Synthesis of type‐C virus particles from murine cultured cells induced by iododeoxyuridine. VI. Biosynthesis of reverse transcriptase

Abstract

Treatment with 5-iodo-Z'-deoxyuridine (IdUrd) of BALB/3T3 cells non-productively transformed with Kirsten murine sarcoma virus (K-BALB) results in the induction of extracellular t y p e 4 virus production with a concomitant appearance of intracellular reverse transcriptase. Production of BALB virus-2 (v-2) and i t s Kirsten sarcoma virus pseudotype, occurring 2-3 days after IdUrd treatment, is inhibited and stimulated by interferon and dexamethasone, respectively, By contrast, and as pre-. viously reported, neither compound affects synthesis of N-tropic virus (BALB virus-1) which i s produced later (5-7 days) after IdUrd treatment. The stimulatory and inhibitory activities of these compounds are partially antagonistic since: (1) the simultaneous presence of both dexamethasone and interferon results i n a virus production level between those observed with either compound alone; and (2) increasing the dexamethasone concentration at a fixed interferon concentration increases virus production. However, the effects of these two compounds on the appearance of an intracellular viral protein (reverse transcriptase) after IdUrd treatment were unexpected. The post-induction appearance of intracellular reverse transcriptase i s inhibited by interferon but is not affected by dexamethasone. This suggests that dexamethasone stimulates a step after protein synthesis, and that interferon inhibits an earlier step (translational or pre-translational) or that it enhances degradation of viral proteins. When interferon and dexamethasone are both present, no inhibition of the appearance of reverse transcriptase is observed. Thus, dexamethasone has a second effect on virus production, namely t o prevent the inhibition by interferon of the appearance of intracellular reverse transcriptase. Since dexamethasone completely overcomes the inhibitory effect of interferon on intracellular reverse transcriptase levels, but only partially reverses the inhibition by interferon of virus production, interferon (in the presence of dexamethasone) must also inhibit a post-translational step i n virus production. This step may or may not be the same as the late dexamethasone-sensitive step. Thus, both dexamethasone and interferon appear t o have both translational (or pre-translational) and post-translational effects on the production of xenotropic (v-2) mouse t y p e 4 virus. This suggests that BALB/c mouse cells restrict the production of xenotropic endogenous virus at two distinct sites.Clones of mouse BALB/3T3 fibroblasts infected with Kirsten murine sarcoma virus contain the sarcoma virus genome, but they do not produce detectable extracellular virions (Aaronson and Weaver, 1971) or gs antigen (Aaronson, 1971). Despite the lack of virus production, these cells are morphologically transformed (Aaronson and Weaver, 1971), contain relatively high levels of Kirsten virusspecific RNA (Benveniste and Scolnick, 1973 ;Wu et al., 1974), and can be induced by treatment with 5-iodo-2'-deoxyuridine (IdUrd) to produce extracellular virus (Aaronson, 1971). Viru...

Cell Surface Receptors for Ecotropic Murine Viruses Are Different from Those for Xenotropic and Amphotropic Viruses

“…natants [12]. The first wave of virus release occurred on the 3rd day after induction, while the second wave of virus release began on the 6th day after induction.…”

“…The media were harvested every day for 7 days, and fresh medium con taining fresh dexaméthasone wasadded toeach culture. The harvested media were stored at -20° for estimation of virus by reverse transcriptase assay in 50-p.l aliquots of the culture supernatant by measuring the incorpora tion of [;iH]-dTMP using (dT)_i5 -(A)" as a primer template as described [12]. Beginning with the 2nd day after IUdR treatment, the cells were monitored in duplicate for binding of radiolabeled gp70 every day for 7 days.…”