The role of protein synthesis in the eclipse period of newcastle disease virus multiplication in HeLa cells as studied with puromycin

Replication of canine herpesvirus: I. Synthesis of viral deoxyribonucleic Acid

This paper reports the results of two series of experiments. The first series indicated that deoxyribonucleic acid (DNA) extracted from partially purified canine herpesvirus virions is characterized by a high guanine plus cytosine molar base ratio (65 to 67 mole%), similar to the DNA of herpes simplex virus. In the second series of experiments it was estimated, on the basis of uptake of tritiated thymidine, that in dog kidney cells canine herpesvirus-DNA synthesis starts at 4 hr and continues until 16 hr after infection. Treatment of infected cells with puromycin during the first 4 hr of infection blocks the onset of viral DNA synthesis, whereas, after this time the uptake of thymidine is unaffected.

INHIBITION OF RIBONUCLEIC ACID SYNTHESIS IN NEWCASTLE DISEASE VIRUS-INFECTED CELLS BY PUROMYCIN AND 6-AZAURIDINE

Wilson, D. E. (Rensselaer Polytechnic Institute, Troy, N.Y.), and P. LoGerfo. Inhibition of ribonucleic acid synthesis in Newcastle disease virus-infected cells by puromycin and 6-azauridine. J. Bacteriol. 88:1550-1555. 1964.-Puromycin and 6-azauridine were used to inhibit protein and ribonucleic acid (RNA) synthesis during Newcastle disease virus replication. Viral RNA, measured by the incorporation of uridine-2-C(14), increased rapidly 6 to 7 hr after infection and reached a peak at 12 hr. Viral RNA synthesis was inhibited by puromycin added at the time of infection or at any time up to 4 hr after infection, but not thereafter. 6-Azauridine (3 mg/ml) inhibited over 90% of the viral RNA synthesis and inhibited protein synthesis to a small extent. Infected cells synthesized more viral RNA than did untreated controls when exposed to azauridine alone for 5 hr, followed by puromycin alone for 9 hr. It was concluded that immediately after virus infection, virus-specific proteins, which are necessary for viral RNA synthesis, were synthesized. Virus-specific protein synthesis may occur even when viral RNA synthesis is greatly inhibited. After virus-specific protein synthesis has taken place, viral RNA synthesis may take place when protein synthesis is almost totally inhibited.

RELATION OF PROTEIN SYNTHESIS TO THE DIVISION CYCLE IN MAMMALIAN CELL CULTURES

Protein synthesis in suspension cultures of human cells in logarithmic growth was inhibited with puromycin or chloramphenicol, and the growth rate and mitotic index were measured as a function of time. The mitotic index remained constant for about 1 hour after addition of inhibitor; this indicates that any protein synthesis necessary for mitosis is completed before the beginning of prophase. For rates of protein synthesis equal to or greater than 0.3 that of untreated cells, the index decreased over a 5- to-7-hour period and then remained constant. The final value of the index relative to that of the uninhibited control was approximately equal to the relative rate of protein synthesis. The period from the end of DNA synthesis to mitosis (G₂) was increased by partial inhibition of protein synthesis. A mathematical model of the inhibition process has been formulated which predicts the shape of the mitotic index curves and the increase in the G₂ period. An interpretation of the model is that the rate-limiting step is the synthesis of an enzyme which catalyzes the formation of a compound necessary to initiate mitosis.

The role of protein synthesis in the stimulation by LH of prostaglandin accumulation in rat preovulatory follicles in vitro

Preovulatory follicles isolated from immature rats, treated in vivo with pregnant mare's serum gonadotropin, were incubated in vitro and the accumulation of prostaglandin E measured. The addition of luteinizing hormone (5 mug/ml) increased this accumulation, after a lag period of 3 hours. This delay suggested the involvement of macromolecular synthesis in the mechanism of prostaglandin stimulation by luteinizing hormone. When the synthesis of protein was inhibited by the addition of puromycin (100 muM), the luteinizing hormone stimulation of prostaglandin E in these follicles was completely abolished. This inhibition was not seen with an analogue of puromycin, which does not inhibit protein synthesis, puromycin amino-nucleoside. These data suggest that concomitant protein synthesis is required for the luteinzing hormone stimulation of prostaglandin accumulation in rat follicles.

Studies on cellular autophagocytosis. The relationship of autophagocytosis to protein synthesis and to energy metabolism in rat liver and flounder kidney tubules in vitro

The purpose of the present study was to elucidate the metabolic requirements of autophagocytosis. Two model systems were used for this purpose: a) glucagon-induced autophagocytosis in the rat liver, and b) the wave of autophagocytosis which occurs when isolated flounder kidney tubules are incubated in vitro. In the rat liver, protein synthesis was inhibited by the administration of cycloheximide (1.5 mg/kg) to rats 2 hours prior to glucagon injection. In flounder kidney tubules, protein synthesis was inhibited at least 90% by adding cycloheximide, actinomycin D, pactamycin and puromycin to the medium. In both systems the inhibition of protein synthesis failed to inhibit the formation of autophagic vacuoles or their subsequent transformation into autolysosomes, as depicted from electron microscopic histochemical preparations. In flounder kidney tubules no differences were found in the levels of p-nitrophenylphosphates, beta-DL-glycerophosphatase, N-acetyl-beta-D-glucosaminidase, arylsulphatase, beta-D-galactosidase or acid proteinase when tubules were incubated up to 5 hours in the presence or absence of protein synthesis inhibitors. When ethionine was administered to rats 2 hours before glucagon injection, a decrease of approximately 75% in the ATP levels was observed. After ethionine administration, glucagon failed to induce the formation of autophagic vacuoles. The incubation of flounder kidney tubules in the presence of cyanide or in a nitrogen atmosphere decreased the ATP levels to less than 10% of controls and blocked autophagy. On the other hand, cyanide had little effect on acid hydrolase levels at 1 hour of incubation. A wide variety of other inhibitors were also shown to block autophagy. These results further support the hypothesis that, in the formation of antophagic vacuoles, preexisting enzyme and membrane pools are utilized. On the other hand, the esotropy-exotropy membrane conformational changes occurring in the formation of autophagic vacuoles seem to be energy dependent and can therefore be blocked by lowering intracellular ATP levels.

Effect of puromycin and actinomycin D on a persistent mumps virus infection in vitro

Puromycin and actinomycin D were used to treat a line of human conjunctiva cells persistently infected with mumps virus (C-M cells) in order to determine where virus synthesis is inhibited. Although 90% of the cells in C-M cultures are infected, little or no infectious virus is produced by most cells in a growing culture. Adding puromycin to inhibit protein synthesis resulted in the production of infectious virus. Thus, all the viral proteins needed for virus completion were made in the growing cells. When actinomycin D was added to growing cells, infectious virus was again produced. Since mumps virus synthesis is actinomycin D-insensitive, this suggested a host control of the virus. Interferon was not detected. The possible mechanisms of host control are discussed.

Inhibition of HeLa cell protein synthesis by the vaccinia virion

HeLa cell protein synthesis is rapidly suppressed after infection with purified vaccinia virus. This was measured in three ways. (i) In the presence of 5 mug of actinomycin D per ml, viral protein synthesis was prevented and the decline in host protein synthesis was measured directly. (ii) Virus particles irradiated with 800 ergs or more of ultraviolet (UV) light per mm(2) are defective in their ability to initiate viral protein synthesis, but they still inhibit host protein synthesis. After addition of UV-irradiated virus, the decline in host protein synthesis was measured. (iii) Polyacrylamide gel electrophoresis was used to distinguish between host- and virus-induced proteins. The following results were obtained. (i) The inhibition of HeLa cell protein synthesis begins within 20 min after infection with purified vaccinia particles. Greater than 95% inhibition occurs within 1 to 4 hr after infection, depending on the viral multiplicity used. (ii) The synthesis of viral ribonucleic acid or viral protein is not required for the inhibition of host protein synthesis. (iii) The ability of the virus particles to inhibit cell protein synthesis is lost after heat or detergent treatment. (iv) The ability of the virus particles to inhibit cell protein synthesis is retained after UV-irradiation. (v) Vaccinia viral protein synthesis in preinfected cells is resistant to the effects of superinfection with UV-irradiated vaccinia particles. (vi) Inhibition of cell protein synthesis is complete and does not involve the continued synthesis of small polypeptide fragments. (vii) A decrease in the size of host polyribosomes rapidly follows infection with vaccinia virus. The results are interpreted as a selective effect of some constituent of the vaccinia virus particle or virus-activated host enzyme on host protein synthesis at a level beyond that of transcription.

The penetration of reovirus RNA and initiation of its genetic function in L-strain fibroblasts

Reovirus type 3 is phagocytized by L cells and rapidly sequestered inside lysosomes. Hydrolases within these organelles are capable of stripping the viral coat proteins, but they fail to degrade the double-stranded RNA genome. These observations support the view that sojourn of reovirus in lysosomes, when the lytic enzymes uncoat its genome, is an obligatory step in the sequence of infection. Although the mechanism for transferring the uncoated RNA out of lysosomes remains to be elucidated, evidence is presented suggesting that progeny genomes are bound to site(s) possessing the fine structure of viral inclusions or factories. It appears that both the synthesis of single- and double-stranded viral RNA and the morphogenesis of progeny virus particles occur in such factories.

Primary antibody response in organ cultures

Specific antibody formation has been elicited in vitro following antigenic stimulation by either sheep (in a total of 472 of 875 cultures) or chick erythrocytes (in 65 of 135 cultures tested). The response was manifested by mouse spleen and lymph node explants whereas thymus cultures were inactive. The reaction has been characterized as a primary immune response in view of its kinetics as compared to defined primary and secondary responses, the effect of 2-mercaptoethanol on the antibodies formed, its subject to puromycin inhibition and its sensitivity to X-irradiation. Histological studies revealed preservation of the lymphoid cell populations throughout the entire experimental period.

Inhibitory proteins in the Newcastle disease virus-induced suppression of cell protein synthesis

Bolognesi, D. P. (Rensselaer Polytechnic Institute, Troy, N.Y.), and D. E. Wilson. Inhibitory proteins in the Newcastle disease virus-induced suppression of cell protein synthesis. J. Bacteriol. 91:1896-1901. 1966.-Infection by Newcastle disease virus brings about a rapid and marked inhibition of cell protein synthesis (CPS) in chick embryo fibroblast monolayers. The block to CPS is initiated about 5 hr after infection, and by 9 hr about 85% of the host protein synthesis is shut off. Azauridine (3 mg/ml), a ribonucleic acid (RNA) synthesis inhibitor, prevents the virus-induced inhibition of CPS when added at the time of infection; but it does not prevent the inhibition when added at 3 hr after infection. When puromycin (60 mug/ml), a protein synthesis inhibitor, was added at 3.5 hr after infection, viral RNA was synthesized in normal amounts, but the virus-induced inhibition of CPS was prevented. Actinomycin D added at the time of infection does not, however, prevent the virus-induced inhibition of CPS. The results of these experiments indicate that proteins synthesized during Newcastle disease virus replication are responsible for the inhibition of host-cell protein synthesis. The synthesis of these inhibitory proteins depends on the prior synthesis of viral RNA.