An integrated transcriptional regulatory circuit that reinforces the breast cancer stem cell state

Abstract

Cancer stem-like cells (CSCs) are a highly tumorigenic cell type present as a minority population in developmentally diverse tumors and cell lines. Using a genetic screen in an inducible model of CSC formation in a breast cell line, we identify microRNAs (miRNAs) that inhibit CSC growth and are down-regulated in CSCs. Aside from the previously identified miR-200 family, these include the miR-15/16 (miR-16, miR-15b) and miR-103/107 (miR-103, miR-107) families as well as miR-145, miR-335, and miR-128b. Interestingly, these miRNAs affect common target genes that encode the Bmi1 and Suz12 components of the polycomb repressor complexes as well as the DNA-binding transcription factors Zeb1, Zeb2, and Klf4. Conversely, expression of the CSC-modulating miRNAs is inhibited by Zeb1 and Zeb2. There is an inverse relationship between the levels of CSC-regulating miRNAs and their respective targets in samples from triple-negative breast cancer patients, providing evidence for the relevance of these interactions in human cancer. In addition, combinatorial overexpression of these miRNAs progressively attenuates the growth of CSCs derived from triple-negative breast cancers. These observations suggest that CSC formation and function are reinforced by an integrated regulatory circuit of miRNAs, transcription factors, and chromatin-modifying activities that can act as a bistable switch to drive cells into either the CSC or the nonstem state within the population of cancer cells.

The Complex Nature of Breast Cancer Stem-Like Cells: Heterogeneity and Plasticity

“…These data are evidence of the important relationship between p53 and miRNAs in the regulation of the conversion of non-stem breast cancer cells to bCSCs [41]. Polytarchou et al [42] investigated the role of miRNAs in a cell line model of inducible bCSC formation: activation of the Src oncogene in the MCF10A line induces a cellular transformation which includes the production of bCSCs. By transfecting bCSCs from this model with a library of 355 miRNAs, a number were identified as capable of inhibiting bCSCs growth by at least 50%, these included miRs 200, let7, 15, 16, 103, 1107, 145, 335 and 128b.…”

“…Low levels of these miRNAs and high levels of their targets were observed in bCSCs isolated from breast tumour samples but this inverse relationship was most significant in tumour samples which were triple-negative or basal-like. Although not direct evidence of plasticity, any plasticity occurring between the non-stem and bCSC populations investigated may require the downregulation of these microRNAs [42].…”

MicroRNAs, a subpopulation of regulators, are involved in breast cancer progression through regulating breast cancer stem cells (Review)

“…Individual upregulation of these miRNAs restrains the formation of mammospheres by at least 50%. The miR-200 family directly targets the stem cell transcription factor KLF4, enhancer of zeste 2 polycomb repressive complex 2 subunit (EZH2) and polycomb complex protein BMI1 (BMI1) (24). Additionally, miR-200 also targets and inhibits the suppressor of zeste 12 (SUZ12) (25) and BMI1 (26), which, respectively, are are subunits of the polycomb repressive complex (PRC) 2 and PRC1 that repress transcription.…”

Xenopatients 2.0: Reprogramming the epigenetic landscapes of patient-derived cancer genomes

“…CSCs are also made and not just born; individual tumors generally harbor multiple phenotypically or genetically distinct CSCs, because differentiated normal or non-stem cell tumor cells gain CSC cellular properties via the activation of partially known paths to stemness. [14][15][16][17][18][19][20][21][22][23] Critically, "stemness" is an emergent dynamicl state rather than the direct consequence of the activity of a particular stemness gene or a set of stemness genes. The CSC cellular state continuously evolves, and it can be switched on or off in response to cell-intrinsic or microenvironmental cues, including therapeutics.…”