Contact inhibition of cell growth is essential for embryonic development and maintenance of tissue architecture in adult organisms, and the growth of tumors is characterized by a loss of contact inhibition of proliferation. The recently identified Hippo signaling pathway has been implicated in contact inhibition of proliferation as well as organ size control. The modulation of the phosphorylation and nuclear localization of Yes-associated protein (YAP) by the highly conserved kinase cascade of the Hippo signaling pathway has been intensively studied. However, cellsurface receptors regulating the Hippo signaling pathway in mammals are not well understood. In this study, we show that Hippo signaling pathway components are required for E-cadherindependent contact inhibition of proliferation. Knockdown of the Hippo signaling components or overexpression of YAP inhibits the decrease in cell proliferation caused by E-cadherin homophilic binding at the cell surface, independent of other cell-cell interactions. We also demonstrate that the E-cadherin/catenin complex functions as an upstream regulator of the Hippo signaling pathway in mammalian cells. Expression of E-cadherin in MDA-MB-231 cells restores the density-dependent regulation of YAP nuclear exclusion. Knockdown of β-catenin in densely cultured MCF10A cells, which mainly depletes E-cadherin-bound β-catenin, induces a decrease in the phosphorylation of S127 residue of YAP and its nuclear accumulation. Moreover, E-cadherin homophilic binding independent of other cell interactions is sufficient to control the subcellular localization of YAP. Therefore, Our results indicate that, in addition to its role in cell-cell adhesion, E-cadherin-mediated cell-cell contact directly regulates the Hippo signaling pathway to control cell proliferation.α-catenin | cell density | Merlin/Nf2 | NHERF

Autotaxin (ATX, nucleotide pyrophosphate/phosphodiesterase-2) is an autocrine motility factor initially characterized from A2058 melanoma cell-conditioned medium. ATX is known to contribute to cancer cell survival, growth, and invasion. Recently ATX was shown to be responsible for the lysophospholipase D activity that generates lysophosphatidic acid (LPA). Production of LPA is sufficient to explain the effects of ATX on tumor cells. Cyclic phosphatidic acid (cPA) is a naturally occurring analog of LPA in which the sn-2 hydroxy group forms a 5-membered ring with the sn-3 phosphate. Cellular responses to cPA generally oppose those of LPA despite activation of apparently overlapping receptor populations, suggesting that cPA also activates cellular targets distinct from LPA receptors. cPA has previously been shown to inhibit tumor cell invasion in vitro and cancer cell metastasis in vivo. However, the mechanism governing this effect remains unresolved. Here we show that 3-carba analogs of cPA lack significant agonist activity at LPA receptors yet are potent inhibitors of ATX activity, LPA production, and A2058 melanoma cell invasion in vitro and B16F10 melanoma cell metastasis in vivo.

Krü ppel-like factor 4 (KLF4) is a transcription factor that plays an important role in cell differentiation, proliferation, and survival, especially in the context of cancers. This study revealed that KLF4 activates glycolytic metabolism in breast cancer cells by up-regulating the platelet isoform of phosphofructokinase (PFKP). KLF4 activated the transcription of the PFKP gene by directly binding to the PFKP promoter. Whereas glucose uptake and lactate production were inhibited by the knockdown of KLF4, they were activated by the overexpression of KLF4. Unlike PFKP, the expressions of the other isoforms of phosphofructokinase and glycolytic genes were unaffected by KLF4. The human breast cancer tissues showed a close correlation between KLF4 and PFKP expression. This study also showed that PFKP plays a critical role in cell proliferation in breast cancer cells. In conclusion, it is suggested that KLF4 plays a role in maintenance of high glycolytic metabolism by transcriptional activation of the PFKP gene in breast cancer cells.Breast cancer is the most common type of cancer in women in Western countries (1). Breast cancer shows elevated glycolytic metabolism, which is one of the common characteristics of the malignant cancers (2). The increase in glycolytic rate is a result of the up-regulation of the metabolic transporters and glycolytic enzymes whose expressions are controlled by the transcriptional regulation of genes as well as post-translational modifications of the enzymes (2, 3).The conversion of fructose 6-phosphate to fructose 1,6-bisphosphate is the first committed step in the glycolytic pathway catalyzed by phosphofructokinase (PFK-1) (4, 5). PFK-1 is a complex tetrameric enzyme and exists in three isoforms: liver (PFKL), muscle (PFKM), and platelet (PFKP). The activity of PFK-1 is regulated by both quantitative changes and isozymic alterations secondary to altered gene expression during neoplastic transformation in vivo and in vitro (6, 7). The expression of PFK-1 is up-regulated in cancer cells, where glycolysis is enhanced (7,8). Although an increase in PFKP expression is a characteristic feature of malignant tissues (8), little is known about how PFKP expression is regulated during the development and progression of cancers or the change of cancer phenotypes.Krüppel-like factor 4 (KLF4) is a transcriptional factor that modulates the expression of several genes that are involved in cell cycle regulation and differentiation (9, 10). The KLF4 levels rise following DNA damage, cell cycle arrest in response to serum withdrawal, and contact inhibition (10). Elevated KLF4 level has also attributed to certain types of cancers. KLF4 mRNA and protein are overexpressed in up to 70% of breast cancers (11,12). The increased nuclear expression of KLF4 is considered to be associated with the aggressiveness of breast cancer phenotypes (12). KLF4 has been found to be overexpressed in oral and skin squamous carcinoma cells as well (13). In addition, KLF4 exhibits potent transforming activity when expressed in cult...

BackgroundParaxial protocadherin (PAPC) and fibronectin leucine-rich domain transmembrane protein-3 (FLRT3) are induced by TGFβ signaling in Xenopus embryos and both regulate morphogenesis by inhibiting C-cadherin mediated cell adhesion.Principal FindingsWe have investigated the functional and physical relationships between PAPC, FLRT3, and C-cadherin. Although neither PAPC nor FLRT3 are required for each other to regulate C-cadherin adhesion, they do interact functionally and physically, and they form a complex with cadherins. By itself PAPC reduces cell adhesion physiologically to induce cell sorting, while FLRT3 disrupts adhesion excessively to cause cell dissociation. However, when expressed together PAPC limits the cell dissociating and tissue disrupting activity of FLRT3 to make it effective in physiological cell sorting. PAPC counteracts FLRT3 function by inhibiting the recruitment of the GTPase RND1 to the FLRT3 cytoplasmic domain.Conclusions/SignificancePAPC and FLRT3 form a functional complex with cadherins and PAPC functions as a molecular “governor” to maintain FLRT3 activity at the optimal level for physiological regulation of C-cadherin adhesion, cell sorting, and morphogenesis.

Background: Autotaxin (ATX, NPP-2), originally purified as a potent tumor cell motility factor, is now known to be the long-sought plasma lysophospholipase D (LPLD). The integrity of the enzymatic active site, including three crucial histidine moieties, is required for motility stimulation, as well as LPLD and 5'nucleotide phosphodiesterase (PDE) activities. Except for relatively nonspecific chelation agents, there are no known inhibitors of the ATX LPLD activity.