Fibrillin-1, a novel TGF-beta-induced factor, is preferentially expressed in metaplastic carcinoma with spindle sarcomatous metaplasia.

TGF-β induces epithelial-mesenchymal transition (EMT), which is involved in tumour progression. This study aims to identify and characterise novel factors potentially related to TGF-β-mediated tumour aggression in breast cancer. We treated the human mammary epithelial cell line MCF10A with TGF-β and observed TGF-β-dependent upregulation of FBN1, involving demethylation of CpG sites, in MCF10A cells undergoing EMT. The biological importance of fibrillin-1, encoded by FBN1, was evaluated through immunohistochemistry on 225 breast cancer specimens of various subtypes. Fibrillin-1 expression was observed only in metaplastic carcinoma of the breast (MCB) (51.7%), and the expression was observed in spindle sarcomatous metaplasia (SSM), but not in other metaplasia, including matrix-producing, pleomorphic, and squamous metaplasia, and carcinomatous components of both MCB and non-MCB. Fibrillin-1 expression was also restricted to the SSM of non-mammary carcinosarcomas of various organs. Overall, fibrillin-1 expression was enriched in MCB and non-mammary carcinosarcoma with SSM (93.7% and 93.3%, respectively), but not in MCBs and non-mammary carcinosarcoma without SSM. FBN1 knockdown in MDA-MB-231 cells with high FBN1 expression did not compromise migration, invasion, and tumourigenesis, and did not alter the expression of other EMT-related markers. In conclusion, fibrillin-1 is a novel TGF-β-induced marker. Fibrillin-1 expression in SSM, but not in other metaplasia and carcinomatous components, in both MCBs and non-mammary carcinosarcomas, together with the inability of FBN1-knockdown to compromise migration and invasion, indicates that fibrillin-1 is a marker induced solely in spindle metaplasia during EMT and does not induce EMT nor lead to tumour aggressiveness.