Enhanced BCAT1 activity and BCAA metabolism promotes RhoC activity in cancer progression

Increased expression of branched-chain amino acid transaminase 1 or 2 (BCAT1 and BCAT2) has been associated with aggressive phenotypes of different cancers. Here we identify a gain of function of BCAT1 glutamic acid to alanine mutation at codon 61 (BCAT1 E61A ) enriched around 2.8% in clinical gastric cancer samples. We found that BCAT1 E61A confers higher enzymatic activity to boost branched-chain amino acid (BCAA) catabolism, accelerate cell growth and motility and contribute to tumor development. BCAT1 directly interacts with RhoC, leading to elevation of RhoC activity. Notably, the BCAA-derived metabolite, branched-chain α-keto acid directly binds to the small GTPase protein RhoC and promotes its activity. BCAT1 knockout-suppressed cell motility could be rescued by expressing BCAT1 E61A or adding branched-chain α-keto acid. We also identified that candesartan acts as an inhibitor of BCAT1 E61A , thus repressing RhoC activity and cancer cell motility in vitro and preventing peritoneal metastasis in vivo. Our study reveals a link between BCAA metabolism and cell motility and proliferation through regulating RhoC activation, with potential therapeutic implications for cancers. In this study, Qian et al. identify a crosstalk between branched-chain amino acid metabolism and cell growth and motility through RhoC. Their work shows how enhanced BCAT1 activity, as identified by a mutation enriched in gastric cancer, leads to increased production of a metabolite that activates RhoC signaling.