GPI promotes immunosuppression in anaplastic thyroid carcinoma via O-GlcNAcylated THBS1-mediated myeloid cell crosstalk.

The aggressive and immunotherapy-resistant characteristics of anaplastic thyroid carcinoma (ATC) are driven by an immunosuppressive tumor microenvironment and intercellular crosstalk; however, its regulatory mechanisms remain poorly understood. Here, we identified Glucose-6-Phosphate Isomerase (GPI) as a pivotal metabolic immune checkpoint that orchestrates myeloid cells-driven immunosuppression in ATC. We demonstrated that GPI enhances the hexosamine biosynthesis pathway to promote O-GlcNAcylation of thrombospondin-1 (THBS1) at serine-1068. This site-specific modification competes with ubiquitination to stabilize THBS1 and augment its secretion. Released THBS1 engages macrophages to trigger a CEBPB-dependent transcriptional program that drives the expression of the chemokine CCL2. Macrophage-derived CCL2 then acts on tumor-associated neutrophils, promoting their STAT3-dependent differentiation into polymorphonuclear myeloid-derived suppressor cells, which ultimately suppresses CD8+ T cell function. Genetic deletion of either GPI or THBS1 robustly inhibited tumor growth and reversed immunosuppression in vivo. To intervene this axis, we repurposed the multi-kinase inhibitor Regorafenib as a novel GPI inhibitor. We confirmed that Regorafenib disrupts this entire axis and, in combination with anti-PD-1 therapy in ATC, overcomes immunosuppression to elicit potent anti-tumor immunity. Our studies revealed the GPI/O-GlcNAcylation/THBS1 signal as a master regulator of myeloid cell crosstalk and established a novel therapeutic strategy for targeting this metabolic checkpoint to potentiate ATC immunotherapy.