ADENOVIRUS E4 OPEN READING FRAME-4 PROTEIN AUTOREGULATES E4 TRANSCRIPTION BY INHIBITING E1A TRANSACTIVATION OF THE E4 PROMOTER

Here we show that the adenovirus early region 4 (E4) open reading fram e 4 (ORF4) protein autoregulates its own transcription by inhibiting a denovirus E1A-induced activation of E4 transcription both in transient transfection experiments and during lytic virus growth, The inhibitor y activity of E4-ORF4 was selective for E1A-CR3-dependent transactivat ion and had no effect on CR1 transactivation. The inhibitory activity of E4-ORF4 was relieved by okadaic acid treatment, which inhibits the cellular protein phosphatase 2A (PP2A), suggesting that E4-ORF4 contro ls the phosphorylated status of transcription factors important for E4 promoter activity, This conclusion agrees with previous demonstration s that E4-ORF4 associates with PP2A and causes a partial dephosphoryla tion of certain transcription factors, including E1A (U. Muller, T. Kl einberger, and T. Shenk, J. Virol, 66:5869-5878, 1992; T. Kleinberger and T. Shenk, J. Virol, 67:7556-7560, 1993), However, our results indi cate that dephosphorylation of E1A itself might not be the primary tar get for E4-ORF4, Instead, the E4-ORF4-PP2A complex appears to work by dephosphorylation of multiple cellular transcription factors that are involved in E1A transactivation of the E4 promoter.