E- and N-cadherin are calcium-dependent cell adhesion molecules that mediate cell–cell adhesion and also modulate cell migration and tumor invasiveness. The loss of E-cadherin–mediated adhesion has been shown to play an important role in the transition of epithelial tumors from a benign to an invasive state. However, recent evidence indicates that another member of the cadherin family, N-cadherin, is expressed in highly invasive tumor cell lines that lacked E-cadherin expression. These findings have raised the possibility that N-cadherin contributes to the invasive phenotype. To determine whether N-cadherin promotes invasion and metastasis, we transfected a weakly metastatic and E-cadherin–expressing breast cancer cell line, MCF-7, with N-cadherin and analyzed the effects on cell migration, invasion, and metastasis. Transfected cells expressed both E- and N-cadherin and exhibited homotypic cell adhesion from both molecules. In vitro, N-cadherin–expressing cells migrated more efficiently, showed an increased invasion of Matrigel, and adhered more efficiently to monolayers of endothelial cells. All cells produced low levels of the matrix metalloproteinase MMP-9, which was dramatically upregulated by treatment with FGF-2 only in N-cadherin–expressing cells. Migration and invasion of Matrigel were also greatly enhanced by this treatment. When injected into the mammary fat pad of nude mice, N-cadherin–expressing cells, but not control MCF-7 cells, metastasized widely to the liver, pancreas, salivary gland, omentum, lung, lymph nodes, and lumbar spinal muscle. The expression of both E- and N-cadherin was maintained both in the primary tumors and metastatic lesions. These results demonstrate that N-cadherin promotes motility, invasion, and metastasis even in the presence of the normally suppressive E-cadherin. The increase in MMP-9 production by N-cadherin–expressing cells in response to a growth factor may endow them with a greater ability to penetrate matrix protein barriers, while the increase in their adherence to endothelium may improve their ability to enter and exit the vasculature, two properties that may be responsible for metastasis of N-cadherin–expressing cells.

Two seven-gene phenazine biosynthetic loci were cloned from Pseudomonas aeruginosa PAO1. The operons, designated phzA1B1C1D1E1F1G1 and phzA2B2C2D2E2F2G2, are homologous to previously studied phenazine biosynthetic operons from Pseudomonas fluorescens and Pseudomonas aureofaciens. Functional studies of phenazine-nonproducing strains of fluorescent pseudomonads indicated that each of the biosynthetic operons from P. aeruginosa is sufficient for production of a single compound, phenazine-1-carboxylic acid (PCA). Subsequent conversion of PCA to pyocyanin is mediated in P. aeruginosa by two novel phenazine-modifying genes, phzM and phzS, which encode putative phenazine-specific methyltransferase and flavin-containing monooxygenase, respectively. Expression of phzS alone in Escherichia coli or in enzymes, pyocyanin-nonproducing P. fluorescens resulted in conversion of PCA to 1-hydroxyphenazine. P. aeruginosa with insertionally inactivated phzM or phzS developed pyocyanin-deficient phenotypes. A third phenazine-modifying gene, phzH, which has a homologue in Pseudomonas chlororaphis, also was identified and was shown to control synthesis of phenazine-1-carboxamide from PCA in P. aeruginosa PAO1. Our results suggest that there is a complex pyocyanin biosynthetic pathway in P. aeruginosa consisting of two core loci responsible for synthesis of PCA and three additional genes encoding unique enzymes involved in the conversion of PCA to pyocyanin, 1-hydroxyphenazine, and phenazine-1-carboxamide.Phenazine compounds produced by fluorescent Pseudomonas species are biologically active metabolites that function in microbial competitiveness (37), the suppression of soilborne plant pathogens (1,11,55,56), and virulence in human and animal hosts (35).The most widely studied phenazine-producing fluorescent pseudomonad is P. aeruginosa, a gram-negative opportunistic pathogen of animals, insects, nematodes, and plants (30,33,35,46). In humans, P. aeruginosa infects immunocompromised, burned, or injured patients and can cause both acute and chronic lung disease. Strains of P. aeruginosa produce a variety of redox-active phenazine compounds, including pyocyanin, phenazine-1-carboxylic acid (PCA), 1-hydroxyphenazine (1-OH-PHZ), and phenazine-1-carboxamide (PCN) (7,52,57).From 90 to 95% of P. aeruginosa isolates produce pyocyanin (52), and the presence of high concentrations of pyocyanin in the sputum of cystic fibrosis patients has suggested that this compound plays a role in pulmonary tissue damage observed with chronic lung infections (64). This idea is supported by several recent studies which demonstrated that pyocyanin contributes in a variety of ways to the pathophysiological effects observed in airways infected by P. aeruginosa. Pyocyanin interferes with the regulation of ion transport, ciliary beat frequency, and mucus secretion in airway epithelial cells by altering the cytosolic concentration of calcium (15). It may interact with endothelium-derived relaxing factor or with nitric oxide (which plays a central role in the control ...

The clustered protocadherins (Pcdhs) comprise >50 putative synaptic recognition molecules that are related to classical cadherins and highly expressed in the nervous system. Pcdhs are organized into three gene clusters (alpha, beta, and gamma). Within the alpha and gamma clusters, three exons encode the cytoplasmic domain for each Pcdh, making these domains identical within a cluster. Using an antibody to the Pcdh-gamma constant cytoplasmic domain, we find that all interneurons in cultured hippocampal neurons express high levels of Pcdh-gamma(s) in a nonsynaptic distribution. In contrast, only 48% of pyramidal-like cells expressed appreciable levels of these molecules. In these cells, Pcdh-gamma(s) were associated with a subset of excitatory synapses in which they may mediate presynaptic to postsynaptic recognition in concert with classical cadherins. Immunogold localization in hippocampal tissue showed Pcdh-gamma(s) at some synapses, in nonsynaptic plasma membranes, and in axonal and dendritic tubulovesicular structures, indicating that they may be exchanged among synapses and intracellular compartments. Our results show that although Pcdh-gamma(s) can be synaptic molecules, synapses form lacking Pcdh-gamma(s). Thus, Pcdh-gamma(s) and their relatives may be late additions to the classical cadherin-based synaptic adhesive scaffold; their presence in intracellular compartments suggests a role in modifying synaptic physiology or stability.