Regulation of neuronal mRNA translation by CaM-Kinase I phosphorylation of eIF4GII

Vollum Institute, Oregon Health and Science University, Portland, Oregon 97239, USA.
The Journal of Neuroscience : The Official Journal of the Society for Neuroscience (Impact Factor: 6.34). 04/2012; 32(16):5620-30. DOI: 10.1523/JNEUROSCI.0030-12.2012
Source: PubMed


Ca²⁺/calmodulin-dependent kinases (CaMKs) are essential for neuronal development and plasticity, processes requiring de novo protein synthesis. Roles for CaMKs in modulating gene transcription are well established, but their involvement in mRNA translation is evolving. Here we report that activity-dependent translational initiation in cultured rat hippocampal neurons is enhanced by CaMKI-mediated phosphorylation of Ser1156 in eukaryotic initiation factor eIF4GII (4GII). Treatment with bicuculline or gabazine to enhance neuronal activity promotes recruitment of wild-type 4GII, but not the 4GII S1156A mutant or 4GI, to the heterotrimeric eIF4F (4F) complex that assembles at the 5' cap structure (m⁷GTP) of mRNA to initiate ribosomal scanning. Recruitment of 4GII to 4F is suppressed by pharmacological inhibition (STO-609) of CaM kinase kinase, the upstream activator of CaMKI. Post hoc in vitro CaMKI phosphorylation assays confirm that activity promotes phosphorylation of S1156 in transfected 4GII in neurons. Changes in cap-dependent and cap-independent translation were assessed using a bicistronic luciferase reporter transfected into neurons. Activity upregulates cap-dependent translation, and RNAi knockdown of CaMKIβ and γ isoforms, but not α or δ, led to its attenuation as did blockade of NMDA receptors. Furthermore, RNAi knockdown of 4GII attenuates cap-dependent translation and reduces density of dendritic filopodia and spine formation without effect on dendritic arborization. Together, our results provide a mechanistic link between Ca²⁺ influx due to neuronal activity and regulation of cap-dependent RNA translation via CaMKI activation and selective recruitment of phosphorylated 4GII to the 4F complex, which may function to regulate activity-dependent changes in spine density.

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    • "Through these interactions, CaMKI has been shown to play a contributing role in many neuronal functions including axon formation and elongation, dendritic arborization, spine formation and morphology, and synaptic plasticity (Wayman et al., 2008). Furthermore, CaMKI has been shown to mediate the expression of the previously mentioned genes via phosphorylating the initiation factor 4GII (Srivastava et al., 2012). Robust expression of CaMKI isoform d was reported in rodents in the extended amygdala, which includes the BFCN (Sakagami et al., 2005). "
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    • "Finally, the specialization of eIF4G isoforms can be achieved through their specific phosphorylation (see Dobrikov et al., 2014; Srivastava et al., 2012; and references therein). Phosphorylation of eIF4E (Ser 209 in human eIF4E) by MNK1/2 kinases in metazoans is one more way to diversify the function of eIF4F. "
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    • "Block of CaMKKa/b also impairs synthesis of plasticity-related proteins after strong LTP induction that is thought to contribute to LTM formation (Redondo et al. 2010). Other in vitro studies, which include inhibition of CaMKKa/b, have suggested that there is crosstalk between the CaM kinase cascade and ERK (Schmitt et al. 2005) or Akt signaling (Fortin et al. 2012), and that the kinase cascade regulates local protein synthesis via CaMKI activation (Fortin et al. 2012; Srivastava et al. 2012). However, it remains unknown whether these mechanisms are relevant for memory formation in the intact brain. "
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