Transforming Growth Factor-Beta is a Key Regulator of Oncogene Expression and Immune Microenvironment in Osteosarcoma 9272

Abstract Description Osteosarcoma (OS) is an aggressive primary bone cancer. While survival rates for non-metastatic OS have improved, pulmonary metastatic OS (pOS) remains a significant challenge, with a 5-year survival rate of only 20%. Therefore, novel biomarkers and therapeutic strategies are urgently needed. The OS tumor microenvironment (TME), composed of immune cells, fibroblasts and stromal cells, drives chemoresistance. Targeting key factors secreted in the OS TME would be a promising strategy for developing therapies for pOS. Transforming growth factor-β (TGF-β), an immunosuppressive cytokine, is elevated in the sera and tumor tissues of OS patients and correlates with metastases. We found that TGF-β induces c-Myc oncogene expression in human and mouse OS cells. To investigate the mechanism underlying TGF-β regulation of c-Myc expression, we performed RT-PCR, Western blotting, ChIP assays, and luciferase assays, revealing that TGF-β signaling directly regulates c-Myc mRNA expression in OS cells. We identified that M2-like tumor-associated macrophages (TAMs) were significantly enriched in metastatic pOS mouse models. Moreover, TGF-β-treated OS supernatants polarized M0 macrophages into the M2 macrophage phenotype more effectively than direct TGF-β treatment in vitro experiments. These findings highlight TGF-β as a key driver of OS progression by promoting oncogene expression in OS cells and pro-tumor TAMs in the TME, positioning it as a promising target for metastatic OS therapy. Funding Sources R03CA273468, P30CA043703, St. Baldrick’ ‘s Foundation, Hyundai Hope-on-Wheels Scholar Hope Grant, Andrew McDonough B+ Foundation, Curing Kids Cancer, MIB Agents, Sarcoma Foundation of America, Sam Day Foundation, Alex’s Lemonade Stand Foundation, Children’ ‘s Cancer Research Fund, Center for Pediatric Immunotherapy at Rainbow Topic Categories Tumor Immunology: Cellular Responses and Tumor Microevironment (TIME)