E3 PreliminaryPreliminaryPEM not requiredMechanisticPeer-reviewedMachine draft
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Membrane fusion and cell entry of XMRV are pH-independent and modulated by the envelope glycoprotein's cytoplasmic tail.
Côté, Marceline, Zheng, Yi-Min, Liu, Shan-Lu · PloS one · 2012 · DOI
Quick Summary
This study examined how XMRV, a virus once suspected to be linked to ME/CFS, enters human cells. Researchers found that XMRV enters cells differently than many other viruses—it doesn't require acidic conditions inside the cell. They also discovered that a small tail-like structure on the virus's outer coating controls whether the virus can fuse with and infect cells.
Why It Matters
Understanding XMRV's mechanisms of cell entry is important for clarifying the virus's relationship (or lack thereof) to ME/CFS, given the initial but later disputed association. These mechanistic insights may help explain why XMRV infection patterns differ from other retroviruses and could inform future investigations into potential viral cofactors in ME/CFS pathogenesis.
Observed Findings
XMRV entry was not blocked by lysosomotropic agents or cellular protease inhibitors, indicating pH-independent entry mechanisms.
Truncation of the C-terminal 21 or 33 amino acid residues of the XMRV Env cytoplasmic tail induced substantial membrane fusion in both permissive and non-permissive cells.
Truncated Env variants showed enhanced SU shedding into culture media, suggesting conformational changes in the ectodomain.
Further proximal truncation of the cytoplasmic tail severely impaired Env fusogenicity and viral incorporation into vector particles.
XMRV infection occurred in non-permissive CHO cells lacking functional XPR1 receptor when Env was truncated.
Inferred Conclusions
XMRV entry does not require low pH or pH-dependent host proteases, distinguishing it from many other enveloped viruses.
The cytoplasmic tail of XMRV Env is a critical negative regulator of membrane fusion and cell entry.
Cellular factors besides XPR1 are likely involved in XMRV entry, suggesting a more complex receptor-ligand interaction.
The Env cytoplasmic tail modulates viral fusogenicity through conformational changes in the surface glycoprotein ectodomain.
Remaining Questions
What are the specific cellular factors besides XPR1 that facilitate XMRV entry?
What This Study Does Not Prove
This study does not demonstrate that XMRV actually causes or contributes to ME/CFS in humans; it only describes how the virus enters cells in laboratory conditions. The finding that XMRV is a recombinant mouse retrovirus (mentioned in the abstract) questions its natural association with human disease. This in vitro mechanistic work cannot establish clinical relevance to ME/CFS patients.
About the PEM badge: “PEM required” means post-exertional malaise was an explicit required diagnostic criterion for participant inclusion in this study — not that PEM was studied, observed, or discussed. Studies using criteria that do not require PEM (e.g. Fukuda, Oxford) are tagged “PEM not required”. How the atlas works →