Cancer stem cells (CSCs) represent a subset of cells within tumours that exhibit self-renewal properties and the capacity to seed tumours. CSCs are typically refractory to conventional treatments and ...have been associated to metastasis and relapse. Salinomycin operates as a selective agent against CSCs through mechanisms that remain elusive. Here, we provide evidence that a synthetic derivative of salinomycin, which we named ironomycin (AM5), exhibits a more potent and selective activity against breast CSCs in vitro and in vivo, by accumulating and sequestering iron in lysosomes. In response to the ensuing cytoplasmic depletion of iron, cells triggered the degradation of ferritin in lysosomes, leading to further iron loading in this organelle. Iron-mediated production of reactive oxygen species promoted lysosomal membrane permeabilization, activating a cell death pathway consistent with ferroptosis. These findings reveal the prevalence of iron homeostasis in breast CSCs, pointing towards iron and iron-mediated processes as potential targets against these cells.
Breast cancer stem cells (bCSCs) have been implicated in tumor progression and therapeutic resistance; however, the molecular mechanisms that define this state are unclear. We have performed two ...microRNA (miRNA) gain- and loss-of-function screens to identify miRNAs that regulate the choice between bCSC self-renewal and differentiation. We find that micro-RNA (miR)-600 silencing results in bCSC expansion, while its overexpression reduces bCSC self-renewal, leading to decreased in vivo tumorigenicity. miR-600 targets stearoyl desaturase 1 (SCD1), an enzyme required to produce active, lipid-modified WNT proteins. In the absence of miR-600, WNT signaling is active and promotes self-renewal, whereas overexpression of miR-600 inhibits the production of active WNT and promotes bCSC differentiation. In a series of 120 breast tumors, we found that a low level of miR-600 is correlated with active WNT signaling and a poor prognosis. These findings highlight a miR-600-centered signaling network that governs bCSC-fate decisions and influences tumor progression.
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•miR-600 expression balances self-renewal and differentiation of bCSCs•miR-600 acts as a regulator of WNT signaling through SCD1 modulation•Low miR-600 expression in breast tumors is associated with poor prognosis
El Helou et al. identify miRNAs that are able to balance bCSC fate. They find that miR-600 silencing results in bCSC expansion, while its overexpression reduces bCSC self-renewal. miR-600 was further found to regulate WNT signaling through SCD1, and miR-600 expression correlates with clinical outcome.
Replication stress (RS) has a pivotal role in tumor initiation, progression, or therapeutic resistance. In this study, we depicted the mechanism of breast cancer stem cells' (bCSCs) response to RS ...and its clinical implication. We demonstrated that bCSCs present a limited level of RS compared with non-bCSCs in patient samples. We described for the first time that the spatial nuclear location of BMI1 protein triggers RS response in breast cancers. Hence, in bCSCs, BMI1 is rapidly located to stalled replication forks to recruit RAD51 and activate homologous-recombination machinery, whereas in non-bCSCs BMI1 is trapped on demethylated 1q12 megasatellites precluding effective RS response. We further demonstrated that BMI1/RAD51 axis activation is necessary to prevent cisplatin-induced DNA damage and that treatment of patient-derived xenografts with a RAD51 inhibitor sensitizes tumor-initiating cells to cisplatin. The comprehensive view of replicative-stress response in bCSC has profound implications for understanding and improving therapeutic resistance.
There is increasing evidence that breast tumors are organized in a hierarchy, with a subpopulation of tumorigenic cancer cells, the cancer stem cells (CSCs), which sustain tumor growth. The ...characterization of protein networks that govern CSC behavior is paramount to design new therapeutic strategies targeting this subpopulation of cells. We have sought to identify specific molecular pathways of CSCs isolated from 13 different breast cancer cell lines of luminal or basal/mesenchymal subtypes. We compared the gene expression profiling of cancer cells grown in adherent conditions to those of matched tumorsphere cultures. No specific pathway was identified to be commonly regulated in luminal tumorspheres, resulting from a minor CSC enrichment in tumorsphere passages from luminal cell lines. However, in basal/mesenchymal tumorspheres, the enzymes of the mevalonate metabolic pathway were overexpressed compared to those in cognate adherent cells. Inhibition of this pathway with hydroxy-3-methylglutaryl CoA reductase blockers resulted in a reduction of breast CSC independent of inhibition of cholesterol biosynthesis and of protein farnesylation. Further modulation of this metabolic pathway demonstrated that protein geranylgeranylation (GG) is critical to breast CSC maintenance. A small molecule inhibitor of the geranylgeranyl transferase I (GGTI) enzyme reduced the breast CSC subpopulation both in vitro and in primary breast cancer xenografts. We found that the GGTI effect on the CSC subpopulation is mediated by inactivation of Ras homolog family member A (RHOA) and increased accumulation of P27(kip1) in the nucleus. The identification of protein GG as a major contributor to CSC maintenance opens promising perspectives for CSC targeted therapy in basal breast cancer.
Cancer stem-like cells (CSC) have been widely studied, but their clinical relevance has yet to be established in breast cancer. Here, we report the establishment of primary breast tumor-derived ...xenografts (PDX) that encompass the main diversity of human breast cancer and retain the major clinicopathologic features of primary tumors. Successful engraftment was correlated with the presence of ALDH1-positive CSCs, which predicted prognosis in patients. The xenografts we developed showed a hierarchical cell organization of breast cancer with the ALDH1-positive CSCs constituting the tumorigenic cell population. Analysis of gene expression from functionally validated CSCs yielded a breast CSC signature and identified a core transcriptional program of 19 genes shared with murine embryonic, hematopoietic, and neural stem cells. This generalized stem cell program allowed the identification of potential CSC regulators, which were related mainly to metabolic processes. Using an siRNA genetic screen designed to target the 19 genes, we validated the functional role of this stem cell program in the regulation of breast CSC biology. Our work offers a proof of the functional importance of CSCs in breast cancer, and it establishes the reliability of PDXs for use in developing personalized CSC therapies for patients with breast cancer.
The cancer stem cell (CSC) hypothesis implicates the development of new therapeutic approaches to target the CSC population. Characterization of the pathways that regulate CSCs activity will ...facilitate the development of targeted therapies. We recently reported that the enzymatic activity of ALDH1, as measured by the ALDELFUOR assay, can be utilized to isolate normal and malignant breast stem cells in both primary tumors and cell lines. In this study, utilizing a tumorsphere assay, we have demonstrated the role of retinoid signaling in the regulation of breast CSCs self-renewal and differentiation. Utilizing the gene set enrichment analysis (GSEA) algorithm we identified gene sets and pathways associated with retinoid signaling. These pathways regulate breast CSCs biology and their inhibition may provide novel therapeutic approaches to target breast CSCs.
Therapeutic resistance is a major clinical challenge in oncology. Evidence identifies cancer stem cells (CSCs) as a driver of tumor evolution. Accordingly, the key stemness property unique to CSCs ...may represent a reservoir of therapeutic target to improve cancer treatment. Here, we carried out a genome‐wide RNA interference screen to identify genes that regulate breast CSCs‐fate (bCSC). Using an interactome/regulome analysis, we integrated screen results in a functional mapping of the CSC‐related processes. This network analysis uncovered potential therapeutic targets controlling bCSC‐fate. We tested a panel of 15 compounds targeting these regulators. We showed that mifepristone, salinomycin, and JQ1 represent the best anti‐bCSC activity. A combination assay revealed a synergistic interaction of salinomycin/JQ1 association to deplete the bCSC population. Treatment of primary breast cancer xenografts with this combination reduced the tumor‐initiating cell population and limited metastatic development. The clinical relevance of our findings was reinforced by an association between the expression of the bCSC‐related networks and patient prognosis. Targeting bCSCs with salinomycin/JQ1 combination provides the basis for a new therapeutic approach in the treatment of breast cancer.
Synopsis
The development of cancer stem cell‐targeting therapies is of major interest and requires insight into the underlying mechanisms. In this study, a genome‐wide RNAi screen was established, and revealed essential therapeutic targets of breast cancer stem cells (bCSC).
bCSC‐related processes were identified by functional mapping integrating RNAi screens.
bCSC‐related processes represented a reservoir of therapeutic target.
Salinomycin synergized with JQ1 treatment to reduce the bCSC population and limit tumor progression.
bCSC‐related processes were associated with poor prognosis in breast cancer patients.
The development of cancer stem cell‐targeting therapies is of major interest and requires insight into the underlying mechanisms. In this study, a genome‐wide RNAi screen was established, and revealed essential therapeutic targets of breast cancer stem cells (bCSC).
Primary human mammary epithelial cells (pHMECs) are known to be remarkably difficult to engineer genetically. Here, we present a protocol for efficient transduction of pHMECs using a baboon ...retroviral envelope glycoprotein for pseudotyping of lentiviral vectors (BaEV-LVs). We describe the preparation of the BaEV-LVs, the isolation of pHMECs from breast samples, and the subsequent transduction of pHMECs. We also detail the use of CRISPRi technology to efficiently silence gene expression in pHMECs, which can then be used for functional assays.
For complete details on the use and execution of this protocol, please refer to Richart et al. (2022).1
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•Protocol to produce baboon envelope pseudotyped lentiviral vectors•Isolation of primary human mammary epithelial cells (pHMECS) from breast samples•Engineering of pHMECs with CRISPRi technology and lentiviral transduction•Flow-cytometry-based sorting of CRISPRi-engineered pHMECs
Publisher’s note: Undertaking any experimental protocol requires adherence to local institutional guidelines for laboratory safety and ethics.
Primary human mammary epithelial cells (pHMECs) are known to be remarkably difficult to engineer genetically. Here, we present a protocol for efficient transduction of pHMECs using a baboon retroviral envelope glycoprotein for pseudotyping of lentiviral vectors (BaEV-LVs). We describe the preparation of the BaEV-LVs, the isolation of pHMECs from breast samples, and the subsequent transduction of pHMECs. We also detail the use of CRISPRi technology to efficiently silence gene expression in pHMECs, which can then be used for functional assays.
Luminal B breast cancers represent a fraction of oestrogen receptor (ER)‐positive tumours associated with poor recurrence‐free and disease‐specific survival in all adjuvant systemic treatment ...categories including hormone therapy alone. Identification of specific signalling pathways driving luminal B biology is paramount to improve treatment. We have studied 100 luminal breast tumours by combined analysis of genome copy number aberrations and gene expression. We show that amplification of the ZNF703 gene, located in chromosomal region 8p12, preferentially occurs in luminal B tumours. We explored the functional role of ZNF703 in luminal B tumours by overexpressing ZNF703 in the MCF7 luminal cell line. Using mass spectrometry, we identified ZNF703 as a co‐factor of a nuclear complex comprising DCAF7, PHB2 and NCOR2. ZNF703 expression results in the activation of stem cell‐related gene expression leading to an increase in cancer stem cells. Moreover, we show that ZNF703 is implicated in the regulation of ER and E2F1 transcription factor. These findings point out the prominent role of ZNF703 in transcription modulation, stem cell regulation and luminal B oncogenesis.
→See accompanying Closeup by Vessela Kristensen DOI 10.1002/emmm201100128
Tumor initiation, progression, and therapeutic resistance have been proposed to originate from a subset of tumor cells, cancer stem cells (CSCs). However, the current understanding of the mechanisms ...involved in their self-renewal and tumor initiation capacity remains limited. Here, we report that expression of LANO/LRRC1, the vertebrate paralog of SCRIB tumor suppressor, is associated with a stem cell signature in normal and tumoral mammary epithelia. Through in vitro and in vivo experiments including a Lano/Lrrc1 knockout mouse model, we demonstrate its involvement in the regulation of breast CSC (bCSC) fate. Mechanistically, we demonstrate that Lano/LRRC1-depleted cells secrete increased levels of WNT ligands, which act in a paracrine manner to positively deregulate the WNT/β-catenin pathway in bCSCs. In addition to describing the first function of LANO/LRRC1, our results suggest that its expression level could be used as a biomarker to stratify breast cancer patients who could benefit from WNT/β-catenin signaling inhibitors.
•Lano/LRRC1 expression level is associated with stem cell transcription signatures•Lano/LRRC1 is involved in the regulation of breast cancer stem cell fate•Lano/LRRC1 represses WNT ligand secretion
In this article, Santoni and colleagues report that expression of LANO/LRRC1, the paralog of SCRIB tumor suppressor, is associated with normal and tumoral mammary stem cell signature. Lano/LRRC1 represses expansion of cancer stem cell pool through inhibition of WNT ligand secretion and related WNT/β-catenin pathway activation. LANO/LRRC1 might have theranostic value to steer patient treatment by WNT/β-catenin signaling inhibitors.
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