MSL2 and head and neck squamous cell carcinoma: We recently reported for the first time that monoubiquitylation of lysine 120 on histone H2B is promoted in HeLa and HNSCC cells in response to CDD induced by low-energy (11 MeV mean energy incident on the cells) protons at the distal edge of an SOBP, catalyzed by the E3 ubiquitin ligases ring finger 20/40 complex (RNF20/40) and male-specific lethal 2 homolog (MSL2) [37].