Eukaryotic initiation factor 2B: identification of multiple phosphorylation sites in the epsilon-subunit and their functions in vivo

Abstract

contributed equally to this work Eukaryotic initiation factor (eIF) 2B is a heteromeric guanine nucleotide exchange factor that plays an important role in regulating mRNA translation. Here we identify multiple phosphorylation sites in the largest, catalytic, subunit (e) of mammalian eIF2B. These sites are phosphorylated by four different protein kinases. Two conserved sites (Ser712/713) are phosphorylated by casein kinase 2. They lie at the extreme C-terminus and are required for the interaction of eIF2Be with its substrate, eIF2, in vivo and for eIF2B activity in vitro. Glycogen synthase kinase 3 (GSK3) is responsible for phosphorylating Ser535. This regulatory phosphorylation event requires both the fourth site (Ser539) and a distal region, which acts to recruit GSK3 to eIF2Be in vivo. The ®fth site, which lies outside the catalytic domain of eIF2Be, can be phosphorylated by casein kinase 1. All ®ve sites are phosphorylated in the eIF2B complex in vivo.

Structure of the Catalytic Fragment of Translation Initiation Factor 2B and Identification of a Critically Important Catalytic Residue

“…The residues in the N terminus may require residues upstream in eIF2B⑀ or other residues in eIF2B to become ordered, whereas those in the C terminus may become ordered during complex formation with eIF2 (see below). Alternatively, phosphorylation of two conserved serines in the C terminus, as demonstrated for mammalian eIF2B⑀, could have an effect on the structure of this region (4).…”

“…The activity of mammalian eIF2B can also be controlled directly in response to insulin signaling, which causes glycogen synthase kinase 3 inactivation and thereby contributes to activation of eIF2B (4). This permits increased eIF2B activity and protein synthesis in response to growth-promoting signals.…”

Fibronectin controls cap-dependent translation through β1 integrin and eukaryotic initiation factors 4 and 2 coordinated pathways

“…We performed a full analysis of limiting factors eIF4F and eIF2. eIF2-mediated ternary complex formation is negatively regulated by phosphorylation of eIF2␣ subunit activated by several stimuli (18,(20)(21)(22)(23)(24)(25). Deprivation of matrix attachment strongly induced phosphorylation of eIF2␣, but left eIF4F formation almost unchanged (Fig.…”

“…In mammals, eIF2-␣ mediated down-regulation of translation is under the control of four different eIF2-␣ kinases and occurs in response to negative conditions for growth as diverse as amino acid deprivation (17), iron deficiency (18), heat shock and viral infection (19), endoplasmic reticulum stress (20,21), and UV exposure (22,23). Additionally, eIF2B activity is modulated by a PI3K-glycogen synthase kinase-3 pathway (24,25). Thus, the combination of different pathways converging to the translational machinery results in quantitative and qualitative changes of the mRNAs to be translated.…”

VSV-tumor selective replication and protein translation

“…Plausibly, overexpression of the e subunit, as observed in transformed MEFs could also stimulate guanine nucleotide exchange activity and overcome the translation-inhibitory consequences of eIF2a phosphorylation (Gomez et al, 2002). Further, the activity and allosteric regulation of eIF2B can also be potently affected by post-translational modifications such as phosphorylation (Wang et al, 2001). Collectively, a number of aberrancies at this level of regulation such as posttranslational modifications, may play roles in disrupting the eIF2a checkpoint following cellular transformation, although this remains to be further examined Pavitt et al, 1997Pavitt et al, , 1998Proud, 2001;Williams et al, 2001).…”