Hypoxic Upregulation of IER2 Increases Paracrine GMFG Signaling of Endoplasmic Reticulum Stress‐CAF to Promote Chordoma Progression via Targeting ITGB1

Abstract Currently, the oncogenic mechanism of endoplasmic reticulum stress‐CAF (ERS‐CAF) subpopulation in chordoma remains unknown. Here, single‐cell RNA sequencing, spatial transcriptomics, GeoMx Digital Spatial Profiler, data‐independent acquisition proteomics, bulk RNA‐seq, and multiplexed quantitative immunofluorescence are used to unveil the precise molecular mechanism of how ERS‐CAF affected chordoma progression. Results show that hypoxic microenvironment reprograms CAFs into ERS‐CAF subtype. Mechanistically, this occurrs via hypoxia‐mediated transcriptional upregulation of IER2. Overexpression of IER2 in CAFs promotes chordoma progression, which can be impeded by IER2 knockdown or use of ERS inhibitors. IER2 also induces expression of ERS‐CAF marker genes and results in production of a pro‐tumorigenic paracrine GMFG signaling, which exert its biological function via directly binding to ITGB1 on tumor cells. ITGB1 inhibition attenuates tumor malignant progression, which can be partially reversed by exogenous GMFG intervention. Further analyses reveal a positive correlation between ITGB1 high tumor cell counts and SPP1 + macrophage density, as well as the spatial proximity of these two cell types. Clinically, a significant correlation of high IER2/ITGB1 expression with tumor aggressive phenotype and poor patient survival is observed. Collectively, the findings suggest that ERS‐CAF regulates SPP1 + macrophage to aggravate chordoma progression via the IER2/GMFG/ITGB1 axis, which may be targeted therapeutically in future.