Transforming growth factor ␤ (TGF␤) induces an epithelial to mesenchymal transition (EMT) during both physiological and pathological processes; however, the mechanism underlying this transition is not fully eluci- Epithelial to mesenchymal transition (EMT)1 is a fundamental multistep process that occurs during both physiological and pathological states (1, 2). By allowing cells to detach from the epithelial tissue where they originate and to migrate, such transitions are necessary for proper embryonic development. However, they also provide a way for epithelium-derived tumors from a benign stage to become invasive and metastasize throughout the body. It has been demonstrated that there is commonality in the signaling pathways regulating EMT during both embryonic development and tumor progression, suggesting that similar molecular mechanisms underlie these processes and raising the possibility that tumor metastasis might simply be considered as a reactivation of some aspects of the embryonic program of EMT.The process of EMT requires loss of cell-cell interaction and acquisition of fibroblastic morphology with increased expression of mesenchymal markers, such as N-cadherin (3). Among growth factors that can promote this structural conversion, transforming growth factor ␤ (TGF␤) has been well characterized as an important inducer of EMT during development as well as during cancerogenesis (4). Indeed, although TGF␤ is considered a tumor suppressor during the first stage of tumorigenesis, principally through its ability to cause growth arrest and apoptosis in many non-transformed epithelial cell types, numerous reports show that TGF␤ can also promote tumor progression, particularly through its ability to promote EMT (4, 5). Moreover, it has been shown that blocking TGF␤ signaling in transgenic mice that develop multifocal metastatic mammary tumors reduces mammary tumor intravasation and lung metastasis and increases mammary tumor cell apoptosis (6).TGF␤ exerts its biological effects by inducing the formation of a heteromeric complex composed of type I and type II serine/ threonine kinases receptors. The activated receptor complex, in turn, phosphorylates and activates the receptor-regulated

Transforming growth factor-β (TGF-β) regulates a wide variety of biological processes through two types of Ser/Thr transmembrane receptors: the TGF-β type I receptor and the TGF-β type II receptor (TβRII). Upon ligand binding, TGF-β type I receptor activated by TβRII propagates signals to Smad proteins, which mediate the activation of TGF-β target genes. In this study, we identify ADAM12 (a disintegrin and metalloproteinase 12) as a component of the TGF-β signaling pathway that acts through association with TβRII. We found that ADAM12 functions by a mechanism independent of its protease activity to facilitate the activation of TGF-β signaling, including the phosphorylation of Smad2, association of Smad2 with Smad4, and transcriptional activation. Furthermore, ADAM12 induces the accumulation of TβRII in early endosomal vesicles and stabilizes the TβRII protein presumably by suppressing the association of TβRII with Smad7. These results define ADAM12 as a new partner of TβRII that facilitates its trafficking to early endosomes in which activation of the Smad pathway is initiated.

CCN5 is a member of the CCN (connective tissue growth factor/cysteine-rich 61/nephroblastoma overexpressed) family and was identified as an estrogen-inducible gene in estrogen receptor-positive cell lines. However, the role of CCN5 in breast carcinogenesis remains unclear. We report here that the CCN5 protein is localized mostly in the cytoplasm and in part in the nucleus of human tumor breast tissue. Using a heterologous transcription assay, we demonstrate that CCN5 can act as a transcriptional repressor presumably through association with histone deacetylase 1 (HDAC1). Microarray gene expression analysis showed that CCN5 represses expression of genes associated with epithelial-mesenchymal transition (EMT) as well as expression of key components of the transforming growth factor ␤ (TGF-␤) signaling pathway, prominent among them TGF-␤RII receptor. We show that CCN5 is recruited to the TGF-␤RII promoter, thereby providing a mechanism by which CCN5 restricts transcription of the TGF-␤RII gene. Consistent with this finding, CCN5, we found, functions to suppress TGF-␤-induced transcriptional responses and invasion that is concomitant with EMT. Thus, our data uncovered CCN5 as a novel transcriptional repressor that plays an important role in regulating tumor progression functioning, at least in part, by inhibiting the expression of genes involved in the TGF-␤ signaling cascade that is known to promote EMT.CCN5 (previously known as WISP-2) is a 29-kDa protein member of the connective tissue growth factor/cysteine-rich 61/nephroblastoma overexpressed (CCN) family (2, 5, 23). The CCN family is composed of six members grouped on the basis of similar structural analogies (7). CCN proteins appear to play important roles in several biological processes, including cell growth, adhesion, and migration as well as numerous endocrine-regulated functions (9,39,41). CCN proteins encompass four structural domains: an insulin-like growth factor-binding protein (IGF-BP) domain, a von Willebrand factor type C (VWC) domain, a thrombospondin (TSP-1) domain, and a cysteine knot (CT) domain reported to act as a potential proliferation module (29). Although the physiological function of CCN5 is not well defined, its domain structure suggests that its function may be different from that of other members of the CCN family. CCN5 contains only three structural domains and lacks the CT domain (7,8,35). It has been shown that CCN5 suppresses proliferation and its expression is reduced in cancers (14,31,35). Previously, we showed that upon hormone binding, the estrogen receptor (ER) directly regulates the ccn5 gene in all ER-positive breast cancer cell lines tested (17). Moreover, we found that CCN5 knockdown not only induced estradiol-independent growth of these cells, owing to a loss of estrogen receptor ␣ (ER␣) expression, but also promoted epithelial-mesenchymal transition (EMT) (18), a process involved in tumor invasiveness and metastasis (13,43,46,51).Consistent with its role in tumor progression, our recent studies have shown that CCN5 is ...