Sindbis virus infection decreases intracellular pH: alkaline medium inhibits processing of Sindbis virus polyproteins.

Infection of baby hamster kidney cells by Sindbis virus, an alphavirus, resulted in a decrease in the intracellular pH of approximately 0.5 units within the first 1-2 hr after infection as measured either by equilibrium labeling with [14C]benzoic acid or by use of a pH-sensitive fluorescent probe, 2,7-bis-carboxyethyl-5,6-carboxyfluorescein-acetooxymethyl ester. In contrast, intralysosomal pH, as measured using an endocytized pH-sensitive probe, fluorescein isothiocyanate-labeled dextran, was not altered by Sindbis virus infection. Production of Sindbis virus was reduced by more than 90% and post-translational processing of Sindbis virus envelope precursors was inhibited in infected cells incubated in alkaline medium.

Cell surface effects of human immunodeficiency virus.

Cell killing by human immunodeficiency virus (HIV) is thought to contribute to many of the defects of the acquired immunodeficiency syndrome (AIDS). Two types of cytopathology are observed in HIV-infected cultured cells: cell-cell fusion and killing of single cells. Both killing processes appear to involve cell surface effects of HIV. A model is proposed for the HIV-mediated cell surface processes which could result in cell-cell fusion and single cell killing. The purpose of this model is to define the potential roles of individual viral envelope and cell surface molecules in cell killing processes and to identify alternative routes to the establishment of persistently-infected cells. Elucidation of HIV-induced cell surface effects may provide the basis for a rational approach to the design of antiviral agents which are selective for HIV-infected cells.

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.

Sindbis virus infection increases hexose transport in quiescent cells.

Sindbis virus infection of baby hamster kidney cells or chick embryo cells resulted in a significant increase in the rate of uptake of [2-3H]deoxy-D-glucose ([3H]dGlu). Stimulation of hexose transport in Sindbis virus-infected cells occurred only if the cells were rendered quiescent by culturing at high density or by serum starvation. In contrast, Sindbis virus-induced inhibition of potassium transport, measured as a decrease in the uptake of 86Rb+, was independent of cell growth state. Stimulation of [3H]dGlu uptake in Sindbis virus-infected cells was the result of an increase in the Vmax of the hexose transporter, but not a change in the Km. The stimulation of [3H]dGlu uptake induced by Sindbis virus was insensitive to the drug actinomycin D, but was blocked by cordycepin. The stimulation was also insensitive to treatment with tunicamycin, which prevented the virally induced inhibition of the plasma membrane-associated Na+/K+ ATPase and termination of host protein synthesis.

Intracellular K+ and the expression of transformation parameters by chick cells transformed with the Bryan strain of Rous sarcoma virus.

As normal chick embryo (CE) cells entered quiescence the intracellular concentrations of both Na+ and K+ declined. Comparable decreases in intracellular concentrations of Na+ and K+ were not observed in CE cells transformed by either the Schmidt-Ruppin (SR) or the Bryan (B) strain of Rous sarcoma virus (RSV). Intracellular concentrations of Na+ were higher in SR-RSV-transformed CE cells than in B-RSV-transformed cells and uninfected CE cells at all times after plating. In contrast, intracellular concentrations of K+ were higher in B-RSV-transformed CE cells than in SR-RSV-transformed cells. Uninfected CE cells incubated in medium containing an elevated concentration of K+ (an increase from 5 to 30 mM) exhibited several, but not all, of the transformation parameters expressed by B-RSV-transformed CE cells.

The ratio of plasma membrane cholesterol to phospholipid and the inhibition of Sindbis virus maturation by low NaCl medium.

Sindbis virus maturation is inhibited by low NaCl medium in chick embryo cells and in one strain of BHK cells, but not in another strain of BHK cells which has a different passage history. The plasma membrane of the cells in which Sindbis virus maturation is resistant to low NaCl medium has a higher ratio of cholesterol to phospholipid than the other cells. Cholesterol-containing liposomes, but not cholesterol-free liposomes, can release Sindbis virus from low NaCl-inhibited cells. These results suggest that low NaCl medium may block Sindbis virus maturation by a mechanism which is influenced by the ratio of plasma membrane cholesterol to phospholipid.