TGF-βs are potent inhibitors of epithelial cell proliferation. However, in established carcinomas, autocrine/paracrine TGF-β interactions can enhance tumor cell viability and progression. Thus, we studied the effect of a soluble Fc:TGF-β type II receptor fusion protein (Fc: TβRII) on transgenic and transplantable models of breast cancer metastases. Systemic administration of Fc: TβRII did not alter primary mammary tumor latency in MMTV-Polyomavirus middle T antigen transgenic mice. However, Fc: TβRII increased apoptosis in primary tumors, while reducing tumor cell motility, intravasation, and lung metastases. These effects correlated with inhibition of Akt activity and FKHRL1 phosphorylation. Fc: TβRII also inhibited metastases from transplanted 4T1 and EMT-6 mammary tumors in syngeneic BALB/c mice. Tumor microvessel density in a mouse dorsal skin window chamber was unaffected by Fc: TβRII. Therefore, blockade of TGF-β signaling may reduce tumor cell viability and migratory potential and represents a testable therapeutic approach against metastatic carcinomas.
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