Descripción: Stress granules are cytoplasmic mRNA-silencing foci that form transiently during the stress response. Stress granules harbor abortive translation initiation complexes and are in dynamic equilibrium with translating polysomes. Mammalian Staufen 1 (Stau1) is a ubiquitous double-stranded RNA-binding protein associated with polysomes. Here, we show that Stau1 is recruited to stress granules upon induction of endoplasmic reticulum or oxidative stress as well in stress granules induced by translation initiation blockers. We found that stress granules lacking Stau1 formed in cells depleted of this molecule, indicating that Stau1 is not an essential component of stress granules. Moreover, Stau1 knockdown facilitated stress granule formation upon stress induction. Conversely, transient transfection of Stau1 impaired stress granule formation upon stress or pharmacological initiation arrest. The inhibitory capacity of Stau1 mapped to the amino-terminal half of the molecule, a region known to bind to polysomes. We found that the fraction of polysomes remaining upon stress induction was enriched in Stau1, and that Stau1 overexpression stabilized polysomes against stress. We propose that Stau1 is involved in recovery from stress by stabilizing polysomes, thus helping stress granule dissolution.

Descripción: Cytoplasmic events depending on RNA-binding proteins contribute to the fine-tuning of gene expression. Sterile α motif-containing RNA-binding proteins constitute a novel family of post-transcriptional regulators that recognize a specific RNA sequence motif known as Smaug recognition element (SRE). The Drosophila member of this family, dSmaug, triggers the translational repression and deadenylation of maternal mRNAs by independent mechanisms, and the yeast homologue Vts1 stimulates degradation of SRE-containing messengers. Two homologous genes are present in the mammalian genome. Here we showed that hSmaug 1, encoded in human chromosome 14, represses the translation of reporter transcripts carrying SRE motifs. When expressed in fibroblasts, hSmaug 1 forms cytoplasmic granules that contain polyadenylated mRNA and the RNA-binding proteins Staufen, TIAR, TIA-1, and HuR. Smaug 1 foci are distinct from degradation foci. The murine protein mSmaug 1 is expressed in the central nervous system and is abundant in post-synaptic densities, a subcellular region where translation is tightly regulated by synaptic stimulation. Biochemical analysis indicated that mSmaug 1 is present in synaptoneurosomal 20 S particles. These results suggest a role for mammalian Smaug 1 in RNA granule formation and translation regulation in neurons. © 2005 by The American Society for Biochemistry and Molecular Biology, Inc.

Descripción: Human immunodeficiency virus type 1 (HIV-1) Gag selects for and mediates genomic RNA (vRNA) encapsidation into progeny virus particles. The host protein, Staufen1 interacts directly with Gag and is found in ribonucleoprotein (RNP) complexes containing vRNA, which provides evidence that Staufen1 plays a role in vRNA selection and encapsidation. In this work, we show that Staufen1, vRNA and Gag are found in the same RNP complex. These cellular and viral factors also colocalize in cells and constitute novel Staufen1 RNPs (SHRNPs) whose assembly is strictly dependent on HIV-1 expression. SHRNPs are distinct from stress granules and processing bodies, are preferentially formed during oxidative stress and are found to be in equilibrium with translating polysomes. Moreover, SHRNPs are stable, and the association between Staufen1 and vRNA was found to be evident in these and other types of RNPs. We demonstrate that following Staufen1 depletion, apparent supraphysiologic-sized SHRNP foci are formed in the cytoplasm and in which Gag, vRNA and the residual Staufen1 accumulate. The depletion of Staufen1 resulted in reduced Gag levels and deregulated the assembly of newly synthesized virions, which were found to contain several-fold increases in vRNA, Staufen1 and other cellular proteins. This work provides new evidence that Staufen1-containing HIV-1 RNPs preferentially form over other cellular silencing foci and are involved in assembly, localization and encapsidation of vRNA.