CRISPR Screen Uncovers Gene That Blocks Zika and Dengue Viruses
Scientists used CRISPR to find SPART, a human gene that restricts a whole family of dangerous flaviviruses including Zika and dengue.
Summary
Researchers used a genome-wide CRISPR activation screen to identify SPART (also called Spartin/SPG20) as a powerful restriction factor against Zika virus and related orthoflaviviruses like dengue, Japanese encephalitis, and West Nile virus. SPART works by interfering with a protein called ITCH, an E3-ubiquitin ligase that normally tags the Zika virus capsid with ubiquitin molecules, triggering the virus to uncoat and begin replicating. When SPART is present, it disrupts ITCH's ability to do this job, effectively blocking the virus. Mouse experiments showed that animals lacking SPART had higher viral loads and worse fetal outcomes during maternal Zika infection, while mice lacking ITCH were protected. This discovery identifies a potential broad-spectrum antiviral target across a medically important virus family.
Detailed Summary
Orthoflaviviruses — a family that includes Zika, dengue, Japanese encephalitis, and West Nile viruses — collectively infect hundreds of millions of people each year, causing conditions ranging from mild fever to devastating neurological disease and fetal abnormalities. Despite their global burden, antiviral options remain limited, making the search for host-based defense mechanisms a research priority.
To find new antiviral targets, researchers conducted a genome-wide CRISPR activation screen — a method that systematically switches on individual genes across the entire human genome to see which ones block viral infection. This unbiased approach identified SPART (Spartin/SPG20), a gene previously linked to a rare hereditary spastic paraplegia syndrome, as a pan-orthoflavivirus restriction factor capable of inhibiting Zika and related viruses.
Mechanistically, SPART blocks virus replication by interacting with and disrupting the endosomal activity of ITCH, an E3-ubiquitin ligase. ITCH normally ubiquitinates the Zika virus capsid protein, a step that triggers viral uncoating — the process by which the virus sheds its protein shell to release its genetic material and begin replication. By neutralizing ITCH's localization, SPART effectively jams this early replication step.
In vivo experiments confirmed these findings. Mice lacking SPART (Spg20-/-) showed elevated maternal and fetal viral loads during Zika infection and more severe fetal developmental abnormalities. Conversely, mice lacking ITCH were protected, with reduced viral burden. These opposing phenotypes held when the animals were challenged with other orthoflaviviruses, suggesting the pathway is broadly relevant.
The identification of SPART as a broad restriction factor opens a potential avenue for antiviral drug development targeting the SPART-ITCH-capsid axis. Caveats include reliance on mouse models and the abstract-only availability limiting full methodological scrutiny.
Key Findings
- SPART gene identified as a pan-orthoflavivirus restriction factor via genome-wide CRISPR activation screen.
- SPART blocks Zika replication by disrupting ITCH E3-ubiquitin ligase, preventing viral capsid uncoating.
- Mice lacking SPART had higher Zika viral loads and worse fetal outcomes; ITCH-knockout mice were protected.
- Findings extended to dengue, Japanese encephalitis, and West Nile viruses, suggesting broad applicability.
- SPART-ITCH axis represents a potential new target for broad-spectrum antiviral drug development.
Methodology
Researchers performed a genome-wide CRISPR activation screen to identify host genes that restrict Zika virus infection. Mechanistic studies used knockout and double-knockout cell lines and gene-edited mouse models (Spg20-/- and Itch-/-) with maternal Zika infection protocols. Related orthoflaviviruses were also tested in the same models.
Study Limitations
This summary is based on the abstract only, as the full text is not open access, limiting assessment of methodology and statistical rigor. Results were obtained in mouse models, and translation to human clinical outcomes requires further validation. SPART's previously known role in hereditary spastic paraplegia (SPG20) raises potential safety concerns for any therapeutic strategy targeting this gene.
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