Differential inhibition of Epstein-Barr virus induction by the amino acid analogue, L-canavanine

12-O-tetradecanoylphorbol 13-acetate-inducible proteins are synthesized at an increased rate in Bloom syndrome fibroblasts

A set of proteins, which in normal fibroblasts were barely, if at all, detectable, were synthesized at an increased rate in fibroblasts from patients with Bloom syndrome (BS). The same set of proteins was induced in normal human fibroblasts by treatment with 12-O-tetradecanoylphorbol 13-acetate (TPA). In BS cells, TPA caused a further 2-fold increase in the rate of synthesis. Production of these proteins was inhibited by the addition of fluocinolone acetonide to the culture medium. One of the proteins (XHF1) present at high levels in BS fibroblasts and in TPA-treated cells was also induced by irradiation with ultraviolet light. This protein was secreted into the culture medium. Most other TPA-inducible proteins were cytoplasmic. Among other human mutants prone to chromosome aberrations we found one of three tested cases of Fanconi anemia and one case of ataxia-telangiectasia that showed increased spontaneous rates of synthesis of the TPA-inducible proteins. In these cases, however, the induction by TPA was like that seen in healthy fibroblasts.

Effect of the arginine analog canavanine on the synthesis of Epstein-Barr virus-induced proteins in superinfected Raji cells

The addition of canavanine to cultures of superinfected Raji cells in the absence of arginine prevented the appearance of early antigens as defined by immunofluorescent staining. Addition of various amounts of arginine permitted the identification of at least three groups of proteins, each responding differently to the various concentrations of arginine-canavanine.

The relationship between tumor promoter binding and Epstein-Barr virus induction in human lymphoblastoid cell lines

The tumor promoter TPA (12-0-tetradecanoyl-phorbol-13-acetate) efficiently induces the synthesis of Epstein-Barr virus (EBV) antigens in EBV-genome-harboring human lymphoblastoid cells. We attempted to obtain information on the binding of TPA to cells and on the relationship between TPA-binding and EBV induction by the use of tritiated TPA (3H-TPA). Our data show: (1) In the absence of cells TPA can bind to serum completely within 60 minutes. (2) Cells can compete for a proportion of serum-bound TPA. (3) Binding of TPA to cells reaches equilibrium within 60 minutes and is higher at 37 degrees than 0 degrees C. In the absence of serum, the rate of binding is about twice as high as in the presence of serum. (4) Dissociation of TPA from cells also seems to be rapid. When the cells are incubated with cold TPA after prior treatment with 3H-TPA, followed by washing, a much higher rate of release of labeled TPA is observed than in cultures to which fresh medium is added exclusively. Dissociation is higher in the presence of serum than in the absence of it. If radiolabeled cells are analyzed after serial washing, the rate of cell-associated/noncell-associated radioactivity indicates that the proportion of molecules required for EBV induction is dissociated rapidly.

Induction of target antigens and conversion to susceptible phenotype of NK-cell-resistant lymphoid cell line

Two autologous Herpesvirus papio producer lymphoid cell lines and one autologous non-producer line were compared for susceptibility to natural killer (NK) cell-mediated lysis. The non-producer cell line, 26CB-1, was more resistant to NK cell killing compared to one viral producer counterpart 13CB-1, but equally resistant when compared to another, 8CB-1. Treatment with chemical agents that affect differentiation or activate the viral cycle, including n-butyrate, IuDR, 5-azacytidine and tunicamycin, increased the susceptibility to killing of the non-producer line but had less effect on the 13CB-1 producer line. The increase in susceptibility was due to induction of new target antigens: activated 26CB-1 cells were more effective at inhibiting NK-cell-mediated lysis and were bound by more NK cells than untreated control cells. The expression of NK target structures may be related to the differentiated state rather than to the viral production status to target cells.

Induction of type-C retrovirus by the tumor promotor TPA

The tumor promotor 12-0-tetradecanoyl-phorbol-13-acetate (TPA) induced endogenous murine xenotropic type-C retrovirus from A1-2 cells, derived from the BALB/c mouse, as determined by infectious center focus-forming assay on permissive normal rat kidney (NRK) cells. Kinetic dose-response studies showed that the number of cells induced to release virus was dependent on TPA concentration and the time of assay following TPA exposure. Maximal induction occurred when cells were treated with 80 ng/ml of TPA for 24 h and assayed at 24 or 48 h. A 30-min pulsed TPA exposure and 200 ng/ml induced virus levels approximating those observed after a continuous 24-h exposure to 80 ng/ml. The combination of TPA at concentrations of 10 and 20 ng/ml and a suboptimal level of 5-iodo-2-deoxyuridine (IdUrd) enhanced retrovirus induction threefold above that seen by the optimum IdUrd concentration alone. The protease inhibitors, antipain and leupeptin, decreased virus induction by TPA, a protease inducer. The capacity of TPA to induce type-C retrovirus complements results demonstrating the enhancement of Epstein-Barr virus (EBV) and murine mammary tumor virus (MMTV) synthesis by TPA.