WNT signaling regulates crucial aspects of cell fate determination. For the WNT/β-catenin branch, LRP5/6 are essential co-receptors and are considered to be its limiting factor for mediating WNT signaling. Importantly, WNT signaling is commonly upregulated in aggressive breast cancers, However, how this occurs is poorly understood. Recently our laboratory has identified a novel negative regulator of LRP6, the microRNA miR-424/503. MicroRNAs are non-coding small RNAs that control gene expression at post-transcriptional level. Deletion of miR-424/503 can explain some cases of elevated WNT signaling but it cannot explain all of them. We hypothesized that mutations in the microRNA binding sequence of LRP6 may also disrupt the negative control that miR424/503 exerts over this gene inducing upregulation of WNT signaling. Thus, our research will investigate this possibility using a collection of breast cancer cell lines to sequence the binding site of the miR-424/503 at the LRP6 gene.