H19/let-7/LIN28 reciprocal negative regulatory circuit promotes breast cancer stem cell maintenance

Fei Peng,Wen-Jun Fan,Kai-Li Wang,Eric W-F Lam,Fei-Meng Zheng,Ju-Hong Wang,Quentin Liu,Hong-Jiang Wang,Zhi-Jie Kang,Li-Li Zhu,Bai Cui,Hai-Dong Zhao,Guo-Qing Xiao,Jie Xu,Ting-Ting Li,Mei Li,Bo Wang

doi:10.1038/cddis.2016.438

Abstract

Long noncoding RNA-H19 (H19), an imprinted oncofetal gene, has a central role in carcinogenesis. Hitherto, the mechanism by which H19 regulates cancer stem cells, remains elusive. Here we show that breast cancer stem cells (BCSCs) express high levels of H19, and ectopic overexpression of H19 significantly promotes breast cancer cell clonogenicity, migration and mammosphere-forming ability. Conversely, silencing of H19 represses these BCSC properties. In concordance, knockdown of H19 markedly inhibits tumor growth and suppresses tumorigenesis in nude mice. Mechanistically, we found that H19 functions as a competing endogenous RNA to sponge miRNA let-7, leading to an increase in expression of a let-7 target, the core pluripotency factor LIN28, which is enriched in BCSC populations and breast patient samples. Intriguingly, this gain of LIN28 expression can also feedback to reverse the H19 loss-mediated suppression of BCSC properties. Our data also reveal that LIN28 blocks mature let-7 production and, thereby, de-represses H19 expression in breast cancer cells. Appropriately, H19 and LIN28 expression exhibits strong correlations in primary breast carcinomas. Collectively, these findings reveal that lncRNA H19, miRNA let-7 and transcriptional factor LIN28 form a double-negative feedback loop, which has a critical role in the maintenance of BCSCs. Consequently, disrupting this pathway provides a novel therapeutic strategy for breast cancer.

Highlights

Breast cancer is the leading cause of cancer-related death among females worldwide.[1,2] early diagnosis and more effective treatment strategies have diminished the mortality rates in recent years,[3,4,5] the development of recurrence, metastasis and chemoresistance is, in most cases, still inevitable.[6]
To investigate the relationship between H19 and Breast cancer stem cells (BCSCs), we assessed the expression of H19 in breast cancer tissues and breast cancer cells
H19 expression was detected at higher levels in breast cancer cells than in breast epithelial cells and stemness-related factors OCT4, SOX2 and NANOG were expressed at higher levels in MDA-MB-231 cells compared with MCF-10A cells (Figure 1e and Supplementary Figure 1A)

Summary

Introduction

Breast cancer is the leading cause of cancer-related death among females worldwide.[1,2] early diagnosis and more effective treatment strategies have diminished the mortality rates in recent years,[3,4,5] the development of recurrence, metastasis and chemoresistance is, in most cases, still inevitable.[6]. A highly conserved RNA-binding protein LIN28 is a member of reprogramming factors acted in concert with KLF4, SOX2 and NANOG, to induce pluripotency in adult human fibroblast cells.[24,25] Accumulating evidence has indicated that LIN28 is overexpressed in advanced human malignancies and has a key role in the maintenance of CSCs.[26,27] LIN28A binds to conserved terminal loop of pre-let-7 elements and induce terminal uridylation (addition of uridine nucleotides) of pre-let[7] via recruitment of Zcchc[11], a terminal uridylyl transferase (TUTase) and TUT4.28 After that, DICER is unable to cleave uridylated pre-let-7 transcript, inhibiting the production of mature let-7 miRNAs (a key ‘keeper’ of the differentiated state of embryonic stem cells).[29] blockage of let-7 production and subsequent de-repression of let-7 miRNA target genes (RAS, MYC and HMGA2) by LIN28 has an essential function in CSC maintenance.[30,31] LIN28 posttranscriptionally upregulates LGR5 and PROM1 through let-7independent mechanism, promoting colon cancer progression and metastasis.[26]

Methods

Results

Conclusion