de Bossoreille, S. | bioRxiv Science

bioRxiv2023

HTLV-1 Rex hijacks UPF1 in a CRM1 dependent manner, leading to NMD inhibition and revealing unexpected proviral roles of UPF1

The hijacking of CRM1 export is an important step of the retroviral replication cycle. Here, we investigated the consequences of this hijacking for the host. During HTLV-1 infection, we identified that this hijacking by the viral protein Rex favours the association between CRM1 and the RNA helicase UPF1, leading to a decreased affinity of UPF1 for cellular RNA and its nuclear retention. As a consequence, we found that the nonsense mediated mRNA decay (NMD), known to have an antiviral function, was inhibited. Corroborating these results, we described a similar process with Rev, the functional homolog of Rex from HIV-1. Unexpectedly, we also found that, for HTLV-1, this process is coupled with the specific loading of UPF1 onto vRNA, independently of NMD. In this latter context, UPF1 positively regulates several steps of the viral replication cycle, from the nuclear export of vRNA to the production of mature viral particles. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=112 SRC="FIGDIR/small/545693v2_ufig1.gif" ALT="Figure 1"> View larger version (26K): org.highwire.dtl.DTLVardef@1e91e61org.highwire.dtl.DTLVardef@1c9951borg.highwire.dtl.DTLVardef@15c6021org.highwire.dtl.DTLVardef@1ab35ff_HPS_FORMAT_FIGEXP M_FIG O_FLOATNOGraphical abstractC_FLOATNO During retroviral replication, the nuclear export unspliced vRNA is conducted via the hijacking of the exportin CRM1 by the viral protein Rex. In parallel, the RNA helicase UPF1 is naturally exported in a CRM1 dependent manner. In the cytoplasm it drives NMD, whose substrates include vRNA. Here we demonstrated that HTLV-1 Rex dependent hijacking of CRM1 is associated with the nuclear accumulation of UPF1 and the stabilization of the interaction between CRM1 and UPF1 (1). In this complex, UPF1 shows a decreased affinity for cellular RNA associated to NMD inhibition (2). We also observed that UPF1 is selectively loaded onto vRNA and stimulates vRNA export (3). In this context, UPF1 is driven in the viral particles (without NMD cofactors) where it plays critical role in virion assembly, maturation (4) and ultimately viral infection (5). Created in BioRender. PROCHASSON, L. (2025) https://BioRender.com/urj0cvo". C_FIG

molecular biology↗

bioRxiv2018

Differential requirement of MED14 and UVH6 for heterochromatin transcription upon destabilization of silencing

Constitutive heterochromatin is commonly associated with high levels of repressive epigenetic marks and is stably maintained transcriptionally silent by the concerted action of different, yet convergent, silencing pathways. Reactivation of heterochromatin transcription is generally associated with alterations in levels of these epigenetic marks. However, in mutants for particular epigenetic regulators, or upon particular environmental changes such as heat stress, heterochromatin-associated silencing is destabilized without noticeable changes in epigenetic marks. This suggests that transcription can occur in a non-permissive chromatin context, yet the factors involved remain poorly known. Here, we show that heat stress-induced transcription of heterochromatin depends on the TFIIH component UVH6 and the Mediator subunit MED14. Mutants for these two factors exhibit hypersensitivity to heat stress, and under these conditions, UVH6 and MED14 are required for transcription of a high number of loci. We further show that MED14, but not UVH6, is required for transcription when heterochromatin silencing is destabilized in the absence of stress. In this case, MED14 requires proper chromatin patterns of repressive epigenetic marks for its function. We also uncover that MED14 regulates non-CG DNA methylation at a subset of RNA-directed DNA methylation target loci. These findings provide insight into the control of heterochromatin transcription upon silencing destabilization and identify MED14 as a regulator of DNA methylation.

plant biology↗