SUMMARYThe development of neural crest cells involves an epithelial-mesenchymal transition (EMT) associated with the restriction of cadherin 6B expression to the pre-migratory neural crest cells (PMNCCs), as well as a loss of N-cadherin expression. We find that cadherin 6B, which is highly expressed in PMNCCs, persists in early migrating neural crest cells and is required for their emigration from the neural tube. Cadherin 6B-expressing PMNCCs exhibit a general loss of epithelial junctional polarity and acquire motile properties before their delamination from the neuroepithelium. Cadherin 6B selectively induces the de-epithelialization of PMNCCs, which is mediated by stimulation of BMP signaling, whereas N-cadherin inhibits de-epithelialization and BMP signaling. As BMP signaling also induces cadherin 6B expression and represses N-cadherin, cadherin-regulated BMP signaling may create two opposing feedback loops. Thus, the overall EMT of neural crest cells occurs via two distinct steps: a cadherin 6B and BMP signaling-mediated de-epithelialization, and a subsequent delamination through the basement membrane.

ABSTRACT

Inactivating mutations in the adenomatous polyposis coli gene (APC), and activating mutations in RAS, occur in a majority of colorectal carcinomas. However, the relationship between these changes and tumorigenesis is poorly understood. RAS-induced activation of the ERK pathway was reduced by overexpressing APC in DLD-1 colorectal cancer cells. ERK activity was increased by Cre-virus-induced Apc knockout in primary Apcflox/flox mouse embryonic fibroblasts, indicating that APC inhibits ERK activity. ERK activity was increased by overexpression and decreased by knock down of β-catenin. The activation of Raf1, MEK and ERK kinases by β-catenin was reduced by co-expression of APC. These results indicate that APC inhibits the ERK pathway by an action on β-catenin. RAS-induced activation of the ERK pathway was reduced by the dominant negative form of TCF4, indicating that the ERK pathway regulation by APC/β-catenin signaling is, at least, partly caused by effects on β-catenin/TCF4-mediated gene expression. The GTP loading and the protein level of mutated RAS were decreased in cells with reduced ERK activity as a result of APC overexpression, indicating that APC regulates RAS-induced ERK activation at least partly by reduction of the RAS protein level. APC regulates cellular proliferation and transformation induced by activation of both RAS and β-catenin signaling.

No abstract

Transforming growth factor‐beta (TGF‐β) induces the migration and mobilization of bone marrow‐derived mesenchymal stem cells (BM‐MSCs) to maintain bone homeostasis during bone remodeling and facilitate the repair of peripheral tissues. Although many studies have reported the mechanisms through which TGF‐β mediates the migration of various types of cells, including cancer cells, the intrinsic cellular mechanisms underlying cellular migration, and mobilization of BM‐MSCs mediated by TGF‐β are unclear. In this study, we showed that TGF‐β activated noncanonical signaling molecules, such as Akt, extracellular signal‐regulated kinase 1/2 (ERK1/2), focal adhesion kinase (FAK), and p38, via TGF‐β type I receptor in human BM‐MSCs and murine BM‐MSC‐like ST2 cells. Inhibition of Rac1 by NSC23766 and Src by PP2 resulted in impaired TGF‐β‐mediated migration. These results suggested that the Smad‐independent, noncanonical signals activated by TGF‐β were necessary for migration. We also showed that N‐cadherin‐dependent intercellular interactions were required for TGF‐β‐mediated migration using functional inhibition of N‐cadherin with EDTA treatment and a neutralizing antibody (GC‐4 antibody) or siRNA‐mediated knockdown of N‐cadherin. However, N‐cadherin knockdown did not affect the global activation of noncanonical signals in response to TGF‐β. Therefore, these results suggested that the migration of BM‐MSCs in response to TGF‐β was mediated through N‐cadherin and noncanonical TGF‐β signals.

Mechanical stimulation is a known modulator of survival and proliferation for many cells, including endothelial cells, smooth muscle cells, and bone marrow-derived mesenchymal stem cells. In this study, we found that mechanical strain prevents apoptosis and increases the adhesive ability of dermal fibroblasts in vitro and thus confers the survival advantage in vivo after transplantation of fibroblasts into the full-thickness wound of diabetic mice. Cyclic stretch at a frequency of 0.5 Hz and maximum elongation of 20% stimulates cellular survival mediated by the activation of extracellular signal-regulated kinases (ERKs), c-Jun N-terminal kinases (JNKs), and the serine/threonine kinase Akt (AKT). Stretching of the fibroblasts increases the synthesis of extracellular matrix proteins and the formation of denser focal adhesion structures, both of which are required for fibroblast adhesion. The stretched fibroblasts also upregulate the expression of vascular endothelial growth factor (VEGF) and stromal cell-derived factor-1a (SDF-1a), which enhanced wound healing in vivo. Indeed, preconditioning with mechanical stretch allows better survival of the transplanted fibroblasts, when compared to unstretched control cells, in the wound environment of mice with streptozotocin-induced diabetes and thus accelerates the wound-healing process in these mice.

Bone morphogenetic protein (BMP) signaling and Notch signaling play important roles in tumorigenesis in various organs and tissues, including the breast. BMP-4 enhanced epithelial mesenchymal transition (EMT) and stem cell properties in both mammary epithelial cell line and breast carcinoma cell line. BMP-4 increased the expression of EMT biomarkers, such as fibronectin, laminin, N-cadherin, and Slug. BMP-4 also activated Notch signaling in these cells and increased the sphere forming efficiency of the non-transformed mammary epithelial cell line MCF-10A. In addition, BMP-4 upregulated the sphere forming efficiency, colony formation efficiency, and the expression of cancer stem cell markers, such as Nanog and CD44, in the breast carcinoma cell line MDA-MB-231. Inhibition of Notch signaling downregulated EMT and stem cell properties induced by BMP-4. Down-regulation of Smad4 using siRNA impaired the BMP-4-induced activation of Notch signaling, as well as the BMP-4-mediated EMT. These results suggest that EMT and stem cell properties are increased in mammary epithelial cells and breast cancer cells through the activation of Notch signaling in a Smad4-dependent manner in response to BMP-4.

1 Zinc is an important trace element in the body and is involved in both the proliferation and growth arrest of many kinds of cells including colorectal epithelial cells. The aim of this study was to identify the molecular mechanism of the growth regulation of colorectal cancer cells by extracellular zinc. 2 Zinc-stimulated activation of the mitogen-activated protein kinase (MAPK) cascade was measured by immunoblotting and Elk-1 dependent trans-reporter gene expression, and zincstimulated p21 Cip/WAF1 activation by immunoblotting, Northern blot analysis and immunochemistry. Cell proliferation was measured by thymidine and bromodeoxyuridine (BrdU) incorporation. 3 By treating colorectal cancer cells with 100 mM ZnCl 2 , MAPKs were activated in two di erent phases, the initial weak activation occurred within 5 min and this was followed by a stronger and more prolonged activation. 4 Zinc concomitantly activated Raf-1-MEK-MAPK kinases, and induced Elk-1 dependent transreporter gene expression. 5 Prolonged activation of MAPKs by 100 mM of ZnCl 2 resulted in the induction and nuclear localization of p21 Cip/WAF1 and was related to the inhibition of both thymidine and BrdU incorporations. 6 These results not only suggest the presence of a mechanism for p21 Cip/WAF1 dependent negative regulation of colorectal cancer cell growth by zinc but also suggest potential usage of zinc to control the growth of colorectal cancer cells.