Interaction of cadherin cadherin may lead to

Interaction of cadherin–cadherin may lead to intercellular activation of cellular pathways, initiating through lamellipodial protrusions and is followed by the cadherin–catenin–actin cluster formation. The association of cadherin with catenin promotes and stabilizes the AJs, while order RPC1063 polymerization leads to AJ expansion and maturation, further stabilizing and aligning adjacent cell membranes (Harris and Tepass, 2010). In particular, β-catenin binds to the cadherin cytoplasmic tail and interacts with α-catenin, which modulates the actin cytoskeleton (Cavallaro and Dejana, 2011; Stepniak et al., 2009). The intracellular domains of the cadherins also bind to p120 catenin, which links cadherin to microtubules (Harris and Tepass, 2010) and regulates GTPases such as Rho, Rac1 and Cdc42 (Cavallaro and Dejana, 2011; Reynolds and Carnahan, 2004; Yonemura, 2011; Grosheva et al., 2001; Anastasiadis et al., 2000; Anastasiadis and Reynolds, 2000; Noren et al., 2000) (Fig. 1). Disrupting Rac or Rho activity perturbs AJ assembly, while Cdc42 affects AJ maintenance (Yap and Kovacs, 2003; Braga, 2002). The function of GTPases is linked to cadherins and may control various cellular processes including polarization, migration and apoptosis. Specifically, CDH2 regulates spatially polarized signals through distinct p120 and β-catenin-dependent signaling pathways (Ouyang et al., 2013). Interestingly, CDH2 mediated cell adhesion is important for collective 3D migration (Peglion et al., 2014; Shih and Yamada, 2012a, b), while CDH11 is required for directional migration in vivo (Becker et al., 2013). Several reports showed that cadherins are affected by growth factors and activate signaling pathways as a result of physical interactions with growth factor receptors. On exposure to shear stress, VE-cadherin binds to platelet endothelial cell adhesion molecule (PECAM-1) and vascular endothelial growth factor receptor (VEGFR2) and this complex may lead to integrin activation and actin cytoskeleton reorganization (Shay-Salit et al., 2002; Tzima et al., 2005). Epidermal growth factor receptor (EGFR) forms a complex with CDH1, leading to activation of the mitogen-activated protein kinases (MAPK) pathway in epithelial cells (Pece and Gutkind, 2000; Hoschuetzky et al., 1994) with implications for cell survival (Shen and Kramer, 2004) or EMT (Wendt et al., 2010; Jia et al., 2012). Fibroblast growth factor receptors (FGFRs) were shown to stimulate CDH2 during neurite outgrowth (Williams et al., 1994, 2002), while FGF plays a critical role in the maintenance of vascular integrity by enhancing the stability of VE-cadherin at AJ sites (Hatanaka et al., 2012). Hepatocyte growth factor (HGF) modulates the expression of the cell adhesion molecule VE-cadherin and consequently endothelial cell motility, migration and angiogenesis (Martin et al., 2001). Finally, transforming growth factor beta 1 (TGF-β1) increases keratinocyte migration by increasing the levels of CDH2 and this action is counteracted by EGF (Diamond et al., 2008). Several reports have shown that cadherins are not only chemically but also mechanically regulated. Recently, our laboratory showed that substrate stiffness regulated AJ formation between epithelial cells in two-dimensional (2D) cultures and in three-dimensional (3D) epidermal tissues in vivo and in vitro by regulating the phosphorylation levels of the c-Janus N-terminal kinase (JNK) (You et al., 2013). Rigid substrates led to JNK activation and AJ disassembly, while soft matrices suppressed JNK activity leading to AJ formation. The results held true in 3D bioengineered epidermis as well as in the epidermis of knockout (jnk1−/− or jnk2−/−) mice. In conclusion, we discovered that the JNK pathway mediated the effects of substrate stiffness on AJ formation in 2D and 3D context in vitro as well in vivo. These findings shed light into the mechanisms of AJ formation and dissolution during tissue development and may provide novel guiding principles to control cell–cell vs. cell–substrate adhesion in 3D as a therapeutic strategy to promote tissue regeneration or inhibit tumor invasion.