The role of epithelial-mesenchymal transition (EMT) in metastasis remains controversial. EMT has been postulated as an absolute requirement for tumor invasion and metastasis. Three different models including incomplete EMT, mesenchymal-epithelial transition (MET), and collective migration have been proposed for the role of EMT in cancer invasion and metastasis. However, skepticism remains about whether EMT truly occurs during cancer progression, and if it does, whether it plays an indispensible role in metastasis. Our recent findings suggest that EMT cells are responsible for degrading the surrounding matrix to enable invasion and intravasation of both EMT and non-EMT cells. Only non-EMT cells that have entered the blood stream are able to reestablish colonies in the secondary sites. Here, we discuss an alternative model for the role of EMT in cancer metastasis in which EMT and non-EMT cells cooperate to complete the entire process of spontaneous metastasis. [Cancer Res 2009;69(18):7135-9] Epithelial-Mesenchymal Transition and Cancer MetastasisEpithelial-mesenchymal transition (EMT) was first recognized as a central differentiation process in early embryogenic morphogenesis (1). It is a coordinated molecular and cellular change defined as a reduction in cell-cell adhesion, apical-basolateral polarity, and epithelial markers, as well as an acquisition of motility, spindle-cell shape, and mesenchymal markers. The definition of EMT in embryo development, which includes an ordered series of transcriptional events and a switch in cell fate, has not been strictly followed in cancer research, in which this term has been more liberally referred to as a recognizable change in cellular phenotype characterized as loss of cell junctions and gain of migratory behaviors (2).This more inclusive EMT process has been proposed and supported by numerous publications to be a potent mechanism that enhances the detachment of cancer cells from primary tumors. However, it is still controversial whether transformation of a noninvasive tumor into a metastatic tumor truly represents an EMT, and if it is, how important it is in the process of cancer metastasis (3, 4). The main argument for the lack of a role of EMT in cancer is that metastases seem histopathologically similar to the primary tumors from which they are derived. To resolve this apparent contradiction, a mesenchymal-epithelial transition (MET) process in the metastatic sites has been postulated as part of the process of metastatic tumor formation (5). MET is an attractive hypothesis that can explain the histopathological similarity between primary and metastatic tumors. In support of the MET hypothesis, dynamic expression of E-cadherin (CDH1) in cancer progression has been documented. However, direct experimental data supporting MET in cancer metastasis are still lacking. For example, Graff and colleagues showed that the DNA methylation status of the CDH1 promoter varies at different stages of the metastatic process (6). In primary breast cancers, the tumor cells ...

Connective tissue growth factor (CTGF/CCN2) is a member of the CCN family of matricellular proteins and also has been designated Hcs24, FISP12, IGFBP8, IGFBP-rP2, ␤IG-M2, and ecogenin. The other CCN proteins include Cyr61/CCN1, NOV/CCN3, WISP1/CCN4, WISP2/CCN5, and WISP3/CCN6 (5, 26, 38, 39) as well, and they are structurally and functionally related glycoproteins involved in cell differentiation, proliferation, adhesion, migration, and the formation of the extracellular matrix. These matricellular functions of CCNs are involved in physiological processes such as wound healing, angiogenesis, morphogenesis, and embryogenesis as well as in pathological states including fibrotic disorders, cancer, and arthritis.Earlier we showed that CCN2 promotes endochondral ossification by acting on chondrocytes, osteoblasts, and endothelial cells (35,37,46). For example, CCN2 promotes physiological chondrocytic proliferation and extracellular matrix (ECM) formation. We also reported the regeneration of defects in articular cartilage in rat knee joints following treatment with recombinant CCN2 (36). Furthermore, ctgf-null mice were dead on delivery and were characterized by defective angiogenesis, the derangement of endochondral ossification, and dysmorphisms that occurred as a result of impaired chondrocyte proliferation and an abnormal ECM composition within the hypertrophic zone (24).Matrix metalloproteinases (MMPs) are zinc-dependent endopeptidases that are involved in the remodeling and turnover of the ECM in physiological processes such as angiogenesis, wound healing, embryogenesis, and morphogenesis as well as in pathological states including cancers, myocardial infarction, fibrotic disorders, rheumatism, and osteoarthritis (33, 49). Cartilage is a connective tissue that is constructed by chondrocytes embedded within an ECM predominantly composed of collagens and proteoglycans. ECM remodeling is achieved by regulating the production and degradation of specific ECM components. MMPs, which comprise a large family of enzymes with differential abilities to degrade specific ECM components, play a vital role in this process. MMPs also cleave growth factors and their binding proteins, thereby activating or inhibiting specific signaling events (15). Of note, the expression and role of MMP3 have been investigated in the pathological status of articular cartilage, such as in osteoarthritis and rheumatism (1,52).Recent study has demonstrated the existence and functions of intracellular MMPs and tissue inhibitors of metalloproteinases (TIMPs). TIMP-1 accumulates in the cellular nuclei in association with the cell cycle (54). Alternative splicing and promoter usage generate an intracellular MMP11 isoform directly translated as an active MMP (31). MMP2 is found in the nuclei of cardiac myocytes and is capable of cleaving poly-(ADP-ribose) polymerase (PARP) in vitro (28). MMP3 also is detected in the nuclei of hepatocytes and is involved in apop-* Corresponding author. Mailing address:

Epithelial-mesenchymal transition (EMT) has been considered essential for metastasis, a multistep process including local invasion, intravasation, extravasation, and proliferation at distant sites. However, controversy remains as to whether EMT truly happens and how important it is to metastasis. We studied the involvement of EMT in individual steps of metastasis and found that p12, a down-stream effector of transforming growth factor B, induced EMT of hamster cheek pouch carcinoma-1 cells by promoting the expression of Twist2. EMT cells have an increased invasive but decreased metastatic phenotype. When s.c. inoculated, both EMT and non-EMT cells established primary tumors, but only EMT cells invaded into the adjacent tissues and blood vessels; however, neither cells formed lung metastases. When i.v. inoculated, only non-EMT cells established lung metastases. Moreover, s.c. inoculation of a mixture of the two cell types resulted in intravasation of both cell types and formation of lung metastasis from non-EMT cells. Our results allowed us to propose a novel model for the role of EMT in cancer metastasis. We showed that EMT and non-EMT cells cooperate to complete the spontaneous metastasis process. We thus hypothesize that EMT cells are responsible for degrading the surrounding matrix to lead the way of invasion and intravasation. Non-EMT cells then enter the blood stream and reestablish colonies in the secondary sites. [Cancer Res 2008;68(24):10377-86]

SOX9 is a transcription factor that plays a critical role in the development of multiple tissues. We previously reported that SOX9 in normal human adult prostate was restricted to basal epithelium. SOX9 was also expressed in a subset of prostate cancer (PCa) cells and was increased in relapsed hormonerefractory PCa. Moreover, SOX9 expression in PCa cell lines enhanced tumor cell proliferation and was B-catenin regulated. Here we report additional in vivo results showing that SOX9 is highly expressed during fetal prostate development by epithelial cells expanding into the mesenchyme, suggesting it may contribute to invasive growth in PCa. Indeed, SOX9 overexpression in LNCaP PCa xenografts enhanced growth, angiogenesis, and invasion. Conversely, short hairpin RNAmediated SOX9 suppression inhibited the growth of CWR22Rv1 PCa xenografts. These results support important functions of SOX9 in both the development and maintenance of normal prostate, and indicate that these functions contribute to PCa tumor growth and invasion. [Cancer Res 2008;68(6):1625-30]