Metastatic growth in distant organs is the major cause of cancer mortality. The development of metastasis is a multistage process with several rate-limiting steps 1 . Although dissemination of tumour cells seems to be an early and frequent event 2 , the successful initiation of metastatic growth, a process termed 'metastatic colonization', is inefficient for many cancer types and is accomplished only by a minority of cancer cells that reach distant sites 3,4 . Prevalent target sites are characteristic of many tumour entities 5 , suggesting that inadequate support by distant tissues contributes to the inefficiency of the metastatic process. Here we show that a small population of cancer stem cells is critical for metastatic colonization, that is, the initial expansion of cancer cells at the secondary site, and that stromal niche signals are crucial to this expansion process. We find that periostin (POSTN), a component of the extracellular matrix, is expressed by fibroblasts in the normal tissue and in the stroma of the primary tumour. Infiltrating tumour cells need to induce stromal POSTN expression in the secondary target organ (in this case lung) to initiate colonization. POSTN is required to allow cancer stem cell maintenance, and blocking its function prevents metastasis. POSTN recruits Wnt ligands and thereby increases Wnt signalling in cancer stem cells. We suggest that the education of stromal cells by infiltrating tumour cells is an important step in metastatic colonization and that preventing de novo niche formation may be a novel strategy for the treatment of metastatic disease.We aimed to explore limiting factors that determine metastatic success using the MMTV-PyMT mouse breast cancer model, which spontaneously metastasizes to the lungs 6 . We reasoned that the recently identified cancer stem cells (CSCs, also called tumour-initiating cells), a subset of cancer cells that allow long-term tumour growth and are thought to be responsible for remissions 7,8 , might also be relevant to the development of metastatic disease ( Supplementary Fig. 1). We measured the relative size of the population of CSCs from primary MMTV-PyMT tumours and their pulmonary metastases using the previously established markers CD90 and CD24, which label a subset of the CD24 1 CD29hi or CD241 CD49f hi population used earlier to isolate CSCs and normal mammary gland stem cells 9-13 (Supplementary Fig. 2). This CSC subset accounts for 3 6 2.1% (s.d.) of all tumour cells from both primary tumours and metastases (Fig. 1a). When CD90 1 CD241 CSCs or CD90 1 CD24 1 -depleted non-CSCs are separately isolated from GFP 1 tumours and directly introduced into mice through tail vein injection (GFP, green fluorescent protein), only the CSC population is able to produce lung metastases (Fig. 1b). Moreover, CD90 1 CD241 cells isolated subsequently from pulmonary metastases are again the only tumour cell population that efficiently initiates secondary metastases (Fig. 1c). This is not due to differences in the extravasation capabilities of CSCs an...

BackgroundObesity is a strong predictor of poor prognosis in breast cancer, especially in postmenopausal women. In particular, tumors in obese patients tend to seed more distant metastases, although the biology behind this observation remains poorly understood.MethodsTo elucidate the effects of the obese microenvironment on metastatic spread, we ovariectomized C57BL/6 J female mice and fed them either a regular diet (RD) or a high-fat diet (HFD) to generate a postmenopausal diet-induced obesity model. We then studied tumor progression to metastasis of Py230 and EO771 grafts. We analyzed and phenotyped the RD and HFD tumors and the surrounding adipose tissue by flow cytometry, qPCR, immunohistochemistry (IHC) and western blot. The influence of the microenvironment on tumor cells was assessed by performing cross-transplantation of RD and HFD tumor cells into other RD and HFD mice. The results were analyzed using the unpaired Student t test when comparing two variables, otherwise we used one-way or two-way analysis of variance. The relationship between two variables was calculated using correlation coefficients.ResultsOur results show that tumors in obese mice grow faster, are also less vascularized, more hypoxic, of higher grade and enriched in CD11b+Ly6G+ neutrophils. Collectively, this favors induction of the epithelial-to-mesenchymal transition and progression to claudin-low breast cancer, a subtype of triple-negative breast cancer that is enriched in cancer stem cells. Interestingly, transplanting HFD-derived tumor cells in RD mice transfers enhanced tumor growth and lung metastasis formation.ConclusionsThese data indicate that a pro-metastatic effect of obesity is acquired by the tumor cells in the primary tumor independently of the microenvironment of the secondary site.Graphical abstractEffects of postmenopausal obesity on primary breast cancer tumoursᅟElectronic supplementary materialThe online version of this article (10.1186/s13058-018-1029-4) contains supplementary material, which is available to authorized users.

Integrins play an important role in haematopoietic stem cell (HSC) maintenance in the bone marrow niche. Here, we demonstrate that Periostin (Postn) via interaction with Integrin-αv (Itgav) regulates HSC proliferation. Systemic deletion of Postn results in peripheral blood (PB) anaemia, myelomonocytosis and lymphopenia, while the number of phenotypic HSCs increases in the bone marrow. Postn−/− mice recover faster from radiation injury with concomitant loss of primitive HSCs. HSCs from Postn−/− mice show accumulation of DNA damage generally associated with aged HSCs. Itgav deletion in the haematopoietic system leads to a similar PB phenotype and HSC-intrinsic repopulation defects. Unaffected by Postn, Vav-Itgav−/− HSCs proliferate faster in vitro, illustrating the importance of Postn-Itgav interaction. Finally, the Postn-Itgav interaction inhibits the FAK/PI3K/AKT pathway in HSCs, leading to increase in p27Kip1 expression resulting in improved maintenance of quiescent HSCs. Together, we demonstrate a role for Itgav-mediated outside-in signalling in regulation of HSC proliferation and stemness.

Breast cancer metastasis is a complex process that depends on intrinsic characteristics of metastatic stem cells, but also on the particular microenvironment that supports their growth and modulates the plasticity of the system. In search for microenvironmental factors supporting cancer stem cell (CSC) growth and tumour progression to metastasis, we here investigated the role of the matricellular protein Transforming Growth Factor Beta Induced (TGFBI) in breast cancer. We crossed the MMTV-PyMT model of mammary gland tumourigenesis with a Tgfbi / mouse, and studied the CSC content of the tumours. We performed RNAseq on wt and ko tumours, and analysed the tumour vasculature and the immune compartment by IHC and FACS. The source of TGFBI expression was determined by qPCR and by bone marrow transplantation experiments. Finally, we performed in silico analyses using the METABRIC cohort to assess the potential prognostic value of TGFBI. We observed that deletion of Tgfbi led to a dramatic decrease in CSC content and lung metastasis. Our results show that lack of TGFBI resulted in tumour vessel normalisation, with improved vessel perfusion and decreased hypoxia, a major factor controlling CSCs and metastasis. Furthermore, human data

Membrane-associated guanylate kinase (MAGUK) with inverted domain structure-1 (MAGI1) is an intracellular adaptor protein that stabilizes epithelial junctions consistent with a tumor suppressive function in several cancers of epithelial origin. Here we report, based on experimental results and human breast cancer (BC) patients’ gene expression data, that MAGI1 is highly expressed and acts as tumor suppressor in estrogen receptor (ER)+/HER2− but not in HER2+ or triple negative breast cancer (TNBC). Within the ER+/HER2− subset, high MAGI1 expression associates with ESR1 and luminal genes GATA3 and FOXA1 expression and better prognosis, while low MAGI1 levels correlates with higher histological grade, more aggressive phenotype and worse prognosis. Experimentally, MAGI1 downregulation in the ER+ human BC cells MCF7 impairs ER expression and signaling, promotes cell proliferation, and reduces apoptosis and epithelial differentiation. MAGI1 downregulation in the ER+ murine BC cell line 67NR accelerates primary tumor growth and enhances experimental lung metastasis formation. MAGI1 expression is upregulated by estrogen/ER, downregulated by prostaglandin E2/COX-2axis, and negatively correlates with inflammation in ER+/HER2− BC patients. Taken together, we show that MAGI1 is a new potential tumor suppressor in ER+/HER2− breast cancer with possible prognostic value for the identification of patients at high-risk of relapse within this subset.

Background: The human Sex Hormone Binding Globulin (SHBG) gene, located at 17p13.1, comprises, at least, two different transcription units regulated by two different promoters. The first transcription unit begins with the exon 1 sequence and is responsible for the production of plasma SHBG by the hepatocytes, while the second begins with an alternative exon 1 sequence, which replaces the exon 1 present in liver transcripts. Alternative exon 1 transcription and translation has only been demonstrated in the testis of transgenic mice containing an 11-kb human SHBG transgene and in the human testis. Our goal has been to further characterize the 5' end of the SHBG gene and analyze the presence of the SHBG alternative transcripts in human prostate tissue and derived cell lines.

Summary Cancer stem cells (CSCs) are defined by their ability to regenerate a tumor upon transplantation. However, it is not yet clear whether tumors contain a single CSC population or different subsets of cells with mixed capacities for initiating primary and secondary tumors. Using two different identification strategies, we studied the overlap between metastatic stem cells and tumor-initiating cells (TICs) in the MMTV-PyMT model. Our results show that in the MMTV-PyMT model, Lin − CD90 − ALDH high cells retained a high tumor-initiating potential (TIP) in orthotopic transplants, in contrast to Lin − CD24 + CD90 + , which retained higher metastatic capacity. Interestingly, suppression of TGFβ signaling increased TIC numbers. We here describe the existence of distinct populations of CSCs with differing capacities to initiate tumors in the primary or the secondary site. Inhibiting TGFβ signaling shifts the balance toward the former, which may have unanticipated implications for the therapeutic use of TGFβ/TGFBR1 inhibitors.

Abstract. Santamaria-Martínez A, Huelsken J (Swiss