RACK1 Is a Ribosome Scaffold Protein for β-actin mRNA/ZBP1 Complex

Abstract

In neurons, specific mRNAs are transported in a translationally repressed manner along dendrites or axons by transport ribonucleic-protein complexes called RNA granules. ZBP1 is one RNA binding protein present in transport RNPs, where it transports and represses the translation of cotransported mRNAs, including β-actin mRNA. The release of β-actin mRNA from ZBP1 and its subsequent translation depends on the phosphorylation of ZBP1 by Src kinase, but little is known about how this process is regulated. Here we demonstrate that the ribosomal-associated protein RACK1, another substrate of Src, binds the β-actin mRNA/ZBP1 complex on ribosomes and contributes to the release of β-actin mRNA from ZBP1 and to its translation. We identify the Src binding and phosphorylation site Y246 on RACK1 as the critical site for the binding to the β-actin mRNA/ZBP1 complex. Based on these results we propose RACK1 as a ribosomal scaffold protein for specific mRNA-RBP complexes to tightly regulate the translation of specific mRNAs.

Translation factors and ribosomal proteins control tumor onset and progression: how?

“…A recent hypomorphic model for RACK1 shows a pretty unique phenotype, characterized by reduced translation and a white bellyspot. 113 These data suggest that RACK1 affects the specific translation of mRNAs, as recently suggested by its binding to the b-actin mRNA/ZBP1 complex, 114 and its essential role in miRNA-regulated translation. 115,116 A powerful oncogenic pathway converging on translation is driven by Myc oncogene.…”

Asc1p/RACK1 Connects Ribosomes to Eukaryotic Phosphosignaling

“…Our results showed specific sensitivity of the asc1 Y250F strain, and especially the asc1 Y250F DE strain, to inhibitors of protein biosynthesis, suggesting a relevant role of this phosphosite in translational processes. As shown here for the Y250F exchange within yeast Asc1p, the exchange at the corresponding site within mammalian RACK1 (Y246F) does not affect the association of the protein with ribosomes, implying that the effect of this exchange on cellular processes is not caused by the protein's release from the site of translation (17). Since Y250 is located opposite the ribosome binding site at the bottom of Asc1p, it might be responsible for the binding of other regulatory proteins.…”

“…Phosphorylation of Y246 is also important for the interaction of RACK1 with the mRNA-binding protein ZBP1, another target of the Src kinase at the ribosome. ZBP1 binds the ␤-actin mRNA and regulates its local translation together with the Src kinase and RACK1 (17). Our results showed specific sensitivity of the asc1 Y250F strain, and especially the asc1 Y250F DE strain, to inhibitors of protein biosynthesis, suggesting a relevant role of this phosphosite in translational processes.…”

“…Asc1p/RACK1 affects translation, depending on the 5= untranslated regions of mRNAs (15) and through its interaction with mRNA-binding proteins, such as Scp160p in S. cerevisiae (16) and ZBP1 in mammalian neuronal cells (17). Mammalian RACK1 also regulates protein expression at a posttranslational level by affecting the degradation of certain proteins, e.g., the ␣-subunit of the transcription factor hypoxia-inducible factor 1 (HIF1␣) (18).…”

Anticorpos conformacionais para PKCs clássicas e suas aplicações

“…Isso ocorre porque a fosforilação de ZBP1 (Zipcode-Binding Protein 1), uma proteína que reprime a tradução de mRNAs durante o seu transporte para locais específicos, determina a liberação e por consequência a tradução de mRNAs codificadores de -actina (Ceci et al, 2012). Além disso, é bem estabelecido que a fosforilação regula a atividade de eIF6 (Eukaryotic Initiation Factor 6) e por consequência a síntese de proteínas (Ceci et al, 2012). Estudos subsequentes poderão determinar se essas proteínas podem ser substratos nas células MDA-MB-231.…”