Adenovirus E4orf4 Protein DownregulatesMYCExpression through Interaction with the PP2A-B55 Subunit

Abstract

The adenovirus E4 open reading frame 4 (E4orf4) protein is a multifunctional viral regulator that is involved in the temporal regulation of viral gene expression by modulating cellular and viral genes at the transcription and translation levels and by controlling alternative splicing of adenoviral late mRNAs. When expressed individually, E4orf4 induces apoptosis in transformed cells. Using oligonucleotide microarray analysis, validated by quantitative real time PCR, we found that MYC (also known as c-Myc) is downregulated early after the induction of E4orf4 expression. As a result, Myc protein levels are reduced in E4orf4-expressing cells. MYC downregulation is observed both when E4orf4 is expressed individually and within the context of viral infection. E4orf4 reduces MYC transcription but does not affect transcriptional elongation or RNA stability. An interaction with the PP2A-B55 subunit is required for the downregulation of MYC by E4orf4. Since Myc overexpression was previously shown to inhibit adenovirus replication, the downregulation of Myc by E4orf4 would contribute to efficient virus infection.

CIP2A signature reveals the MYC dependency of CIP2A-regulated phenotypes and its clinical association with breast cancer subtypes

“…Moreover, these results identify PP2A complexes containing the B subunits B55a, or B56b being involved in MYC and proliferation regulation by CIP2A. Identification of the involvement of several PP2A B subunits, including B55a, in the negative regulation of MYC protein expression is consistent with recently published findings (Arnold and Sears, 2006;Ben-Israel et al, 2008;Sablina et al, 2010).…”

Genomic landscape of positive natural selection in Northern European populations

“…The PPP2R2B gene regulates neuronal apoptosis and may affect adenovirus replication. 32,33 Yet another intriguing gene is RGS9 that affects vision adaptation in different light conditions. 34,35 However, lack of selection signal in individual loci in this study should not be interpreted as absence of selection, as there are several interesting regions lacking sufficient SNP coverage -including the loci of, for example, the LCT and OCA2 genes and the CYP3A region, all well-known candidates for recent natural selection.…”

Structure- and Modeling-based Identification of the Adenovirus E4orf4 Binding Site in the Protein Phosphatase 2A B55α Subunit

“…E4orf4 expression was induced by the addition of 1 g/ml doxycycline (Sigma). IRB␣ cells (1) were propagated in DMEM supplemented with 10% FCS and 1 g/ml puromycin. Transfections were carried out using the jetPEI TM reagent according to the manufacturer's instructions (Polyplus Transfection).…”

“…PP2A is a major E4orf4 partner, and its interaction with E4orf4 was shown to contribute to all E4orf4 functions known to date (1,6,8,12,16,21). PP2A is composed of three subunits: the catalytic C subunit, a scaffolding A subunit, and one of several regulatory B subunits encoded by at least four unrelated gene families, PR55/B55/B, PR61/B56/BЈ, BЉ, and Bٞ (22), which dictate substrate specificity of the PP2A holoenzyme.…”

“…Its contribution involves down-regulation of expression of cellular and early viral genes (1)(2)(3)(4)(5), induction of alternative splicing of viral mRNAs (6,7), and regulation of protein translation through an interaction with the mTOR pathway (8). When expressed outside the context of viral infection, E4orf4 induces nonclassical apoptosis that is caspase-independent in many cell lines and which is preceded by G 2 /M arrest (9 -11).…”