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Christine J Watson

Publications and source records attributed to Christine J Watson.

13 recordsLinked to original sources
PubMed2006

Post-lactational mammary gland regression: molecular basis and implications for breast cancer.

During pregnancy, there is a massive increase in the number of luminal epithelial cells in the breast, which are destined to become the milk factories after birth. These cells are no longer required when the young are weaned, and are removed in a carefully orchestrated event called involution. In this process, the secretory epithelial cells die and are replaced by adipocytes, which redifferentiate as the epithelium is removed. It is essential that the gland is properly remodelled to a pre-pregnant state so that successful lactation can occur following a subsequent pregnancy. Furthermore, failure to remove unnecessary lactational alveoli during weaning could result in inflammation and tissue damage. Recently, it has been shown that components in the fatty stroma in involuting breast can promote metastasis. Thus, it is important to understand the molecular mechanisms that regulate involution, how these can fail, the consequences of the remodelling process, and how this knowledge can inform us about breast cancer. In this review, I discuss the roles of the JAK-STAT, NF-kappaB and other signalling pathways in the regulation of apoptosis and tissue remodelling during involution.

Animals↗
PubMed2006

c-myc as a mediator of accelerated apoptosis and involution in mammary glands lacking Socs3.

Suppressor of cytokine signalling (SOCS) proteins are critical attenuators of cytokine-mediated signalling in diverse tissues. To determine the importance of Socs3 in mammary development, we generated mice in which Socs3 was deleted in mammary epithelial cells. No overt phenotype was evident during pregnancy and lactation, indicating that Socs3 is not a key physiological regulator of prolactin signalling. However, Socs3-deficient mammary glands exhibited a profound increase in epithelial apoptosis and tissue remodelling, resulting in precocious involution. This phenotype was accompanied by augmented Stat3 activation and a marked increase in the level of c-myc. Moreover, induction of c-myc before weaning using an inducible transgenic model recapitulated the Socs3 phenotype, and elevated expression of likely c-myc target genes, E2F-1, Bax and p53, was observed. Our data establish Socs3 as a critical attenuator of pro-apoptotic pathways that act in the developing mammary gland and provide evidence that c-myc regulates apoptosis during involution.

Animals↗
PubMed2006

IKKbeta/2 induces TWEAK and apoptosis in mammary epithelial cells.

The Nuclear Factor-kappaB (NF-kappaB) family of transcription factors are ubiquitously expressed and control a wide range of cellular responses, including apoptosis, proliferation, differentiation, inflammation and immunity. Here, we investigated the function of the NF-kappaB upstream regulator IkappaB kinase 2/beta (IKK2) in apoptosis regulation in the normal physiological setting of regressing mammary gland. Conditional deletion of the gene encoding IKK2 resulted, surprisingly, in delayed apoptosis and remodelling, and abrogation of caspase 3 cleavage. This failure to induce involution was associated with reduced expression, within 24 hours of involution, of the death receptor (DR) ligand TNF and its receptor TNFR1, which are known NF-kappaB targets. This was associated with elevated levels of active AKT and phosphorylated FOXO3a. Furthermore, we show that expression of TWEAK, another DR ligand, is dramatically downregulated, even in heterozygous IKK2 mammary glands. Unlike other DR ligands, the TWEAK promoter has six consensus FOXO-binding sites, further suggesting that it is differentially regulated. Interestingly, a cleaved form of TWEAK is upregulated during involution. This unexpected function of the IKK2/NF-kappaB pathway as a regulator of TWEAK expression and inducer of apoptosis has significant consequences for future therapeutic approaches for cancer and inflammatory diseases.

Animals↗
PubMed2006

Involution: apoptosis and tissue remodelling that convert the mammary gland from milk factory to a quiescent organ.

Involution of the mammary gland is an essential process that removes the milk-producing epithelial cells when they become redundant at weaning. It is a two-step process that involves the death of the secretory epithelium and its replacement by adipocytes. During the first phase, remodelling is inhibited and apoptotic cells can be seen in the lumena of the alveoli. In the second phase, apoptosis is accompanied by remodelling of the surrounding stroma and re-differentiation of the adipocytes. Considerable effort has been directed towards understanding the molecular mechanisms of the involution process and this has resulted in the identification of the principal signalling pathways involved.

Apoptosis↗
PubMed2006

Epithelial-to-mesenchymal transition confers resistance to apoptosis in three murine mammary epithelial cell lines.

Epithelial-to-mesenchymal transition (EMT) is an essential embryogenic and developmental process, characterized by altered cellular morphology, loss of cell adhesion, and gain of migratory ability. Dysregulation of this process has been implicated in tumorigenesis, mediating the acquisition of migratory and invasive phenotypes by tumor cells. Mammary epithelial cells provide an excellent model in which to study the process, being derived from mammary gland tissue that utilizes EMT to facilitate branching morphogenesis through which the developing gland migrates into and invades the fat pad. Inappropriate EMT has been heavily implicated in the progression of ductal hyperplasia and mammary tumor metastasis. We examined the morphological and molecular changes of three murine mammary epithelial cell lines following EMT induction. EMT was induced in the EpH-4 and NMuMG cell lines by transforming growth factor (TGF)-beta1 but not by ethanol, while the KIM-2 cell line was partially resistant to TGF-beta1 but responded fully to ethanol. The response to EMT-inducing reagent was shown to be critically dependent on the time of treatment, with confluent cells failing to respond. Timelapse photography identified increased motility during wound healing in cells pre-treated with EMT-inducing reagent compared with untreated controls. Furthermore, EMT conferred resistance to UV-induced apoptosis. Our data indicate that evaluation of characteristics other than loss and gain of phenotypic markers may be of benefit when assessing EMT, and contribute to the evidence suggesting that inappropriate EMT facilitates the acquisition of resistance to apoptosis, a key characteristic required for tumor survival.

Animals↗
PubMed2005

The genes induced by signal transducer and activators of transcription (STAT)3 and STAT5 in mammary epithelial cells define the roles of these STATs in mammary development.

Prolactin and leukemia inhibitory factor (LIF) have different roles in the adult mammary gland, which are mediated in part by the signal transducers and activators of transcription (STAT)5 and STAT3. In vivo studies have shown that STAT5 contributes to prolactin-dependent lobuloalveolar development and lactation whereas STAT3 mediates LIF-dependent epithelial apoptosis during postlactational involution. To understand the molecular basis of these STAT-dependent pathways, we demonstrate the ligand-independent effects of STAT5 and STAT3 in mammary epithelial cells in vitro and also identify the genes regulated by these related transcription factors. Thus, using conditionally active STAT3- or STAT5a-GyraseB fusion proteins, we observed that enforced and specific dimerization of STAT3 induced apoptosis whereas STAT5 induced differentiation of mammary epithelial cells. Furthermore, STAT5 attenuated apoptosis mediated by LIF, the physiological inducer of STAT3. Microarray analysis of STAT3- and STAT5-induced genes using this system demonstrated a marked specificity, which reflected their different physiological effects in vitro and in vivo. STAT5-specific gene targets included the milk protein genes alpha-casein and kallikrein-8 and the survival factors prosaposin and Grb10. STAT3-specific genes included the apoptosis regulators CCAAT enhancer binding protein-delta, phosphatidylinositol 3-kinase-regulatory subunits, purine nucleoside phosphorylase, and c-fos. These data illustrate that specific activation of STAT3 and STAT5 alone is sufficient to induce and suppress apoptosis, respectively, and that these transcription factors elicit their actions by inducing distinct subsets of target genes in mammary epithelial cells.

Animals↗
PubMed2005

The Jak/Stat pathway: a novel way to regulate PI3K activity.

Phosphoinositide 3-kinases (PI3Ks) have been grouped into three major classes that have different substrate specificities. Class IA PI3Ks consist of a catalytic and a regulatory subunit and have multiple isoforms that arise from different subunit combinations. The role of two of the small regulatory subunits, p55alpha and p50alpha, is poorly understood. We have now identified a novel function for these subunits and have shown that their expression is specifically induced in the involuting mouse mammary gland where they are involved in the downregulation of PI3K signalling and Akt/PKB activity. This abrogation of survival signalling thru Akt/PKB and its downstream targets is essential for the induction of apoptosis. The switch from lactation to involution is associated with activation of the transcription factor Stat3, by the cytokine LIF. Stat3 is essential for the induction of apoptosis and, in the absence of Stat3 or LIF, expression of the p55alpha and p50alpha subunits is abrogated. Surprisingly, Stat3 is a direct regulator of p55alpha and p50alpha expression, as demonstrated using ChIP assays, and therefore these subunits are not splicing isoforms as previously thought. An important implication of our results is that the p55alpha and p50alpha small regulatory subunits are regulated independently of the larger p85alpha subunit, and have an essential role in Stat3-mediated apoptosis in mammary gland.

Animals↗
PubMed2005

Stat3-induced apoptosis requires a molecular switch in PI(3)K subunit composition.

Physiological apoptosis is induced by a switch from survival to death signalling. Dysregulation of this process is frequently associated with cancer. A powerful model for this apoptotic switch is mammary gland involution, during which redundant milk-producing epithelial cells undergo apoptosis. Signal transducer and activator of transcription 3 (Stat3) is an essential mediator of this switch but the mechanism has not yet been defined. Stat3-dependent cell death during involution can be blocked by activation of Akt/protein kinase B (PKB), a downstream effector of the phosphoinositide-3-OH kinase (PI(3)K) pathway. Here we show that expression of the PI(3)K regulatory subunits p55alpha and p50alpha is induced by Stat3 during involution. In the absence of Stat3 in vivo, upregulation of p55alpha and p50alpha is abrogated, levels of activated Akt are sustained and apoptosis is prevented. Chromatin immunoprecipitation assays show that Stat3 binds directly to the p55alpha and p50alpha promoters in vivo. Overexpression of either p55alpha or p50alpha reduces levels of activated Akt. We propose a novel mechanism in which Stat3 regulates apoptosis by inducing expression of distinct PI(3)K regulatory subunits to downregulate PI(3)K-Akt-mediated survival signalling.

Animals↗
PubMed2003

Gene expression profiling of mammary gland development reveals putative roles for death receptors and immune mediators in post-lactational regression.

INTRODUCTION: In order to gain a better understanding of the molecular processes that underlie apoptosis and tissue regression in mammary gland, we undertook a large-scale analysis of transcriptional changes during the mouse mammary pregnancy cycle, with emphasis on the transition from lactation to involution. METHOD: Affymetrix microarrays, representing 8618 genes, were used to compare mammary tissue from 12 time points (one virgin, three gestation, three lactation and five involution stages). Six animals were used for each time point. Common patterns of gene expression across all time points were identified and related to biological function. RESULTS: The majority of significantly induced genes in involution were also differentially regulated at earlier stages in the pregnancy cycle. This included a marked increase in inflammatory mediators during involution and at parturition, which correlated with leukaemia inhibitory factor-Stat3 (signal transducer and activator of signalling-3) signalling. Before involution, expected increases in cell proliferation, biosynthesis and metabolism-related genes were observed. During involution, the first 24 hours after weaning was characterized by a transient increase in expression of components of the death receptor pathways of apoptosis, inflammatory cytokines and acute phase response genes. After 24 hours, regulators of intrinsic apoptosis were induced in conjunction with markers of phagocyte activity, matrix proteases, suppressors of neutrophils and soluble components of specific and innate immunity. CONCLUSION: We provide a resource of mouse mammary gene expression data for download or online analysis. Here we highlight the sequential induction of distinct apoptosis pathways in involution and the stimulation of immunomodulatory signals, which probably suppress the potentially damaging effects of a cellular inflammatory response while maintaining an appropriate antimicrobial and phagocytic environment.

Acute-Phase Reaction↗
PubMed2003

Microarray analysis of the involution switch.

Mammary epithelial cells (MEC) undergo a series of developmental decisions during a pregnancy cycle. The switches from proliferation to differentiation to secretion and then to cell death are precisely controlled. In order to identify critical changes associated with the transition from a secretory phenotype during lactation to dedifferentiation and cell death, we have undertaken a microarray analysis of mouse mammary gland development. We have focused on the involution switch and on the transcription profiles of genes that are targets of transcription factors known to influence involution and apoptosis. Our results show that both Stat3 and NF-kB target genes are induced by the involution switch while Stat5 target genes are distinct from Stat3 induced genes. Furthermore, a substantial number of genes that were specifically upregulated at the start of involution are regulators of inflammation and the acute phase response. These results provide a novel insight into the involution process and demonstrate the value of microarray analysis in defining molecular events associated with critical developmental transitions in mammary gland.

Animals↗
PubMed2003

Mammary-specific deletion of parathyroid hormone-related protein preserves bone mass during lactation.

Large amounts of calcium are transferred to offspring by milk. This demand results in negative calcium balance in lactating mothers and is associated with rapid bone loss. The mechanisms of bone loss during lactation are only partly understood. Several studies have suggested that parathyroid hormone-related protein (PTHrP) might be secreted into the circulation by the lactating mammary gland and regulate bone turnover during lactation. Because mammary development fails in the absence of PTHrP, conventional PTHrP knockout mice cannot be used to address this possibility. To examine this hypothesis, we therefore used mice carrying a beta-lactoglobulin promoter-driven Cre transgene, one null PTHrP allele, and one floxed PTHrP allele. Expression of Cre specifically in mammary epithelial cells during late pregnancy and lactation resulted in efficient deletion of the PTHrP gene; mammary gland PTHrP mRNA and milk PTHrP protein were almost completely absent. Removal of PTHrP from the lactating mammary glands resulted in reductions in levels of circulating PTHrP and 1,25-dihydroxy vitamin D and urinary cAMP. In addition, bone turnover was reduced and bone loss during lactation was attenuated. We conclude that during lactation mammary epithelial cells are a source of circulating PTHrP that promotes bone loss by increasing rates of bone resorption.

Animals↗
PubMed2003

A dual, non-redundant, role for LIF as a regulator of development and STAT3-mediated cell death in mammary gland.

STAT3 is the key mediator of apoptosis in mammary gland. We demonstrate here that LIF is the physiological activator of STAT3, because in involuting mammary glands of Lif(-/-) mice, pSTAT3 is absent and the STAT3 target, C/EBPdelta, is not upregulated. Similar to Stat3 knockouts, Lif(-/-) mammary glands exhibit delayed involution, reduced apoptosis and elevated levels of p53. Significantly, Lif(-/-) glands display precocious development during pregnancy, when pSTAT3 is not normally detected. We show that pERK1/2 is significantly reduced in Lif(-/-) glands at this time, suggesting that at this stage LIF mediates its effects through pERK1/2. Inhibition of LIF-mediated ERK1/2 phosphorylation potentiates the proapoptotic effects of STAT3. LIF therefore signals alternately through ERK1/2, then STAT3, to regulate mammary growth and apoptosis.

Animals↗