| eIF4B functions as a eukaryotic translation initiation factor that enhances ribosomal recruitment to mRNA within the eIF4F complex during cap-dependent translation. It contains an RNA recognition motif domain and multiple RNA-binding regions that facilitate interactions with structured mRNAs, alongside conserved serine-rich motifs serving as phosphorylation sites. Phosphorylation at multiple residues, including Ser422 and Ser504, occurs through convergent signaling from mTORC1/S6K1, PI3K/Akt, ERK/RSK, and Pim kinases downstream of growth factors, mitogens, and synaptic activity, boosting eIF4B affinity for eIF4A and eIF3 to stimulate helicase activity and scanning efficiency on transcripts with complex 5' UTRs. This modification promotes assembly of the 48S preinitiation complex by stabilizing 40S subunit binding near the cap structure and accelerating 60S joining for elongation, particularly favoring translation of proliferation-associated mRNAs encoding cyclins, c-Myc, and HIF1α. eIF4B binds along the full length of mRNA transcripts in a position-dependent manner, interacting with UPF1 to regulate nonsense-mediated decay and stem-loop structures in replication-dependent histone mRNAs, thus controlling their turnover at S-phase exit. Metabotropic glutamate receptor activation drives Ser504 phosphorylation via casein kinases, linking synaptic plasticity to local dendritic translation. Dephosphorylation under stress like heat shock or nutrient deprivation correlates with translation repression. Elevated eIF4B phosphorylation and expression mark oncogenic states in leukemias, lymphomas, and solid tumors, where it sustains survival under PI3K/mTOR hyperactivation. |
Lane 1: PANC-1, Lane 2: Hela
