microRNA‐140‐3p modulates invasiveness, motility, and extracellular matrix adhesion of breast cancer cells by targeting syndecan‐4

Syndecan‐4, a predicted target of the microRNA miR‐140‐3p, plays an important role in multiple steps of tumor progression and is the second most abundant heparan sulfate proteoglycan produced by breast carcinoma cell lines. To investigate the potential functional relationship of miR‐140‐3p and syndecan‐4, MDA‐MB‐231, SKBR3, and MCF‐7 breast cancer (BC) cells were transiently transfected with pre‐miR‐140‐3p, syndecan‐4 small interfering RNAJ, or control reagents, respectively. Altered cell behavior was monitored by adhesion, migration, and invasion chamber assays. Moreover, the prognostic value of syndecan‐4 was assessed by Kaplan–Maier Plotter analysis of gene expression data from tumor samples of 4929 patients. High expression of syndecan‐4 was associated with better relapse‐free survival in the whole collective of BC patients, but correlated with a worse survival in the subgroup of estrogen receptor negative and estrogen/progesterone‐receptor negative patients. miR‐140‐3p expression was associated with improved survival irrespective of hormone receptor status. miR‐140‐3p overexpression induced posttranscriptional downregulation of syndecan‐4, as demonstrated by quantitative real‐time PCR (qPCR), flow cytometry, and luciferase assays, resulting in decreased BC cell migration and matrigel invasiveness. Furthermore, miR‐140‐3p overexpression and syndecan‐4 silencing increased the adhesion of BC to fibronectin and laminin. qPCR analysis demonstrated that syndecan‐4 silencing leads to altered gene expression of adhesion‐related molecules, such as fibronectin and focal adhesion kinase, as well as in the gene expression of the proinvasive factors matrix metalloproteinase 2 and heparanase (also known as HPSE). We conclude that syndecan‐4 is a novel target of miR‐140‐3p that regulates BC cell invasiveness and cell‐matrix interactions in the tumor microenvironment.