MiR-137 Suppresses Triple-Negative Breast Cancer Stemness and Tumorigenesis by Perturbing BCL11A-DNMT1 Interaction

Background/aims: Triple negative breast cancer (TNBC) is resistant to conventional chemotherapy due to high proportions of cancer stem cells (CSCs). The aim of this study is to unravel the miR-137-mediated regulatory mechanism of B-cell lymphoma/leukemia 11A (BCL11A) in TNBC.

Methods: A corhort of 34 TNBC tumor tissues and paired adjacent normal tissues, as well as 25 non-TNBC tumor tissues and paired adjacent normal tissues were collected post-operatively from patients with breast cancer. Q-PCR was performed to determine the mRNA levels of miR-137 and BCL11A in breast tissues and cell lines. Bioinformatics analysis and dual luciferase reporter assay were used to verify the direct interaction between miR-137 and BCL11A. After up-/down-regulation of BCL11A, miR-137, or DNMT1 via lentiviral transduction in TNBC cell lines SUM149 and MDA-MB-231 cells, Q-PCR and Western blot assays were used to detect the expression levels of BCL11A, DNA methyltransferases 1 (DNMT1), and Islet-1 (ISL1). Mammosphere assay was conducted to assess tumorosphere formation ability of cells, coupled with flow cytometry to determine the percentage of breast cancer stem cells. Co-immunoprecipitation assay was used to determine the interaction between BCL11A and DNMT1. Xenograft tumorigenesis assay was performed to monitor tumor formation in vivo.

Results: BCL11A was highly expressed in TNBC, whereas miR-137 was significantly lower in both TNBC tissues and cell lines. miR-137 suppressed BCL11A expression at both mRNA and protein levels by directly targeting its 3'UTR. In both SUM149 and MDA-MB-231 cells, overexpression of miR-137 or knockdown of BCL11A reduced the number of tumoroshperes and the percentage of cancer stem cells in vitro, and inhibited tumor development in vivo. Furthermore, BCL11A interacted with DNMT1 in TNBC cells. Silencing of either BCL11A or DNMT1 impaired cancer stemness and tumorigenesis of TNBC via suppressing ISL1 expression both in vitro, and in vivo.

Conclusions: By perturbing BCL11A-DNMT1 interaction, miR-137 impairs cancer stemness and suppresses tumor development in TNBC.