A PP2A Regulatory Subunit Regulates C. elegans Insulin/IGF-1 Signaling by Modulating AKT-1 Phosphorylation

Abstract

Summary The C. elegans insulin/IGF-1 signaling (IIS) cascade plays a central role in the regulation of lifespan, dauer diapause, metabolism and stress response. The major regulatory control of IIS is through phosphorylation of its components by serine/threonine-specific protein kinases. In a RNAi screen for serine/threonine protein phosphatases that counter-balance the effect of the kinases in the IIS pathway, we identified pptr-1, a B56 regulatory subunit of the PP2A holoenzyme. Modulation of pptr-1 affects phenotypes associated with the IIS pathway including lifespan, dauer, stress resistance and fat storage. We show that PPTR-1 functions by regulating worm AKT-1 phosphorylation at Thr 350. With striking conservation, mammalian B56β regulates Akt phosphorylation at Thr 308 in 3T3-L1 adipocytes. In C. elegans, this modulation ultimately leads to changes in subcellular localization and transcriptional activity of the forkhead transcription factor DAF-16. This study reveals a conserved role for the B56 regulatory subunit in modulating insulin signaling through AKT dephosphorylation and thereby has widespread implications in cancer and diabetes research.

Heavy Metal-induced Metallothionein Expression Is Regulated by Specific Protein Phosphatase 2A Complexes

“…Consistent with these observations, a previous study reported that the activation of PI3K/AKT pathway was involved in suppression of MT expression in primary hepatocellular carcinoma (HCC) cells through inhibition of glycogen synthase kinase-3/C/EBP␣ signaling (56). PP2A B56␤ has been implicated in the dephosphorylation of AKT (57,58). Because glycogen synthase kinase-3 and C/EBP␣ are the downstream targets of PP2A, which plays a role in the regulation of cell growth and survival (59, 60), we thus speculate that PP2A B56␤ may affect MT expression via PI3K/AKT pathway.…”

Akt-dependent Pp2a activity is required for epidermal barrier formation during late embryonic development

“…Therefore, it is plausible that Ppp2r2a is downstream of Akt and that another Pp2a regulatory subunit controls the subsequent downregulation of Akt. This is consistent with findings in Caenorhabditis elegans, in which B56β and not B55α (Ppp2r2a) is responsible for dephosphorylation of AKT-1 at the equivalent serine (Padmanabhan et al, 2009). RESEARCH ARTICLE Akt-dependent phosphatases and epidermal barrier Ppp2r2a knockdown leads to hyperphosphorylation of Jun, and Ppp2r2a and Jun bind in immunoprecipitation assays, providing evidence that Pp2a holoenzymes containing this regulatory subunit can directly target Jun, in agreement with reports that Pp2a interacts with Jun in bacterial two-hybrid assays (Avdi et al, 2002;Zhao et al, 2008).…”

Noncanonical control of C. elegans germline apoptosis by the insulin/IGF-1 and Ras/MAPK signaling pathways

“…20 To investigate the phosphorylation state of AKT-1 we raised two mono-specific polyclonal antisera against different regions of AKT-1 (Supplementary Figure S2), immunoprecipitated endogenous protein from worm lysates and probed blots with phospho-specific antibodies to T350 (homologous to T308) and S517 (homologous to S473) previously generated. 22 In the absence of IR both T350 and S517 were phosphorylated, consistent with tonic insulin/IGF-1 signaling under normal growth conditions. Consistent with our genetic data suggesting noncanonical regulation of AKT-1, radiation did not dramatically alter the phosphorylation state of T350/ T308 in the wild-type compared to the unirradiated controls ( Figure 3a).…”