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Adult bone marrow-derived cells (BMDC) are shown to contribute to muscle tissue in a step-wise biological progression. Following irradiation-induced damage, transplanted GFP-labeled BMDC become satellite cells: membrane-ensheathed mononucleate muscle stem cells. Following a subsequent exercise-induced damage, GFP-labeled multinucleate myofibers are detected. Isolated GFP-labeled satellite cells are heritably myogenic. They express three characteristic muscle markers, are karyotypically diploid, and form clones that can fuse into multinucleate cells in culture or into myofibers after injection into mouse muscles. These results suggest that two temporally distinct injury-related signals first induce BMDC to occupy the muscle stem cell niche and then to help regenerate mature muscle fibers. The stress-induced progression of BMDC to muscle satellite cell to muscle fiber results in a contribution to as many as 3.5% of muscle fibers and is due to developmental plasticity in response to environmental cues. [Copyright &y& Elsevier]

Epithelial-mesenchymal transition (EMT) is a developmental process in which epithelial cells acquire the motile, migratory properties of mesenchymal cells. In a recent issue of Cell, Mani et at. (2008) show that induction of EMT stimulates cultured breast cells to adopt characteristics of stem cells. [ABSTRACT FROM AUTHOR]

Dysregulation of the transcriptional or translational machinery can alter the stoichiometry of multiprotein complexes and occurs in natural processes such as aging. Loss of stoichiometry has been shown to alter protein complex functions. We provide a protocol and associated code that use omics data to quantify these stoichiometric changes via statistical dispersion utilizing the interquartile range of expression values per grouping variable. This descriptive statistical approach enables the quantification of stoichiometry changes without additional data acquisition. For complete details on the use and execution of this protocol, please refer to Hinz et al. (2021)., Competing Interests: The authors declare no competing interests., (© 2022 The Author(s).)

Age is the major risk factor in most carcinomas, yet little is known about how proteomes change with age in any human epithelium. We present comprehensive proteomes comprised of >9,000 total proteins and >15,000 phosphopeptides from normal primary human mammary epithelia at lineage resolution from ten women ranging in age from 19 to 68 years. Data were quality controlled and results were biologically validated with cell-based assays. Age-dependent protein signatures were identified using differential expression analyses and weighted protein co-expression network analyses. Upregulation of basal markers in luminal cells, including KRT14 and AXL, were a prominent consequence of aging. PEAK1 was identified as an age-dependent signaling kinase in luminal cells, which revealed a potential age-dependent vulnerability for targeted ablation. Correlation analyses between transcriptome and proteome revealed age-associated loss of proteostasis regulation. Age-dependent proteome changes in the breast epithelium identified heretofore unknown potential therapeutic targets for reducing breast cancer susceptibility., Competing Interests: The authors declare no competing interests., (© 2021 The Author(s).)

A long-standing constraint on organoid culture is the need to add exogenous substances to provide hydrogel matrix, which limits the study of fully human or fully native organoids. This paper introduces an approach to culture reconstituted mammary organoids without the impediment of exogenous matrix. We enclose organoids in nanoliter-scale, topologically enclosed, fluid compartments surrounded by agar. Organoids cultured in these "microcontainers" appear to secrete enough extracellular matrix to yield a self-sufficient microenvironment without exogenous supplements. In microcontainers, mammary organoids exhibit contractility and a high-level, physiological, myoepithelial (MEP) behavior that has not been previously reported in reconstituted organoids. The presence of contractility suggests that microcontainers elicit MEP functional differentiation, an important milestone. Microcontainers yield thousands of substantially identical and individually trackable organoids within a single culture vessel, enabling longitudinal studies and statistically powerful experiments, such as the evaluation of small effect sizes. Microcontainers open new doors for researchers who rely on organoid models., Competing Interests: A provisional patent application has been filed on the basis of this work., (© 2021 The Authors.)

The receptor tyrosine kinase AXL is associated with epithelial plasticity in several solid tumors including breast cancer and AXL-targeting agents are currently in clinical trials. We hypothesized that AXL is a driver of stemness traits in cancer by co-option of a regulatory function normally reserved for stem cells. AXL-expressing cells in human mammary epithelial ducts co-expressed markers associated with multipotency, and AXL inhibition abolished colony formation and self-maintenance activities while promoting terminal differentiation in vitro . Axl -null mice did not exhibit a strong developmental phenotype, but enrichment of Axl + cells was required for mouse mammary gland reconstitution upon transplantation, and Axl- driven mammary tumors. An AXL-dependent gene signature is a feature of transcriptomes in basal breast cancers and reduced patient survival irrespective of subtype. Our interpretation is that AXL regulates access to epithelial plasticity programs in MaSCs and, when co-opted, maintains acquired stemness in breast cancer cells.Wnt1- driven mammary tumors. An AXL-dependent gene signature is a feature of transcriptomes in basal breast cancers and reduced patient survival irrespective of subtype. Our interpretation is that AXL regulates access to epithelial plasticity programs in MaSCs and, when co-opted, maintains acquired stemness in breast cancer cells., Competing Interests: J.B.L. is founder and shareholder of BerGenBio ASA. K.W.L., G.G. and J.B.L. are former or current employees of BerGenBio ASA. J.P.T. is scientific founder and CSO of Biocheetah Pte Ltd Singapore and consultant/shareholder Biosyngen Pte Lte Limited and ACTgenomics Taipei Taiwan. S.C. and R.A.B. signed Sponsored Research Agreements with BerGenBio ASA related to a separate research project. The remaining authors declare no conflict of interest., (© 2020 The Author(s).)

The epidemiological association between disrupted circadian rhythms and metabolic diseases is implicated in increased risk of human breast cancer and poor therapeutic outcomes. To define a metabolic phenotype and the underlying molecular mechanism, we applied chronic insulin treatment (CIT) to an in vitro model of triple-negative breast cancer to directly address how BMAL1, a key circadian transcription factor, regulates cancer cell respiration and governs tumor progression. At the cellular level, BMAL1 suppresses the flexibility of mitochondrial substrate usage and the pyruvate-dependent mitochondrial respiration induced by CIT. We established an animal model of diet-induced obesity/hyperinsulinemia and observed that BMAL1 functions as a tumor suppressor in obese, but not lean, mice. Downregulation of BMAL1 is associated with higher risk of metastasis in human breast tumors. In summary, loss of BMAL1 in tumors confers advantages to cancer cells in both intrinsic mitochondrial metabolism and extrinsic inflammatory tumor microenvironment during pre-diabetic obesity/hyperinsulinemia., Competing Interests: Declaration of Interests The authors declare no competing interests., (Copyright © 2020 The Authors. Published by Elsevier Inc. All rights reserved.)

Potential for cancers to form metastases requires cell dissemination utilizing epithelial-to-mesenchymal transition (EMT) program. In this issue of Cancer Cell, Ishay-Ronen et al. show that plasticity intrinsic to the EMT program can be exploited to divert cancer cells into becoming post-mitotic adipocytes, thus preventing formation of metastases., (Copyright © 2019 Elsevier Inc. All rights reserved.)

Aging is associated with tissue-level changes in cellular composition that are correlated with increased susceptibility to disease. Aging human mammary tissue shows skewed progenitor cell potency, resulting in diminished tumor-suppressive cell types and the accumulation of defective epithelial progenitors. Quantitative characterization of these age-emergent human cell subpopulations is lacking, impeding our understanding of the relationship between age and cancer susceptibility. We conducted single-cell resolution proteomic phenotyping of healthy breast epithelia from 57 women, aged 16-91 years, using mass cytometry. Remarkable heterogeneity was quantified within the two mammary epithelial lineages. Population partitioning identified a subset of aberrant basal-like luminal cells that accumulate with age and originate from age-altered progenitors. Quantification of age-emergent phenotypes enabled robust classification of breast tissues by age in healthy women. This high-resolution mapping highlighted specific epithelial subpopulations that change with age in a manner consistent with increased susceptibility to breast cancer., (Copyright © 2018 The Authors. Published by Elsevier Inc. All rights reserved.)

To address cancer as a multifaceted adaptive system, the increasing momentum for cross-disciplinary connectivity between cancer biologists, physical scientists, mathematicians, chemists, biomedical engineers, computer scientists, clinicians, and advocates is fueling the emergence of new scientific frontiers, principles, and opportunities within physical sciences and oncology. In parallel to highlighting the advances, challenges, and acceptance of advocates as credible contributors, we offer recommendations for addressing real world hurdles in advancing equitable partnerships among advocacy stakeholders., (Copyright © 2018 Elsevier Inc. All rights reserved.)

Tumor microenvironments are a driver of resistance to anti-cancer drugs. Dissecting cell-microenvironment interactions into tractable units of study presents a challenge. Here, we assess the impact of hundreds of tumor-inspired microenvironments, in parallel, on lapatinib responses in four cancer cell lines. Combinations of ECM and soluble factors were printed on stiffness-tunable substrata to generate a collection of controlled microenvironments in which to explore cell-based functional responses. Proliferation, HER2 protein expression and phosphorylation, and morphology were measured in single cells. Using dimension reduction and linear modeling, the effects of microenvironment constituents were identified and then validated empirically. Each of the cell lines exhibits unique microenvironment-response patterns. Fibronectin, type IV collagen, and matrix rigidity are significant regulators of lapatinib resistance in HER2-amplified breast cancer cells. Small-molecule inhibitors were identified that could attenuate microenvironment-imposed resistance. Thus, we demonstrate a strategy to identify resistance- and sensitivity-driving microenvironments to improve the efficacy of anti-cancer therapeutics., (Copyright © 2017 The Author(s). Published by Elsevier Inc. All rights reserved.)

We hypothesize that breast cancer susceptibility stems from interactions between difficult-to-modify cultural and dietary habits and aging processes that are modifiable. We propose a pathway to prevention that uses human organotypic systems that recapitulate hallmarks of aging in order to better understand and to modulate the biological consequences of aging in breast., (Copyright © 2017 Elsevier Inc. All rights reserved.)

Dysfunctional progenitor and luminal cells with acquired basal cell properties accumulate during human mammary epithelial aging for reasons not understood. Multipotent progenitors from women aged <30 years were exposed to a physiologically relevant range of matrix elastic modulus (stiffness). Increased stiffness causes a differentiation bias towards myoepithelial cells while reducing production of luminal cells and progenitor maintenance. Lineage representation in progenitors from women >55 years is unaffected by physiological stiffness changes. Efficient activation of Hippo pathway transducers YAP and TAZ is required for the modulus-dependent myoepithelial/basal bias in younger progenitors. In older progenitors, YAP and TAZ are activated only when stressed with extraphysiologically stiff matrices, which bias differentiation towards luminal-like phenotypes. In vivo YAP is primarily active in myoepithelia of younger breasts, but localization and activity increases in luminal cells with age. Thus, aging phenotypes of mammary epithelia may arise partly because alterations in Hippo pathway activation impair microenvironment-directed differentiation and lineage specificity., (Copyright © 2014 The Authors. Published by Elsevier Inc. All rights reserved.)

Matrix metalloproteases promote tumor cell invasion, epithelial-to-mesenchymal transitions, and metastases, but whether they directly regulate stem cells is unknown. In this issue of Cell Stem Cell, Kessenbrock et al. (2013) now show that MMP3, independent of its proteolytic activity, regulates murine mammary stem cells by sequestering noncanonical Wnt signaling ligands, which has implications for breast cancer pathogenesis., (Copyright © 2013 Elsevier Inc. All rights reserved.)

Variability in signaling pathway activation between neighboring epithelial cells can arise from local differences in the microenvironment, noisy gene expression, or acquired genetic changes. To investigate the consequences of this cell-to-cell variability in signaling pathway activation on coordinated multicellular processes such as morphogenesis, we use DNA-programmed assembly to construct three-dimensional MCF10A microtissues that are mosaic for low-level expression of activated H-Ras. We find two emergent behaviors in mosaic microtissues: cells with activated H-Ras are basally extruded or lead motile multicellular protrusions that direct the collective motility of their wild-type neighbors. Remarkably, these behaviors are not observed in homogeneous microtissues in which all cells express the activated Ras protein, indicating that heterogeneity in Ras activity, rather than the total amount of Ras activity, is critical for these processes. Our results directly demonstrate that cell-to-cell variability in pathway activation within local populations of epithelial cells can drive emergent behaviors during epithelial morphogenesis., (Copyright © 2012 The Authors. Published by Elsevier Inc. All rights reserved.)