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

Programmed death-ligand 1, PD-L1 (CD274) facilitates immune evasion and exerts pro-survival functions in cancer cells. Here, we report a new 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- 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 -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.