Increased sugar transport in BHK cells infected with Semliki Forest virus or with herpes simplex virus

Investigation of cell culture conditions for optimal foot-and-mouth disease virus production

Background

Foot-and-mouth disease is a highly contagious and economically devastating disease with endemic occurrence in many parts of the world. Vaccination is the method of choice to eradicate the disease and to limit the viral spread. The vaccine production process is based on mammalian cell culture, in which the viral yield varies in dependence of the composition of the culture media. For foot-and-mouth disease virus (FMDV), very little is known about the culture media components that are necessary to grow the virus to high titers in cell culture.

Results

This study examined the influence of increasing concentrations of glucose, glutamine, ammonium chloride and different cell densities on the yield of FMDV. While an excess of glucose or glutamine does not affect the viral yield, increasing cell density reduces the viral titer by a log₁₀ step at a cell density of 3 × 10⁶ cells/mL. This can be mitigated by performing a 100% media exchange before infection of the cells.

Conclusions

The reasons for the diminished viral growth, if no complete media exchange has been performed prior to infection, remain unclear and further studies are necessary to investigate the causes more deeply. For now, the results argue for a vaccine production process with 100% media exchange to reliably obtain high viral titers.

Electronic supplementary material

The online version of this article (10.1186/s12896-019-0527-5) contains supplementary material, which is available to authorized users.

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.

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.

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.

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.

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.

Modification of membrane permeability by animal viruses

Animal viruses modify membrane permeability during lytic infection. There is a co-entry of macromolecules and virion particules during virus penetration and a drastic change in transport and membrane permeability at the late stages of the lytic cycle. Both events are of importance to understand different molecular aspects of viral infection, as virus entry into the cell and the interference of virus infection with cellular metabolism. Other methods of cell permeabilization of potential relevance to understand the mechanism of viral damage of the membrane are also discussed.

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.

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.

Stress induces an increased hexose uptake in cultured cells

Temperature-sensitive mutants have revealed a region of the herpes simplex virus 1 genome that affects both the uptake of hexose and the synthesis of heat shock proteins. Other inducers of heat-shock proteins, namely heat shock itself and arsenite, likewise induce an increased uptake of hexose. The increased uptake, like that induced by insulin, is insensitive to the presence of actinomycin D or cycloheximide. It is concluded that an increased hexose uptake, reflecting an activation or relocation of existing hexose transport protein, is a general biochemical response of stressed cells.