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Background: Circadian rhythms maintain tissue homeostasis during the 24-h day-night cycle. Cell-autonomous circadian clocks play fundamental roles in cell division, DNA damage responses and metabolism. Circadian disruptions have been proposed as a contributing factor for cancer initiation and progression, although definitive evidence for altered molecular circadian clocks in cancer is still lacking. In this study, we looked at circadian clocks in breast cancer., Methods: We isolated primary tumours and normal tissues from the same individuals who had developed breast cancer with no metastases. We assessed circadian clocks within primary cells of the patients by lentiviral expression of circadian reporters, and the levels of clock genes in tissues by qPCR. We histologically examined collagen organisation within the normal and tumour tissue areas, and probed the stiffness of the stroma adjacent to normal and tumour epithelium using atomic force microscopy., Results: Epithelial ducts were disorganised within the tumour areas. Circadian clocks were altered in cultured tumour cells. Tumour regions were surrounded by stroma with an altered collagen organisation and increased stiffness. Levels of Bmal1 messenger RNA (mRNA) were significantly altered in the tumours in comparison to normal epithelia., Conclusion: Circadian rhythms are suppressed in breast tumour epithelia in comparison to the normal epithelia in paired patient samples. This correlates with increased tissue stiffness around the tumour region. We suggest possible involvement of altered circadian clocks in the development and progression of breast cancer.

Integrins are cell surface receptors that bind cells to their physical external environment, linking the extracellular matrix to cell function. They are essential in the biology of all animals. In the late 1980s, we discovered that integrins are required for the ability of breast epithelia to do what they are programmed to do, which is to differentiate and make milk. Since then, integrins have been shown to control most other aspects of phenotype: to stay alive, to divide, and to move about. Integrins also provide part of the mechanism that allows cells to form tissues. Here I discuss how we discovered that integrins control mammary gland differentiation and explore the role of integrins as central architects of other aspects of cell behavior., (© 2016 Streuli This article is distributed by The American Society for Cell Biology under license from the author(s). Two months after publication it is available to the public under an Attribution–Noncommercial–Share Alike 3.0 Unported Creative Commons License (http://creativecommons.org/licenses/by-nc-sa/3.0).)

The immune system is not normally viewed as a regulator of breast development. However, in this issue of Developmental Cell, Plaks et al. (2015) reveal that antigen-presenting cells and T cells have a key role in controlling the development of the mammary gland's epithelial ductal network., (Copyright © 2015 Elsevier Inc. All rights reserved.)

This article explores new ideas about how the ECM-integrin axis controls normal and malignant breast biology. We discuss the role of integrins in mammary stem cells, and how cell-matrix interactions regulate ductal and alveolar development and function. We also examine the contribution of integrins to tissue disorganisation and metastasis, and how an altered stromal and ECM tumour microenvironment affects the cancer cell niche both within primary tumours and at distant sites. Finally, we mention novel strategies for integrin-directed breast cancer treatment., (Copyright © 2013 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Epithelial cell survival is dependent on extracellular signals provided by both soluble factors and by adhesion. In the mammary gland, extensive apoptosis of epithelial cells occurs rapidly when lactation ceases, but the mechanism of apoptosis induction is not known. In tissue culture, mammary epithelial cells require laminin as a survival ligand and specific beta1 integrins are necessary to suppress apoptosis. To explore the possibility that dynamic changes in cell-matrix interactions contribute to the onset of apoptosis during mammary involution in vivo, a detailed immunohistochemical analysis of the expression of integrin subunits and their extracellular matrix ligands during mouse mammary gland development has been performed. The kinetics of apoptosis were determined by using tissue samples obtained from virgin, pregnant, lactating, and involuting gland. The maximal elevation of apoptosis occurred within 24 hr of weaning as determined by histologic analysis and caspase-3 staining. A wide variety of laminin subunits, together with nidogen-1 and -2, and perlecan were identified within the basement membrane region of epithelial ducts, lobules, and alveoli in both human and mouse mammary gland. However, no change in the distribution of any of the basement membrane proteins or their cognate integrin receptors was observed during the transition from lactation to apoptosis. Instead, we discovered that altered ligand-binding conformation of the beta1 integrin to a nonbinding state coincided with the immediate onset of mammary apoptosis. This finding may provide a novel dynamic mechanism for inhibiting the transduction of extracellular matrix survival signals, thereby contributing to the onset of apoptosis in a developmental context in vivo., (Copyright 2002 Wiley-Liss, Inc.)

Insulin-like growth factor (IGF)-mediated proliferation and survival are essential for normal development in the mammary gland during puberty and pregnancy. IGFs interact with IGF-binding proteins and regulate their function. The present review focuses on the role of IGFs and IGF-binding proteins in the mammary gland and describes how modulation of their actions occurs by association with hormones, other growth factors and the extracellular matrix. The review will also highlight the involvement of the IGF axis in breast cancer.

Cell-autonomous circadian clocks coordinate tissue homeostasis with a 24-hourly rhythm. The molecular circadian clock machinery controls tissue- and cell type-specific sets of rhythmic genes. Disruptions of clock mechanisms are linked to an increased risk of acquiring diseases, especially those associated with aging, metabolic dysfunction and cancer. Despite rapid advances in understanding the cyclic outputs of different tissue clocks, less is known about how the clocks adapt to their local niche within tissues. We have discovered that tissue stiffness regulates circadian clocks, and that this occurs in a cell-type-dependent manner. In this Review, we summarise new work linking the extracellular matrix with differential control of circadian clocks. We discuss how the changes in tissue structure and cellular microenvironment that occur throughout life may impact on the molecular control of circadian cycles. We also consider how altered clocks may have downstream impacts on the acquisition of diseases. [ABSTRACT FROM AUTHOR]

FGF signaling is essential for mammary gland development, yet the mechanisms by which different members of the FGF family control stem cell function and epithelial morphogenesis in this tissue are not well understood. Here, we have examined the requirement of Fgfr2 in mouse mammary gland morphogenesis using a postnatal organ regeneration model. We found that tissue regeneration from basal stem cells is a multistep event, including luminal differentiation and subsequent epithelial branching morphogenesis. Basal cells lacking Fgfr2 did not generate an epithelial network owing to a failure in luminal differentiation. Moreover, Fgfr2 null epithelium was unable to undergo ductal branch initiation and elongation due to a deficiency in directional migration. We identified FGF10 and FGF2 as stromal ligands that control distinct aspects of mammary ductal branching. FGF10 regulates branch initiation, which depends on directional epithelial migration. By contrast, FGF2 controls ductal elongation, requiring cell proliferation and epithelial expansion. Together, our data highlight a pleiotropic role of Fgfr2 in stem cell differentiation and branch initiation, and reveal that different FGF ligands regulate distinct aspects of epithelial behavior. [ABSTRACT FROM AUTHOR]

Cell polarity is characterised by differences in structure, composition and function between at least two poles of a cell. In epithelial cells, these spatial differences allow for the formation of defined apical and basal membranes. It has been increasingly recognised that cell -- matrix interactions and integrins play an essential role in creating epithelial cell polarity, although key gaps in our knowledge remain. This Commentary will discuss the mounting evidence for the role of integrins in polarising epithelial cells. We build a model in which both inside-out signals to polarise basement membrane assembly at the basal surface, and outside-in signals to control microtubule apical -- basal orientation and vesicular trafficking are required for establishing and maintaining the orientation of epithelial cell polarity. Finally, we discuss the relevance of the basal integrin polarity axis to cancer. This article is part of a Minifocus on Establishing polarity. For further reading, please see related articles: 'ERM proteins at a glance' by Andrea McClatchey (J. Cell Sci. 127, 3199-3204). 'Establishment of epithelial polarity -- GEF who's minding the GAP?' by Siu Ngok et al. (J. Cell Sci. 127, 3205-3215). [ABSTRACT FROM AUTHOR]

Abstract: The development of the mammary gland is spatially regulated by the interaction of the mammary epithelium with the extracellular matrix (ECM). Cells receive cues from the ECM through a family of adhesion receptors called integrins, consisting of α- and β-chain dimers. Integrins assist cells in sensing their appropriate developmental context in response to both hormones and growth factors. Here we argue that cell adhesion to the ECM plays a key role in specific developmental checkpoints, particularly in alveolar survival, morphogenesis and function. Specific ablation of αβ1-integrins in the luminal epithelium of the mammary gland shows that this sub-type of receptors is required for proliferation, accurate morphological organisation, as well as milk secretion. Downstream, small Rho GTPases mediate cellular polarisation and differentiation. Current challenges in studying the integration of signals in checkpoints of mammary gland development are discussed. [Copyright &y& Elsevier]

Circadian clocks respond to environmental time cues to coordinate 24-hour oscillations in almost every tissue of the body. In the breast, circadian clocks regulate the rhythmic expression of numerous genes. Disrupted expression of circadian genes can alter breast biology and may promote cancer. Here we overview circadian mechanisms, and the connection between the molecular clock and breast biology. We describe how disruption of circadian genes contributes to cancer via multiple mechanisms, and link this to increased tumour risk in women who work irregular shift patterns. Understanding the influence of circadian rhythms on breast cancer could lead to more efficacious therapies, reformed public health policy and improved patient outcome. [ABSTRACT FROM AUTHOR]

Background: High mammographic density is a therapeutically modifiable risk factor for breast cancer. Although mammographic density is correlated with the relative abundance of collagen-rich fibroglandular tissue, the causative mechanisms, associated structural remodelling and mechanical consequences remain poorly defined. In this study we have developed a new collaborative bedside-to-bench workflow to determine the relationship between mammographic density, collagen abundance and alignment, tissue stiffness and the expression of extracellular matrix organising proteins.Methods: Mammographic density was assessed in 22 post-menopausal women (aged 54-66 y). A radiologist and a pathologist identified and excised regions of elevated non-cancerous X-ray density prior to laboratory characterization. Collagen abundance was determined by both Masson's trichrome and Picrosirius red staining (which enhances collagen birefringence when viewed under polarised light). The structural specificity of these collagen visualisation methods was determined by comparing the relative birefringence and ultrastructure (visualised by atomic force microscopy) of unaligned collagen I fibrils in reconstituted gels with the highly aligned collagen fibrils in rat tail tendon. Localised collagen fibril organisation and stiffness was also evaluated in tissue sections by atomic force microscopy/spectroscopy and the abundance of key extracellular proteins was assessed using mass spectrometry.Results: Mammographic density was positively correlated with the abundance of aligned periductal fibrils rather than with the abundance of amorphous collagen. Compared with matched tissue resected from the breasts of low mammographic density patients, the highly birefringent tissue in mammographically dense breasts was both significantly stiffer and characterised by large (>80 μm long) fibrillar collagen bundles. Subsequent proteomic analyses not only confirmed the absence of collagen fibrosis in high mammographic density tissue, but additionally identified the up-regulation of periostin and collagen XVI (regulators of collagen fibril structure and architecture) as potential mediators of localised mechanical stiffness.Conclusions: These preliminary data suggest that remodelling, and hence stiffening, of the existing stromal collagen microarchitecture promotes high mammographic density within the breast. In turn, this aberrant mechanical environment may trigger neoplasia-associated mechanotransduction pathways within the epithelial cell population. [ABSTRACT FROM AUTHOR]

Cell-matrix adhesion is essential for the development and tissue-specific functions of epithelia. For example, in the mammary gland, β1-integrin is necessary for the normal development of alveoli and for the activation of endocrine signalling pathways that determine cellular differentiation. However, the adhesion complex proteins linking integrins with downstream effectors of hormonal signalling pathways are not known. To understand the mechanisms involved in connecting adhesion with this aspect of cell phenotype, we examined the involvement of two proximal β1-integrin signalling intermediates, integrin-linked kinase (ILK) and focal adhesion kinase (FAK). By employing genetic analysis using the Cre-LoxP system, we provide evidence that ILK, but not FAK, has a key role in lactogenesis in vivo and in the differentiation of cultured luminal epithelial cells. Conditional deletion of ILK both in vivo and in primary cell cultures resulted in defective differentiation, by preventing phosphorylation and nuclear translocation of STAT5, a transcription factor required for lactation. Expression of an activated RAC (RAS-related C3 botulinum substrate) in ILK-null acini restored the lactation defect, indicating that RAC1 provides a mechanistic link between the integrin/ILK adhesion complex and the differentiation pathway. Thus, we have determined that ILK is an essential downstream component of integrin signalling involved in differentiation, and have identified a high degree of specificity within the integrin-based adhesome that links cell-matrix interactions with the tissue-specific function of epithelia. [ABSTRACT FROM AUTHOR]