Induction of virus enzymes by phorbol esters and n-butyrate in Epstein-Barr virus genome-carrying Raji cells.

Phorbol esters and n-butyrate (SB) together could induce Epstein-Barr virus (EBV) DNA polymerase and DNase activities in Raji cells (virus nonproducer). Neither 12-O-tetradecanoylphorbol-13-acetate (TPA) nor SB alone could induce these EBV enzyme activities, transcription of the EcoRI C-region or other EBV proteins in Raji cells. The enzyme induction caused by exposure of Raji cells to TPA-SB was the result of the synthesis of virus-specified RNA, and the increase of linear EBV DNA content in Raji cells caused by TPA alone was not sufficient for induction of EBV-enzyme activities. Temporal characteristics of the TPA-SB induction process, but not the phorbol 12,13-dibutyrate-SB induction process, in Raji cells were observed; a critical phase (10-24 h) postphorbol ester treatment in phorbol 12,13-dibutyrate-SB-treated Raji cells which was responsible for the synthesis of virus RNA and enzymes was found. Phospholipase C, which increases intracellular diacylglycerols (and subsequently activates protein kinase C) was able to partially substitute for TPA in the TPA-SB induction for EBV polymerase and DNase activities. Sphingosine, a protein kinase C inhibitor, partially prevented the induction of virus enzyme activities in Raji cells treated with phorbol 12,13-dibutyrate and SB. No apparent changes in the methylation state of EBV DNA (EcoRI C region) were observed when Raji cells were treated with SB and TPA, alone or in combination. These results suggest that induction of EBV polymerase and DNase activities by TPA-SB may involve protein kinase C activation and another factor triggered by SB which together increase transcription of EBV DNA.