Previous studies in breast cancer cell lines demonstrated that truncated neurokinin receptor-1 (NK1R-Tr) was able to promote malignant transformation and distant metastasis in human breast cancer. Bioinformatics analyses revealed that NK1R-Tr 3'UTR contained putative miR-22 binding sites. The aim of the present study is to explore the role of miR-22 in regulating the NK1R-Tr expression in breast cancer cells.
We assessed the miR-22 and NK1R-Tr expression patterns in three breast cancer cell lines and 98 clinical biopsies. Using luciferase constructs containing the 3'-UTR of NK1R-Tr sequence, pre-miR-22 and antagomiR-22 were conducted to breast cancer cell lines to investigate the interaction between NK1R-Tr and miR-22.
Test on breast cancer tissues showed that lower expression of NK1R-Tr corresponded to higher expression of miR-22. MiR-22 expressions were significantly decreased in tumor specimens, particularly in metastatic carcinomas. MiR-22 levels were higher in SK-BR-3 cells which NK1R-Tr were low expression than MB-MDA-231 and MCF-7 cells which NK1R-Tr were high expression. Transfection of MDA-MB-231 cells with pre-miR-22 or antagomiR-22 was specifically decreased or increased, respectively, NK1R-Tr mRNA levels the same. Overexpression of pre-miR-22 reduced NK1R-Tr protein levels. Reporter constructs containing the NK1R-Tr binding sites inserted into the 3'-untranslated region of the luciferase mRNA conferred a 2.8 fold repression of luciferase activity, in MDA-MB-231 cells. MiR-22 expression was strongly inhibited by NK1R agonist substance P (SP), in MDA-MB-231 cells. Our in vitro data showed that MiR-22 expression was inversely associated with proliferation, invasiveness and metastasis of MDA-MB-231 cells, but inhibited by NK1R agonists was able to promote tumor progression and promote distant metastasis in human breast cancer.
Our data demonstrate that miR-22 can regulate NK1R-Tr expression and influence invasion and migration of breast cancer cells.
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All authors have declared no conflicts of interest.