During epithelial tumor progression, the loss of E-cadherin expression and inappropriate expression of mesenchymal cadherins coincide with increased invasiveness. Reexpression experiments have established E-cadherin as an invasion suppressor. However, the mechanism by which E-cadherin suppresses invasiveness and the role of mesenchymal cadherins are poorly understood. We show that both p120 catenin and mesenchymal cadherins are required for the invasiveness of E-cadherin–deficient cells. p120 binding promotes the up-regulation of mesenchymal cadherins and the activation of Rac1, which are essential for cell migration and invasiveness. p120 also promotes invasiveness by inhibiting RhoA activity, independently of cadherin association. Furthermore, association of endogenous p120 with E-cadherin is required for E-cadherin–mediated suppression of invasiveness and is accompanied by a reduction in mesenchymal cadherin levels. The data indicate that p120 acts as a rheostat, promoting a sessile cellular phenotype when associated with E-cadherin or a motile phenotype when associated with mesenchymal cadherins.

p120 catenin is a cadherin-associated protein that regulates Rho GTPases and promotes the invasiveness of E-cadherin-deficient cancer cells. Multiple p120 isoforms are expressed in cells via alternative splicing, and all of them are essential for HGF signaling to Rac1. However, only full-length p120 (isoform 1) promotes invasiveness. This selective ability of p120 isoform 1 is mediated by reduced RhoA activity, both under basal conditions and following HGF treatment. All p120 isoforms can bind RhoA in vitro, via a central RhoA binding site. However, only the cooperative binding of RhoA to the central p120 domain and to the alternatively spliced p120 N terminus stabilizes RhoA binding and inhibits RhoA activity. Consistent with this, increased expression of p120 isoform 1, when compared with other p120 isoforms, is predictive of renal tumor micrometastasis and systemic progression, following nephrectomy. Furthermore, ectopic expression of the RhoA-binding, N-terminal domain of p120 is sufficient to block the ability of p120 isoform 1 to inhibit RhoA and to promote invasiveness. The data indicate that the increased expression of p120 isoform 1 during tumor progression contributes to the invasive phenotype of cadherin-deficient carcinomas and that the N-terminal domain of p120 is a valid therapeutic target.During epithelial tumor progression, tumor cells acquire the ability to invade surrounding tissues and eventually metastasize. A number of pathways have been uncovered to date that promote local invasiveness and metastatic tumor spread, and recent evidence argues that most of these converge on the loss of E-cadherin expression or function (1, 2). E-cadherin is the main epithelial cell-cell adhesion molecule, and its loss in most of these tumors coincides with an epithelial to mesenchymal transition (EMT), 2 where cells shed their epithelial characteristics and acquire a more mesenchymal phenotype. EMT is associated with normal development and wound healing, but its aberrant regulation contributes to cancer progression and metastasis (3). External cues, such as growth factors, can promote EMT via signaling pathways that are not well characterized but may involve the function of Snail family transcriptional repressors. The best characterized function of these transcription factors (i.e. Snail, Slug, and SIP1) is down-regulation of E-cadherin expression (4 -7). Consistent with this, experiments in transgenic mice strongly suggest that loss of E-cadherin directly promotes the transition of a benign adenoma into a carcinoma (8). Furthermore, reestablishing E-cadherin function in cadherin-deficient cell lines can reverse the invasive phenotype, suggesting that E-cadherin acts as a suppressor of cell invasion (9). The mechanism by which E-cadherin promotes suppression of invasiveness is still unclear. However, the adhesive function, which is mediated by its extracellular domain, is not thought to be involved in this effect (10). The intracellular domain of E-cadherin interacts directly with ␤-catenin and p120 catenin (p...

p120-catenin exists in a membrane-associated cadherin-bound pool, a cytosolic pool that affects Rho GTPases, and a nuclear pool that is thought to associate with the methylation-relevant transcriptional repressor Kaiso. We show here that cytoplasmic p120 can also associate both directly and indirectly with the microtubule network, and that p120 traffics along microtubules toward their plus ends. The direct binding required most of the armadillo repeats and was mutually exclusive for interaction with E-cadherin. Perturbing the p120-microtubule interaction with nocodazole or taxol markedly affected both the tubulin interaction and the balance between cytoplasmic and nuclear p120. The indirect binding occurred via a novel interaction between a segment of the p120 N-terminal domain and conventional kinesin heavy chains. Selective uncoupling of the p120-kinesin interaction by overexpression of the respective p120 and kinesin-binding fragments promoted nuclear p120 accumulation. In addition, expression of full-length kinesin reduced the nuclear accumulation of p120 and blocked the branching phenotype associated with p120 overexpression. Taken together, the data suggest that kinesin affects both the targeting and activity of p120 at several cellular locations.

p120 catenin regulates the activity of the Rho family guanosine triphosphatases (including RhoA and Rac1) in an adhesion-dependent manner. Through this action, p120 promotes a sessile cellular phenotype when associated with epithelial cadherin (E-cadherin) or a motile phenotype when associated with mesenchymal cadherins. In this study, we show that p120 also exerts significant and diametrically opposing effects on tumor cell growth depending on E-cadherin expression. Endogenous p120 acts to stabilize E-cadherin complexes and to actively promote the tumor-suppressive function of E-cadherin, potently inhibiting Ras activation. Upon E-cadherin loss during tumor progression, the negative regulation of Ras is relieved; under these conditions, endogenous p120 promotes transformed cell growth both in vitro and in vivo by activating a Rac1–mitogen-activated protein kinase signaling pathway normally activated by the adhesion of cells to the extracellular matrix. These data indicate that both E-cadherin and p120 are important regulators of tumor cell growth and imply roles for both proteins in chemoresistance and targeted therapeutics.

Hyperphosphorylated tau is the major component of paired helical filaments in neurofibrillary tangles found in Alzheimer's disease brains, and tau hyperphosphorylation is thought to be a critical event in the pathogenesis of this disease. The objective of this study was to reproduce tau hyperphosphorylation in an animal model by inducing hypoglycemia. Food deprivation of mice for 1 to 3 days progressively enhanced tau hyperphosphorylation in the hippocampus, to a lesser extent in the cerebral cortex, but the effect was least in the cerebellum, in correspondence with the regional selectivity of tauopathy in Alzheimer's disease. This hyperphosphorylation was reversible by refeeding for 1 day. We discuss possible mechanisms of this phenomenon, and propose the starved mouse as a simple model to study in vivo tau phosphorylation and dephosphorylation which are altered in Alzheimer's disease.z 1999 Federation of European Biochemical Societies.

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Peroxisome proliferator-activated receptor ␥ (PPAR␥) causes epithelial to mesenchymal transformation (EMT) in intestinal epithelial cells, as evidenced by reorganization of the actin cytoskeleton, acquisition of a polarized, mesenchymal cellular morphology, increased cellular motility, and colony scattering. This response is due to activation of Cdc42, resulting in p21-activated kinase-dependent phosphorylation and activation of MEK1 Ser 298 and activation of ERK1/2. Dominant negative MEK1, MEK2, and ERK2 block PPAR␥-induced EMT, whereas constitutively active MEK1 and MEK2 induce a mesenchymal phenotype similar to that evoked by PPAR␥. PPAR␥ also stimulates ERK1/2 phosphorylation in the intestinal epithelium in vivo. PPAR␥ induces the p110␣ subunit of phosphoinositide 3-kinase (PI3K), and inhibition of PI3K blocks PPAR␥-dependent phosphorylation of MEK1 Ser 298 , activation of ERK1/2, and EMT. We conclude that PPAR␥ regulates the motility of intestinal epithelial cells through a mitogen-activated protein kinase cascade that involves PI3K, Cdc42, p21-activated kinase, MEK1, and ERK1/2. Regulation of cellular motility through Rho family GTPases has not been previously reported for nuclear receptors, and elucidation of the mechanism that accounts for the role of PPAR␥ in regulating motility of intestinal epithelial cells provides fundamental new insight into the function of this receptor during renewal of the intestinal epithelium.The nuclear receptor peroxisome proliferator-activated receptor (PPAR) 2 ␥1 is expressed at high levels in many cells of epithelial origin, including those of the gastrointestinal tract (1, 2). PPAR␥ is activated by the thiazolidinedione class of drugs (3), which inhibit azoxymethane-induced colon carcinogenesis in wild type mice (4, 5). Furthermore, hemizygous knock-out of PPAR␥ exacerbates colon tumor formation in azoxymethanetreated mice (6). Paradoxically, thiazolidinediones appear to promote intestinal tumor growth in mice that harbor mutations in the adenomatous polyposis coli (APC ϩ/Min ) gene (7,8), and long term treatment with high concentrations of thiazolidinediones induces caecal tumors in mice (9, 10). These observations suggest that PPAR␥ may, under different circumstances, function as a tumor suppressor or as a tumor promoter. However, little is known about the physiological role of PPAR␥ in the gastrointestinal epithelium, which makes it difficult to construct testable hypotheses concerning those aspects of PPAR␥ signaling that may account for these paradoxical effects of thiazolidinediones.To address these questions, we carried out a series of studies to elucidate the functions of PPAR␥ in nontransformed gastrointestinal epithelial cells. Our initial studies indicate that PPAR␥ plays a critical role in a number of processes that are central to renewal of the intestinal epithelium (11). The intestinal epithelium is one of the most dynamic tissues in the adult. The entire epithelium is replaced every 3 days or so by a highly orchestrated process that involves proliferation,...

Localization of presynaptic components to synaptic sites is critical for hippocampal synapse formation. Cell adhesion–regulated signaling is important for synaptic development and function, but little is known about differentiation of the presynaptic compartment. In this study, we describe a pathway that promotes presynaptic development involving p120catenin (p120ctn), the cytoplasmic tyrosine kinase Fer, the protein phosphatase SHP-2, and β-catenin. Presynaptic Fer depletion prevents localization of active zone constituents and synaptic vesicles and inhibits excitatory synapse formation and synaptic transmission. Depletion of p120ctn or SHP-2 similarly disrupts synaptic vesicle localization with active SHP-2, restoring synapse formation in the absence of Fer. Fer or SHP-2 depletion results in elevated tyrosine phosphorylation of β-catenin. β-Catenin overexpression restores normal synaptic vesicle localization in the absence of Fer or SHP-2. Our results indicate that a presynaptic signaling pathway through p120ctn, Fer, SHP-2, and β-catenin promotes excitatory synapse development and function.