Characterization of the Expression of Angiogenic Factors in Cutaneous Squamous Cell Carcinoma of Domestic Cats

SIMPLE SUMMARY: Squamous cell carcinoma (SCC) is a malignant skin cancer that affects domestic animal species and humans with similar characteristics. Our research seeks to understand the mechanisms by which SCC progression depends on the development of a new blood supply (angiogenesis) in the host. Here, we queried our archive of cat SCC tumor samples to measure expression of genes coding for angiogenic signaling proteins that can exist in closely related forms with distinct biological properties. We observed that, when compared to normal skin, SCC tissues contained a greater abundance of gene transcripts encoding a form of the growth factor PLGF, predicted to have an altered distribution in the body. Similarly, altered patterns of expression were observed for forms of the PLGF receptor Flt-1, which can modulate angiogenesis. Future studies will test the relationship between these gene expression changes and the severity of SCC in order to establish them as predictive biomarkers of SCC progression in individual patients. ABSTRACT: Cutaneous squamous cell carcinoma (CSCC) is a common malignant skin cancer with a significant impact on health, and it is important to determine the degree of reliance of CSCC on angiogenesis for growth and metastasis. Major regulators of angiogenesis are the vascular endothelial growth factor (VEGF) family and their associated receptors. Alternative pre-mRNA splicing produces multiple isoforms of VEGF-A and PLGF with distinct biological properties. Several studies highlight the function of VEGF-A in CSCC, but there are no studies of the different isoforms of VEGF-A and PLGF for this neoplasm. We characterized the expression of three isoforms of VEGF-A, two isoforms of PLGF, and their receptors in cat CSCC biopsies compared to normal haired skin (NHS). Although our results revealed no significant changes in transcript levels of panVEGF-A or their isoforms, the mRNA levels of PLGF I and the receptors Flt-1 and KDR were downregulated in CSCC compared to NHS. Differences were observed in ligand:receptor mRNA expression ratio, with the expression of VEGF-A relative to its receptor KDR higher in CSCC, which is consistent with our hypothesis and prior human SCC studies. Immunolocalization in tissue showed increased expression of all measured factors and receptors in tumor cells compared to NHS and surrounding vasculature. We conclude that the factors measured may play a pivotal role in CSCC growth, although further studies are needed to clarify the role of angiogenic factors in feline CSCC.