Mammary cancers have become more common in both humans and animals in recent years, and they are now regarded as one of the leading causes of death (Ferlay et al., 2015, Johnston et al., 2001). As a result, there is a lot of research on biomarkers that can be used for early detection or treatment of breast cancer. For the detection of these biomarkers, new techniques for measuring both tissue and plasma levels are rapidly developing (Baker et al., 2000, Diamandis and Yousef, 2002, Nerurkar et al., 1989). The goal of this study is to evaluate any potential candidate of Na+/K+-ATPase and BMP-2, as well as to determine the expression of these markers in both parenchymal and stromal cells in benign and malignant canine mammary tumors.
Na+/K+-ATPase is a major plasma membrane ion transporter with three different types of subunits (Geering, 1990). Due to the numerous physiological functions of Na+/K+-ATPase in various biological systems, it is unsurprising that dysfunction or altered expression of Na+/K+-ATPase could be linked to the pathogenesis of many diseases. As a result, there have been some reports of altered expression and activity of Na+/K+-ATPase in various human cancers. In many tumors, intracellular Na+ increased, while K+ decreased. In malignant cells, there may be some changes in intracellular homeostasis for Na+ and K+. These alterations could be caused by changes in Na+/K+-ATPase pump activity (Blok et al., 1999, Rajasekaran et al., 1999, Espineda et al., 2003). Furthermore, canine mammary tumors and Na+/K+-ATPase activity are poorly understood (Freeman et al., 2010). They discovered that neither normal nor neoplastic stromal cells express Na+/K+-ATPase. This study showed an increase in Na+/K+-ATPase in parenchymal cells of canine mammary tumors, which was closely related to malignancy. In contrast to Freeman et al., there was an increased expression in stromal cells.
Growth factors play critical roles in tumor progression. BMPs are members of the transforming growth factor-β (TGF-β) superfamily, which regulates apoptosis and motility, cellular differentiation, and proliferation and is particularly important in tissue homeostasis and embryonic development (Davis et al., 2016, Nohe et al., 2004, Ye et al., 2009). Huang et al. reported that BMP-2 promotes EMT and invasion of the breast cancer cells in women (Huang et al., 2017). However, there are very few reports for BMP-2 and canine mammary tumors (Wensman et al., 2009, Klopfleisch et al., 2010). Both previous studies only examined parenchymal cells of the tumors, no information of stromal cells was found. This study showed that BMP-2 is closely related to malignancy of the canine mammary tumors. In this study, intense marked expression was also observed in the parenchymal and stromal cells of mammary tumors, with expression being much stronger in malignant cases.
Recently in tumor studies, the importance of the tumor microenvironment has been highlighted. It is made up of a heterogeneous mixture of endogenous host stroma and tumor cells, and it serves an important function during the disease progression period (Bussard et al., 2016). In general, authors examined only parenchymal expressions of the markers in immunohistochemical studies of tumoral tissues. However, stroma plays an important role in tumoral progression, and stromal cells secrete a variety of pro-tumorigenic factors. This study showed that stromal cells in canine mammary tumors also expressed Na+/K+-ATPase and BMP-2. The expressions were similar to those found in parenchymal and stromal cells and were strongly linked to cancer.
Generally, either experimental animal models or cell cultures have been used for studies on human breast tumors. Human and canine breast tumors have been found to have a close relationship. Therefore, researchers have begun to evaluate human breast tumors using canine breast tumors. Numerous studies have shown that a variety of factors can be adapted to human and canine tumors (Sultan and Ganaie, 2018). Human and canine tumors are closely related in terms of spontaneous tumor development, homologous genome sequencing, genetic differences, coexistence, and many other factors. In addition, numerous studies have revealed many similarities, such as the presence of inflammatory reactions with the tumor microenvironment and the use of similar markers in evaluations (Carvalho et al., 2016, Queiroga et al., 2011). Recently, the comparisons between human and canine mammary tumors have been increasing rapidly (Nerurkar et al., 1989, Cassali, 2013, Sorenmo
et al., 2009). Therefore, studies on canine breast tumors are also interpreted in human tumors. The results of this study also showed that Na+/K+-ATPase and BMP-2 expressions may play a role in human breast tumor malignancy.
In this study, we used ten malignant and ten benign mammary tumors, as well as five normal breast tissues from our department archives. To begin, tumoral masses were reassessed for potential misdiagnoses. Following that, sections of all tumors were immunohistochemically stained and tested for Na+/K+-ATPase and BMP-2 expressions. In addition, the sections were investigated to determine whether there is a relationship between malignancy and the release of Na+/K+-ATPase and BMP-2 from parenchymal and stromal cells. Despite the small number of tumors used in our study, it was one of the most important studies on the increased expressions of markers from tumoral stromal cells as well as parenchymal cells.
According to the findings of this study, the expression of Na+/K+-ATPase and BMP-2 in canine mammary tumors differed significantly between benign and malignant tumors and increased significantly with malignancy. These results were consistent with previous studies (Freeman et al., 2010, Kaszak et al., 2018). Although these markers were strongly expressed by tumoral parenchymal cells, they were also expressed by stromal cells. Since the study was an archive study, it was not possible to determine whether there was a relationship between Na+/K+-ATPase and BMP-2 expressions and survival time. However, increased expiration of Na+/K+-ATPase and BMP-2 in malignant tumors has been linked to a lower survival rate in dogs. More in-depth studies are expected to shed light on the subject. In addition, in new studies, plasma levels of these Na+/K+-ATPase and BMP-2 expressions should be examined and correlated with tissue levels.