Circulating tumor cells (CTCs) are shed from cancerous tumors, enter the circulatory system, and migrate to distant organs to form metastases that ultimately lead to the death of most patients with cancer. Identification and characterization of CTCs provides a means to study, monitor, and potentially interfere with the metastatic process. Isolation of CTCs from blood is challenging because CTCs are rare and possess characteristics that reflect the heterogeneity of cancers. Various methods have been developed to enrich CTCs from many millions of normal blood cells. Microfluidics offers an opportunity to create a next generation of superior CTC enrichment devices. This review focuses on various microfluidic approaches that have been applied to date to capture CTCs from the blood of patients with cancer.

The ␤-N-acetylglucosaminidase of Escherichia coli was found to have a novel specificity and to be encoded by a gene (nagZ) that maps at 25.1 min. It corresponds to an open reading frame, ycfO, whose predicted amino acid sequence is 57% identical to that of Vibrio furnissii ExoII. NagZ hydrolyzes the ␤-1,4 glycosidic bond between N-acetylglucosamine and anhydro-N-acetylmuramic acid in cell wall degradation products following their importation into the cell during the process for recycling cell wall muropeptides. From amino acid sequence comparisons, the novel ␤-N-acetylglucosaminidase appears to be conserved in all 12 gram-negative bacteria whose complete or partial genome sequence data are available.␤-N-Acetylglucosaminidase in Escherichia coli K-12 was first described by Yem and Wu in 1976 (18, 19). It was shown to be a cytoplasmic enzyme active against both p-nitrophenyl-␤-Nacetyl-D-glucosaminide and a muropeptide released by lysozyme from E. coli cell wall murein (peptidoglycan). However, based on indirect evidence, it was clear that the enzyme would also be active against anhydro-muropeptides (6). These muropeptides contain N-acetylglucosamine (GlcNAc) linked ␤-1,4 to anhydro-N-acetylmuramyl peptides (aMurNAc-peptides) (15). aMurNAc, which possesses a 1,6 anhydro bond, is formed by the lytic transglycosylases of E. coli that digest murein during normal growth as the initial step of the murein tripeptide recycling pathway. The murein tripeptide recycling pathway is a major metabolic pathway of E. coli (3) in which, during each generation of growth, about 40% of the cell wall murein is broken down into anhydro-muropeptides (3, 6). The anhydro-muropeptides are then transported into the cytoplasm via AmpG permease (6) and are rapidly degraded by the combined actions of ␤-N-acetylglucosaminidase (NagZ), anhydro-N-acetylmuramyl-L-alanine amidase (AmpD) (5, 7), and an LD-carboxypeptidase (LdcA) (17) to release GlcNAc, aMurNAc, D-alanine, and the murein tripeptide (L-alanyl-␥-D-glutamylmeso-diaminopimelic acid). The tripeptide is then linked to UDP-MurNAc by the murein peptide ligase, Mpl (10), and efficiently recycled to form murein de novo.Previous results imply the participation of a ␤-N-acetylglucosaminidase in recycling (6), and the present results identify NagZ as the enzyme involved. In this work, we also identify the gene encoding ␤-N-acetylglucosaminidase (nagZ), characterize a null mutation and a mutation in the structural gene, and report initial observations on the specificity of NagZ. MATERIALS AND METHODSBacterial strains, plasmids, and growth conditions. The E. coli K-12 strains and plasmids used in this work are listed in Table 1. Bacteria were grown aerobically at 37°C in L broth, which is LB broth (12) modified to contain only 5 g of NaCl per liter. Ampicillin (100 g/ml), kanamycin (25 g/ml), and chloramphenicol (10 g/ml) were used as required.Isolation of a ␤-N-acetylglucosaminidase-deficient mutant. E. coli TP71 cells were treated with nitrosoguanidine (10, 20, or 40 g/ml in 0.1 M citrate buffer ...

The Rho GTPase signaling pathway is required for actin cytoskeletal organization and serum response factor-dependent gene transcription. Lbc is a Rho-specific guanine nucleotide exchange factor that contains a modulatory C-terminal region. To elucidate Lbc regulatory mechanism(s), a yeast two-hybrid screen for proteins that interact with the Lbc C-terminal region was carried out, resulting in multiple isolation of cDNAs encoding the same 734-amino acid Lbc interacting protein. The Lbc interacting protein has homology with the ␣-catenin cell adhesion component and is identical to the ␣-catenin-like ␣-catulin protein of unknown function. The human ␣-catulin gene (CTNNAL1) maps to 9q31-32. Here we identify the predicted endogenous ␣-catulin product, document ␣-catulin and Lbc co-expression in multiple human cell lines, and show ␣-catulin and Lbc subcellular co-fractionation and intracellular localization. The required regions for Lbc and ␣-catulin interaction were mapped, and complex formation between Lbc and ␣-catulin in mammalian cells was detected. Functionally, ␣-catulin co-expression leads to increased Lbc-induced serum response factor activation in vivo as measured by a transcriptional reporter assay. Furthermore, ␣-catulin co-expression enhances Lbcinduced GTP-Rho formation in vivo. These results support the concept that the recently identified ␣-catulin protein may modulate Rho pathway signaling in vivo by providing a scaffold for the Lbc Rho guanine nucleotide exchange factor.

␣-Catenin, an integral part of cadherin-catenin adhesion complexes, is a major binding partner of ␤-catenin, a key component of the Wnt pathway, which activates T-cell factor (TCF)/lymphoid enhancer factor (LEF) transcription and is often upregulated in cancers. Recently, we identified an ␣-catenin-related protein, ␣-catulin, whose function is poorly understood, as part of a Rho GTPase signaling complex. Here, based on evidence suggesting that ␣-catulin may associate with a ␤-catenin fraction, we investigated the role of ␣-catenin family members in ␤-catenin-mediated signals. Expression of the full length or a 103-residue region of ␣-catenin strongly inhibits the induction of the TCF/LEF-responsive TOPFLASH reporter in HEK293T cells expressing activated ␤-catenin or in cancer cells with constitutively upregulated Wnt signaling, whereas ␣-catulin expression had no effect. Interestingly, ␣-catulin expression attenuates the activation of the cyclin D1 promoter, a target of Wnt pathway signals. ␣-Catulin appears to inhibit Ras-mediated signals to the cyclin D1 promoter, rather than ␤-catenin signals, and the synergy between Ras and ␤-catenin required to fully activate this promoter. Data suggesting the involvement of Rho in this response are presented and discussed. These results suggest a novel function for ␣-catulin and imply that ␣-catenin and ␣-catulin have distinct activities that downregulate, respectively, ␤-catenin and Ras signals converging on the cyclin D1 promoter.

A key issue regarding the role of ␣6␤4 in cancer biology is the mechanism by which this integrin exerts its profound effects on intracellular signaling, including growth factor-mediated signaling. One approach is to evaluate the intrinsic signaling capacity of the unique ␤4 intracellular domain in the absence of contributions from the ␣6 subunit and tetraspanins and to assess the ability of growth factor receptor signaling to cooperate with this domain. Here, we generated a chimeric receptor composed of the TrkB extracellular domain and the ␤4 transmembrane and intracellular domains. Expression of this chimeric receptor in ␤4-null cancer cells enabled us to assess the signaling potential of the ␤4 intracellular domain alone or in response to dimerization using brain-derived neurotrophic factor, the ligand for TrkB. Dimerization of the ␤4 intracellular domain results in the binding and activation of the tyrosine phosphatase SHP-2 and the activation of Src, events that also occur upon ligation of intact ␣6␤4. In contrast to ␣6␤4 signaling, however, dimerization of the chimeric receptor does not activate either Akt or Erk1/2. Growth factor stimulation induces tyrosine phosphorylation of the chimeric receptor but does not enhance its binding to SHP-2. The chimeric receptor is unable to amplify growth factor-mediated activation of Akt and Erk1/2, and growth factorstimulated migration. Collectively, these data indicate that the ␤4 intracellular domain has some intrinsic signaling potential, but it cannot mimic the full signaling capacity of ␣6␤4. These data also question the putative role of the ␤4 intracellular domain as an "adaptor" for growth factor receptor signaling.The ␣6␤4 integrin is a structural and functional anomaly among the integrin family of receptors. This integrin, which is expressed primarily on the basal surface of epithelia and in a few other cell types, is defined as an adhesion receptor for most of the known laminins (1-3). The distinguishing structural feature of ␣6␤4 is the atypical intracellular domain of the ␤4 subunit. Two pairs of fibronectin type III repeats separated by a connecting segment characterize this domain, and it is distinct both in size (ϳ1000 amino acids) and structure from any other integrin subunit (4). Although the ␣6␤4 integrin provides a well characterized adhesive function in normal epithelial cells by anchoring the epithelium to its underlying basement membrane, the carcinoma-associated functions of this integrin are becoming increasingly recognized (5). Importantly, the expression of this integrin is often maintained as epithelial structures dissociate during the initiation and progression of carcinomas, and, consequently, many carcinomas express ␣6␤4 (6, 7). Numerous studies by our groups and others have revealed that ␣6␤4 can facilitate the ability of carcinoma cells to migrate, invade, and resist apoptotic stimuli (8 -16). More recently, ␣6␤4 has been implicated in the genesis of squamous and breast carcinomas (17)(18)(19). The ability of ␣6␤4 to impact these diverse...