Renal FGF23 signaling depends on redox protein Memo1 and promotes orthovanadate-sensitive protein phosphotyrosyl phosphatase activity

Memo1 deletion in mice causes premature aging and an unbalanced metabolism partially resembling Fgf23 and Klotho loss-of-function animals. We report a role for Memo's redox function in renal FGF23-Klotho signaling using mice with postnatally induced Memo deficiency in the whole body (cKO). Memo cKO mice showed impaired FGF23-driven renal ERK phosphorylation and transcriptional responses. FGF23 actions involved activation of oxidation-sensitive protein phosphotyrosyl phosphatases in the kidney. Redox proteomics revealed excessive thiols of Rho-GDP dissociation inhibitor 1 (Rho-GDI1) in Memo cKO, and we detected a functional interaction between Memo's redox function and oxidation at Rho-GDI1 Cys79. In isolated cellular systems, Rho-GDI1 did not directly affect FGF23-driven cell signaling, but we detected disturbed Rho-GDI1 dependent small Rho-GTPase protein abundance and activity in the kidney of Memo cKO mice. Collectively, this study reveals previously unknown layers in the regulation of renal FGF23 signaling and connects Memo with the network of small Rho-GTPases.

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.

Abstract 3685: Sustained Ret expression during mammary gland post-lactation induces premature involution and enhances cancer potential

Loss of normal development is a hallmark of cancer. Thus, understanding the mechanisms of tissue-specific developmental regulation and the changes that occur during tumorigenesis may provide insights of both diagnostic and therapeutic importance. In breast cancer, several members of the receptor tyrosine kinases (RTK) family that are well known to promote aggressive breast cancers also have roles in normal breast. We found that Ret, a RTK member, is normally expressed in the mouse glands in lactation. We determined that inhibition of Ret activity in vivo does not alter lactation, however impacts in the transition to involution. Involution is the period with high inflammation which returns the lactating mammary gland to a quiescent state after weaning. Involution has been well described as a post-lactation stage that drives cancer progression. Ret is overexpressed in about 40% of human breast tumors. Previously, using a doxycycline-inducible transgenic mouse model (Ret/MTB) we determined that chronic expression of Ret is oncogenic in the mammary epithelium. However, the stage of development at which Ret expression results in increase mammary tumor incidence has not been identified. To address this, we used the Ret/MTB system, to conditionally overexpress Ret during discrete periods of mammary gland development. We found that Ret is required for efficient transition to involution. We determined that the induction of Ret in Ret/MTB females promotes the expression of factors that drives involution, including premature Stat3 activation. RNA-seq data in Ret-overexpressing glands is supporting these findings, which were confirmed by several techniques. In addition, sustained expression of Ret during post-lactation enhances cancer potential showing a significant increase in pre-neoplastic lesions, defective milk recycling and disrupting Stat3 signaling. These results demonstrate that Ret deregulation increases cancer potential in post-lactation and might be considered as a prognostic marker for post-partum breast cancer.

Citation Format: Sabrina A. Vallone, Martín García Solá, Robert D. Cardiff, Roberto P. Meiss, Lewis A. Chodosh, Carolina Shere-Levy, Edith C C. Kordon, Nancy E. Hynes, Albana Gattelli. Sustained Ret expression during mammary gland post-lactation induces premature involution and enhances cancer potential [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 3685.

Elevated serum magnesium lowers calcification propensity in Memo1-deficient mice

MEdiator of cell MOtility1 (MEMO1) is a ubiquitously expressed redox protein involved in extracellular ligand-induced cell signaling. We previously reported that inducible whole-body Memo1 KO (cKO) mice displayed a syndrome of premature aging and disturbed mineral metabolism partially recapitulating the phenotype observed in Klotho or Fgf23-deficient mouse models. Here, we aimed at delineating the contribution of systemic mineral load on the Memo1 cKO mouse phenotype. We attempted to rescue the Memo1 cKO phenotype by depleting phosphate or vitamin D from the diet, but did not observe any effect on survival. However, we noticed that, by contrast to Klotho or Fgf23-deficient mouse models, Memo1 cKO mice did not present any soft-tissue calcifications and displayed even a decreased serum calcification propensity. We identified higher serum magnesium levels as the main cause of protection against calcifications. Expression of genes encoding intestinal and renal magnesium channels and the regulator epidermal growth factor were increased in Memo1 cKO. In order to check whether magnesium reabsorption in the kidney alone was driving the higher magnesemia, we generated a kidney-specific Memo1 KO (kKO) mouse model. Memo1 kKO mice also displayed higher magnesemia and increased renal magnesium channel gene expression. Collectively, these data identify MEMO1 as a novel regulator of magnesium homeostasis and systemic calcification propensity, by regulating expression of the main magnesium channels.

Ret Receptor Has Distinct Alterations and Functions in Breast Cancer

Ret receptor tyrosine kinase is a proto-oncogene that participates in development of various cancers. Several independent studies have recently identified Ret as a key player in breast cancer. Although Ret overexpression and function have been under investigation, mainly in estrogen receptor positive breast cancer, a more comprehensive analysis of the impact of recurring Ret alterations in breast cancer is needed. This review consolidates the current knowledge of Ret alterations and their potential effects in breast cancer. We discuss and integrate data on Ret changes in different breast cancer subtypes and potential function in progression, as well as the participation of distinct Ret network signaling partners in these processes. We propose that it will be essential to define a shared molecular feature of tumors with alteration in Ret receptor, be this at the genetic level or via overexpression in order to design effective therapies to target the Ret pathway. Here we review experimental evidence from basic research and pre-clinical studies concentrating on Ret alterations as potential biomarkers for recurrence, and we discuss the possibility that targeting the Ret pathway might in the future become a treatment for breast cancer.

A conditional inducible JAK2V617F transgenic mouse model reveals myeloproliferative disease that is reversible upon switching off transgene expression

Aberrant activation of the JAK/STAT pathway is thought to be the critical event in the pathogenesis of the chronic myeloproliferative neoplasms, polycythemia vera, essential thrombocythemia and primary myelofibrosis. The most frequent genetic alteration in these pathologies is the activating JAK2^V617F mutation, and expression of the mutant gene in mouse models was shown to cause a phenotype resembling the human diseases. Given the body of genetic evidence, it has come as a sobering finding that JAK inhibitor therapy only modestly suppresses the JAK2^V617F allele burden, despite showing clear benefits in terms of reducing splenomegaly and constitutional symptoms in patients. To gain a better understanding if JAK2^V617F is required for maintenance of myeloproliferative disease once it has evolved, we generated a conditional inducible transgenic JAK2^V617F mouse model using the SCL-tTA-2S tet-off system. Our model corroborates that expression of JAK2^V617F in hematopoietic stem and progenitor cells recapitulates key hallmarks of human myeloproliferative neoplasms, and exhibits gender differences in disease manifestation. The disease was found to be transplantable, and importantly, reversible when transgenic JAK2^V617F expression was switched off. Our results indicate that mutant JAK2^V617F-specific inhibitors should result in profound disease modification by disabling the myeloproliferative clone bearing mutant JAK2.

SYK inhibition blocks proliferation and migration of glioma cells and modifies the tumor microenvironment

Background

Glioblastoma (GBM) is one of the most aggressive human brain tumors, with a median survival of 15-18 months. There is a desperate need to find novel therapeutic targets. Various receptor protein kinases have been identified as potential targets; however, response rates in clinical studies have been somewhat disappointing. Targeting the spleen tyrosine kinase (SYK), which acts downstream of a range of oncogenic receptors, may therefore show more promising results.

Methods

Kinase expression of brain tumor samples including GBM and low-grade tumors were compared with normal brain and normal human astrocytes by microarray analysis. Furthermore, SYK, LYN, SLP76, and PLCG2 protein expressions were analyzed by immunohistochemistry, western blot, and immunofluorescence of additional GBM patient samples, murine glioma samples, and cell lines. SYK was then blocked chemically and genetically in vitro and in vivo in 2 different mouse models. Multiphoton intravital imaging and multicolor flow cytometry were performed in a syngeneic immunocompetent C57BL/6J mouse GL261 glioma model to study the effect of these inhibitors on the tumor microenvironment.

Results

SYK, LYN, SLP76, and PLCG2 were found expressed in human and murine glioma samples and cell lines. SYK inhibition blocked proliferation, migration, and colony formation. Flow cytometric and multiphoton imaging imply that targeting SYK in vivo attenuated GBM tumor growth and invasiveness and reduced B and CD11b+ cell mobility and infiltration.

Conclusions

Our data suggest that gliomas express a SYK signaling network important in glioma progression, inhibition of which results in reduced invasion with slower tumor progression.

Renal Memo1 Differentially Regulates the Expression of Vitamin D-Dependent Distal Renal Tubular Calcium Transporters

Ablation of the Mediator of ErbB2-driven Cell Motility 1 (Memo1) in mice altered calcium homeostasis and renal calcium transporter abundance by an unknown mechanism. Here, we investigated the role of intrarenal Memo in renal calcium handling. We have generated a mouse model of inducible kidney-specific Memo1 deletion. The Memo-deficient mice showed normal serum concentration and urinary excretion of calcium and phosphate, but elevated serum FGF23 concentration. They displayed elevated gene expression and protein abundance of the distal renal calcium transporters NCX1, TRPV5, and calbindin D28k. In addition, Claudin 14 gene expression was increased. When the mice were challenged by a vitamin D deficient diet, serum FGF23 concentration and TRPV5 membrane abundance were decreased, but NCX1 abundance remained increased. Collectively, renal distal calcium transport proteins (TRPV5 and Calbindin-D28k) in this model were altered by Memo- and vitamin-D dependent mechanisms, except for NCX1 which was vitamin D-independent. These findings highlight the existence of distinct regulatory mechanisms affecting TRPV5 and NCX1 membrane expression in vivo.

Chronic expression of wild-type Ret receptor in the mammary gland induces luminal tumors that are sensitive to Ret inhibition

The receptor tyrosine kinase Ret, a key gain-of-function mutated oncoprotein in thyroid carcinomas, has recently been implicated in other cancer types. While Ret copy number gains and mutations have been reported at low frequencies in breast tumors, we and others have reported that Ret is overexpressed in about 40% of human tumors and this correlates with poor patient prognosis. Ret activation regulates numerous intracellular pathways related to proliferation and inflammation, but it is not known whether abnormal Ret expression is sufficient to induce mammary carcinomas. Using a novel doxycycline-inducible transgenic mouse model with the MMTV promoter controlling Ret expression, we show that overexpression of wild-type Ret in the mammary epithelium produces mammary tumors, displaying a morphology that recapitulates characteristics of human luminal breast tumors. Ret-evoked tumors are estrogen receptor positive and negative for progesterone receptor. Moreover, tumors rapidly regress after doxycycline withdrawal, indicating that Ret is the driving oncoprotein. Using next-generation sequencing, we examined the levels of transcripts in these tumors, confirming a luminal signature. Ret-evoked tumors have been passaged in mice and used to test novel therapeutic approaches. Importantly, we have determined that tumors are resistant to endocrine therapy, but respond successfully to treatment with a Ret kinase inhibitor. Our data provide the first compelling evidence for an oncogenic role of non-mutated Ret in the mammary gland and are an incentive for clinical development of Ret as a cancer biomarker and therapeutic target.

Serpin E2 promotes breast cancer metastasis by remodeling the tumor matrix and polarizing tumor associated macrophages

The extracellular serine protease inhibitor serpinE2 is overexpressed in breast cancer and has been shown to foster metastatic spread. Here, we investigated the hypothesis that serpinE2 creates tumor-promoting conditions in the tumor microenvironment (TME) by affecting extracellular matrix remodeling. Using two different breast cancer models, we show that blocking serpinE2, either by knock-down (KD) in tumor cells or in response to a serpinE2 binding antibody, decreases metastatic dissemination from primary tumors to the lungs. We demonstrate that in response to serpinE2 KD or antibody treatment there are dramatic changes in the TME. Multiphoton intravital imaging revealed deposition of a dense extracellular collagen I matrix encapsulating serpinE2 KD or antibody-treated tumors. This is accompanied by a reduction in the population of tumor-promoting macrophages, as well as a decrease in chemokine ligand 2, which is known to affect macrophage abundance and polarization. In addition, TIMP-1 secretion is increased, which may directly inhibit matrix metalloproteases critical for collagen degradation in the tumor. In summary, our findings suggest that serpinE2 is required in the extracellular milieu of tumors where it acts in multiple ways to regulate tumor matrix deposition, thereby controlling tumor cell dissemination.

Redox-Dependent Bone Alkaline Phosphatase Dysfunction Drives Part of the Complex Bone Phenotype in Mice Deficient for Memo1

Mediator of ErbB2-driven cell Motility 1 (MEMO1) is an intracellular redox protein that integrates growth factors signaling with the intracellular redox state. We have previously reported that mice lacking Memo1 displayed higher plasma calcium levels and other alterations of mineral metabolism, but the underlying mechanism was unresolved and the bone phenotype was not described. Here, we show that Cre/lox-mediated MEMO1 deletion in the whole body of C57Bl/6 mice (Memo cKO) leads to severely altered trabecular bone and lower mineralization, with preserved osteoblast and osteoclast number and activity, but altered osteoblast response to epidermal growth factor (EGF) and FGF2. More strikingly, Memo cKO mice display decreased alkaline phosphatase (ALP) activity in serum and in bone, while ALPL expression level is unchanged. Bone intracellular redox state is significantly altered in Memo cKO mice and we inferred that ALP dimerization was reduced in Memo cKO mice. Indeed, despite similar ALP oxidation, we found increased ALP sensitivity to detergent in Memo cKO bone leading to lower ALP dimerization capability. Thus, we report a severe bone phenotype and dysfunctional bone ALP with local alteration of the redox state in Memo cKO mice that partially mimics hypophosphatasia, independent of ALPL mutations. These findings reveal Memo as a key player in bone homeostasis and underline a role of bone redox state in controlling ALP activity.

Memo interacts with c-Src to control Estrogen Receptor alpha sub-cellular localization

Understanding the complex interaction between growth factor and steroid hormone signaling pathways in breast cancer is key to identifying suitable therapeutic strategies to avoid progression and therapy resistance. The interaction between these two pathways is of paramount importance for the development of endocrine resistance. Nevertheless, the molecular mechanisms behind their crosstalk are still largely obscure. We previously reported that Memo is a small redox-active protein that controls heregulin-mediated migration of breast cancer cells. Here we report that Memo sits at the intersection between heregulin and estrogen signaling, and that Memo controls Estrogen Receptor alpha (ERα) sub-cellular localization, phosphorylation, and function downstream of heregulin and estrogen in breast cancer cells. Memo facilitates ERα and c-Src interaction, ERα Y537 phosphorylation, and has the ability to control ERα extra-nuclear localization. Thus, we identify Memo as an important key mediator between the heregulin and estrogen signaling pathways, which affects both breast cancer cell migration and proliferation.

Expression of the mRNA stability regulator Tristetraprolin is required for lactation maintenance in the mouse mammary gland

Tristetraprolin (TTP), an mRNA-binding protein that negatively controls levels of inflammatory factors, is highly expressed in the lactating mouse mammary gland. To determine the biological relevance of this expression profile, we developed bi-transgenic mice in which this protein is specifically down-regulated in the secretory mammary epithelium in the secretory mammary epithelium during lactation. Our data show that TTP conditional KO mice produced underweight litters, possibly due to massive mammary cell death induced during lactation without the requirement of additional stimuli. This effect was linked to overexpression of inflammatory cytokines, activation of STAT3 and down-regulation of AKT phosphorylation. Importantly, blocking TNFα activity in the lactating conditional TTP KO mice inhibited cell death and similar effects were observed when this treatment was applied to wild-type animals during 48 h after weaning. Therefore, our results demonstrate that during lactation TTP wards off early involution by preventing the increase of local inflammatory factors. In addition, our data reveal the relevance of locally secreted TNFα for triggering programmed cell death after weaning.

NADPH oxidase-mediated redox signaling promotes oxidative stress resistance and longevity through memo-1 in C. elegans

Transient increases in mitochondrially-derived reactive oxygen species (ROS) activate an adaptive stress response to promote longevity. Nicotinamide adenine dinucleotide phosphate (NADPH) oxidases produce ROS locally in response to various stimuli, and thereby regulate many cellular processes, but their role in aging remains unexplored. Here, we identified the C. elegans orthologue of mammalian mediator of ErbB2-driven cell motility, MEMO-1, as a protein that inhibits BLI-3/NADPH oxidase. MEMO-1 is complexed with RHO-1/RhoA/GTPase and loss of memo-1 results in an enhanced interaction of RHO-1 with BLI-3/NADPH oxidase, thereby stimulating ROS production that signal via p38 MAP kinase to the transcription factor SKN-1/NRF1,2,3 to promote stress resistance and longevity. Either loss of memo-1 or increasing BLI-3/NADPH oxidase activity by overexpression is sufficient to increase lifespan. Together, these findings demonstrate that NADPH oxidase-induced redox signaling initiates a transcriptional response that protects the cell and organism, and can promote both stress resistance and longevity.

DOI:http://dx.doi.org/10.7554/eLife.19493.001

Breast Cancer Patients Have Greatly Benefited from the Progress in Molecular Oncology

Cancer research has become a global enterprise, and the number of researchers, as well as the cost for their activities, has skyrocketed. The budget for the National Cancer Institute of the United States National Institutes of Health alone was US$5.2 billion in 2015. Since most of the research is funded by public money, it is perfectly legitimate to ask if these large expenses are worth it. In this brief commentary, we recapitulate some of the breakthroughs that mark the history of breast cancer research over the past decades and emphasize the resulting benefits for afflicted women. In 1971, only 40% of women diagnosed with breast cancer would live another 10 years. Today, nearly 80% of women reach that significant milestone in most developed countries. This dramatic change has afforded breast cancer patients many productive years and a better quality of life. Progress resulted largely from advances in the understanding of the molecular details of the disease and their translation into innovative, rationally designed therapies. These developments are founded on the revolution in molecular and cellular biology, an entirely new array of methods and technologies, the enthusiasm, optimism, and diligence of scientists and clinicians, and the considerable funding efforts from public and private sources. We were lucky to be able to spend our productive years in a period of scientific upheaval in which methods and concepts were revolutionized and that allowed us to contribute, within the global scientific community, to the progress in basic science and clinical practice.

Decreased NK-cell tumour immunosurveillance consequent to JAK inhibition enhances metastasis in breast cancer models

The JAK/STAT pathway is an attractive target for breast cancer therapy due to its frequent activation, and clinical trials evaluating JAK inhibitors (JAKi) in advanced breast cancer are ongoing. Using patient biopsies and preclinical models of breast cancer, we demonstrate that the JAK/STAT pathway is active in metastasis. Unexpectedly, blocking the pathway with JAKi enhances the metastatic burden in experimental and orthotopic models of breast cancer metastasis. We demonstrate that this prometastatic effect is due to the immunosuppressive activity of JAKi with ensuing impairment of NK-cell-mediated anti-tumour immunity. Furthermore, we show that immunostimulation with IL-15 overcomes the enhancing effect of JAKi on metastasis formation. Our findings highlight the importance of evaluating the effect of targeted therapy on the tumour environment. The impact of JAKi on NK cells and the potential value of immunostimulators to overcome the weakened tumour immunosurveillance, are worthwhile considering in the clinical setting of breast cancer.

JAK inhibitors are currently undergoing evaluation in clinical trials for advanced breast cancer. Here, the authors show that JAK pathway inhibition increases metastasis in mouse models of breast cancer by impairing NK anti-tumour activity and that these side effects can be overcome by addition of IL-15.

Targeting a Novel ER/HOXB7 Signaling Loop in Tamoxifen-Resistant Breast Cancer

The majority of patients with breast cancer present with an estrogen receptor-positive (ER(+)) tumor, and the endocrine agent tamoxifen is a mainstay for their treatment. Unfortunately, however, resistance remains a major problem because most patients who respond eventually have a recurrence. Thus, an enduring challenge in the breast cancer field is to identify mechanisms underlying tamoxifen resistance. Jin and colleagues describe a novel ER/HOXB7 signaling loop in tamoxifen-resistant breast cancer models. Importantly, they reveal that targeting this signaling loop has great promise as an approach to treat patients with tamoxifen-resistant breast cancer.

MEMO1 drives cranial endochondral ossification and palatogenesis

The cranial base is a component of the neurocranium and has a central role in the structural integration of the face, brain and vertebral column. Consequently, alteration in the shape of the human cranial base has been intimately linked with primate evolution and defective development is associated with numerous human facial abnormalities. Here we describe a novel recessive mutant mouse strain that presented with a domed head and fully penetrant cleft secondary palate coupled with defects in the formation of the underlying cranial base. Mapping and non-complementation studies revealed a specific mutation in Memo1 - a gene originally associated with cell migration. Expression analysis of Memo1 identified robust expression in the perichondrium and periosteum of the developing cranial base, but only modest expression in the palatal shelves. Fittingly, although the palatal shelves failed to elevate in Memo1 mutants, expression changes were modest within the shelves themselves. In contrast, the cranial base, which forms via endochondral ossification had major reductions in the expression of genes responsible for bone formation, notably matrix metalloproteinases and markers of the osteoblast lineage, mirrored by an increase in markers of cartilage and extracellular matrix development. Concomitant with these changes, mutant cranial bases showed an increased zone of hypertrophic chondrocytes accompanied by a reduction in both vascular invasion and mineralization. Finally, neural crest cell-specific deletion of Memo1 caused a failure of anterior cranial base ossification indicating a cell autonomous role for MEMO1 in the development of these neural crest cell derived structures. However, palate formation was largely normal in these conditional mutants, suggesting a non-autonomous role for MEMO1 in palatal closure. Overall, these findings assign a new function to MEMO1 in driving endochondral ossification in the cranium, and also link abnormal development of the cranial base with more widespread effects on craniofacial shape relevant to human craniofacial dysmorphology.

Abstract LB-013: The immunomodulatory effect of JAK inhibitors enhances metastasis by impairing antitumor immunity in preclinical models of breast cancer

The JAK-STAT pathway is an attractive therapeutic target in breast cancer due to its frequent activation. Clinical trials testing JAK inhibitors in breast cancer are ongoing, making it important to understand the effect of this therapeutic approach on metastasis. While it is recognized that tumor growth in primary and metastatic sites is influenced by the local environment, little is known about the effect of targeted therapies on metastases or on host cells interacting with tumor cells at distant locations. Our goal was to determine the effect of JAK inhibitors on breast cancer in the bone environment, a common site of metastasis. Using patient biopsies and preclinical models of breast cancer metastasis, we demonstrate that the JAK-STAT pathway is active in bone metastasis, both in the cancer cells and in the tumor environment. To study the effect of JAK inhibitors, we established preclinical models of bone metastatic tumors, taking advantage of the bone tropism when injected via the intracardiac route, of the breast cancer cell lines, human MDA-MB231 scp1833 and mouse EO771. In vivo, in both models, STAT3 was active and treatment with the JAK1-JAK2 inhibitor ruxolitinib decreased pSTAT3 levels in primary tumors and in bone metastases. Unexpectedly, blocking the pathway with ruxolitinib, or with the JAK2 inhibitor BSK805, enhanced the metastatic burden in both models. To investigate the effect of JAK inhibition on tumor cell dissemination from the primary site, we employed the 4T1.2 model, which spontaneously metastasizes from the mammary tumor to the bone and the lungs. As seen with the other models, there was a significant increase in tumor cell numbers in the bone and in the lungs in response to JAK inhibitor treatment. To understand the mechanism underlying the increase in metastatic load, we considered the host immune system as a potential bystander target of the JAK inhibitors. Indeed, in response to JAK inhibitor treatment we observed a major reduction in the NK cell population. The effect of JAK inhibitors on NK cells was systemic since they were also reduced in the bone marrow and in the peripheral blood of tumor-bearing mice. To mechanistically explain the impact of JAK inhibitors on NK cells, we used the NK cell line, NK-92. Upon treatment of NK-92 cells with JAK inhibitors, activation of multiple STATs decreased and cell proliferation was strongly inhibited. In cytotoxic assays, treatment with JAK inhibitors significantly decreased the killing ability of NK-92 cells against carcinoma cells. To test the in vivo relevance of NK cells in metastatic growth we used NSG mice, which are devoid of NK cell activity. Remarkably, in contrast to the results obtained with 4T1.2 mammary tumors grown in immunocompetent hosts, no increase in bone or lung metastases was observed in tumor-bearing NSG hosts treated with ruxolitinib, providing strong evidence that JAK inhibition increases metastasis by interfering with NK cell mediated anti-tumor innate immunity. These results suggest that the immunomodulatory effect of JAK inhibitors in breast cancer patients undergoing clinical trials should be monitored. Moreover, our work highlights the importance of evaluating the effect of targeted therapy on cell populations in the tumor environment in order to predict and overcame bystander effects that might impact on therapy response.

Citation Format: Nancy E. Hynes, Alessia Bottos, Jason Gill, Thomas Radimerski, Alexander Tzankov, Aleksandra Wodnar-Filipowicz. The immunomodulatory effect of JAK inhibitors enhances metastasis by impairing antitumor immunity in preclinical models of breast cancer. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr LB-013. doi:10.1158/1538-7445.AM2015-LB-013

Abstract P1-07-19: Effects of JAK pathway inhibition in pre-clinical models of breast cancer bone marrow metastases

Bone marrow (BM) metastases are an important problem in metastatic breast cancer. Metastatic-relapse occurs even decades after the first diagnosis and can show different clinical features compared to the primary disease. The cross-talk between cancer cells and the microenvironment influences tumor behaviour and impinges on therapeutic efficiency.

To uncover new targets for the inhibition of BM metastases, we performed a transcriptional analysis of BM stromal cells using in-vivo models of breast cancer bone metastases. We identified IL6, and its downstream JAK kinases pathway, as major up-regulated signals in the bone stroma of tumor-bearing mice. Moreover, we found that a significant proportion of BM metastases from breast cancer patient biopsies are positive for pSTAT3 staining, attesting to activation of JAK-STAT signaling. These results provide a rational to investigate the therapeutic potential of a JAK inhibition in bone metastases. We evaluated the effect of two JAK inhibitors: the BSK805, a JAK2 inhibitor, and ruxolitinib a JAK1-JAK2 inhibitor currently in clinical trials for metastatic breast cancer. In pre-clinical models of breast cancer metastases (the triple negative MDA-MB231 SCP1833 and the ER+ EO771), treatment with the JAK inhibitors decreased pSTAT3 signaling in the bone, but surprisingly increased metastastic tumor burden.

Considering the importance of the JAK-STAT pathway as a therapeutic target, we are investigating the possible bystander effects of blocking JAK kinases. Analysis of the BM stoma showed that JAK inhibition decreased TRAP+ osteoclasts and affected the mesenchymal compartment, with a significant increase in the BM fat compartment in tumor-bearing animals. The reasons for and the consequences of these changes in the bone stroma are under investigation. As the JAK-STAT signaling pathway is also a key regulator of the hematopoietic compartment, we are studying how JAK inhibitors influence the immune response in tumor bearing mice. Further dissection of the immunomodulatory effect of JAK inhibition and how this influences tumor dissemination and expansion is warranted.

Citation Format: Alessia Bottos, Jason Gill, Thomas Radimerski, Alexandar Tzankov, Aleksandra Wodnar-Filipowicz, Nancy E Hynes. Effects of JAK pathway inhibition in pre-clinical models of breast cancer bone marrow metastases [abstract]. In: Proceedings of the Thirty-Seventh Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2014 Dec 9-13; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2015;75(9 Suppl):Abstract nr P1-07-19.

Transcriptional regulation of tenascin-W by TGF-beta signaling in the bone metastatic niche of breast cancer cells

Tenascin‐W is a matricellular protein with a dynamically changing expression pattern in development and disease. In adults, tenascin‐W is mostly restricted to stem cell niches, and is also expressed in the stroma of solid cancers. Here, we analyzed its expression in the bone microenvironment of breast cancer metastasis. Osteoblasts were isolated from tumor‐free or tumor‐bearing bones of mice injected with MDA‐MB231‐1833 breast cancer cells. We found a fourfold upregulation of tenascin‐W in the osteoblast population of tumor‐bearing mice compared to healthy mice, indicating that tenascin‐W is supplied by the bone metastatic niche. Transwell and co‐culture studies showed that human bone marrow stromal cells (BMSCs) express tenascin‐W protein after exposure to factors secreted by MDA‐MB231‐1833 breast cancer cells. To study tenascin‐W gene regulation, we identified and analyzed the tenascin‐W promoter as well as three evolutionary conserved regions in the first intron. 5′RACE analysis of mRNA from human breast cancer, glioblastoma and bone tissue showed a single tenascin‐W transcript with a transcription start site at a noncoding first exon followed by exon 2 containing the ATG translation start. Site‐directed mutagenesis of a SMAD4‐binding element in proximity of the TATA box strongly impaired promoter activity. TGFβ1 induced tenascin‐W expression in human BMSCs through activation of the TGFβ1 receptor ALK5, while glucocorticoids were inhibitory. Our experiments show that tenascin‐W acts as a niche component for breast cancer metastasis to bone by supporting cell migration and cell proliferation of the cancer cells.

What's new?

Once breast cancer metastasizes, it is generally incurable. Proteins in the extracellular matrix play a crucial role in launching the tumor cells to a new site. These authors investigated one such protein, tenascin‐W, which can be found surrounding not only tumor cells but also in bone tissue. Among other things, they studied how breast cancer cells affected tenascin‐W expression. The tumor cells induced bone marrow stromal cells to make more tenascin‐W, suggesting that the protein may pave the way for the cancer to spread to the bone.

Abstract SY20-02: Insights into mechanisms of breast cancer metastasis

Breast carcinoma is the most frequent cancer in women, affecting one million yearly. In the past decades there have been great improvements in surgery, screening and therapy. These have led to dramatic changes in the 5-year overall survival rates, which have gone from 40% in the 1950's up to 86% in the past decade (Maxmen 2012). However, many patients who present with early stage disease die from metastases, despite complete surgical removal of primary breast tumors. Indeed, if a tumor has spread to distant organs at the time of presentation, the 5-year overall survival is only 23% compared to 90% or higher for patients with localized tumors. Today, primary tumors are efficiently removed by surgical intervention, but there are essentially no successful therapeutic options for metastatic disease.

Metastasis is a complex process whereby tumor cells detach from the primary site, acquire migratory properties, enter and survive in the circulation, and colonize and grow at distant sites (Gupta and Massague 2006). Metastatic relapse can occur years after surgery, suggesting that tumor cells have the ability to survive in a dormant state in metastatic niches (Karrison, Ferguson et al. 1999). Typical sites of relapse of breast cancer are the bone, lungs, liver and brain (Weigelt, Peterse et al. 2005; Nguyen, Bos et al. 2009). Thus, the most relevant clinical and experimental questions in the breast cancer field revolve around metastasis. Important research areas are: the identification of specific molecules and pathways contributing to metastatic spread, tumor cell survival and growth in distant sites, as well as uncovering metastatic therapies. My presentation will cover our recent work on: 1-targeting receptor tyrosine kinases (RTKs) in metastatic breast cancer models; 2- Memo, a novel enzyme that affects intracellular ROS production, and is essential for in vivo metastasis; 3- analyses aimed at uncovering molecular mechanisms involved in crosstalk between tumor cells and the bone marrow (BM) environment.

1-Targeting RTKs with antibodies or small molecular inhibitors is a clinically validated approach for cancer therapy. In breast cancer, the ErbB2/HER2 specific antibody trastuzumab is routinely given in combination with chemotherapy to ErbB2/HER2-positive breast cancer patients and has had a significant impact on patient mortality (Gianni, Dafni et al., 2011). Only a sub-set of patients, however, are eligible for this treatment, making it essential to uncover additional RTKs that could be useful in for therapy; the Ret kinase might be an interesting new target. Ret was discovered as an outlier kinase in breast cancer, with unexpectedly high expression levels detected in many breast tumors (Esseghir, Todd et al. 2007; Boulay, Breuleux et al. 2008; Kothari, Wei et al. 2013). Unlike thyroid or lung tumors that carry oncogenic Ret, as fusion proteins or with activating mutations, Ret appears to be wild type in breast cancer. We have shown that elevated Ret levels are found in different sub-types of human breast cancers and that high Ret correlates with decreased metastasis-free survival. Using a metastatic breast cancer model, we showed that in vivo blockade of Ret inhibits tumor outgrowth and metastatic potential (Gattelli, Nalvarte et al. 2013). Our results suggest that Ret has an important role in tumor growth and metastasis.

Multiple RTKs are often active in cancer cells and combining RTK inhibitors has been shown to have strong anti-tumor activity (e.g., Stommel, Kimmelman et al. 2007). Considering that breast tumors often co-express ErbB and FGFRs (Cancer Genome Atlas Network, 2012), we have tested the impact of blocking both in metastatic breast cancer models. We have recently shown that only when both RTKs are blocked do we observe: blockade of the ERK and PI3K pathways, prolonged tumor-stasis and a significant decrease in metastasis (Dey, Bianchi et al. 2010; Issa, Gill et al. 2013).

2-Our group originally identified Memo as being essential for breast cancer cell motility in response to several RTKs (Marone, Hess et al. 2004; Meira, Masson et al. 2009). The 2.1 Å crystal structure of Memo revealed its structural homology with bacterial enzymes (Qiu, Lienhard et al. 2008); we have recently discovered that Memo is a metal-binding enzyme that requires Cu(II) for its oxidase-like activity. Memo knock-down (KD) in breast cancer models affects localized intracellular ROS production, cell migration and invasion, as well as in vivo spontaneous lung metastasis from xenografts. To investigate if Memo plays a role in human breast disease, immunohistochemistry (IHC) was carried out on breast cancer tissue microarrays (TMAs). Memo expression is low in non-neoplastic breast tissue and exhibits significantly higher expression in > 40% of tumors. Memo is diffusely localized to the cytoplasm and the nucleus and accumulates at the membrane upon growth factor stimulation (Schlatter, Meira et al. 2012). To examine if the sub-cellular localization of Memo correlates with clinical or histopathological parameters, we categorized the breast tumor samples according to expression and localization of Memo. We found that elevated Memo was prognostic of poor outcome; elevated levels of cytoplasmic Memo, but not nuclear Memo, significantly predicted early metastasis and death at 5 years in a multivariable Cox model. These data suggest that Memo has distinct roles in different cellular compartments and that its cytoplasmic function regulates pathways that promote tumor dissemination.

3- Bone marrow is particularly permissive for disseminated tumor cells since structural and environmental features needed to allow trafficking of hematopoietic stem cells and their progeny can also be employed by the tumor cells. The fenestration of bone sinusoidal capillaries facilitates the entrance of tumor cells. Moreover, bone stroma is a potent source of CXCL12 that attracts tumor cells expressing its receptor CXCR4, making BM a perfect soil for circulating tumor cells (Morrison and Spradling 2008). Metastatic tumors show different molecular features compared to primary tumors, which could reflect tumor-cell selection for particular conditions in the distant site and/or the influence of the surrounding stroma on a disseminated tumor cells (Kang, Siegel et al. 2003; Minn, Gupta et al. 2005). The BM niche is a complex, multicellular structure composed of osteoblasts, osteoclasts, stromal fibroblasts, endothelial cells, and mesenchymal progenitors, all of which contribute to general bone homeostasis (Mendez-Ferrer, Michurina et al. 2010; Ehninger and Trumpp 2011). Considering the strong interplay between these elements, it has been suggested that blocking the crosstalk between tumor and the bone environment would be a potential strategy to inhibit tumor expansion. To uncover molecular mechanisms involved in the crosstalk between tumor cells and the BM environment, we compared the transcriptome of different cell populations from the BM environment from tumor-bearing and tumor-free mice. For this, we used purified stromal cell subsets of: endothelial and osteoblastic cells, as well as mesenchymal and osteogenic progenitors. These analyses revealed that BM is strongly affected by breast cancer cell dissemination. Indeed, several components of key molecular pathways involved in tumor development, including TGFBR, PDGFRB, EGFR, HGFR, IGFR and JAK/Stat, are modulated in the BM of mice with tumor cells.

References

1. Bos, P. D., X. H. Zhang, et al. (2009). Nature 459(7249): 1005-1009.

2. Cancer Genome Atlas Network (2012). ” Nature 490: 61-70.

3. Dey, J.H., F. Bianchi, et al. (2010). Cancer Research 70: 4151-4162.

4. Ehninger, A. and A. Trumpp (2011). J Exp Med 208(3): 421-428.

5. Gianni, L., U. Dafni, et al. (2011). Lancet Oncol 12: 236-244.

6. Gupta, G. P. and J. Massague (2006). Cell 127(4): 679-695.

7. Issa, A., J. W. Gill, et al. (2013). Breast Cancer Research 15:R8.

8. Karrison, T. G., D. J. Ferguson, et al. (1999). J Natl Cancer Inst 91(1): 80-85.

9. Kang, Y., P. M. Siegel, et al. (2003). Cancer Cell 3(6): 537-549.

10. Kothari, V., I. Wei, et al. (2013). Cancer Discov 3: 280-293.

11. Marone, R., D. Hess, et al (2004). Nature Cell Biology 6: 515-522.

12. Maxmen, A. (2012). Nature 485(7400): S50-51.

13. Meira, M., R. Masson, et al (2009). Journal of Cell Science 122: 787-797.

14. Mendez-Ferrer, S., T. V. Michurina, et al. (2010). Nature 466(7308): 829-834.

15. Minn, A. J., G. P. Gupta, et al. (2005). Nature 436(7050): 518-524.

16. Morrison, S. J. and A. C. Spradling (2008). Cell 132(4): 598-611.

17. Qiu, C., S. Lienhard, et al. (2008). The Journal of Biological Chemistry 283: 2734-2740.

18. Schlatter, I.D., M. Meira, et al. (2012). PloS one 7: e32501.

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Citation Format: Nancy E. Hynes. Insights into mechanisms of breast cancer metastasis. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr SY20-02. doi:10.1158/1538-7445.AM2014-SY20-02

AXL/epidermal growth factor receptor (EGFR) complexes in breast cancer--culprits for resistance to EGFR inhibitors?

Epidermal growth factor receptor (EGFR) is highly expressed in triple-negative breast cancer (TNBC), and elevated levels correlate with poor prognosis. In analogy with the paradigm of oncogene addiction, blocking EGFR in TNBC was expected to have clinical efficacy – but this has not been the case. Reasons for these results have remained elusive. Recently, Meyer and colleagues showed interplay between EGFR and the epithelial-to-mesenchymal transition-associated AXL receptor in TNBC cells, which might provide some clues.

Memo is a copper-dependent redox protein with an essential role in migration and metastasis

Memo is an evolutionarily conserved protein with a critical role in cell motility. We found that Memo was required for migration and invasion of breast cancer cells in vitro and spontaneous lung metastasis from breast cancer cell xenografts in vivo. Biochemical assays revealed that Memo is a copper-dependent redox enzyme that promoted a more oxidized intracellular milieu and stimulated the production of reactive oxygen species (ROS) in cellular structures involved in migration. Memo was also required for the sustained production of the ROS O2- by NADPH (reduced form of nicotinamide adenine dinucleotide phosphate) oxidase 1 (NOX1) in breast cancer cells. Memo abundance was increased in >40% of the primary breast tumors tested, was correlated with clinical parameters of aggressive disease, and was an independent prognostic factor of early distant metastasis.

Science Signaling Podcast: 10 June 2014

The copper-binding enzyme Memo promotes breast cancer metastasis.

Memo has a novel role in S1P signaling and is [corrected] crucial for vascular development

Memo is a conserved protein that was identified as an essential mediator of tumor cell motility induced by receptor tyrosine kinase activation. Here we show that Memo null mouse embryonic fibroblasts (MEFs) are impaired in PDGF-induced migration and this is due to a defect in sphingosine-1-phosphate (S1P) signaling. S1P is a bioactive phospholipid produced in response to multiple stimuli, which regulates many cellular processes. S1P is secreted to the extracellular milieu where it exerts its function by binding a family of G-protein coupled receptors (S1PRs), causing their activation in an autocrine or paracrine manner. The process, termed cell-autonomous S1PR signaling, plays a role in survival and migration. Indeed, PDGF uses cell-autonomous S1PR signaling to promote cell migration; we show here that this S1P pathway requires Memo. Using vascular endothelial cells (HUVECs) with Memo knock-down we show that their survival in conditions of serum-starvation is impaired. Furthermore, Memo loss in HUVECs causes a reduction of junctional VE-cadherin and an increase in sprout formation. Each of these phenotypes is rescued by S1P or S1P agonist addition, showing that Memo also plays an important role in cell-autonomous S1PR signaling in endothelial cells. We also produced conventional and endothelial cell-specific conditional Memo knock-out mouse strains and show that Memo is essential for embryonic development. Starting at E13.5 embryos of both strains display bleeding and other vascular problems, some of the phenotypes that have been described in mouse strains lacking S1PRs. The essential role of Memo in embryonic vascular development may be due in part to alterations in S1P signaling. Taken together our results show that Memo has a novel role in the S1P pathway and that Memo is needed to promote cell-autonomous S1PR activation.

EGF receptor family: twisting targets for improved cancer therapies

The epidermal growth factor receptor (EGFR) undergoes a conformational change in response to ligand binding. The ligand-induced changes in cell surface aggregation and mobility have a profound effect on the function of all the family members. Ligand also activates the EGFR intracellular kinase, stimulating proliferation and cell survival. The EGFR family are often activated, overexpressed or mutated in cancer cells and therapeutic drugs (including antibodies) can slow the progress of some cancers. This article provides a brief, annotated summary of the presentations and discussion which occurred at the Epidermal Growth Factor Receptor - Future Directions Conference held in Jerusalem in November 2013.

Loss of Memo, a novel FGFR regulator, results in reduced lifespan

Memo is a widely expressed 33-kDa protein required for heregulin (HRG)-, epidermal growth factor (EGF)-, and fibroblast growth factor (FGF)-induced cell motility. Studies in mouse embryonic fibroblasts, wild-type or knockout for Memo, were performed to further investigate the role of Memo downstream of FGFR. We demonstrated that Memo associates with the FGFR signalosome and is necessary for optimal activation of signaling. To uncover Memo's physiological role, Memo conditional-knockout mice were generated. These animals showed a reduced life span, increased insulin sensitivity, small stature, graying hair, alopecia, kyphosis, loss of subcutaneous fat, and loss of spermatozoa in the epididymis. Memo-knockout mice also have elevated serum levels of active vitamin D, 1,25-dihydroxyvitamin D3 (1,25(OH)2D), and calcium compared to control littermates expressing Memo. In summary, the results from in vivo and in vitro models support the hypothesis that Memo is a novel regulator of FGFR signaling with a role in controlling 1,25(OH)2D production and normal calcium homeostasis.

Ret inhibition decreases growth and metastatic potential of estrogen receptor positive breast cancer cells

We show that elevated levels of Ret receptor are found in different sub-types of human breast cancers and that high Ret correlates with decreased metastasis-free survival. The role of Ret in ER+ breast cancer models was explored combining in vitro and in vivo approaches. Our analyses revealed that ligand-induced Ret activation: (i) stimulates migration of breast cancer cells; (ii) rescues cells from anti-proliferative effects of endocrine treatment and (iii) stimulates expression of cytokines in the presence of endocrine agents. Indeed, we uncovered a positive feed-forward loop between the inflammatory cytokine IL6 and Ret that links them at the expression and the functional level. In vivo inhibition of Ret in a metastatic breast cancer model inhibits tumour outgrowth and metastatic potential. Ret inhibition blocks the feed-forward loop by down-regulating Ret levels, as well as decreasing activity of Fak, an integrator of IL6-Ret signalling. Our results suggest that Ret kinase should be considered as a novel therapeutic target in subsets of breast cancer.

Signalling change: signal transduction through the decades

The past few years have marked significant anniversaries in signal transduction, including the identification of classic growth factors and morphogens, the notion of protein modification through phosphorylation and the characterization of protein interaction domains. Here, six researchers reflect on the context in which these discoveries were made, and how our concept of cell signalling has evolved during the past three decades.

Pharmacological inhibition of fibroblast growth factor (FGF) receptor signaling ameliorates FGF23-mediated hypophosphatemic rickets

Fibroblast growth factor 23 (FGF23) is a circulating factor secreted by osteocytes that is essential for phosphate homeostasis. In kidney proximal tubular cells FGF23 inhibits phosphate reabsorption and leads to decreased synthesis and enhanced catabolism of 1,25-dihydroxyvitamin D3 (1,25[OH]2 D3 ). Excess levels of FGF23 cause renal phosphate wasting and suppression of circulating 1,25(OH)2 D3 levels and are associated with several hereditary hypophosphatemic disorders with skeletal abnormalities, including X-linked hypophosphatemic rickets (XLH) and autosomal recessive hypophosphatemic rickets (ARHR). Currently, therapeutic approaches to these diseases are limited to treatment with activated vitamin D analogues and phosphate supplementation, often merely resulting in partial correction of the skeletal aberrations. In this study, we evaluate the use of FGFR inhibitors for the treatment of FGF23-mediated hypophosphatemic disorders using NVP-BGJ398, a novel selective, pan-specific FGFR inhibitor currently in Phase I clinical trials for cancer therapy. In two different hypophosphatemic mouse models, Hyp and Dmp1-null mice, resembling the human diseases XLH and ARHR, we find that pharmacological inhibition of FGFRs efficiently abrogates aberrant FGF23 signaling and normalizes the hypophosphatemic and hypocalcemic conditions of these mice. Correspondingly, long-term FGFR inhibition in Hyp mice leads to enhanced bone growth, increased mineralization, and reorganization of the disturbed growth plate structure. We therefore propose NVP-BGJ398 treatment as a novel approach for the therapy of FGF23-mediated hypophosphatemic diseases.

Combinatorial targeting of FGF and ErbB receptors blocks growth and metastatic spread of breast cancer models

Introduction

Targeting receptor tyrosine kinases (RTKs) with kinase inhibitors is a clinically validated anti-cancer approach. However, blocking one signaling pathway is often not sufficient to cause tumor regression and the effectiveness of individual inhibitors is often short-lived. As alterations in fibroblast growth factor receptor (FGFR) activity have been implicated in breast cancer, we examined in breast cancer models with autocrine FGFR activity the impact of targeting FGFRs in vivo with a selective kinase inhibitor in combination with an inhibitor of PI3K/mTOR or with a pan-ErbB inhibitor.

Methods

Using 4T1 or 67NR models of basal-like breast cancer, tumor growth was measured in mice treated with an FGFR inhibitor (dovitinib/TKI258), a PI3K/mTOR inhibitor (NVP-BEZ235) or a pan-ErbB inhibitor (AEE788) individually or in combination. To uncover mechanisms underlying inhibitor action, signaling pathway activity was examined in tumor lysates and transcriptome analysis carried out to identify pathways upregulated by FGFR inhibition. Anti-phosphotyrosine receptor antibody arrays (P-Tyr RTK) were also used to screen 4T1 tumors.

Results

The combination of dovitinib + NVP-BEZ235 causes tumor stasis and strong down-regulation of the FRS2/Erk and PI3K/Akt/mTOR signaling pathways. P-Tyr RTK arrays identified high levels of P-EGFR and P-ErbB2 in 4T1 tumors. Testing AEE788 in the tumor models revealed that the combination of dovitinib + AEE788 resulted in blockade of the PI3K/Akt/mTOR pathway, prolonged tumor stasis and in the 4T1 model, a significant decrease in lung metastasis. The results show that in vivo these breast cancer models become dependent upon co-activation of FGFR and ErbB receptors for PI3K pathway activity.

Conclusions

The work presented here shows that in the breast cancer models examined, the combination of dovitinib + NVP-BEZ235 or dovitinib + AEE788 results in strong inhibition of tumor growth and a block in metastatic spread. Only these combinations strongly down-regulate the FGFR/FRS2/Erk and PI3K/Akt/mTOR signaling pathways. The resultant decrease in mitosis and increase in apoptosis was consistently stronger in the dovitinib + AEE788 treatment-group, suggesting that targeting ErbB receptors has broader downstream effects compared to targeting only PI3K/mTOR. Considering that sub-classes of human breast tumors co-express ErbB receptors and FGFRs, these results have implications for targeted therapy.

The 14-3-3σ tumor suppressor has multiple functions in ErbB2-induced breast cancer

Ling and colleagues demonstrated that loss of the conditional 14-3-3σ allele results in accelerated HER2/ERBB2-driven mammary tumorigenesis and metastasis. This study underscores the role of 14-3-3σ as a potent tumor suppressor in ERBB2-driven tumor initiation and progression.

Abstract PD01-06: Inhibition of the Ret receptor tyrosine kinase in combination with endocrine therapy impacts on migration and metastatic potential of estrogen receptor positive breast cancer models

The Ret receptor tyrosine kinase is overexpressed in approximately 30% of human breast cancers, many of which are estrogen receptor-alpha positive (ER+). Using the ER+ breast cancer models MCF7 and T47D, we have shown that RET is an ER target gene and that Ret signaling enhances estrogen-driven anchorage-dependent and -independent proliferation (Boulay et al 2008). In our current work we are investigating the potential role of Ret in endocrine therapy response using in vivo and in vitro models. Ret is activated by peptides of the glial derived neurotrophic factor (GDNF) family. GDNF treatment of ER+ T47D and MCF7 breast cancer cell lines stimulates activation of multiple intracellular pathways, increases anchorage-dependent and -independent growth, as well as migration. To test if Ret activation impacts on endocrine therapy response, we treated MCF7/Aromatase (Aro)-expressing cells for seven days with different endocrine agents in the presence or absence of GDNF to activate Ret. Activation of Ret signaling rescued the proliferative block that resulted from treatment of the MCF7/Aro cells with tamoxifen, fulvestrant or letrozole. A transcriptome analysis was performed and an Ingenuity Pathway Analysis of the transcripts altered in MCF7/Aro cells treated with fulvestrant or letrozole revealed that the highest pathways altered by addition of GDNF are related to interferon signaling and inflammation. Indeed, proinflammatory RNAs, including IL6, IL8 and CXCL10 are among the top transcripts upregulated in cultures treated with fulvestrant plus GDNF, or letrozole plus GDNF. Elevated IL6 serum levels in breast cancer patients correlate with poor prognosis. We have concentrated on IL6 in the work that will be presented based on this clinical data, as well as our finding that IL6 stimulates Ret expression and activation in ER+ breast cancer models. We verified that addition of GDNF to MDCF/Aro cultures treated with fulvestrant or with letrozole led to an increase of IL6 in the conditional medium of the cultures. Moreover, addition of GDNF to fulvestrant- or tamoxifen-treated tumor cells increased migration, which could be inhibited by an IL6 blocking antibody, showing the importance of this cytokine for tumor cell motility. Additional data will be presented showing there is a Ret-IL6 feed-forward loop present in ER+ tumor cell models and that this is important for migration. In order to examine the role of Ret in vivo, in a metastatic breast cancer model, we have used the ER+/Ret+ J110 tumor cell line, generated from mammary tumors of MMTV-AIB1 transgenic females. Ret is active in J110 mammary tumors and its activity can be blocked with a Ret selective kinase inhibitor. In vivo data will be presented showing the effect of blocking Ret alone, or in combination with endocrine agents, on metastatic spread of primary tumors to the lungs.

Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr PD01-06.

Differential roles of fibroblast growth factor receptors (FGFR) 1, 2 and 3 in the regulation of S115 breast cancer cell growth

Fibroblast growth factors (FGFs) regulate the growth and progression of breast cancer. FGF signaling is transduced through FGF receptors 1–4, which have oncogenic or anti-oncogenic roles depending on the ligand and the cellular context. Our aim was to clarify the roles of FGFR1–3 in breast cancer cell growth in vitro and in vivo. Pools of S115 mouse breast cancer cells expressing shRNA against FGFR1, 2 and 3 were created by lentiviral gene transfer, resulting in cells with downregulated expression of FGFR1, FGFR2 or FGFR3 (shR1, shR2 and shR3 cells, respectively) and shLacZ controls. FGFR1-silenced shR1 cells formed small, poorly vascularized tumors in nude mice. Silencing of FGFR2 in shR2 cells was associated with strong upregulation of FGFR1 expression and the formation of large, highly vascularized tumors compared to the control tumors. Silencing FGFR3 did not affect cell survival or tumor growth. Overexpressing FGFR2 in control cells did not affect FGFR1 expression, suggesting that high FGFR1 expression in shR2 cells and tumors was associated with FGFR2 silencing by indirect mechanisms. The expression of FGFR1 was, however, increased by the addition of FGF-8 to starved shLacZ or MCF-7 cells and decreased by the FGFR inhibitor PD173074 in shR2 cells with an elevated FGFR1 level. In conclusion, our results demonstrate that FGFR1 is crucial for S115 breast cancer cell proliferation and tumor growth and angiogenesis, whereas FGFR2 and FGFR3 are less critical for the growth of these cells. The results also suggest that the expression of FGFR1 itself is regulated by FGF-8 and FGF signaling, which may be of importance in breast tumors expressing FGFs at a high level.

Co-expression of HER2 and HER3 receptor tyrosine kinases enhances invasion of breast cells via stimulation of interleukin-8 autocrine secretion

Introduction

The tyrosine kinase receptors HER2 and HER3 play an important role in breast cancer. The HER2/HER3 heterodimer is a critical oncogenic unit associated with reduced relapse-free and decreased overall survival. While signaling cascades downstream of HER2 and HER3 have been studied extensively at the level of post-translational modification, little is known about the effects of HER2/HER3 overexpression and activation on gene expression in breast cancer. We have now defined the genetic landscape induced by activation of the HER2/HER3 unit in mammary cells, and have identified interleukin (IL)8 and CXCR1 as potential therapeutic targets for the treatment of HER2/HER3-overexpressing breast cancers.

Methods

Three-dimensional (3D) cultures, invasion and migration assays were used to determine the effects of HER2 and HER3 co-expression and activation. Gene expression analysis was performed to identify the gene network induced by HER2/HER3 in 3D cultures. Bioinformatic analysis and neutralizing antibodies were used to identify key mediators of HER2/HER3-evoked invasion.

Results

Co-expression of the tyrosine kinase receptors HER2 and HER3 induced migration and invasion of MCF10A cells. Microarray analysis of these cells revealed a specific "HER2/HER3 signature" comprising 80 upregulated transcripts, with IL8 being the highest (11-fold upregulation). Notably, examination of public datasets revealed high levels of IL8 transcripts in HER2-enriched as well as basal-like primary breast tumors, two subtypes characterized by a particularly poor prognosis. Moreover, IL8 expression correlated with high tumor grade and ER-negative status. Importantly, treatment with IL8-neutralizing antibodies prevented invasion of MCF10A-HER2/HER3 and BT474 cells in 3D cultures, highlighting the importance of IL8 autocrine signaling upon HER2/HER3 activation.

Conclusions

Our findings demonstrate that HER2 and HER3 co-expression induces IL8 autocrine signaling, leading to the invasion of mammary cells. Agents targeting IL8 or its receptor CXCR1 may be useful for the treatment of HER2/HER3/IL8-positive breast cancers with invasive traits.

Abstract 1479: Targeting breast cancer bone metastases looking at the cross-talk between tumor cells and bone environment

Metastatic dissemination is a major cause of cancer associated death; in breast cancer, bone, lung and brain are the major sites of tumor relapse. Bone marrow (BM) is a reservoir for metastatic breast cancer cells that can enter into a quiescent state and remain latent even for decades after dissemination. By still unknown mechanisms, dormant tumor cells can reacquire proliferative ability, thereby causing osteolytic or osteoblastic lesions. During these processes BM environment and tumor cells strongly influence each other. We aimed to analyze molecular mechanisms involved in the liaison between tumor cells and BM microenvironment. More specifically, we investigated how breast cancer cells can affect BM stoma when they home to the endosteal niche and how bone microenvironment can influence the behavior of tumor cells. We took advantage of the MDA-MB231 SCP1833 subclone, which after intracardiac injection has a high propensity for bone metastases. Tumor cell dissemination was followed by bioluminescence imaging and when BM metastases were detected different cell populations from the bone environment were isolated by cell sorting. We excluded cells of the hematopoietic compartment from the analysis, concentrating on the CD45- population. We used the best available antibodies that define osteoblast (CD45-, TR119-, Sca1-, CD51+), endothelial cells (CD45-, TR119-, Sca1+, CD31+) and mesenchymal progenitors (CD45-, TR119-, CD31-, Sca1+) for sorting in order to compare BM populations from tumor-bearing mice with un-injected control mice by a genome wide-transcriptome study. Microarray analysis revealed that BM is strongly affected by breast cancer cell dissemination. Indeed, several components of key molecular pathways involved in tumor development (including TGFBR, PDGFRB, EGFR, HGFR and IGFR signaling pathways) are modulated in the BM of mice with tumor cells. We are following up this analysis by testing the effects of the PI3K-mTOR inhibitor BEZ-235 in breast cancer bone metastases. PIK3CA, that is a downstream effector of several of the above-mentioned pathways, is up-regulated in the bone stroma of tumor-bearing mice. Besides the effect of BEZ-235 on tumor cells, we want to elucidate how the BM responds to PI3K pathway inhibition, and how this influences survival and proliferation of tumor cells. To investigate the effect of BM environment on disseminated tumor cells, we compared the expression profile of MDA-MB231 SCP1833 from the mammary fad pad, i.e, the primary tumor, with tumor cells isolated from BM. We have uncovered some transcripts for surface proteins whose expression is down-regulated in cancer cells that have homed to the BM, compared to tumor cells growing in the mammary fad pad. These and other results that will be presented show the important role that the environment plays on the tumor cell transcriptome and ultimately on the response to therapy.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 1479. doi:1538-7445.AM2012-1479

MHO1, an evolutionarily conserved gene, is synthetic lethal with PLC1; Mho1p has a role in invasive growth

The novel protein Memo (Mediator of ErbB2 driven cell motility) was identified in a screen for ErbB2 interacting proteins and found to have an essential function in cell motility. Memo is evolutionarily conserved with homologs found in all branches of life; the human and yeast proteins have a similarity of >50%. In the present study we used the model organism S. cerevisiae to characterize the Memo-homologue Mho1 (Yjr008wp) and to investigate its function in yeast. In a synthetic lethal screen we found MHO1 as a novel synthetic lethal partner of PLC1, which encodes the single phospholipase C in yeast. Double-deleted cells lacking MHO1 and PLC1, proliferate for up to ten generations. Introduction of human Memo into the memoΔplc1Δ strain rescued the synthetic lethal phenotype suggesting that yeast and human proteins have similar functions. Mho1 is present in the cytoplasm and the nucleus of yeast cells; the same distribution of Memo was found in mammalian cells. None of the Memo homologues have a characteristic nuclear localization sequence, however, a conserved nuclear export sequence is found in all. In mammalian cells, blocking nuclear export with Leptomycin B led to nuclear Memo accumulation, suggesting that it is actively exported from the nucleus. In yeast MHO1 expression is induced by stress conditions. Since invasive growth in S. cerevisiea is also stress-induced, we tested Mho1's role in this response. MHO1 deletion had no effect on invasion induced by nutrient deprivation, however, Mho1 overexpression blocked the invasive ability of yeast cells, suggesting that Mho1 might be acting in a dominant negative manner. Taken together, our results show that MHO1 is a novel synthetic lethal interactor with PLC1, and that both gene products are required for proliferation. Moreover, a role for Memo in cell motility/invasion appears to be conserved across species.

FGF receptors control vitamin D and phosphate homeostasis by mediating renal FGF-23 signaling and regulating FGF-23 expression in bone

The functional interaction between fibroblast growth factor 23 (FGF-23) and Klotho in the control of vitamin D and phosphate homeostasis is manifested by the largely overlapping phenotypes of Fgf23- and Klotho-deficient mouse models. However, to date, targeted inactivation of FGF receptors (FGFRs) has not provided clear evidence for an analogous function of FGFRs in this process. Here, by means of pharmacologic inhibition of FGFRs, we demonstrate their involvement in renal FGF-23/Klotho signaling and elicit their role in the control of phosphate and vitamin D homeostasis. Specifically, FGFR loss of function counteracts renal FGF-23/Klotho signaling, leading to deregulation of Cyp27b1 and Cyp24a1 and the induction of hypervitaminosis D and hyperphosphatemia. In turn, this initiates a feedback response leading to high serum levels of FGF-23. Further, we show that FGFR inhibition blocks Fgf23 transcription in bone and that this is dominant over vitamin D-induced Fgf23 expression, ultimately impinging on systemic FGF-23 protein levels. Additionally, we identify Fgf23 as a specific target gene of FGF signaling in vitro. Thus, in line with Fgf23- and Klotho-deficient mouse models, our study illustrates the essential function of FGFRs in the regulation of vitamin D and phosphate levels. Further, we reveal FGFR signaling as a novel in vivo control mechanism for Fgf23 expression in bone, suggesting a dual function of FGFRs in the FGF-23/Klotho pathway leading to vitamin D and phosphate homeostasis.

P-Rex1, a guanine exchange factor that is overexpressed in breast cancer, is a convergence node for ErbB and CXCR4 signaling

In a recent issue of Molecular Cell, Kazanietz and colleagues (Sosa et al., 2010) show that P-Rex1, a Rac1 GEF, is overexpressed in ER+ and/or ErbB2+ breast cancers, suggesting that P-Rex1 might be a convergence node downstream of these receptors and an attractive therapeutic target.

Potential for targeting the fibroblast growth factor receptors in breast cancer

Breast cancer is the most common cancer of women, accounting yearly for approximately 30% of newly diagnosed cases and ranking second as a cause of death. Despite improvements in breast cancer detection and development of new therapeutic approaches, there are still tumors for which no targeted therapies are available. This review summarizes recent findings on the fibroblast growth factor receptors (FGFR) and the data supporting their role in breast cancer. We will describe the approaches being made to develop therapeutics targeting these receptors. Finally, to improve the chances for success with FGFR signal transduction inhibitors, strategies to choose appropriate breast cancer patients for treatment will be discussed.

Mammary gland growth factors: roles in normal development and in cancer

Normal development of the mammary gland proceeds via interactions between the epithelium and the mesenchyme that start during embryogenesis and continue during pubertal outgrowth and differentiation. The function of specific peptide growth factors that bind members of the receptor tyrosine kinase family and the cytokine receptor family are required at each stage. In many cases the peptides are produced in one compartment and act on receptors in the other compartment. One of the striking differences between normal development and cancer is the loss of this cross-talk. Mammary tumor cells often produce a peptide and express the receptor on the same cell leading to autocrine activation of signaling pathways, a mechanism that is characteristic for cancer cells. We will discuss different peptides in the context of normal development and cancer in this review.

Targeting fibroblast growth factor receptors blocks PI3K/AKT signaling, induces apoptosis, and impairs mammary tumor outgrowth and metastasis

Members of the fibroblast growth factor receptor (FGFR) family have essential roles in normal physiology and in cancer where they control diverse processes. FGFRs have been associated with breast cancer development. Thus, models to study the role of FGFR in breast cancer and their targeting potential are important. We present an in vitro and in vivo analysis of FGFRs in the breast cancer model cell lines 67NR and 4T1. We show that both tumor cell lines coexpress FGFRs and ligands and display autocrine FGFR signaling activity. Fibroblast growth factor receptor substrate 2 (FRS2), a downstream mediator of FGFR, is constitutively tyrosine phosphorylated and multiple signaling pathways are active. Treatment of 67NR and 4T1 cultures with TKI258, an FGFR tyrosine kinase inhibitor (TKI), caused a rapid decrease in FRS2 phosphorylation; decreased the activity of extracellular signal-regulated kinase 1/2 (ERK1/2), AKT, and phospholipase Cgamma; and blocked proliferation of both tumor lines. Furthermore, TKI258 induced 4T1 apoptotic cell death via blockade of the phosphoinositide 3-kinase/AKT pathway. In vivo, one dose of TKI258 rapidly lowered FRS2 phosphorylation and ERK1/2 and AKT activity in mammary tumors. Long-term TKI258 treatment of 4T1 tumor- and 67NR tumor-bearing mice had a significant effect on primary tumor outgrowth and 4T1 tumor-induced lung metastases. A microarray analysis was carried out to identify targets with roles in TKI258 antitumor activity and potential prognostic markers in human breast tumors. Of interest are the downregulated matrix metalloproteases (MMP), in particular MMP9, which is essential for metastatic spread of 4T1 tumors.

Abstract 3380: The serine protease inhibitor PN-1 induces activation of FGFR-mediated signaling

We are studying the role of PN-1 (Protease Nexin-1) in breast cancer. PN-1 is a serine protease inhibitor (serpin) that blocks a broad spectrum of proteases including among others tPA, uPA and thrombin. Once bound to a target protease, the PN-1/protease complexes bind with high affinity to Low Density Lipoprotein Receptor related Protein (LRP-1). A bioinformatic analysis revealed that PN-1 is overexpressed in a significant proportion of human tumors from different origins. Moreover, PN-1 expression levels correlate with markers of poor prognosis in breast cancer. PN-1 is also expressed in breast tumor cell lines and we recently showed that PN-1 is required by the malignant 4T1 mammary cancer cell line to metastasize to the lungs. Indeed, when mammary fat pads of Balb/c mice were injected with PN-1-knock down (KD)-4T1 cells, primary mammary tumors developed and these grew similarly as control 4T1 cells. However, the PN-1 KD tumors displayed a significant decrease in their potential to form lung metastasis, in comparison to control tumors.

The mechanism by which complexes of serpin/protease mediate their effects in cancer cells is still largely unknown. Thus, our current studies are aimed at deciphering how the protease/PN-1 complex impacts on intracellular signaling in order to promote metastasis. Using the PN-1 negative 168FARN mammary tumor cell line, we have found that PN-1/protease complexes bind LRP-1 receptor and induce MMP-9 expression via Erk1/2 pathway activation. Importantly, the PN-1-driven regulation of MMP-9 expression was also demonstrated to be central to PN-1's prometastatic effect in 4T1 cells.

Here by the use of Western Blot and specific inhibitors, we show that PN-1/protease complex treatment of fibroblast growth factor receptor (FGFR)-expressing tumor cells induces Erk signaling. Furthermore, fibroblast growth factor receptor substrate 2 (FRS2), a lipid anchored docking protein that plays a crucial role in mediating FGFR and tropomyosin receptor kinase (Trk)-induced signaling, was also found to be phosphorylated upon PN-1/protease complex addition. Preincubation of the cells with the FGFR inhibitor, TKI 258, abrogated phosphorylation of FRS2, Erk and Shc upon PN-1/protease complex treatment. In contrast, inhibitors of EGFR or PDGR did not have any effect on PN-1-induced phosphorylation of these proteins. This suggests that the PN-1/protease complex via binding to LRP-1 may transactivate FGFR and potentially other receptors known to activate mitogenic signaling in cancer cells. Our results are in agreement with a recent study showing that other ligands for LRP-1, (e.g, tPA and α2-macroglobulin), could transactivate TrkA receptor. Thus, PN-1 may also transactivate tyrosine kinase receptors. Hence, these results suggest that PN-1/protease complexes might be considered as a new target in cancer therapy.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 3380.

Key signalling nodes in mammary gland development and cancer: Myc

Myc has been intensely studied since its discovery more than 25 years ago. Insight has been gained into Myc's function in normal physiology, where its role appears to be organ specific, and in cancer where many mechanisms contribute to aberrant Myc expression. Numerous signals and pathways converge on Myc, which in turn acts on a continuously growing number of identified targets, via transcriptional and nontranscriptional mechanisms. This review will concentrate on Myc as a signaling mediator in the mammary gland, discussing its regulation and function during normal development, as well as its activation and roles in breast cancer.

Copine-III interacts with ErbB2 and promotes tumor cell migration

ErbB2 amplification and overexpression in breast cancer correlates with aggressive disease and poor prognosis. To find novel ErbB2-interacting proteins, we used stable isotope labeling of amino acids in cell culture followed by peptide affinity pull-downs and identified specific binders using relative quantification by mass spectrometry. Copine-III, a member of a Ca(2+)-dependent phospholipid-binding protein family, was identified as binding to phosphorylated Tyr1248 of ErbB2. In breast cancer cells, Copine-III requires Ca(2+) for binding to the plasma membrane, where it interacts with ErbB2 upon receptor stimulation, an interaction that is dependent on receptor activity. Copine-III also binds receptor of activated C kinase 1 and colocalizes with phosphorylated focal adhesion kinase at the leading edge of migrating cells. Importantly, knockdown of Copine-III in T47D breast cancer cells causes a decrease in Src kinase activation and ErbB2-dependent wound healing. Our data suggest that Copine-III is a novel player in the regulation of ErbB2-dependent cancer cell motility. In primary breast tumors, high CPNE3 RNA levels significantly correlate with ERBB2 amplification. Moreover, in an in situ tissue microarray analysis, we detected differential protein expression of Copine-III in normal versus breast, prostate and ovarian tumors, suggesting a more general role for Copine-III in carcinogenesis.

c-Myc affects mRNA translation, cell proliferation and progenitor cell function in the mammary gland

Background

The oncoprotein c-Myc has been intensely studied in breast cancer and mouse mammary tumor models, but relatively little is known about the normal physiological role of c-Myc in the mammary gland. Here we investigated functions of c-Myc during mouse mammary gland development using a conditional knockout approach.

Results

Generation of c-myc^fl/fl mice carrying the mammary gland-specific WAPiCre transgene resulted in c-Myc loss in alveolar epithelial cells starting in mid-pregnancy. Three major phenotypes were observed in glands of mutant mice. First, c-Myc-deficient alveolar cells had a slower proliferative response at the start of pregnancy, causing a delay but not a block of alveolar development. Second, while milk composition was comparable between wild type and mutant animals, milk production was reduced in mutant glands, leading to slower pup weight-gain. Electron microscopy and polysome fractionation revealed a general decrease in translational efficiency. Furthermore, analysis of mRNA distribution along the polysome gradient demonstrated that this effect was specific for mRNAs whose protein products are involved in milk synthesis. Moreover, quantitative reverse transcription-polymerase chain reaction analysis revealed decreased levels of ribosomal RNAs and ribosomal protein-encoding mRNAs in mutant glands. Third, using the mammary transplantation technique to functionally identify alveolar progenitor cells, we observed that the mutant epithelium has a reduced ability to repopulate the gland when transplanted into NOD/SCID recipients.

Conclusion

We have demonstrated that c-Myc plays multiple roles in the mouse mammary gland during pregnancy and lactation. c-Myc loss delayed, but did not block proliferation and differentiation in pregnancy. During lactation, lower levels of ribosomal RNAs and proteins were present and translation was generally decreased in mutant glands. Finally, the transplantation studies suggest a role for c-Myc in progenitor cell proliferation and/or survival.

See related minireview by Evan et al: