Britta M. Jacobsen

Differential Gene Regulation by the Two Progesterone Receptor Isoforms in Human Breast Cancer Cells

The PR-A and PR-B isoforms of progesterone receptors (PR) have different physiological functions, and their ratio varies widely in breast cancers. To determine whether the two PR regulate different genes, we used human breast cancer cell lines engineered to express one or the other isoform. Cells were treated with progesterone in triplicate, time-separated experiments, allowing statistical analyses of microarray gene expression data. Of 94 progesterone-regulated genes, 65 are uniquely regulated by PR-B, 4 uniquely by PR-A, and only 25 by both. Almost half the genes encode proteins that are membrane-bound or involved in membrane-initiated signaling. We also find an important set of progesterone-regulated genes involved in mammary gland development and/or implicated in breast cancer. This first, large scale study of PR gene regulation has important implications for the measurement of PR in breast cancers and for the many clinical uses of synthetic progestins. It suggests that it is important to distinguish between the two isoforms in breast cancers and that isoform-specific genes can be used to screen for ligands that selectively modulate the activity of PR-A or PR-B. Additionally, use of natural target genes, rather than “consensus” response elements, for transcription studies should improve our understanding of steroid hormone action.

Role of the androgen receptor in breast cancer and preclinical analysis of enzalutamide

IntroductionThe androgen receptor (AR) is widely expressed in breast cancers and has been proposed as a therapeutic target in estrogen receptor alpha (ER) negative breast cancers that retain AR. However, controversy exists regarding the role of AR, particularly in ER + tumors. Enzalutamide, an AR inhibitor that impairs nuclear localization of AR, was used to elucidate the role of AR in preclinical models of ER positive and negative breast cancer.MethodsWe examined nuclear AR to ER protein ratios in primary breast cancers in relation to response to endocrine therapy. The effects of AR inhibition with enzalutamide were examined in vitro and in preclinical models of ER positive and negative breast cancer that express AR.ResultsIn a cohort of 192 women with ER + breast cancers, a high ratio of AR:ER (≥2.0) indicated an over four fold increased risk for failure while on tamoxifen (HR = 4.43). The AR:ER ratio had an independent effect on risk for failure above ER % staining alone. AR:ER ratio is also an independent predictor of disease-free survival (HR = 4.04, 95% CI: 1.68, 9.69; p = 0.002) and disease specific survival (HR = 2.75, 95% CI: 1.11, 6.86; p = 0.03). Both enzalutamide and bicalutamide inhibited 5-alpha-dihydrotestosterone (DHT)-mediated proliferation of breast cancer lines in vitro; however, enzalutamide uniquely inhibited estradiol (E2)-mediated proliferation of ER+/AR + breast cancer cells. In MCF7 xenografts (ER+/AR+) enzalutamide inhibited E2-driven tumor growth as effectively as tamoxifen by decreasing proliferation. Enzalutamide also inhibited DHT- driven tumor growth in both ER positive (MCF7) and negative (MDA-MB-453) xenografts, but did so by increasing apoptosis.ConclusionsAR to ER ratio may influence breast cancer response to traditional endocrine therapy. Enzalutamide elicits different effects on E2-mediated breast cancer cell proliferation than bicalutamide. This preclinical study supports the initiation of clinical studies evaluating enzalutamide for treatment of AR+ tumors regardless of ER status, since it blocks both androgen- and estrogen- mediated tumor growth.

DNA profiling analysis of endometrial and ovarian cell lines reveals misidentification, redundancy and contamination

OBJECTIVES Cell lines derived from human ovarian and endometrial cancers, and their immortalized non-malignant counterparts, are critical tools to investigate and characterize molecular mechanisms underlying gynecologic tumorigenesis, and facilitate development of novel therapeutics. To determine the extent of misidentification, contamination and redundancy, with evident consequences for the validity of research based upon these models, we undertook a systematic analysis and cataloging of endometrial and ovarian cell lines. METHODS Profiling of cell lines by analysis of DNA microsatellite short tandem repeats (STR), p53 nucleotide polymorphisms and microsatellite instability was performed. RESULTS Fifty-one ovarian cancer lines were profiled with ten found to be redundant and five (A2008, OV2008, C13, SK-OV-4 and SK-OV-6) identified as cervical cancer cells. Ten endometrial cell lines were analyzed, with RL-92, HEC-1A, HEC-1B, HEC-50, KLE, and AN3CA all exhibiting unique, uncontaminated STR profiles. Multiple variants of Ishikawa and ECC-1 endometrial cancer cell lines were genotyped and analyzed by sequencing of mutations in the p53 gene. The profile of ECC-1 cells did not match the EnCa-101 tumor, from which it was reportedly derived, and all ECC-1 isolates were genotyped as Ishikawa cells, MCF-7 breast cancer cells, or a combination thereof. Two normal, immortalized endometrial epithelial cell lines, HES cells and the hTERT-EEC line, were identified as HeLa cervical carcinoma and MCF-7 breast cancer cells, respectively. CONCLUSIONS Results demonstrate significant misidentification, duplication, and loss of integrity of endometrial and ovarian cancer cell lines. Authentication by STR DNA profiling is a simple and economical method to verify and validate studies undertaken with these models.

New Human Breast Cancer Cells to Study Progesterone Receptor Isoform Ratio Effects and Ligand-independent Gene Regulation

All known progesterone target cells coexpress two functionally different progesterone receptor (PR) isoforms: 120-kDa B-receptors (PR-B) and N-terminally truncated, 94-kDa A-receptors (PR-A). Their ratio varies in normal and malignant tissues. In human breast cancer cells, homodimers of progesterone-occupied PR-A or PR-B regulate different gene subsets. To study PR homo- and heterodimers, we constructed breast cancer cell lines in which isoform expression is controlled by an inducible system. PR-negative cells or cells that stably express one or the other isoform were used to construct five sets of cells: (i) PR-negative control cells (Y iNull), (ii) inducible PR-A cells (Y iA), (iii) inducible PR-B cells (Y iB), (iv) stable PR-B plus inducible PR-A cells (B iA), and (v) stable PR-A plus inducible PR-B cells (A iB). Expression levels of each isoform and/or the PR-A/PR-B ratios could be tightly controlled by the dose of inducer as demonstrated by immunoblotting and transcription studies. Induced PRs underwent normal progestin-dependent phosphorylation and down-regulation and regulated exogenous promoters as well as endogenous gene expression. Transcription of exogenous promoters was dependent on the PR-A/PR-B ratio, whereas transcription of endogenous genes was more complex. Finally, we have described several genes that are regulated by induced PR-A even in the absence of ligand.

Multiple Molecular Subtypes of Triple-Negative Breast Cancer Critically Rely on Androgen Receptor and Respond to Enzalutamide In Vivo

Triple-negative breast cancer (TNBC) has the lowest 5-year survival rate of invasive breast carcinomas, and currently there are no approved targeted therapies for this aggressive form of the disease. The androgen receptor (AR) is expressed in up to one third of TNBC and we find that all AR+ TNBC primary tumors tested display nuclear localization of AR, indicative of transcriptionally active receptors. While AR is most abundant in the “luminal AR (LAR)” molecular subtype of TNBC, here, for the first time, we use both the new-generation anti-androgen enzalutamide and AR knockdown to demonstrate that the other non-LAR molecular subtypes of TNBC are critically dependent on AR protein. Indeed, AR inhibition significantly reduces baseline proliferation, anchorage-independent growth, migration, and invasion and increases apoptosis in four TNBC lines (SUM159PT, HCC1806, BT549, and MDA-MB-231), representing three non-LAR TNBC molecular subtypes (mesenchymal-like, mesenchymal stem–like, and basal-like 2). In vivo, enzalutamide significantly decreases viability of SUM159PT and HCC1806 xenografts. Furthermore, mechanistic analysis reveals that AR activation upregulates secretion of the EGFR ligand amphiregulin (AREG), an effect abrogated by enzalutamide in vitro and in vivo. Exogenous AREG partially rescues the effects of AR knockdown on proliferation, migration, and invasion, demonstrating that upregulation of AREG is one mechanism by which AR influences tumorigenicity. Together, our findings indicate that non-LAR subtypes of TNBC are AR dependent and, moreover, that enzalutamide is a promising targeted therapy for multiple molecular subtypes of AR+ TNBC. Mol Cancer Ther; 14(3); 769–78. ©2015 AACR.

Progestin suppression of miR-29 potentiates dedifferentiation of breast cancer cells via KLF4

The female hormone progesterone (P4) promotes the expansion of stem-like cancer cells in estrogen receptor (ER)- and progesterone receptor (PR)-positive breast tumors. The expanded tumor cells lose expression of ER and PR, express the tumor-initiating marker CD44, the progenitor marker cytokeratin 5 (CK5) and are more resistant to standard endocrine and chemotherapies. The mechanisms underlying this hormone-stimulated reprogramming have remained largely unknown. In the present study, we investigated the role of microRNAs in progestin-mediated expansion of this dedifferentiated tumor cell population. We demonstrate that P4 rapidly downregulates miR-29 family members, particularly in the CD44+ cell population. Downregulation of miR-29 members potentiates the expansion of CK5+ and CD44+ cells in response to progestins, and results in increased stem-like properties in vitro and in vivo. We demonstrate that miR-29 directly targets Krüppel-like factor 4 (KLF4), a transcription factor required for the reprogramming of differentiated cells to pluripotent stem cells, and for the maintenance of breast cancer stem cells. These results reveal a novel mechanism, whereby progestins increase the stem cell-like population in hormone-responsive breast cancers, by decreasing miR-29 to augment PR-mediated upregulation of KLF4. Elucidating the mechanisms whereby hormones mediate the expansion of stem-like cells furthers our understanding of the progression of hormone-responsive breast cancers.

Functional properties of the N-terminal region of progesterone receptors and their mechanistic relationship to structure ☆

Progesterone receptors (PR) are present in two isoforms, PR-A and PR-B. The B-upstream segment (BUS) of PR-B is a 164 amino acid N-terminal extension that is missing in PR-A and is responsible for the functional differences reported between the two isoforms. BUS contains an activation function (AF3) which is defined by a core domain between residues 54-154 whose activity is dependent upon a single Trp residue and two LXXLL motifs. We have also identified sites both within and outside of BUS that repress the strong synergism between AF3 and AF1 in the N-terminal region and AF2 in the hormone binding domain. One of these repressor sites is a consensus binding motif for the small ubiquitin-like modifier protein, SUMO-1 (387IKEE). The DNA binding domain (DBD) structure is also important for function. When BUS is linked to the glucocorticoid receptor DBD, AF3 activity is substantially attenuated, suggesting that binding to a DNA response element results in allosteric communication between the DBD and N-terminal functional regions. Lastly, biochemical and biophysical analyses of highly purified PR-B and PR-A N-terminal regions reveal that they are unstructured unless the DBD is present. Thus, the DBD stabilizes N-terminal structure. We propose a model in which the DBD through DNA binding, and BUS through protein-protein interactions, stabilize active receptor conformers within an ensemble distribution of active and inactive conformational states. This would explain why PR-B are stronger transactivators than PR-A.

Expression profiling of human breast cancers and gene regulation by progesterone receptors.

Even the first expression profiling studies of breast cancers have generated new insights. They suggest for example, that information about tumor aggressiveness, prognosis, metastatic potential, or treatment outcome is encoded in, and can be deduced from, the primary tumor. On the other hand no clinical genomic array data have yet been published that deal with hormonal aspects of breast tumorigenesis, tumor progression, or therapeutics. Rather, studies have focused on experimental model systems. We review below the currently published data on array profiling in clinical breast cancer, then describe our studies in breast cancer cell lines and xenograft models dealing with progesterone receptors (PRs) and the role of progesterone. We demonstrate that the two PR isoforms, PR-A and PR-B, have mostly nonoverlapping molecular signatures when liganded by progesterone, with PR-B the more active form. Additionally, we document the surprising finding that unliganded PRs can regulate gene transcription, with PR-A the more active form. In ovariectomized mice supplemented with estradiol but lacking measurable progesterone, PR-B-expressing tumors grow to twice the size of PR-A-expressing ones. We conclude that in breast cancers, PRs are more than simple markers of estrogen receptor function. Rather, presence of PRs and the ratio of the two isoforms directly influence tumor phenotype, even in the absence of ligand.

The progestational and androgenic properties of medroxyprogesterone acetate: gene regulatory overlap with dihydrotestosterone in breast cancer cells

IntroductionMedroxyprogesterone acetate (MPA), the major progestin used for oral contraception and hormone replacement therapy, has been implicated in increased breast cancer risk. Is this risk due to its progestational or androgenic properties? To address this, we assessed the transcriptional effects of MPA as compared with those of progesterone and dihydrotestosterone (DHT) in human breast cancer cells.MethodA new progesterone receptor-negative, androgen receptor-positive human breast cancer cell line, designated Y-AR, was engineered and characterized. Transcription assays using a synthetic promoter/reporter construct, as well as endogenous gene expression profiling comparing progesterone, MPA and DHT, were performed in cells either lacking or containing progesterone receptor and/or androgen receptor.ResultsIn progesterone receptor-positive cells, MPA was found to be an effective progestin through both progesterone receptor isoforms in transient transcription assays. Interestingly, DHT signaled through progesterone receptor type B. Expression profiling of endogenous progesterone receptor-regulated genes comparing progesterone and MPA suggested that although MPA may be a somewhat more potent progestin than progesterone, it is qualitatively similar to progesterone. To address effects of MPA through androgen receptor, expression profiling was performed comparing progesterone, MPA and DHT using Y-AR cells. These studies showed extensive gene regulatory overlap between DHT and MPA through androgen receptor and none with progesterone. Interestingly, there was no difference between pharmacological MPA and physiological MPA, suggesting that high-dose therapeutic MPA may be superfluous.ConclusionOur comparison of the gene regulatory profiles of MPA and progesterone suggests that, for physiologic hormone replacement therapy, the actions of MPA do not mimic those of endogenous progesterone alone. Clinically, the complex pharmacology of MPA not only influences its side-effect profile; but it is also possible that the increased breast cancer risk and/or the therapeutic efficacy of MPA in cancer treatment is in part mediated by androgen receptor.

Tissue-Specific Pathways for Estrogen Regulation of Ovarian Cancer Growth and Metastasis

Menopausal estrogen (E2) replacement therapy increases the risk of estrogen receptor (ER)-positive epithelial ovarian cancers (EOC). Whether E2 is tumorigenic or promotes expansion of undiagnosed preexisting disease is unknown. To determine E2 effects on tumor promotion, we developed an intraperitoneal mouse xenograft model using ZsGreen fluorescent ER(-) 2008 and ER(+) PEO4 human EOC cells. Tumor growth was quantified by in vivo fluorescent imaging. In ER(+) tumors, E2 significantly increased size, induced progesterone receptors, and promoted lymph node metastasis, confirming that ERs are functional and foster aggressiveness. Laser-captured human EOC cells from ER(-) and ER(+) xenografted tumors were profiled for expression of E2-regulated genes. Three classes of E2-regulated EOC genes were defined, but <10% were shared with E2-regulated breast cancer genes. Because breast cancer selective ER modulators (SERM) are therapeutically ineffective in EOC, we suggest that our EOC-specific E2-regulated genes can assist pharmacologic discovery of ovarian-targeted SERM.