Steroid induction of therapy-resistant cytokeratin-5-positive cells in estrogen receptor-positive breast cancer through a BCL6-dependent mechanism.
ABSTRACT: Therapy resistance remains a major problem in estrogen receptor-? (ER?)-positive breast cancer. A subgroup of ER?-positive breast cancer is characterized by mosaic presence of a minor population of ER?-negative cancer cells expressing the basal cytokeratin-5 (CK5). These CK5-positive cells are therapy resistant and have increased tumor-initiating potential. Although a series of reports document induction of the CK5-positive cells by progestins, it is unknown if other 3-ketosteroids share this ability. We now report that glucocorticoids and mineralocorticoids effectively expand the CK5-positive cell population. CK5-positive cells induced by 3-ketosteroids lacked ER? and progesterone receptors, expressed stem cell marker, CD44, and displayed increased clonogenicity in soft agar and broad drug-resistance in vitro and in vivo. Upregulation of CK5-positive cells by 3-ketosteroids required induction of the transcriptional repressor BCL6 based on suppression of BCL6 by two independent BCL6 small hairpin RNAs or by prolactin. Prolactin also suppressed 3-ketosteroid induction of CK5+ cells in T47D xenografts in vivo. Survival analysis with recursive partitioning in node-negative ER?-positive breast cancer using quantitative CK5 and BCL6 mRNA or protein expression data identified patients at high or low risk for tumor recurrence in two independent patient cohorts. The data provide a mechanism by which common pathophysiological or pharmacologic elevations in glucocorticoids or other 3-ketosteroids may adversely affect patients with mixed ER?+/CK5+ breast cancer. The observations further suggest a cooperative diagnostic utility of CK5 and BCL6 expression levels and justify exploring efficacy of inhibitors of BCL6 and 3-ketosteroid receptors for a subset of ER?-positive breast cancers.
Project description:BCL6 is a transcriptional repressor that recognizes DNA target sequences similar to those recognized by signal transducer and activator of transcriptions 5 (Stat5). BCL6 disrupts differentiation of breast epithelia, is downregulated during lactation, and is upregulated in poorly differentiated breast cancer. In contrast, Stat5a mediates prolactin-induced differentiation of mammary epithelia, and loss of Stat5 signaling in human breast cancer is associated with undifferentiated histology and poor prognosis. Here, we identify the mammary cell growth factor prolactin as a potent suppressor of BCL6 protein expression in human breast cancer through a mechanism that requires Stat5a, but not prolactin-activated Stat5b, MEK-ERK, or PI3K-AKT pathways. Prolactin rapidly suppressed BCL6 mRNA in T47D, MCF7, ZR75.1, and SKBr3 breast cancer cell lines, followed by prolonged reduction of BCL6 protein levels within 3 hours. Prolactin suppression of BCL6 was enhanced by overexpression of Stat5a but not Stat5b, was mimicked by constitutively active Stat5a, but did not require the transactivation domain of Stat5a. Stat5 chromatin immunoprecipitation demonstrated physical interaction with a BCL6 gene regulatory region, and BCL6 transcript repression required histone deacetylase activity based on sensitivity to trichostatin A. Functionally, BCL6 overexpression disrupted prolactin induction of Stat5 reporter genes. Prolactin suppression of BCL6 was extended to xenotransplant tumors in nude mice in vivo and to freshly isolated human breast cancer explants ex vivo. Quantitative immunohistochemistry revealed elevated BCL6 in high-grade and metastatic breast cancer compared with ductal carcinoma in situ and nonmalignant breast, and cellular BCL6 protein levels correlated negatively with nuclear Stat5a (r = -0.52; P < 0.001) but not with Stat5b. Loss of prolactin-Stat5a signaling and concomitant upregulation of BCL6 may represent a regulatory switch facilitating undifferentiated histology and poor prognosis of breast cancer.
Project description:Estrogen receptor (ER) positive breast cancers often contain subpopulations of cells that express the intermediate filament protein cytokeratin 5 (CK5). CK5+ cells are enriched in cancer stem cell (CSC) properties, can be induced by progestins, and predict poor prognosis in ER+ breast cancer. We established through CK5 knockout and overexpression in ER+ breast cancer cell lines that CK5 is important for tumorsphere formation, prompting us to speculate that CK5 has regulatory activity in CSCs. To interrogate CK5 interacting proteins that may be functionally cooperative, we performed immunoprecipitation-mass spectrometry for CK5 in ER+ breast cancer cells. Focusing on proteins with signaling activity, we identified ?-catenin, a key transcription factor of the Wnt signaling pathway and cell adhesion molecule, as a CK5 interactor, which we confirmed by co-immunoprecipitation in several breast cancer models. We interrogated the dual functions of ?-catenin in relation to CK5. Knockout or knockdown of CK5 ablated ?-catenin transcriptional activity in response to progestins and Wnt stimuli. Conversely, CK5 induced by progestins or overexpression was sufficient to promote the loss of ?-catenin at the cell membrane and total E-cadherin loss. A breast cancer patient-derived xenograft showed similar loss of membrane ?-catenin and E-cadherin in CK5+ but not intratumoral CK5- cells and single-cell RNA sequencing found the top enriched pathways in the CK5+ cell cluster were cell junction remodeling and signaling. This report highlights that CK5 actively remodels cell morphology and that blockade of CK5-?-catenin interaction may reverse the detrimental properties of CK5+ breast cancer cells.
Project description:Progestins play a deleterious role in the onset of breast cancer, yet their influence on existing breast cancer and tumor progression is not well understood. In luminal estrogen receptor (ER)- and progesterone receptor (PR)-positive breast cancer, progestins induce a fraction of cells to express cytokeratin 5 (CK5), a marker of basal epithelial and progenitor cells in the normal breast. CK5(+) cells lose expression of ER and PR and are relatively quiescent, increasing their resistance to endocrine and chemotherapy compared to intratumoral CK5(-)ER(+)PR(+) cells. Characterization of live CK5(+) cells has been hampered by a lack of means for their direct isolation. Here, we describe optical (GFP) and bioluminescent (luciferase) reporter models to quantitate and isolate CK5(+) cells in luminal breast cancer cell lines utilizing the human KRT5 gene promoter and a viral vector approach. Using this system, we confirmed that the induction of GFP(+)/CK5(+) cells is specific to progestins, is dependent on PR, can be blocked by antiprogestins, and does not occur with other steroid hormones. Progestin-induced, fluorescence-activated cell sorting-isolated CK5(+) cells had lower ER and PR mRNA, were slower cycling, and were relatively more invasive and sphere forming than their CK5(-) counterparts in vitro. Repeated progestin treatment and selection of GFP(+) cells enriched for a persistent population of CK5(+) cells, suggesting that this transition can be semi-permanent. These data support that in PR(+) breast cancers, progestins induce a subpopulation of CK5(+)ER(-)PR(-) cells with enhanced progenitor properties and have implications for treatment resistance and recurrence in luminal breast cancer.
Project description:There are two major subtypes of human breast cancers: the luminal, estrogen, and progesterone receptor-positive, cytokeratin 18-positive (ER(+)PR(+)CK18(+)) subtype, and the basal ER(-)PR(-)CK18(-)CK5(+) subtype. Tumor-initiating cells (CD44(+)) have been described for human breast cancers; whether these are common to the two subtypes is unknown. We have identified a rare population of cells that are both CD44(+) and ER(-)PR(-)CK5(+) in luminal-like ER(+)PR(+) T47D human breast tumor xenografts. The tumor-isolated CD44(+) cell fraction was highly enriched for clonogenic (in vitro culture) and tumorigenic (in vivo reimplantation) cells compared with the CD44(-) cell fraction. Rare ER(-)PR(-)CK5(+) cells were present within CD44(+)-derived colonies. Tumor-isolated cells placed in minimal media also contained rare ER(-)PR(-)CK5(+) cells at early time points (<10 cells); however, this population did not expand with increasing colony size. The number of ER(+)PR(+)CK5(-) cells, conversely, increased linearly with colony growth. Similary, tumors originating in vivo from CD44(+) cells contained a rare static ER(-)PR(-)CK5(+) population, an intermediate ER(-)PR(-)CK5(-) population, and an expanding ER(+)PR(+)CK5(-) population. Putative ER(+)PR(+)CK5(+) transitional cells could be seen only in colonies or tumors treated with a progestin. We propose that luminal ER(+)PR(+) breast tumors contain a minor ER(-)PR(-)CK5(+) population that has the capacity to generate the majority of ER(+)PR(+)CK18(+)CK5(-) cells. Luminal breast cancers are treated with endocrine therapies that target ER. The rare ER(-)PR(-)CK5(+) progenitor cells would escape such treatments and survive to repopulate the tumor.
Project description:OBJECTIVE:Cytokeratin 5 (CK5) is an epithelial cell marker implicated in stem and progenitor cell activity in glandular reproductive tissues and endocrine and chemotherapy resistance in estrogen receptor (ER)(+) breast cancer. The goal of this study was to determine the prevalence of CK5 expression in ovarian cancer and the response of CK5(+) cell populations to cisplatin therapy. MATERIALS AND METHODS:Cytokeratin 5 expression was evaluated in 2 ovarian tissue microarrays, representing 137 neoplasms, and 6 ovarian cancer cell lines. Cell lines were treated with IC(50) (half-maximal inhibitory concentration) cisplatin, and the prevalence of CK5(+) cells pretreatment and posttreatment was determined. Proliferation of CK5(+) versus CK5(-) cell populations was determined using 5-bromo-2'-deoxyuridine incorporation. Chemotherapy-induced apoptosis in CK5(+) versus CK5(-) cells was measured using immunohistochemical staining for cleaved caspase-3. RESULTS:Cytokeratin 5 was expressed in 39.3% (42 of 107) of epithelial ovarian cancers with a range of 1% to 80% positive cells. Serous and endometrioid histologic subtypes had the highest percentage of CK5(+) specimens. Cytokeratin 5 expression correlated with ER positivity (38 of 42 CK5(+) tumors were also ER(+)). Cytokeratin 5 was expressed in 5 of 6 overall and 4 of 4 ER(+) epithelial ovarian cancer cell lines ranging from 2.4% to 52.7% positive cells. Cytokeratin 5(+) compared with CK5(-) cells were slower proliferating. The prevalence of CK5(+) cells increased after 48-hour cisplatin treatment in 4 of 5 cell lines tested. Cytokeratin 5(+) ovarian cancer cells compared with CK5(-) ovarian cancer cells were more resistant to cisplatin-induced apoptosis. CONCLUSIONS:Cytokeratin 5 is expressed in a significant proportion of epithelial ovarian cancers and represents a slower proliferating chemoresistant subpopulation that may warrant cotargeting in combination therapy.
Project description:Breast cancers expressing hormone receptors for estrogen (ER) and progesterone (PR) represent ~70% of all cases and are treated with both ER-targeted and chemotherapies, with near 40% becoming resistant. We have previously described that in some ER(+) tumors, the resistant cells express cytokeratin 5 (CK5), a putative marker of breast stem and progenitor cells. CK5(+) cells have lost expression of ER and PR, express the tumor-initiating cell surface marker CD44, and are relatively quiescent. In addition, progestins, which increase breast cancer incidence, expand the CK5(+) subpopulation in ER(+)PR(+) breast cancer cell lines. We have developed models to induce and quantitate CK5(+)ER(-)PR(-) cells, using CK5 promoter-driven luciferase (Fluc) or green fluorescent protein (GFP) reporters stably transduced into T47D breast cancer cells (CK5Pro-GFP or CK5Pro-Luc). We validated the CK5Pro-GFP-T47D model for high-content screening in 96-well microplates and performed a pilot screen using a focused library of 280 compounds from the National Institutes of Health clinical collection. Four hits were obtained that significantly abrogated the progestin-induced CK5(+) cell population, three of which were members of the retinoid family. Hence, this approach will be useful in discovering small molecules that could potentially be developed as combination therapies, preventing the acquisition of a drug-resistant subpopulation.
Project description:Breast cancer is the most common cancer among women, and its incidence is on a constant rise. Previous studies suggest that higher levels of plasma prolactin are associated with escalated risk of breast cancer, however, these results are contradictory and inconclusive. PubMed and Medline were used to search and identify published observational studies that assessed the relationship between plasma prolactin levels and the risk of breast cancer. The pooled relative risks (RRs) with 95% confidence intervals (CIs) were calculated using a fixed-effects or random-effects model. A total of 7 studies were included in our analysis. For the highest versus lowest levels of plasma prolactin, the pooled RR (95% CI) of breast cancer were 1.16 (1.04, 1.29). In subgroup analyses, we found a positive association between plasma prolactin levels and the risk of breast cancer among the patients who were postmenopausal, ER(+)/PR(+) or in situ and invasive carcinoma. However, this positive association was not detected in the premenopausal and ER(-)/PR(-) patients. In conclusion, the present study provides evidence supporting a significantly positive association between plasma prolactin levels and the risk of breast cancer.
Project description:BACKGROUND:This study aimed to determine if associations of pre-diagnostic percent breast density, absolute dense area, and non-dense area with subsequent breast cancer risk differ by the tumour's molecular marker status. METHODS:We included 1010 postmenopausal women with breast cancer and 2077 matched controls from the Nurses' Health Study (NHS) and the Nurses' Health Study II (NHS II) cohorts. Breast density was estimated from digitised film mammograms using computer-assisted thresholding techniques. Information on breast cancer risk factors was obtained prospectively from biennial questionnaires. Polychotomous logistic regression was used to assess associations of breast density measures with tumour subtypes by the status of selected tissue markers. All tests of statistical significance were two sided. RESULTS:The association of percent density with breast cancer risk appeared to be stronger in ER- as compared with ER+ tumours, but the difference did not reach statistical significance (density ?50% vs <10% odds ratio (OR)=3.06, 95% confidence interval (CI) 2.17-4.32 for ER+; OR=4.61, 95% CI 2.36-9.03 for ER-, Pheterogeneity=0.08). Stronger positive associations were found for absolute dense area and CK5/6- and EGFR- as compared with respective marker-positive tumours (Pheterogeneity=0.002 and 0.001, respectively). Stronger inverse associations of non-dense area with breast cancer risk were found for ER- as compared with ER+ tumours (Pheterogeneity=0.0001) and for AR+, CK5/6+, and EGFR+ as compared with respective marker-negative tumours (Pheterogeneity=0.03, 0.005, and 0.009, respectively). The associations of density measures with breast cancer did not differ by progesterone receptor and human epidermal growth factor receptor 2 status. CONCLUSIONS:Breast density influences the risk of breast cancer subtypes by potentially different mechanisms.
Project description:Prolactin (PRL) plays a critical role in breast cancer progression by activating its cognate receptor and promotes the growth and differentiation of breast cancer cells. Studies have shown that B-cell lymphoma 6 (BCL6) is the target gene of microRNA-339-5p (miR-339-5p) and that BCL6 expression contributes to breast cancer progression. Herein, we identified PRL as a potent suppressor of BCL6 expression in human breast cancer cells.Western blotting and quantitative reverse transcription-polymerase chain reaction were used to investigate molecular mechanisms underlying miR-339-5p expression and BCL6 manipulation in MCF-7, T47D, and SKBR3 breast cancer cells. Phenotypic changes in these breast cancer cell lines were assessed by performing cell viability (MTT), colony formation, migration, and invasion assays.PRL suppressed BCL6 protein and mRNA expression and upregulated miR-339-5p expression in MCF-7 and T47D breast cancer cells. Selective downregulation of miR-339-5p expression significantly reversed PRL-induced suppression of BCL6 mRNA and protein expression. Exogenous PRL stimulation significantly decreased the proliferation, colony formation, migration, and invasion of breast cancer cells, and suppression of miR-339-5p expression reversed these processes in vitro.These results indicated that PRL inhibited BCL6 expression and regulated breast cancer progression through a miR-339-5p-dependent pathway.
Project description:INTRODUCTION: Basal-phenotype or basal-like breast cancers are characterized by basal epithelium cytokeratin (CK5/14/17) expression, negative estrogen receptor (ER) status and distinct gene expression signature. We studied the clinical and biological features of the basal-phenotype tumors determined by immunohistochemistry (IHC) and cDNA microarrays especially within the ER-negative subgroup. METHODS: IHC was used to evaluate the CK5/14 status of 445 stage II breast cancers. The gene expression signature of the CK5/14 immunopositive tumors was investigated within a subset (100) of the breast tumors (including 50 ER-negative tumors) with a cDNA microarray. Survival for basal-phenotype tumors as determined by CK5/14 IHC and gene expression signature was assessed. RESULTS: From the 375 analyzable tumor specimens, 48 (13%) were immunohistochemically positive for CK5/14. We found adverse distant disease-free survival for the CK5/14-positive tumors during the first years (3 years hazard ratio (HR) 2.23, 95% confidence interval (CI) 1.17 to 4.24, p = 0.01; 5 years HR 1.80, 95% CI 1.02 to 3.15, p = 0.04) but the significance was lost at the end of the follow-up period (10 years HR 1.43, 95% CI 0.84 to 2.43, p = 0.19). Gene expression profiles of immunohistochemically determined CK5/14-positive tumors within the ER-negative tumor group implicated 1,713 differently expressed genes (p < 0.05). Hierarchical clustering analysis with the top 500 of these genes formed one basal-like and a non-basal-like cluster also within the ER-negative tumor entity. A highly concordant classification could be constructed with a published gene set (Sorlie's intrinsic gene set, concordance 90%). Both gene sets identified a basal-like cluster that included most of the CK5/14-positive tumors, but also immunohistochemically CK5/14-negative tumors. Within the ER-negative tumor entity there was no survival difference between the non-basal and basal-like tumors as identified by immunohistochemical or gene-expression-based classification. CONCLUSION: Basal cytokeratin-positive tumors have a biologically distinct gene expression signature from other ER-negative tumors. Even if basal cytokeratin expression predicts early relapse among non-selected tumors, the clinical outcome of basal tumors is similar to non-basal ER-negative tumors. Immunohistochemically basal cytokeratin-positive tumors almost always belong to the basal-like gene expression profile, but this cluster also includes few basal cytokeratin-negative tumors. Keywords: Disease state analysis Overall design: 100 breast cancer tumor samples were analyzed on 2-color cDNA microarrays using the Stratagene Universal Human Reference RNA as the common reference sample.