Bicuculline regulated protein synthesis is dependent on Homer1 and promotes its interaction with eEF2K through mTORC1‐dependent phosphorylation

• Published in: Journal of neurochemistry 2021-05, Vol.157 (4), p.1086-1101
• Main Authors: Gladulich, Luis F. H., Xie, Jianling, Jensen, Kirk B., Kamei, Makoto, Paes‐de‐Carvalho, Roberto, Cossenza, Marcelo, Proud, Christopher G.
• Format: Article
• Language: English
• Subjects: Bicuculline; Calcium ions; Calcium signalling; Developmental plasticity; eEF2K; Elongation; Homer1; Kinases; Localization; mTORC1; Neuroblasts; Neurons; Phosphorylation; Protein biosynthesis; Protein synthesis; Proteins; Scaffolding; Signal transduction; Signaling; Substrates; synapse; Synapses; Synaptic plasticity; Synaptogenesis
• ISSN: 0022-3042; 1471-4159
• DOI: 10.1111/jnc.15178

The regulation of protein synthesis is a vital and finely tuned process in cellular physiology. In neurons, this process is very precisely regulated, as which mRNAs undergo translation is highly dependent on context. One of the most prominent regulators of protein synthesis is the enzyme eukaryotic elongation factor kinase 2 (eEF2K) that regulates the elongation stage of protein synthesis. This kinase and its substrate, eukaryotic elongation factor 2 (eEF2) are important in processes such as neuronal development and synaptic plasticity. eEF2K is regulated by multiple mechanisms including Ca2+‐ions and the mTORC1 signaling pathway, both of which play key roles in neurological processes such as learning and memory. In such settings, the localized control of protein synthesis is of crucial importance. In this work, we sought to investigate how the localization of eEF2K is controlled and the impact of this on protein synthesis in neuronal cells. In this study, we used both SH‐SY5Y neuroblastoma cells and mouse cortical neurons, and pharmacologically and/or genetic approaches to modify eEF2K function. We show that eEF2K activity and localization can be regulated by its binding partner Homer1b/c, a scaffolding protein known for its participation in calcium‐regulated signaling pathways. Furthermore, our results indicate that this interaction is regulated by the mTORC1 pathway, through a known phosphorylation site in eEF2K (S396), and that it affects rates of localized protein synthesis at synapses depending on the presence or absence of this scaffolding protein. We studied how neurotransmitter release can modulate protein synthesis in central nervous system cell cultures in a localized fashion through multiple signaling pathways. Bicuculline activates both mTORC1 and eEF2K pathways, but mTORC1 activation can promote Homer1‐eEF2K binding, potentially limiting its kinase activity and modulating translation in different ways depending on the presence of Homer1 and eEF2K phosphorylation by mTORC1 at the S396 site. These results provide a new point of view into the complex dynamics of neuronal and protein synthesis in response to neurotransmission, potentially leading to better understanding of physiological and pathological mechanisms controlling translation in neuronal cells.