The molecular basis for breast cancer metastasis to the brain is largely unknown 1,2 . Brain relapse typically occurs years after the removal of a breast tumour [2][3][4] , suggesting that disseminated cancer cells must acquire specialized functions to overtake this organ. Here we show that breast cancer metastasis to the brain involves mediators of extravasation through non-fenestrated capillaries, complemented by specific enhancers of blood-brain barrier crossing and brain colonization. We isolated cells that preferentially infiltrate the brain from patients with advanced disease. Gene expression analysis of these cells and of clinical samples, coupled with functional analysis, identified the cyclooxygenase COX2 (also known as PTGS2), the epidermal growth factor receptor (EGFR) ligand HBEGF, and the α2,6-sialyltransferase ST6GALNAC5 as mediators of cancer cell passage through the blood-brain barrier. EGFR ligands and COX2 were previously linked to breast cancer infiltration of the lungs, but not the bones or liver 5,6 , suggesting a sharing of these mediators in cerebral and pulmonary metastases. In contrast, ST6GALNAC5 specifically mediates brain metastasis. Normally restricted to the brain 7 , the expression of ST6GALNAC5 in breast cancer cells enhances their adhesion to brain endothelial cells and their passage through the blood-brain barrier. This co-option of a brain sialyltransferase highlights the role of cell-surface glycosylation in organspecific metastatic interactions.Brain metastasis affects an estimated 10% of cancer patients with disseminated disease 2,8,9 . Even small lesions can cause neurological disability, and the median survival time of patientsCorrespondence and requests for materials should be addressed to J.M. (E-mail: j-massague@ski.mskcc.org). † Present addresses: Institut de Malalties Hemato-Oncològiques, Hospital Clínic, 08036 Barcelona, Spain (C.N.); Oncology Programme, Institute for Research in Biomedicine, 08028 Barcelona, Spain (R.R.G.). Author InformationThe clinical microarray data on the brain metastatic cell lines have been deposited in NCBI's Gene Expression Omnibus (GEO, http://www.ncbi.nlm.nih.gov/geo) under the GEO series accession number GSE12237.Supplementary Information is linked to the online version of the paper at www.nature.com/nature. Full Methods and any associated references are available in the online version of the paper at www.nature.com/nature. 11 and also by tight junctions and astrocyte foot processes in the blood-brain barrier (BBB) 2,8 , whereas the capillaries in the bone marrow and the liver are fenestrated 11,12 . The composition of the parenchyma also varies extensively between these organs. The protracted progression of disseminated cancer cells in different environments may give rise to metastatic speciation, as suggested by the coexistence of malignant cells with different organ tropisms in fluids from patients with advanced disease 5,13 . Analysis of such malignant cell populations has revealed genes that selectively mediate breast cance...

Summary The dissemination of cancer cells from a primary tumor is conventionally viewed as a unidirectional process that culminates with the metastatic colonization of distant organs. Here we show that circulating tumor cells (CTCs) can also colonize their tumors of origin, in a process that we call “tumor self-seeding”. Self-seeding of breast cancer, colon cancer, and melanoma tumors in mice is preferentially mediated by aggressive CTCs, including those with bone, lung or brain metastatic tropism. The tumor-derived cytokines IL-6 and IL-8 acted as CTC attractants and the poor-prognosis markers MMP1/collagenase-1 and the actin cytoskeleton component fascin-1 as mediators of CTC infiltration into mammary tumors. Self-seeding can accelerate tumor growth, angiogenesis, and stromal recruitment through seed-derived factors including, in a breast cancer model, the chemokine CXCL1. Tumor self-seeding could explain the relationships between anaplasia, tumor size, vascularity and prognosis, and local recurrence seeded by disseminated cells following ostensibly complete tumor excision.

Cells released from primary tumors seed metastases to specific organs by a nonrandom process, implying the involvement of biologically selective mechanisms. Based on clinical, functional, and molecular evidence, we show that the cytokine TGFbeta in the breast tumor microenvironment primes cancer cells for metastasis to the lungs. Central to this process is the induction of angiopoietin-like 4 (ANGPTL4) by TGFbeta via the Smad signaling pathway. TGFbeta induction of Angptl4 in cancer cells that are about to enter the circulation enhances their subsequent retention in the lungs, but not in the bone. Tumor cell-derived Angptl4 disrupts vascular endothelial cell-cell junctions, increases the permeability of lung capillaries, and facilitates the trans-endothelial passage of tumor cells. These results suggest a mechanism for metastasis whereby a cytokine in the primary tumor microenvironment induces the expression of another cytokine in departing tumor cells, empowering these cells to disrupt lung capillary walls and seed pulmonary metastases.

SUMMARY A large proportion of colorectal cancers (CRCs) display mutational inactivation of the TGF-beta pathway yet paradoxically, they are characterized by elevated TGF-beta production. Here, we unveil a prometastatic programme induced by TGF-beta in the microenvironment that associates with a high-risk of CRC relapse upon treatment. The activity of TGF-beta on stromal cells increases the efficiency of organ colonization by CRC cells whereas mice treated with a pharmacological inhibitor of TGFBR1 are resilient to metastasis formation. Secretion of IL11 by TGF-beta-stimulated cancer-associated fibroblasts (CAFs) triggers GP130/STAT3 signalling in tumour cells. This crosstalk confers a survival advantage to metastatic cells. The dependency on the TGF-beta stromal programme for metastasis initiation could be exploited to improve the diagnosis and treatment of CRC.

Brain metastasis is an ominous complication of cancer, yet most cancer cells that infiltrate the brain die of unknown causes. Here we identify plasmin from the reactive brain stroma as a defense against metastatic invasion, and plasminogen activator (PA) inhibitory serpins in cancer cells as a shield against this defense. Plasmin suppresses brain metastasis in two ways: by converting membrane-bound astrocytic FasL into a paracrine death signal for cancer cells, and by inactivating the axon pathfinding molecule L1CAM that metastatic cells express for spreading along brain capillaries and for metastatic outgrowth. Brain metastatic cells from lung cancer and breast cancer express high levels of anti-PA serpins, including neuroserpin and serpin B2, to prevent plasmin generation and its deleterious consequences. By protecting cancer cells from death signals and fostering vascular cooption, anti-PA serpins provide a unifying mechanism for the initiation of brain metastasis in lung and breast cancers.

We report that breast cancer cells that infiltrate the lungs support their own metastasis-initiating ability by expressing tenascin C (TNC). We find that the expression of TNC, an extracellular matrix protein of stem cell niches, is associated with the aggressiveness of pulmonary metastasis. Cancer cell–derived TNC promotes the survival and outgrowth of pulmonary micrometastases. TNC enhances the expression of stem cell signaling components, musashi homolog 1 (MSI1) and leucine-rich repeat–containing G protein– coupled receptor 5 (LGR5). MSI1 is a positive regulator of NOTCH signaling, whereas LGR5 is a target gene of the WNT pathway. TNC modulation of stem cell signaling occurs without affecting the expression of transcriptional enforcers of the stem cell phenotype and pluripotency, namely nanog homeobox (NANOG), POU class 5 homeobox 1 (POU5F1), also known as OCT4, and SRY-box 2 (SOX2). TNC protects MSI1-dependent NOTCH signaling from inhibition by signal transducer and activator of transcription 5 (STAT5), and selectively enhances the expression of LGR5 as a WNT target gene. Cancer cell– derived TNC remains essential for metastasis outgrowth until the tumor stroma takes over as a source of TNC. These findings link TNC to pathways that support the fitness of metastasis-initiating breast cancer cells and highlight the relevance of TNC as an extracellular matrix component of the metastatic niche.

Recent studies by our group and others demonstrated a required and conserved role of Stim in store-operated Ca 2؉ influx and Ca 2؉ release-activated Ca 2؉ (CRAC) channel activity. By using an unbiased genome-wide RNA interference screen in Drosophila S2 cells, we now identify 75 hits that strongly inhibited Ca 2؉ influx upon store emptying by thapsigargin. Among these hits are 11 predicted transmembrane proteins, including Stim, and one, olf186-F, that upon RNA interference-mediated knockdown exhibited a profound reduction of thapsigargin-evoked Ca 2؉ entry and CRAC current, and upon overexpression a 3-fold augmentation of CRAC current. CRAC currents were further increased to 8-fold higher than control and developed more rapidly when olf186-F was cotransfected with Stim. olf186-F is a member of a highly conserved family of four-transmembrane spanning proteins with homologs from Caenorhabditis elegans to human. The endoplasmic reticulum (ER) Ca 2؉ pump sarco-͞ER calcium ATPase (SERCA) and the single transmembrane-soluble N-ethylmaleimide-sensitive (NSF) attachment receptor (SNARE) protein Syntaxin5 also were required for CRAC channel activity, consistent with a signaling pathway in which Stim senses Ca 2؉ depletion within the ER, translocates to the plasma membrane, and interacts with olf186-F to trigger CRAC channel activity.capacitative calcium entry (CCE) ͉ genome-wide screen ͉ CRAC channel ͉ RNA interference ͉ store-operated calcium (SOC) influx P atch-clamp experiments have identified the biophysical characteristics of Ca 2ϩ release-activated Ca 2ϩ (CRAC) channels in lymphocytes and other human cell types (1, 2). Despite the acknowledged functional importance of storeoperated Ca 2ϩ (SOC) influx in cell biology (2) and of CRAC channels for immune cell activation (3), the intrinsic channel components and signaling pathways that lead to channel activation remain unidentified. In previous work (4), we demonstrated that SOC influx in S2 cells occurs through a channel that shares biophysical properties with CRAC channels in human T lymphocytes. In a medium-throughput RNA interference (RNAi) screen targeting 170 candidate genes in S2 cells, we discovered an essential conserved role of Stim and the mammalian homolog STIM1 in SOC influx and CRAC channel activity (5). STIM1 and STIM2 also were identified in an independently performed screen of HeLa cells by using the Drosophila enzyme Dicer to generate small interfering RNA species from dsRNA (6). Drosophila Stim and the mammalian homolog STIM1 appear to play dual roles in the CRAC channel activation sequence, sensing the luminal Ca 2ϩ store content through an EF hand motif and trafficking from an endoplasmic reticulum (ER)-like localization to the plasma membrane to trigger CRAC channel activity (6-8). However, as single-pass transmembrane proteins, Stim and its mammalian homolog STIM1 are unlikely to form the CRAC channel itself. To search systematically for additional components of the CRAC channel, and to analyze the signaling network and other required factors th...

Metastasis may arise years after removal of a primary tumor. The mechanisms allowing latent disseminated cancer cells to survive are unknown. We report that a gene-expression signature of c-Src activation is associated with late-onset bone metastasis in breast cancer. This link is independent of hormone receptor status or breast cancer subtype. In breast cancer cells, c-Src is dispensable for homing to the bones or lungs critical for the survival and outgrowth of these cells in the bone marrow. c-Src mediates AKT regulation and cancer cell survival responses to CXCL12 and TRAIL, factors which are distinctively expressed in the bone metastasis microenvironment. Breast cancer cells that lodge in the bone marrow succumb in this environment when deprived of c-Src activity.