HBO1 suppresses anti-tumor immunity of CD8⁺ T Cells in thyroid cancer by recruiting BRD4 to regulate VTCN1 expression

Thyroid cancer is the most common endocrine malignancy. Although surgery remains the primary treatment, advanced disease frequently recurs or metastasizes, and subsequent therapies yield suboptimal outcomes. Immunotherapy holds promise, yet the underlying immune-evasion mechanisms remain incompletely understood. HBO1, a multifunctional acyltransferase, plays a significant role in tumor immune regulation. Our previous research revealed that HBO1 is highly expressed in thyroid cancer tissues, promotes malignant progression, and inhibits CD8⁺ T cell function. To further elucidate the role and mechanism of HBO1 in thyroid cancer immune regulation, we conducted the following investigations. Firstly, using an in vitro co-culture model analyzed by flow cytometry and ELISA assays, we found that HBO1 overexpression induces CD8⁺ T cell apoptosis and significantly suppresses their cytotoxic function and secretion of effector molecules. Secondly, leveraging bioinformatic analysis of CUT&Tag datasets combined with in vitro cellular experiments, we found that HBO1 was associated with increased VTCN1 expression in an H3K14 acetylation-dependent manner, thereby contributing to CD8⁺ T cell dysfunction. Subsequently, employing RNA-seq analysis, ChIP-qPCR, dual-luciferase reporter assays, co-immunoprecipitation (Co-IP), and in vivo experiments, we further explored the underlying mechanism and found that HBO1 may facilitate BRD4 enrichment at the VTCN1 promoter through H3K14 acetylation, thereby promoting VTCN1 transcription and contributing to anti-tumor immune suppression in thyroid cancer. Finally, through IP-MS and Co-IP experiments, we identified the E3 ligase TRIM21 as a potential upstream regulator of HBO1. TRIM21 modulates HBO1 acetyltransferase activity by promoting its ubiquitination-mediated degradation, consequently influencing HBO1-associated immune escape in thyroid cancer. In summary, this study suggests that HBO1 may regulate VTCN1 expression through an H3K14ac-BRD4-associated mechanism in thyroid cancer, thereby contributing to suppression of CD8⁺ T cell anti-tumor immunity. In addition, TRIM21 may participate in the regulation of HBO1 protein stability and its associated immune-related signaling. Our findings provide new experimental evidence for understanding immune escape mechanisms and exploring potential immunotherapeutic targets in thyroid cancer.