Although the role of miR-200s in regulating E-cadherin expression and epithelial-mesenchymal transition is well established, their influence on metastatic colonization remains controversial. Here, we use clinical and experimental models of breast cancer metastasis to discover a pro-metastatic role of miR-200s that goes beyond their regulation of E-cadherin and epithelial phenotype. Overexpression of miR-200s is associated with increased risk of metastasis in breast cancer and promotes metastatic colonization in mouse models, phenotypes that cannot be recapitulated by E-cadherin expression alone. Genomic and proteomic analyses revealed global shifts in gene expression upon miR-200 overexpression toward that of highly metastatic cells. MiR-200s promote metastatic colonization partly through direct targeting of Sec23a, which mediates secretion of metastasis suppressive proteins, including Igfbp4 and Tinagl1, as validated by functional and clinical correlation studies. Overall, these findings suggest a pleiotropic role of miR-200s in promoting metastatic colonization by influencing E-cadherin-dependent epithelial traits and Sec23a-mediated tumor cell secretome.

The tumour stroma is an active participant during cancer progression. Stromal cells promote tumour progression and metastasis through multiple mechanisms including enhancing tumour invasiveness and angiogenesis, and suppressing immune surveillance. We report here that miR-126/miR-126*, a microRNA pair derived from a single precursor, independently suppress the sequential recruitment of mesenchymal stem cells and inflammatory monocytes into the tumour stroma to inhibit lung metastasis by breast tumour cells in a mouse xenograft model. miR-126/miR-126* directly inhibit stromal cell-derived factor-1 alpha (Sdf-1α) expression, and indirectly suppress the expression of chemokine (C–C motif) ligand 2 (Ccl2) by cancer cells in an Sdf-1α-dependent manner. miR-126/miR-126* expression is downregulated in cancer cells by promoter methylation of their host gene Egfl7. These findings determine how this microRNA pair alters the composition of the primary tumour microenvironment to favour breast cancer metastasis, and demonstrate a correlation between miR-126/126* downregulation and poor metastasis-free survival of breast cancer patients.

SUMMARY Understanding the mechanism by which tumor cells influence osteoclast differentiation is crucial for improving treatment of osteolytic metastasis. Here, we report broad microRNA (miRNA) expression changes in differentiating osteoclasts after exposure to tumor-conditioned media, in part through activation of NFκB signaling by soluble intracellular adhesion molecule (sICAM1) secreted from bone-metastatic cancer cells. Ectopic expression of multiple miRNAs down-regulated during osteoclastogenesis suppresses osteoclast differentiation by targeting important osteoclast genes. Intravenous delivery of these miRNAs in vivo inhibits osteoclast activity and reduces osteolytic bone metastasis. Importantly, serum levels of sICAM1 and two osteoclast miRNAs, miR-16 and miR-378, which are elevated in osteoclast differentiation, correlate with bone metastasis burden. These findings establish miRNAs as potential therapeutic targets and clinical biomarkers of bone metastasis.

Emerging evidence suggests that cancer is populated and maintained by tumor initiating cells (TICs) with stem-like properties similar to that of adult tissue stem cells. Despite recent advances, the molecular regulatory mechanisms that may be shared between normal and malignant stem cells remain poorly understood. Here we show that the ΔNp63 isoform of the Trp63 transcription factor promotes normal mammary stem cell (MaSC) activity by increasing the expression of the Wnt receptor Fzd7, thereby enhancing Wnt signaling. Importantly, Fzd7-dependent enhancement of Wnt signaling by ΔNp63 also governs tumor initiating activity of the basal subtype of breast cancer. These findings establish ΔNp63 as a key regulator of stem cells in both normal and malignant mammary tissues and provide direct evidence that breast cancer TICs and normal MaSCs share common regulatory mechanisms.

Epithelial–mesenchymal transition (EMT) is a complex process which occurs during organogenesis and in cancer metastasis. Despite recent progress, the molecular pathways connecting the physiological and pathological functions of EMT need to be better defined. Here we show that the transcription factor Elf5, a key regulator of mammary gland alveologenesis, controls EMT in both mammary gland development and metastasis. We uncovered this role of Elf5 through analyses of Elf5 conditional knockout animals, various in vitro and in vivo models of EMT and metastasis, an MMTV-neu transgenic model of mammary tumor progression, and clinical breast cancer samples. Furthermore, we demonstrate that Elf5 suppresses EMT by directly repressing the transcription of Snail2/Slug, a master regulator of mammary stem cells and a known inducer of EMT. These findings establish Elf5 not only as a key cell lineage regulator during normal mammary gland development, but also as a suppressor of EMT and metastasis in breast cancer.

Prostate cancer is the second leading cause of cancer-related death in men. A typical feature of this disease is its ability to metastasize to bone. It is mainly osteosclerotic, and is caused by a relative excess of osteoblast activity, leading to an abnormal bone formation. Bone metastases are the result of a complex series of steps that are not yet fully understood and depend on dynamic crosstalk between metastatic cancer cells, cellular components of the bone marrow microenvironment, and bone matrix (osteoblasts and osteoclasts). Prostate cancer cells from primary tissue undergo an epithelial-mesenchymal transition to disseminate and acquire a bone-like phenotype to metastasize in bone tissue. This review discusses the biological processes and the molecules involved in the progression of bone metastases. Here we focus on the routes of osteoblast differentiation and activation, the crosstalk between bone cells and tumor cells, and the molecules involved in these processes that are expressed by both osteoblasts and tumor cells. Furthermore, this review deals with the recently elucidated role of osteoclasts in prostate cancer bone metastases. Certainly, to better understand the underlying mechanisms of bone metastasis and so improve targeted bone therapies, further studies are warranted to shed light on the probable role of the premetastatic niche and the involvement of cancer stem cells. Cancer 2010;116:1406-18. V C 2010 American Cancer Society.KEYWORDS: osteoblasts, osteoclasts, prostate cancer, bone, metastasization.Solid tumors, such as breast and prostate cancer, have an affinity to metastasize to bone, causing osteolysis and abnormal bone formation. Bone metastasis starts with the tropism of cancer cells to the bone through specific migratory and invasive processes. Once in the bone marrow, metastatic cells are able to survive and grow. Here, they actively interact with bone marrow stem cells and hematopoietic progenitors in the so-called metastatic niche, where they acquire a bonelike phenotype. This leads to the formation of bone lesions (lytic or osteoblastic), obtained through reciprocal paracrine amplification and cell-to-cell communication with bone cells. The complex molecular pathogenesis mechanisms of bone metastasis offer several potential targets for prevention and therapy.Prostate cancer is the second leading cause of cancer-related death in men, and a typical feature of this disease is its ability to metastasize to bone. Indeed, it has been estimated that >80% of men who die from prostate cancer develop bone metastases.1,2 Although most bone metastases from prostate cancer have been classified as osteoblastic, based on the radiographic appearance of lesions, it is clear that bone resorption and bone formation are dysregulated. 3-5The Metastatic Process: From Primary Tumor to Growth in Bone Tissue The first step in metastasization is the acquisition of motility and invasiveness; capabilities that are not compatible with normal tissue. Cancer cells must therefore shed many of their epithelial ch...

Sarcomas are a heterogeneous group of mesenchymal tumors arising from soft tissue or bone, with an uncertain etiology and difficult classification. Soft tissue sarcomas (STSs) account for around 1% of all adult cancers. Till date, more than 50 histologic subtypes have been identified. Adipocyte sarcoma or liposarcoma (LPS) is one of the most common STS subtypes, accounting for 15% of all sarcomas, with an incidence of 24% of all extremity STSs and 45% of all retroperitoneal STSs. The new World Health Organization classification system has divided LPS into four different subgroups: atypical lipomatous tumor/well-differentiated LPS, dedifferentiated LPS, myxoid LPS, and pleomorphic LPS. These lesions can develop at any location and exhibit different aggressive potentials reflecting their morphologic diversity and clinical behavior. Patients affected by LPS should be managed in specialized multidisciplinary cancer centers. Whereas surgical resection is the mainstay of treatment for localized disease, the benefits of adjuvant and neoadjuvant chemotherapy are still unclear. Systemic treatment, particularly chemotherapy, is still limited in metastatic disease. Despite the efforts toward a better understanding of the biology of LPS, the outcome of advanced and metastatic patients remains poor. The advent of targeted therapies may lead to an improvement of treatment options and clinical outcomes. A larger patient enrollment into translational and clinical studies will help increase the knowledge of the biological behavior of LPSs, test new drugs, and introduce new methodological studies, that is, on treatment response.

Bone metastasis is a complex process that needs to be better understood in order to help clinicians prevent and treat it. Xenografts using patient-derived material (PDX) rather than cancer cell lines are a novel approach that guarantees more clinically realistic results. A primary culture of bone metastasis derived from a 67-year-old patient with breast cancer was cultured and then injected into zebrafish (ZF) embryos to study its metastatic potential. In vivo behavior and results of gene expression analyses of the primary culture were compared with those of cancer cell lines with different metastatic potential (MCF7 and MDA-MB-231). The MCF7 cell line, which has the same hormonal receptor status as the bone metastasis primary culture, did not survive in the in vivo model. Conversely, MDA-MB-231 disseminated and colonized different parts of the ZF, including caudal hematopoietic tissues (CHT), revealing a migratory phenotype. Primary culture cells disseminated and in later stages extravasated from the vessels, engrafting into ZF tissues and reaching the CHT. Primary cell behavior reflected the clinical course of the patient’s medical history. Our results underline the potential for using PDX models in bone metastasis research and outline new methods for the clinical application of this in vivo model.