The miR200 family regulates EMT through E-cadherin modulation and has been proposed to contribute to metastasis thusly. This report identifies a promoting role of miR-200 in metastatic colonization that involves a novel target, the tumor secretome. The correlation between miR-200 and metastasis in people with cancer supports the relevance of this biphasic, multifaceted role of miR-200. Although the role of miR-200s in regulating E-cadherin expression and epithelial-to-mesenchymal transition is well established, their influence on metastatic colonization remains controversial. Here we have used 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 epithelial–mesenchymal transition (EMT) is a complex process that 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 for 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 tumour progression and clinical breast cancer samples. Furthermore, we demonstrate that Elf5 suppresses EMT by directly repressing the transcription of Snail2, 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.

Emerging evidence suggests that cancer is populated and maintained by tumour-initiating cells (TICs) with stem-like properties similar to those 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 signalling. Importantly, Fzd7-dependent enhancement of Wnt signalling by ΔNp63 also governs tumour-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.

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. © 2010 American Cancer Society.