Exploring the anti-cancer effect of dietary compound isoliquiritigenin as a novel drug candidate for modulating miR-374a/PTEN and miR-200c/C-JUN in breast cancer

Abstract

Breast cancer is the one of the most common and lethal malignancies among women worldwide, especially in Hong Kong, with a sharp increase of incidence since 2008. Thus, it is urgent to explore novel regulators and targeted drug applications for the inhibition on breast cancer initiation and development. Since 2002, microRNAs (miRNAs) gradually attached the importance to the gene regulation in major aspects of cancer hallmarks in tumor microenvironment, including cell proliferation, drug resistance, immune disability, and metastatic acquisition. Targeting of aberrant miRNAs via single compounds from Chinese medicine (CM) has become a promising effective approach in breast cancer therapy. This study aims to test the anti-breast cancer effect of the natural product Isoliquiritigenin (ISL) based on the regulation of miRNA expression. ISL was a naturally isolated flavonoid from licorice and Spatholobus Suberectus, and possessed potent anti-cancer effects on breast cancer cell viability, angiogenesis, migration and cancer stem cell survival according to our previous publication. Anyway, there is lacking in studies that have investigated the detail mechanisms of ISL regulating miRNAs in breast cancer. Through microarray screening after ISL treatment, we found that miR-374a was expressed at high level and miR-200c was expressed at low level in breast cancer cells, particularly in triple negative breast cancer (TNBC), and dramatically decreased and increased in ISL-treated groups, respectively. Therefore, we hypothesized that ISL could inhibit breast cancer growth and invasion through the down-regulation of miR-374a and up-regulation of miR-200c. We found that ISL could induce apoptosis and inhibit cell movement in breast cancer cells through the decrease of miR-374a. Luciferase assay showed that miR-374a directly targeted 3’ untranslated region (UTR) of PTEN. Further study confirmed that ISL could promote PTEN expression by down-regulating miR-374a, resulting in the inactivation of Akt pathway. Akt pathway is an oncogenic signaling promoting breast cancer cell proliferation, migration and invasion. We also found that ISL could inhibit breast cancer invasion through the increase of miR-200c. Further study showed that ISL could block Epithelial-Mesenchymal Transition (EMT) process, which was an initiation of cell invasion, by up-regulating miR-200c. Luciferase assay showed that miR-200c could directly target 3’UTR of C-JUN. C-Jun is an oncogene promoting transcription of SNAI1 to accelerate EMT process. Further study confirmed that ISL could inhibit c-Jun expression by up-regulating miR-200c, resulting in the inhibition of breast cancer migration, invasion and metastasis. Interestingly, ISL might increase miR-200c expression through the demethylation of miR-200c promoter region. Taken together, ISL showed a significant inhibitory effect on breast cancer development and progression through the regulation of miR-374a and miR-200c. These findings indicated that ISL could be potentially developed as a promising drug candidate for breast cancer treatment regulating miR-374a and miR-200c.