Exploring the Interspecific Interactions and the Metabolome of the Soil Isolate Hylemonella gracilis.

Microbial community analysis of aquatic environments showed that an important component of its microbial diversity consists of bacteria with cell sizes of ~0.1 µm. Such small bacteria can show genomic reductions and metabolic dependencies with other bacteria. However, so far, no study has investigated if such bacteria exist in terrestrial environments like soil. Here, we isolated soil bacteria that passed through a 0.1-µm filter. The complete genome of one of the isolates was sequenced and the bacterium was identified as Hylemonella gracilis. A set of coculture assays with phylogenetically distant soil bacteria with different cell and genome sizes was performed. The coculture assays revealed that H. gracilis grows better when interacting with other soil bacteria like Paenibacillus sp. AD87 and Serratia plymuthica. Transcriptomics and metabolomics showed that H. gracilis was able to change gene expression, behavior, and biochemistry of the interacting bacteria without direct cell-cell contact. Our study indicates that in soil there are bacteria that can pass through a 0.1-µm filter. These bacteria may have been overlooked in previous research on soil microbial communities. Such small bacteria, exemplified here by H. gracilis, can induce transcriptional and metabolomic changes in other bacteria upon their interactions in soil. In vitro, the studied interspecific interactions allowed utilization of growth substrates that could not be utilized by monocultures, suggesting that biochemical interactions between substantially different sized soil bacteria may contribute to the symbiosis of soil bacterial communities. IMPORTANCE Analysis of aquatic microbial communities revealed that parts of its diversity consist of bacteria with cell sizes of ~0.1 µm. Such bacteria can show genomic reductions and metabolic dependencies with other bacteria. So far, no study investigated if such bacteria exist in terrestrial environments such as soil. Here, we show that such bacteria also exist in soil. The isolated bacteria were identified as Hylemonella gracilis. Coculture assays with phylogenetically different soil bacteria revealed that H. gracilis grows better when cocultured with other soil bacteria. Transcriptomics and metabolomics showed that H. gracilis was able to change gene expression, behavior, and biochemistry of the interacting bacteria without direct contact. Our study revealed that bacteria are present in soil that can pass through 0.1-µm filters. Such bacteria may have been overlooked in previous research on soil microbial communities and may contribute to the symbiosis of soil bacterial communities.

Bio-distribution and longevity of mesenchymal stromal cell derived membrane particles.

Vesicle-based medicines hold great promise for therapy development but essential knowledge on the bio-distribution and longevity of vesicles after administration is lacking. We generated vesicles from the membranes of human mesenchymal stromal cells (MSC) and we demonstrated earlier that these so-called membrane particles (MP) mediate immunomodulatory and regenerative responses in target cells. In the present study we examined the bio-distribution and longevity of MP after intravenous administration in mice. While most vesicle tracking methods are based on imaging techniques, which require labeling of vesicles and can only detect dense accumulations of vesicles, we used proteomics analysis to detect the presence of MP-derived proteins in multiple organs and tissues. MP proteins were mainly present in plasma and leukocytes at 1 h after injection, indicating that MP - in contrast to whole MSC - do not accumulate in the lungs upon first passage but remain in circulation. After 24 h, MP proteins were still present in plasma but were most abundant in the liver. RNA sequencing of livers demonstrated that MP impact liver function and in particular induce metabolic pathways. These data provide a clear view of the bio-distribution and longevity of MP, which is likely extrapolatable to other types of vesicles, and demonstrate that MP circulate for up to 24 h and may be a tool for targeting the liver.

A kinase inhibitor screen reveals MEK1/2 as a novel therapeutic target to antagonize IGF1R-mediated antiestrogen resistance in ERα-positive luminal breast cancer.

Antiestrogen resistance of breast cancer has been related to enhanced growth factor receptor expression and activation. We have previously shown that ectopic expression and subsequent activation of the insulin-like growth factor-1 receptor (IGF1R) or the epidermal growth factor receptor (EGFR) in MCF7 or T47D breast cancer cells results in antiestrogen resistance. In order to identify novel therapeutic targets to prevent this antiestrogen resistance, we performed kinase inhibitor screens with 273 different inhibitors in MCF7 cells overexpressing IGF1R or EGFR. Kinase inhibitors that antagonized antiestrogen resistance but are not directly involved in IGF1R or EGFR signaling were prioritized for further analyses. Various ALK (anaplastic lymphoma receptor tyrosine kinase) inhibitors inhibited cell proliferation in IGF1R expressing cells under normal and antiestrogen resistance conditions by preventing IGF1R activation and subsequent downstream signaling; the ALK inhibitors did not affect EGFR signaling. On the other hand, MEK (mitogen-activated protein kinase kinase)1/2 inhibitors, including PD0325901, selumetinib, trametinib and TAK-733, selectively antagonized IGF1R signaling-mediated antiestrogen resistance but did not affect cell proliferation under normal growth conditions. RNAseq analysis revealed that MEK inhibitors PD0325901 and selumetinib drastically altered cell cycle progression and cell migration networks under IGF1R signaling-mediated antiestrogen resistance. In a group of 219 patients with metastasized ER + breast cancer, strong pMEK staining showed a significant correlation with no clinical benefit of first-line tamoxifen treatment. We propose a critical role for MEK activation in IGF1R signaling-mediated antiestrogen resistance and anticipate that dual-targeted therapy with a MEK inhibitor and antiestrogen could improve treatment outcome.

Hemolysis in the spleen drives erythrocyte turnover.

Red pulp macrophages (RPMs) of the spleen mediate turnover of billions of senescent erythrocytes per day. However, the molecular mechanisms involved in sequestration of senescent erythrocytes, their recognition, and their subsequent degradation by RPMs remain unclear. In this study, we provide evidence that the splenic environment is of substantial importance in facilitating erythrocyte turnover through induction of hemolysis. Upon isolating human spleen RPMs, we noted a substantial lack of macrophages that were in the process of phagocytosing intact erythrocytes. Detailed characterization of erythrocyte and macrophage subpopulations from human spleen tissue led to the identification of erythrocytes that are devoid of hemoglobin, so-called erythrocyte ghosts. By using in vivo imaging and transfusion experiments, we further confirmed that senescent erythrocytes that are retained in the spleen are subject to hemolysis. In addition, we showed that erythrocyte adhesion molecules, which are specifically activated on aged erythrocytes, cause senescent erythrocytes to interact with extracellular matrix proteins that are exposed within the splenic architecture. Such adhesion molecule-driven retention of senescent erythrocytes under low shear conditions was found to result in steady shrinkage of the cell and ultimately resulted in hemolysis. In contrast to intact senescent erythrocytes, the remnant erythrocyte ghost shells were prone to recognition and breakdown by RPMs. These data identify hemolysis as a key event in the turnover of senescent erythrocytes, which alters our current understanding of how erythrocyte degradation is regulated.

Progression of ductal carcinoma in situ to invasive breast cancer: comparative genomic sequencing.

Several models have been described as potential mechanisms for the progression of ductal carcinoma in situ (DCIS) to invasive breast cancer (IBC). The aim of our study was to increase our understanding of DCIS progression by using massive parallel sequencing of synchronous DCIS and IBC. We included patients with synchronous DCIS and IBC (n = 4). Initially, IBC and normal tissue were subjected to whole exome sequencing. Subsequently, targeted sequencing was performed to validate those tumor-specific variants identified by whole exome sequencing. Finally, we analyzed whether those specific variants of the invasive component were also present in the DCIS component. There was a high genomic concordance between synchronous DCIS and IBC (52 out of 92 mutations were present in both components). However, the remaining mutations (40 out of 92) were restricted to the invasive component. The proportion of tumor cells with these mutations was higher in the invasive component compared to the DCIS component in a subset of patients. Our findings support the theory that the progression from DCIS to IBC could be driven by the selection of subclones with specific genetic aberrations. This knowledge improves our understanding of DCIS progression, which may lead to the identification of potential markers of progression and novel therapeutic targets in order to develop a more personalized treatment of patients with DCIS.

Nimbus: a design-driven analyses suite for amplicon-based NGS data.

Motivation: PCR-based DNA enrichment followed by massively parallel sequencing is a straightforward and cost effective method to sequence genes up to high depth. The full potential of amplicon-based sequencing assays is currently not achieved as analysis methods do not take into account the source amplicons of the detected variants. Tracking the source amplicons has the potential to identify systematic biases, enhance variant calling and improve the designs of future assays. Results: We present Nimbus, a software suite for the analysis of amplicon-based sequencing data. Nimbus includes tools for data pre-processing, alignment, single nucleotide polymorphism (SNP), insertion and deletion calling, quality control and visualization. Nimbus can detect SNPs in its alignment seeds and reduces alignment issues by the usage of decoy amplicons. Tracking the amplicons throughout analysis allows easy and fast design optimization by amplicon performance comparison. It enables detection of probable false positive variants present in a single amplicon from real variants present in multiple amplicons and provides multiple sample visualization. Nimbus was tested using HaloPlex Exome datasets and outperforms other callers for low-frequency variants. The variants called by Nimbus were highly concordant between twin samples and SNP-arrays. The Nimbus suite provides an end-to-end solution for variant calling, design optimization and visualization of amplicon-derived next-generation sequencing datasets. Availability and implementation: https://github.com/erasmus-center-for-biomics/Nimbus. Supplementary information: Supplementary data are available at Bioinformatics online.

Sensitive detection of mitochondrial DNA variants for analysis of mitochondrial DNA-enriched extracts from frozen tumor tissue.

Large variation exists in mitochondrial DNA (mtDNA) not only between but also within individuals. Also in human cancer, tumor-specific mtDNA variation exists. In this work, we describe the comparison of four methods to extract mtDNA as pure as possible from frozen tumor tissue. Also, three state-of-the-art methods for sensitive detection of mtDNA variants were evaluated. The main aim was to develop a procedure to detect low-frequent single-nucleotide mtDNA-specific variants in frozen tumor tissue. We show that of the methods evaluated, DNA extracted from cytosol fractions following exonuclease treatment results in highest mtDNA yield and purity from frozen tumor tissue (270-fold mtDNA enrichment). Next, we demonstrate the sensitivity of detection of low-frequent single-nucleotide mtDNA variants (≤1% allele frequency) in breast cancer cell lines MDA-MB-231 and MCF-7 by single-molecule real-time (SMRT) sequencing, UltraSEEK chemistry based mass spectrometry, and digital PCR. We also show de novo detection and allelic phasing of variants by SMRT sequencing. We conclude that our sensitive procedure to detect low-frequent single-nucleotide mtDNA variants from frozen tumor tissue is based on extraction of DNA from cytosol fractions followed by exonuclease treatment to obtain high mtDNA purity, and subsequent SMRT sequencing for (de novo) detection and allelic phasing of variants.

Germline variant in MSX1 identified in a Dutch family with clustering of Barrett's esophagus and esophageal adenocarcinoma.

The vast majority of esophageal adenocarcinoma cases are sporadic and caused by somatic mutations. However, over the last decades several families have been identified with clustering of Barrett's esophagus and esophageal adenocarcinoma. This observation suggests that one or more hereditary factors may play a role in the initiation of Barrett's esophagus and esophageal adenocarcinoma in these families. A Dutch family with clustering of Barrett's esophagus and esophageal adenocarcinoma was identified. Normal DNA obtained from the proband diagnosed with Barrett's esophagus was analyzed with SNP array and exome sequencing. A custom-made panel consisting of potential germline variants was verified in the normal DNA of the affected family members. In addition, the respective tumors were analyzed for somatic loss of the wild type allele or the presence of an inactivating somatic mutation in the wild type allele. Exome sequencing revealed 244 candidate variants in the normal DNA of the proband, of which 212 variants were verified successfully. After the normal DNA of the affected family members was analyzed for the presence of the 212 potential germline variants and subsequently the respective tumors, only one potential germline variant in MSX1 (chr4: 4861985 T > G, c.359T > G, p.V120G, NM_002448) showed loss of the wild type allele in the tumor DNAs of the affected family members. A germline variant in MSX1 was identified in a Dutch family with clustering of Barrett's esophagus and esophageal adenocarcinoma. This finding indicates that the germline defect in MSX1 may be associated with Barrett's esophagus and cancer in this particular family.

A rare missense variant in RCL1 segregates with depression in extended families.

Depression is the most prevalent psychiatric disorder with a complex and elusive etiology that is moderately heritable. Identification of genes would greatly facilitate the elucidation of the biological mechanisms underlying depression, however, its complex etiology has proved to be a major bottleneck in the identification of its genetic risk factors, especially in genome-wide association-like studies. In this study, we exploit the properties of a genetic isolate and its family-based structure to explore whether relatively rare exonic variants influence the burden of depressive symptoms in families. Using a multistep approach involving linkage and haplotype analyses followed by exome sequencing in the Erasmus Rucphen Family (ERF) study, we identified a rare (minor allele frequency (MAF)=1%) missense c.1114C>T mutation (rs115482041) in the RCL1 gene segregating with depression across multiple generations. Rs115482041 showed significant association with depressive symptoms (N=2393, ßT-allele=2.33, P-value=1 × 10-4) and explained 2.9% of the estimated genetic variance of depressive symptoms (22%) in ERF. Despite being twice as rare (MAF<0.5%), c.1114C>T showed similar effect and significant association with depressive symptoms in samples from the independent population-based Rotterdam study (N=1604, ßT-allele=3.60, P-value=3 × 10-2). A comparison of RCL1 expression in human and mouse brain revealed a striking co-localization of RCL1 with the layer 1 interlaminar subclass of astrocytes found exclusively in higher-order primates. Our findings identify RCL1 as a novel candidate gene for depression and offer insights into mechanisms through which RCL1 may be relevant for depression.

An interaction network of mental disorder proteins in neural stem cells.

Mental disorders (MDs) such as intellectual disability (ID), autism spectrum disorders (ASD) and schizophrenia have a strong genetic component. Recently, many gene mutations associated with ID, ASD or schizophrenia have been identified by high-throughput sequencing. A substantial fraction of these mutations are in genes encoding transcriptional regulators. Transcriptional regulators associated with different MDs but acting in the same gene regulatory network provide information on the molecular relation between MDs. Physical interaction between transcriptional regulators is a strong predictor for their cooperation in gene regulation. Here, we biochemically purified transcriptional regulators from neural stem cells, identified their interaction partners by mass spectrometry and assembled a protein interaction network containing 206 proteins, including 68 proteins mutated in MD patients and 52 proteins significantly lacking coding variation in humans. Our network shows molecular connections between established MD proteins and provides a discovery tool for novel MD genes. Network proteins preferentially co-localize on the genome and cooperate in disease-relevant gene regulation. Our results suggest that the observed transcriptional regulators associated with ID, ASD or schizophrenia are part of a transcriptional network in neural stem cells. We find that more severe mutations in network proteins are associated with MDs that include lower intelligence quotient (IQ), suggesting that the level of disruption of a shared transcriptional network correlates with cognitive dysfunction.

Exome-sequencing in a large population-based study reveals a rare Asn396Ser variant in the LIPG gene associated with depressive symptoms.

Despite a substantial genetic component, efforts to identify common genetic variation underlying depression have largely been unsuccessful. In the current study we aimed to identify rare genetic variants that might have large effects on depression in the general population. Using high-coverage exome-sequencing, we studied the exonic variants in 1265 individuals from the Rotterdam study (RS), who were assessed for depressive symptoms. We identified a missense Asn396Ser mutation (rs77960347) in the endothelial lipase (LIPG) gene, occurring with an allele frequency of 1% in the general population, which was significantly associated with depressive symptoms (P-value=5.2 × 10-08, ß=7.2). Replication in three independent data sets (N=3612) confirmed the association of Asn396Ser (P-value=7.1 × 10-03, ß=2.55) with depressive symptoms. LIPG is predicted to have enzymatic function in steroid biosynthesis, cholesterol biosynthesis and thyroid hormone metabolic processes. The Asn396Ser variant is predicted to have a damaging effect on the function of LIPG. Within the discovery population, carriers also showed an increased burden of white matter lesions (P-value=3.3 × 10-02) and a higher risk of Alzheimer's disease (odds ratio=2.01; P-value=2.8 × 10-02) compared with the non-carriers. Together, these findings implicate the Asn396Ser variant of LIPG in the pathogenesis of depressive symptoms in the general population.

Regulated genes in psoriatic skin during treatment with fumaric acid esters.

BACKGROUND: Fumaric acid esters (FAEs) are widely used in Europe for the treatment of psoriasis because of their clinical efficacy and favourable safety profile. However, the mechanisms of action by which FAEs improve psoriasis remain largely unknown. OBJECTIVES: To identify pathways and mechanisms affected by FAE treatment and to compare these with pathways affected by treatment with the antitumour necrosis factor (anti-TNF)-α biologic etanercept. METHODS: In a prospective cohort study, 50 patients with plaque psoriasis were treated with FAEs for 20 weeks. Nine patients were randomly selected for gene expression profiling of plaque biopsies from week 0 and week 12. The groups consisted of FAE responders [> Psoriasis Area and Severity Index (PASI)-75 improvement] and nonresponders (< PASI-50 improvement). Changes in gene expression profiles were analysed using Ingenuity Pathway Analysis (IPA) and the outcome was compared with gene expression affected by etanercept. RESULTS: Response to FAE treatment was associated with a ≥ 2-fold change (P < 0.05) in the expression of 458 genes. In FAE responders the role of interleukin-17A in the psoriasis pathway was most significantly activated. Glutathione and Nrf2 pathway molecules were specifically induced by FAE treatment and not by etanercept treatment, representing an FAE-specific effect in psoriatic skin. In addition, FAE treatment specifically induced the transcription factors PTTG1, NR3C1, GATA3 and NFκBIZ in responding patients. CONCLUSIONS: FAE treatment induces glutathione and Nrf2 pathway genes in lesional skin of patients with psoriasis. In responders, FAEs specifically regulate the transcription factors PTTG1, NR3C1, GATA3 and NFκBIZ, which are important in normal cutaneous development, and the T-helper (Th)2 and Th17 pathways, respectively.

NARWHAL, a primary analysis pipeline for NGS data.

UNLABELLED: The NARWHAL software pipeline has been developed to automate the primary analysis of Illumina sequencing data. This pipeline combines a new and flexible de-multiplexing tool with open-source aligners and automated quality assessment. The entire pipeline can be run using only one simple sample-sheet for diverse sequencing applications. NARWHAL creates a sample-oriented data structure and outperforms existing tools in speed. AVAILABILITY: https://trac.nbic.nl/narwhal/.

Discovery of new microRNAs by small RNAome deep sequencing in childhood acute lymphoblastic leukemia.

MicroRNAs (miRNAs) relevant to acute lymphoblastic leukemia (ALL) in children are hypothesized to be largely unknown as most miRNAs have been identified in non-leukemic tissues. In order to discover these miRNAs, we applied high-throughput sequencing to pooled fractions of leukemic cells obtained from 89 pediatric cases covering seven well-defined genetic types of ALL and normal hematopoietic cells. This resulted into 78 million small RNA reads representing 554 known, 28 novel and 431 candidate novel miR genes. In all, 153 known, 16 novel and 170 candidate novel mature miRNAs and miRNA-star strands were only expressed in ALL, whereas 140 known, 2 novel and 82 candidate novel mature miRNAs and miRNA-star strands were unique to normal hematopoietic cells. Stem-loop reverse transcriptase (RT)-quantitative PCR analyses confirmed the differential expression of selected mature miRNAs in ALL types and normal cells. Expression of 14 new miRNAs inversely correlated with expression of predicted target genes (-0.49 ≤ Spearman's correlation coefficients (Rs)≤ -0.27, P ≤ 0.05); among others, low levels of novel sol-miR-23 associated with high levels of its predicted (antiapoptotic) target BCL2 (B-cell lymphoma 2) in precursor B-ALL (Rs -0.36, P = 0.007). The identification of >1000 miR genes expressed in different types of ALL forms a comprehensive repository for further functional studies that address the role of miRNAs in the biology of ALL.

Inflammatory conditions affect gene expression and function of human adipose tissue-derived mesenchymal stem cells.

There is emerging interest in the application of mesenchymal stem cells (MSC) for the prevention and treatment of autoimmune diseases, graft-versus-host disease and allograft rejection. It is, however, unknown how inflammatory conditions affect phenotype and function of MSC. Adipose tissue-derived mesenchymal stem cells (ASC) were cultured with alloactivated peripheral blood mononuclear cells (PBMC) (mixed lymphocyte reaction: MLR), with proinflammatory cytokines [interferon (IFN)-γ, tumour necrosis factor (TNF)-α and interleukin (IL)-6] or under control conditions, and their full genome expression and function examined. Proinflammatory cytokines mainly increased indoleamine-2,3-dioxygenase expression, whereas ASC cultured with MLR showed increased expression of COX-2, involved in prostaglandin E(2) production. Both conditions had a stimulatory, but differential, effect on the expression of proinflammatory cytokines and chemokines, while the expression of fibrotic factors was decreased only in response to proinflammatory cytokines. Functional analysis demonstrated that inflammatory conditions affected morphology and proliferation of ASC, while their differentiation capacity and production of trophic factors was unaffected. The immunosuppressive capacity of ASC was enhanced strongly under inflammatory conditions. In conclusion, ASC showed enhanced immunosuppressive capacity under inflammatory conditions, while their differentiation capacity was preserved. Therefore, in vitro preconditioning provides ASC with improved properties for immediate clinical immune therapy.

Pandemic 2009 H1N1 influenza virus causes diffuse alveolar damage in cynomolgus macaques.

The pathogenesis of lower respiratory tract disease from the pandemic 2009 H1N1 (H1N1v) influenza A virus is poorly understood. Therefore, either H1N1v virus or a seasonal human H1N1 influenza A virus was inoculated into cynomolgus macaques as a nonhuman primate model of influenza pneumonia, and virological, pathological, and microarray analyses were performed. Macaques in the H1N1v group had virus-associated diffuse alveolar damage involving both type I and type II alveolar epithelial cells and affecting an average of 16% of the lung area. In comparison, macaques in the seasonal H1N1 group had milder pulmonary lesions. H1N1v virus tended to be reisolated from more locations in the respiratory tract and at higher titers than seasonal H1N1 virus. In contrast, differential expression of messenger RNA transcripts between H1N1v and seasonal H1N1 groups did not show significant differences. The most upregulated genes in H1N1v lung samples with lesions belonged to the innate immune response and proinflammatory pathways and correlated with histopathological results. Our results demonstrate that the H1N1v virus infects alveolar epithelial cells and causes diffuse alveolar damage in a nonhuman primate model. Its higher pathogenicity compared with a seasonal H1N1 virus may be explained in part by higher replication in the lower respiratory tract.

CITED2 and NCOR2 in anti-oestrogen resistance and progression of breast cancer.

BACKGROUND: Endocrine therapies of breast cancer are effective but ultimately fail because of the development of treatment resistance. We have previously revealed several genes leading to tamoxifen resistance in vitro by retroviral insertion mutagenesis. To understand the manner in which these genes yield tamoxifen resistance, their effects on global gene expression were studied and those genes resulting in a distinct gene expression profile were further investigated for their clinical relevance. METHODS: Gene expression profiles of 69 human breast cancer cell lines that were made tamoxifen resistant through retroviral insertion mutagenesis were obtained using oligonucleotide arrays and analysed with bioinformatic tools. mRNA levels of NCOR2 and CITED2 in oestrogen receptor-positive breast tumours were determined by quantitative RT-PCR. mRNA levels were evaluated for association with metastasis-free survival (MFS) in 620 patients with lymph node-negative primary breast cancer who did not receive systemic adjuvant therapy, and with clinical benefit in 296 patients receiving tamoxifen therapy for recurrent breast cancer. RESULTS: mRNA expression profiles of most tamoxifen-resistant cell lines were strikingly similar, except for the subgroups of cell lines in which NCOR2 or CITED2 were targeted by the retrovirus. Both NCOR2 and CITED2 mRNA levels were associated with MFS, that is, tumour aggressiveness, independently of traditional prognostic factors. In addition, high CITED2 mRNA levels were predictive for a clinical benefit from first-line tamoxifen treatment in patients with advanced disease. CONCLUSIONS: Most retrovirally targeted genes yielding tamoxifen resistance in our cell lines do not impose a distinctive expression profile, suggesting that their causative role in cell growth may be accomplished by post-transcriptional processes. The associations of NCOR2 and CITED2 with outcome in oestrogen receptor-positive breast cancer patients underscore the clinical relevance of functional genetic screens to better understand disease progression, which may ultimately lead to the development of improved treatment options.

The hormone replacement therapy drug tibolone acts very similar to medroxyprogesterone acetate in an estrogen-and progesterone-responsive endometrial cancer cell line.

Tibolone, a steroidogenic compound with both estrogenic and progestagenic properties, is used as an alternative for estrogen or estrogen plus progesterone hormone therapy for the treatment of symptoms associated with menopause and osteoporosis. We have evaluated whether the effect of tibolone on a human endometrial cell line is similar to, or comparable with, the effect of estradiol (E(2)), medroxyprogesterone acetate (MPA) or E(2) + MPA treatment. Using stable transfection techniques, the estrogen receptor (ER) expressing human endometrial cancer cell line, ECC1, was altered to also express both progesterone receptors (PRs). These cells were then used to assess growth regulation and expression profiling (Affymetrix U133plus2) under the influence of E(2) (1 nM), MPA (1 nM), E(2) + MPA or tibolone (100 nM). Growth assessment and comparison of profiles indicate that tibolone behaves predominantly like MPA. Furthermore, regulation of prereplication complex genes, such as the minichromosome maintenance genes, could be involved in the observed strong inhibition of growth by tibolone as well as MPA. In addition, in total, 15 genes were found to be specific for tibolone treatment. These genes were predominantly involved in regulation of the cell cycle and differentiation.