Infiltrating myeloid cells drive osteosarcoma progression via GRM4 regulation of IL23

Abstract

The glutamate metabotropic receptor 4 (GRM4) locus is linked to susceptibility to human osteosarcoma, through unknown mechanisms. We show that Grm4−/− gene– targeted mice demonstrate accelerated radiation-induced tumor development to an extent comparable with Rb1+/− mice. GRM4 is expressed in myeloid cells, selectively regulating expression of IL23 and the related cytokine IL12. Osteosarcoma-conditioned media induce myeloid cell Il23 expression in a GRM4-dependent fashion, while suppressing the related cytokine Il12. Both human and mouse osteosarcomas express an increased IL23:IL12 ratio, whereas higher IL23 expression is associated with worse survival in humans. Consistent with an oncogenic role, Il23 mice are strikingly resistant to osteosarcoma development. Agonists −/− of GRM4 or a neutralizing antibody to IL23 suppressed osteosarcoma growth in mice. These findings identify a novel, druggable myeloid suppressor pathway linking GRM4 to the proinflammatory IL23/IL12 axis. SIGNIFICANCE: Few novel systemic therapies targeting osteosarcoma have emerged in the last four decades. Using insights gained from a genome-wide association study and mouse modeling, we show that GRM4 plays a role in driving osteosarcoma via a non–cell-autonomous mechanism regulating IL23, opening new avenues for therapeutic intervention.