title: Protein kinase A is part of a mechanism that regulates nuclear reimport of the nuclear tRNA export receptors Los1p and Msn5p.
abstract: The two main signal transduction mechanisms that allow eukaryotes to sense and respond to changes in glucose availability in the environment are the cyclic AMP (cAMP)/protein kinase A (PKA) and AMP-activated protein kinase (AMPK)/Snf1 kinase-dependent pathways. Previous studies have shown that the nuclear tRNA export process is inhibited in Saccharomyces cerevisiae deprived of glucose. However, the signal transduction pathway involved and the mechanism by which glucose availability regulates nuclear-cytoplasmic tRNA trafficking are not understood. Here, we show that inhibition of nuclear tRNA export is caused by a block in nuclear reimport of the tRNA export receptors during glucose deprivation. Cytoplasmic accumulation of the tRNA export receptors during glucose deprivation is not caused by activation of Snf1p. Evidence obtained suggests that PKA is part of the mechanism that regulates nuclear reimport of the tRNA export receptors in response to glucose availability. This mechanism does not appear to involve phosphorylation of the nuclear tRNA export receptors by PKA. The block in nuclear reimport of the tRNA export receptors appears to be caused by activation of an unidentified mechanism when PKA is turned off during glucose deprivation. Taken together, the data suggest that PKA facilitates return of the tRNA export receptors to the nucleus by inhibiting an unidentified activity that facilitates cytoplasmic accumulation of the tRNA export receptors when glucose in the environment is limiting. A PKA-independent mechanism was also found to regulate nuclear tRNA export in response to glucose availability. This mechanism, however, does not regulate nuclear reimport of the tRNA export receptors.
authors.affiliation: Department of Molecular and Cellular Biology, University of Guelph, Guelph, Ontario, Canada.
authors.forename: Jacqueline B
authors.initials: JB
authors.lastname: Pierce
authors.forename: George
authors.initials: G
authors.lastname: van der Merwe
authors.forename: Dev
authors.initials: D
authors.lastname: Mangroo
mesh_terms: D021581:Active Transport, Cell Nucleus; D002467:Cell Nucleus / Q000378:metabolism*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000235:genetics / Q000378:metabolism*; D005947:Glucose / Q000378:metabolism; D028884:Karyopherins / Q000235:genetics / Q000378:metabolism*; D028861:Nuclear Pore Complex Proteins / Q000235:genetics / Q000378:metabolism*; D034443:RNA Transport; D012343:RNA, Transfer / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000235:genetics* / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: D028884:Karyopherins; C408090:Los1 protein, S cerevisiae; C401306:MSN5 protein, S cerevisiae; D028861:Nuclear Pore Complex Proteins; D029701:Saccharomyces cerevisiae Proteins; D012343:RNA, Transfer; D017868:Cyclic AMP-Dependent Protein Kinases; D005947:Glucose