Transforming growth factor beta3 induces cell death during the first stage of mammary gland involution

Genome-wide in vivo CRISPR screen identifies TGFβ3 as actionable biomarker of palbociclib resistance in triple negative breast cancer

Triple negative breast cancer (TNBC) remains exceptionally challenging to treat. While CDK4/6 inhibitors have revolutionized HR + breast cancer therapy, there is limited understanding of their efficacy in TNBC and meaningful predictors of response and resistance to these drugs remain scarce. We conducted an in vivo genome-wide CRISPR screen using palbociclib as a selection pressure in TNBC. Hits were prioritized using microarray data from a large panel of breast cancer cell lines to identify top palbociclib sensitizers. Our study defines TGFβ3 as an actionable determinant of palbociclib sensitivity that potentiates its anti-tumor effects. Mechanistically, we show that chronic palbociclib exposure depletes p21 levels, contributing to acquired resistance, and that TGFβ3 treatment can overcome this. This study defines TGFβ3 as an actionable biomarker that can be used to improve patient stratification for palbociclib treatment and exploits the synergistic interaction between CDK4/6 and TGFβ3 to propose a new combinatorial treatment for TNBC.

Protein Dynamic Landscape during Mouse Mammary Gland Development from Virgin to Pregnant, Lactating, and Involuting Stages

The mammary gland undergoes significant physiological changes as it undergoes a transition from virgin to pregnancy, lactation, and involution. However, the dynamic role of proteins in regulating these processes during mouse mammary gland development has not been thoroughly explored. In this study, we collected mouse mammary gland tissues from mature virgins aged 8-10 weeks (V), day 16 of pregnancy (P16d), day 12 of lactation (L12d), day 1 of forced weaning (FW 1d), and day 3 of forced weaning (FW 3d) stages for analysis using DIA-based quantitative proteomics technology. A total of 3,312 proteins were identified, of which 843 were DAPs that were categorized into nine clusters based on their abundance changes across developmental stages. Notably, DAPs in cluster 2, which peaked at the L12d stage, were primarily associated with mammary gland development and lactation. The protein-protein interaction network revealed that the epidermal growth factor (EGF) was central to this cluster. Our study provides a comprehensive overview of the mouse mammary gland development proteome and identifies some important proteins, such as EGF, Janus kinase 1 (JAK1), and signal transducer and activator of transcription 6 (STAT6) that may serve as potential targets for future research to provide guidelines for a deeper understanding of the developmental biology of mammary glands.

Intracellular calcium links milk stasis to lysosome-dependent cell death during early mammary gland involution

Involution of the mammary gland after lactation is a dramatic example of coordinated cell death. Weaning causes distension of the alveolar structures due to the accumulation of milk, which, in turn, activates STAT3 and initiates a caspase-independent but lysosome-dependent cell death (LDCD) pathway. Although the importance of STAT3 and LDCD in early mammary involution is well established, it has not been entirely clear how milk stasis activates STAT3. In this report, we demonstrate that protein levels of the PMCA2 calcium pump are significantly downregulated within 2-4 h of experimental milk stasis. Reductions in PMCA2 expression correlate with an increase in cytoplasmic calcium in vivo as measured by multiphoton intravital imaging of GCaMP6f fluorescence. These events occur concomitant with the appearance of nuclear pSTAT3 expression but prior to significant activation of LDCD or its previously implicated mediators such as LIF, IL6, and TGFβ3, all of which appear to be upregulated by increased intracellular calcium. We further demonstrate that increased intracellular calcium activates STAT3 by inducing degradation of its negative regulator, SOCS3. We also observed that milk stasis, loss of PMCA2 expression and increased intracellular calcium levels activate TFEB, an important regulator of lysosome biogenesis through a process involving inhibition of CDK4/6 and cell cycle progression. In summary, these data suggest that intracellular calcium serves as an important proximal biochemical signal linking milk stasis to STAT3 activation, increased lysosomal biogenesis, and lysosome-mediated cell death.

Intracellular Calcium links Milk Stasis to Lysosome Dependent Cell Death by Activating a TGFβ3/TFEB/STAT3 Pathway Early during Mammary Gland Involution

Involution of the mammary gland after lactation is a dramatic example of coordinated cell death. Weaning causes distension of the alveolar structures due to the accumulation of milk, which, in turn, activates STAT3 and initiates a caspase-independent but lysosome-dependent cell death (LDCD) pathway. Although the importance of STAT3 and LDCD in early mammary involution is well established, it has not been entirely clear how milk stasis activates STAT3. In this report, we demonstrate that protein levels of the PMCA2 calcium pump are significantly downregulated within 2-4 hours of experimental milk stasis. Reductions in PMCA2 expression correlate with an increase in cytoplasmic calcium in vivo as measured by multiphoton intravital imaging of GCaMP6f fluorescence. These events occur concomitant with the appearance of nuclear pSTAT3 expression but prior to significant activation of LDCD or its previously implicated mediators such as LIF, IL6 and TGFβ3, all of which appear to be upregulated by increased intracellular calcium. We also observed that milk stasis, loss of PMCA2 expression and increased intracellular calcium levels activate TFEB, an important regulator of lysosome biogenesis. This is the result of increased TGFβ signaling and inhibition of cell cycle progression. Finally, we demonstrate that increased intracellular calcium activates STAT3 by inducing degradation of its negative regulator, SOCS3, a process which also appears to be mediated by TGFβ signaling. In summary, these data suggest that intracellular calcium serves as an important proximal biochemical signal linking milk stasis to STAT3 activation, increased lysosomal biogenesis, and lysosome-mediated cell death.

Hormonal regulation of mammary gland development and lactation

Lactation is critical to infant short-term and long-term health and protects mothers from breast cancer, ovarian cancer and type 2 diabetes mellitus. The mammary gland is a dynamic organ, regulated by the coordinated actions of reproductive and metabolic hormones. These hormones promote gland development from puberty onwards and induce the formation of a branched, epithelial, milk-secreting organ by the end of pregnancy. Progesterone withdrawal following placental delivery initiates lactation, which is maintained by increased pituitary secretion of prolactin and oxytocin, and stimulated by infant suckling. After weaning, local cytokine production and decreased prolactin secretion trigger large-scale mammary cell loss, leading to gland involution. Here, we review advances in the molecular endocrinology of mammary gland development and milk synthesis. We discuss the hormonal functions of the mammary gland, including parathyroid hormone-related peptide secretion that stimulates maternal calcium mobilization for milk synthesis. We also consider the hormonal composition of human milk and its associated effects on infant health and development. Finally, we highlight endocrine and metabolic diseases that cause lactation insufficiency, for example, monogenic disorders of prolactin and prolactin receptor mutations, maternal obesity and diabetes mellitus, interventions during labour and delivery, and exposure to endocrine-disrupting chemicals such as polyfluoroalkyl substances in consumer products and other oestrogenic compounds.

Association between Maternal Characteristics and Immune Factors TGF-β1, TGF-β2, and IgA in Colostrum: An Exploratory Study in Japan

Colostrum is the first food for newborns and it contains various crucial immune factors. The concentrations of immune factors in breast milk may change depending on maternal characteristics such as body mass index, collection day, and age at first pregnancy. In this exploratory study, we investigated the association between TGF-β1, TGF-β2, and IgA in colostrum and rarely studied factors that affect breast milk components, including the use of labor-inducing medication, colostrum secretion, sex of newborns, breast or nipple problems, and nipple care. Breast milk samples were collected from 42 mothers and analyzed for TGF-β1, TGF-β2, and IgA. The results suggest that parity and mode of delivery may be correlated with the concentrations of immune factors in colostrum. However, we found no association between the immune factors in colostrum and the use of labor-inducing medications, colostrum secretion, sex of newborns, breast or nipple problems, and nipple care. These findings have some implications for further analysis of the effects of immune factors in breast milk on the prognosis of allergies in children.

The Bright and the Dark Side of TGF-β Signaling in Hepatocellular Carcinoma: Mechanisms, Dysregulation, and Therapeutic Implications

Simple Summary

Transforming growth factor β (TGF-β) signaling is a preeminent regulator of diverse cellular and physiological processes. Frequent dysregulation of TGF-β signaling has been implicated in cancer. In hepatocellular carcinoma (HCC), the most prevalent form of primary liver cancer, the autocrine and paracrine effects of TGF-β have paradoxical implications. While acting as a potent tumor suppressor pathway in the early stages of malignancy, TGF-β diverts to a promoter of tumor progression in the late stages, reflecting its bright and dark natures, respectively. Within this context, targeting TGF-β represents a promising therapeutic option for HCC treatment. We discuss here the molecular properties of TGF-β signaling in HCC, attempting to provide an overview of its effects on tumor cells and the stroma. We also seek to evaluate the dysregulation mechanisms that mediate the functional switch of TGF-β from a tumor suppressor to a pro-tumorigenic signal. Finally, we reconcile its biphasic nature with the therapeutic implications.

Abstract

Hepatocellular carcinoma (HCC) is associated with genetic and nongenetic aberrations that impact multiple genes and pathways, including the frequently dysregulated transforming growth factor β (TGF-β) signaling pathway. The regulatory cytokine TGF-β and its signaling effectors govern a broad spectrum of spatiotemporally regulated molecular and cellular responses, yet paradoxically have dual and opposing roles in HCC progression. In the early stages of tumorigenesis, TGF-β signaling enforces profound tumor-suppressive effects, primarily by inducing cell cycle arrest, cellular senescence, autophagy, and apoptosis. However, as the tumor advances in malignant progression, TGF-β functionally switches to a pro-tumorigenic signal, eliciting aggressive tumor traits, such as epithelial–mesenchymal transition, tumor microenvironment remodeling, and immune evasion of cancer cells. On this account, the inhibition of TGF-β signaling is recognized as a promising therapeutic strategy for advanced HCC. In this review, we evaluate the functions and mechanisms of TGF-β signaling and relate its complex and pleiotropic biology to HCC pathophysiology, attempting to provide a detailed perspective on the molecular determinants underlying its functional diversion. We also address the therapeutic implications of the dichotomous nature of TGF-β signaling and highlight the rationale for targeting this pathway for HCC treatment, alone or in combination with other agents.

Aberrant RET expression impacts on normal mammary gland post-lactation transition enhancing cancer potential

RET is a receptor tyrosine kinase with oncogenic potential in the mammary epithelium. Several receptors with oncogenic activity in the breast are known to participate in specific developmental stages. We found that RET is differentially expressed during mouse mammary gland development: RET is present in lactation and its expression dramatically decreases in involution, the period during which the lactating gland returns to a quiescent state after weaning. Based on epidemiological and pre-clinical findings, involution has been described as tumor promoting. Using the Ret/MTB doxycycline-inducible mouse transgenic system, we show that sustained expression of RET in the mammary epithelium during the post-lactation transition to involution is accompanied by alterations in tissue remodeling and an enhancement of cancer potential. Following constitutive Ret expression, we observed a significant increase in neoplastic lesions in the post-involuting versus the virgin mammary gland. Furthermore, we show that abnormal RET overexpression during lactation promotes factors that prime involution, including premature activation of Stat3 signaling and, using RNA sequencing, an acute-phase inflammatory signature. Our results demonstrate that RET overexpression negatively affects the normal post-lactation transition.

Summary: We show that RET activation stimulates Stat3 signaling in mammary epithelial cell culture and in vivo during post-lactation transition, demonstrating that the RET receptor participates in the post-lactation transition priming tumorigenesis.

Molecular mechanisms of mammary gland remodeling: A review of the homeostatic versus bisphenol a disrupted microenvironment

Mammary gland (MG) undergoes critical points of structural changes throughout a woman's life. During the perinatal and pubertal stages, MG develops through growth and differentiation to establish a pre-mature feature. If pregnancy and lactation occur, the epithelial compartment branches and differentiates to create a specialized structure for milk secretion and nurturing of the newborn. However, the ultimate MG modification consists of a regression process aiming to reestablish the smaller and less energy demanding structure until another production cycle happens. The unraveling of these fascinating physiologic cycles has helped the scientific community elucidate aspects of molecular regulation of proliferative and apoptotic events and remodeling of the stromal compartment. However, greater understanding of the hormonal pathways involved in MG developmental stages led to concern that endocrine disruptors such as bisphenol A (BPA), may influence these specific development/involution stages, called "windows of susceptibility". Since it is used in the manufacture of polycarbonate plastics and epoxy resins, BPA is a ubiquitous chemical present in human everyday life, exerting an estrogenic effect. Thus, descriptions of its deleterious effects on the MG, especially in terms of serum hormone concentrations, hormonal receptor expression, molecular pathways, and epigenetic alterations, have been widely published. Therefore, allied to a didactic description of the main physiological mechanisms involved in different critical points of MG development, the current review provides a summary of key mechanisms by which the endocrine disruptor BPA impacts MG homeostasis at different windows of susceptibility, causing short- and long-term effects.

The molecular basis of mammary gland development and epithelial differentiation

Our understanding of the molecular events underpinning the development of mammalian organ systems has been increasing rapidly in recent years. With the advent of new and improved next-generation sequencing methods, we are now able to dig deeper than ever before into the genomic and epigenomic events that play critical roles in determining the fates of stem and progenitor cells during the development of an embryo into an adult. In this review, we detail and discuss the genes and pathways that are involved in mammary gland development, from embryogenesis, through maturation into an adult gland, to the role of pregnancy signals in directing the terminal maturation of the mammary gland into a milk producing organ that can nurture the offspring. We also provide an overview of the latest research in the single-cell genomics of mammary gland development, which may help us to understand the lineage commitment of mammary stem cells (MaSCs) into luminal or basal epithelial cells that constitute the mammary gland. Finally, we summarize the use of 3D organoid cultures as a model system to study the molecular events during mammary gland development. Our increased investigation of the molecular requirements for normal mammary gland development will advance the discovery of targets to predict breast cancer risk and the development of new breast cancer therapies.

Effects of Probiotic Supplementation on TGF-β1, TGF-β2, and IgA Levels in the Milk of Japanese Women: An Open-Label Pilot Study

Background: Dietary probiotics supplementation in lactating mothers may help prevent allergic disease in infants. However, owing to a lack of consistency in nutritional and safety outcomes associated with probiotics, this topic remains controversial.

Methods: In this open-label pilot trial conducted between April 2013 and December 2013, we evaluated the safety of probiotic supplementation with 5 × 10⁹ CFU of Lactobacillus casei LC5, 5 × 10⁹ CFU of Bifidobacterium longum BG7, and 2 × 10⁸ CFU of Bacillus coagulans SANK70258 in lactating women who exhibited allergies for 2 months (1–3 months postpartum); we also evaluated the effects of probiotic supplementation on transforming growth factor-β (TGF-β) and immunoglobulin A (IgA) levels in human milk. Participants self-selected to join the probiotic (n = 41; age [median (interquartile range [IQR]), y] 33 [27–39], body mass index [BMI] [median (IQR), kg/m²] 21.8 [19.5–22.8]) or no supplementation control group (n = 19; age [median (IQR), y] 33 [23–43], BMI [median (IQR), kg/m²) 19.6 [18.4–22.1]). Probiotics (three tablets) received were taken as daily supplements. Milk samples were collected at 1, 2, and 3 months postpartum, and TGF-β1, TGF-β2, and IgA levels were measured.

Results: No adverse effects were observed in the probiotic group, according to the self-recorded diary during the study period. Milk IgA decreased with increasing postpartum months in both groups. In contrast, TGF- β1 and β2 were not affected by lactation periods, and showed different patterns over time between the two groups. TGF-β1, TGF-β1, and IgA levels were significantly correlated at baseline (respectively p < 0.05). However, the correlation between TGF-β1 and IgA became non-significant by the end of the intervention (p = 0.063).

Conclusion: Altogether, probiotic supplementation was tolerated with respect to no dropout and 91.5% adherence. Although probiotic supplementation might affect human milk TGF-β levels, a positive effect of probiotic supplementation was not entirely supported. Future placebo-controlled studies are needed to further support the efficacy and safety of probiotic supplementation.

Clinical Trial Registration:www.umin.ac.jp/ctr/, identifier: UMIN000036059.

Prognostic role of Tif1γ expression and circulating tumor cells in patients with breast cancer

Transcription intermediary factor 1γ (Tif1γ), a ubiquitous nuclear protein, is a regulator of transforming growth factor-β (TGF-β)/Smad signaling. Tif1γ can function as an oncogene and as a tumor suppressor. In the present study, Tif1γ levels were measured in the plasma of patients with breast cancer in order to investigate the association of Tif1γ with overall survival (OS). The results indicated that Tif1γ is an independent prognostic and predictive factor in breast cancer, and thus, a promising target protein for use in diagnostics and patient follow-up. Plasma levels of Tif1γ were measured in samples obtained from 110 patients with operable breast cancer and in 110 healthy volunteers at the Breast Cancer Department of Yangpu Hospital between 2008 and 2016. The association between Tif1γ levels and clinicopathologic parameters, and the OS in a follow-up period of 98 months was evaluated. The prognostic significance was assessed using the Kaplan-Meier method. The levels of Tif1γ were significantly lower in patients with breast cancer compared with healthy controls. The average concentration of 18.40 ng/ml was used to discriminate between Tif1γ-positive (52) and Tif1γ-negative patients (58). Tif1γ-positive patients had a significantly improved OS compared with Tif1γ-negative patients. In the multivariate analysis, Tif1γ was an independent predictor of a favorable OS in a prospective follow-up setting; thus, Tif1γ plasma levels are an independent prognostic factor for patients with breast cancer. These findings support the potential of using measurements of Tif1γ plasma levels to guide breast cancer therapy and monitoring. Further studies are required to validate Tif1γ as an easily detectable, non-invasive prognostic biomarker for breast cancer.

Forkhead box protein A1 confers resistance to transforming growth factor-β-induced apoptosis in breast cancer cells through inhibition of Smad3 nuclear translocation

Transforming growth factor-β (TGF-β) induces apoptosis of normal epithelial cells, such as mammary epithelium. Although breast cancer progression associates with acquisition of resistance to TGF-β-induced apoptosis, the molecular mechanisms underlying this resistance are largely unknown. Here, we show that forkhead box protein A1 (FOXA1), which is known as a pioneer transcription factor, suppresses TGF-β-induced apoptosis of estrogen receptor-positive breast cancer cells. FOXA1 is found to inhibit nuclear translocation of Smad3, a key transcription factor downstream of TGF-β signaling, through suppression of the binding of Smad3 to the nuclear import receptor importin7. Furthermore, RNA sequencing analyses show that knockdown of FOXA1 upregulates Smad3-mediated proapoptotic gene expression. These results demonstrate that FOXA1 as a potent survival factor that suppresses TGF-β-induced apoptosis by inhibiting Smad3 signaling in estrogen receptor-positive breast cancer cells. Thus, we provide evidence for the first time that FOXA1 localizing to the cytoplasm negatively regulates Smad3-induced apoptosis in TGF-β-mediated signal transduction.

TGF-beta signalling in bovine mammary gland involution and a comparative assessment of MAC-T and BME-UV1 cells as in vitro models for its study

The goal of the dairy industry is ultimately to increase lactation persistency, which is the length of time during which peak milk yield is sustained. Lactation persistency is determined by the balance of cell apoptosis and cell proliferation; when the balance is skewed toward the latter, this results in greater persistency. Thus, we can potentially increase milk production in dairy cows through manipulating apoptogenic and antiproliferative cellular signaling that occurs in the bovine mammary gland. Transforming growth factor beta 1 (TGFβ1) is an antiproliferative and apoptogenic cytokine that is upregulated during bovine mammary gland involution. Here, we discuss possible applications of TGFβ1 signaling for the purposes of increasing lactation persistency. We also compare the features of mammary alveolar cells expressing SV-40 large T antigen (MAC-T) and bovine mammary epithelial cells-clone UV1 (BME-UV1) cells, two extensively used bovine mammary epithelial cell lines, to assess their appropriateness for the study of TGFβ1 signaling. TGFβ1 induces apoptosis and arrests cell growth in BME-UV1 cells, and this was reported to involve suppression of the somatotropic axis. Conversely, there is no proof that exogenous TGFβ1 induces apoptosis of MAC-T cells. In addition to TGFβ1's different effects on apoptosis in these cell lines, hormones and growth factors have distinct effects on TGFβ1 secretion and synthesis in MAC-T and BME-UV1 cells as well. MAC-T and BME-UV1 cells may behave differently in response to TGFβ1 due to their contrasting phenotypes; MAC-T cells have a profile indicative of both myoepithelial and luminal populations, while the BME-UV1 cells exclusively contain a luminal-like profile. Depending on the nature of the research question, the use of these cell lines as models to study TGFβ1 signaling should be carefully tailored to the questions asked.

Reawakening of dormant estrogen-dependent human breast cancer cells by bone marrow stroma secretory senescence

Background

Dormant estrogen receptor positive (ER+) breast cancer micrometastases in the bone marrow survive adjuvant chemotherapy and recur stochastically for more than 20 years. We hypothesized that inflammatory cytokines produced by stromal injury can re-awaken dormant breast cancer cells.

Methods

We used an established in vitro dormancy model of Michigan Cancer Foundation-7 (MCF-7) breast cancer cells incubated at clonogenic density on fibronectin-coated plates to determine the effects of inflammatory cytokines on reactivation of dormant ER+ breast cancer cells. We measured induction of a mesenchymal phenotype, motility and the capacity to re-enter dormancy. We induced secretory senescence in murine stromal monolayers by oxidation, hypoxia and estrogen deprivation with hydrogen peroxide (H₂O₂), carbonyl-cyanide m-chlorophenylhydrazzone (CCCP) and Fulvestrant (ICI 182780), respectively, and determined the effects on growth of co-cultivated breast cancer cells.

Results

Exogenous recombinant human (rh) interleukin (IL)-6, IL-8 or transforming growth factor β1 (TGFβ1) induced regrowth of dormant MCF-7 cells on fibronectin-coated plates. Dormant cells had decreased expression of E-cadherin and estrogen receptor α (ERα) and increased expression of N-cadherin and SNAI2 (SLUG). Cytokine or TGFβ1 treatment of dormant clones induced formation of growing clones, a mesenchymal appearance, increased motility and an impaired capacity to re-enter dormancy. Stromal injury induced secretion of IL-6, IL-8, upregulated tumor necrosis factor alpha (TNFα), activated TGFβ and stimulated the growth of co-cultivated MCF-7 cells. MCF-7 cells induced secretion of IL-6 and IL-8 by stroma in co-culture.

Conclusions

Dormant ER+ breast cancer cells have activated epithelial mesenchymal transition (EMT) gene expression programs and downregulated ERα but maintain a dormant epithelial phenotype. Stromal inflammation reactivates these cells, induces growth and a mesenchymal phenotype. Reactivated, growing cells have an impaired ability to re-enter dormancy. In turn, breast cancer cells co-cultured with stroma induce secretion of IL-6 and IL-8 by the stroma, creating a positive feedback loop.

The Multifaceted Role of STAT3 in Mammary Gland Involution and Breast Cancer

Since seminal descriptions of signal transducer and activator of transcription 3 (STAT3) as a signal transducer and transcriptional regulator, which is most usually activated by phosphorylation of a specific tyrosine residue, a staggering wealth of research has delineated the key role of this transcription factor as a mediator of mammary gland postlactational regression (involution), and paradoxically, a pro-survival factor in breast cancer and some breast cancer cell lines. STAT3 is a critical regulator of lysosomal-mediated programmed cell death (LM-PCD) during mammary gland involution, where uptake of milk fat globules, and consequent high levels of free fatty acids, cause permeabilisation of lysosomal vesicle membranes, in turn leading to cathepsin protease leakage and cell death. A recent proteomic screen of STAT3-induced changes in lysosomal membrane protein components has highlighted wide-ranging effects of STAT3, which may coordinate LM-PCD via the stimulation of endocytosis, intracellular trafficking, and lysosome biogenesis. In parallel, STAT3 regulates the acute phase response during the first phase of involution, and it contributes to shaping the pro-tumourigenic 'wound healing' signature of the gland during the second phase of this process. STAT3 activation during involution is important across species, although some differences exist in the progression of involution in dairy cows. In breast cancer, a number of upstream regulators can lead to STAT3 activation and the effects of phosphorylation of STAT3 are equally wide-ranging. Recent studies have implicated microRNAs in some regulatory pathways. In this review, we will examine the multifaceted role of STAT3 in mammary gland involution and tumourigenesis, incorporating a review of these fundamental processes in tandem with a discussion of recent developments in this field.

The cJUN NH2-terminal kinase (JNK) pathway contributes to mouse mammary gland remodeling during involution

Involution returns the lactating mammary gland to a quiescent state after weaning. The mechanism of involution involves collapse of the mammary epithelial cell compartment. To test whether the cJUN NH₂-terminal kinase (JNK) signal transduction pathway contributes to involution, we established mice with JNK deficiency in the mammary epithelium. We found that JNK is required for efficient involution. JNK deficiency did not alter the STAT3/5 or SMAD2/3 signaling pathways that have been previously implicated in this process. Nevertheless, JNK promotes the expression of genes that drive involution, including matrix metalloproteases, cathepsins, and BH3-only proteins. These data demonstrate that JNK has a key role in mammary gland involution post lactation.

TGF-β Family Signaling in Ductal Differentiation and Branching Morphogenesis

Epithelial cells contribute to the development of various vital organs by generating tubular and/or glandular architectures. The fully developed forms of ductal organs depend on processes of branching morphogenesis, whereby frequency, total number, and complexity of the branching tissue define the final architecture in the organ. Some ductal tissues, like the mammary gland during pregnancy and lactation, disintegrate and regenerate through periodic cycles. Differentiation of branched epithelia is driven by antagonistic actions of parallel growth factor systems that mediate epithelial-mesenchymal communication. Transforming growth factor-β (TGF-β) family members and their extracellular antagonists are prominently involved in both normal and disease-associated (e.g., malignant or fibrotic) ductal tissue patterning. Here, we discuss collective knowledge that permeates the roles of TGF-β family members in the control of the ductal tissues in the vertebrate body.

Differential expression of TGFβ isoforms in breast cancer highlights different roles during breast cancer progression

While TGFβ plays a critical role in tumor formation and progression, the role and contribution of its three different isoforms remain unclear. In this study, we aimed at elucidating the prognostic value of the TGFβ isoforms and assessed their expression levels in breast cancer patients at different stages of the disease. We found higher levels of TGFβ1 and TGFβ3 in cancer patients compared to normal tissues, with no significant changes in TGFβ2 expression. Similarly, TGFβ1 and TGFβ3, but not TGFβ2, showed higher expression levels in advanced lymph node-positive and metastatic tumors, suggesting different roles for the different isoforms in tumor progression and the metastatic process, while in the least aggressive molecular subtype (luminal A), expression of the three TGFβ isoforms significantly correlated with expression of both TGFβ receptors, such correlation only occurred between TGFβ1 and TGFβ3 and the TGFβ type II receptor (TβRII) in the highly aggressive basal-like subtype. Interestingly, a distinct and somehow opposite pattern was observed in HER-2 tumors, only showing significant association pattern between TGFβ2 and the TGFβ type I receptor (TβRI). Finally, the three TGFβ isoforms showed distinct association patterns with patient outcome depending on the different molecular subtype, highlighting context-dependent, differential prognostic values.

Cytokines in milk and the role of TGF-beta

Cytokines are required for normal growth and development of the mammary gland and TGF-β prominently represents an established effector of apoptosis, e.g., during involution of the mammary gland. By the control of intracellular signaling pathways, including JAK/STAT, MAPK, PI-3K, and NF-κB, cytokines efficiently regulate cell proliferation and inflammation in the breast. Therefore, cytokines are discussed also in a context of malignant mammary growth. As a group of tissue hormones produced by somatic cells or by cells from the immune system, cytokines are defined by their immunomodulatory potential. Over the past 40 years, multiple cytokines were identified in colostrum and milk. Importantly, cytokines derived from mammary secretions after birth are required for maturation of the immune system in the developing gastrointestinal tract from the suckling. Moreover, recent studies have further assessed the particular interactions between probiotic bacterial strains and cytokines. In light of the increasing prevalence of inflammatory diseases of the gastrointestinal system, the effects of probiotic microorganisms during milk fermentation may have immunotherapeutic potential in the future.

Postlactational involution biomarkers plasminogen and phospho-STAT3 are linked with active age-related lobular involution

Purpose

Breast terminal duct lobular units undergo two distinctive physiological processes of involution: age-related lobular involution (LI), which is gradual and associated with decreased breast cancer risk, and postlactational involution, which is relatively precipitous, occurs with weaning, and has been associated with potentiation of tumor aggressiveness in animal models. Here we assessed whether markers of postlactational involution are associated with ongoing LI in a retrospective tissue cohort.

Methods

We selected 57 women from the Mayo Clinic Benign Breast Disease Cohort who underwent multiple biopsies and who were average age 48 at initial biopsy. Women were classified as having progressive or non-progressive LI between initial and subsequent biopsy. Serial tissue sections were immunostained for plasminogen, matrix metalloproteinase 9 (MMP-9), phospho-STAT3 (pSTAT3), tenascin C, Ki67, CD44, cytokeratin 14 (CK14), cytokeratin 19 (CK19), and c-myc. All but Ki67 were digitally quantified. Associations between maximal marker expression per sample and progressive versus non-progressive LI were assessed using logistic regression and adjusted for potential confounders.

Results

While no biomarker showed statistically significant association with LI progression when evaluated individually, lower expression of pSTAT3 (OR 0.35, 95% CI 0.13–0.82, p = 0.01) and higher expression of plasminogen (OR 2.89, 95% CI 1.14–8.81, p = 0.02) were associated with progressive LI in models simultaneously adjusted for all biomarkers. Sensitivity analyses indicated that the strengthening in association for pSTAT3 and plasminogen with progressive LI was due to collinearity between these two markers.

Conclusions

This is the first study to identify biomarkers of active LI. Our findings that plasminogen and pSTAT3 are significantly associated with LI suggest that they may represent signaling nodes or biomarkers of pathways common to the processes of postlactational involution and LI.

Electronic supplementary material

The online version of this article (doi:10.1007/s10549-017-4413-3) contains supplementary material, which is available to authorized users.

miR-424(322)/503 is a breast cancer tumor suppressor whose loss promotes resistance to chemotherapy

In this study, Rodriguez-Barrueco et al. analyzed ∼3000 primary tumors and show that miR-424(322)/503 is commonly lost in a subset of aggressive breast cancers; they then describe the genetic aberrations that inactivate its expression. Their data show that miR-424(322)/503 is a tumor suppressor in breast cancer and provide a link between mammary epithelial involution, tumorigenesis, and the phenomenon of chemoresistance.

The female mammary gland is a very dynamic organ that undergoes continuous tissue remodeling during adulthood. Although it is well established that the number of menstrual cycles and pregnancy (in this case transiently) increase the risk of breast cancer, the reasons are unclear. Growing clinical and experimental evidence indicates that improper involution plays a role in the development of this malignancy. Recently, we described the miR-424(322)/503 cluster as an important regulator of mammary epithelial involution after pregnancy. Here, through the analysis of ∼3000 primary tumors, we show that miR-424(322)/503 is commonly lost in a subset of aggressive breast cancers and describe the genetic aberrations that inactivate its expression. Furthermore, through the use of a knockout mouse model, we demonstrate for the first time that loss of miR-424(322)/503 promotes breast tumorigenesis in vivo. Remarkably, we found that loss of miR-424(322)/503 promotes chemoresistance due to the up-regulation of two of its targets: BCL-2 and insulin-like growth factor-1 receptor (IGF1R). Importantly, targeted therapies blocking the aberrant activity of these targets restore sensitivity to chemotherapy. Overall, our studies reveal miR-424(322)/503 as a tumor suppressor in breast cancer and provide a link between mammary epithelial involution, tumorigenesis, and the phenomenon of chemoresistance.

Physiologically activated mammary fibroblasts promote postpartum mammary cancer

Women diagnosed with breast cancer within 5 years of childbirth have poorer prognosis than nulliparous or pregnant women. Weaning-induced breast involution is implicated, as the collagen-rich, immunosuppressive microenvironment of the involuting mammary gland is tumor promotional in mice. To investigate the role of mammary fibroblasts, isolated mammary PDGFRα⁺ cells from nulliparous and postweaning mice were assessed for activation phenotype and protumorigenic function. Fibroblast activation during involution was evident by increased expression of fibrillar collagens, lysyl oxidase, Tgfb1, and Cxcl12 genes. The ability of mammary tumors to grow in an isogenic, orthotopic transplant model was increased when tumor cells were coinjected with involution-derived compared with nulliparous-derived mammary fibroblasts. Mammary tumors in the involution-fibroblast group had increased Ly6C⁺ monocytes at the tumor border, and decreased CD8⁺ T cell infiltration and tumor cell death. Ibuprofen treatment suppressed involution-fibroblast activation and tumor promotional capacity, concurrent with decreases in tumor Ly6C⁺ monocytes, and increases in intratumoral CD8⁺ T cell infiltration, granzyme levels, and tumor cell death. In total, our data identify a COX/prostaglandin E2 (PGE2)-dependent activated mammary fibroblast within the involuting mammary gland that displays protumorigenic, immunosuppressive activity, identifying fibroblasts as potential targets for the prevention and treatment of postpartum breast cancer.

MicroRNA roles in signalling during lactation: an insight from differential expression, time course and pathway analyses of deep sequence data

The study examined microRNA (miRNA) expression and regulatory patterns during an entire bovine lactation cycle. Total RNA from milk fat samples collected at the lactogenesis (LAC, day1 [D1] and D7), galactopoiesis (GAL, D30, D70, D130, D170 and D230) and involution (INV, D290 and when milk production dropped to 5 kg/day) stages from 9 cows was used for miRNA sequencing. A total of 475 known and 238 novel miRNAs were identified. Fifteen abundantly expressed miRNAs across lactation stages play regulatory roles in basic metabolic, cellular and immunological functions. About 344, 366 and 209 miRNAs were significantly differentially expressed (DE) between GAL and LAC, INV and GAL, and INV and LAC stages, respectively. MiR-29b/miR-363 and miR-874/miR-6254 are important mediators for transition signals from LAC to GAL and from GAL to INV, respectively. Moreover, 58 miRNAs were dynamically DE in all lactation stages and 19 miRNAs were significantly time-dependently DE throughout lactation. Relevant signalling pathways for transition between lactation stages are involved in apoptosis (PTEN and SAPK/JNK), intracellular signalling (protein kinase A, TGF-β and ERK5), cell cycle regulation (STAT3), cytokines, hormones and growth factors (prolactin, growth hormone and glucocorticoid receptor). Overall, our data suggest diverse, temporal and physiological signal-dependent regulatory and mediator functions for miRNAs during lactation.

Mammary Gland Involution Provides a Unique Model to Study the TGF-β Cancer Paradox

Transforming Growth Factor-β (TGF-β) signaling in cancer has been termed the “TGF-β paradox”, acting as both a tumor suppresser and promoter. The complexity of TGF-β signaling within the tumor is context dependent, and greatly impacted by cellular crosstalk between TGF-β responsive cells in the microenvironment including adjacent epithelial, endothelial, mesenchymal, and hematopoietic cells. Here we utilize normal, weaning-induced mammary gland involution as a tissue microenvironment model to study the complexity of TGF-β function. This article reviews facets of mammary gland involution that are TGF-β regulated, namely mammary epithelial cell death, immune activation, and extracellular matrix remodeling. We outline how distinct cellular responses and crosstalk between cell types during physiologically normal mammary gland involution contribute to simultaneous tumor suppressive and promotional microenvironments. We also highlight alternatives to direct TGF-β blocking anti-cancer therapies with an emphasis on eliciting concerted microenvironmental-mediated tumor suppression.

Multiple Roles of WNT5A in Breast Cancer

Breast cancer is one of the most common malignant tumors of women. Modern combinatorial therapeutic regimens can reduce patient tumor burdens to undetectable levels, yet in many cases these tumors will relapse. Understanding of breast cancer biology, developing more potent therapeutic approaches, and overcoming resistance are of great importance. WNT5A is a non-canonical signaling member of the WNT family. Its role in breast cancer still remains unclear. Most of the evidence shows that WNT5A is a suppressor in breast cancer and loss of its expression is associated with poor prognosis, while some evidence suggests the tumorigenicity of WNT5A. WNT signaling molecules are potent targets for treatment of cancer. Therefore, understanding the role of WNT5A in breast cancer may provide new ideas and methods for breast cancer treatment. We review the evidence concerning WNT5A and breast cancer involving the signaling pathways and the molecular-targeted therapy of WNT5A. Our results show that the role WNT5A plays depends on the availability of key receptors and intercellular interactions among different cell types.

Colostrum and Mature Human Milk of Women from London, Moscow, and Verona: Determinants of Immune Composition

Cytokines and growth factors in colostrum and mature milk may play an important role in infant immune maturation, and may vary significantly between populations. We aimed to examine associations between environmental and maternal factors, and human milk (HM) cytokine and growth factor levels. We recruited 398 pregnant/lactating women in the United Kingdom, Russia, and Italy. Participants underwent skin prick testing, questionnaire interview, and colostrum and mature milk sampling. HM cytokine and growth factor levels were quantified by electro-chemiluminescence. We found significant geographical variation in growth factor levels, but no evidence of variation between sites in cytokine detectability. There was an inverse correlation between time of milk sampling and growth factor levels in colostrum for Hepatocyte Growth Factor (HGF) and TGFβ1 and TGFβ3, but not TGFβ2, and levels were significantly higher in colostrum than mature milk for all growth factors. The kinetics of decline were different for each growth factor. Cytokines were present at much lower levels than growth factors, and the decline over time was less consistent. HM growth factors and cytokine levels vary between populations for unknown reasons. Levels of HM mediators decline at different rates postpartum, and these findings suggest specific biological roles for HM growth factors and cytokines in early postnatal development.

Stat3 modulates chloride channel accessory protein expression in normal and neoplastic mammary tissue

Mammary gland regression at the cessation of lactation (involution) is an exquisitely orchestrated process of cell death and tissue remodelling in which Stat3 signalling has an essential role. The involution microenvironment of the mammary gland is considered to be pro-tumourigenic and a proportion of cases of pregnancy-associated breast cancer are suggested to originate in tandem with involution. However, the apparent paradox that STAT3 is required for cell death in normal mammary gland, but is associated with breast cancer cell survival, has not been resolved. Herein, we investigate Stat3-mediated regulation of expression of members of the calcium-activated chloride channel regulator (CLCA) family of proteins during involution and mammary carcinogenesis. Using the conditionally immortal mammary epithelial cell line KIM-2, together with mice exhibiting mammary epithelial cell-specific deletion of Stat3 during lactation, we demonstrate that expression of mCLCA1 and mCLCA2 is elevated in concert with activation of Stat3. By contrast, murine CLCA5 (mCLCA5), the murine orthologue of human CLCA2, is significantly upregulated at 24, 72 and 96 h of involution in Stat3 knockout mice, suggesting a reciprocal regulation of these proteins by Stat3 in vivo. Interestingly, orthotopic tumours arising from transplantation of 4T1 murine mammary tumour cells exhibit both phosphorylated Stat3 and mCLCA5 expression. However, we demonstrate that expression is highly compartmentalized to distinct subpopulations of cells, and that Stat3 retains a suppressive effect on mCLCA5 expression in 4T1 tumour cells. These findings enhance our understanding of the regulation of CLCA channel expression both in vitro and in vivo, and in particular, demonstrate that expression of mCLCA1 and mCLCA2 during involution is profoundly dependent upon Stat3, whereas the relationship between mCLCA5 and Stat3 activity is reciprocal and restricted to different subpopulations of cells.

Augmentation of gonadotropin-releasing hormone receptor expression in the post-lactational mammary tissues of rats

Gonadotropin-releasing hormone (GnRH) is a neurohormone of the hypothalamus controlling pituitary gonadotropin secretion and hence gametogenesis. While it has also been believed that GnRH is synthesized and functions in various peripheral tissues, the expression of GnRH receptor (GnRH-R) in peripheral tissues is not well-described. We previously found that annexin A5, which is increased in the pituitary gonadotropes by GnRH, is dramatically increased in rat mammary epithelial cells after weaning, suggesting that local GnRH is responsible for this increase. Annexin A5 is a member of the annexin family of proteins and is thought to be involved in various regulatory mechanisms, including apoptosis. In the present study, we examined GnRH-R expression in the mammary tissues after weaning. Although GnRH-R mRNA was not detected in the mammary tissues during lactation, it was dramatically increased after weaning. Forced weaning at mid-lactation (day 10) also promoted the expression of GnRH-R transcripts in mammary tissues within 2 days. Furthermore, western blotting analysis with anti-GnRH-R showed that the expression of an immuno-positive 60-kDa protein, whose size was equivalent to that of rat GnRH-R, was confirmed to increase after weaning. These findings clarified the induction of GnRH-R in the mammary tissues after weaning and suggest that GnRH is involved in the involution and tissue remodeling of post-lactating rat mammary tissues.

Mammary epithelial cell phagocytosis downstream of TGF-β3 is characterized by adherens junction reorganization

After weaning, during mammary gland involution, milk-producing mammary epithelial cells undergo apoptosis. Effective clearance of these dying cells is essential, as persistent apoptotic cells have a negative impact on gland homeostasis, future lactation and cancer susceptibility. In mice, apoptotic cells are cleared by the neighboring epithelium, yet little is known about how mammary epithelial cells become phagocytic or whether this function is conserved between species. Here we use a rat model of weaning-induced involution and involuting breast tissue from women, to demonstrate apoptotic cells within luminal epithelial cells and epithelial expression of the scavenger mannose receptor, suggesting conservation of phagocytosis by epithelial cells. In the rat, epithelial transforming growth factor-β (TGF-β) signaling is increased during involution, a pathway known to promote phagocytic capability. To test whether TGF-β enhances the phagocytic ability of mammary epithelial cells, non-transformed murine mammary epithelial EpH4 cells were cultured to achieve tight junction impermeability, such as occurs during lactation. TGF-β3 treatment promoted loss of tight junction impermeability, reorganization and cleavage of the adherens junction protein E-cadherin (E-cad), and phagocytosis. Phagocytosis correlated with junction disruption, suggesting junction reorganization is necessary for phagocytosis by epithelial cells. Supporting this hypothesis, epithelial cell E-cad reorganization and cleavage were observed in rat and human involuting mammary glands. Further, in the rat, E-cad cleavage correlated with increased γ-secretase activity and β-catenin nuclear localization. In vitro, pharmacologic inhibitors of γ-secretase or β-catenin reduced the effect of TGF-β3 on phagocytosis to near baseline levels. However, β-catenin signaling through LiCl treatment did not enhance phagocytic capacity, suggesting a model in which both reorganization of cell junctions and β-catenin signaling contribute to phagocytosis downstream of TGF-β3. Our data provide insight into how mammary epithelial cells contribute to apoptotic cell clearance, and in light of the negative consequences of impaired apoptotic cell clearance during involution, may shed light on involution-associated breast pathologies.

The BH3-only protein BIM contributes to late-stage involution in the mouse mammary gland

After cessation of lactation, involution of the mouse mammary gland proceeds in two distinct phases, a reversible and an irreversible one, which leads to the death and removal of alveolar cells. Cell death is preceded by the loss of STAT5 activity, which abrogates cell differentiation and gain of STAT3 activity. Despite early observations implicating BCL2 (B cell lymphoma 2) family proteins in this process, recent evidence suggests that STAT3-controlled cathepsin activity is most critical for cell death at the early stage of involution. Somewhat surprisingly, this cell death associates with but does not depend on the activation of pro-apoptotic effector caspases. However, transgenic overexpression of BCL2, that blocks caspase activation, delays involution while conditional deletion of BclX accelerates this process, suggesting that BCL2 family proteins are needed for the effective execution of involution. Here, we report on the transcriptional induction of multiple pro-apoptotic BCL2 family proteins of the 'BH3-only' subgroup during involution and the rate-limiting role of BIM in this process. Loss of Bim delayed epithelial cell clearance during involution after forced weaning in mice, whereas the absence of related Bmf had minor and loss of Bad or Noxa no impact on this process. Consistent with a contribution of BCL2 family proteins to the second wave of cell death during involution, loss of Bim reduced the number of apoptotic cells in this irreversible phase. Notably, the expression changes observed within the BCL2 family did not depend on STAT3 signalling, in line with its initiating role early in the process, but rather appear to result from relief of repression by STAT5. Our findings support the existence of a signalling circuitry regulating the irreversible phase of involution in mice by engaging BH3-only protein-driven mitochondrial apoptosis.

Involvement of Different networks in mammary gland involution after the pregnancy/lactation cycle: Implications in breast cancer

Early pregnancy is associated with a reduction in a woman's lifetime risk for breast cancer. However, different studies have demonstrated an increase in breast cancer risk in the years immediately following pregnancy. Early and long-term risk is even higher if the mother age is above 35 years at the time of first parity. The proinflammatory microenvironment within the mammary gland after pregnancy renders an "ideal niche" for oncogenic events. Signaling pathways involved in programmed cell death and tissue remodeling during involution are also activated in breast cancer. Herein, the major signaling pathways involved in mammary gland involution, signal transducer and activator of transcription (STAT3), nuclear factor-kappa B (NF-κB), transforming growth factor beta (TGFβ), and retinoid acid receptors (RARs)/retinoid X receptors (RXRs), are reviewed as part of the complex network of signaling pathways that crosstalk in a contextual-dependent manner. These factors, also involved in breast cancer development, are important regulatory nodes for signaling amplification after weaning. Indeed, during involution, p65/p300 target genes such as MMP9, Capn1, and Capn2 are upregulated. Elevated expression and activities of these proteases in breast cancer have been extensively documented. The role of these proteases during mammary gland involution is further discussed. MMPs, calpains, and cathepsins exert their effect by modification of the extracellular matrix and intracellular proteins. Calpains, activated in the mammary gland during involution, cleave several proteins located in cell membrane, lysosomes, mitochondria, and nuclei favoring cell death. Besides, during this period, Capn1 is most probably involved in the modulation of preadipocyte differentiation through chromatin remodeling. Calpains can be implicated in cell anchoring loss, providing a proper microenvironment for tumor growth. A better understanding of the role of any of these proteases in tumorigenesis may yield novel therapeutic targets or prognostic markers for breast cancer.

Hormonal induction and roles of Disabled-2 in lactation and involution

Disabled-2 (Dab2) is a widely expressed endocytic adaptor that was first isolated as a 96 KDa phospho-protein, p96, involved in MAPK signal transduction. Dab2 expression is lost in several cancer types including breast cancer, and Dab2 is thought to have a tumor suppressor function. In mammary epithelia, Dab2 was induced upon pregnancy and further elevated during lactation. We constructed mutant mice with a mosaic Dab2 gene deletion to bypass early embryonic lethality and to investigate the roles of Dab2 in mammary physiology. Loss of Dab2 had subtle effects on lactation, but Dab2-deficient mammary glands showed a strikingly delayed cell clearance during involution. In primary cultures of mouse mammary epithelial cells, Dab2 proteins were also induced by estrogen, progesterone, and/or prolactin. Dab2 null mammary epithelial cells were refractory to growth suppression induced by TGF-beta. However, Dab2 deletion did not affect Smad2 phosphorylation; rather TGF-beta-stimulated MAPK activation was enhanced in Dab2-deficient cells. We conclude that Dab2 expression is induced by hormones and Dab2 plays a role in modulating TGF-beta signaling to enhance apoptotic clearance of mammary epithelial cells during involution.

The microRNA 424/503 cluster reduces CDC25A expression during cell cycle arrest imposed by transforming growth factor β in mammary epithelial cells

Recently, we demonstrated that the microRNA 424(322)/503 [miR-424(322)/503] cluster is transcriptionally controlled by transforming growth factor β (TGF-β) in the mammary epithelium. Induction of this microRNA cluster impacts mammary epithelium fate by regulating apoptosis and insulin-like growth factor 1 (IGF1) signaling. Here, we expanded our finding to demonstrate that miR-424(322)/503 is an integral component of the cell cycle arrest mediated by TGF-β. Mechanistically, we showed that after TGF-β exposure, increased levels of miR-424(322)/503 reduce the expression of the cell cycle regulator CDC25A. miR-424(322)/503-dependent posttranscriptional downregulation of CDC25A cooperates with previously described transcriptional repression of the CDC25A promoter and proteasome-mediated degradation to reduce the levels of CDC25A expression and to induce cell cycle arrest. We also provide evidence that the TGF-β/miR-424(322)/503 axis is part of the mechanism that regulates the proliferation of hormone receptor-positive (HR(+)) mammary epithelial cells in vivo.

Wound healing-like immune program facilitates postpartum mammary gland involution and tumor progression

Women diagnosed with breast cancer within 5 years postpartum have poor survival rates. The process of postpartum mammary gland involution, whereby the lactating gland remodels to its prepregnant state, promotes breast cancer progression in xenograft models. Macrophage influx occurs during mammary gland involution, implicating immune modulation in the promotion of postpartum breast cancer. Herein, we characterize the postpartum murine mammary gland and find an orchestrated influx of immune cells similar to that which occurs during wound healing. Further, the normal involuting gland may be in an immunosuppressed state as discerned by the transient presence of Foxp3(+) regulatory T cells and IL-10(+) macrophages with T cell suppressive function. To determine the influence of the postpartum immune microenvironment on mammary tumor promotion, we developed an immune-competent model. In this model, mammary tumors in the involution group are sixfold larger than nulliparous group tumors, have decreased CD4(+) and CD8(+) T cell infiltrates and contain a greater number of macrophages with the ability to inhibit T cell activation. Targeting involution with a neutralizing antibody against the immunosuppressive cytokine IL-10 reduces tumor growth in involution group mice but not in nulliparous mice, implicating the involution microenvironment as the primary target of αIL-10 treatment. Relevance to women is implicated, as we find postlactational human breast tissue has transient high IL-10(+) and Foxp3(+) immune cell infiltrate. These data show an immune modulated microenvironment within the normal involuting mammary gland suggestive of immunosuppression, that when targeted reduces tumor promotion, revealing possible immune-based strategies for postpartum breast cancer.

Cleavage of Histone 3 by Cathepsin D in the involuting mammary gland

The post-lactational regression of mammary gland is a complex multi-step process designed to conserve the biological function of the gland for next pregnancy. This developmental stage is a biological intrigue with great relevance to breast cancer research, and thus has been the subject of intensive scrutiny. Multipronged studies (microarray, proteomics profiling, animal knock-out models) have provided a repertoire of genes critical to involution. However, the caveat of these approaches remains in their failure to reveal post-translational modification(s), an emerging and critical aspect of gene regulation in developmental processes and mammary gland remodeling. The massive surge in the lysosomal enzymes concurrent with the onset of involution has been known for decades, and considered essential for “clearance” purposes. However, functional significance of these enzymes in diverse biological processes distinct from their proteolytic activity is just emerging. Studies from our laboratory had indicated specific post-translational modifications of the aspartyl endopeptidase Cathepsin D (CatD) at distinct stages mammary gland development. This study addresses the biological significance of these modifications in the involution process, and reveals that post-translational modifications drive CatD into the nucleus to cleave Histone 3. The cleavage of Histone 3 has been associated with cellular differentiation and could be critical instigator of involution process. From functional perspective, deregulated expression and increased secretion of CatD are associated with aggressive and metastatic phenotype of breast cancer. Thus unraveling CatD’s physiological functions in mammary gland development will bridge the present gap in understanding its pro-tumorigenic/metastatic functions, and assist in the generation of tailored therapeutic approaches.

Mammary gland involution as an immunotherapeutic target for postpartum breast cancer

Postpartum mammary gland involution has been identified as tumor-promotional and is proposed to contribute to the increased rates of metastasis and poor survival observed in postpartum breast cancer patients. In rodent models, the involuting mammary gland microenvironment is sufficient to induce enhanced tumor cell growth, local invasion, and metastasis. Postpartum involution shares many attributes with wound healing, including upregulation of genes involved in immune responsiveness and infiltration of tissue by immune cells. In rodent models, treatment with non-steroidal anti-inflammatory drugs (NSAIDs) ameliorates the tumor-promotional effects of involution, consistent with the immune milieu of the involuting gland contributing to tumor promotion. Currently, immunotherapy is being investigated as a means of breast cancer treatment with the purpose of identifying ways to enhance anti-tumor immune responses. Here we review evidence for postpartum mammary gland involution being a uniquely defined 'hot-spot' of pro-tumorigenic immune cell infiltration, and propose that immunotherapy should be explored for prevention and treatment of breast cancers that arise in this environment.

The spectrum of STAT functions in mammary gland development

The signal transducer and activator of transcription (STAT) family of transcription factors have a spectrum of functions in mammary gland development. In some cases these roles parallel those of STATs in other organ systems, while in other instances the function of individual STATs in the mammary gland is specific to this tissue. In the immune system, STAT6 is associated with differentiation of T helper cells, while in the mammary gland, it has a fundamental role in the commitment of luminal epithelial cells to the alveolar lineage. STAT5A is required for the production of luminal progenitor cells from mammary stem cells and is essential for the differentiation of milk producing alveolar cells during pregnancy. By contrast, the initiation of regression following weaning heralds a dramatic and specific activation of STAT3, reflecting its pivotal role in the regulation of cell death and tissue remodeling during mammary involution. Although it has been demonstrated that STAT1 is regulated during a mammary developmental cycle, it is not yet determined whether it has a specific, non-redundant function. Thus, the mammary gland constitutes an unusual example of an adult organ in which different STATs are sequentially activated to orchestrate the processes of functional differentiation, cell death and tissue remodeling.

Genetics of breast cancer bone metastasis: a sequential multistep pattern

Bone metastasis accounts for the vast majority of breast cancer (BC) metastases, and is related to a high rate of morbidity and mortality. A number of seminal studies have uncovered gene expression signatures involved in BC development and bone metastasis; each of them points at a distinct step of the 'invasion-metastasis cascade'. In this review, we provide most recently discovered functions of sets of genes that are selected from widely accepted gene signatures that are implicate in BC progression and bone metastasis. We propose a possible sequential pattern of gene expression that may lead a benign primary breast tumor to get aggressiveness and progress toward bone metastasis. A panel of genes which primarily deal with features like DNA replication, survival, proliferation, then, angiogenesis, migration, and invasion has been identified. TGF-β, FGF, NFκB, WNT, PI3K, and JAK-STAT signaling pathways, as the key pathways involved in breast cancer development and metastasis, are evidently regulated by several genes in all three signatures. Epithelial to mesenchymal transition that is also an important mechanism in cancer stem cell generation and metastasis is evidently regulated by these genes. This review provides a comprehensive insight regarding breast cancer bone metastasis that may lead to a better understanding of the disease and take step toward better treatments.

ΔFosB regulates Ca²⁺ release and proliferation of goat mammary epithelial cells

ΔFosB is a member of the family of transcription factor activating proteins-1 (AP-1) and is known to play important roles in Ca(2+) metabolism processes of osteoblast formation and differentiation in humans and rodents. The postpartum mammary gland is one of the significant organs for Ca(2+) metabolism processes. However, very little information is available on the role of ΔFosB in goat mammary gland. In this investigation, the full-length cDNA of ΔFosB from Xinong Saanen dairy goats was cloned, which contains an open-reading frame (ORF) of 723 bp encoding 240 amino acids. The amino acid sequence is highly homologous with cattle (99.17%). Quantitative real time PCR (QRT-PCR) and western blotting assays showed that ΔFosB was expressed in goat heart, liver, lung, and breast, but little in the hypophysis and spleen. The fluorescence signals revealed that the Ca(2+) was decreased in goat mammary epithelial cells (GMECs) over-expressed ΔFosB at 72h. Consistently, intracellular Ca(2+) was increased in GMECs suppressing expressed ΔFosB at 72 h. QRT-PCR assay showed that ΔFosB positively regulated the mRNA expression of runt related transcription factor 2 (Runx2), SMAD family member 4 (Smad4), S100 calcium binding protein A4 (S100A4) and S100 calcium binding protein A13 (S100A13) genes in GMECs, which had been proven to be relative to calcium metabolism in humans and rodents. Ca(2+) could induce a dose-dependent increase of the ΔFosB mRNA expression and a dose-dependent decrease in cell viability when the GMECs were treated with CaCl2. Suppressing ΔFosB expression in GMECs also inhibited the cell viability. These discoveries suggest that ΔFosB plays important roles in regulating Ca(2+) release and proliferation of the GMECs, which may prove useful in regulation of milk production.

The miR-424(322)/503 cluster orchestrates remodeling of the epithelium in the involuting mammary gland

The mammary gland undergoes continuous remodeling. Llobet-Navas et al. identify the microRNA cluster miR-424(322)/503 as an important regulator of epithelial involution after pregnancy. TGF-β regulates the expression of this miR cluster, which in turn targets BCL-2 and IGF1R. This work suggests a model in which activation of the TGF-β pathway after weaning induces the transcription of the miR-424(322)/503 cluster to down-regulate the expression of key genes.

The mammary gland is a very dynamic organ that undergoes continuous remodeling. The critical regulators of this process are not fully understood. Here we identify the microRNA cluster miR-424(322)/503 as an important regulator of epithelial involution after pregnancy. Through the generation of a knockout mouse model, we found that regression of the secretory acini of the mammary gland was compromised in the absence of miR-424(322)/503. Mechanistically, we show that miR-424(322)/503 orchestrates cell life and death decisions by targeting BCL-2 and IGF1R (insulin growth factor-1 receptor). Furthermore, we demonstrate that the expression of this microRNA cluster is regulated by TGF-β, a well-characterized regulator of mammary involution. Overall, our data suggest a model in which activation of the TGF-β pathway after weaning induces the transcription of miR-424(322)/503, which in turn down-regulates the expression of key genes. Here, we unveil a previously unknown, multilayered regulation of epithelial tissue remodeling coordinated by the microRNA cluster miR-424(322)/503.

The Stat3 paradox: a killer and an oncogene

Stat proteins regulate many aspects of mammary gland development, including the profound changes that occur during pregnancy, lactation and involution. Stat3 induces transcriptional activation of genes involved in the inflammatory response, and in seemingly contradictory cellular events such as apoptosis, differentiation and stem cell maintenance. While Stat3 signalling during mammary gland involution induces epithelial cell death, aberrant Stat3 activation is widely implicated in breast tumourigenesis. Specific cytokines may initiate either a Stat3-driven proliferative or death response depending on the cell-type and cell-context specific availability of particular combinations of signals and receptors. The paradoxical functions of Stat3 may also be due to the degree and extent of activation in different circumstances, in addition to paracrine signalling between mammary epithelial cells and the surrounding microenvironment. Deciphering the enigmatic nature of Stat3 in the mammary gland may benefit future therapeutic strategies for inducing cell death in breast tumours.

Ltbp1L is focally induced in embryonic mammary mesenchyme, demarcates the ductal luminal lineage and is upregulated during involution

Introduction

Latent TGFβ binding proteins (LTBPs) govern TGFβ presentation and activation and are important for elastogenesis. Although TGFβ is well-known as a tumor suppressor and metastasis promoter, and LTBP1 is elevated in two distinct breast cancer metastasis signatures, LTBPs have not been studied in the normal mammary gland.

Methods

To address this we have examined Ltbp1 promoter activity throughout mammary development using an Ltbp1L-LacZ reporter as well as expression of both Ltbp1L and 1S mRNA and protein by qRT-PCR, immunofluorescence and flow cytometry.

Results

Our data show that Ltbp1L is transcribed coincident with lumen formation, providing a rare marker distinguishing ductal from alveolar luminal lineages. Ltbp1L and Ltbp1S are silent during lactation but robustly induced during involution, peaking at the stage when the remodeling process becomes irreversible. Ltbp1L is also induced within the embryonic mammary mesenchyme and maintained within nipple smooth muscle cells and myofibroblasts. Ltbp1 protein exclusively ensheaths ducts and side branches.

Conclusions

These data show Ltbp1 is transcriptionally regulated in a dynamic manner that is likely to impose significant spatial restriction on TGFβ bioavailability during mammary development. We hypothesize that Ltbp1 functions in a mechanosensory capacity to establish and maintain ductal luminal cell fate, support and detect ductal distension, trigger irreversible involution, and facilitate nipple sphincter function.

ATG proteins mediate efferocytosis and suppress inflammation in mammary involution

Involution is the process of post-lactational mammary gland regression to quiescence and it involves secretory epithelial cell death, stroma remodeling and gland repopulation by adipocytes. Though reportedly accompanying apoptosis, the role of autophagy in involution has not yet been determined. We now report that autophagy-related (ATG) proteins mediate dead cell clearance and suppress inflammation during mammary involution. In vivo, Becn1^+/− and Atg7-deficient mammary epithelial cells (MECs) produced ‘competent’ apoptotic bodies, but were defective phagocytes in association with reduced expression of the MERTK and ITGB5 receptors, thus pointing to defective apoptotic body engulfment. Atg-deficient tissues exhibited higher levels of involution-associated inflammation, which could be indicative of a tumor-modulating microenvironment, and developed ductal ectasia, a manifestation of deregulated post-involution gland remodeling. In vitro, ATG (BECN1 or ATG7) knockdown compromised MEC-mediated apoptotic body clearance in association with decreased RAC1 activation, thus confirming that, in addition to the defective phagocytic processing reported by other studies, ATG protein defects also impair dead cell engulfment.

 

Using two different mouse models with mammary gland-associated Atg deficiencies, our studies shed light on the essential role of ATG proteins in MEC-mediated efferocytosis during mammary involution and provide novel insights into this important developmental process. This work also raises the possibility that a regulatory feedback loop exists, by which the efficacy of phagocytic cargo processing in turn regulates the rate of engulfment and ultimately determines the kinetics of phagocytosis and dead cell clearance.

The Dual Role of TGFβ in Human Cancer: From Tumor Suppression to Cancer Metastasis

The transforming growth factor-beta (TGFβ) superfamily encompasses widespread and evolutionarily conserved polypeptide growth factors that regulate and orchestrate growth and differentiation in all cell types and tissues. While they regulate asymmetric cell division and cell fate determination during early development and embryogenesis, TGFβ family members play a major regulatory role in hormonal and immune responses, cell growth, cell death and cell immortalization, bone formation, tissue remodeling and repair, and erythropoiesis throughout adult life. The biological and physiological functions of TGFβ, the founding member of this family, and its receptors are of central importance to human diseases, particularly cancer. By regulating cell growth, death, and immortalization, TGFβ signaling pathways exert tumor suppressor effects in normal cells and early carcinomas. Thus, it is not surprising that a high number of human tumors arise due to mutations or deletions in the genes coding for the various TGFβ signaling components. As tumors develop and progress, these protective and cytostatic effects of TGFβ are often lost. TGFβ signaling then switches to promote cancer progression, invasion, and tumor metastasis. The molecular mechanisms underlying this dual role of TGFβ in human cancer will be discussed in depth in this paper, and it will highlight the challenge and importance of developing novel therapeutic strategies specifically aimed at blocking the prometastatic arm of the TGFβ signaling pathway without affecting its tumor suppressive effects.