Abstract
The Wnt/β-catenin pathway is constitutively active and promotes multiple tumor processes, including breast cancer metastasis. However, the underlying mechanism by which the Wnt/β-catenin pathway is constitutively activated in breast cancer metastasis remains unclear. Inhibition of Wnt antagonists is important for Wnt/β-catenin signaling activation, and post-transcriptional regulation of these antagonists by microRNAs (miRNAs) might be a possible mechanism underlying signaling activation. Regulation of nuclear pre-mRNA domain-containing 1A (RPRD1A) is a known inhibitor of cell growth and Wnt/β-catenin signaling activity, but the function and regulatory mechanism of RPRD1A in breast cancer have not been clarified. The aim of this study was to understand how regulators of the Wnt/β-catenin pathway may play a role in the metastasis of this cancer. Methods: RPRD1A expression and its association with multiple clinicopathological characteristics was analyzed immunohistochemically in human breast cancer specimens. miR-454-3p expression was analyzed using real-time PCR. RPRD1A or miR-454-3p knockdown and overexpression were used to determine the underlying mechanism of their functions in breast cancer cells. Xenografted tumor model, 3D invasive culture, cell migration and invasion assays and sphere formation assay were used to determine the biofunction of RPRD1A and miR-454-3p in breast cancer. Electrophoretic mobility shift assay (EMSA), luciferase reporter assay, and RNA immunoprecipitation (RIP) were performed to study the regulation and underlying mechanisms of RPRD1A and miR-454-3p expression and their correlation with the Wnt/β-catenin pathway in breast cancer. Results: The Wnt/β-catenin signaling antagonist RPRD1A was downregulated and its upstream regulator miR-454-3p was amplified and overexpressed in metastatic breast cancer, and both were correlated with overall and relapse-free survival in breast cancer patients. The suppression by miR-454-3p on RPRD1A was found to activate Wnt/β-catenin signaling, thereby promoting metastasis. Simultaneously, three other negative regulators of the Wnt/β-catenin pathway, namely, AXIN2, dickkopf WNT signaling pathway inhibitor (DKK) 3 and secreted frizzled related protein (SFRP) 1, were also found to be targets of miR-454-3p and were involved in the signaling activation. miR-454-3p was found to be involved in early metastatic processes and to promote the stemness of breast cancer cells and early relapse under both in vitro and in vivo conditions. Conclusions: The findings indicate that miR-454-3p-mediated suppression of Wnt/β-catenin antagonist RPRD1A, as well as AXIN2, DKK3 and SFRP1, sustains the constitutive activation of Wnt/β-catenin signaling; thus, miR-454-3p and RPRD1A might be potential diagnostic and therapeutic targets for breast cancer metastasis.