MALAT1 upregulates SMYD3 by competition with miR-124 and promotes proliferation and migration of breast cancer cells

To investigate whether lncRNA MALAT1 affects the migration and proliferation of breast cancer cells through the regulation with histone methyltransferase SMYD3, the endogenous MALAT1 in the MCF-7 and MDA-MB-231 breast cancer cells were knocked down by siRNA, and then the migration and proliferation of cells were detected by wound healing migration and MTT assay. The effects of si-MALAT1 on the mRNA and protein levels of miRNA-124, SMYD3 and its downstream genes were detected by Real time PCR and Western blot. The results showed that siRNA-targeted knockdown of MALAT1 reduced the migration and proliferation of breast cancer cells, and inhibited the transcriptional expression of SMYD3 and its downstream genes, including N-cadherin, MYL9, MMP9 and CYR61, and up-regulated miR-124. Overexpression of miR-124 reduced the expression of SMYD3 in breast cancer cells, and knockdown of MALAT1 attenuated the promotion of SMYD3 protein expression by miR-124 inhibitors. In addition, SMYD3 overexpression activated MALAT1 transcription, whereas siRNA interference with SMYD3 downregulated MALAT1. These results indicate that LncRNA MALAT1 acted as a competing endogenous RNA(ceRNA)of miR-124 to regulate expression of SMYD3 in breast cancer cells, and SMYD3 can activate the transcription of MALAT1, which will affect the proliferation and migration of breast cancer cells.