Li Y, et al. (2008) Cdc55p-mediated E4orf4 growth inhibition in Saccharomyces cerevisiae is mediated only in part via the catalytic subunit of protein phosphatase 2A. J Virol 82(7):3612-23
Abstract: The adenovirus early region 4 open reading frame 4 (E4orf4) protein specifically induces p53-independent cell death of transformed but not normal human cells, suggesting that elucidation of its mechanism may provide important new avenues for cancer therapy. Wild-type E4orf4 and mutants that retain cancer cell toxicity also induce growth inhibition in S. cerevisiae, which provides a genetically tractable system for studying E4orf4 function. Interaction with PP2A B regulatory subunit is required for E4orf4's effects, suggesting that E4orf4 may function by regulating B subunit-containing heterotrimeric PP2A holoenzymes (PP2ABAC), which consist of B subunit complexed with the PP2A structural (A) and catalytic (C) subunits. However, it is not known whether E4orf4-induced growth inhibition requires interaction with PP2A C subunit or whether E4orf4 might have PP2A B subunit-dependent effects that are independent of PP2ABAC holoenzyme formation. To test these possibilities in S. cerevisiae, we disrupted the stable formation of PP2ABAC heterotrimers and thus E4orf4/C subunit association by PP2A C subunit point mutations or by deletion of the gene for the PP2A methyltransferase, Ppm1p, and assayed for effects on E4orf4-induced growth inhibition. Our results support a model in which E4orf4 mediates growth inhibition and cell killing both through PP2ABAC heterotrimers and through a B regulatory subunit-dependent pathway(s) that is independent of stable complex formation with PP2A C subunit. They also indicate that Ppm1p has a function other than regulating the assembly of PP2A heterotrimers and suggest that selective PP2A trimer inhibitors and PP6 inhibitors may be useful as adjuvant anti-cancer therapies.
|Status: Published||Type: Journal Article||PubMed ID: 18216111|
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