Northwestern Medicine scientists have uncovered new details explaining how poxviruses manipulate host cells to enhance their own protein production, according to a study published in Cell Reports.
Poxviruses are a family of large, double-stranded DNA viruses, which include variola virus (smallpox), monkeypox virus, and others, that infect both humans and animals. These viruses are unusual in that they replicate entirely in the cytoplasm of host cells and form large DNA-filled replication compartments. To evade antiviral response pathways in its host, the virus encodes nearly 100 immunomodulatory proteins as it spreads.
While previous research from the laboratory of Derek Walsh, PhD, professor of Microbiology-Immunology, showed how poxviruses encode proteins to combat host immune responses, less is currently known about how the viruses hijack host ribosomes to create viral proteins.
“Ribosomes are very large macromolecular machines that very rapidly and precisely decode mRNA into protein. For a long time, they’ve been viewed as kind of ‘dumb code-reading machines’ that don’t have any particular role in controlling translational specification,” said Walsh, who was senior author of the current study. “However, it is becoming clear that ribosomes can change in terms of structure and function, either through changes in their subunit composition or post-translational modifications to ribosomal subunit proteins, or a combination of both.”
In the study, investigators utilized quantitative proteomics and cryoelectron microscopy to track ribosomal subunit proteins (RPs) during poxvirus infection. They found that poxviruses do not alter the composition of ribosomal subunit proteins (RPs). However, the infection did modify the underlying molecular structure of the ribosome, leading to increased poxvirus protein translation.
Genetic knockout screens coupled with metabolic assays identified two key RPs—RACK1 and RPLP2—as regulators of late poxvirus mRNA translation.
“We showed that the RP composition does not change but the structural organization of the 40S head domain does, driven by phosphorylation of proteins such as RACK1,” Walsh said. “In addition, CRISPR knockout screens showed that beyond RACK1, another ribosomal protein, RPLP2, is also important. RPLP2 is a component of an unusual extension to the ribosome called the P-stalk, and this discovery adds to our understanding of its role in translation.”
Together, the findings shed new light on the intricate mechanisms by which poxviruses manipulate host cells to enhance their own protein production.
Moving forward, the Walsh lab will continue to study exactly how RPLP2 functions to better understand how poxviruses tailor ribosomes to their own needs.
Natalia Khalatyan and Daphne Cornish, both PhD students in the Driskill Graduate Program in Life Sciences, were co-authors of the study.
“It is incredibly fascinating that even the smallest changes make such a big impact. Especially with something like the ribosome that is often overlooked,” Khalatyan said. “Viruses are smart, so we have a lot yet to learn from them when it comes to our own biology.”
This study was supported by funding from the National Institutes of Health under grants R01AI165236, R21AI174864, S10OD032464-01A1, R35GM133772 and R01AI127456.
