Regulated stability of eukaryotic elongation factor 2 kinase requires intrinsic but not ongoing activity

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-depended pathway in response to genotoxic stress and that this requires a phosphodegron that includes an autophosphorylation site. Thus, application of eEF2K inhibitors would stabilise eEF2K, partially negating the effects of inhibiting its activity. Here 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 stabilised, as is a mutant lacking a critical autophosphorylation site (Thr348 in eEF2K), which is thought to be required for eEF2K and other a-kinases to achieve their active conformations. In contrast, application of small molecule eEF2K inhibitors does not stabilise the protein. Our data suggest that achieving an active conformation, rather than eEF2K activity per se, are required for its susceptibility to degradation. Additional degrons and E3 ligases beyond those already identified are likely involved in regulating eEF2K levels. Our findings have i...
Source: BJ Signal - Category: Biochemistry Authors: Tags: BJ Signal Source Type: research