Abstract 4145: TRIM21 functions as an oncogene in glioblastoma by transactivating FOSL1 and promoting the ubiquitination of p27 transactivating FOSL1 and promoting the ubiquitination of p27

Abstract Background: Our previous studies demonstrated that FOSL1 promotes glioblastoma (GBM) progression and stemness through multiple pathways such as STAT3 and NF-κB signaling. Recently, we identified that FOSL1 physically interacts with the E3 ligaseTRIM21, which is localized in the nucleus of glioma cells. This study investigates the role of TRIM21 in GBM, its relationship with FOSL1, and its regulation of the TRIM21 ubiquitination target gene p27. Methods: 1) Protein interaction: Immunoprecipitation assays were conducted to examine the physical interaction between TRIM21, FOSL1, and p27. 2) Regulation of p27: TRIM21 overexpression and knockdown (via siRNA) were used to analyze the effects on p27 protein levels. 3) Ubiquitination assay: TRIM21 knockdown followed by p27 immunoprecipitation and anti-ubiquitin probing was performed to assess ubiquitination. 4) Clinical data analysis: TCGA datasets were analyzed to correlate TRIM21 expression with glioma subtype and patient survival. 5) Functional assays: Glioma cell growth (MTT, colony formation) and invasion (transwell assay) were measured following TRIM21manipulation. 6) Histopathology: IHC was performed to evaluate TRIM21 expression in glioma patient tissues and its relationship with FOSL1 expression. 7) Nuclear TRIM21: The effects of nuclear-localized TRIM21 in regulating FOSL1 was assessed, including its ability to stimulate FOSL1 promoter activity via AP-1 binding sites. Results: 1) TRIM21 physically interacts with FOSL1 and p27. 2) TRIM21 promotes p27 degradation through ubiquitination in a dose-dependent manner. 3) TCGA analysis reveals high TRIM21 expression in GBM patients, particularly in the mesenchymal subtypes. 4) TRIM21 enhances glioma growth and invasion in short-term and long-term assays. 5) IHC data show elevated TRIM21 levels in grade IV GBM tissues, correlating with FOSL1 expression. 6) nuclear-localized TRIM21 promotes FOSL1 transactivation via AP-1 sites and simultaneously mediates p27 degradation. Conclusion: TRIM21 functions as an oncogene in GBM by driving FOSL1 transactivation and degrading the tumor suppressor gene of p27, thereby promoting GBM progression and aggressiveness. Citation Format: Vanajothi Ramar, Rajveer Sidhu, Osei Pako, Cheyenne R. Cisse, Shanchun Guo, Mingli Liu. TRIM21 functions as an oncogene in glioblastoma by transactivating FOSL1 and promoting the ubiquitination of p27 transactivating FOSL1 and promoting the ubiquitination of p27 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 4145.