Phosphorylation Screening Identifies Translational Initiation Factor 4GII as an Intracellular Target of Ca2+/Calmodulin-dependent Protein Kinase I

Hui, Qin; Raught, Brian; Sonenberg, Nahum; Goldstein, Elaine G.; Edelman, Arthur M.

doi:10.1074/jbc.m308781200

Cited by 30 publications

(35 citation statements)

References 69 publications

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“…Myc-MARK2-KA was used as substrate in these studies to prevent autophosphorylation. GST-CaMKI was preactivated by phosphorylation with CaMKK, which is essential for full-activation of the kinase and efficient phosphorylation of other substrates (Matsushita and Nairn, 1998;Suizu et al, 2002;Qin et al, 2003). Activated GSTCaMKI phosphorylated myc-MARK2-KA, whereas no significant 32 P incorporation occurred after addition of CaMKK alone or without addition of any kinases (Fig.…”

Section: Camki Phosphorylates Mark2 On Novel Sitesmentioning

confidence: 99%

A Calcium- and Calmodulin-Dependent Kinase Iα/Microtubule Affinity Regulating Kinase 2 Signaling Cascade Mediates Calcium-Dependent Neurite Outgrowth

Uboha¹,

Flajolet²,

Nairn³

et al. 2007

J. Neurosci.

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Calcium is a critical regulator of neuronal differentiation and neurite outgrowth during development, as well as synaptic plasticity in adulthood. Calcium-and calmodulin-dependent kinase I (CaMKI) can regulate neurite outgrowth; however, the signal transduction cascades that lead to its physiological effects have not yet been elucidated. CaMKI␣ was therefore used as bait in a yeast two-hybrid assay and microtubule affinity regulating kinase 2 (MARK2)/Par-1b was identified as an interacting partner of CaMKI in three independent screens. The interaction between CaMKI and MARK2 was confirmed in vitro and in vivo by coimmunoprecipitation. CaMKI binds MARK2 within its kinase domain, but only if it is activated by calcium and calmodulin. Expression of CaMKI and MARK2 in Neuro-2A (N2a) cells and in primary hippocampal neurons promotes neurite outgrowth, an effect dependent on the catalytic activities of these enzymes. In addition, decreasing MARK2 activity blocks the ability of the calcium ionophore ionomycin to promote neurite outgrowth. Finally, CaMKI phosphorylates MARK2 on novel sites within its kinase domain. Mutation of these phosphorylation sites decreases both MARK2 kinase activity and its ability to promote neurite outgrowth. Interaction of MARK2 with CaMKI results in a novel, calciumdependent pathway that plays an important role in neuronal differentiation.

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Section: Camki Phosphorylates Mark2 On Novel Sitesmentioning

confidence: 99%

A Calcium- and Calmodulin-Dependent Kinase Iα/Microtubule Affinity Regulating Kinase 2 Signaling Cascade Mediates Calcium-Dependent Neurite Outgrowth

Uboha¹,

Flajolet²,

Nairn³

et al. 2007

J. Neurosci.

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“…28 In addition, CAMK1 has been described as phosphorylating eIF4GII (Fig. 5D) in a similar C-terminal region of the molecule (Ser 1308 22 ), using the numbering from our work which extended the N-terminus from a CUG initiation codon. 8 To delineate the sites of phosphorylation observed in nocodazole treatment, we created cDNAs corresponding to regions of both proteins.…”

Section: Robust Phosphorylation Of Eif2α and 4e-bp1 Does Not Occur Fomentioning

confidence: 99%

Phosphorylation of eIF4GII and 4E-BP1 in response to nocodazole treatment: A reappraisal of translation initiation during mitosis

et al. 2013

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“…However, an important difference has recently been revealed with the discovery that during megakaryocytic differentiation, eIF4GII is selectively recruited into eIF4F complexes (11). In addition, eIF4G homologues differ in their phosphorylation status, with serum-stimulated sites of phosphorylation identified in the C terminus of eIF4GI but not in eIF4GII (44,46), suggesting a possible isoform-specific role for this modification. In contrast, eIF4GII phosphorylation is increased primarily at the G 2 /M phase of the cell cycle (44,46), when there is a transient decrease in overall translation rates, although it remains unclear how these individual phosphorylation events modulate translation.…”

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confidence: 99%

Specific Isoforms of Translation Initiation Factor 4GI Show Differences in Translational Activity

Coldwell

Morley

2006

Molecular and Cellular Biology

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The eukaryotic initiation factor (eIF) 4GI gene locus (eIF4GI) contains three identified promoters, generating alternately spliced mRNAs, yielding a total of five eIF4GI protein isoforms. Although eIF4GI plays a critical role in mRNA recruitment to the ribosomes, little is known about the functions of the different isoforms, their partner binding capacities, or the role of the homolog, eIF4GII, in translation initiation. To directly address this, we have used short interfering RNAs (siRNAs) expressed from DNA vectors to silence the expression of eIF4GI in HeLa cells. Here we show that reduced levels of specific mRNA and eIF4GI isoforms in HeLa cells promoted aberrant morphology and a partial inhibition of translation. The latter reflected dephosphorylation of 4E-BP1 and decreased eIF4F complex levels, with no change in eIF2␣ phosphorylation. Expression of siRNA-resistant Myc-tagged eIF4GI isoforms has allowed us to show that the different isoforms exhibit significant differences in their ability to restore translation rates. Here we quantify the efficiency of eIF4GI promoter usage in mammalian cells and demonstrate that even though the longest isoform of eIF4GI (eIF4GIf) was relatively poorly expressed when reintroduced, it was more efficient at promoting the translation of cellular mRNAs than the more highly expressed shorter isoforms used in previous functional studies.Translational control plays a critical role in overall gene expression, allowing the rapid and reversible stimulation of protein synthesis from preexisting mRNAs, the fine-tuning of protein expression levels, and in some cases the production of proteins at specific sites in the cell (reviewed in reference 37). Eukaryotic protein synthesis comprises three stages: initiation, elongation, and termination. The initiation phase refers to the binding of the ribosomal subunits to the mRNA and positioning of the subunits at the first codon of the mRNA open reading frame. Several eukaryotic initiation factors (eIFs) are required for this process, and in most cases, initiation determines both the rate of translation of individual mRNAs and the overall rate of protein synthesis (17,19,32,36). The inappropriate expression of several initiation factors has been noted for a number of diseases and cancers (1, 34), and the improper recruitment of mRNAs to the ribosome may also play a role in the deregulation of gene expression.The multidomain factor eIF4G, expressed as two isoforms in mammalian cells sharing 46% identity at the amino acid level (eIF4GI/II), plays an essential role in mRNA recruitment by acting as a molecular focal point upon which the translation initiation complex is assembled to bring together the mRNA and the ribosome. eIF4G is part of the eIF4F complex (17, 36), which also comprises the mRNA cap-binding protein (eIF4E) and an ATP-dependent RNA helicase activity (eIF4A, in concert with eIF4B). The yeast, wheat, and mammalian homologs bind to RNA in a sequence-independent manner (6, 28, 30), although mammalian eIF4G also binds specifically to...

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Phosphorylation Screening Identifies Translational Initiation Factor 4GII as an Intracellular Target of Ca2+/Calmodulin-dependent Protein Kinase I

Cited by 30 publications

References 69 publications

A Calcium- and Calmodulin-Dependent Kinase Iα/Microtubule Affinity Regulating Kinase 2 Signaling Cascade Mediates Calcium-Dependent Neurite Outgrowth

A Calcium- and Calmodulin-Dependent Kinase Iα/Microtubule Affinity Regulating Kinase 2 Signaling Cascade Mediates Calcium-Dependent Neurite Outgrowth

Phosphorylation of eIF4GII and 4E-BP1 in response to nocodazole treatment: A reappraisal of translation initiation during mitosis

Specific Isoforms of Translation Initiation Factor 4GI Show Differences in Translational Activity

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