title: Proline-rich Akt substrate of 40-kDa contains a nuclear export signal.
abstract: The proline-rich Akt substrate of 40-kDa (PRAS40) has been linked to the regulation of the activity of the mammalian target of rapamycin complex 1 as well as insulin action. Despite these cytosolic functions, PRAS40 was originally identified as nuclear phosphoprotein in Hela cells. This study aimed to detail mechanisms and consequences of the nucleocytosolic trafficking of PRAS40. Sequence analysis identified a potential leucine-rich nuclear export signal (NES) within PRAS40. Incubation of A14 fibroblasts overexpressing human PRAS40 (hPRAS40) resulted in nuclear accumulation of the protein. Furthermore, mutation of the NES mimicked the effects of leptomycin B, a specific inhibitor of nuclear export, on the subcellular localization of hPRAS40. Finally, A14 cells expressing the NES-mutant showed impaired activation of components of the Akt-pathway as well as of the mTORC1 substrate p70 S6 kinase after insulin stimulation. This impaired insulin signaling could be ascribed to reduced protein levels of insulin receptor substrate 1 in cells expressing mutant NES. In conclusion, PRAS40 contains a functional nuclear export signal. Furthermore, enforced nuclear accumulation of PRAS40 impairs insulin action, thereby substantiating the function of this protein in the regulation of insulin sensitivity.
authors.affiliation: Institute for Clinical Biochemistry and Pathobiochemistry, German Diabetes Center, Duesseldorf, Germany.
authors.forename: Claudia
authors.initials: C
authors.lastname: Wiza
authors.forename: Emmani B M
authors.initials: EB
authors.lastname: Nascimento
authors.forename: Margot M L
authors.initials: MM
authors.lastname: Linssen
authors.forename: Françoise
authors.initials: F
authors.lastname: Carlotti
authors.forename: Daniella
authors.initials: D
authors.lastname: Herzfeld de Wiza
authors.forename: Gerard C M
authors.initials: GC
authors.lastname: van der Zon
authors.forename: J Antonie
authors.initials: JA
authors.lastname: Maassen
authors.forename: Michaela
authors.initials: M
authors.lastname: Diamant
authors.forename: Bruno
authors.initials: B
authors.lastname: Guigas
authors.forename: D Margriet
authors.initials: DM
authors.lastname: Ouwens
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000032:analysis* / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D002467:Cell Nucleus / Q000378:metabolism; D006801:Humans; D007328:Insulin / Q000378:metabolism; D008565:Membrane Proteins; D051379:Mice; D009154:Mutation; D041681:NIH 3T3 Cells; D049790:Nuclear Export Signals; D011392:Proline / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism*; D051381:Rats; D029701:Saccharomyces cerevisiae Proteins
chemical_list: C484523:AKT1S1 protein, human; C438144:ASI1 protein, S cerevisiae; D048868:Adaptor Proteins, Signal Transducing; D007328:Insulin; D008565:Membrane Proteins; D049790:Nuclear Export Signals; D029701:Saccharomyces cerevisiae Proteins; D011392:Proline; D051057:Proto-Oncogene Proteins c-akt