Evidence of epithelial–mesenchymal transition in canine prostate cancer metastasis

Highlights

• Normal prostatic tissue was negative for the mesenchymal marker.

• Pre-neoplastic lesions had vimentin-positive cells without loss of epithelial markers.

• EMT occurs in canine prostatic neoplasia, similar to the process in humans.

Abstract

The epithelial–mesenchymal transition (EMT) is a fundamental event responsible for the invasiveness and metastasis of epithelial tumours. The EMT has been described in many human cancers, but there are few reports of this phenomenon in veterinary oncology. Due to the importance of this process, the current study evaluated mesenchymal and epithelial marker protein expression in prostate lesions from dogs. Our results indicate both a loss of E-cadherin and translocation of β-catenin from the membrane to the cytoplasm and nucleus in the tumour group. Vimentin expression in the tumour group was higher than in normal tissue. All of the metastases were positive for prostate-specific antigen, pan-cytokeratin and E-cadherin, although fewer positive cells were present than in the primary tumours. The immunohistochemical results showed a loss of epithelial markers and a gain of a mesenchymal marker among metastatic cells, suggesting that the EMT occurs during the metastatic process of canine prostate carcinoma.

Introduction

The leading cause of death related to cancer in the Western world is metastasis, which represents a final stage of the disease and is associated with a poor prognosis (Pani et al., 2010). Death of patients with metastasis occurs due to failure of the affected tissues, concomitant paraneoplastic syndromes and metabolic changes (Steeg, 2006). Metastasis is a very complex process. Information about metastasis in humans has increased over the years (Pani et al., 2010) but is still limited in veterinary medicine.

Other than humans, dogs are the only species that naturally develops prostatic carcinoma (PCa) with high frequency (Fonseca-Alves et al, 2013a, Palmieri et al, 2014). In dogs, PCa is highly metastatic, and the disease is usually at an advanced stage at diagnosis (Argyle, 2009, Fonseca-Alves et al, 2013b). Many studies from the human cancer literature have described a correlation between the epithelial–mesenchymal transition (EMT) and human PCa (Brabletz, 2012, Frederick et al, 2007, Mani et al, 2008, Thiery et al, 2009). The EMT is an important process in the biology of metastasis. During the EMT, epithelial cells lose their polarity and cell–cell adhesion function and gain invasive and migratory properties (Mani et al., 2008). In this process, the cellular–extracellular matrix interactions and the cellular cytoskeleton are modified to confer migratory and invasive abilities (Radisky, 2005). The EMT and its converse process, the mesenchymal–epithelial transition (MET), are crucial to the carcinogenic process (Frederick et al., 2007).

The E-cadherin/β-catenin complex plays an important role in cell-to-cell adhesion. These molecules are associated with the canonical WNT signalling pathway in human prostate cancer (Schmalhofer et al., 2009). E-cadherin and β-catenin are associated with the epithelial tissue phenotype and are responsible for regulating cell migration and differentiation (Comijn et al., 2001). In the carcinogenic process in epithelial tissues, the absence of these molecules is associated with the invasion of adjacent tissues and metastasis implantation (Schmalhofer et al., 2009).

Loss of E-cadherin protein expression is associated with high-grade prostate cancer in humans, and these tumours demonstrate a metastatic phenotype (Graff et al., 1995). The localisation of β-catenin plays an important role in cell proliferation. When β-catenin is localised in the membrane, it is responsible for cell-to-cell adhesion and has an important role in the cytoskeleton (Schmalhofer et al., 2009). In the metastatic process of human PCa, cancer cells lose E-cadherin and develop β-catenin nuclear staining (Graff et al., 1995). The translocation of membranous β-catenin to the nucleus activates the WNT pathway and promotes cell proliferation.

In veterinary medicine, there are few studies on the EMT in PCa. Changes in E-cadherin (Fonseca-Alves et al, 2013a, Rodrigues et al, 2013), β-catenin (Lean et al, 2014, Rodrigues et al, 2013) and vimentin (Grieco et al, 2003, Lean et al, 2014, Rodrigues et al, 2011) expression were previously described in canine PCa, but these markers have not been evaluated in metastatic prostate carcinomas.

Due to the importance of metastasis to the treatment protocol and survival time of patients, this research aimed to verify evidence of the EMT in canine pre-neoplastic prostate lesions and in prostate carcinomas and their metastases.