Identification of PCBP2, a facilitator of IRES-mediated translation, as a novel constituent of stress granules and processing bodies

Abstract

Recent advances in microscopic techniques have shed light on the roles of specific subcellular structures in the regulation of gene expression. One such structure is the stress granule (SG), which is engaged in stress-triggered translational arrest by sequestering pre-initiation complexes of translation. Recent studies revealed the spatial, compositional, and functional linkage of the SG to the processing body (P-body), another cytoplasmic structure that has been implicated in mRNA degradation and siRNA-or miRNA-mediated gene silencing. In this study, we report that PCBP2, a facilitator of IRES (Internal Ribosomal Entry Site)-mediated translation, is a novel constituent of the SG and P-body. Immunofluorescence studies revealed that while PCBP2 is diffusely distributed throughout the nucleoplasm and the cytoplasm, the protein is enriched in a subset of P-bodies under normal conditions. Upon exposure to heat and arsenic stress, PCBP2 became predominantly accumulated at the SG, but was still present in Dcp1a-positive P-bodies. Live-cell imaging revealed the dynamic association of PCBP2-enriched P-bodies and the SG, and FRAP experiments demonstrated that PCBP2 actively moves in and out of the SG and P-body. Taken together, these results suggest that PCBP2 shuttles between the cytoplasm and the two structures under stress. We propose that PCBP2 may be involved in stress-induced remodeling of mRNP complexes and that it may also play a role in the rapid transition of certain silenced mRNAs into a translationally active state. Additionally, given the property of PCBP2 as a nuclear-cytoplasmic shuttling protein, PCBP2 may play a role in directly targeting nascent mRNPs to specific P-bodies for storage.

Expression and functional role of a transcribed noncoding RNA with an ultraconserved element in hepatocellular carcinoma

“…The sequence of TUC338 overlaps with that of PCBP2, an RNA binding protein involved in mRNA processing in humans (40)(41)(42). Interestingly, exonic ultraconserved regions are frequently associated with RNA processing, such as RNA binding or RNA splicing, suggesting a potential role as regulators of RNA.…”

Stable Formation of Compositionally Unique Stress Granules in Virus-Infected Cells

“…Alternatively, it is possible that release is triggered by as-yet-unidentified mechanisms, followed soon thereafter by cleavage. Interestingly, PCBP-2, an RNA binding protein that plays an important role in translation and replication of the viral RNA genome, was recently shown to be recruited to SGs during heat shock and oxidative stress (3,15,16,39,49). As PCBP2 is also cleaved by the viral 3C protease (41), it will be interesting to see if it also is initially recruited and then released from poliovirus-induced SGs.…”

Cytoplasmic mRNP granules at a glance

“…Fluorescence recovery after photobleaching (FRAP) experiments revealed that many components cycle rapidly in and out of PBs and SGs, although a subset are more static (Aizer et al, 2008;Andrei et al, 2005;Eisinger-Mathason et al, 2008;Fujimura et al, 2008a;Fujimura et al, 2008b;Guil et al, 2006;Kedersha et al, 2000;Kedersha et al, 2005;Leung et al, 2006;Mollet et al, 2008). Realtime imaging of human cell lines shows that most PBs and SGs move in an apparently random manner.…”

“…FRAP experiments show that many factors rapidly cycle in and out of PBs (Aizer et al, 2008;Andrei et al, 2005;Fujimura et al, 2008b;Kedersha et al, 2005;Leung et al, 2006), and PBs rapidly disappear when new mRNPs are prevented from entering PBs upon treatment of S. cerevisiae, Drosophila or human cells with translation elongation inhibitors (Cougot et al, 2004;Eulalio et al, 2007b;Teixeira et al, 2005). Evidence suggests that the release of mRNPs from PBs involves either mRNA decay or release of the mRNP back into translation.…”