Abstract PR001: TRIM29 is required for basal bladder cancer invasive progression

Abstract TRIM29 (Tripartite Motif 29) also known ATDC, is an E3 ubiquitin ligase frequently upregulated in muscle-invasive bladder cancer (MIBC). We have previously shown TRIM29 global overexpression in a genetically engineered mouse model (GEMM) is sufficient to ` bladder cancer development and progression to MIBC. Other studies strongly suggest cytokeratin-5/14 (Krt5+/Krt14+) expressing basal-stem progenitor cells in the urothelium are the cells of origin for MIBC in mice. We therefore hypothesized that Trim29 expression in Krt5+ basal urothelial cells is required for development of MIBC in mice. To test this, we generated a GEMM harboring a Trim29 conditional KO allele and tamoxifen responsive Cre under control of the bovine Krt5promoter. Exposure of Krt5-CreERT2 Trim29flox/flox mice to tamoxifen resulted in activation of Cre and loss of Trim29 expression only in the Krt5+ basal urothelium. To induce bladder tumorigenesis, we utilized the urothelial specific carcinogen N-butyl-N- (4-hydroxybutyl) nitrosamine (BBN) in drinking water at 0. 05%. After 6 months, tumor invasion was staged by a genitourinary pathologist based on depth of invasion: T1 (stromal invasive), T2 (muscle invasive) and T3 (deep muscle/peri-vesicular invasion). In agreement with previous studies, BBN exposure resulted in loss of Krt5-negative intermediate and superficial cells, and expansion of Krt5+/Krt14+ basal cells across the urothelium. In combination with a tamoxifen treatment this led to total Trim29 KO in the urothelium. All male Trim29 WT mice exposed to BBN developed Trim29+ bladder tumors, 50% of which demonstrated extensive progression to muscle-invasion (57% n=23). In contrast, only 16% of mice with Trim29 loss in Krt5+ basal cells developed MIBC (n=18). As an E3 ubiquitin ligase TRIM29 is known to target immune adaptor molecules, notably the stimulator of interferon genes (STING), for proteasomal degradation. We hypothesized TRIM29 targets STING during invasive progression and supports the establishment of an immune-privileged niche at the bladder cancer invasive front. We find TRIM29 expression in human bladder tissues is upregulated in the urothelium under stress and in MIBC tumors. In mice, BBN exposure upregulated Trim29 expression in the bladder urothelium which correlated with low urothelial Sting. In contrast, Krt5+ Trim29 loss resulted in significantly elevated Sting in the bladder urothelium. Multiplex immunofluorescence imaging and immunotyping of Trim29 KO mouse tissues revealed peritumoral enrichment of CD4+ and CD8+ T cells, CD206+ immunosuppressive macrophages, and CD4+FoxP3+ regulatory T cells. Taken together, these results suggest that TRIM29-mediated downregulation of STING in the bladder urothelium results in decreased immune surveillance at the tumor-stromal interface which expedites invasion and tumor burden. Citation Format: Alan Kelleher, Luke Broses, Yin Wang, Marian Henderson, Mark Day, Aaron Udager, Phillip Palmbos. TRIM29 is required for basal bladder cancer invasive progression abstract. In: Proceedings of the AACR Special Conference on Bladder Cancer: Transforming the Field; 2024 May 17-20; Charlotte, NC. Philadelphia (PA): AACR; Clin Cancer Res 2024;30 (10Suppl): Abstract nr PR001.