Subcellular Redistribution of Endomembrane GPR15 Promotes NAD+-Mediated Metabolic Reprogramming and Boosts 5-FU Chemosensitivity in Colorectal Cancer

G protein-coupled receptors (GPCRs) are increasingly recognized for their organelle-specific functions in cancer. A better understanding of the mechanisms governing their dynamic subcellular distribution and functional coordination is essential for developing spatially targeted therapies that exploit the subcellular signaling networks of GPCRs. Here, we found that Golgi-localized GPR15 underwent spatiotemporal trafficking to enhance 5-fluorouracil (5-FU) chemosensitivity in colorectal cancer. Dependent on Gαq, GPR15 associated with and restrained PARP4 enzymatic activity in the Golgi apparatus to drive cytosolic NAD⁺ accumulation. MGST1 interacted with and navigated GPR15 redistribution to mitochondria to increase mitochondrial NAD+ abundance, which fueled central carbon metabolism and activated downstream metabolic networks to prime tumors for 5-FU cytotoxicity. Treatment with the PARP inhibitor rucaparib showed potent synergy with 5-FU and demonstrated robust tumor suppression in patient-derived organoids and xenograft models through NAD⁺-mediated metabolic perturbation. This work establishes spatially encoded GPCR signaling as a druggable axis to potentiate chemotherapy efficacy, redefining intracellular receptor trafficking as an important regulator of metabolic plasticity in cancer therapy.