16S V3-V4 reads from mouse fecal samples Raw sequence reads

Accumulating evidence points to an important role for the gut microbiome in anti-tumor immunity. However, how interactions between the host and the microbiota influence the ability of the immune system to restrain tumor growth is poorly understood. Here, we show that altered intestinal microbiota flora and enhanced Toll-like receptors (TLRs), dendritic cells (DCs) and T-cell dependent anti-tumor immunity, limit tumor expansion. These changes seen in mice lacking the RING finger protein 5 (RNF5) ubiquitin ligase, which exhibit attenuated activation of the unfolded protein response (UPR) components, including spliced X-box-binding protein-1 (sXBP1) and activating transcription factor 4 (ATF4). Reduced expression of UPR in intestinal epithelial cells coincided with increased expression of inflammasome components, recruitment and activation of DC and reduced expression of antimicrobial peptides. Reduced UPR expression was also seen in murine and human melanoma specimens that responded to immune checkpoint therapy. Co-housing of Rnf5–/– and WT mice largely abolishes the anti-tumor immunity and tumor inhibition phenotype, whereas transfer of 11 bacterial strains, including B. rodentium, that were enriched in Rnf5-/- mice establishes anti-tumor immunity and restricted melanoma growth in germ-free WT mice. Collectively, our data suggest that altered UPR signaling, exemplified in Rnf5-/- mice, causes changes in gut microbiota composition and anti-tumor immunity to control melanoma growth.