MiRNA-520b and miR-520e sensitize breast cancer cells to complement attack via directly targeting 3′UTR of CD46

Abstract

MicroRNAs (miRNAs) are non-coding RNAs that function as post-transcriptional gene regulators. MiRNAs play a pivotal role in cancer development. In the present study, we elucidated the roles of miR-520b and miR-520e in breast cancer cells involving complement attack. We examined the expression levels of miR-520b and miR-520e in immortalized breast cell line HBL-100 and in three breast cancer cell lines, including MCF-7, LM-MCF-7 and MDA-MB-231. The data showed that the expression levels of miR-520b and miR-520e in the three breast cancer cell lines were lower than that in HBL-100 cells, which were correlated with the less sensitivity of the breast cancer cell lines to complement-dependent cytotoxicity (CDC). While, we found that the overexpression of miR-520b and miR-520e could increase the sensitivity of the breast cancer cells to CDC, but the suppression of miR-520b and miR-520e mediated by anti-miRNAs could decrease the sensitivity of the breast cancer cells to CDC. Then, we identified that miR-520b and miR-520e were able to directly target the 3′untranslated regions (3'UTR) of the membrane-bound complement regulatory protein CD46, suggesting that miR-520b and miR-520e downregulate CD46 at post-transcriptional level. Enzyme-linked immunosorbent assay (ELISA) showed that the overexpression of miR-520b and miR-520e resulted in the increase of deposition of C3b mediated by downregulated CD46, suggesting that miRNA-520b and miR-520e involving CD46 mediate the cancer cell opsonization via an alternative pathway activation leading to CDC involving complement activation. Thus, we conclude that miR-520b and miR-520e contribute to CDC in breast cancer cells via directly targeting 3′UTR of CD46. © 2010 Landes Bioscience.