Alterations of Ceramide Synthesis Induce PD-L1 Internalization and Signaling to Regulate Tumor Metastasis and Immunotherapy Response 2131

Abstract Description Programmed death-ligand 1, PD-L1 (CD274) facilitates immune evasion and exerts pro-survival functions in cancer cells. Here, we report a mechanism whereby internalization of PD-L1 in response to alterations of bioactive lipid/ceramide metabolism by ceramide synthase 4 (CerS4) induces sonic-hedgehog (Shh) and TGF-b receptor signaling to enhance tumor metastasis in triple-negative breast cancers (TNBC), exhibiting immunotherapy resistance. Mechanistically, data showed that internalized PD-L1 interacts with an RNA-binding protein Caprin-1 to stabilize Shh/TGFBR1/Wnt mRNAs to induce b-catenin signaling and TNBC growth/metastasis, consistent with increased infiltration of FoxP3+ T regs and resistance to immunotherapy. While mammary tumors developed in MMTV-PyMT/CerS4-/- were highly metastatic, targeting the Shh/PD-L1 axis using Sonidegib and anti-PD-L1 antibody vastly decreased tumor growth and metastasis, consistent with the inhibition of PD-L1 internalization and Shh/Wnt signaling, restoring anti-tumor immune response. These data, validated in clinical samples and databases, provide a mechanism-based therapeutic strategy to improve immunotherapy responses in metastatic TNBCs. Our recent and unpublished data also revealed that attenuation of CerS4 expression and increased intracellular PD-L1 signaling in TNBC tumors result in resistance to anti-PD-1 or anti-PD-L1-based immunotherapy in TNBCs. Inhibition of intracellular PD-L1 signaling resensitized resistant TNBCs in vivo. Funding Sources This work was supported by research funding from the National Institutes of Health (CA214461, DE016572, and P01 CA203628 to BO). Topic Categories Tumor Immunology: Checkpoints, Prevention, and Treatment (TIPT)