Viral infections have been estimated to contribute to 15–20% of cancers in humans and animals.1,2 Gammaherpesviruses are the causative agents of several cancers. A current limitation to studying gammaherpesvirus-dependent tumorigenesis is the lack of appropriate laboratory animal models.
California sea lions (CSL, Zalophus californianus) have been found to have an extremely high incidence of urogenital carcinoma, strongly associated with a gammaherpesvirus, Otarine herpesvirus 1 (OtHV1).3,4 Formation of a primary tumor occurs in the cervix or penis, followed by aggressive metastasis. The objective of this project was to clarify the role OtHV1 plays in this cancer by sequencing the OtHV1 genome and determining the presence of any known herpesvirus oncogenes.
Cervical tumor tissue from a stranded adult CSL collected during necropsy was histologically confirmed to be urogenital carcinoma, and qPCR indicated high OtHV1 viral load (> 150,000 copies/ng DNA). To obtain the full genome sequence of OtHV1, MiSEQ (2 x 300 nt paired-end protocol) and PacBio SMRT sequencing (2 SMRT cells with N50 read length of 14,646 bp) were utilized. Annotation was performed using CLC Genomic Workbench 7, Artemis and the pfam database of known oncogenic gammaherpesviruses.
Two potential oncogenes in OtHV1 were identified: viral B-cell lymphoma 2 gene (vBCL2) and viral Fas-associated death-like interleukin-1 beta-converting enzyme-inhibitory protein (vFLIP). Both genes are of host origin, and are found in other gammaherpesviruses known to induce cancer in humans and animals, by preventing apoptosis during cell division.
These findings strengthen the suspected role OtHV1 plays in CSL urogenital carcinoma. The high incidence of urogenital carcinoma in California sea lions provides a unique opportunity to study naturally occurring, virally induced cancer in non-laboratory animals; giving insight into viral carcinogenesis in an immune competent host. Future work to better understand differential gene expression as a result of these potential oncogenes is currently underway.
The authors wish to thank The Marine Mammal Center (TMMC) veterinarians, veterinary technicians, research scientists, and volunteers for their ongoing support of this project and for providing funding through the Geoffrey C. Hughes Veterinary Research Fellowship. We also thank the support of The American Association of Zoo Veterinarians in the form of the Zoological Medicine and Wildlife Health Research Grant.
* Presenting author
+ Student presenter
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