SOX9 is a Target of miR-134-3p And miR-224-3p in Beast Cancer Cell Lines

Abstract

SOX9 represents a transcription factor identified as an important mediator of cancer progression in breast cancer. miRNAs are small non-coding RNAs that can inhibit translation of target genes by binding to the 3’-UTR region of the respective mRNA molecule. Deregulated miRNA expression plays a pivotal role in hallmarks of cancer such as sustained proliferation and inhibition of apoptosis. In this study we investigated the miRNA-mediated regulation of SOX9 expression in two breast cancer cell lines providing further insights into cellular mechanisms driving breast cancer progression. The effect of miR-134-3p, miR-224-3p and miR-6859-3p on SOX9 expression was tested on mRNA as well as protein level in the human breast cancer cell line MDA-MB-231. Furthermore, direct binding of these miRNAs to the SOX9 3’-UTR was assessed by luciferase reporter assays and site-directed mutagenesis in MDA-MB-231 and MCF-7 cells. SOX9 expression was significantly reduced on mRNA and protein level by transfection of either miR-134-3p, miR-224-3p or miR-6859-3p. Luciferase reporter assays proved direct binding of miR-134-3p and miR-224-3p to the SOX9 3’-UTR in MDA-MB-231 and MCF-7 cells. Expression analysis performed in silico revealed reduced expression of both miRNAs in breast cancer tissues. We describe three novel miRNAs capable of targeting SOX9 in human breast cancer cell lines. For miR-134-3p and miR-224-3p direct interaction with the SOX9 3’-UTR was proven. Furthermore, miR-134-3p and miR-224-3p reduced breast cancer cell viability, which is in line with the tumorigenic effects reported for SOX9 in breast cancer.