Transforming growth factor-β and epithelial-mesenchymal transition are associated with pulmonary metastasis in adenoid cystic carcinoma.

OBJECTIVES: Adenoid cystic carcinoma (ACC) is one of the most common malignancies of salivary glands, characterized by poor prognosis, particularly due to pulmonary metastasis. We previously reported that transforming growth factor (TGF)-β1 promoted ACC cell migration and invasion via the Smad pathway in vitro. The aim of this study was to establish the underlying mechanisms.

MATERIALS AND METHODS: TGF-β1, phospho-Smad2 and β-catenin expression in ACC tissues derived from patients was evaluated by immunohistochemistry. The role of TGF- β1 on the invasive capacity of ACC cells was determined by transwell assays in SACC-83 cells transfected with TGF-β1 and TGF-β type II dominant-negative receptor (TβRIIDN) plasmids or silenced by TGF-β1 siRNA. Expression of the epithelial-mesenchymal transition (EMT) markers, β-catenin, E-cadherin and Nectin-1, was determined by real-time PCR and immunochemistry. In vivo investigations were performed by inoculating nude mice with the transfected ACC cells and examining metastasis in bilateral lung tissues by immunohistochemistry.

RESULTS: Overexpression of TGF-β1 and phospho-Smad2, and reduced expression of membrane β-catenin, were closely associated with lung metastasis in ACC. Furthermore, the EMT markers were downregulated. In vitro, cells transfected with TGF-β1 exhibited altered morphology and increased invasive capacity compared to TβRIIDN-transfected cells or TGF-β1 siRNA silenced cells. In vivo, mice inoculated with TGF-β1 transfected ACC cells exhibited more metastases than other cells.

CONCLUSION: TGF-β1, phospho-Smad2 and β-catenin were significantly correlated with ACC metastasis. Blockade of TGF-β signaling by TβRIIDN or siRNA may offer potential gene therapies against pulmonary metastasis in patients with ACC.