Localization of reverse-transcriptase in interferon-treated mouse cells chronically infected with Moloney leukemia virus

Accelerated heme synthesis and degradation in transformed fibroblasts

Various parameters of the heme biosynthetic pathway were studied in two cell lines, one nontransformed and the other malignantly transformed (MLV/MS), both replicating at the same rate. Using the above system enabled us to distinguish between phenomena characteristic of the malignant transformation per se and those due to accelerated growth rate. Heme synthesis and degradation as well as the activities of ALAS, ALAD, PBGD, and FC were found to be increased in the transformed cells. However, the concentration of intracellular heme was markedly reduced from 30.4 +/- 4.4 pmole/mg protein in nontransformed cells to 10.5 +/- 2.6 pmole/mg protein in transformed cells. These observations show that malignant transformation leads to changes in heme metabolism unrelated to growth rate in this cell line.

Effect of N-methylisatin-beta-4':4'-diethylthiosemicarbazone on intracellular Moloney leukemia virus constituents

N-Methylisatin-beta-4':4'-diethylthiosemicarbazone (M-IBDET) inhibits intracellular production of viral constituents in a mouse cell line, 3T3/MLV, chronically infected with Moloney leukemia virus. Electron microscopic observations confirmed that inhibition of virus production by the drug was not associated with any structural changes in the cell morphology or any damage to the plasma membrane, the site of viral assembly and 'budding'. Treatment of the cells with 17 microM M-IBDET for 6 h inhibited extracellular virus production by 80% but did not affect the level of viral RNA in the cytoplasm or in the plasma membrane. Intracellular reverse transcriptase activity and levels of viral structural proteins were significantly inhibited. Thus, although the drug did not affect viral RNA, it reduced viral protein synthesis.

Inhibition of the synthesis of Moloney leukemia virus structural proteins by N-methylisatin-beta-4',4'-diethylthiosemicarbazone

The mechanism of inhibition of Moloney leukemia virus by N-methylisatin-beta-4',4'-diethylthiosemicarbazone was studied. Experiments that used [3H]leucine for short-pulse labeling in the presence of the drug resulted in a 71% inhibition in the synthesis of Pr-80, the polypeptide precursor of the gag viral proteins. The radioactive pulse products of the polypeptide precursors after a further 2-h chase period showed a normal cleavage of the precursors, with the formation of a reduced amount of final mature viral structural proteins. The experimental evidence indicated that at the inhibitory concentration of 17 microM N-methylisatin-beta-4',4'-diethylthiosemicarbazone, the amount of intracellular viral RNA was not affected, whereas the activities of reverse transcriptase and the other viral protein syntheses were suppressed.