KMT5B and head and neck squamous cell carcinoma: With the exception of this cell line, these results, when compared to the effect of siRNA-mediated SUV420H1 depletion inducing ~90–100% decrease in the proliferative and colony forming capacity, support that the catalytic activity of SUV420H1 is dispensable for the proliferation of the majority of HPV-negative HNSCC cell lines.