Abstract We investigated the possible role of protein kinase C (PKC) in the progression of Moloney murine leukemia virus (Mo‐MuLV)‐induced lymphoma in BALB/c mice. Mice injected with Mo‐MuLV on the first day after birth developed lymphoma within 1 1/2 3 months. The development of lymphoma was characterized by a gradual increase in the number of spleen cells. However, no analogous changes could be detected in the thymuses of these mice, although cells of both organs were found to be virus producers as early as 3‐4 weeks after inoculation. PKC activity, which was assayed in extracts of spleen and thymus cells, declined gradually during the development of lymphoma. Concomitantly with this decline, a progressive appearance of Ca 2+ / lipid‐independent protein kinase activity was observed. TPA treatment of intact cells from normal mice reduced the level of soluble PKC activity, while inducing Ca 2+ /lipid‐independent phosphorylation. By contrast, TPA had no effect on these enzymatic activities in cells derived from leukemic mice. Spleen enlargement caused by injection of a non‐leukemogenic inflammatory agent such as mineral oil was ineffective in this respect, suggesting that the PKC‐Ca 2+ /lipid‐independent protein kinase modulation is associated with the virally induced leukemogenesis.
The capacity of interferon to inhibit virus production in cells chronically infected with oncornavirus enabled us to develop a simple system for interferon quantitation that was independent of exogenous viral infection. The release of the virus to the culture medium was determined by its reverse transcriptase activity. The inhibitory effect of interferon in this system was linearly proportional to the log of its dilution over a range between 5 and 80% inhibiton. The sensitivity of the system was comparable to that of the vexicular stomatitis virus plaque reduction assay, whereas its reproducibility was found to be even better. This method is very rapid and can be completed within less than 24 h.
Using the human T-cell leukemia virus type I (HTLV-I) infected SLB-I T-cell line, we showed in this study that 5-d treatment with the maximal subtoxic 3-methylcholanthrene (3-MC) dose (0.25 microgram/ml), as well as with a 3-MC dose that inhibits 50% of the cell growth (5 micrograms/ml), profoundly increased the level of viral RNA. Exposure to these 3-MC doses for 5 d before transient transfection of HTLV-I LTR-CAT construct into these cells markedly stimulated CAT activity, indicating that 3-MC exerted its effect by a trans-acting mechanism. A similar stimulation was observed when this construct was transfected into 3-MC treated uninfected Jurkat cells, indicating that this trans-acting effect was independent of the viral tax protein. However, although the subtoxic 3-MC dose increased also the capacity of SLB-I cells to transmit the virus to normal peripheral blood lymphocytes in coculture, the toxic dose strongly reduced this capacity. No inhibition by this toxic dose was observed in the viral protein synthesis or processing nor in the final release of the virus from the cells. However, the virions released under the influence of this 3-MC dose were found to contain mainly the uncleaved gag precursor polypeptide and a low level of reverse transcriptase. Thus, the reduced virus transmission capacity of the host cells can be ascribed to this structural defect, which presumably lowered the viral infectivity.
Summary This investigation has been focused on the significance of residual growth in the latent period after ultraviolet irradiation of a lysogenic strain of Staphylococcus aureus (111). It was shown that the organisms divide once or twice before the development of free phage and the number of infective centres are increased by about 100 % in 30 min. after irradiation. When celbenin (sodium 6-(2,6 dimethoxy benzamido) penicillinate) was added to the culture after irradiation, the number of infective centres decreased progressively, and no free phage developed. A delay of 10, 20 or 30 min. in introduction of the drug allowed an increasing fraction of the infective centres to develop and to yield free phage. These observations lead to the suggestion that ultraviolet irradiation inhibits the synthesis of new repressor of vegetative phage development, but has no influence on repressor molecules present beforehand. Residual growth of the irradiated bacteria serves to dilute the intracellular repressor concentration below an effective level.
SUMMARY Radioactively labelled virus particles of intracellular origin were isolated from the cytoplasmic fraction of disrupted NIH/3T3 cells chronically infected with Moloney murine leukaemia virus [NIH/3T3 (MLV)]. Interferon (IFN) treatment for 48 h, which arrested more than 90% of virus release, resulted in a remarkable accumulation of these intracellular virions. However, no major effect of such treatment was apparent on their structural properties. Transmission electron microscopic examination revealed that these intracellular virions were located within cytoplasmic vacuoles. IFN treatment resulted in a considerable increase in the number of virus-containing vacuoles, as well as the total number of vacuolar virions. It seems that IFN inhibits the final release of vacuolar virions from the cells, thus leading to their intracellular accumulation.
Using two cell clones derived from 3LL Lewis carcinoma; an NK-resistant (designated A6) and an NK-susceptible (designated F2) clone, we investigated the effect of the NK system on local tumor growth and metastasis. Both clones generated local tumors at the inoculation site somewhat faster in NK-deficient (bg/bg) than in normal mice. In addition, these tumors grew slightly faster in the bg/bg mice. However, the effect of the NK system on the metastatic spread of these clones was much more prominent. The F2 cells were profoundly less metastatic than the A6 cells when inoculated into normal mice, whereas in the NK-deficient mice, both clones were highly metastatic. Thus, the NK system appears to be effective primarily in controlling the metastatic spread of the 3LL cells and has a lesser effect on their local tumor formation.
