SMYD3 drives cell cycle and epithelial-mesenchymal transition pathways through dual gene transcriptional repression and activation in HPV-negative head and neck cancer.

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, activates gene transcription and enhances several oncogenic pathways, including epithelial-mesenchymal transition and cell cycle related pathways, in various cancer types. It was also recently shown that SMYD3 is overexpressed in HPV-negative HNSCC, and represses the expression of type I IFN response genes, contributing to resistance to anti-PD-1 checkpoint blockade in this disease. In this study, we show that SMYD3 depletion using siRNA interference or CRISPR decreases cellular proliferation and clonal capacity, induces cell cycle arrest and decreases the invasive potential of HPV-negative HNSCC cell lines. Accordingly, xenografts of SMYD3 knockout tumors derived from a human HPV-negative HNSCC cell line grew significantly slower compared to control tumors in mice. Genome-wide mapping for SMYD3 and H3K4me3 in HPV-negative HNSCC cells using cleavage under targets and release using nuclease (CUT&RUN) assays identified direct downstream gene targets regulated by SMYD3, including cell cycle- and EMT-promoting genes. This study provides insights into the epigenetic role of SMYD3 as an oncogene in HPV-negative HNSCC and supports SMYD3 as a rational therapeutic target in HPV-negative HNSCC.