PDPN Is Expressed in Various Types of Canine Tumors and Its Silencing Induces Apoptosis and Cell Cycle Arrest in Canine Malignant Melanoma

Abstract

Podoplanin (PDPN), a small transmembrane mucin-like glycoprotein, is ectopically expressed. It is also known to be linked with several aspects of tumor malignancy in some types of human tumors, including invasion, metastasis, and cancer stemness. However, there are few reports on the expression of dog PDPN (dPDPN) in canine tumors, and the association between dPDPN and tumor malignancy has not been elucidated. We identified that 11 out of 18 types of canine tumors expressed dPDPN. Furthermore, 80% of canine malignant melanoma (MM), squamous cell carcinoma, and meningioma expressed dPDPN. Moreover, the expression density of dPDPN was positively associated with the expression of the Ki67 proliferation marker. The silencing of dPDPN by siRNAs resulted in the suppression of cell migration, invasion, stem cell-like characteristics, and cell viability in canine MM cell lines. The suppression of cell viability was caused by the induction of apoptosis and G2/M phase cell cycle arrest. Overall, this study demonstrates that dPDPN is expressed in various types of canine tumors and that dPDPN silencing suppresses cell viability through apoptosis and cell cycle arrest, thus providing a novel biological role for PDPN in tumor progression.

Phase I/II Clinical Trial of the Anti-Podoplanin Monoclonal Antibody Therapy in Dogs with Malignant Melanoma

“…In this study, the reactivity and ADCC of P38Bf were evaluated using canine malignant melanoma cell lines. This study targets canine malignant melanoma because it was reported that 80% of canine malignant melanomas express dPDPN on tumor cells [ 18 , 45 ]. P38Bf clearly recognized endogenously expressed dPDPN on canine malignant melanoma cell lines and showed significant and dose-dependent ADCC activity on CMM2 at antibody concentrations of 1 and 10 µg/mL.…”

“…In human medicine, PDPN has been reported to be overexpressed in various types of tumors, including squamous cell carcinoma [ 5 ], astrocytoma [ 6 ], malignant mesothelioma [ 7 ], hemangiosarcoma [ 8 ], osteosarcoma [ 9 ], germinoma [ 10 ], and cancer-associated fibroblasts (CAFs) [ 11 , 12 , 13 ]. Similar to humans, PDPN has been reported to be expressed in renal podocytes, alveolar epithelial cells, and lymphatic endothelial cells of dogs, and in various types of canine tumors, including malignant melanoma and squamous cell carcinoma [ 14 , 15 , 16 , 17 , 18 ]. Many reports have demonstrated that PDPN expressed on human and canine tumors is associated with tumor malignancy through the promotion of malignant proliferation and epithelial–mesenchymal transition (EMT), and that it promotes metastasis by enhancing tumor cell migration and platelet aggregation [ 1 , 2 , 18 , 19 , 20 , 21 ].…”

“…Similar to humans, PDPN has been reported to be expressed in renal podocytes, alveolar epithelial cells, and lymphatic endothelial cells of dogs, and in various types of canine tumors, including malignant melanoma and squamous cell carcinoma [ 14 , 15 , 16 , 17 , 18 ]. Many reports have demonstrated that PDPN expressed on human and canine tumors is associated with tumor malignancy through the promotion of malignant proliferation and epithelial–mesenchymal transition (EMT), and that it promotes metastasis by enhancing tumor cell migration and platelet aggregation [ 1 , 2 , 18 , 19 , 20 , 21 ]. These reports promoted the further evaluation of PDPN as a therapeutic target.…”

“…To perform clinical trials using spontaneously occurring canine tumor models, we developed a cancer-specific anti-canine PDPN (dPDPN) monoclonal antibody (mAb), PMab-38, which recognizes only dPDPN expression in canine tumor tissues without recognizing normal canine tissues [ 16 ]. Immunohistochemical evaluation demonstrated 90% of canine melanoma, 83% of canine squamous cell carcinoma, and 82% of canine pulmonary adenocarcinoma cells, and CAFs were positively stained with PMab-38, while normal canine tissues were hardly stained by PMab-38 [ 17 , 18 ]. Furthermore, a cancer-specific mouse–dog chimeric anti-PDPN antibody (P38Bf) originating from mouse monoclonal PMab-38 were shown to reduce immunological reactions, and P38Bf demonstrated strong anti-tumor effects in a PDPN-overexpressed CHO-K1 cell xenograft mouse model [ 36 , 37 ].…”

Immunoexpression of epithelial membrane antigen in canine meningioma: Novel results for perspective considerations

“…Meningiomas are frequently positive for CD34, E‐cadherin, doublecortin and progesterone receptor (PR) 7,11‐13 . More recently, a high rate of somatostatin receptor type 2 (SSTR2) 14 and podoplanin 15 immunohistochemical expression have been reported in canine meningioma. However, any exclusive diagnostic specificity of these markers has not yet been confirmed in the dog.…”