Protein lysine methyltransferase SMYD3 is involved in tumorigenesis through regulation of HER2 homodimerization.

HER2 is a receptor tyrosine kinase, which is amplified and overexpressed in a subset of human cancers including breast and gastric cancers, and is indicated in its involvement in progression of cancer. Although its specific ligand(s) has not been detected, HER2 homodimerization, which is critical for its activation, is considered to be dependent on its expression levels. Here, we demonstrate a significant role of HER2 methylation by protein lysine methyltransferase SMYD3 in HER2 homodimerization. We found that SMYD3 trimethylates HER2 protein at lysine 175. HER2 homodimerization was enhanced in the presence of SMYD3, and substitution of lysine 175 of HER2 with alanine (HER2-K175A) reduced the formation of HER2 homodimers. Furthermore, HER2-K175A revealed lower level of autophosphorylation than wild-type HER2. We also identified that knockdown of SMYD3 attenuated this autophosphorylation in breast cancer cells. Our results imply that SMYD3-mediated methylation of HER2 at Lysine 175 may regulate the formation of HER2 homodimer and subsequent autophosphorylation and suggest that the SMYD3-mediated methylation pathway seems to be a good target for development of novel anti-cancer therapy.