Identification of the adenovirus E4orf4 protein binding site on the B55α and Cdc55 regulatory subunits of PP2A: Implications for PP2A function, tumor cell killing and viral replication.
Adenovirus E4orf4 protein induces the death of human cancer cells and Saccharomyces cerevisiae. Binding of E4orf4 to the B/B55/Cdc55 regulatory subunit of protein phosphatase 2A (PP2A) is required, and such binding inhibits PP2A(B55) activity leading to dose-dependent cell death. We found that E4orf4 binds across the putative substrate binding groove predicted from the crystal structure of B55α such that the substrate p107 can no longer interact with PP2A(B55α). We propose that E4orf4 inhibits PP2A(B55) activity by preventing access of substrates and that at high E4orf4 levels this inhibition results in cell death through the failure to dephosphorylate substrates required for cell cycle progression. However, E4orf4 is expressed at much lower and less toxic levels during a normal adenovirus infection. We suggest that in this context E4orf4 largely serves to recruit novel substrates such as ASF/SF2/SRSF1 to PP2A(B55) to enhance adenovirus replication. Thus E4orf4 toxicity probably represents an artifact of overexpression and does not reflect the evolutionary function of this viral product.
Department of Biochemistry, McGill University, Montreal, Quebec, Canada.
Melissa Z
MZ
Mui
Michael
M
Kucharski
Marie-Joëlle
MJ
Miron
Woosuk Steve
WS
Hur
Albert M
AM
Berghuis
Paola
P
Blanchette
Philip E
PE
Branton
D000256:Adenoviridae / Q000235:genetics / Q000378:metabolism*; D002453:Cell Cycle / Q000235:genetics; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism*; D045744:Cell Line, Tumor; D015967:Gene Expression Regulation, Viral / Q000502:physiology; D006801:Humans; D009363:Neoplasm Proteins / Q000235:genetics / Q000378:metabolism*; D009369:Neoplasms / Q000235:genetics / Q000378:metabolism* / Q000821:virology; D054648:Protein Phosphatase 2 / Q000235:genetics / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000201:enzymology* / Q000235:genetics; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism*; D014764:Viral Proteins / Q000235:genetics / Q000378:metabolism*
C071246:CDC55 protein, S cerevisiae; D018797:Cell Cycle Proteins; C121517:E4orf4 protein, adenovirus; D009363:Neoplasm Proteins; C512974:PPP2R2A protein, human; D029701:Saccharomyces cerevisiae Proteins; D014764:Viral Proteins; D054648:Protein Phosphatase 2