Ets-2 is a ubiquitous transcription factor activated after phosphorylation at threonine-72. Previous studies highlighted the importance of phosphorylated ets-2 in lung inflammation and extracellular matrix remodeling, two pathways involved in pulmonary fibrosis. We hypothesized that phosphorylated ets-2 played an important role in pulmonary fibrosis, and we sought to determine the role of ets-2 in its pathogenesis. We challenged ets-2 (A72/A72) transgenic mice (harboring a mutated form of ets-2 at phosphorylation site threonine-72) and ets-2 (wild-type/wild-type [WT/WT]) control mice with sequential intraperitoneal injections of bleomycin, followed by quantitative measurements of lung fibrosis and inflammation and primary cell in vitro assays. Concentrations of phosphorylated ets-2 were detected via the single and dual immunohistochemical staining of murine lungs and lung sections from patients with idiopathic pulmonary fibrosis. Ets-2 (A72/A72) mice were protected from bleomycin-induced pulmonary fibrosis, compared with ets-2 (WT/WT) mice. This protection was characterized by decreased lung pathological abnormalities and the fibrotic gene expression of Type I collagen, Type III collagen, α–smooth muscle actin, and connective tissue growth factor. Immunohistochemical staining of lung sections from bleomycin-treated ets-2 (WT/WT) mice and from patients with idiopathic pulmonary fibrosis demonstrated increased staining of phosphorylated ets-2 that colocalized with Type I collagen expression and to fibroblastic foci. Lastly, primary lung fibroblasts from ets-2 (A72/A72) mice exhibited decreased expression of Type I collagen in response to stimulation with TGF-β, compared with fibroblasts from ets-2 (WT/WT) mice. These data indicate the importance of phosphorylated ets-2 in the pathogenesis of pulmonary fibrosis through the expression of Type I collagen and (myo)fibroblast activation.

Solid human tumors and their surrounding microenvironment are hypothesized to co-evolve in a manner that promotes tumor growth, invasiveness and spread. Mouse models of cancer have focused on genetic changes in the epithelial tumor cells and therefore have not robustly tested this hypothesis. We have recently developed a murine breast cancer model that ablates the PTEN tumor suppressor pathway in stromal fibroblasts. Remarkably, the model resembles human breast tumors both at morphologic and molecular levels. We propose that such models reflect subtypes of tumor-stromal co-evolution relevant to human breast cancer, and will therefore be useful in defining the mechanisms that underpin tumor-stroma crosstalk. Additionally, these models should also aid in molecularly classifying human breast tumors based on both the microenvironment subtypes they contain as well as on the tumor subtype.

Bronchopulmonary dysplasia is a common pulmonary complication of extreme prematurity. Arrested lung development leads to bronchopulmonary dysplasia, but the molecular pathways that cause this arrest are unclear. Lung injury and inflammation increase disease risk, but the cellular site of the inflammatory response and the potential role of localized inflammatory signaling in inhibiting lung morphogenesis are not known. Here we show that tissue macrophages present in the fetal mouse lung mediate the inflammatory response to lipopolysaccharide and that macrophage activation inhibits airway morphogenesis. Macrophage depletion or targeted inactivation of the NF-κB signaling pathway protected airway branching in cultured lung explants from the effects of lipopolysaccharide. Macrophages also appear to be the primary cellular site of IL-1β production following lipopolysaccharide exposure. Conversely, targeted NF-κB activation in transgenic macrophages was sufficient to inhibit airway morphogenesis. Macrophage activation in vivo inhibited expression of multiple genes critical for normal lung development, leading to thickened lung interstitium, reduced airway branching, and perinatal death. We propose that fetal lung macrophage activation contributes to bronchopulmonary dysplasia by generating a localized inflammatory response that disrupts developmental signals critical for lung formation.

The NF-κB signaling pathway regulates cellular growth, survival, differentiation and development. In this study, the functions of IκB kinase (IKK)β in angiogenesis during mouse development were examined. Conditional disruption of the Ikkβ locus in endothelial cells using the well-characterized Tie2-Cre transgene resulted in embryonic lethality between E13.5-15.5. Examination of the mutant embryos revealed that while deletion of Ikkβ occurred in endothelial cells throughout the embryo, only the vascular network in the fetal liver was affected. Disruption of the fetal liver vasculature was accompanied by decreased cell proliferation and increased apoptosis of hepatocytes, but hematopoiesis was not affected. Increased apoptosis was not observed outside of fetal liver in the mutant embryos. These results indicate that the IKKβ/NF-κB pathway plays a previously unappreciated role in development of the sinusoidal vasculature in the fetal liver and additionally that this pathway is critical in the crosstalk between endothelial cells and hepatocytes during mouse development.

In this study, we describe the use of intravital microscopy in a transgenic mouse model expressing yellow fluorescent protein (YFP) under the control of a monocyte specific promoter c-fms (CD115) to track and quantify specific leukocyte subsets. Flow cytometry on peripheral and bone marrow leukocytes revealed that YFP was predominantly expressed by CD11a+, CD11b+, and CD14+ monocytes. In the bone marrow, 67±4% of Ly6Chigh F4/80+ cells were YFPhigh while 55±1% of Ly6Clow F4/80+ cells were YFPlow supporting the use of c-fmsYFP expression as a marker of monocyte lineage. 70±7% of CD11b+ F4/80+ Ly6C+ (“triple positive”) cells expressed YFP. To assess leukocyte–endothelial interactions in YFP+ cells in c-fmsYFP+ mice, we evaluated leukocyte adhesion, rolling and local shear stress responses in the cremasteric endothelium 4 h following administration of TNFα. TNFα resulted in a five-fold increase in adhesion of YFP+ cells to the endothelium and provided superior discriminative ability in assessing rolling and adhesion events when compared with bright field microscopy. Additionally, when compared with Rhodamine-6G labeled leukocytes or GFP+ cells in mice transplanted with green fluorescent protein (GFP) positive bone marrow, the level of detail observed in the c-fmsYFP+ was greater, with both GFP+ and YFP+ cells demonstrating superior signal to noise compared to bright field microscopy. A weak positive linear correlation between wall shear stress and YFP+ cell adhesion (r2=0.20, p<0.05) was seen in the cremasteric microcirculation. Taken together, these data demonstrate the use of c-fmsYFP+ mice in identifying distinct monocyte subsets and highlight the potential of this model for real-time monocyte–endothelial interactions using intravital microscopy.

Introduction

Metastasis from primary tumor to the lungs is a major cause of the mortality associated with breast cancer. Both immune and inflammatory responses impact whether circulating mammary tumor cells successfully colonize the lungs leading to established metastases. Nuclear factor -kappaB (NF-κB) transcription factors regulate both immune and inflammatory responses mediated in part by the activities of macrophages. Therefore, NF-κB activity specifically within macrophages may be a critical determinant of whether circulating tumor cells successfully colonize the lungs.

Methods

To investigate NF-κB signaling within macrophages during metastasis, we developed novel inducible transgenic models which target expression of the reverse tetracycline transactivator (rtTA) to macrophages using the cfms promoter in combination with inducible transgenics that express either an activator (cIKK2) or an inhibitor (IκBα-DN). Doxycyline treatment led to activation or inhibition of NF-κB within macrophages. We used a tail vein metastasis model with mammary tumor cell lines established from MMTV-Polyoma Middle T-Antigen-derived tumors to investigate the effects of modulating NF-κB in macrophages during different temporal windows of the metastatic process.

Results

We found that activation of NF-κB in macrophages during seeding leads to a reduction in lung metastases. The mechanism involved expression of inflammatory cytokines and reactive oxygen species, leading to apoptosis of tumor cells and preventing seeding in the lung. Activation of NF-κB within macrophages after the seeding phase has no significant impact on establishment of metastases.

Conclusions

Our results have identified a brief, defined window in which activation of NF-κB has significant anti-metastatic effects and inhibition of NF-κB results in a worse outcome.

Summary

To sustain tumor growth, cancer cells must be able to adapt to fluctuations in energy availability. We have identified a single microRNA that controls glioma cell proliferation, migration, and responsiveness to glucose deprivation. Abundant glucose allows relatively high miR-451 expression, promoting cell growth. In low glucose, miR-451 levels decrease, slowing proliferation but enhancing migration and survival. This allows cells to survive metabolic stress and seek out favorable growth conditions. In glioblastoma patients, elevated miR-451 is associated with shorter survival. The effects of miR-451 are mediated by LKB1, which it represses through targeting its binding partner, CAB39 (MO25α). Overexpression of miR-451 sensitized cells to glucose deprivation, suggesting that its downregulation is necessary for robust activation of LKB1 in response to metabolic stress. Thus, miR-451 is a regulator of the LKB1/AMPK pathway, and this may represent a fundamental mechanism that contributes to cellular adaptation in response to altered energy availability.

Tumor associated macrophages (TAMs) are implicated in breast cancer progression and metastasis, but relatively little is known about the genes pathways in these cells that contribute to malignant phenotypes. The transcription factor Ets2 is a direct target of signaling pathways involved in regulating macrophage functions during inflammation. To test whether Ets2 in TAMs modulated mouse mammary tumor growth and metastasis a genetic approach was used to conditionally delete Ets2 in TAMs. Ets2 deletion in TAMs decreased the frequency and size of mammary tumor metastases to lung in three different metastatic models. Expression profiling and chromatin immunoprecipitation assays with isolated TAMs established that Ets2 repressed several well characterized inhibitors of angiogenesis. Consistent with these results, Ets2 ablation in TAMs led to decreased tumor angiogenesis and growth. An Ets2-TAM expression signature was identified within human breast cancer expression data and this signature could retrospectively predict overall survival of breast cancer patients in two independent sets of human breast cancer microarray data. In summary, we have identified Ets2 as a critical factor that acts to enhance mammary tumor growth and metastasis by regulating a transcriptional program in TAMs.

Regulatory T cells (Treg) are critical to the maintenance of immunological self-tolerance and immune homeostasis by suppressing aberrant or excessive immune responses. Treg specifically express the transcription factor Foxp3, which mediates the coordinate activation of genes such as CTLA-4 and GITR along with repression of T effector cytokines such as interleukin-2 and interferon-γ. Despite progress in understanding mechanisms of Foxp3-dependent gene activation, the molecular mechanism of Foxp3-dependent gene repression remains largely unknown. Herein we report the identification of Eos, a zinc-finger transcription factor of the Ikaros family, as a critical mediator of Foxp3-dependent gene silencing in Treg. Eos interacts directly with Foxp3 and is necessary for gene silencing without affecting expression of Foxp3 activated genes. We further demonstrate that Eos and its corepressor C-terminal binding protein 1 (CtBP1) are necessary for histone modifications and ultimately promoter methylation involved in selective gene silencing in Treg. Knockdown of Eos in Treg abrogates their ability to suppress immune responses in vitro and in vivo and endows them with partial effector function. This transcriptional control of Treg function through association between Foxp3 and Eos/co-repressor can potentially be exploited for immune-based therapies.

The three basic DNA-binding domain mutations of the microphthalmia associated transcription factor (Mitf), Mitfmi/mi, Mitfor/or and Mitfwh/wh, affect osteoclast differentiation with variable penetrance while completely impairing melanocyte development. Mitfor/or mice exhibit osteopetrosis that improves with age and their osteoclasts form functional multinuclear osteoclasts, raising the question as to why the Mitfor/or mutation results in osteopetrosis. Here we show that Mitfor/or osteoclasts express normal levels of acid phosphatase 5 (Acp5) mRNA and significantly lower levels of Cathepsin K (Ctsk) mRNA during receptor activator of nuclear factor kappa B (NFκB) ligand (RANKL)-mediated differentiation. Studies using chromatin immunoprecipitation (ChIP) analysis indicate that low levels of Mitfor/or protein are recruited to the Ctsk promoter. However, enrichment of Mitf-transcriptional co-activators PU.1 and Brahma-related gene 1 (Brg1) are severely impaired at the Ctsk promoter of Mitfor/or osteoclast precursors, indicating that defective recruitment of co-activators by the mutant Mitfor/or results in impaired Ctsk expression in osteoclasts. Cathepsin K may thus represent a unique class of Mitf regulated osteoclast-specific genes that are important for osteoclast function.

The interplay between histone modifications and promoter hypermethylation provides a causative explanation for epigenetic gene silencing in cancer. Less is known about the upstream initiators that direct this process. Here, we report that the Cystatin M (CST6) tumor suppressor gene is concurrently down-regulated with other loci in breast epithelial cells co-cultured with cancer-associated fibroblasts (CAFs). Promoter hypermethylation of CST6 is associated with aberrant AKT1 activation in epithelial cells, as well as the disabled INNP4B regulator resulted from the suppression by CAFs. Repressive chromatin, marked by trimethyl-H3K27 and dimethyl-H3K9, and de novo DNA methylation is established at the promoter. The findings suggest that microenvironmental stimuli are triggers in this epigenetic cascade, leading to the long-term silencing of CST6 in breast tumors. Our present findings implicate a causal mechanism defining how tumor stromal fibroblasts support neoplastic progression by manipulating the epigenome of mammary epithelial cells. The result also highlights the importance of direct cell-cell contract between epithelial cells and the surrounding fibroblasts that confer this epigenetic perturbation. Since this two-way interaction is anticipated, the described co-culture system can be used to determine the effect of epithelial factors on fibroblasts in future studies.

The molecular events linking lipid accumulation in atherosclerotic plaques to complications such as aneurysm formation and plaque disruption are poorly understood. Balb-Apoe−/− mice bearing a null mutation in the Npc1 gene display prominent medial erosion and athero-thrombosis, while their macrophages accumulate free cholesterol in late endosomes and show increased cathepsin K (Ctsk) expression. We now show increased cathespin K immunostaining and increased SH-proteinase activity using near infrared fluorescence imaging over proximal aortas of Apoe−/−, Npc1−/− mice. In mechanistic studies, cholesterol loading of macrophage plasma membranes (cyclodextrin-cholesterol) or endosomal system (AcLDL+U18666A or Npc1 null mutation) activated Toll-like receptor signaling, leading to sustained phosphorylation of p38 MAP kinase, and induction of p38 targets, including Ctsk, S100a8, Mmp8, and Mmp14. Studies in macrophages from knock-out mice showed major roles for TLR4, following plasma membrane cholesterol loading, and for TLR3, after late endosomal loading. TLR signaling via p38 led to phosphorylation and activation of the transcription factor MITF, acting at E-box elements in the Ctsk promoter. These studies suggest that free cholesterol enrichment of either plasma or endosomal membranes in macrophages leads to activation of signaling via various TLRs, prolonged p38 MAP kinase activation and induction of Mmps, Ctsk, and S100a8, potentially contributing to plaque complications.

Macrophages are important effectors in the clearance of antibody-coated tumor cells. However, the signaling pathways that regulate macrophage-induced ADCC are poorly defined. To understand the regulation of macrophage-mediated ADCC, we used human B cell lymphoma coated with Rituximab as the tumor target and murine macrophages primed with IFNγ as the effectors. Our data demonstrate that the PtdIns 3-kinase/Akt pathway is activated during macrophage-induced ADCC and that the inhibition of PtdIns 3-kinase results in the inhibition of macrophage-mediated cytotoxicity. Interestingly, downstream of PtdIns 3-kinase, expression of constitutively active Akt (Myr-Akt) in macrophages significantly enhanced their ability to mediate ADCC. Further analysis revealed that in this model, macrophage-mediated ADCC is dependent upon the release of nitric oxide (NO). However, the PtdIns 3-kinase/Akt pathway does not appear to regulate NO production. An examination of the role of the PtdIns 3-kinase/Akt pathway in regulating conjugate formation indicated that macrophages treated with an inhibitor of PtdIns 3-kinase fail to polarize the cytoskeleton at the synapse and show a significant reduction in the number of conjugates formed with tumor targets. Further, inhibition of PtdIns 3-kinase also reduced macrophage spreading on Rituximab-coated surfaces. On the other hand, Myr-Akt expressing macrophages displayed a significantly greater ability to form conjugates with tumor cells. Taken together, these findings illustrate that the PtdIns 3-kinase/Akt pathway plays a critical role in macrophage ADCC through its influence on conjugate formation between macrophages and antibody-coated tumor cells.

Osteoporosis results from an imbalance in skeletal remodeling that favors bone resorption over bone formation. Bone matrix is degraded by osteoclasts, which differentiate from myeloid precursors in response to the cytokine RANKL. To gain insight into the transcriptional regulation of bone resorption during growth and disease, we generated a conditional knockout of the transcription factor nuclear factor of activated T cells c1 (Nfatc1). Deletion of Nfatc1 in young mice resulted in osteopetrosis and inhibition of osteoclastogenesis in vivo and in vitro. Transcriptional profiling revealed NFATc1 as a master regulator of the osteoclast transcriptome, promoting the expression of numerous genes needed for bone resorption. In addition, NFATc1 directly repressed osteoclast progenitor expression of osteoprotegerin, a decoy receptor for RANKL previously thought to be an osteoblast-derived inhibitor of bone resorption. “Cherubism mice”, which carry a gain-of-function mutation in SH3-domain binding protein 2 (Sh3bp2), develop osteoporosis and widespread inflammation dependent on the proinflammatory cytokine, TNF-α. Interestingly, deletion of Nfatc1 protected cherubism mice from systemic bone loss but did not inhibit inflammation. Taken together, our study demonstrates that NFATc1 is required for remodeling of the growing and adult skeleton and suggests that NFATc1 may be an effective therapeutic target for osteoporosis associated with inflammatory states.

Transcription factors MITF and PU.1 collaborate to increase expression of target genes like cathepsin K (Ctsk) and acid phosphatase 5 (Acp5) during osteoclast differentiation. We show that these factors can also repress transcription of target genes in committed myeloid precursors capable of forming either macrophages or osteoclasts. The direct interaction of MITF and PU.1 with the zinc finger protein Eos, an Ikaros family member, was necessary for repression of Ctsk and Acp5. Eos formed a complex with MITF and PU.1 at target gene promoters and suppressed transcription through recruitment of corepressors CtBP (C-terminal binding protein) and Sin3A, but during osteoclast differentiation, Eos association with Ctsk and Acp5 promoters was significantly decreased. Subsequently, MITF and PU.1 recruited coactivators to these target genes, resulting in robust expression of target genes. Overexpression of Eos in bone marrow-derived precursors disrupted osteoclast differentiation and selectively repressed transcription of MITF/PU.1 targets, while small interfering RNA knockdown of Eos resulted in increased basal expression of Ctsk and Acp5. This work provides a mechanism to account for the modulation of MITF and PU.1 activity in committed myeloid progenitors prior to the initiation of osteoclast differentiation in response to the appropriate extracellular signals.

The microphthalmia-associated transcription factor (MITF) is required for terminal osteoclast differentiation and is a target for signaling pathways engaged by colony stimulating factor (CSF)-1 and receptor-activator of nuclear factor-κB ligand (RANKL). Work presented here demonstrates that MITF can shuttle from cytoplasm to nucleus dependent upon RANKL/CSF-1 action. 14-3-3 was identified as a binding partner of MITF in osteoclast precursors, and overexpression of 14-3-3 in a transgenic model resulted in increased cytosolic localization of MITF and decreased expression of MITF target genes. MITF/14-3-3 interaction was phosphorylation dependent, and Ser173 residue, within the minimal interaction region of amino acid residues 141–191, was required. The Cdc25C-associated kinase (C-TAK)1 interacted with an overlapping region of MITF. C-TAK1 increased MITF/14-3-3 complex formation and thus promoted cytoplasmic localization of MITF. C-TAK1 interaction was disrupted by RANKL/CSF-1 treatment. The results indicate that 14-3-3 regulates MITF activity by promoting the cytosolic localization of MITF in the absence of signals required for osteoclast differentiation. This work identifies a mechanism that regulates MITF activity in monocytic precursors that are capable of undergoing different terminal differentiation programs, and it provides a mechanism that allows committed precursors to rapidly respond to signals in the bone microenvironment to promote specifically osteoclast differentiation.

The transcription factor ets-2 was phosphorylated at residue threonine 72 in a colony-stimulating factor 1 (CSF-1)- and mitogen-activated protein kinase-independent manner in macrophages isolated from motheaten-viable (me-v) mice. The CSF-1 and ets-2 target genes coding for Bcl-x, urokinase plasminogen activator, and scavenger receptor were also expressed at high levels independent of CSF-1 addition to me-v cells. Akt (protein kinase B) was constitutively active in me-v macrophages, and an Akt immunoprecipitate catalyzed phosphorylation of ets-2 at threonine 72. The p54 isoform of c-jun N-terminal kinase–stress-activated kinase (JNK- SAPK) coimmunoprecipitated with Akt from me-v macrophages, and treatment of me-v cells with the specific phosphatidylinositol 3-kinase inhibitor LY294002 decreased cell survival, Akt and JNK kinase activities, ets-2 phosphorylation, and Bcl-x mRNA expression. Therefore, ets-2 is a target for phosphatidylinositol 3-kinase–Akt–JNK action, and the JNK p54 isoform is an ets-2 kinase in macrophages. Constitutive ets-2 activity may contribute to the pathology of me-v mice by increasing expression of genes like the Bcl-x gene that promote macrophage survival.

An antibody that specifically recognized phosphothreonine 72 in ets-2 was used to determine the phosphorylation status of endogenous ets-2 in response to colony-stimulating factor 1 (CSF-1)/c-fms signaling. Phosphorylation of ets-2 was detected in primary macrophages, cells that normally express c-fms, and in fibroblasts engineered to express human c-fms. In the former cells, ets-2 was a CSF-1 immediate-early response gene, and phosphorylated ets-2 was detected after 2 to 4 h, coincident with expression of ets-2 protein. In fibroblasts, ets-2 was constitutively expressed and rapidly became phosphorylated in response to CSF-1. In both cell systems, ets-2 phosphorylation was persistent, with maximal phosphorylation detected 8 to 24 h after CSF-1 stimulation, and was correlated with activation of the CSF-1 target urokinase plasminogen activator (uPA) gene. Kinase assays that used recombinant ets-2 protein as a substrate demonstrated that mitogen-activated protein (MAP) kinases p42 and p44 were constitutively activated in both cell types in response to CSF-1. Immune depletion experiments and the use of the MAP kinase kinase inhibitor PD98059 indicate that these two MAP kinases are the major ets-2 kinases activated in response to CSF-1/c-fms signaling. In the macrophage cell line RAW264, conditional expression of raf kinase induced ets-2 expression and phosphorylation, as well as uPA mRNA expression. Transient assays mapped ets/AP-1 response elements as critical for basal and CSF-1-stimulated uPA reporter gene activity. These results indicate that persistent activation of the raf/MAP kinase pathway by CSF-1 is necessary for both ets-2 expression and posttranslational activation in macrophages.

Translational research projects target a wide variety of diseases, test many different kinds of biomedical hypotheses, and employ a large assortment of experimental methodologies. Diverse data, complex execution environments, and demanding security and reliability requirements make the implementation of these projects extremely challenging and require novel e-Science technologies.

Background

Classical NF-κB signaling functions as a negative regulator of skeletal myogenesis through potentially multiple mechanisms. The inhibitory actions of TNFα on skeletal muscle differentiation are mediated in part through sustained NF-κB activity. In dystrophic muscles, NF-κB activity is compartmentalized to myofibers to inhibit regeneration by limiting the number of myogenic progenitor cells. This regulation coincides with elevated levels of muscle derived TNFα that is also under IKKβ and NF-κB control.

Methodology/Principal Findings

Based on these findings we speculated that in DMD, TNFα secreted from myotubes inhibits regeneration by directly acting on satellite cells. Analysis of several satellite cell regulators revealed that TNFα is capable of inhibiting Notch-1 in satellite cells and C2C12 myoblasts, which was also found to be dependent on NF-κB. Notch-1 inhibition occurred at the mRNA level suggesting a transcriptional repression mechanism. Unlike its classical mode of action, TNFα stimulated the recruitment of Ezh2 and Dnmt-3b to coordinate histone and DNA methylation, respectively. Dnmt-3b recruitment was dependent on Ezh2.

Conclusions/Significance

We propose that in dystrophic muscles, elevated levels of TNFα and NF-κB inhibit the regenerative potential of satellite cells via epigenetic silencing of the Notch-1 gene.

SUMMARY

The tumor stroma is believed to contribute to some of the most malignant characteristics of epithelial tumors. However, signaling between stromal and tumor cells is complex and remains poorly understood. Here we show that the genetic inactivation of Pten in stromal fibroblasts of mouse mammary glands accelerated the initiation, progression and malignant transformation of mammary epithelial tumors. This was associated with the massive remodeling of the extra-cellular matrix (ECM), innate immune cell infiltration and increased angiogenesis. Loss of Pten in stromal fibroblasts led to increased expression, phosphorylation (T72) and recruitment of Ets2 to target promoters known to be involved in these processes. Remarkably, Ets2 inactivation in Pten stroma-deleted tumors ameliorated disruption of the tumor microenvironment and was sufficient to decrease tumor growth and progression. Global gene expression profiling of mammary stromal cells identified a Pten-specific signature that was highly represented in the tumor stroma of breast cancer patients. These findings identify the Pten-Ets2 axis as a critical stroma-specific signaling pathway that suppresses mammary epithelial tumors.

Angiogenesis is a complex process orchestrated by both growth factors and cell adhesion and is initiated by focal degradation of the vascular basement membrane with subsequent migration and proliferation of endothelial cells. The Ras/Raf/MEK/ERK pathway is required for EC function during angiogenesis. Although in vitro studies implicate ERK1 and ERK2 in endothelial cell survival, their precise role in angiogenesis in vivo remains poorly defined. Cre/loxP technology was used to inactivate Erk1 and Erk2 in endothelial cells during murine development, resulting in embryonic lethality due to severely reduced angiogenesis. Deletion of Erk1 and Erk2 in primary endothelial cells resulted in decreased cell proliferation and migration, but not in increased apoptosis. Expression of key cell cycle regulators was diminished in the double knockout cells, and decreased DNA synthesis could be observed in endothelial cells during embryogenesis. Interestingly, both Paxillin and Focal Adhesion Kinase were expressed at lower levels in endothelial cells lacking Erk1 and Erk2 both in vivo and in vitro, leading to defects in the organization of the cytoskeleton and in cell motility. The regulation of Paxillin and Focal Adhesion Kinase expression occurred post-transcriptionally. These results demonstrate that ERK1 and ERK2 coordinate endothelial cell proliferation and migration during angiogenesis.