Novel Staufen1 ribonucleoproteins prevent formation of stress granules but favour encapsidation of HIV-1 genomic RNA

Abstract

SummaryHuman 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.

T-body formation precedes virus-like particle maturation inS. cerevisiae

“…Interestingly, HIV-1 regulates viral assembly by local accumulation of viral components and the host factor Staufen 1 into SHRNPs outside of P-bodies and stress granules. 23 Thus, the assembly of immature Ty1 VLPs resembles the behavior of HIV-1, where Gag and HIV-1 RNA accumulation in the plasma membrane occurs prior to virion assembly. 24,25 The fact that T-bodies do not seem to be required for VLP maturation and cDNA synthesis "per se", along with the Gag self-assembly properties to form VLPs in an heterologous prokaryote host, raises the question of the functionality of T-bodies in S. cerevisiae.…”

Translation initiation of the HIV-1 mRNA

“…This is also consistent with earlier work showing that expression of HIV-1 prevents stress granule formation induced by arsenite treatment. 167 These data lead to a model in which these cytoplasmic spots would be the location for assembly of a minimal preinitiation complex on the HIV-1 genomic RNA. Such a complex is constituted by the assembly of DDX3/eIF4G/PABP at the 5 0 end of the HIV-1 genomic RNA where it locally unwinds the basis of TAR to create a single stranded RNA region accessible for ribosomal binding.…”

Depletion of hnRNP A2/B1 overrides the nuclear retention of the HIV-1 genomic RNA

“…S2). However, whereas puromycin led to the sequestration of the HIV-1 vRNA into translationally silent stress granules, 44 the vRNA was found to be refractory to EDTA treatment (ref. 45; and Valiente-Echeverria et al, submitted).…”

“…PABP has also been found in translationally silent RNA trafficking granules and intracellular stress granules. 38,44,46 The dense polyribosomal fraction 1 contains poorly translated mRNAs…”

“…The distribution of Staufen1 was unaffected by siA2/B1 treatment, however. While we now understand that there are differential roles for Staufen1 isoforms during HIV-1 replication, 44 isoform, implicates the lower molecular isoform in HIV-1 RNP biogenesis. Indeed, this would be consistent with the roles for this isoform in HIV-1 assembly as well as in vRNA packaging that we have defined earlier.…”