首都医科大学

PNAS  2026  Vol. 123  No. 30 e2533427123 https://doi.org/10.1073/pnas.2533427123 1 of 12   RESEARCH ARTICLE | CELL BIOLOGY α- fluoro-β-alanine functions as a β-ar restin1-biased ligan d of S1PR2 to upregulate DPD expression in cancer cells Mingyong Tana, Hanbing Shaoa, Xinan Zhanga , Yuyao Chenga, Zhimeng Sunb, Ming Yangb, Siyuan Mub, Weishi Liangc,d, Bo Hanc,d, Xinfeng Wub, Xiaohui Liub, Yong Haic,d, Shuxiang Cuia,c,1 , and Xianjun Qub,c,1 Edited by John J. G. Tesmer, Purdue University, West Lafayette, IN; received December 16, 2025; accepted June 18, 2026 by Editorial Board Member Melanie H. Cobb Author affiliations: aToxicology and Sanitary Chemistry, School of Public Health, Capital Medical University, Beijing 100069, China; bPharmacology, School of Basic Medical Sciences, Capital Medical University, Beijing 100069, China; cJoint Laboratory for Research and Treatment of Spinal Cord Injury in Spinal Deformity, Capital Medical University, Beijing 100069, China; and dDepartment of Orthopedic Surgery, Beijing Chaoyang Hospital, Capital Medical University, Beijing 100020, China Author contributions: M.T., S.C., and X.Q. designed research; M.T. performed research; H.S., X.Z., Y.C., Z.S., M.Y., S.M., W.L., B.H., X.W., X.L., and Y.H. contributed new reagents/analytic tools; M.T. analyzed data; and M.T., S.C., and X.Q. wrote the paper. The authors declare no competing interest. This article is a PNAS Direct Submission. J.J.G.T. is a guest editor invited by the Editorial Board. Copyright © 2026 the Author(s). Published by PNAS. This article is distributed under Creative Commons Attribution- NonCommercial-NoDerivatives License 4.0 (CC BY-NC-ND). 1To whom correspondence may be addressed. Email: cuisx@ccmu.edu.cn or qxj@ccmu.edu.cn. This article contains supporting information online at https://www.pnas.org/lookup/suppl/doi:10.1073/pnas. 2533427123/-/DCSupplemental. Published July 20, 2026. Significance Herein, we identify α-fluoro- β- alanine (FBAL), a metabolite of 5-fluorouracil (5-FU), as a β-arrestin1-biased ligand of sphingosine 1-phosphate receptor 2 (S1PR2) to upregulate dihydropyrimidine dehydrogenase (DPD) expression in cancer cells. DPD, the rate- limiting enzyme responsible for 5-FU catabolism, drives acquired resistance to 5-FU. Our study redefines FBAL from a toxic byproduct to a central driver of resistance and identifies S1PR2 as a promising target for restoring chemosensitivity in 5-FU-resistant cancers, thus offering a rationale for combining S1PR2 antagonists with fluoropyrimidine-based chemotherapy to overcome acquired resistance. α- fluoro-β-alanine (FBAL), a catabolite of the chemotherapeutic agent 5- fluorouracil (5- FU), has attracted significant attention due to its cardiotoxicity and neurotoxicity. However, its association with 5-FU r esistance, a major obstacle in cancer treatment, has rarely been reported. In this study, FBAL was identified as a β-arr estin1- biased ligand of sphingosine 1- phosphate receptor 2 (S1PR2), which upregulates dihydro- pyrimidine dehydrogenase (DPD) expression and drives 5-FU r esistance in colorectal cancer. Mechanistically, following exposure to FBAL, S1PR2, a G protein–coupled receptor (GPCR), is phosphorylated by recruiting G protein–coupled receptor kinase 6 (GRK6). Phosphorylated S1PR2 coupled with β- arrestin1, but not G proteins, to activate the MEK/ERK/AP- 1 pathway and promote DPYD transcription. Ser343 was identified as the key phosphorylation site of S1PR2 using IP-MS analysis. This r esidue within the C- terminal domain mediates receptor interaction with β- arrestin- 1 to acti- vate the β-arr estin-1 -dependent ERK pathway , as was confirmed in HCT116S1PR2KO-ΔC cells and HCT116S1PR2KO- S343A cells. In vivo, mice bearing orthotopic xenografts of HCT116S1PR2KO- S343A cells exhibited significantly enhanced higher sensitivity to 5- FU treatment compared to those