In the early 1930s in northwestern Iowa, a group of hunters gathered around their catch, befuddled. Tales of a mythical jackrabbit with antelope horns—known as the jackalope—had circulated for centuries, dating back to reports as early as the 1600s. The cottontail rabbits they’d harvested had what appeared to be horns jutting from their heads and necks. Were these really the fabled creature?
Stories of the jackelope remain popular even today, especially around the Midwest where they were popularized, but the legend isn’t the only outcome of this strange phenomenon. In fact, there’s a connection to cancer.
Intrigued by the mystery behind the growths, cancer researcher Richard E. Shope investigated the rabbits and identified the cottontail rabbit papillomavirus (CRPV) as the cause. A few years later, Peyton Rous demonstrated that the virus could cause cancer.
This finding advanced human cancer research, too, and laid the foundation for studying human papillomavirus (HPV), a related virus with devastating effects, most commonly known to cause cervical cancers, of which there are about 11,500 new cases and from which about 4,000 women die annually in the U.S., according to the Centers for Disease Control and Prevention.
CRPV has long served as a stand-in for studying HPV. However, researchers at NCI Frederick and Pennsylvania State University Cancer Institute have only recently decoded its transcriptome—the complete map of its active RNA—revealing how CRPV’s RNA toggles genes on and off in host cells, allowing the virus to replicate and modulating the cells’ functions.
‘Looking Deeper’ Into CRPV, Thanks to Transcription Map
HPV only infects humans, which prevents HPV animal model generation, so scientists use similar animal viruses, like CRPV, to better understand HPV transmission, pathogenesis, immunity, and treatment. In rabbits, CRPV follows a disease course similar to HPV, making it a valuable model for understanding and treating HPV-related illness.
“[CRPV is] considered the ‘gold standard’ model for human papillomavirus,” said Jiafen Hu, Ph.D., an assistant professor and researcher at the Department of Pathology and Laboratory Medicine and the Penn State Cancer Institute and co-first author on the paper. It’s been used for decades to test antiviral and anti-tumor compounds as potential treatments.
“Most compounds didn’t work, but we never got a chance to really understand why,” Hu explained.
Without a mapped transcriptome, researchers lacked insight into how CRPV regulates gene expression and influences tumor development. Now, they and others can use the CRPV transcriptome map like a blueprint that shows them which genes are active at different stages of infection. By analyzing how gene activity changes over time, they can identify which genes might be driving cancer growth.
This helps researchers understand the virus’s behavior and test treatments more effectively. They can examine how different compounds interact with the virus at a molecular level, potentially uncovering why previous treatments failed and paving the way for better therapies.
Essentially, “[now] we can look a little bit deeper,” Hu said.
Years of Research and Collaboration to Detail One ‘Essential’ Map
To chart the transcriptome, the researchers performed complex analysis of CRPV RNA using various RNA sequencing techniques, including a relatively new technique known as single-molecule, real-time sequencing, which allowed them to track viral components live. Extensive analysis of the resulting data allowed them to examine the individual nucleotides—the sequential building blocks—of the viral RNA sequence, a highly detailed view.
“Putting everything together took quite a while [seven years], but … we wanted to make sure that there were no mistakes, that everything works together. Once you publish this kind of reference paper, it’s very hard to go back,” said Vladimir Majerciak, Ph.D., an associate scientist in NCI’s Center for Cancer Research (CCR)’s HIV Dynamics and Replication Program and first author on the paper.
They relied on the help and expertise of collaborators at Frederick National Laboratory’s Sequencing Facility and Bioinformatics Resources, which primarily serve NCI’s Center for Cancer Research. Majerciak speaks highly of these colleagues, explaining that without them, this type of study wouldn’t be possible.
“It’s absolutely essential in today’s world to have this data. We know how valuable this kind of annotation is for humans and other model organisms,” he said.
Mouse papillomavirus is one of those more commonly used models. Majerciak, along with others, previously mapped its transcriptome. Because of the wealth of existing CRPV research, the new transcriptome map strengthens CRPV as a model for understanding papillomaviruses relevant to human disease.
Hu previously detailed the advantages of modeling HPV-associated diseases and cancer in CRPV, along with CCR’s Zhi-Ming Zheng, Ph.D., the principal investigator on this study. Now that the transcriptome can be fully understood, the 90-plus-year body of research can offer additional insights.
Adding Value to the Field
Beyond its contributions to CRPV and HPV research, this study also provides a plot for mapping other viral transcriptomes that are often overlooked and neglected. Researchers looking to undertake similar work can follow the methodology outlined by the team.
“I think definitely more is coming, either from our group or someone else,” said Majerciak.
By offering a clearer way to investigate how the virus infects animals and drives cancer, the team hopes this work will advance the field and help researchers extrapolate insights into human disease.
“It’s a huge value-add to the field,” Majerciak said.
“I can’t say enough of the significance of this study because I have worked with this model for more than 20 years—and this is revolutionary,” Hu added.
For them, the potential implications for eventually developing human treatments are the clear motivator. Majerciak notes that most everyone personally knows someone impacted by cancer.
“And we don’t have many efficient treatments yet. Basically, that’s the whole reason [we continue this research],” he said.
The illustration depicts several rabbits, including one with horns protruding from its head, much like the descriptions of the mythical jackalope.
Karolina Wilk is a technical editor in Scientific Publications, Graphics & Media (SPGM), where she writes for NCI Frederick and Frederick National Laboratory’s news outlets and edits scientific manuscripts, corporate documentation, and other writing. SPGM is the facilities’ creative services department and hub for editing, illustration, graphic design, formatting, and multimedia training and support.