Angera H. Kuo

miR-142 regulates the tumorigenicity of human breast cancer stem cells through the canonical WNT signaling pathway

MicroRNAs (miRNAs) are important regulators of stem and progenitor cell functions. We previously reported that miR-142 and miR-150 are upregulated in human breast cancer stem cells (BCSCs) as compared to the non-tumorigenic breast cancer cells. In this study, we report that miR-142 efficiently recruits the APC mRNA to an RNA-induced silencing complex, activates the canonical WNT signaling pathway in an APC-suppression dependent manner, and activates the expression of miR-150. Enforced expression of miR-142 or miR-150 in normal mouse mammary stem cells resulted in the regeneration of hyperproliferative mammary glands in vivo. Knockdown of endogenous miR-142 effectively suppressed organoid formation by BCSCs and slowed tumor growth initiated by human BCSCs in vivo. These results suggest that in some tumors, miR-142 regulates the properties of BCSCs at least in part by activating the WNT signaling pathway and miR-150 expression. DOI: http://dx.doi.org/10.7554/eLife.01977.001

Targeting Unique Metabolic Properties of Breast Tumor Initiating Cells

Normal stem cells from a variety of tissues display unique metabolic properties compared to their more differentiated progeny. However, relatively little is known about metabolic properties of cancer stem cells, also called tumor initiating cells (TICs). In this study we show that, analogous to some normal stem cells, breast TICs have distinct metabolic properties compared to nontumorigenic cancer cells (NTCs). Transcriptome profiling using RNA‐Seq revealed TICs underexpress genes involved in mitochondrial biology and mitochondrial oxidative phosphorylation, and metabolic analyses revealed TICs preferentially perform glycolysis over oxidative phosphorylation compared to NTCs. Mechanistic analyses demonstrated that decreased expression and activity of pyruvate dehydrogenase (Pdh), a key regulator of oxidative phosphorylation, plays a critical role in promoting the proglycolytic phenotype of TICs. Metabolic reprogramming via forced activation of Pdh preferentially eliminated TICs both in vitro and in vivo. Our findings reveal unique metabolic properties of TICs and demonstrate that metabolic reprogramming represents a potential therapeutic strategy for targeting these cells. Stem Cells 2014;32:1734–1745

A cell-intrinsic role for TLR2–MYD88 in intestinal and breast epithelia and oncogenesis

It has been postulated that there is a link between inflammation and cancer. Here we describe a role for cell-intrinsic toll-like receptor-2 (TLR2; which is involved in inflammatory response) signalling in normal intestinal and mammary epithelial cells and oncogenesis. The downstream effectors of TLR2 are expressed by normal intestinal and mammary epithelia, including the stem/progenitor cells. Deletion of MYD88 or TLR2 in the intestinal epithelium markedly reduces DSS-induced colitis regeneration and spontaneous tumour development in mice. Limiting dilution transplantations of breast epithelial cells devoid of TLR2 or MYD88 revealed a significant decrease in mammary repopulating unit frequency compared with the control. Inhibition of TLR2, its co-receptor CD14, or its downstream targets MYD88 and IRAK1 inhibits growth of human breast cancers in vitro and in vivo. These results suggest that inhibitors of the TLR2 pathway merit investigation as possible therapeutic and chemoprevention agents.

Neuregulin Autocrine Signaling Promotes Self-Renewal of Breast Tumor-Initiating Cells by Triggering HER2/HER3 Activation

Currently, only patients with HER2-positive tumors are candidates for HER2-targeted therapies. However, recent clinical observations suggest that the survival of patients with HER2-low breast cancers, who lack HER2 amplification, may benefit from adjuvant therapy that targets HER2. In this study, we explored a mechanism through which these benefits may be obtained. Prompted by the hypothesis that HER2/HER3 signaling in breast tumor-initiating cells (TIC) promotes self-renewal and survival, we obtained evidence that neuregulin 1 (NRG1) produced by TICs promotes their proliferation and self-renewal in HER2-low tumors, including in triple-negative breast tumors. Pharmacologic inhibition of EGFR, HER2, or both receptors reduced breast TIC survival and self-renewal in vitro and in vivo and increased TIC sensitivity to ionizing radiation. Through a tissue microarray analysis, we found that NRG1 expression and associated HER2 activation occurred in a subset of HER2-low breast cancers. Our results offer an explanation for why HER2 inhibition blocks the growth of HER2-low breast tumors. Moreover, they argue that dual inhibition of EGFR and HER2 may offer a useful therapeutic strategy to target TICs in these tumors. In generating a mechanistic rationale to apply HER2-targeting therapies in patients with HER2-low tumors, this work shows why these therapies could benefit a considerably larger number of patients with breast cancer than they currently reach.

Identifying the metastatic seeds of breast cancer

Two studies show that circulating tumor cells from breast cancer patients give rise to metastases in mice.

Role of epithelial to mesenchymal transition associated genes in mammary gland regeneration and breast tumorigenesis

Previous studies have proposed that epithelial to mesenchymal transition (EMT) in breast cancer cells regulates metastasis, stem cell properties and chemo-resistance; most studies were based on in vitro culture of cell lines and mouse transgenic cancer models. However, the identity and function of cells expressing EMT-associated genes in normal murine mammary gland homeostasis and human breast cancer still remains under debate. Using in vivo lineage tracing and triple negative breast cancer (TNBC) patient derived xenografts we demonstrate that the repopulating capacity in normal mammary epithelial cells and tumorigenic capacity in TNBC is independent of expression of EMT-associated genes. In breast cancer, while a subset of cells with epithelial and mesenchymal phenotypes have stem cell activity, in many cells that have lost epithelial characteristics with increased expression of mesenchymal genes, have decreased tumor-initiating capacity and plasticity. These findings have implications for the development of effective therapeutic agents targeting tumor-initiating cells.The contribution of EMT in mammary gland homeostasis and human breast cancer is still unclear. Here, using in vivo lineage tracing and breast cancer PDXs the authors demonstrate that the repopulating capacity in normal mammary epithelial cells and tumorigenic capacity in breast cancer is independent of expression of EMT-associated genes.

Cell-intrinsic TLR2/MyD88 pathway in breast and colon cancer

Breast and colon cancers are the leading causes of cancer related deaths in western countries. Both cancers originate from an epithelial compartment, which has a cellular hierarchy. This hierarchy is defined by cells with self-renewal capacity and cells that are differentiated without self-renewal capacity and thus have limited proliferative capacity. Although the cellular hierarchies of the mammary gland and the intestinal tract have been and are currently under intense investigation, several findings still require further clarification (e.g., the presence or the absence of a bipotent stem cell compartment in the mammary gland.1,2)

CDK19 is a Regulator of Triple-Negative Breast Cancer Growth

Triple-negative breast cancer (TNBC) is a poor prognosis disease with no clinically approved targeted therapies. Here, using in vitro and in vivo RNA interference (RNAi) screens in TNBC patient-derived xenografts (PDX), we identify cyclin dependent kinase 19 (CDK19) as a potential therapeutic target. Using in vitro and in vivo TNBC PDX models, we validated the inhibitory effect of CDK19 knockdown on tumor initiation, proliferation and metastases. Despite this, CDK19 knockdown did not affect the growth of non-transformed mammary epithelial cells. Using CD10 and EpCAM as novel tumor initiating cell (TIC) markers, we found the EpCAMmed/high/CD10−/low TIC sub-population to be enriched in CDK19 and a putative cellular target of CDK19 inhibition. Comparative gene expression analysis of CDK19 and CDK8 knockdowns revealed that CDK19 regulates a number of cancer-relevant pathways, uniquely through its own action and others in common with CDK8. Furthermore, although it is known that CDK19 can act at enhancers, our CHIP-Seq studies showed that CDK19 can also epigenetically modulate specific H3K27Ac enhancer signals which correlate with gene expression changes. Finally, to assess the potential therapeutic utility of CDK19, we showed that both CDK19 knockdown and chemical inhibition of CDK19 kinase activity impaired the growth of pre-established PDX tumors in vivo. Current strategies inhibiting transcriptional co-factors and targeting TICs have been limited by toxicity to normal cells. Because of CDK19’s limited tissue distribution and the viability of CDK19 knockout mice, CDK19 represents a promising therapeutic target for TNBC.