Andrei, M. A. et al. A role for eIF4E and eIF4E-transporter in targeting mRNPs to mammalian processing bodies. RNA 11, 717-727

Department of Cellular Biochemistry, Max-Planck-Institute of Biophysical Chemistry, D-37077 Göttingen, Germany.
RNA (Impact Factor: 4.94). 05/2005; 11(5):717-27. DOI: 10.1261/rna.2340405
Source: PubMed


mRNP remodeling events required for the transition of an mRNA from active translation to degradation are currently poorly understood. We identified protein factors potentially involved in this transition, which are present in mammalian P bodies, cytoplasmic foci enriched in 5' --> 3' mRNA degrading enzymes. We demonstrate that human P bodies contain the cap-binding protein eIF4E and the related factor eIF4E-transporter (eIF4E-T), suggesting novel roles for these proteins in targeting mRNAs for 5' --> 3' degradation. Furthermore, fluorescence resonance energy transfer (FRET) studies indicate that eIF4E interacts with eIF4E-T and the putative DEAD box helicase rck/p54 in the P bodies in vivo. RNAi-mediated knockdowns revealed that a subset of P body factors, including eIF4E-T, LSm1, rck/p54, and Ccr4 are required for the accumulation of each other and eIF4E in P bodies. In addition, treatment of HeLa cells with cycloheximide, which inhibits translation, revealed that mRNA is also required for accumulation of mRNA degradation factors in P bodies. In contrast, knockdown of the decapping enzyme Dcp2, which initiates the actual 5' --> 3' mRNA degradation did not abolish P body formation, indicating it first functions after mRNPs have been targeted to these cytoplasmic foci. These data support a model in which mRNPs undergo several successive steps of remodeling and/or 3' trimming until their composition or structural organization promotes their accumulation in P bodies.

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    • "The release of an mRNA from the translation machinery seems to be a perquisite for its targeting to PBs, since ribosomal proteins and translation initiation factors are excluded from PBs with the exception of eIF4E. The simultaneous presence of eIF4E-T (an eIF4E-binding protein that inhibits translation) however suggests that eIF4E is associated with translationally repressed, not active, molecules (Andrei et al., 2005; Ferraiuolo et al., 2005). Conversely , not all mRNAs found in PBs are committed to decapping and decay and intact transcripts can exit PBs and return to translation (Bhattacharyya et al., 2006; Brengues et al., 2005). "
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    • "It has also been reported that mRNA is required for cytoplasmic P-body maintenance (Cougot et al., 2004; Andrei et al., 2005; Ferraiuolo et al., 2005). Furthermore, a recent study showed that after nocodazole treatment, HIF-1a mRNA, which is overexpressed in solid tumors, accumulates in Pbodies . "
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    • "ctable . Indeed , P - bodies do not contain PABP - 1 ( Kedersha et al . , 2005 ) , suggesting that mRNA in P - bodies is deadenylated . P - bodies contain four deadenylation nucleases ( Pan2 , Pan3 , Ccr4 and Caf1 ) and cannot form if deadenylation is impaired as observed in yeast and mouse cells ( Sheth and Parker , 2003 ; Cougot et al . , 2004 ; Andrei et al . , 2005 ; Zheng et al . , 2008 ) . It has been suggested that the first phase of deadenylation involves the dissociation of PABP from the transcript , and this occurs before messenger ribonucleoproteins ( mRNPs ) enter P - bodies ( Zheng et al . , 2008 ) . Given that the FISH experiments demonstrated that most of the mRNAs tested could be detec"
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