Abstract Recent evidence indicates that a high-fat diet (HFD) can promote tumor development, especially colorectal cancer (CRC), by influencing the microbiota. Regulatory circular RNAs (circRNAs) play an important role in modulating host–microbe interactions; however, the specific mechanisms by which circRNAs influence cancer progression by regulating these interactions remain unclear. Here, we report that consumption of a HFD modulates the microbiota by specifically upregulating the expression of the noncoding RNA hsa_circ_0126925 (herein referred to as circ_0126925) in CRC. Acting as a scaffold, circ_0126925 hinders the recruitment of the E3 ubiquitin ligase tripartite motif-containing protein 21 (TRIM21) to branched-chain amino acid transaminase 2 (BCAT2), leading to reduced degradation of BCAT2. This reduction in targeted degradation of BCAT2 can protect tumours from limited branched-chain amino acids (BCAAs) interference by improving the metabolism of BCAAs in CRC. Taken together, these data demonstrate that circ_0126925 plays a critical role in promoting the progression of CRC by maintaining BCAA metabolism and provide insight into the functions and crosstalk of circ_0126925 in host–microbe interactions in CRC. Implications: This study preliminarily confirms that circRNAs do indeed respond to microbiota/microbial metabolites, providing further evidence for the potential development of circRNAs as diagnostic tools and/or therapeutic agents to alleviate microbiome related pathology in humans.

Gut microbiota-mediated hsa_circ_0126925 targets BCAA metabolic enzyme BCAT2 to exacerbate colorectal cancer progression