Abstract
BACKGROUND: Immune checkpoint blockade (ICB) therapy has demonstrated significant clinical potential in a variety of cancers; however, its efficacy in clear cell renal cell carcinoma (ccRCC) remains suboptimal. In ccRCC, an increased infiltration of CD8(+) T cells does not necessarily correlate with improved prognosis, indicating the presence of unique immune evasion mechanisms within the tumor microenvironment (TME). METHODS: Tripartite motif-containing 28 (TRIM28) was identified as a potential therapeutic target through single-cell transcriptomics (GSE159115) and Geneformer-based perturbation screening. Functional validation was performed by constructing shTRIM28 and overexpression cell models to assess tumor proliferation, CD8(+) T cell co-cultures, flow cytometry, and patient-derived xenograft models. Co-immunoprecipitation and GST pull-down assays were used to analyze the TRIM28-poly (ADP-ribose) polymerase 1 (PARP1) interaction. SUMOylation/ubiquitination studies elucidated the mechanism regulating PARP1 stability, and chromatin immunoprecipitation-quantitative PCR identified the transcriptional regulation of programmed death-ligand 1 (PD-L1). High-throughput screening was conducted with RNA-seq, liquid chromatography-tandem mass spectrometry, and metabolomics. Virtual screening identified the TRIM28 inhibitor Eltrombopag, which was tested in combination with anti-programmed cell death protein-1 (PD-1) therapy for in vivo efficacy and metabolic reprogramming. RESULTS: We identified TRIM28 as a central regulator of immune evasion in ccRCC. Using high-throughput gene knockout screening, we demonstrated that TRIM28 depletion reprograms malignant epithelial cells toward a less aggressive phenotype and significantly enhances tumor cell susceptibility to cytotoxic T lymphocyte killing. Mechanistically, TRIM28 promotes immune resistance through dual immunometabolic mechanisms: first, by stabilizing PARP1 and promoting its SUMOylation, which in turn amplifies PD-L1 expression via NAD(+)-SIRT1-p65 signaling; second, by depleting NAD(+) in the TME, limiting NAD(+) availability for CD8(+) T cells and impairing their respiration and effector function. These findings provide a novel mechanistic framework for TRIM28-driven immune suppression, integrating tumor-intrinsic metabolic reprogramming with CD8(+) T cell dysfunction. Notably, we identified Eltrombopag as a candidate TRIM28 inhibitor, which synergized with anti-PD-1 therapy to enhance antitumor immunity and overcome ICB resistance in murine models. CONCLUSIONS: This study reveals that TRIM28 is a key regulator of PD-L1 expression and T cell dysfunction in ccRCC through PARP1 stabilization and NAD(+) metabolic reprogramming. Targeting TRIM28/PARP1/PDL1 with Eltrombopag reshapes the immunosuppressive TME and enhances checkpoint blockade efficacy, providing a novel combinatorial strategy for ccRCC immunotherapy.