Cell stress is related to re-localization of Argonaute 2 and to decreased RNA interference in human cells

Abstract

Various kinds of stress on human cells induce the formation of endogenous stress granules (SGs). Human Argonaute 2 (hAgo2), the catalytic core component of the RNA-induced silencing complex (RISC), can be recruited to SGs as well as P-bodies (PBs) indicating that the dynamic intracellular distribution of hAgo2 in SGs, in PBs or at other sub-cellular sites could be related to the efficiency of the RNA interference (RNAi) machinery. Here, we studied the influence of heat shock, sodium arsenite (NaAsO2), cycloheximide (CHX) and LipofectamineTM 2000-mediated transfection of phosphorothioate (PS)-modified oligonucleotides (ON) on the intracellular localization of hAgo2 and the efficiency of RNAi.Fluorescence microscopy and sedimentation analysis of cell fractions indicate stress-induced accumulation of hAgo2 in SGs and the loss of distinctly composed complexes containing hAgo2 or their sub-cellular context. Transfection of cells with PS-ON induces cell stress that is phenotypically similar to the established inducers heat shock and NaAsO2. The intracellular re-distribution of hAgo2 is related to its increased metabolic stability and to decreased RNAi directed by microRNA or by short interfering RNA. Here, we propose a functional model of the relationship between cell stress, translocation of hAgo2 to SGs providing a depot function, and loss of RNAi activity.

Cell Type- and Tissue Context-dependent Nuclear Distribution of Human Ago2

“…Upon cellular stress induced by arsenite, both Ago2 and TIA-1, a stress granule (SG)-specific marker, are recruited to SGs involved in translation inhibition (Fig. 1D) (4,18,19). By IFA staining of Ago2 and TIA-1 in arsenite-treated HeLa cells, we found that both cytoplasmic Ago2 and TIA-1, but not nuclear Ago2 and TIA-1, are co-stained in numerous cytoplasmic SGs (Fig.…”

Cavin-1 and Caveolin-1 are both required to support cell proliferation, migration and anchorage-independent cell growth in rhabdomyosarcoma

“…Indeed, nuclear proteins are more resistant to knockdown mediated by shRNA because of the reduced availability of RNAi cellular machinery into the nucleus. 70 In contrast, Cavin-1 downregulation in RH30 cells did not affect the subcellular localization of Cav-1 (Figure 6b, bottom panels). We next assayed the cell proliferation, migration and chemoresistance of the different clones by means of the Crystal violet, Boyden chamber and Neutral Red assays, respectively.…”

tRNA modifications: Necessary for correct tRNA‐derived fragments during the recovery from stress?

“…Since Dicers and Argonautes can associate with tRNA-derived sequences [24,25], it follows that specific stress conditions might favor such association. Ago-2 has been found in stress granules, which also correlated with decreased RNAi in human cells [26]. In addition, Drosophila Ago-2 loading with specific small RNAs has been shown to increase after heat shock [27].…”