Stress induces an increased hexose uptake in cultured cells

Nutritional demands and metabolic characteristics of the DSIR-HA-1179 insect cell line during growth and infection with the Oryctes nudivirus

The DSIR-HA-1179 coleopteran cell line has been identified as a susceptible and permissive host for the in vitro replication of the Oryctes nudivirus, which can be used as a biopesticide against the coconut rhinoceros beetle, pest of palms. The major challenge to in vitro large-scale Oryctes nudivirus production is ensuring process economy. This rests, among other requisites, on the use of low-cost culture media tailored to the nutritional and metabolic needs of the cell line, both in uninfected and infected cultures. The aim of the present study was to characterize the nutritional demands and the metabolic characteristics of the DSIR-HA-1179 cell line during growth and subsequent infection with Oryctes nudivirus in the TC-100 culture medium. Serum-supplementation of the culture medium was found to be critical for cell growth, and addition of 10% fetal bovine serum v/v led to a maximum viable cell density (16.8 × 10⁵ cells ml^-1) with a population doubling time of 4.2 d. Nutritional and metabolic characterization of the cell line revealed a trend of glucose and glutamine consumption but minimal uptake of other amino acids, negligible production of lactate and ammonia, and the accumulation of alanine, both before and after infection. The monitoring of virus production kinetics showed that the TC-100 culture medium was nutritionally sufficient to give a peak yield of 7.38 × 10⁷ TCID₅₀ ml^-1 of OrNV at the 6th day post-infection in attached cultures of DSIR-HA-1179 cells in 25 cm² T-flasks. Knowledge of the cell line's nutritional demands and virus production kinetics will aid in the formulation of a low-cost culture medium and better process design for large-scale OrNV production in future.

Examination of the effects of arsenic on glucose homeostasis in cell culture and animal studies: development of a mouse model for arsenic-induced diabetes

Previous epidemiologic studies found increased prevalences of type 2 diabetes mellitus in populations exposed to high levels of inorganic arsenic (iAs) in drinking water. Although results of epidemiologic studies in low-exposure areas or occupational settings have been inconclusive, laboratory research has shown that exposures to iAs can produce effects that are consistent with type 2 diabetes. The current paper reviews the results of laboratory studies that examined the effects of iAs on glucose metabolism and describes new experiments in which the diabetogenic effects of iAs exposure were reproduced in a mouse model. Here, weanling male C57BL/6 mice drank deionized water with or without the addition of arsenite (25 or 50 ppm As) for 8 weeks. Intraperitoneal glucose tolerance tests revealed impaired glucose tolerance in mice exposed to 50 ppm As, but not to 25 ppm As. Exposure to 25 and 50 ppm As in drinking-water resulted in proportional increases in the concentration of iAs and its metabolites in the liver and in organs targeted by type 2 diabetes, including pancreas, skeletal muscle and adipose tissue. Dimethylarsenic was the predominant form of As in the tissues of mice in both 25 and 50 ppm groups. Notably, the average concentration of total speciated arsenic in livers from mice in the 50 ppm group was comparable to the highest concentration of total arsenic reported in the livers of Bangladeshi residents who had consumed water with an order of magnitude lower level of iAs. These data suggest that mice are less susceptible than humans to the diabetogenic effects of chronic exposure to iAs due to a more efficient clearance of iAs or its metabolites from target tissues.

Cell signaling, the essential role of O-GlcNAc!

An increasing body of evidence points to a central regulatory role for glucose in mediating cellular processes and expands the role of glucose well beyond its traditional role(s) in energy metabolism. Recently, it has been recognized that one downstream effector produced from glucose is UDP-GlcNAc. Levels of UDP-GlcNAc, and the subsequent addition of O-linked beta-N-acetylglucosamine (O-GlcNAc) to Ser/Thr residues, is involved in regulating nuclear and cytoplasmic proteins in a manner analogous to protein phosphorylation. O-GlcNAc protein modification is essential for life in mammalian cells, highlighting the importance of this simple post-translational modification in basic cellular regulation. Recent research has highlighted key roles for O-GlcNAc serving as a nutrient sensor in regulating insulin signaling, the cell cycle, and calcium handling, as well as the cellular stress response.

Arsenic exposure and type 2 diabetes: a systematic review of the experimental and epidemiological evidence

Chronic arsenic exposure has been suggested to contribute to diabetes development. We performed a systematic review of the experimental and epidemiologic evidence on the association of arsenic and type 2 diabetes. We identified 19 in vitro studies of arsenic and glucose metabolism. Five studies reported that arsenic interfered with transcription factors involved in insulin-related gene expression: upstream factor 1 in pancreatic beta-cells and peroxisome proliferative-activated receptor gamma in preadipocytes. Other in vitro studies assessed the effect of arsenic on glucose uptake, typically using very high concentrations of arsenite or arsenate. These studies provide limited insight on potential mechanisms. We identified 10 in vivo studies in animals. These studies showed inconsistent effects of arsenic on glucose metabolism. Finally, we identified 19 epidemiologic studies (6 in high-arsenic areas in Taiwan and Bangladesh, 9 in occupational populations, and 4 in other populations). In studies from Taiwan and Bangladesh, the pooled relative risk estimate for diabetes comparing extreme arsenic exposure categories was 2.52 (95% confidence interval, 1.69-3.75), although methodologic problems limit the interpretation of the association. The evidence from occupational studies and from general populations other than Taiwan or Bangladesh was inconsistent. In summary, the current available evidence is inadequate to establish a causal role of arsenic in diabetes. Because arsenic exposure is widespread and diabetes prevalence is reaching epidemic proportions, experimental studies using arsenic concentrations relevant to human exposure and prospective epidemiologic studies measuring arsenic biomarkers and appropriately assessing diabetes should be a research priority.

Dynamic O-GlcNAc modification of nucleocytoplasmic proteins in response to stress. A survival response of mammalian cells

Cellular response to environmental, physiological, or chemical stress is key to survival following injury or disease. Here we describe a unique signaling mechanism by which cells detect and respond to stress in order to survive. A wide variety of stress stimuli rapidly increase nucleocytoplasmic protein modification by O-linked beta-N-acetylglucosamine (O-GlcNAc), an essential post-translational modification of Ser and Thr residues of metazoans. Blocking this post-translational modification, or reducing it, renders cells more sensitive to stress and results in decreased cell survival; and increasing O-GlcNAc levels protects cells. O-GlcNAc regulates both the rates and extent of the stress-induced induction of heat shock proteins, providing a molecular basis for these findings.

Effects of mistletoe lectin I and ionizing radiation on the glucose and thymidine uptake in tumour cells in vitro

The increased uptake of hexose by mammalian cells is considered to be a general response to stress. Nowadays, mistletoe lectin separated from the extracts of the European mistletoe (Viscum album L.) is often used in adjuvant cancer therapy. The present work studies the effect of the lectin on unirradiated and x-irradiated tumour cells. The response of cultured human lung carcinoma cells (Calu-1) was followed by radioactive glucose uptake as well as by tritiated thymidine incorporation. The cells were maintained either in a complete or a so-called restrictive medium. Slight metabolic changes were found in the restrictive medium but not in the complete one. Mistletoe lectin I at a very low concentration (0.001 ng/mL) increased the glucose uptake and thymidine incorporation. Ionizing radiation (1 Gy) did not influence the hexose uptake but it enhanced the incorporation of thymidine. It seems that the actions of two different factors (mistletoe lectin I and radiation) proved to be rather provoking stress effects for the tumour cells as detected in the restrictive medium.

The effect of oxygen radicals on rat thymocyte glucose transport is independent of the site of their generation

We studied the relationship between the site of production of oxygen radicals and their effect on a rat thymocyte functional activity, the glucose transport, measured using a radioactive analogue of glucose, 2-deoxy-glucose. We compared the effects of a hydrophilic thermolabile azo compound, mimicking a radical attack outside the cell, with the lipid-soluble cumene hydroperoxide, which initiates lipid peroxidation in cell membranes. Our results show that a low grade oxidative stress stimulated glucose uptake rapidly, independently of the site of radical generation. In the presence of the azocompound, glucose uptake increased smoothly, attaining its maximum extent within 1 h. In thymocytes treated with cumene hydroperoxide the rate of glucose transport increased suddenly and remained constant over 1 h. The effects of the radical donors on TBARS production and protein sulfhydryl groups content were also evaluated. In thymocytes treated with the azo derivative no lipid peroxidation was observed, but a slow decrease of protein thiol groups occurred; after the addition of cumene hydroperoxide sulfhydryl groups did not change and TBARS increased significantly. The water-soluble antioxidant Trolox was able to remove the glucose uptake increase induced by the hydrophilic initiator and to delay the loss of membrane integrity.

Transforming oncogenes regulate glucose transport by increasing transporter affinity for glucose: contrasting effects of oncogenes and heat stress in a murine marrow-derived cell line

Transforming oncogenes often overcome the growth factor requirements of cells by activating growth factor signal transduction pathways. Increased energy utilization by transformed cells is a well known phenomenon, but whether glucose uptake is regulated at the level of the glucose transporter has not been clearly established. To determine whether cell transformation by specific oncogenes like, v-H-ras and v-abl affects the activation state of glucose transporters, bone marrow-derived IL-3-dependent 32D (clone3) cells transfected with temperature-sensitive ras and abl oncogenes were used to compare proliferative responses and glucose transporting ability of these cells with the parental cell line at permissive (32 degrees C) and non-permissive (40 degrees C) temperatures. Transformed cells showed elevated incorporation of [3H]thymidine and enhanced tyrosine kinase activity, both of which were abrogated in temperature-sensitive mutants maintained at the non-permissive temperature. Compared with control cells, 2-deoxy-D-[1-(3)H]glucose (2-DOG) uptake was not significantly different in transformed cells at the permissive temperature. However, transformation was associated with a 2-2.5-fold greater affinity of glucose transporters for glucose (Km) and this was reversed following treatment with tyrosine kinase inhibitor, genistein. Maximum velocity of glucose transport (Vmax) and membrane expression of transporters were reduced in oncogene-transformed cells. At the non-permissive temperature, glucose uptake was elevated in both control and oncogene-transformed cells. This increase in glucose transport was not associated with a change in transporter affinity for glucose, but increased Glut-1 expression was observed indicating a 'heat stress' effect that overrode the effects attributable to oncogene loss. The 'heat stress' effect was inhibited by protein synthesis inhibitor cycloheximide. These results provide evidence for intrinsic activation of glucose transporters by the transforming oncogenes ras and abl, and indicate that oncogenes and 'heat stress' regulate glucose transport by different mechanisms.

Mechanisms of signal transduction in the stress response of hepatocytes

Adaptation of animals to stress is a unique property of life which allows the survival of the species. The stress response of hepatocytes is a very complex phenomenon, sometimes involving a cascade of events. The general stress signals are elucidated by mobilization of carbohydrate stores and akin to the insulin mediators. Oxidative signals are generated by pesticides, heavy metals, drugs, and alcohol which may or may not be under the purview of peroxisomes. Peroxisomal responses are well-defined involving specific receptors, whereas nonperoxisomal responses may be signaled by calcium, the Ah receptor, or built-in antioxidant systems. The intoxication signals are generally thought to be membrane defects induced by xenobiotics which then lead to highly nonspecific responses of hepatocytes. Detoxication signals, on the other hand, are specific responses of hepatocytes triggering de novo syntheses of detoxifier proteins or enzymes. Evidence reveals the existence of two distinct mechanisms of signal transduction in stressed hepatocytes--one involving the peroxisome and the other the plasma membrane.

Effects of antitumor agents on 3H-2-deoxyglucose uptake in tumor cells and their relationship with the main targets of the antitumor agents

To investigate the effects of antitumor drugs on 3H-2-deoxyglucose (DG) uptake in tumor cells, we performed DG uptake studies of the short-term treatment of four kinds of antitumor drugs in a cell culture system. The antitumor drugs adriamycin (ADM) and cisplatin (cDDP), which affect on DNA synthesis, did not greatly affect DG uptake, but DG uptake was lowered by antitumor drugs, actinomycin D (AcD) and cycloheximide (CHX), which target the gene expression system. To investigate the mechanism of DG uptake changes, we also tested the effects of some glucose metabolic inhibitors on DG uptake. An inhibitor of glycolytic flow (iodoacetate) lowered DG uptake whereas mitochondrial inhibition increased DG uptake. These results on the inhibition of glucose metabolism indicated that there were two types of factors affecting DG uptake directly; one affects glycolysis and the other affects oxidative phosphorylation. The two antitumor drugs with effects on gene expression were thought to act by the former. The effects of the drug treatments for tumors on DG uptake could be divided into three groups; glycolysis inhibition, mitochondrial inhibition and no relation to glucose metabolism. With the further observations of FDG uptake changes based on this prediction, the biochemical relationship between treatment effects and FDG uptake changes will be clarified.

Analysis of epithelial cell stress response during infection by Shigella flexneri

Shigella flexneri-infected macrophage cells undergo an apoptotic-like death as early as one hour after infection (A. Zychlinsky, M. C. Prévost, and P. J. Sansonetti, Nature [London] 358:167-168, 1992). To determine the fate of infected epithelial cells, we characterized the viability, morphology, and several metabolic activities of HeLa cells after treatment with M90T, an invoffve isolate of S. flexneri serotype 5, or BS176, a noninvasive isolate cured of the 220-kb virulence plasmid. Using standard assays, we found that for at least 4 h after infection with M90T, HeLa cells remained viable and did not detach or lyse. The ultrastructural morphology of HeLa cells heavily infected with M90T was free of hallmarks associated with cells undergoing apoptosis. Consistent with the idea that intracellular bacterial growth is metabolically stressful to the host cell, we observed that, compared with BS176 treated-HeLa cells, M90T-treated HeLa cells showed (i) a significant decrease in the total pool size of nucleoside triphosphates, (ii) a reduced ability to incorporate extracellular radiolabeled methionine into the soluble and insoluble cell fractions, and (iii) a stimulation of glucose uptake. However, there was no detectable increase in expression of the stress-inducible hsp70 gene in M90T-infected HeLa cells or activation of the anaerobic metabolic pathway as determined by measuring total lactate levels. These results demonstrate clearly that the fate of S.flexneri-infected cells can vary dramatically between cell types and agree with the hypothesis that the destruction of epithelial cells observed in experimental models of shigellosis is due to the host inflammatory response and probably not bacterial intracellular multiplication per se.

Control of glucose transport by GLUT1: regulated secretion in an unexpected environment

Studies designed to elucidate the mechanism of regulation of the GLUT1 isoform of the glucose transporter in response to a variety of cellular stresses are reviewed. Using ts mutants of vesicular stomatitis virus, it was shown that the viral L gene was responsible for the stimulation of glucose transport in infected cells. Immunofluorescence of GLUT1 demonstrated that the increase in glucose transport was the consequence of a translocation of the transporter from a reservoir in cytoplasmic vesicles to the plasma membrane. When cells were cycled between deficient and standard medium, the change in glucose transport rates was paralleled by a cycling of the transporter between the plasma membrane and the cytoplasmic vesicles. The redistribution of GLUT1 was not a consequence of a general redistribution of recycling plasma membrane proteins. Instead, the findings focus attention on the regulated exocytosis of specific membrane constituents in cells that, until recently, were not thought to exhibit this capacity.

Effects of mild heat shock on glycogenesis and its regulation by insulin in cultured fetal hepatocytes

The effects of a mild heat shock were investigated using cultured 15-day-old fetal rat hepatocytes in which an acute glucocorticoid-dependent glycogenic response to insulin was present. After exposure from 15 min to 2 h at 42.5 degrees C, cell surface [125I]insulin binding progressively decreased down to 60% of the value shown in cells kept at 37 degrees C, due toa decrease in the apparent number of insulin binding sites with little change in insulin receptor affinity. In parallel cultures, protein labeling with [35S]methionine exhibited stimulated synthesis of specific proteins, in particular, 73-kDa Hsc (heat shock cognate) and 72-kDa Hsp (heat shock protein). When cells were returned to 37 degrees C after 2 h at 42.5 degrees C, cell surface insulin binding showed a two-third restoration within 3 h (insulin receptor half-life = 13 h), with similar concomitant return of Hsps72,73 synthesis to preinduction levels. The rate of [14C]glucose incorporation into glycogen measured at 37 degrees C after 1- to 2-h heat treatment revealed a striking yet transient increase in basal glycogenesis (up to 5-fold). At the same time, the glycogenesis stimulation by insulin was reduced (from 3.2 to 1.4-fold), whereas that induced by a glucose load was maintained. Induction of thermotolerance after a first heating was obtained for the heat shock-dependent events except for the enhanced basal glycogenesis. In insulin-unresponsive cells grown in the absence of glucocorticoids, heat shock decreased the glycogenic capacity without modifying the glucose load stimulation, supporting the hypothesis that insulin and thermal stimulation of glycogenesis share at least part of the same pathway. Inverse variations were observed between Hsps72,73 synthesis and both cell surface insulin receptor level and insulin glycogenic response in fetal hepatocytes experiencing heat stress.

Analyses of the effect of monensin on glycosphingolipid metabolism

The effect of monensin on glycosphingolipid metabolism was reinvestigated. It was found that monensin increased the uptake of [3H]galactose by human fibroblasts, causing an enhanced metabolic labelling of glycosphingolipids. The preferential incorporation of radioactivity into ceramide monosaccharide in the presence of monensin was accompanied by an equally increased rate of degradation. However, using radiolabelled precursors of the ceramide moiety, a generally diminished uptake of radioactivity into all glycosphingolipids was observed under the influence of monensin, with the exception of mono- and di-hexosylceramide. The enhanced incorporation of radiolabel by these two glycolipids, as well as their increased cellular chemical content, may reflect early synthesis in a monensin-insensitive pre-Golgi compartment after disruption of the cellular Golgi transport system by monensin.

Regulation of glucose uptake by stressed cells

Lactate production by BHK cells is stimulated by arsenite, azide, or by infection with Semliki Forest virus (SFV). In the case of arsenite or SFV infection, the increase correlates approximately with the increase in glucose transport as measured by uptake of [3H] deoxy glucose (dGlc); in the case of azide, the increase in lactate production exceeds that of glucose transport. Hence glucose utilization by BHK cells and its stimulation by anaerobic and other types of cellular stress is controlled at least in part at the level of glucose transport. The glucose uptake by BHK cells is also stimulated by serum and by glucose deprivation. In these circumstances, as with arsenite, stimulation is reversible, with t1/2 of 1-2 hours; stimulation is compatible with a translocation of the glucose transporter protein between an intracellular site and the plasma membrane (shown here for serum and previously for arsenite). The surface binding and rate of internalization of [125I]-labelled transferrin and [125I] alpha 2-macroglobulin was studied to determine whether changes in glucose transport are accompanied by changes in the surface concentration or rate of internalization of membrane proteins. The findings indicate that changes in glucose transport do not reflect a consistent and general redistribution of membrane receptors. Taken together, the results are compatible with the proposal that BHK cells exposed to stimuli like insulin or serum, or to stresses like arsenite, azide, SFV infection, or deprivation of glucose, respond in the same manner: namely, by an increased capacity to transport glucose brought about by reversible and specific translocation of the transporter protein from an (inactive) intracellular site to the plasma membrane.

Response of mammalian cells to metabolic stress; changes in cell physiology and structure/function of stress proteins

In response to adverse changes in their local environment, cells or tissues from all organisms increase the expression of a group of proteins referred to as heat shock or stress proteins. Collectively, the stress proteins are thought to provide the cell with some degree of protection during the environmental insult as well as facilitate the repair and recovery of metabolic pathways perturbed as a consequence of the stress event. Within the past few years it has become apparent that most all of the stress proteins are present in appreciable levels in the unstressed cell and are involved in a number of very basic and essential biochemical pathways. The present review has discussed pertinent changes in cell physiology in mammalian cells experiencing metabolic stress. In addition, considerable attention has been given to discussing the properties and possible functions of the individual stress proteins.

Membrane transport and disease

Four situations in which membrane transport is altered by disease are discussed: (a) non-specific leaks induced by poreforming agents; (b) glucose transport and cellular stress; (c) Ca2+-ATPase and hypertension; (d) Na+ channels and HSV infection.

Differential effects of follicle-stimulating hormone, insulin, and insulin-like growth factor I on hexose uptake and lactate production by rat Sertoli cells

The stimulatory effects of follicle-stimulating hormone (FSH), insulin, and insulin-like growth factor I (IGF-I) on lactate production and hexose uptake by Sertoli cells from immature rats were studied. The time-courses and the maximal stimulatory effects of FSH, insulin, and IGF-I on lactate production were virtually identical. When Sertoli cells were incubated in the presence of FSH in combination with insulin or IGF-I (submaximal doses), additive but no pronounced synergistic effects were observed. The stimulatory effects of FSH and insulin were not dependent on the presence of extracellular calcium. 2-Deoxy-D-glucose (2-DOG), an analogue of D-glucose, was used to investigate the hexose transport system of Sertoli cells. Uptake of 2-DOG was linear in time and virtually all of the intracellular 2-DOG was phosphorylated up to 30 min of incubation; 2-DOG uptake was inhibited by cytochalasin B, but not by cytochalasin E. D-glucose, but not D-galactose, appeared to be an effective competitor of 2-DOG uptake. The Km of 2-DOG uptake was not influenced by FSH, insulin, and IGF-I. FSH had no effect on the Vmax of 2-DOG uptake, whereas insulin and IGF-I caused a 30% stimulation of the Vmax. It is concluded that FSH, insulin, and IGF-I stimulate lactate production by cultured Sertoli cells, but that only insulin and IGF-I stimulate hexose transport. The insulin-like effect of FSH on Sertoli cells may principally involve stimulation of glycolytic enzyme activities.

Common pathway for the induction of hexose transport by insulin and stress

The effect of stress (heat shock, arsenite, or Semliki Forest virus [SFV] infection) on the induction of increased hexose transport has been compared with that of insulin. All four treatments increase the Vmax for transport by BHK cells three- to five-fold, with little effect (less than 40% decrease) on Km. Hydrogen peroxide and phenylarsine oxide (PAO) prevent the increase in hexose transport induced by stress treatments as effectively as they do that induced by insulin. Pinocytosis is not affected by any of the four treatments. On the other hand, the induction by insulin is sensitive to amiloride, whereas that by arsenite is not. Rat embryo fibroblasts, which respond poorly to insulin, respond well to arsenite, heat shock, or SFV infection. It is concluded that the stress response is mediated by certain compounds that may be common to those required for the action of insulin, but that those compounds act at a stage subsequent to the function of the insulin receptor.

Stress-induced increase of hexose transport as a novel index of cytopathic effects in virus-infected cells: role of the L protein in the action of vesicular stomatitis virus

The VSV-specific increase in hexose transport by BHK cells has been measured by assay of the [3H]dGlc/[14C]AIB uptake ratio. The effect was abolished by uv-irradiation of the virus, indicating that viral gene expression is required. Cells infected with the T1026 R1 mutant of VSV, which causes only slight cytopathic changes, exhibited only a slight increase in hexose uptake. Cells infected with temperature-sensitive (ts) mutants of VSV that are defective in the function of the viral N, NS, G, or M proteins at the restrictive temperature (39.5 degrees) exhibited increased [3H]dGLC/[14C]AIB uptake ratios typical of wild-type virus at either restrictive (39.5 degrees) or permissive temperature (34 degrees). Cells infected with a mutant defective in the function of the viral L protein exhibited an increased [3H]dGlc/[14C]AIB uptake ratio at permissive temperature (34 degrees) only; at restrictive temperature (39.5 degrees) the uptake ratio was essentially the same as that of mock-infected cells. Temperature-shift experiments indicated that the effect on hexose transport persisted for at least 6 hr in cells which no longer expressed function L protein, and that when expression of L was restricted to the first 2 hr of infection, an almost complete stimulation of hexose transport was observed 4 hr later. These results indicate that expression of the L gene is a necessary factor for inducing an increased hexose uptake in VSV-infected BHK cells. They also suggest that the action of the L protein on hexose transport is indirect, and is presumably mediated by other cellular constituents. The studies support the concept that an increased dGlc uptake may be a useful index of the cytopathic consequences of virus infection.

Induction of the stress response: alterations in membrane-associated transport systems and protein modification in heat shocked or Sindbis virus-infected cells

Heat shock or Sindbis virus infection of chick embryo (CE) or baby hamster kidney (BHK) cells resulted in a decrease in the uptake of 86Rubidium+, a K+ tracer. Both stressful treatments decreased 86Rb+ uptake by inhibition of the ouabain-sensitive Na+/K+ ATPase. Alterations in the intracellular levels of monovalent ions may be involved in translational or transcriptional control of the stress response. Heat shock or Sindbis virus infection also resulted in an increase in rate of uptake of [3H]deoxy-D-glucose and a decrease in the incorporation of [3H]glucosamine or [3H]mannose into most cellular proteins. These results suggested that heat shock or Sindbis virus infection alter hexose metabolism and that abnormally glycosylated proteins may accumulate in stressed cells. Exposure of uninfected chick embryo cells to elevated temperature had little effect on the overall rate of incorporation of [32P]orthophosphate into cellular proteins. However, one protein (Mr 31,000; pp31) displayed increased incorporation of [32P]orthophosphate and two other proteins (Mr 33,000 and 20,000; pp33 and pp20) displayed decreased incorporation. Sindbis virus infection failed to mimic or to modify these heat shock induced alterations in protein phosphorylation.

Increased sensitivity of virus-infected cells to inhibitors of protein synthesis does not correlate with changes in plasma membrane permeability

Semliki Forest virus-infected BHK cells or herpes simplex virus-infected Vero cells were incubated with the protein synthesis inhibitors hygromycin B and gougerotin. Infected cells take up no more [3H]hygromycin or [3H]gougerotin than do mock-infected cells, at a time p.i. at which either compound is more inhibitory to protein synthesis in infected, than in mock-infected cells. The concentrations of hygromycin and gougerotin required to inhibit protein synthesis in intact cells (irrespective of whether they are infected or not) are several orders of magnitude higher than those required in either permeabilized cells or in cell-free systems. Infected cells take up 86Rb+ at the same rate as mock-infected cells, their intracellular content of K+ is the same, and the activity of the Na+ pump is the same. It is concluded that the increased efficacy of hygromycin and gougerotin in virus-infected cells is a consequence of altered intracellular compartmentation and that increases in permeability of the plasma membrane, if any, are so small as to be undetectable by direct methods.