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A Luminal, Steroid Receptor-Positive Breast Cancer Stem Cell that Generates Intratumoral Heterogeneity is Preserved by Progesterone and Depleted by Estradiol

ABSTRACT: Most breast cancers are luminal, depending on estrogens for growth. The remainder lack estrogen receptors, are hormone-resistant and basal-like. It is thought that breast cancers arise from self-renewing normal stem cells that have undergone malignant transformation. However currently reported cancer stem cells are hormone insensitive and generate basal, rather than luminal tumors. We now describe true luminal hormone-responsive breast cancer stem cells that express estrogen and progesterone receptors. Their self-renewal capacity is protected by progesterone. Stem cell levels are depleted by estrogens as tumors transition into differentiated and homogeneous luminal states. But, if added to estrogens, progesterone promotes heterogeneity and “rescues” the stem cells. By keeping luminal cancer stem cells “safe”, progesterone, widely used for contraception and hormone replacement, could be harmful to breast cancer survivors or women with occult disease.

ORGANISM(S): Homo sapiens

PROVIDER: GSE65407 | GEO | 2016/01/31

SECONDARY ACCESSION(S): PRJNA273890

REPOSITORIES: GEO

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Project description:Breast cancer is a heterogeneous disease comprised of at least five major subtypes. Luminal subtype tumors confer a more favourable patient prognosis, which is in part, attributed to the Estrogen Receptor-alpha (ER) positivity and anti-hormone responsiveness of these tumors. Expression of the forkhead box transcription factor, FOXA1, also correlates with the luminal subtype and patient survival, but is present in a subset of ER-negative tumors. Similarly, FOXA1 is consistently expressed in luminal breast cancer cell lines even in the absence of ER. In contrast, basal breast cancer cell lines do not express FOXA1, and loss of FOXA1 in luminal cells increases migration and invasion, characteristics of the basal subtype. To delineate an ER-independent role for FOXA1 in maintaining the luminal phenotype, and hence a more favourable prognosis, we performed cDNA microarray analyses on luminal FOXA1-positive, ER-positive (MCF7, T47D) and FOXA1-positive, ER-negative (MDA-MB-453, SKBR3) cell lines in the presence or absence of transient FOXA1 silencing. This resulted in three FOXA1 transcriptomes: (1) a luminal-signature (consistent across cell lines), (2) an ER-positive signature (restricted to MCF7 and T47D) and (3) an ER-negative signature (restricted to MDA-MB-453 and SKBR3). Use of Gene Set Enrichment Analyses (GSEA) as a phenotyping tool revealed that FOXA1 silencing resulted in a transcriptome shift from luminal to basal gene expression signatures. FOXA1 binds to both luminal and basal genes within luminal breast cancer cells, suggesting that it not only transactivates luminal genes, but also represses basal-associated genes. From these results we conclude that FOXA1 controls plasticity between basal and luminal cells, playing a dominant role in repressing the basal phenotype, and thus tumor aggressiveness, in luminal breast cancer cells. Although it has been proposed that FOXA1-targeting agents may be useful for treating luminal tumors, these data suggest that this approach may promote transitions toward a more aggressive cancer. FOXA1 siRNA treated breast cell lines compared directly to nonspecific siRNA treated cell lines using Agilent 4X44 microarrays.

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A Luminal, Steroid Receptor-Positive Breast Cancer Stem Cell that Generates Intratumoral Heterogeneity is Preserved by Progesterone and Depleted by Estradiol

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