Epithelial-to-mesenchymal transition activates Bcat1 expression to promote recurrent tumor growth

Branched-chain amino acid metabolism has emerged as a crucial regulator of tumor proliferation. In particular, the branched-chain amino acid transaminase 1 (BCAT1), which catalyzes the conversion of branched-chain amino acids to -keto acids in the cytoplasm, has been identified as a promising therapeutic target for several different cancer types, including gliomas and leukemias. BCAT1 expression has also been associated with resistance to anti-estrogen therapy in breast cancer, suggesting a role in therapeutic resistance and tumor progression. Yet a functional role for BCAT1 in promoting breast cancer recurrence has not been described. Further, BCAT1 expression is restricted to just a few specialized tissues, such as the testes and central nervous system, and the mechanism by which it becomes transcriptionally activated in tumors that arise from tissues that do not typically express BCAT1 is unclear. Here, we report that Bcat1 is upregulated in recurrent breast tumors to promote recurrent tumor growth. We find that Bcat1 is upregulated by the epithelial-to-mesenchymal transition (EMT) in mammary epithelial cells and breast cancer cells. Finally, we analyze human tumor datasets to show that BCAT1 expression is strongly correlated with epithelial-to-mesenchymal gene signatures, suggesting that EMT is the predominant regulator of BCAT1 expression in cancer. Because EMT is associated with therapy resistance, metastasis, and tumor recurrence, these findings suggest a broad clinical potential for BCAT1 inhibition.