Uncoupling of nucleo-cytoplasmic RNA export and localization during stress

Abstract

Eukaryotic cells contain sub-cellular compartments that are not membrane bound. Some structures are always present, such as nuclear speckles that contain RNA-binding proteins (RBPs) and poly(A)+ RNAs. Others, like cytoplasmic stress granules (SGs) that harbor mRNAs and RBPs, are induced upon stress. When we examined the formation and composition of nuclear speckles during stress induction with tubercidin, an adenosine analogue previously shown to affect nuclear speckle composition, we unexpectedly found that it also led to the formation of SGs and to the inhibition of several crucial steps of RNA metabolism in cells, thereby serving as a potent inhibitor of the gene expression pathway. Although transcription and splicing persisted under this stress, RBPs and mRNAs were mislocalized in the nucleus and cytoplasm. Specifically, lncRNA and RBP localization to nuclear speckles was disrupted, exon junction complex (EJC) recruitment to mRNA was reduced, mRNA export was obstructed, and cytoplasmic poly(A)+ RNAs localized in SGs. Furthermore, nuclear proteins that participate in mRNA export, such as nucleoporins and mRNA export adaptors, were mislocalized to SGs. This study reveals structural aspects of granule assembly in cells, and describes how the flow of RNA from the nucleus to the cytoplasm is severed under stress.

The Ebola Virus Nucleoprotein Recruits the Nuclear RNA Export Factor NXF1 into Inclusion Bodies to Facilitate Viral Protein Expression

“…As previously shown [5,6], NP formed the typical inclusion bodies in the cytoplasm when expressed alone ( Figure 5), and thus was used as a marker for these structures, while overexpression of NXF1 alone showed a localization in the nucleus and in the perinuclear region. This is in line with previous publications, which have described both a nuclear localization, and particularly a nuclear rim staining mediated by the NTF2 and UBA domains of NXF1 [27], as well as a cytoplasmic localization of NXF1, e.g., inside stress granules [47]. Co-expression of NP and wildtype NXF1 led to no dramatic changes in the intracellular distribution of NXF1, although small amounts of NXF1 could be detected in the NP-derived inclusion bodies.…”

The Sub-Nuclear Localization of RNA-Binding Proteins in KSHV-Infected Cells

“…The polyA(+) RNA signal in these foci did not originate from the nuclear speckle lncRNA MALAT1 or from the paraspeckle lncRNA Neat1, as they were dispersed throughout the nucleoplasm of the infected cells. MALAT1 has been previously shown to disperse in the nucleoplasm in response to different stresses [ 83 , 84 ], and nuclear speckles continued to form even when MALAT1 was lacking from the nuclear bodies [ 85 ], as observed here as well. The viral orf29 and orf57 spliced mRNAs dispersed throughout the cell and occasionally could be seen in the peripheral layer of nuclear speckles and seldom even more internally.…”

Dance with the Devil: Stress Granules and Signaling in Antiviral Responses

“…Proteome analyses of purified SGs induced by oxidative stress confirmed the presence of multiple DEAD/H-box proteins inside SGs, including DDX1, DDX2 (eIF4A), DDX3, DDX6 (Rck), DDX19 (Dbp5), DDX21, DDX47, and DDX50 as well as DHX30 and DHX36 [70]. Localization in SGs could also be confirmed by immunofluorescence microscopy for DDX1, DDX2, DDX3, DDX6, DDX19, and DHX36 [201,[268][269][270][271][272][273][274][275][276][277]. Currently, it is not well understood if the immune regulatory functions of these proteins are affected by their localization in SGs, and localization in SGs during viral infections has so far only been addressed for DDX3, DDX6, and DHX36 [201,271,274,366].…”