Histone methyltransferase SMYD3 promotes MRTF-A-mediated transactivation of MYL9 and migration of MCF-7 breast cancer cells

Myocardin-related transcription factor-A (MRTF-A) is a Rho signal-responsive transcriptional coactivator of serum response factor (SRF). Recent studies indicated that MRTF-A might be an important regulator of mammary gland and be involved in cancer metastasis. However, the roles of histone modification in the MRTF-A-dependent signal pathway and tumor migration are still not very clear. Here, we report that histone methylation is required for the MRTF-A-mediated upregulation of myosin regulatory light chain 9 (MYL9), an important cytoskeletal component which is implicated in cell migration. Furthermore, we demonstrate that SET and MYND domain containing protein 3 (SMYD3), a hitone methyltransferase (HMT) associated with carcinogenesis, might be the one which is responsible for the histone methylation occurred in the MRTF-A-mediated- transactivation of MYL9 and migration of breast cancer cells. Overexpression of SMYD3 promotes MRTF-A-mediated upregulation of MYL9 and migration of MCF-7 breast cancer cells, while contrary results were observed when the endogenous MRTF-A and SMYD3 were suppressed with specific siRNAs. In addition, the mutation analysis suggested that this cooperative transactivation is mainly mediated via the proximal binding element of MRTF-A in the promoter of MYL9, and the HMT activity of SMYD3 is required as well. Our findings reveal a new mechanism by which MRTF-A and SMYD3 functions in transcriptional regulation and cell migration, and provide a better understanding for metastasis of breast cancer.