title: Akt and its downstream targets play key roles in mediating dormancy in land snails.
abstract: Estivation, a state of aerobic dormancy, facilitates survival during adverse environmental conditions and is characterized at the molecular level by regulatory protein phosphorylation. The Akt (protein kinase B) signaling pathway regulates diverse responses in cells and the present study analyzes its role in the estivating desert snail Otala lactea. Kinetic analysis (maximal velocity, substrate affinities) determined that Akt was activated in tissues of estivating snails and Western blotting and in vitro incubations promoting changes to Akt phosphorylation state both confirmed that higher amounts of active (phosphorylated Ser473) Akt were present during estivation. Akt protein stability was also enhanced during estivation as assessed from urea denaturation studies. Multiple downstream targets of Akt were differentially regulated during estivation. Estivating animals showed elevated levels of phosphorylated FOXO3a (Ser253) and BAD (Ser136), no change in mTOR (Ser2481 and Ser2448), and reduced amounts of phosphorylated glycogen synthase kinase-3 (GSK-3) beta subunit (Ser9). Kinetic analysis of GSK-3 showed 1.5-1.7 fold higher activities in estivating snails coupled with increased GSK-3 substrate affinities in hepatopancreas. The data suggest an active role for Akt signaling during estivation emphasizing anti-apoptotic actions but uncoupling growth/proliferation actions to help achieve life extension on a limited energy budget.
authors.affiliation: Vanderbilt University School of Medicine, Department of Molecular Physiology, 710 Robinson Research Building, 2200 Pierce Avenue, Nashville, TN 37232, USA. chris.ramnanan@vanderbilt.edu
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Ramnanan
authors.forename: Amy G
authors.initials: AG
authors.lastname: Groom
authors.forename: Kenneth B
authors.initials: KB
authors.lastname: Storey
mesh_terms: D000818:Animals; D004591:Electrophoresis, Polyacrylamide Gel; D038362:Glycogen Synthase Kinase 3 / Q000378:metabolism; D007700:Kinetics; D010766:Phosphorylation; D011494:Protein Kinases / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism*; D012908:Snails / Q000502:physiology*; D013379:Substrate Specificity; D058570:TOR Serine-Threonine Kinases
chemical_list: D011494:Protein Kinases; D051057:Proto-Oncogene Proteins c-akt; D058570:TOR Serine-Threonine Kinases; D038362:Glycogen Synthase Kinase 3