The mRNA-binding Protein YB-1 (p50) Prevents Association of the Eukaryotic Initiation Factor eIF4G with mRNA and Inhibits Protein Synthesis at the Initiation Stage

Abstract

The cytoplasmic messenger ribonucleoprotein particles of mammalian somatic cells contain the protein YB-1, also called p50, as a major core component. YB-1 is multifunctional and involved in regulation of mRNA transcription and translation. Our previous studies demonstrated that YB-1 stimulates initiation of translation in vitro at a low YB-1/mRNA ratio, whereas an increase of YB-1 bound to mRNA resulted in inhibition of protein synthesis in vitro and in vivo. Here we show that YB-1-mediated translation inhibition in a rabbit reticulocyte cell-free system is followed by a decay of polysomes, which is not a result of mRNA degradation or its functional inactivation. The inhibition does not change the ribosome transit time, and therefore, it affects neither elongation nor termination of polypeptide chains and only occurs at the stage of initiation. YB-1 induces accumulation of mRNA in the form of free messenger ribonucleoprotein particles, i.e. it blocks mRNA association with the small ribosomal subunit. The accumulation is accompanied by eukaryotic initiation factor eIF4G dissociation from mRNA. The C-terminal domain of YB-1 is responsible for inhibition of translation as well as the disruption of mRNA interaction with eIF4G.All mRNAs in eukaryotic cells are associated with proteins and form messenger ribonucleoprotein particles (mRNPs) 1 (1-6). Some mRNA-associated proteins exhibit specificity for certain mRNA(s); others are universal. To date, two universal major proteins of cytoplasmic mRNPs tightly bound to mRNA are well characterized. One of them is poly(A)-binding protein that stabilizes mRNA (7, 8) and promotes protein synthesis at the initiation stage (9, 10). It is suggested that the protein biosynthesis promotion occurs due to binding of multimerized poly(A)-binding protein associated with poly(A) to eIF4G and 1) mRNA cyclization and facilitation of ribosomal recycling (11, 12) and/or 2) a conformational change in eIF4F and an increase in affinity of eIF4E for the 5Ј-cap (13).The other common mRNP component is YB-1, a 36-kDa protein with abnormal mobility in SDS gel electrophoresis that is typical for this 50-kDa protein (14 -16). According to its primary structure, YB-1 from rabbit reticulocytes was identified as a member of the Y-box (YB) transcription factor family: it was virtually identical (ϳ98% identity) to human YB-1. YB-1 has been shown to participate in different steps of mRNA biogenesis, including mRNA transcription, processing, and transport from the nucleus into the cytoplasm (5, 17, 18) where it can regulate mRNA localization, translation, and mRNA stability (15,16,19). YB-1 displays DNA and RNA melting, annealing, and strand exchange activities, which probably underlies many functions of the YB protein family (20,21).The characteristic feature of these proteins is a central, highly conserved, cold shock domain (CSD) that consists of 80 amino acid residues and exhibits 43% identity to the major Escherichia coli cold shock protein CspA (4, 5). CSD comprises a five-stranded ␤-barrel with RNP ...

Attentional dysfunction, impulsivity, and resistance to change in a mouse model of fragile X syndrome.

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Y-box Binding Protein 1: Providing a New Angle on Translational Regulation

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Expression of YB-1 enhances production of murine leukemia virus vectors by stabilizing genomic viral RNA

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