparable glucose transport increases under the same incubation conditions. After long-term stimulation (24 h), Western analysis indicated that ASP had a permissive effect on insulin stimulated increases in total GLUT3 and GLUT4 cellular transporter content. These results suggest that muscle is also responsive to ASP and that ASP may play a role in glucose metabolism in both muscle and adipose tissue.

Insulin-like growth factor 1 and insulin inhibit HIV type 1 replication in cultured cells

Insulin-like growth factor 1 and insulin, considered primarily as metabolic and growth modulatory hormones, were found to inhibit the replication of HIV-1 in cultured cord blood mononuclear cells and chronically HIV-infected U937 cells. The effect of IGF-1 was seen at physiological concentrations or lower (1.7 x 10(-10) M) while that of insulin was observed at supraphysiological concentrations (8 x 10(-7) M). The EC50 for IGF-1 was found to be in the physiological range (2.5-4.5 x 10(-9) M) while that for insulin was considerably higher (1.1-3.3 x 10(-6) M). Insulin-like growth factor 1 and insulin at the concentrations employed exhibited no toxicity on the cells used in these studies. Furthermore, neither IGF-1 nor insulin exhibited any inhibitory activity on purified reverse transcriptase in vitro. Epidermal growth factor from 1.6 x 10(-10) to 1.6 x 10(-8) M demonstrated no inhibition of HIV-1 replication, while IGF-1 inhibited p24 antigen production 49 and 42% at 1.3 x 10(-9) and 1.3 x 10(-8) M IGF-1, respectively. These results suggest that IGF-1 under certain conditions has significant inhibitory effects on HIV-1 replication at physiological concentrations. This may prove to be of therapeutic value in patients infected with HIV-1.

Evidence that modulation of glucose transporter intrinsic activity is the mechanism involved in the allose-mediated depression of hexose transport in mammalian cells

In serum starved V79 Chinese hamster lung fibroblast cells, replacement of D-glucose with D-allose resulted in a significant 38 +/- 18% (P < 0.05) reduction of 2-deoxy-D-glucose (2-DG) transport. Similarly, in a respiration-deficient mutant cell line (V79-G14), which has elevated 2-DG transport activity, D-allose reduced 2-DG transport by 59 +/- 18% (P < 0.05). [3H]D-allose uptake by V79 cells occurred slowly and was not inhibited by cytochalasin B, suggesting diffusion as the mode of D-allose entry. Western blot analysis using a rabbit polyclonal antibody to the human erythrocyte glucose transporter (GT) demonstrated that, in both cell lines, GT content and GT subcellular distribution were not significantly different in D-glucose vs. D-allose-treated cells. delta-Antibody, which has been shown to bind to exofacial epitopes of the GT (Harrison et al., 1990, J. Biol. Chem., 265:5793-5801), did not demonstrate any differences in surface binding to D-glucose vs. D-allose-treated intact V79 cells. D-allose treatment of 3T3 fibroblasts resulted in a similar decrease (72%) of 2-DG transport, however D-allose had no apparent effect on basal sugar transport in 3T3 adipocytes. These results suggest that D-allose reduces sugar transport through a modulation of the intrinsic activity of the GT, and that D-allose may act in a tissue-specific manner.

Differential glycosylation of the glucose transporter coincides with enhanced sugar transport in respiration deficient cells

Sugar transport regulation was characterized in terms of the expression and subcellular distribution of the glucose transporter (GT) in the V79 hamster fibroblast cell line and in a respiration deficient mutant (G14) of the V79 cell line. Comparison of GT content in V79 and G14 cells and cell fractions revealed that the 3-fold elevation in basal sugar transport observed in the G14 cell line did not coincide with any significant difference in either the whole cell or plasma membrane GT content when compared to the V79 parental cell line. Determination of delta-antibody binding to intact cell monolayers supported the finding that the two cell lines demonstrate equivalent plasma membrane GT content. Further, D-glucose inhibitable cytochalasin B binding to total cell membranes indicates that additional, unrecognized GT isoforms do not occur in either cell line. A higher average molecular weight GT was detected in the G14 cell line, and treatment of GT enriched preparations with endoglycosidase F established that the G14 cell line exhibits a hyperglycosylated form of the same core GT protein expressed in V79. These results suggest that an enhancement of the intrinsic activity of the GT expressed in G14 is responsible for its increased sugar transport capabilities and this may be related to differences in GT post-translational processing.

Mutant cell line demonstrating a block in insulin and insulin-like growth factor type 1 (IGF-1) induced mitogenesis

Recently, we have isolated a Chinese hamster cell variant (IV-A1-j) resistant to an insulin-diphtheria-A chain toxic conjugate (Leckett and Germinario: Cytotechnology [in press]. This cell line exhibited a decreased level of insulin binding, but normal growth in serum-containing medium when compared to the parental cell line (V-79). In this paper we further demonstrate that while IV-A1-j cells are capable of growing in serum-containing medium, they are insensitive to the mitogenic actions of either insulin or IGF-1. In contrast, epidermal growth factor (EGF) and/or alpha-thrombin (THR) generate a mitogenic effect in IV-A1-j cells comparable to that observed in the parental V-79 cells. The combination of EGF and/or THR with either insulin or IGF-1 results in an increase in V-79 cell growth above EGF and/or THR alone. On the other hand, insulin or IGF-1 in the presence of other mitogens did not stimulate further growth in IV-A1-j cells. While insulin binding was lower in IV-A1-j cells, internalization of 125I-insulin was not different in the two cell types. Additionally, insulin-stimulated glycogen synthesis and protein synthesis were not different in the two cell types. These observations are consistent with insulin and IGF-1 sharing a mitogenic signalling pathway in Chinese hamster fibroblasts and that this pathway is distinct from other growth factor signalling pathways. The fact that this pathway is defective in the IV-A1-j cell line indicates the potential usefulness of these cells in identifying a key step(s) in the insulin (IGF-1) mitogenic pathway.

Inhibitors of protein synthesis cause increased hexose transport in cultured human fibroblasts by a mechanism other than transporter translocation

We have investigated the effect of various inhibitors of protein synthesis on hexose transport in human skin fibroblasts using 2-deoxy-D-glucose (2-DG) and 3-0-methyl-D-glucose (3-OMG) to measure hexose transport. Exposure of glucose-fed, serum-free cultures to cycloheximide (CHX) (50 micrograms/ml) for 6 h resulted in increased 2-DG transport (3.81 +/- .53 vs. 6.62 +/- .88 nmoles/mg protein/2 min; n = 9) and 3-OMG transport (1.36 +/- .66 vs. 3.18 +/- .83 nmoles/mg protein/30 sec; n = 4) in the CHX exposed group. Under these conditions inhibition of protein synthesis was greater than 90%. This CHX induced transport increase was time dependent (approaching maximum within 1 h of exposure to CHX) and related to an increase in the Vmax of hexose transport in the CHX exposed group (18.4 +/- 2.4 vs. 4.8 +/- 1.1 nmoles 2-DG/mg protein/min) with no difference in the transport Km (1.55 +/- .63 vs. 2.92 +/- .59 mM). Further, the CHX induced increase in hexose transport was reversible. Exposure of human fibroblasts to inhibitors of protein synthesis with different mechanisms of action (e.g., puromycin, pactamycin, or CHX) all generated hexose transport increases in a concentration-dependent fashion correlating with their increasing inhibitory effects on protein synthesis. Nucleotidase enriched (i.e., plasma membrane) fractions of control and CHX-exposed cells showed no differences in D-glucose inhibitable cytochalasin B binding activity. Further, quantitative Western analysis of nucleotidase enriched fractions indicated CHX exposure resulted in no significant increase in glucose transporter mass compared with control plasma membrane fractions. Glucose deprived cells, however, which exhibited increased sugar transport comparable to the CHX-exposed group, did show increased glucose transporter mass in the plasma membrane fraction. The data indicate that inhibitors of protein synthesis can cause a significant elevation in hexose transport and that the hexose transporter mass in the isolated plasma membrane fractions did not reflect the whole cell transport change. It is suggested that a mechanism other than glucose transporter translocation to the plasma membrane may be involved in causing this sugar transport increase.

Construction of a toxic insulin molecule: selection and partial characterization of cells resistant to its killing effects

We have constructed an insulin-diphtheria hormono-toxin which migrates as a single 29 kd band on 10% SDS polyacrylamide gel electrophoresis. This corresponds to a one to one molar ratio of the diphtheria A-chain (23 kDa) and insulin (6 kDa) molecules. The diphtheria A-chain: insulin (DTaI) hormono-toxin demonstrates cytotoxicity in V-79 Chinese hamster cells exhibiting an LD50 of 1.1 x 10(-8) M, which is 22 x more potent than whole diphtheria toxin. Also, DTaI can competitively displace [125I]-insulin with an ED50 of 1.1 x 10(-8) M, which is identical to the ED50 of insulin (1.1 x 10(-8) M) and showed limited cross-reactivity with the IGF-1 receptor (12% displacement of [125I]-IGF-1 with a DTaI concentration of 1.1 x 10(-8) M). We have used DTaI to select conjugate-resistant clones from the V-79 Chinese hamster fibroblast parental cell line. Conjugate-resistant variants expressed insulin binding levels ranging from 8.0 +/- 2.0 fmoles/mg protein down to 3.6 +/- 0.5 fmoles/mg protein while insulin binding in the V-79 parental cell line was 11.2 +/- 0.2 fmoles/mg protein. Additionally, a number of conjugate resistant clones expressed variable ability to grow in medium containing 5% serum. The altered ability of these clones to grow in a serum-containing medium did not correlate directly with the changes observed for insulin binding. One mutant, IV-A1-j, did not grow in a serum-free defined medium containing insulin as the predominant mitogen. This IV-A1-j mutant had a lower number of insulin receptors, no change in insulin binding affinity, no change in the rate of internalization of [125I]-insulin and no apparent difference in [125I]-IGF-1 binding. Further, insulin-stimulated sugar transport was similar to that observed in the parental cell line. Based on these observations we suggest that 1) DTaI elicits its cytotoxicological effects through the insulin receptor trafficking pathway, 2) DTaI can be used to isolate cells altered at the level of insulin binding and/or action, and 3) signal transduction mechanisms responsible for mediating insulin-dependent cell growth can be pursued using mutants such as IV-A1-j.

Permanent hexose transport upregulation in a respiration-deficient human fibroblast cell strain

The regulation of hexose transport was studied in a human diploid fibroblast respiration-deficient cell strain (WG750). Transport of 2-deoxy-D-glucose (2-DG) was greater than sixfold higher compared with an in vivo age-matched normal cell strain (MCH55). In addition, 3-O-methylglucose transport and 14CO2 production were elevated in the mutant cell strain. Kinetic analysis revealed that the increased sugar transport in mutant cells was due to an average 5.7-fold increase in the 2-DG maximal transport rate, with no observed differences in the transport Michaelis constant for both normal and mutant cells. Also, the inhibitor constants for D-glucose inhibition of 2-DG transport were nearly identical for both cell types. Glucose deprivation led to a similar time-dependent increase in hexose transport in both cell strains. Serum refeeding of glucose-fed serum-deprived cultures led to a progressive increase in 2-DG transport in normal cells, whereas mutant cells displayed a time-delayed increase in 2-DG transport. Exposure to 67 and 670 nM insulin stimulated 2-DG transport on average 1.99 +/- 0.25- and 2.33 +/- 0.26-fold, respectively, over basal transport in the normal cells, whereas the mutant cells were significantly less sensitive to the stimulatory effects of the hormone. Insulin binding and amino acid transport (i.e., alpha-aminoisobutyric acid uptake) in the normal and mutant cells were not different. Data obtained using Western blot analysis showed that WG750 (mutant) cells expressed an increase (approximately 4-fold) in total cellular HepG2 (erythroid-brain) transporter protein compared with normal cells, thus reflecting the changes seen in hexose transport.(ABSTRACT TRUNCATED AT 250 WORDS)

Inability of insulin and insulinlike growth factor-1 to stimulate sugar or amino acid transport and thymidine incorporation in cultured myeloma cells

NS-1 mouse plasmacytoma cells were examined for their insulin and insulinlike growth factor-1 (IGF-1) binding characteristics and ability to produce peptide-dependent cellular effects. At concentrations of labelled insulin (i.e., 1.7 x 10(-10) M) or IGF-1 (i.e., 1.5 x 10(-10) M), NS-1 cells specifically bind 0.2 +/- 0.06 fmol insulin per 10(6) cells (n = 7), where little, if any, IGF-1 specific binding was observed (0.02 +/- 0.01 fmol/10(6) cells) (n = 3). Additionally, the data indicate that the total number of insulin binding sites per cell was 3200 +/- 390 (n = 3). Insulin was employed at various concentrations (6.7-667 nM) and failed to stimulate either sugar or amino acid transport. Insulin at low concentrations (i.e., 6.7 or 67 nM) did not stimulate DNA synthesis, yet a small but significant increase was observed at a concentration of 667 nM insulin. IGF-1 did not stimulate DNA synthesis at all concentrations employed (1.4-143 nM). In summary, there exists a small but significant number of insulin receptors, little insulin-stimulated DNA synthesis, and no apparent insulin stimulation of sugar or amino acid transport. Also, since there is no significant IGF-1 binding and no IGF-1 stimulation of DNA synthesis, these findings indicate that this cell line might be a good candidate for the study of insulin receptor function as a transfection recipient of insulin receptor genes.

Characterization of the D-allose-mediated regulation of sugar transport in Chinese hamster fibroblasts

Exposure to D-allose has been demonstrated to lead to decreased 2-deoxy-D-glucose (2-DG) and 3-0-methyl-D-glucose transport in the V79 Chinese hamster lung fibroblast cell line. The effect of D-allose 1) was maximal after 4 hours exposure to the cells; 2) was optimal between 2.77 and 5.55 mM D-allose; and 3) led to a decreased Vmax for 2-DG transport with no change in the transport Km value. The decrease in 2-DG transport induced by D-allose was reversible and the reversal was differentially affected by cycloheximide, being blocked by a low concentration of cycloheximide (0.05 micrograms/ml) but not a high concentration of the inhibitor (5 micrograms/ml). D-allose did not competitively inhibit the transport of 2-DG while D-glucose under similar conditions yielded a Kl for 2-DG transport inhibition of 1.7 mM. Additionally, D-allose did not affect the phosphorylation of 2-DG by hexokinase in cell-free cytosol. The data indicate that D-allose has significant lowering effects on sugar transport activity. Additionally, while the sugar itself may be the active component in sugar transport regulation, the effect is not blocked by inhibition of protein synthesis but the synthesis of a regulatory protein(s) may be involved in the return of sugar transport following D-allose removal.

Regulation of hexose transport in respiration deficient hamster lung fibroblasts

The transport of [3H]2-deoxy-D-glucose (2DG) and [3H]3-O-methyl-D-glucose (3-OMG) was elevated in a respiration deficient (NADH coenzyme Q [Co Q] reductase deficient) Chinese hamster lung fibroblast cell line (G14). This sugar transport increase was related to an increased Vmax for 2DG transport, 26.9 +/- 4.2 nmoles 2DG/mg protein/30 sec in the G14 cell line vs 9.5 +/- 0.6 nmoles 2DG/mg protein/30 sec in the parental V79 cell line. No differences were observed in their respective Km values for 2DG transport (3.9 +/- .6 vs. 3.0 +/- .13 mM). Factors which increase sugar transport (e.g., glucose deprivation, serum or insulin exposure) or decrease sugar transport (e.g., serum deprivation) in the parental V79 cell line had little effect on sugar transport in the G14 respiration deficient cell lines. Amino acid transport, specific 125I-insulin binding to cells, and insulin-stimulated DNA synthesis, however, were similar in both cell lines. Exposure of both cell lines to varying concentrations of cycloheximide (0.1-50 micrograms/ml) for 4 h resulted in differential effects on 2DG transport. In the parental cell line (V79) low cycloheximide concentrations resulted in decreased 2DG transport, while higher concentrations (greater than or equal to 1 microgram/ml) resulted in elevated 2DG transport. In the G14 cell line, 2DG transport decreased at all concentrations of cycloheximide (up to 50 micrograms/ml). The data indicate that the G14 mutant has been significantly and specifically affected in the expression of sugar transport activity and in the regulatory controls affecting sugar transport activity.

Kinetic characteristics and regulation of hexose transport in a galactokinase-negative Chinese hamster fibroblast cell line: a good model for studies on sugar transport in cultured mammalian cells

We report the kinetic characteristics for D-galactose, 2-deoxy-D-glucose and 3-O-methyl-D-glucose transport in a galactokinase null-allele mutant of a Chinese hamster V79 cell line. GalKl cells exhibited a Km and Vmax for D-galactose, 2-deoxy-D-glucose, and 3-O-methyl-D-glucose transport of 8.6 +/- 2.6 mM and 26.1 +/- 7.2 nmol/mg p/min, 4.1 +/- 1.2 mM and 40.3 +/- 9.5 nmol/mg p/min, and 7.01 +/- .85 mM and 11.6 +/- 4.8 nmol/mg p/30 s, respectively. Nonsaturable hexose uptake was determined using cytochalasin B inhibition of galactose uptake (89.6 +/- 3.7% of galactose uptake was cytochalasin B inhibitable) and L-glucose uptake (7.5% of the galactose uptake). D-Galactose was not metabolized and effluxed rapidly from preloaded cells. The Kls for the inhibition of D-galactose transport were 4.5 +/- 2.5 mM for D-glucose, 7.0 +/- 2.0 mM for 2-deoxy-D-glucose, 6 mM for 2-deoxy-D-galactose and 6.0 +/- 0.6 mM for 3-O-methyl-D-glucose. This indicates the operation of a single common carrier. The hexose transport rate decreased 50-60% after 24 h serum deprivation. Addition of insulin was shown to increase hexose transport (more than twofold) in serum-deprived cells. Hexose transport rates increased substantially in glucose-deprived, D-fructose- or D-galactose-fed cells as compared to glucose-fed cells. Since GalKl does not metabolize galactose, the hexose transport increases induced by feeding cells galactose suggest that carrier interaction with ligand is not a significant factor in transport regulation in GalKl. The kinetic and regulatory characteristics of D-galactose transport in the GalKl cell line indicate that this system is a good model to study sugar transport from a mechanistic and regulatory point of view.

Evidence for the autocrine inhibition of glycolysis in human fibroblasts

We investigated the mechanism by which glucose refeeding can reverse the enhancement of glycolysis caused by glucose starvation. Human fibroblasts were deprived of glucose for 18 hr and then refed for 1 hr with either (a) medium from sister glucose-starved cultures (controls), (b) fresh, glucose-containing medium (fresh medium), or (c) medium conditioned for 18 hr by glucose-fed cells (conditioned medium). Despite a lower glucose content, conditioned medium was significantly more effective at inhibiting the accumulation of radio-labeled glucose than fresh medium (74 vs. 49% inhibition). The uptake of 2-deoxyglucose was not affected by either medium, indicating that the site of control of glycolysis was distal to glucose transport and phosphorylation. The active principle was heat labile, dialyzable (Mr less than 12,000) and unrelated to the lactate content of conditioned medium. Medium conditioned by cells exposed to 3-O-methylglucose did not inhibit glycolysis in glucose-starved cells even though long-term exposure to this hexose, like glucose, results in the repression of transport.

Presence of insulin binding sites on viral particles

Using a standard radio-receptor assay, we have demonstrated that [125I]insulin can bind specifically to each of two types of purified enveloped viruses, influenza A virus and Rous sarcoma virus. A non-enveloped icosahedral virus (echovirus 11) and herpes simplex virus type 2, which acquires its envelope from the nuclear membrane of the cell, did not possess insulin receptor activity. Displacement of specifically bound radiolabelled insulin from the viral surface was achieved by addition of an excess of unlabelled insulin but not by addition of another unrelated protein, cytochrome C. We conclude that certain types of enveloped viruses may acquire insulin binding sites from the plasma membrane of their host cell.

Hexose transport regulation in cultured fibroblasts derived from normal and type II diabetic patients

The kinetics of saturable and nonsaturable sugar transport were studied in normal and Type II diabetic cultured skin fibroblasts under fast or slowly growing conditions. The Km of hexose transport for fast and slow-growing normal fibroblasts was 1.38 +/- 0.3 and 0.88 +/- 0.12 mM, respectively, while those of the diabetic fibroblasts were 1.57 +/- 0.29 and 0.8 +/- 0.19 mM, respectively. The respective transport Vmax for normal and diabetic fast-growing cells was 13.9 +/- 0.8 and 12.95 +/- 2.4 nmoles 2-DG/mg protein/min. For slowly growing cells of both groups, a transport Vmax of 11.5 +/- 2.4 and 11.3 +/- 1.7 nmoles 2-DG/mg protein/min was obtained. No significant differences were observed in the Km or Vmax of hexose transport under these various growth conditions between normal and diabetic cell cultures. Nonsaturable sugar uptake as determined by L-glucose or cytochalasin B inhibited 2-DG uptake was variable, but no significant differences were observed between the normal and Type II diabetic cells. The activation energies for saturable and nonsaturable sugar uptake were not different among the two donor groups. Insulin stimulation of hexose transport was studied in the presence and absence of dexamethasone (5 X 10(-6) M) at varying insulin concentrations. No difference was observed in the amount of insulin necessary to obtain a maximum stimulatory response (approximately 33 nM insulin in both groups). Also, the insulin concentration required to achieve a one-half maximal response was not significantly different in the donor groups (i.e., 3.53 +/- 0.6 nM for normals and 3.98 +/- 1.1 nM for diabetics.(ABSTRACT TRUNCATED AT 250 WORDS)

The effects of sulfhydryl modifying reagents on nonhormonal and hormonally regulated hexose transport in cultured human skin fibroblasts

The effects of various sulfhydryl modifying reagents on hexose transport in cultured human skin fibroblasts were studied. H2O2 was observed to have no effect on 2-deoxy-D-glucose transport in serum-starved glucose-fed cells. The elevation of hexose transport rates in cells by glucose deprivation, insulin, or serum stimulation rendered them sensitive to H2O2. Hexose transport in glucose-deprived cells was inhibited 51-55% by 1-2 mM H2O2, while hexose transport in insulin or serum-stimulated glucose-fed cells was inhibited 45% and 46%, respectively. H2O2 inhibition was blocked or reversed by 8 mM dithiothreitol. N-ethyl-maleimide (NEM), a permeant, sulfhydryl reagent, elicited effects on hexose transport similar to those effected by H2O2 (i.e., in glucose-deprived and insulin-stimulated cells, inhibition of hexose transport was 44% and 23%, respectively). Impermeant sulfhydryl reagents such as dithio(bis)nitrobenzoic acid (DTNB) and N-iodoacetyl-N'-(5-sulfo-1-naphthly-ethylenediame (1,5,-I-AEDANS) had no inhibitory effect on hexose transport under any conditions (i.e., glucose-fed, glucose-deprived, and insulin-stimulated cells). DTNB and 1,5-I-AEDANS afforded no protection from the action of H2O2 on hexose transport. The data suggest that the sensitive sites are thiol in nature and are located at an intramembrane or intracellular site and probably not exofacial.

Hexose transport after glucose refeeding of glucose-starved human fibroblasts: 1. The effects of tunicamycin and cycloheximide. 2. Insulin binding and action

Hexose transport in glucose-starved human fibroblasts was readily reversed by glucose refeeding. This hexose transport reversal was not inhibited by tunicamycin (1.5 microgram/ml) but was blocked by cycloheximide (20 micrograms/ml). The ability of insulin (100 mU/ml) to stimulate hexose transport was returned by glucose refeeding and this was not affected by tunicamycin. Cycloheximide which blocked the glucose refeeding effect on hexose transport, decreased the ability of insulin to stimulate hexose transport. Specific 125I-insulin binding was increased by glucose refeeding of glucose-starved cells and this change in binding was inhibited by tunicamycin and cycloheximide. Thus, it appears that under the conditions employed in human fibroblasts, the ability of insulin to stimulate hexose transport is differentially regulated more by factors affecting basal hexose transport than by those affecting changes in insulin binding.

Characteristics of normal and maturity-onset diabetic (type II diabetes) cell cultures: life spans and DNA synthetic capabilities

The replicative ability of fibroblasts derived from normal and type II diabetic (non-insulin-dependent) donors and their DNA synthetic capabilities in response to serum and insulin (+/- dexamethasone) have been studied. Comparative replicative life spans of the fibroblasts studied using several lots of serum showed no significant differences between the two donor groups with any lot of serum (p greater than 0.05). Insulin (i.e. 700 nM) and serum (10% v/v) stimulation of DNA synthesis in normal and type II diabetic cultures exhibited no differences in responses. The insulin:control ratios of the normal vs. type II diabetic were 1.61 +/- 0.08 vs. 1.81 +/- 0.11, respectively (p greater than 0.05) while the serum:control ratios were 3.55 +/- 0.58 vs. 4.02 +/- 0.54, respectively (p greater than 0.05). Dexamethasone amplification of the insulin-stimulated DNA synthetic response over a range of insulin concentrations (i.e. 1.6-66.6 nM) expressed no differences between the two donor groups. Additionally, calculation of the insulin concentration necessary for the half-maximal response showed no differences between the normal and diabetic groups (3.47 +/- 0.5 vs. 4.44 +/- 0.8 nM, respectively) (p greater than 0.05). The data suggest that there are no general age-related abnormalities inherent to the type II diabetic cultured cell.

Control of sugar transport in human fibroblasts independent of glucose metabolism or carrier-substrate interaction

Transport regulation by different metabolizable and nonmetabolizable sugars was studied in human fibroblasts. Sugars were classed as glucose-like (D-mannose, 3-0-methyl-D-glucose, thio-D-glucose, and D-allose) and starvation-like (D-galactose, D-fructose, L-glucose, D-xylose, 6-deoxy-D-glucose and 2-deoxy-D-glucose) based on their competence in curbing glucose starvation enhanced transport. No significant correlation existed between the ability of a sugar to curb hexose transport and the KI of that sugar in inhibiting hexose transport. Independence of the transport curb from glucose metabolism was observed since nonmetabolizable analogs of D-glucose when substituted for D-glucose in the culture medium effected glucose [i.e. 3-0-methyl-D-glucose (3-OMG)] and starvation-like (i.e. 6- and 2-deoxy-D-glucose) effects. The KI of inhibition pf 2-deoxy-D-glucose transport for 3-OMG was 8.5 mM, similar to those obtained for 6-deoxyglucose and 2-deoxyglucose on 2-deoxyglycose transport (7.5 and 3.5 mM, respectively) and on 3-0-methylglucose transport (3.5 and 2.5 mM, respectively). An equimolar mixture of D-glucose and 3-OMG (5.55 mM each) was more effective than 11.1 mM D-glucose or 3-OMG alone in curbing hexose transport or reversing hexose starvation induced increases in transport. The effect of 3-OMG may be independent of glucose metabolism but it is possible that 3-OMG structurally mimics a metabolite of glucose that may interact with intracellular regulators of carrier degradation and or expression.

Glucocorticoid-induced modulation of insulin-stimulated DNA synthesis: differential responsiveness in cell cultures derived from donors of different ages

The replicative ability of variously 'aged' cell cultures, their insulin binding and biological responsiveness under control and glucocorticoid (i.e. hydrocortisone) amplified conditions have been studied in human fibroblast cultures. Insulin stimulation of DNA synthesis in early and late passage cultures and in cultures from young and old donors showed no age-related difference in insulin responsiveness. Hydrocortisone amplification of insulin-stimulated DNA synthesis in early and late passage cells expressed no age-related differences. Hydrocortisone affected basal DNA synthesis in cultures from in vivo young and old donors differently. Additionally, hydrocortisone amplified insulin-stimulated DNA synthesis in young donor cell cultures was observed to be higher than in old donor cell cultures. Specific 125I-insulin binding was increased by hydrocortisone in both early and late passage cultures and in cultures from young and old donors but no age-related differences in 125I-insulin binding were observed in the presence or absence of hydrocortisone. The data suggest that an age-related loss of an insulin postreceptor interaction during hydrocortisone amplification of insulin-stimulated DNA synthesis is being expressed in the cultures from old donors.

Regulation of insulin binding and stimulation of sugar transport in cultured human fibroblasts by sugar levels in the culture medium

Studies were carried out on cultures of human skin fibroblasts to explore the effects of culture medium glucose levels on insulin binding and action. Cell cultures in 5.55 mM glucose-containing medium depleted their medium glucose within 3 days, and at that time exhibited elevated deoxy-D-glucose (2-DG) transport (84% greater than control cultures fed 22.2 mM glucose) and failure of insulin to stimulate 2-DG transport (an insulin:control transport ratio of 1.02). There was also a significant negative correlation between basal 2-DG transport and insulin binding (r = -0.621; n = 29; P less than 0.01), while insulin binding exhibited a significant positive correlation with insulin action (r = 0.816; n = 12; P less than 0.01). Glucose starvation of cultures for 18 h resulted in several changes: a 49% decrease in specific 125I-insulin binding due to a reduction in binding capacity; elevated basal 2-DG transport; and an absence of insulin stimulation of 2-DG transport. Exposure to increasing concentrations of glucose for 18 h led to a glucose concentration-dependent increase in specific insulin binding. Additionally, the various changes in the glucose-starved group were reversed after as little as 6 h of glucose refeeding. The results indicate that basal sugar transport, and insulin binding and action can be regulated by the amount of glucose in the medium.

Enhanced insulin stimulation of sugar transport and DNA synthesis by glucocorticoids in cultured human skin fibroblasts

Glucocorticoids will enhance the growth of cultured human skin fibroblasts in serum-containing medium. In serum-free cultures hydrocortisone (5 X 10(-6) M) will enhance insulin stimulation of sugar transport and DNA synthesis (as measured by thymidine incorporation into trichloroacetic acid-precipitable material). The optimal concentration for the glucocorticoid effect on DNA synthesis was 5 X 10(-8) M for dexamethasone and 5 X 10(-7) M for hydrocortisone. In dexamethasone-treated cells, concentrations of insulin as low as 250 microU/ml (10 ng/ml) were effective in stimulating DNA synthesis. Further, hydrocortisone and dexamethasone (both at 5 X 10(-6) M) exhibited potentiating effects on insulin-stimulated sugar transport. These effects appeared to be mediated via inhibitory actions on the hexose transport system with the preservation of a functional insulin-receptor interaction resulting in insulin stimulation of deoxy-D-glucose transport at physiological insulin concentrations, 250 microU/ml (10 ng/ml). Hydrocortisone also enhanced specific [125I]insulin binding in these cells. The data indicate that the mechanism(s) of glucocorticoid enhancement of two actions of insulin may be different.

A direct solubilization procedure for the determination of DNA and protein in cultured fibroblast monolayers

A procedure for the direct solubilization of fibroblast monolayers allowing precise determination of DNA and protein content has been developed. This simple procedure is applicable to the analysis of these macromolecules in fibroblast cultures containing small numbers of cells (less than 1 X 10(5].

Regulation of sugar transport in cultured diploid human skin fibroblasts

The regulation of hexose transport under glucose-starvation conditions was studied in cultured human skin fibroblasts. Glucose starvation enhanced the transport of 2-DG and 3-0-methyl-D-glucose (3-OMG) but not of L-glucose. Glucose-starvation enhanced transport was inhibited by cytochalasin B (10 microM). The starvation-induced change in 2-DG transport was due to an increase in the Vmax of both the high and low affinity transport sites (2.8- and 2.4-fold, respectively) with no effect on their Kms. The presence of 5.55 mM glucose, fructose, or L-glucose in the medium resulted in transport increases similar to those seen in glucose-starved cells, while the presence of 5.55 mM glucose, mannose, or 3-OMG repressed 2-DG transport. Glucose-starvation enhancement of 2-DG transport was blocked by cycloheximide (20 micrograms/ml) but not by actinomycin D (0.03 microgram/ml) or alpha-amanitin (3.5 microM). Readdition of glucose (5.55 mM) for six hours to glucose-starved cells led to a rapid decrease in hexose transport that could be blocked by cycloheximide but not actinomycin D. Although readdition of 3-OMG to glucose-starved cells had little effect on reversing the transport increases, glucose plus 3-OMG were more effective than glucose alone. Serum containing cultures (10% v/v) of glucose-fed or glucose-starved cells exhibited rapid decreases in 2-DG transport when exposed to glucose-containing serum-free medium. These decreases were prevented by employing glucose-free, serum-free medium. The data indicate that hexose transport regulation in cultured human fibroblasts involves protein synthesis of hexose carriers balanced by interactions of glucose with a regulatory protein(s) and glucose metabolism as they affect the regulation and/or turnover of the carrier molecules.

Phenotypic differences between tumor cells derived from different stages of neoplastic growth

Under conditions employed in our laboratory, tumors which are induced by avian sarcoma virus (ASV) usually grow progressively for several weeks and then regress. In order to further understand the basis for tumor regression in this model, we compared avian sarcoma cells which were cultured from tumors at different stages of development in terms of various phenotypic properties. The results indicate that tumor cells which are derived from progressively-growing sarcomas are rapidly growing, produce large quantities of the enzyme plasminogen activator, and have much in common generally with chicken embryo fibroblast (CEF) cells that have been transformed by ASV. In contrast, tumor cells that are obtained from regressors have elevated levels of hexose transport, grow very slowly, are greatly enlarged and display properties that are characteristic of senescent cells in culture.

Studies on the effects of in vitro ageing on saturable and nonsaturable sugar uptake in cultured human skin fibroblasts

The Vmax for saturable (i.e. 2-deoxy-D-glucose) sugar transport in cultured human fibroblasts was found to increase with in vitro ageing when the results were expressed per 10(6) cells. No age-related changes were observed in the Km for 2-deoxy-D-glucose transport or in nonsaturable (i.e. L-glucose) sugar uptake.

Saturable and nonsaturable hexose uptake in cultured human skin fibroblasts

The saturable transport of 2-deoxy-D-glucose across the cell membrane of cultured human skin fibroblasts was measured in sparse and confluent cultures. The contribution of nonsaturable sugar uptake to total sugar uptake was monitored by determining L-glucose uptake. The uptake of 2-deoxy-D-glucose was studied as a function of time and substrate concentration. Greater than 70% of transported 2-deoxy-D-glucose was phosphorylated after incubation for 2 min or less at all substrate concentrations employed (0.1 to 3.0 mM), and phosphorylation paralleled sugar uptake at these time intervals. Experiments with cytochalasin B demonstrated that an inhibition of transport was always paralleled by an equal inhibition of sugar phosphorylation.The kinetic constants for the uptake and phosphorylation of 2-deoxy-D-glucose and the inhibition of transport by competing sugars and cytochalasin B were calculated from Line-weaver-Burk plots. The Km and Vmax for saturable sugar uptake were calculated for sparse and confluent cultures after subtracting the contribution of nonsaturable sugar uptake. The resulting Km values for sugar uptake in the sparse and confluent cultures were 1.21 ± 0.04 and 0.88 ± 0.2 mM respectively. The corresponding Vmax values were 15.5 ± 1 nmol/mg protein∙min−1 for the sparse cultures and 10.1 ± 1 nmol/mg protein∙min−1 for the confluent cultures. In both sparse and confluent cultures, the Ki values for the competitive inhibition of sugar transport by D-glucose and 3-O-methyl-D-glucose were 0.8 and 2.7 mM respectively; the Ki value for the noncompetitive inhibition of sugar transport by cytochalasin B was 0.5 μM. The Km values for sugar phosphorylation by cell-free homogenates of sparse and confluent cultures were 0.57 ± 0.1 and 0.6 ± 0.1 mM respectively, while their respective Vmax values were 160 ± 53 and 139 ± 43 nmol/mg protein∙min−1.The data are in agreement with the concept that in cultured human skin fibroblasts sugar transport is the rate-limiting step in 2-deoxy-D-glucose metabolism and that phosphorylation is distinct from transport.

Transport of pantothenic acid in Lactobacillus plantarum

The characteristics of pantothenic acid (PA) transport into nonproliferating cells of Lactobacillus plantarum were studied. These characteristics included the effects of pH and temperature variations and the energy requirement for transport and binding of the vitamin. At pH 7.5 and 38 °C the intracellular vitamin was in the form of phosphopantothenic acid (P-PA) and was not exchangeable with external PA. Vitamin transport appeared separate from phosphorylation since significant free PA was observed only at elevated temperatures (e.g. 45 °C) and at low pH values. PA uptake and accumulation were energy-dependent, being inhibited completely by 10−2 M iodoacetate and the absence of glucose, exhibited pH and temperature optima of 7.5 and 38 °C, respectively, and were linear with time for at least 60 min. PA uptake exhibited substrate saturation. No free PA was observed when cells were incubated in PA concentrations above saturation levels. Apparent Km and Vmax values of 7.85 × 10−7 M and 5.35 μmol of PA/mg cells (dry weight) per minute, respectively, were determined from Lineweaver–Burk plots. Competitive inhibition of transport was observed with panthenol and pantoyl taurine. Ki values were, respectively, 3.55 × 10−5 M and 3.07 × 10−6 M. Pantoyl lactone, at concentrations which inhibited growth by 78%, had no effect on transport. The data reported suggest that PA transport is an active, mediated process and that transport may limit the phosphorylation of PA into P-PA. Inhibitor studies showed that PA transport was at least 150 times more sensitive to analogue inhibition than was growth itself, suggesting that transport of PA was not a limiting factor in the growth of L. plantarum.

Phosphopantothenic acid--the major product of pantothenic acid accumulation and a significant growth stimulatn in Lactobacillus plantarum

Non-proliferating cells of Lactobacillus plantarum accumulated about 1.3 mug of pantothenic acid (PA) per milligram dry cells when placed in a phosphate-buffered solution containing glucose, NaCl, and PA for 21 h. Under the conditions applied for PA uptake, pH 7.5 and 38 degrees C, the accumulated PA existed almost exclusively in a bound form. Free PA was observed only occasionally and then at questionably significant levels. All bound PA was released quantitatively by enzyme hydrolysis with alkaline (intestinal) phosphatase. Chromatographic analysis coupled with differential microbiological analysis of cell extracts using Saccharomyces cerevisiae, Lactobacillus helveticus, and L. plantarum identified the accumulated PA as phosphopantothenic acid (P-PA). Assay of P-PA loaded cell extracts (devoid of free PA) by L. plantarum before and after alkaline phosphatase hydrolysis showed that the growth of this primary assay organism was stimulated by 8.3%.

The disorder of hyaluronic acid metabolism in cultured skin fibroblasts derived from a patient with the Hurler syndrome

The metabolism of hyaluronic acid in cultured skin fibroblasts derived from a patient with the Hurler syndrome and from a normal subject was examined. 1. An increased net incorporation of [(3)H]glucose into the hyaluronic acid fraction of the Hurler-syndrome cells occurred when compared with normal cells. 2. During a ;chase' period, approx. 35% of the radioactivity derived from glucose was lost from the hyaluronic acid fraction of the Hurler-syndrome cells, whereas the normal cells retained all their radioactivity. 3. Although the Hurler-syndrome cells contained a ninefold greater amount of hyaluronic acid than normal cells, simultaneous determination of the specific radioactivity derived from the label revealed a value for the Hurler-syndrome cells one-half that of normal cells. These results are taken to indicate that the Hurler cells synthesize hyaluronic acid de novo at a higher rate than do normal cells. 4. Exposure of Hurler-syndrome cultured fibroblasts to a crude urine corrective-factor preparation (Neufeld & Cantz, 1971), now known to contain alpha-l-iduronidase, the specific Hurler-syndrome corrective factor (Bach et al., 1972), decreased the hyaluronic acid content to near-normal values before any effect was observed on [(3)H]glucose incorporation into the hyaluronic acid fraction. 5. In addition, the hyaluronic acid content of the normal cells decreased after exposure to the corrective factor of urine. 6. The mobilization of hyaluronic acid in Hurler-syndrome and normal cells exposed to the crude corrective-factor preparation of urine caused a decrease in specific radioactivity in the ;corrected' Hurler-syndrome cells and an increase in specific radioactivity in the ;corrected' normal cells.

Biochemical studies on the sulphated glycosaminoglycan fraction of skin fibroblasts cultured from a patient with the Hurler syndrome

1. The metabolism of the sulphated glycosaminoglycan fraction in cultured skin fibroblasts derived from a patient with the Hurler syndrome and from a normal subject was studied. Two labelled precursors, Na(2) (35)SO(4) and d-[2-(3)H]glucose, were used and their intracellular fates during uptake and ;chase' periods were assessed after separation of sulphated glycosaminoglycans from hyaluronic acid. After 4 or 8h of exposure to culture medium containing both labels, [(35)S]sulphate incorporation into the sulphated glycosaminoglycan fraction was twofold greater in Hurler-syndrome cells than in normal cells. At the same time, the rate of incorporation of [(3)H]glucose into the sulphated glycosaminoglycan fraction was approximately the same for both cell types. Consequently, an increased (35)S/(3)H ratio (nmol of [(35)S]sulphate incorporated/nmol of [(3)H]glucose incorporated) was observed for Hurler-syndrome cells compared with normal cells. 2. The results of ;chase' experiments revealed that although the expected loss and relative retention of labelled sulphate occurred in the sulphated glycosaminoglycan fraction of normal and Hurler-syndrome cells, both cell types retained all of their radioactivity derived from [(3)H]glucose. 3. After 34h exposure to a ;corrective-factor' preparation from urine, the sulphated glycosaminoglycan content (as hexosamine and [(35)S]sulphate) of the Hurler-syndrome cells approached normal values. At the same time, there was an increase in specific radioactivity of ;corrected' Hurler-syndrome cells.