14-3-3s regulate global cleavage of their diverse binding partners in sugar-starved Arabidopsis cells.
Despite 14-3-3 proteins being implicated in the control of the eukaryotic cell cycle, metabolism, cell signalling and survival, little is known about the global regulation or functions of the phosphorylation-dependent binding of 14-3-3s to diverse target proteins. We identified Arabidopsis cytosolic proteins that bound 14-3-3s in competition with a 14-3-3-binding phosphopeptide, including nitrate reductase, glyceraldehyde- 3-phosphate dehydrogenase, a calcium-dependent protein kinase, sucrose-phosphate synthase (SPS) and glutamyl-tRNA synthetase. Remarkably, in cells starved of sugars or fed with non-metabolizable glucose analogues, all 14-3-3 binding was lost and the target proteins were selectively cleaved into proteolytic fragments. 14-3-3 binding reappeared after several hours of re-feeding with sugars. Starvation-induced degradation was blocked by 5-amino imidazole-4-carboxamide riboside (which is converted to an AMP-mimetic) or the protease inhibitor MG132 (Cbz-leu-leu-leucinal). Extracts of sugar-starved (but not sugar-fed) Arabidopsis cells contained an ATP-independent, MG132-sensitive, neutral protease that cleaved Arabidopsis SPS, and the mammalian 14-3-3-regulated transcription factor, FKHR. Cleavage of SPS and phosphorylated FKHR in vitro was blocked by binding to 14-3-3s. The finding that 14-3-3s participate in a nutrient-sensing pathway controlling cleavage of many targets may underlie the effects of these proteins on plant development.
Cotelle
V
V
Medical Research Council Protein Phosphorylation Unit, Department of Biochemistry, MSI/WTB Complex, University of Dundee, Dundee DD1 5EH, UK.
Meek
S E
SE
Provan
F
F
Milne
F C
FC
Morrice
N
N
MacKintosh
C
C
D048948:14-3-3 Proteins; D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000166:cytology / Q000378:metabolism*; D001667:Binding, Competitive; D002241:Carbohydrates / Q000172:deficiency*; D002478:Cells, Cultured; D003600:Cytosol / Q000378:metabolism; D010450:Endopeptidases / Q000378:metabolism; D005947:Glucose / Q000031:analogs & derivatives; D008969:Molecular Sequence Data; D010748:Phosphopeptides / Q000378:metabolism; D010940:Plant Proteins / Q000378:metabolism*; D011485:Protein Binding; D011506:Proteins / Q000378:metabolism*; D015398:Signal Transduction; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D014446:Tyrosine 3-Monooxygenase
D048948:14-3-3 Proteins; D002241:Carbohydrates; D010748:Phosphopeptides; D010940:Plant Proteins; D011506:Proteins; D014446:Tyrosine 3-Monooxygenase; D010450:Endopeptidases; D005947:Glucose