Abstract 2959: Investigating the oncogenic effects and mechanisms of the SMYD3 methyltransferase in HPV-negative head and neck squamous cell carcinoma

Abstract Human papillomavirus (HPV)-negative head and neck squamous cell carcinoma (HNSCC) is the sixth most common cancer type in the world and is associated with an overall poor prognosis. The protein methyltransferase SET and MYND domain-containing 3 (SMYD3), which trimethylates H3K4 and H4K20, can stimulate gene transcription and activate several oncogenic pathways, including epithelial-mesenchymal transition, and cell cycle related pathways. Additionally, its expression is associated with a poor prognosis in various cancer types, such as colon and ovarian cancer. This study aims to decipher whether SMYD3 has direct oncogenic effects and relevant mechanisms in HPV-negative HNSCC. Our preliminary results have demonstrated that SMYD3 is significantly overexpressed in HPV-negative HNSCC compared to normal and dysplastic epithelium. SMYD3 knockdown decreased cellular proliferation and clonal capacity in CFAs after siRNA-mediated SMYD3 knockdown in several HPV-negative HNSCC cell lines or CRISPR-mediated SMYD3 knockout. Cell cycle analysis of CRISPR SMYD3 KO cell lines showed a significant decrease in the S phase, supporting that cell cycle arrest may be a mechanism through which this decreased cellular proliferation occurs. Nuclear/cytoplasmic dissociation and western blotting of 6 HPV-negative HNSCC cell lines, and immunohistochemistry for SMYD3 in primary and recurrent/metastatic HPV-negative HNSCC tumor tissues have identified the expression of SMYD3 in both the cytoplasm and nucleus, with greater expression in the cytoplasm than the nucleus. Ongoing experiments aim to investigate the effects of SMYD3 knockdown on the global proteome, as well as its effects on histone post-translational modifications in HPV-negative HNSCC cell lines. Genome-wide mapping for SMYD3, H3K4me3 and H4K20me3 in HPV- negative HNSCC cells using CUT&RUN assays are ongoing with the goal to identify direct downstream gene targets regulated by human SMYD3. Finally, we plan to investigate if SMYD3 knockout decreases tumor growth in NSG xenografts. This study may provide the biological rational to target SMYD3 as a novel therapeutic avenue in HPV-negative HNSCC. Citation Format: Madhavi Murali, Daniel Tsai, Nupur Nigam, Kyunghee Burkitt, Sohyoung Kim, Hui Cheng, Vassiliki Saloura. Investigating the oncogenic effects and mechanisms of the SMYD3 methyltransferase in HPV-negative head and neck squamous cell carcinoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2959.