TMIC-28. TARGETING TUMOR-ASSOCIATED SMOOTH MUSCLE ACTIN (ACTA2) EXPRESSION IN MOUSE PRE-CLINICAL GLIOMA MODELS REDUCES TUMOR PROGRESSION AND EXTENDS SURVIVAL

Abstract The ACTA2 gene, which encodes α-smooth-muscle actin, is known to be involved in contractility and oncogenic transformation. However, the specific role of tumor-associated ACTA2 mesenchymal cells in gliomas is unknown. Using genetically engineered mouse models (GEMM) of glioma, we discovered that ACTA2 expression was increased within oncostreams, which are malignant multicellular structures found in high-grade gliomas. Furthermore, we observed reduced expression of ACAT2 mRNA in IDH-Mut mouse gliomas vs WT tumors. Analyzing human glioma TCGA and CCGA databases revealed a negative correlation between tumor ACTA2 expression and overall survival in glioma patients. ACTA2 mRNA expression was also higher in grade IV and recurrent tumors. To investigate the role of ACTA2 in glioma cells, we created ACTA2 knockdown GEMM of glioma. These mice showed very large increases (~300%) in median survival (NPDS: 253 days, NPAS: 329 days) in comparison to their respective control groups (NPD: 89 days, NPA: 97 days). Glioma neurospheres derived from knockdown tumors confirmed downregulation of ACTA2, and showed reduced cell proliferation compared to controls. Moreover, orthotopic models revealed a decreased potential for tumor development in vivo. To explore the mechanism mediating the effects of ACTA2 downregulation, we conducted RNA-Seq analysis of ACTA2 knockdown neurospheres. This analysis identified approximately 5000 differentially expressed genes, with gene ontology analysis highlighting significant enrichment in biological processes such as cell adhesion, cell communication, and regulation of locomotion. Pathway analysis identified cytokine-receptor interactions, focal adhesion, and NFK-B signaling as the most significant signaling pathways affected by ACTA2 downregulation. Finally, we evaluated the release of cytokines into the cell-conditioned media and found significantly decreased levels of GSCF and GMSCF cytokines in ACTA2 knockdown compared to controls. These findings indicate that ACTA2 expression is a pro-tumoral gene involved in glioma progression and plays an essential role in altering the TME.