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.
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).
Many solid cancers are hierarchically organized with a small number of cancer stem cells (CSCs) able to regrow a tumor, while their progeny lacks this feature. Breast CSC is known to contribute to ...therapy resistance. The study of those cells is usually based on their cell‐surface markers like CD44high/CD24low/neg or their aldehyde dehydrogenase (ALDH) activity. However, these markers cannot be used to track the dynamics of CSC. Here, a transcriptomic analysis is performed to identify segregating gene expression in CSCs and non‐CSCs, sorted by Aldefluor assay. It is observed that among ALDH‐associated genes, only ALDH1A1 isoform is increased in CSCs. A CSC reporter system is then developed by using a far red‐fluorescent protein (mNeptune) under the control of ALDH1A1 promoter. mNeptune‐positive cells exhibit higher sphere‐forming capacity, tumor formation, and increased resistance to anticancer therapies. These results indicate that the reporter identifies cells with stemness characteristics. Moreover, live tracking of cells in a microfluidic system reveals a higher extravasation potential of CSCs. Live tracking of non‐CSCs under irradiation treatment show, for the first time, live reprogramming of non‐CSCs into CSCs. Therefore, the reporter will allow for cell tracking to better understand the implication of CSCs in breast cancer development and recurrence.
The apoptosis inducing receptor CD95/Fas has multiple tumorigenic activities. In different genetically engineered mouse models tumor-expressed CD95 was shown to be critical for cell growth. Using a ...combination of immune-deficient and immune-competent mouse models, we now establish that loss of CD95 in metastatic triple negative breast cancer (TNBC) cells prevents tumor growth by modulating the immune landscape. CD95-deficient, but not wild-type, tumors barely grow in an immune-competent environment and show an increase in immune infiltrates into the tumor. This growth reduction is caused by infiltrating NK cells and does not involve T cells or macrophages. In contrast, in immune compromised mice CD95 k.o. cells are not growth inhibited, but they fail to form metastases. In summary, we demonstrate that in addition to its tumor and metastasis promoting activities, CD95 expression by tumor cells can exert immune suppressive activities on NK cells, providing a new target for immune therapy.
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•CD95 expression promotes primary TNBC growth in immune-competent mice•CD95 KO TNBC cells do not metastasize in immune-deficient mice•Loss of CD95 triggers a pro-inflammatory program affecting the immune landscape•Loss of CD95 causes tumor destruction by NK cells in immune-competent mice
Immunology; Cell biology; Cancer
X inactivation (XCI) is triggered by upregulation of XIST, which coats the chromosome in cis, promoting formation of a heterochromatic domain (Xi). XIST role beyond initiation of XCI is only ...beginning to be elucidated. Here, we demonstrate that XIST loss impairs differentiation of human mammary stem cells (MaSCs) and promotes emergence of highly tumorigenic and metastatic carcinomas. On the Xi, XIST deficiency triggers epigenetic changes and reactivation of genes overlapping Polycomb domains, including Mediator subunit MED14. MED14 overdosage results in increased Mediator levels and hyperactivation of the MaSC enhancer landscape and transcriptional program, making differentiation less favorable. We further demonstrate that loss of XIST and Xi transcriptional instability is common among human breast tumors of poor prognosis. We conclude that XIST is a gatekeeper of human mammary epithelium homeostasis, thus unveiling a paradigm in the control of somatic cell identity with potential consequences for our understanding of gender-specific malignancies.
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•XIST-null cells display reactivation of a few X-linked genes, including MED14•MED14 overdosage impacts stem cell homeostasis through Mediator stabilization•Loss of XIST enhances the tumorigenic potential of cells upon transformation•Xi transcriptional reactivation is common among aggressive breast tumors
Outside the context of initiating X chromosome inactivation, XIST contributes to human mammary stem cell homeostasis, and loss of XIST and Xi transcriptional instabilities enhances tumorigenesis and is a common feature among human breast tumors with poor prognosis.
Abstract 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.
Abstract Many solid cancers are hierarchically organized with a small number of cancer stem cells (CSCs) able to regrow a tumor, while their progeny lacks this feature. Breast CSC is known to ...contribute to therapy resistance. The study of those cells is usually based on their cell‐surface markers like CD44 high /CD24 low/neg or their aldehyde dehydrogenase (ALDH) activity. However, these markers cannot be used to track the dynamics of CSC. Here, a transcriptomic analysis is performed to identify segregating gene expression in CSCs and non‐CSCs, sorted by Aldefluor assay. It is observed that among ALDH‐associated genes, only ALDH1A1 isoform is increased in CSCs. A CSC reporter system is then developed by using a far red‐fluorescent protein (mNeptune) under the control of ALDH1A1 promoter. mNeptune‐positive cells exhibit higher sphere‐forming capacity, tumor formation, and increased resistance to anticancer therapies. These results indicate that the reporter identifies cells with stemness characteristics. Moreover, live tracking of cells in a microfluidic system reveals a higher extravasation potential of CSCs. Live tracking of non‐CSCs under irradiation treatment show, for the first time, live reprogramming of non‐CSCs into CSCs. Therefore, the reporter will allow for cell tracking to better understand the implication of CSCs in breast cancer development and recurrence.
Abstract Many solid cancers are hierarchically organized with a small number of cancer stem cells (CSCs) able to regrow a tumor, while their progeny lacks this feature. Breast CSC is known to ...contribute to therapy resistance. The study of those cells is usually based on their cell‐surface markers like CD44 high /CD24 low/neg or their aldehyde dehydrogenase (ALDH) activity. However, these markers cannot be used to track the dynamics of CSC. Here, a transcriptomic analysis is performed to identify segregating gene expression in CSCs and non‐CSCs, sorted by Aldefluor assay. It is observed that among ALDH‐associated genes, only ALDH1A1 isoform is increased in CSCs. A CSC reporter system is then developed by using a far red‐fluorescent protein (mNeptune) under the control of ALDH1A1 promoter. mNeptune‐positive cells exhibit higher sphere‐forming capacity, tumor formation, and increased resistance to anticancer therapies. These results indicate that the reporter identifies cells with stemness characteristics. Moreover, live tracking of cells in a microfluidic system reveals a higher extravasation potential of CSCs. Live tracking of non‐CSCs under irradiation treatment show, for the first time, live reprogramming of non‐CSCs into CSCs. Therefore, the reporter will allow for cell tracking to better understand the implication of CSCs in breast cancer development and recurrence.
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.
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