Interaction of viruses with tumor promotors

The effects of tumor promoters on HTLV-1 expression in a low-virus producer and a non-virus producer cell line

Chemical agents including 5-iodo-2'-deoxyuridine (IUdR), 4-O-methyl 12-O-tetradecanoyl phorbol-13-acetate (TPA), phorbol, and the tumor promoters teleocidin and TPA were tested for their ability to induce Human T-cell leukemia-lymphoma virus Type I (HTLV-I) expression in the low-virus producer MT-1 cell line and in the non-virus producer C63/CRII-2 cell line, which contains at least one integrated HTLV-I genome equivalent per cell [26]. Viral antigen expression increased from 0.3% to 8.7% in the MT-1 cell line after treatment with IUdR, while TPA and teleocidin were marginally or non-effective as inducers. Chemicals did not induce HTLV-I antigen expression in the C63/CI(II-2) cell line. No enhancement of reverse transcriptase activity or alteration of proviral organization was observed after chemical treatment of MT-1 cells.

Regulation of expression driven by human immunodeficiency virus type 1 and human T-cell leukemia virus type I long terminal repeats in pluripotential human embryonic cells

Human pluripotential embryonic teratocarcinoma cells differentially expressed gene activity controlled by the human immunodeficiency virus type 1 (HIV-1) and human T-cell leukemia virus type I (HTLV-I) long terminal repeats (LTRs) when differentiation was induced by the morphogen all-trans retinoic acid. The alterations occurred after commitment and before the appearance of the multiple cell types characteristic of these pluripotential cells. After commitment, gene activity controlled by the HIV-1 LTR markedly increased, whereas that controlled by the HTLV-I LTR decreased. Steady-state mRNA levels and nuclear run-on transcription indicated that the increased HIV-1-directed activity during differentiation occurred posttranscriptionally, whereas the decreased HTLV-I activity was at the transcriptional level. Phorbol esters did not cause commitment but strongly enhanced expression by both viral LTRs at the transcriptional level. A specific inhibitor of protein kinase C, 1-(5-isoquinolinylsulfonyl)-2-methylpiperazine, indicated that the enhanced activity involved the activation of protein kinase(s) C; altered cyclic nucleotide metabolism was apparently not involved. Differentiating cells gradually lost the ability to respond to phorbol ester stimulation. Experiments with a deletion mutant of the HIV-1 LTR suggested that this was due to imposition of negative regulation during differentiation that was not reversed by phorbol ester induction. Cycloheximide, with or without phorbol ester, slightly stimulated HIV-1-directed activity at the transcriptional level and massively increased the amounts of steady-state mRNA by posttranscriptional superinduction. It appeared, however, that new nuclear protein synthesis was required for maximal transcriptional stimulation by phorbol esters. Thus, changing cellular regulatory mechanisms influenced human retrovirus expression during human embryonic cell differentiation.

Antibody-mediated enhancement of BK virus infection in human monocytes and a human macrophage-like cell line

We have monitored BK virus (BKV) antigen expression and multiplication in human monocytes and in a human macrophage (M luminal diameter)-like cell line (U937) in the presence or absence of dilution series of human or rabbit anti-BKV antisera. After infection with BKV alone, restricted expression (structural antigens and T-antigen) and multiplication was recorded in monocytes from some donors, while in U937 cells and monocytes from other donors, no signs of viral activity were detected. Monocyte cultures established from the same donor at different times demonstrated antigen expression/multiplication on two occasions but not on the third. A pronounced enhancement of BKV expression/multiplication in human monocytes and multiplication in U937 cells was seen with some dilutions of all antisera (human and rabbit) used. The pattern of enhancement and the dilution resulting in maximum viral activity was constant and seemed to be determined by the serum, but the exact level of enhancement for a given serum differed considerably in monocytes from different donors and seemed to be determined by the cells. In the latter respect, monocytes taken from the same donor some weeks apart showed variations at the same level, as did cells from different donors. PMA (phorbol-12-myristate-13-acetate) stimulation of monocytes and U937 cells resulted in stronger antibody enhancement in terms of infectivity, without affecting the number of monocytes showing antigen expression. No expression/multiplication of BKV was detected in the murine M luminal diameter-like cell line P338 DI.

Protein kinase C stimulation increases the transforming ability of the polyoma virus middle T antigen

Exposure of dexamethasone-treated cells of the mT-1 line of F111 rat cells bearing a dexamethasone-inducible polyoma virus middle T (mT) antigen gene to very low concentrations of the protein kinase C-stimulating phorbol ester TPA increased the association of mT antigen with the cellular pp60c-src tyrosine protein kinase, as indicated by an increased phosphorylation of tyrosine residues of mT in mT:pp60c-src complexes precipitated from extracts of the TPA-treated cells by anti-mT antibodies. This TPA (hence probably protein kinase C)-enhanced association of mT with pp60c-src was accompanied by a large increase in the transforming ability of mT as indicated by a much enhanced ability of TPA-treated mT-1 cells producing submaximal levels of mT to proliferate while suspended in semi-solid medium and to form foci on confluent monolayers of normal F111 cells. NRCC NO: 26558.