Fusobacterium nucleatumMetabolites Activate Aryl Hydrocarbon Receptor and Promote Colorectal Cancer Cell Proliferation

Abstract ID 90348 Poster Board 033 The gut microbiota has emerged as a key contributor to host health and disease. A vast cell number and large genome size grant bacteria the ability to produce a myriad of metabolites that can impact host physiology beneficially or pathologically. However, the biological activities of gut microbial metabolites and how the host responds to these metabolites remain largely unknown. Aryl hydrocarbon receptor (AhR) is a ligand-activated transcriptional factor binding structurally diverse chemicals, and its dysregulation is associated with various diseases, including cancer proliferation and metastasis. We hypothesized that AhR senses previously unknown gut bacterial metabolites. To test this hypothesis, we screened gut bacterial species representing six major phyla of the human gut microbiota for AhR activation using luciferase assay in HepG2 cells. Culture supernatants of individual gut bacteria were extracted with ethyl acetate, dried, reconstituted in DMSO, and tested for AhR activation. Fusobacterium nucleatum (Fn) exhibited the highest activation (∼120 fold). We identified the following previously unknown AhR activators in Fn culture extracts: fusotrisindoline (FTIN), trisindoline (TIN), and streptindole (STIN). Using a cell-based ligand competition assay, we demonstrated that these Fn metabolites directly bind to AhR, with FTIN being the most potent AhR activator. Given that Fn is reported to be enriched in colorectal cancer (CRC) tissues and that AhR dysregulation can aggravate cancer progression, we investigated whether Fn-produced AhR-activating metabolites play a role in CRC progression. FTIN promoted the human CRC H508 cell proliferation, which was abrogated by siRNA-mediated AhR knockdown. Moreover, wild-type Fn promoted the proliferation of CRC cells (H508 and SNU-C4), which was abrogated in Fn mutant that does not produce AhR-activating metabolites. Finally, we found that FTIN is more abundant in patient-derived CRC tissues (0.30 ± 0.22 nmol/g) than the matching normal colon tissues (0.09 ± 0.10 nmol/g). Altogether, we have identified AhR-activating metabolites previously unknown to be produced by Fn and revealed their critical contribution to Fn-mediated promotion of CRC cell proliferation via AhR activation. This work is funded by NIH R21 AT011391.