Post-lactational mammary gland regression encompasses extensive programmed cell death and removal... more Post-lactational mammary gland regression encompasses extensive programmed cell death and removal of milk-producing epithelial cells, breakdown of extracellular matrix components and redifferentiation of stromal adipocytes. This highly regulated involution process is associated with a transient increased risk of breast cancer in women. Using a syngeneic tumour model, we show that tumour growth is significantly altered depending on the stage of involution at which tumour cells are implanted. Tumour cells injected at day3 involution grew faster than those in nulliparous mice, while tumours initiated at day6 involution grew significantly slower. These differences in tumour progression correlate with distinct changes in innate immune cells, in particular among F4/80-expressing macrophages and among TCRδ+ unconventional T cells. Breast cancer post-pregnancy risk is exacerbated in older first-time mothers and in our model, initial tumour growth is moderately faster in aged mice compared t...
Under normal conditions, the most significant expansion and differentiation of the adult mammary ... more Under normal conditions, the most significant expansion and differentiation of the adult mammary gland occurs in response to systemic reproductive hormones during pregnancy and lactation to enable milk synthesis and secretion to sustain the offspring. However, human mammary tissue remodelling that takes place during pregnancy and lactation remains poorly understood due to the challenge of acquiring samples. We report here single-cell transcriptomic analysis of 110,744 viable breast cells isolated from human milk or non-lactating breast tissue, isolated from nine and seven donors, respectively. We found that human milk largely contains epithelial cells belonging to the luminal lineage and a repertoire of immune cells. Further transcriptomic analysis of the milk cells identified two distinct secretory cell types that shared similarities with luminal progenitors, but no populations comparable to hormone-responsive cells. Taken together, our data offers a reference map and a window into...
The transcription factors STAT1 and STAT3 appear to play opposite roles in tumorigenesis. While S... more The transcription factors STAT1 and STAT3 appear to play opposite roles in tumorigenesis. While STAT3 promotes cell survival/proliferation, motility and immune tolerance and is considered as an oncogene, STAT1 mostly triggers anti-proliferative and pro-apoptotic responses while enhancing anti-tumor immunity. Despite being activated downstream of common cytokine and growth factor receptors, their activation is reciprocally regulated and perturbation in their balanced expression or phosphorylation levels may re-direct cytokine/growth factor signals from proliferative to apoptotic, or from inflammatory to anti-inflammatory. Here we review the functional canonical and non-canonical effects of STAT1 and STAT3 activation in tumorigenesis and their potential cross-regulation mechanisms.
It is unclear how genetic aberrations impact the state of nascent tumour cells and their microenv... more It is unclear how genetic aberrations impact the state of nascent tumour cells and their microenvironment. BRCA1 driven triple negative breast cancer (TNBC) has been shown to arise from luminal progenitors yet little is known about how BRCA1 loss-of-function (LOF) and concomitant mutations affect the luminal progenitor cell state. Here we demonstrate how time-resolved single-cell profiling of genetically engineered mouse models before tumour formation can address this challenge. We found that perturbing Brca1/p53 in luminal progenitors induces aberrant alveolar differentiation pre-malignancy accompanied by pro-tumourigenic changes in the immune compartment. Unlike alveolar differentiation during gestation, this process is cell autonomous and characterised by the dysregulation of transcription factors driving alveologenesis. Based on our data we propose a model where Brca1/p53 LOF inadvertently promotes a differentiation program hardwired in luminal progenitors, highlighting the dete...
The transcription factor B-cell lymphoma/leukaemia 11A (BCL11A) has essential functions in physio... more The transcription factor B-cell lymphoma/leukaemia 11A (BCL11A) has essential functions in physiological processes as well as haematological and solid malignancies, however, its contribution to tissue development and tumour progression is poorly understood. Here we show the generation of a Bcl11a lineage tracing mouse model to allow for in vivo tracking of Bcl11a-expressing cells and their progeny. We validate the model in the mammary gland by using flow cytometry and whole-tissue 3D imaging to locate labelled cells after induction of tracing in early development. We show that Bcl11a is predominantly expressed in long-lived luminal progenitors which populate mammary alveoli upon pregnancy, confirming bona fide labelling of Bcl11a cells. The Bcl11a lineage tracing mouse model therefore provides a powerful resource to study Bcl11a cells in development, homeostasis, and cancer.
Breast cancers are highly heterogeneous and their metastatic potential and response to therapeuti... more Breast cancers are highly heterogeneous and their metastatic potential and response to therapeutic drugs is difficult to predict. A tool that could accurately gauge tumour invasiveness and drug response would provide a valuable addition to the oncologist's arsenal. We have developed a 3-dimensional (3D) culture model that recapitulates the stromal environment of breast cancers by generating anisotropic (directional) collagen scaffolds seeded with adipocytes and culturing tumour fragments therein. Analysis of tumour cell invasion in the presence of various therapeutic drugs, by immunofluorescence microscopy coupled with an optical clearing technique, demonstrated the utility of this approach in determining both the rate and capacity of tumour cells to migrate through the stroma while shedding light also on the mode of migration. Furthermore, the response of different murine mammary tumour types to chemotherapeutic drugs could be readily quantified.
Patients diagnosed with lung squamous cell carcinoma (LUSC) have limited targeted therapies. We r... more Patients diagnosed with lung squamous cell carcinoma (LUSC) have limited targeted therapies. We report here the identification and characterisation of BCL11A, as a LUSC oncogene. Analysis of cancer genomics datasets revealed BCL11A to be upregulated in LUSC but not in lung adenocarcinoma (LUAD). Experimentally we demonstrate that non-physiological levels of BCL11A in vitro and in vivo promote squamous-like phenotypes, while its knockdown abolishes xenograft tumour formation. At the molecular level we found that BCL11A is transcriptionally regulated by SOX2 and is required for its oncogenic functions. Furthermore, we show that BCL11A and SOX2 regulate the expression of several transcription factors, including SETD8. We demonstrate that shRNA-mediated or pharmacological inhibition of SETD8 selectively inhibits LUSC growth. Collectively, our study indicates that BCL11A is integral to LUSC pathology and highlights the disruption of the BCL11A-SOX2 transcriptional programme as a novel ca...
Characterising the hierarchy of mammary epithelial cells (MECs) and how they are regulated during... more Characterising the hierarchy of mammary epithelial cells (MECs) and how they are regulated during adult development is important for understanding how breast cancer arises. Here we report the use of single-cell RNA sequencing to determine the gene expression profile of MECs across four developmental stages; nulliparous, mid gestation, lactation and post involution. Our analysis of 23,184 cells identifies 15 clusters, few of which could be fully characterised by a single marker gene. We argue instead that the epithelial cells-especially in the luminal compartment-should rather be conceptualised as being part of a continuous spectrum of differentiation. Furthermore, our data support the existence of a common luminal progenitor cell giving rise to intermediate, restricted alveolar and hormone-sensing progenitors. This luminal progenitor compartment undergoes transcriptional changes in response to a full pregnancy, lactation and involution. In summary, our results provide a global, unbi...
Methods in molecular biology (Clifton, N.J.), 2017
Involution of the mammary gland occurs at the end of every period of lactation and is an essentia... more Involution of the mammary gland occurs at the end of every period of lactation and is an essential process to return the gland to a pre-pregnant state in readiness for the next pregnancy. Involution is a complex process of regulated alveolar cell death coupled with tissue remodeling and requires exquisite control of transcription and signaling. These processes can be investigated using a variety of molecular and morphological approaches.In this chapter we describe how to initiate involution and collect mammary glands, measure involution morphologically, and quantify lysosomal leakiness in mammary tissue and in cultured mammary epithelial cells. These procedures encompass a range of microscopy and molecular biology techniques.
Mammary gland regression at the cessation of lactation (involution) is an exquisitely orchestrate... more 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 elevate...
The phosphatidylinositol 3-kinase (PI3K) regulatory subunits p55α and p50α are coordinately trans... more The phosphatidylinositol 3-kinase (PI3K) regulatory subunits p55α and p50α are coordinately transcriptionally upregulated by signal transducer and activator of transcription 3 (Stat3) at the onset of mammary gland involution, a process that requires Stat3. Deletion of both p55α and p50α subunits in vivo abrogated mammary epithelial cell death during involution. This was associated also with reduced cytosolic levels and activity of the cysteine protease cathepsin L, which is implicated in lysosomal-mediated programmed cell death (LM-PCD) and is upregulated in involution. Furthermore, involution is delayed in cathepsin L-deficient mice suggesting that the p55α/p50α subunits mediate cell death in part by elevating the level of cathepsin L resulting in increased cytosolic activity. Surprisingly, we found that p55α/p50α localize to the nucleus where they bind to chromatin and regulate transcription of a subset of inflammatory/acute phase genes that are also Stat3 targets. Our findings re...
Mammary gland involution involves a process that includes one of the most dramatic examples of ce... more Mammary gland involution involves a process that includes one of the most dramatic examples of cell death in an adult mammalian organism. We have previously shown that signal transducer and activator of transcription 3 (Stat3) regulates a lysosomal pathway of cell death in the first 48 h of involution and induces lysosome leakiness in mammary epithelial cells. Interestingly, Stat3 is associated also with the striking induction of autophagy that occurs concomitantly with cell death, presumably as a transient survival mechanism. The phosphatidylinositol 3-kinase regulatory subunits p55α and p50α are dramatically and specifically upregulated at the transcriptional level by Stat3 at the onset of involution. We show here that ablation of either Stat3 or p55α/p50α in vivo affects autophagy during involution. We used two different cell culture models (normal mammary epithelial cells and mouse embryonic fibroblasts) to further investigate the role of p55α/p50α in autophagy regulation. Our r...
Hormone Molecular Biology and Clinical Investigation, 2000
The pro-oncogenic transcription factor STAT3 is constitutively active in tumours of many differen... more The pro-oncogenic transcription factor STAT3 is constitutively active in tumours of many different origins, which often become addicted to its activity. STAT3 is believed to contribute to the initial survival of pre-cancerous cells as well as to hyper-proliferation and, later, metastasis.To evaluate the contribution of enhanced STAT3 activation in a controlled model system, we generated knock-in mice in which a mutant constitutively activeConstitutively active STAT3 could enhance the tumorigenic power of the ratSTAT3 can induce a metabolic switch that predisposes cells to aberrant survival, enhanced proliferation and, finally, tumour transformation. Later, enhanced Cten expression contributes to tissue infiltration and metastasis. While not excluding the contribution of many other tumour-specific STAT3 target genes, our data provide a unifying explanation of several pro-oncogenic STAT3 activities.
Hormone Molecular Biology and Clinical Investigation, 2000
The pro-oncogenic transcription factor STAT3 is constitutively active in tumours of many differen... more The pro-oncogenic transcription factor STAT3 is constitutively active in tumours of many different origins, which often become addicted to its activity. STAT3 is believed to contribute to the initial survival of pre-cancerous cells as well as to hyper-proliferation and, later, metastasis.To evaluate the contribution of enhanced STAT3 activation in a controlled model system, we generated knock-in mice in which a mutant constitutively activeConstitutively active STAT3 could enhance the tumorigenic power of the ratSTAT3 can induce a metabolic switch that predisposes cells to aberrant survival, enhanced proliferation and, finally, tumour transformation. Later, enhanced Cten expression contributes to tissue infiltration and metastasis. While not excluding the contribution of many other tumour-specific STAT3 target genes, our data provide a unifying explanation of several pro-oncogenic STAT3 activities.
Signalling through the janus kinase (JAK)/signal transducer and activator of transcription (Stat)... more Signalling through the janus kinase (JAK)/signal transducer and activator of transcription (Stat) pathway is required at different stages of mammary gland development, and this pathway is frequently hyper-activated in cancer, including tumours of the breast. Stats 3, 5 and 6 have important roles in the differentiation and survival of mammary alveolar cells, but somewhat paradoxically, both Stat3 and 5 can have oncogenic activity in the mammary gland. Constitutive activation of JAK2 could be anticipated to result in hyper-activation of Stats 1, 3, 5 and 6 with concomitant cell transformation, although the outcome is difficult to envisage, particularly since Stats 3 and 5 play opposing roles in normal mammary gland development. Here, we show that expression of a constitutively active JAK2 mutant, JAK2 V617F, leads to hyper-activation of Stat5 in mammary epithelial cells (MECs), and transgenic mice expressing JAK2 V617F specifically in the mammary gland exhibit accelerated alveologenesis during pregnancy and delayed post-lactational regression. Overexpressing JAK2 V617F in MECs in vitro results in elevated proliferation and resistance to cell death. Furthermore, constitutively active JAK2 enhances anchorage-independent cell growth in the presence of a co-operating oncogene and accelerates tumourigenesis in a xenograft model. Taken together, our results provide insights into signalling downstream of constitutively active JAK2 and could be important for understanding the molecular mechanisms of breast tumourigenesis. (MMC) These authors contributed equally to this work.
Post-lactational mammary gland regression encompasses extensive programmed cell death and removal... more Post-lactational mammary gland regression encompasses extensive programmed cell death and removal of milk-producing epithelial cells, breakdown of extracellular matrix components and redifferentiation of stromal adipocytes. This highly regulated involution process is associated with a transient increased risk of breast cancer in women. Using a syngeneic tumour model, we show that tumour growth is significantly altered depending on the stage of involution at which tumour cells are implanted. Tumour cells injected at day3 involution grew faster than those in nulliparous mice, while tumours initiated at day6 involution grew significantly slower. These differences in tumour progression correlate with distinct changes in innate immune cells, in particular among F4/80-expressing macrophages and among TCRδ+ unconventional T cells. Breast cancer post-pregnancy risk is exacerbated in older first-time mothers and in our model, initial tumour growth is moderately faster in aged mice compared t...
Under normal conditions, the most significant expansion and differentiation of the adult mammary ... more Under normal conditions, the most significant expansion and differentiation of the adult mammary gland occurs in response to systemic reproductive hormones during pregnancy and lactation to enable milk synthesis and secretion to sustain the offspring. However, human mammary tissue remodelling that takes place during pregnancy and lactation remains poorly understood due to the challenge of acquiring samples. We report here single-cell transcriptomic analysis of 110,744 viable breast cells isolated from human milk or non-lactating breast tissue, isolated from nine and seven donors, respectively. We found that human milk largely contains epithelial cells belonging to the luminal lineage and a repertoire of immune cells. Further transcriptomic analysis of the milk cells identified two distinct secretory cell types that shared similarities with luminal progenitors, but no populations comparable to hormone-responsive cells. Taken together, our data offers a reference map and a window into...
The transcription factors STAT1 and STAT3 appear to play opposite roles in tumorigenesis. While S... more The transcription factors STAT1 and STAT3 appear to play opposite roles in tumorigenesis. While STAT3 promotes cell survival/proliferation, motility and immune tolerance and is considered as an oncogene, STAT1 mostly triggers anti-proliferative and pro-apoptotic responses while enhancing anti-tumor immunity. Despite being activated downstream of common cytokine and growth factor receptors, their activation is reciprocally regulated and perturbation in their balanced expression or phosphorylation levels may re-direct cytokine/growth factor signals from proliferative to apoptotic, or from inflammatory to anti-inflammatory. Here we review the functional canonical and non-canonical effects of STAT1 and STAT3 activation in tumorigenesis and their potential cross-regulation mechanisms.
It is unclear how genetic aberrations impact the state of nascent tumour cells and their microenv... more It is unclear how genetic aberrations impact the state of nascent tumour cells and their microenvironment. BRCA1 driven triple negative breast cancer (TNBC) has been shown to arise from luminal progenitors yet little is known about how BRCA1 loss-of-function (LOF) and concomitant mutations affect the luminal progenitor cell state. Here we demonstrate how time-resolved single-cell profiling of genetically engineered mouse models before tumour formation can address this challenge. We found that perturbing Brca1/p53 in luminal progenitors induces aberrant alveolar differentiation pre-malignancy accompanied by pro-tumourigenic changes in the immune compartment. Unlike alveolar differentiation during gestation, this process is cell autonomous and characterised by the dysregulation of transcription factors driving alveologenesis. Based on our data we propose a model where Brca1/p53 LOF inadvertently promotes a differentiation program hardwired in luminal progenitors, highlighting the dete...
The transcription factor B-cell lymphoma/leukaemia 11A (BCL11A) has essential functions in physio... more The transcription factor B-cell lymphoma/leukaemia 11A (BCL11A) has essential functions in physiological processes as well as haematological and solid malignancies, however, its contribution to tissue development and tumour progression is poorly understood. Here we show the generation of a Bcl11a lineage tracing mouse model to allow for in vivo tracking of Bcl11a-expressing cells and their progeny. We validate the model in the mammary gland by using flow cytometry and whole-tissue 3D imaging to locate labelled cells after induction of tracing in early development. We show that Bcl11a is predominantly expressed in long-lived luminal progenitors which populate mammary alveoli upon pregnancy, confirming bona fide labelling of Bcl11a cells. The Bcl11a lineage tracing mouse model therefore provides a powerful resource to study Bcl11a cells in development, homeostasis, and cancer.
Breast cancers are highly heterogeneous and their metastatic potential and response to therapeuti... more Breast cancers are highly heterogeneous and their metastatic potential and response to therapeutic drugs is difficult to predict. A tool that could accurately gauge tumour invasiveness and drug response would provide a valuable addition to the oncologist's arsenal. We have developed a 3-dimensional (3D) culture model that recapitulates the stromal environment of breast cancers by generating anisotropic (directional) collagen scaffolds seeded with adipocytes and culturing tumour fragments therein. Analysis of tumour cell invasion in the presence of various therapeutic drugs, by immunofluorescence microscopy coupled with an optical clearing technique, demonstrated the utility of this approach in determining both the rate and capacity of tumour cells to migrate through the stroma while shedding light also on the mode of migration. Furthermore, the response of different murine mammary tumour types to chemotherapeutic drugs could be readily quantified.
Patients diagnosed with lung squamous cell carcinoma (LUSC) have limited targeted therapies. We r... more Patients diagnosed with lung squamous cell carcinoma (LUSC) have limited targeted therapies. We report here the identification and characterisation of BCL11A, as a LUSC oncogene. Analysis of cancer genomics datasets revealed BCL11A to be upregulated in LUSC but not in lung adenocarcinoma (LUAD). Experimentally we demonstrate that non-physiological levels of BCL11A in vitro and in vivo promote squamous-like phenotypes, while its knockdown abolishes xenograft tumour formation. At the molecular level we found that BCL11A is transcriptionally regulated by SOX2 and is required for its oncogenic functions. Furthermore, we show that BCL11A and SOX2 regulate the expression of several transcription factors, including SETD8. We demonstrate that shRNA-mediated or pharmacological inhibition of SETD8 selectively inhibits LUSC growth. Collectively, our study indicates that BCL11A is integral to LUSC pathology and highlights the disruption of the BCL11A-SOX2 transcriptional programme as a novel ca...
Characterising the hierarchy of mammary epithelial cells (MECs) and how they are regulated during... more Characterising the hierarchy of mammary epithelial cells (MECs) and how they are regulated during adult development is important for understanding how breast cancer arises. Here we report the use of single-cell RNA sequencing to determine the gene expression profile of MECs across four developmental stages; nulliparous, mid gestation, lactation and post involution. Our analysis of 23,184 cells identifies 15 clusters, few of which could be fully characterised by a single marker gene. We argue instead that the epithelial cells-especially in the luminal compartment-should rather be conceptualised as being part of a continuous spectrum of differentiation. Furthermore, our data support the existence of a common luminal progenitor cell giving rise to intermediate, restricted alveolar and hormone-sensing progenitors. This luminal progenitor compartment undergoes transcriptional changes in response to a full pregnancy, lactation and involution. In summary, our results provide a global, unbi...
Methods in molecular biology (Clifton, N.J.), 2017
Involution of the mammary gland occurs at the end of every period of lactation and is an essentia... more Involution of the mammary gland occurs at the end of every period of lactation and is an essential process to return the gland to a pre-pregnant state in readiness for the next pregnancy. Involution is a complex process of regulated alveolar cell death coupled with tissue remodeling and requires exquisite control of transcription and signaling. These processes can be investigated using a variety of molecular and morphological approaches.In this chapter we describe how to initiate involution and collect mammary glands, measure involution morphologically, and quantify lysosomal leakiness in mammary tissue and in cultured mammary epithelial cells. These procedures encompass a range of microscopy and molecular biology techniques.
Mammary gland regression at the cessation of lactation (involution) is an exquisitely orchestrate... more 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 elevate...
The phosphatidylinositol 3-kinase (PI3K) regulatory subunits p55α and p50α are coordinately trans... more The phosphatidylinositol 3-kinase (PI3K) regulatory subunits p55α and p50α are coordinately transcriptionally upregulated by signal transducer and activator of transcription 3 (Stat3) at the onset of mammary gland involution, a process that requires Stat3. Deletion of both p55α and p50α subunits in vivo abrogated mammary epithelial cell death during involution. This was associated also with reduced cytosolic levels and activity of the cysteine protease cathepsin L, which is implicated in lysosomal-mediated programmed cell death (LM-PCD) and is upregulated in involution. Furthermore, involution is delayed in cathepsin L-deficient mice suggesting that the p55α/p50α subunits mediate cell death in part by elevating the level of cathepsin L resulting in increased cytosolic activity. Surprisingly, we found that p55α/p50α localize to the nucleus where they bind to chromatin and regulate transcription of a subset of inflammatory/acute phase genes that are also Stat3 targets. Our findings re...
Mammary gland involution involves a process that includes one of the most dramatic examples of ce... more Mammary gland involution involves a process that includes one of the most dramatic examples of cell death in an adult mammalian organism. We have previously shown that signal transducer and activator of transcription 3 (Stat3) regulates a lysosomal pathway of cell death in the first 48 h of involution and induces lysosome leakiness in mammary epithelial cells. Interestingly, Stat3 is associated also with the striking induction of autophagy that occurs concomitantly with cell death, presumably as a transient survival mechanism. The phosphatidylinositol 3-kinase regulatory subunits p55α and p50α are dramatically and specifically upregulated at the transcriptional level by Stat3 at the onset of involution. We show here that ablation of either Stat3 or p55α/p50α in vivo affects autophagy during involution. We used two different cell culture models (normal mammary epithelial cells and mouse embryonic fibroblasts) to further investigate the role of p55α/p50α in autophagy regulation. Our r...
Hormone Molecular Biology and Clinical Investigation, 2000
The pro-oncogenic transcription factor STAT3 is constitutively active in tumours of many differen... more The pro-oncogenic transcription factor STAT3 is constitutively active in tumours of many different origins, which often become addicted to its activity. STAT3 is believed to contribute to the initial survival of pre-cancerous cells as well as to hyper-proliferation and, later, metastasis.To evaluate the contribution of enhanced STAT3 activation in a controlled model system, we generated knock-in mice in which a mutant constitutively activeConstitutively active STAT3 could enhance the tumorigenic power of the ratSTAT3 can induce a metabolic switch that predisposes cells to aberrant survival, enhanced proliferation and, finally, tumour transformation. Later, enhanced Cten expression contributes to tissue infiltration and metastasis. While not excluding the contribution of many other tumour-specific STAT3 target genes, our data provide a unifying explanation of several pro-oncogenic STAT3 activities.
Hormone Molecular Biology and Clinical Investigation, 2000
The pro-oncogenic transcription factor STAT3 is constitutively active in tumours of many differen... more The pro-oncogenic transcription factor STAT3 is constitutively active in tumours of many different origins, which often become addicted to its activity. STAT3 is believed to contribute to the initial survival of pre-cancerous cells as well as to hyper-proliferation and, later, metastasis.To evaluate the contribution of enhanced STAT3 activation in a controlled model system, we generated knock-in mice in which a mutant constitutively activeConstitutively active STAT3 could enhance the tumorigenic power of the ratSTAT3 can induce a metabolic switch that predisposes cells to aberrant survival, enhanced proliferation and, finally, tumour transformation. Later, enhanced Cten expression contributes to tissue infiltration and metastasis. While not excluding the contribution of many other tumour-specific STAT3 target genes, our data provide a unifying explanation of several pro-oncogenic STAT3 activities.
Signalling through the janus kinase (JAK)/signal transducer and activator of transcription (Stat)... more Signalling through the janus kinase (JAK)/signal transducer and activator of transcription (Stat) pathway is required at different stages of mammary gland development, and this pathway is frequently hyper-activated in cancer, including tumours of the breast. Stats 3, 5 and 6 have important roles in the differentiation and survival of mammary alveolar cells, but somewhat paradoxically, both Stat3 and 5 can have oncogenic activity in the mammary gland. Constitutive activation of JAK2 could be anticipated to result in hyper-activation of Stats 1, 3, 5 and 6 with concomitant cell transformation, although the outcome is difficult to envisage, particularly since Stats 3 and 5 play opposing roles in normal mammary gland development. Here, we show that expression of a constitutively active JAK2 mutant, JAK2 V617F, leads to hyper-activation of Stat5 in mammary epithelial cells (MECs), and transgenic mice expressing JAK2 V617F specifically in the mammary gland exhibit accelerated alveologenesis during pregnancy and delayed post-lactational regression. Overexpressing JAK2 V617F in MECs in vitro results in elevated proliferation and resistance to cell death. Furthermore, constitutively active JAK2 enhances anchorage-independent cell growth in the presence of a co-operating oncogene and accelerates tumourigenesis in a xenograft model. Taken together, our results provide insights into signalling downstream of constitutively active JAK2 and could be important for understanding the molecular mechanisms of breast tumourigenesis. (MMC) These authors contributed equally to this work.
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