Inhibition of circulating glycocholic acid-regulated signaling potentiates immune checkpoint therapy in colorectal cancer.

Serum bile acids (BAs) emerge as risk factors for cancer, but their roles in colorectal cancer (CRC) remain unclear. We show that glycocholic acid (GCA), a primary BA, is elevated in the serum of CRC patients. In a mouse CRC model, GCA promotes tumor programmed death-ligand 1 (PD-L1) expression in tumors, suppressing CD8⁺ T cell-mediated antitumor immunity and facilitating tumor growth. Mechanistically, GCA inhibits the BA receptor farnesoid X receptor (FXR), a transcriptional repressor for SRY-box transcription factor 14 (SOX14). Loss of FXR repression upregulates SOX14-mediated expression of zinc finger DHHC-type palmitoyl transferase 9 (DHHC9), thereby reducing PD-L1 palmitoylation and stabilization. Silencing SOX14 or DHHC9, or activating FXR, synergizes with anti-PD-1 therapy, reducing tumor growth in GCA-treated mice. These findings uncover a mechanism that GCA remodels the tumor microenvironment to mediate CRC resistance to immunotherapy, highlighting therapeutic opportunities targeting the FXR-PD-L1 axis in CRC patients with elevated serum GCA.