α-Smooth muscle actin expression in cancerassociated fibroblasts in canine epithelial tumors

Abstract

Tumor tissues contain not only cancer cells but also other cell types including, fibroblasts, immune cells, and endothelial cells, which interact with cancer cells. In human medicine, cancer-associated fibroblasts (CAFs) have been reported to promote tumor growth. CAFs are known to express α-smooth muscle actin (α-SMA), and this expression is correlated with poor prognosis in humans with cancer. However, the role of CAFs in canines and α-SMA expression in canine CAFs remains unknown. This study evaluated whether CAFs are present within the stroma of various types of canine epithelial tumors, for example, mammary gland tumors, squamous cell carcinoma, and anal sac adenocarcinoma, and assessed α-SMA expression in CAFs isolated from canine epithelial tumors. α-SMA analysis of tumor tissues revealed a cytoplasmic localization with variable levels of expression. α-SMA was detected in 60.9% (14/23) of epithelial tumor tissues and in 80% (8/10) of anal sac adenocarcinoma tissues. CAFs and normal fibroblasts (NFs) were isolated from tumor and skin tissues. The size of CAFs was variable, and most CAFs had large cell volume, in contrast to NFs. Most CAFs expressed α-SMA stress fibers and had higher α-SMA protein levels than NFs. Taken together, our findings provide evidence that canine CAFs express α-SMA in various canine epithelial tumors. Further studies are required to investigate the correlation between canine CAFs and clinical parameters and to elucidate the mechanisms underlying the effects of CAFs on cancer progression