The PP2A-Aβ Gene is Regulated by Multiple Transcriptional Factors Including Ets-1, SP1/SP3, and RXRα /β

W.      -J. Han; D.      W.-C. Li; S.      -J. Liu; Y.      Liu; S.      -P. Liang; Y.      -M. Xiao; W.      -B. Liu; Z.      Woodward; J.      Liu; X.      Hu; W.      -F. Hu; P.      -C. Chen; J.      Liu; L.      Chen; M.      Deng; L.      Gong; X.      Zhang; L.      Liu; Y.      Mao; H.      -G. Chen; L.      Zhang; S.      Sun; W.      Ji

doi:10.2174/156652412802480916

Abstract

Protein phosphatase-2A (PP-2A) is a major serine/threonine phosphatase abundantly expressed in eukaryotes. PP-2A is a heterotrimer that contains a 65kD scaffold A subunit, a 36kD catalytic C subunit, and a regulatory B subunit of variable isoforms ranging from 54-130kDs. The scaffold subunits, PP2A-Aα/β, act as platforms for both the C and B subunits to bind, and thus are key structural components for PP-2A activity. Mutations in both genes encoding PP2A-Aα and PP2A-Aβ lead to carcinogenesis and likely other human diseases. Our previous work showed that the gene coding for PP2A-Aα is positively regulated by multiple transcription factors including Ets-1, CREB, and AP-2α but negatively regulated by SP-1/SP-3. In the present study, we have functionally dissected the promoter of the mouse PP2A-Aβ gene. Our results demonstrate that three major cis-elements, including the binding sites for Ets-1, SP1/SP3, and RXRα/β, are present in the proximal promoter of the mouse PP2A-Aβ gene. Gel mobility shifting assays reveal that Ets-1, SP1/SP3, and RXRα/β all bind to PP2A-Aβ gene promoter. In vitro mutagenesis and reporter gene activity assays demonstrate that while Ets-1 displays negative regulation, SP1/SP3 and RXRα/β positively regulate the promoter of the PP2A-Aβ gene. Co-expression of the cDNAs encoding Ets-1, SP1/SP3, or RXRα/β and the luciferase reporter gene driven by PP2A-Aβ promoter further confirm their control over the PP2A-Aβ promoter. Finally, ChIP assays demonstrate that Ets-1, SP1/SP3, and RXRα/β can all bind to the PP2A-Aβ gene promoter. Together, our results reveal that multiple transcription factors regulate the PP2A-Aβ gene. Moreover, our results provide important information explaining why PP2A-Aα and PP2A-Aβ display distinct expression levels.

Keywords: Protein phosphorylation, dephosphorylation, PP-2A, PP2A-Aβ, gene regulation, Ets, SP1, SP3, RXRα/β, lens, retina, cataract, cancer, eukaryotic cells, cell transformation.