title: Interactions between the RNA interference effector protein Ago1 and 14-3-3 proteins: consequences for cell cycle progression.
abstract: The Argonaute family member Ago1 is required for formation of pericentric heterochromatin and small interfering RNA (siRNA)-mediated post-transcriptional gene silencing in the fission yeast Schizosaccharomyces pombe. In addition, we have recently demonstrated that Ago1 function is required for enactment of cell cycle checkpoints (Carmichael, J. B., Provost, P., Ekwall, K., and Hobman, T. C. (2004) Mol. Biol. Cell 15, 1425-1435). Here, we provide evidence that the amino terminus of Ago1 binds to proteins that function in cell cycle regulation including 14-3-3 proteins. Interestingly, the amino terminus of human Ago2, the endonuclease that cleaves siRNA-targeted mRNAs, was also demonstrated to bind 14-3-3 proteins. Overexpression of the Ago1 amino terminus in yeast resulted in cell cycle delay at the G(2)/M boundary. Further investigation revealed that nuclear import of the mitosis-inducing phosphatase Cdc25 is inhibited by overexpression of the Ago1 amino terminus. Under these conditions, we found that the cyclin-dependent kinase Cdc2 is constitutively phosphorylated on tyrosine 15, thereby reducing the activity of this kinase, a situation that delays entry into mitosis. We hypothesize that 14-3-3 proteins are required for Argonaute protein functions in cell cycle and/or gene-silencing pathways.
authors.affiliation: Department of Cell Biology, University of Alberta, Edmonton, Alberta T6G 2H7, Canada.
authors.forename: Cezar
authors.initials: C
authors.lastname: Stoica
authors.forename: Jon B
authors.initials: JB
authors.lastname: Carmichael
authors.forename: Henry
authors.initials: H
authors.lastname: Parker
authors.forename: Justin
authors.initials: J
authors.lastname: Pare
authors.forename: Tom C
authors.initials: TC
authors.lastname: Hobman
mesh_terms: D048948:14-3-3 Proteins / Q000235:genetics / Q000378:metabolism*; D021581:Active Transport, Cell Nucleus; D060565:Argonaute Proteins; D001483:Base Sequence; D016203:CDC2 Protein Kinase / Q000235:genetics / Q000378:metabolism; D002453:Cell Cycle / Q000235:genetics / Q000502:physiology; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism; D004271:DNA, Fungal / Q000235:genetics; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism; D005800:Genes, Fungal; D006367:HeLa Cells; D006801:Humans; D008954:Models, Biological; D010766:Phosphorylation; D011485:Protein Binding; D034622:RNA Interference; D016601:RNA-Binding Proteins; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D012568:Schizosaccharomyces / Q000166:cytology* / Q000235:genetics / Q000378:metabolism*; D029702:Schizosaccharomyces pombe Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D020666:ras-GRF1 / Q000235:genetics / Q000378:metabolism
chemical_list: D048948:14-3-3 Proteins; C481643:Ago1 protein, S pombe; D060565:Argonaute Proteins; D018797:Cell Cycle Proteins; D004271:DNA, Fungal; D005656:Fungal Proteins; D016601:RNA-Binding Proteins; D011994:Recombinant Proteins; D029702:Schizosaccharomyces pombe Proteins; D020666:ras-GRF1; D016203:CDC2 Protein Kinase; C469447:cdc2 protein, S pombe