MicroRNA-455-3p promotes invasion and migration in triple negative breast cancer by targeting tumor suppressor EI24.

Lacking of treatment methods for the patients with triple negative breast cancer (TNBC) underscores the pivotal needs to further understand its biology as well as to find better biomarkers and develop novel therapeutic strategies. Increasing evidences support that aberrantly expressed microRNAs (miRNAs) are involved in tumorigenesis and may serve as biomarkers for diagnostic and prognostic purposes of various cancers. In current study, we found that miR-455-3p and miR-196a-5p were intensively overexpressed in TNBC compared with the hormone receptor (HR) positive breast cancer whereas miR-425-5p was down-regulated by miRNA microarray analysis. qRT-PCR analysis confirmed that the expression of miR-455-3p in TNBC cell lines MDA-MB-231 and MDA-MB-468 was higher than that in HR positive breast cancer cell line MCF-7(p<0.01). Functional experiments in vitro showed that miR-455-3p enhanced cell proliferative, invasive and migrational abilities in TNBC cell lines. miRNA targets prediction showed SMAD2, LTBR and etoposide induced 2.4 (EI24) were potential target genes of miR-455-3p, and then it was confirmed by qRT-PCR assay. Dual luciferase reporter assay showed the specific binding of miR-455-3p to 3' UTR of EI24 in TNBC. Then we found miR-455-3p inhibited the EI24 expression at the levels of mRNA and protein. Through small interfering RNA (siRNA) targeting EI24 gene, there were strengthened capabilities of invasion and migration of TNBC cells, and increased expression of EI24 had the inverse effects. In conclusion, the data suggest that miRNA455-3p promotes invasion and migration by targeting tumor suppressor EI24 and might be a potential prognostic biomarker and therapeutic target in TNBC.