title: Regulated stability of eukaryotic elongation factor 2 kinase requires intrinsic but not ongoing activity.
abstract: Eukaryotic elongation factor 2 kinase (eEF2K) is an atypical protein kinase which negatively regulates protein synthesis, is activated under stress conditions and plays a role in cytoprotection, e.g. in cancer cells. It is regarded as a possible target for therapeutic intervention in solid tumours. Earlier studies showed that eEF2K is degraded by a proteasome-dependent pathway in response to genotoxic stress and that this requires a phosphodegron that includes an autophosphorylation site. Thus, application of eEF2K inhibitors would stabilize eEF2K, partially negating the effects of inhibiting its activity. In the present study, we show that under a range of other stress conditions, including acidosis or treatment of cells with 2-deoxyglucose, eEF2K is also degraded. However, in these settings, the previously identified phosphodegron is not required for its degradation. Nevertheless, kinase-dead and other activity-deficient mutants of eEF2K are stabilized, as is a mutant lacking a critical autophosphorylation site (Thr348 in eEF2K), which is thought to be required for eEF2K and other α-kinases to achieve their active conformations. In contrast, application of small-molecule eEF2K inhibitors does not stabilize the protein. Our data suggest that achieving an active conformation, rather than eEF2K activity per se, is required for its susceptibility to degradation. Additional degrons and E3 ligases beyond those already identified are probably involved in regulating eEF2K levels. Our findings have significant implications for therapeutic targeting of eEF2K, e.g. in oncology.
authors: *Centre for Biological Sciences, Life Sciences Building (B85), University of Southampton, Southampton SO17 1BJ, U.K.
authors: Xuemin
authors: X
authors: Wang
authors: *Centre for Biological Sciences, Life Sciences Building (B85), University of Southampton, Southampton SO17 1BJ, U.K.
authors: Jianling
authors: J
authors: Xie
authors: *Centre for Biological Sciences, Life Sciences Building (B85), University of Southampton, Southampton SO17 1BJ, U.K.
authors: Sergio Regufe
authors: SR
authors: da Mota
authors: *Centre for Biological Sciences, Life Sciences Building (B85), University of Southampton, Southampton SO17 1BJ, U.K.
authors: Claire E
authors: CE
authors: Moore
authors: *Centre for Biological Sciences, Life Sciences Building (B85), University of Southampton, Southampton SO17 1BJ, U.K.
authors: Christopher G
authors: CG
authors: Proud
mesh_terms: D000818:Animals; D000963:Antimetabolites / Q000494:pharmacology; D003847:Deoxyglucose / Q000494:pharmacology; D054736:Elongation Factor 2 Kinase / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D004795:Enzyme Stability / Q000187:drug effects / Q000235:genetics; D057809:HEK293 Cells; D006801:Humans; D051379:Mice; D018345:Mice, Knockout; D009154:Mutation; D010766:Phosphorylation / Q000187:drug effects / Q000235:genetics; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D013312:Stress, Physiological / Q000187:drug effects / Q000235:genetics
chemical_list: D000963:Antimetabolites; D047428:Protein Kinase Inhibitors; D003847:Deoxyglucose; C517689:EEF2K protein, human; C517690:Eef2k protein, mouse; D054736:Elongation Factor 2 Kinase