PI3K-AKT Signaling Stabilizes β-Catenin mRNA and Increases Its Expression

<div><p>(A) Quantitative RT-PCR analysis of both β-catenin and β2-MG transcripts in αT3-1 cells treated with either DMSO (the solvent of LY, control), DMSO plus LiCl, or LY (25 μM for 16 h) plus LiCl. Total RNA was isolated at the indicated times after the addition of actinomycin D. The values shown are averages (±SEM) of three independent experiments performed in duplicate.</p> <p>(B) Quantitative RT-PCR analysis of both β-catenin and β2-MG transcripts in αT3-1 cells treated with either DMSO (the solvent of triciribine, control), DMSO plus LiCl (20 mM for 6 h), or triciribine (1 μM for 1 h) plus LiCl. Total RNA was isolated at the indicated times after the addition of actinomycin D. The values shown are averages (±SEM) of three independent experiments performed in duplicate.</p> <p>(C) In vitro RNA degradation assays using S100s from either LiCl-treated mock αT3-1 or LiCl-treated αT3-1 cells expressing the AKT dominant negative mutant AKT1(K179M) (αT3-1–AKTDN). Internally ³²P-labeled and capped RNA substrates were incubated with S100s for the indicated times and their decay analyzed as described in Materials and Methods.</p> <p>(D) Either mock αT3-1 or αT3-1–myrAKT1 cells were lysed and total extracts were immunoprecipitated (Ip) with either anti-AKT antibody or control IgG (cIgG). Pellets were incubated (20 min at 30 °C) with histone 2B (H2B) in kinase buffer in the presence of [γ-³²P]ATP. Labeled proteins were separated by SDS-PAGE and detected by autoradiography.</p> <p>(E) Expression of β-catenin and β2-MG, monitored by RT-PCR, in either mock αT3-1 or αT3-1–myrAKT1 cells.</p> <p>(F) Quantitative RT-PCR analysis of both β-catenin and β2-MG transcripts in either mock αT3-1 or αT3-1–myrAKT1 cells. Total RNA was isolated at the indicated times after addition of actinomycin D. The values shown are averages (±SEM) of three independent experiments performed in duplicate.</p> <p>(G) Immunoblot analysis of either S100 or nuclear extracts from the indicated cell lines with anti- β-catenin, α-tubulin, and HDAC2 antibodies.</p>