Investigating a genetic basis of urogenital cancer in California sea lions (Zalophus californianus)

The California sea lion (Z. californianus) has an unusually high occurrence of urogenital carcinoma, with one study revealing metastatic carcinoma in 18% of animals admitted to a rehabilitation centre over a 15 year period.² It is likely that the aetiology of this disease is multi-factorial as genetics, viral infection and exposure to contaminants have been associated with this cancer to date. This study concentrates on one area; the potential involvement of genetic factors. A previous investigation into a genetic link found cancer to be more likely in animals with specific microsatellite marker alleles¹ with the marker Pv11 appearing to be significantly associated with the development of the disease¹. This marker is found within an intron of a gene called HPSE2 which codes for the protein heparanase 2. HPSE2 shares approximately 40% sequence homology with the HPSE1 gene which is associated with cancer metastasis.⁴ Therefore a gene which demonstrates homology to it is of potential clinical interest. Recent work into cervical neoplasia in humans has identified an increase in expression of HPSE2 with increasing severity of neoplastic lesion.³ The objective of this study is to characterise the HPSE2 gene in Z. californianus using cervical tissue from animals of known Pv11 genotype. To do this RNA was extracted from six cervical tissue samples and converted to cDNA. PCR reactions were then carried out to target splice variants of HPSE2 expression followed by cloning of products. Sequencing of positive clones resulted in a high identity to the domestic dog (Canis lupus familiaris) heparanase 2 transcript variant 2 via Basic Local Alignment Search Tool (BLAST) confirming the presence of at least one HPSE2 isoform in Z. californianus. In order to investigate differences in expression of HPSE2 in animals suffering from neoplasia and control animals 15 cervical tissue samples were examined. These consisted of nine samples from cancer positive animals and six from control animals. Immunohistochemical assays were carried out on the samples using polyclonal HPSE2 antibody. All of the samples from the control animals stained negative and only three out of the nine cancer animals stained positive. However, all three positive samples were from animals of the same Pv11 genotype. This could suggest that Pv11 genotype is important with regards to HPSE2 expression in cervical cancer but further studies are necessary to confirm this.