SMYD3 and neoplasm: Importantly, MMP9 is one of the downstream target genes of SMYD3 (SET and MYND domain containing protein 3), the histone H3-K4 di-/tri- and H4-K5-methyltransferase, and overexpression of SMYD3 can induce MMP9 expression in human tumor models, e.g., gastric cancer [43].