1140 - hnRNPA1 Impedes the Anti-Tumor Immune Response Effect via Competitively Inhibiting TRIM21-Mediated Ubiquitination and Degradation of CD155

Purpose/Objective(s):

Heterogeneous nuclear ribonucleoproteins (hnRNPs) are a class of essential RNA-binding proteins involved in various RNA metabolic processes. Among them, hnRNPA1 is highly expressed in head and neck squamous cell carcinoma (HNSCC) and is associated with an immunosuppressive tumor microenvironment and poor prognosis. These findings suggest that hnRNPA1 may play a crucial role in tumor immune responses, making it a promising new target for immune therapy and potentially improving the treatment outcomes for HNSCC.

Materials/Methods:

The expression of hnRNPA1 in tumors was analyzed using TCGA data, and survival curves were plotted. Clinical HNSCC samples were collected for immunohistochemical staining and survival analysis, validated with bioinformatics data. Stable hnRNPA1 knockdown HSC-3 and FADU cell lines were established. Transcriptomic and proteomic analyses identified CD155 as a downstream target, with changes confirmed by Western blot and qPCR. The effect of hnRNPA1 on CD155 stability and ubiquitination was examined using CHX half-life assays, MG132 rescue, and Co-IP. Immunoprecipitation-mass spectrometry identified TRIM21 as a CD155 regulator, which was confirmed through various assays. TRIM21 truncation mutants were used to confirm competitive binding between hnRNPA1 and CD155. Finally, the impact of hnRNPA1 knockdown on tumor growth and immune cell infiltration was assessed in a mouse model via immunohistochemistry.

Results:

Our study shows that hnRNPA1 is upregulated in HNSCC and linked to an immunosuppressive tumor microenvironment and poor prognosis. While hnRNPA1 does not affect other immune checkpoints like PD-L1 and CD80, it regulates CD155 protein expression without altering mRNA levels. hnRNPA1 inhibits TRIM21-mediated degradation of CD155, maintaining its surface expression on tumor cells. hnRNPA1 promotes signaling along the CD155/TIGIT axis, leading to the exhaustion of CD8+ T cells in the tumor tissue, without affecting the subpopulations of CD4+ T cells, such as FOXP3+ cells. This results in the formation of an immune desert-like microenvironment, enabling tumor immune escape. Inhibiting hnRNPA1 reverses this effect.

Conclusion:

In conclusion, hnRNPA1 is highly expressed in head and neck squamous cell carcinoma (HNSCC) and promotes tumor immune escape by inhibiting TRIM21-mediated ubiquitination and degradation of CD155, thereby maintaining its stability. hnRNPA1 also facilitates the CD155/TIGIT signaling axis, leading to CD8+ T cell exhaustion and the formation of an immune desert-like microenvironment, which is associated with poor prognosis in patients. These findings highlight the critical role of hnRNPA1 in immune evasion and the regulation of the immune microenvironment in HNSCC, suggesting that hnRNPA1 may serve as a novel target for immune therapy in HNSCC.