Prostaglandin E2-EP4 signaling shapes immunosuppressive tumor microenvironment in human tumors by suppressing bioenergetics and ribosome biogenesis in infiltrating immune cells [scRNA-seq]

Prostaglandins (PGs) are inflammatory mediators. Aspirin-like non-steroidal anti-inflammatory drugs (NSAIDs) inhibit cyclooxygenase (COX), an initiating enzyme of PG biosynthesis1. Daily use of aspirin-like drugs lowers the risk of cancer death not only prophylactically but therapeutically suggesting critical roles of PGs in cancer. However, general mechanisms by which PGs contribute to progression of a wide variety of human cancers remain elusive. Here, using scRNAseq analysis comparing immune cells infiltrating human tumors and a syngeneic mouse tumor, we have dissected this issue. We found that in human tumors, COX is dominantly expressed in infiltrating myeloid cells, and, among PG receptors, PGE receptor EP4 and to a less extent EP2 are expressed in both T cells and myeloid cells. DEG analysis between PTGER4hi and PTGER4lo CD8+ T cells indicates downregulation of IL-2-STAT5 signaling, oxidative phosphorylation, glycolysis and Myc targets in EP4hi CD8+ T cells, as revealed by suppressed expression of IL-2 receptor subunit gene and genes of OXPHOS, glycolytic enzymes and ribosomal proteins (RPs). Similar downregulation of OXPHOS, glycolytic enzymes and RP genes is found in PTGER4hi myeloid cells. Notably, such downregulation of OXPHOS and RP genes was found in immune cells infiltrating LLC1 mouse tumor, and reversed by treatment of tumor-bearing mice with EP2 and EP4 antagonists. In vitro in CD8+ T cells, EP4 is induced upon TCR activation and PGE2 acts on EP4, downregulates Il2ra expression and suppresses expression of Myc and PGC-1, thereby impairing both mitochondria and glycolysis as well as ribosome biogenesis in these cells. Similarly, EP4 is induced upon activation in macrophages and PGE2 downregulates Myc and OXPHOS pathwaysin these cells irrespective of other stimuli. These results demonstrate that PGE2 shapes immunosuppressive tumor microenvironment by hampering bioenergetic metabolism and ribosome biogenesis in infiltrating immune cells via EP4 receptor.