Delineation of a minimal interval and identification of 9 candidates for a tumor suppressor gene in malignant myeloid disorders on 5q31. (33/431)

Interstitial deletion or loss of chromosome 5 is frequent in malignant myeloid disorders, including myelodysplasia (MDS) and acute myeloid leukemia (AML), suggesting the presence of a tumor suppressor gene. Loss of heterozygosity (LOH) analysis was used to define a minimal deletion interval for this gene. Polymorphic markers on 5q31 were identified using a high-resolution physical and radiation hybrid breakpoint map and applied to a patient with AML with a subcytogenetic deletion of 5q. By comparing the DNA from leukemic cells to buccal mucosa cells, LOH was detected with markers D5S476 and D5S1372 with retention of flanking markers D5S500 to D5S594. The D5S500-D5S594 interval, which covers approximately 700 kb, thus represents a minimal localization for the tumor suppressor gene. Further refinement of the physical map enabled the specification of 9 transcription units within the encompassing radiation hybrid bins and 7 in flanking bins. The 9 candidates include genes CDC25, HSPA9, EGR1, CTNNA1, and 5 unknown ESTs. Reverse-transcription polymerase chain reaction confirms that all of them are expressed in normal human bone marrow CD34(+) cells and in AML cell lines and thus represent likely candidates for the MDS-AML tumor suppressor gene at 5q31.  (+info)

alpha-catenin expression is decreased in human gastric cancers and in the gastric mucosa of first degree relatives. (34/431)

BACKGROUND AND AIMS: The role of altered cell adhesion is critical for the development of epithelial cancers. E-cadherin plays an important role in the maintenance of cell-cell adhesion and its function is thought to be regulated by its associated cytoplasmic proteins, such as alpha-catenin and beta-catenin. To determine the role of alpha-catenin expression in gastric carcinogenesis, we studied its expression in human gastric cancer and in the gastric mucosa of first degree relatives with no clinical disease. METHODS: alpha-Catenin expression was assessed by immunohistochemical analysis and reverse transcriptase-polymerase chain reaction (RT-PCR) using gastric tissue specimens from patients with gastric cancer and from the gastric mucosa of first degree relatives of gastric cancer patients and healthy controls. RESULTS: mRNA levels of alpha-catenin were reduced or absent in 13 of 19 gastric cancer tissues, which differed significantly from levels found in the tumour free gastric mucosa of cancer patients (p<0.05). Of the cancer samples with altered alpha-catenin mRNA levels, alpha-catenin expression was negative in seven and decreased in six cases. Interestingly, decreased alpha-catenin mRNA expression also occurred in the mucosa of the corpus (11/18) and antrum (4/18) of first degree relatives. In the corpus biopsies alpha-catenin expression was more often decreased or lost compared with the antrum biopsies in first degree relatives and healthy controls (p<0.05). Immunohistochemical analysis revealed membranous expression of alpha-catenin in gastric cancer cells and the non-malignant gastric epithelium. However, some cancers also exhibited loss of membranous staining. Generally, loss or downregulation of alpha-catenin mRNA in the gastric mucosa was associated with Helicobacter pylori infection (p<0.05). CONCLUSION: Our findings suggest that loss or downregulation of alpha-catenin expression may be an early event in gastric carcinogenesis and may be associated with H pylori infection.  (+info)

Structure of the dimerization and beta-catenin-binding region of alpha-catenin. (35/431)

In adherens junctions, alpha-catenin links the cadherin-beta-catenin complex to the actin-based cytoskeleton. alpha-catenin is a homodimer in solution, but forms a 1:1 heterodimer with beta-catenin. The crystal structure of the alpha-catenin dimerization domain, residues 82-279, shows that alpha-catenin dimerizes through formation of a four-helix bundle in which two antiparallel helices are contributed by each protomer. A slightly larger fragment, comprising residues 57-264, binds to beta-catenin. A chimera consisting of the alpha-catenin-binding region of beta-catenin linked to the amino terminus of alpha-catenin 57-264 behaves as a monomer in solution, as expected, since beta-catenin binding disrupts the alpha-catenin dimer. The crystal structure of this chimera reveals the interaction between alpha- and beta-catenin, and provides a basis for understanding adherens junction assembly.  (+info)

Feedback interactions between cell-cell adherens junctions and cytoskeletal dynamics in newt lung epithelial cells. (36/431)

To test how cell-cell contacts regulate microtubule (MT) and actin cytoskeletal dynamics, we examined dynamics in cells that were contacted on all sides with neighboring cells in an epithelial cell sheet that was undergoing migration as a wound-healing response. Dynamics were recorded using time-lapse digital fluorescence microscopy of microinjected, labeled tubulin and actin. In fully contacted cells, most MT plus ends were quiescent; exhibiting only brief excursions of growth and shortening and spending 87.4% of their time in pause. This contrasts MTs in the lamella of migrating cells at the noncontacted leading edge of the sheet in which MTs exhibit dynamic instability. In the contacted rear and side edges of these migrating cells, a majority of MTs were also quiescent, indicating that cell-cell contacts may locally regulate MT dynamics. Using photoactivation of fluorescence techniques to mark MTs, we found that MTs in fully contacted cells did not undergo retrograde flow toward the cell center, such as occurs at the leading edge of motile cells. Time-lapse fluorescent speckle microscopy of fluorescently labeled actin in fully contacted cells revealed that actin did not flow rearward as occurs in the leading edge lamella of migrating cells. To determine if MTs were required for the maintenance of cell-cell contacts, cells were treated with nocodazole to inhibit MTs. After 1-2 h in either 10 microM or 100 nM nocodazole, breakage of cell-cell contacts occurred, indicating that MT growth is required for maintenance of cell-cell contacts. Analysis of fixed cells indicated that during nocodazole treatment, actin became reduced in adherens junctions, and junction proteins alpha- and beta-catenin were lost from adherens junctions as cell-cell contacts were broken. These results indicate that a MT plus end capping protein is regulated by cell-cell contact, and in turn, that MT growth regulates the maintenance of adherens junctions contacts in epithelia.  (+info)

alpha-catenin inhibits beta-catenin signaling by preventing formation of a beta-catenin*T-cell factor*DNA complex. (37/431)

alpha-Catenin and beta-catenin link cadherins to the cytoskeleton at adherens junctions. beta-Catenin also associates with members of the T-cell factor (Tcf) family of transcription factors, and mutations in beta-catenin lead to activation of Tcf-dependent transcription and increased cell growth. Although the loss of alpha-catenin expression can also promote cell growth, the role of endogenous alpha-catenin in beta-catenin signaling is unclear. Here we show that loss of alpha-catenin expression in a colon cancer cell line correlates with increased Tcf-dependent transcription. The presence of alpha-catenin in colon cancer cell nuclei suggests that it inhibits transcription directly, and, in agreement with this, ectopic expression of alpha-catenin in the nucleus represses Tcf-dependent transcription. Furthermore, recombinant alpha-catenin disrupts the interaction between the beta-catenin.Tcf complex and DNA. We conclude that alpha-catenin inhibits beta-catenin signaling in the nucleus by interfering with the formation of a beta-catenin. Tcf.DNA complex.  (+info)

Cadherin switching in human prostate cancer progression. (38/431)

The progression of carcinomas is associated with the loss of epithelial morphology and a concomitant acquisition of a more mesenchymal phenotype, which in turn is thought to contribute to the invasive and/or metastatic behavior of the malignant process. Changes in the expression of cadherins, "cadherin switching," plays a critical role during embryogenesis, particularly in morphogenetic processes. Loss of E-cadherin is reported to be associated with a poor prognosis; however, thus far, evidence (R. Umbas, et al., Cancer Res. 54: 3929-3933, 1994) for up-regulation of other cadherins has only been reported in vitro, ie., we have found evidence (M. J. G. Bussemakers et al., Int. J. Cancer, 85: 446-450, 2000) for cadherin switching in prostate cancer cell lines (up-regulation of N-cadherin and cadherin-11, two mesenchymal cadherins, in cell lines that lack a functional E-cadherin-catenin adhesion complex). Here, we report on the immunohistochemical analysis of the expression of N-cadherin and cadherin-11 in human prostate cancer specimens. N-cadherin was not expressed in normal prostate tissue; however, in prostatic cancer, N-cadherin was found to be expressed in the poorly differentiated areas, which showed mainly aberrant or negative E-cadherin staining. Cadherin-11 is expressed in the stroma of all prostatic tumors, in the area where stromal and epithelial cells are found. In addition, cadherin-11 is also expressed in a dotted pattern or at the membrane of the epithelial cells of high-grade cancers. In a number of metastatic lesions, N-cadherin and cadherin-11 are expressed homogeneously. These data raise the possibility that cadherin switching plays an important role in prostate cancer metastasis.  (+info)

Cell volume-dependent phosphorylation of proteins of the cortical cytoskeleton and cell-cell contact sites. The role of Fyn and FER kinases. (39/431)

Cell volume affects diverse functions including cytoskeletal organization, but the underlying signaling pathways remained undefined. We have shown previously that shrinkage induces Fyn-dependent tyrosine phosphorylation of the cortical actin-binding protein, cortactin. Because FER kinase was implicated in the direct phosphorylation of cortactin, we investigated the osmotic responsiveness of FER and its relationship to Fyn and cortactin. Shrinkage increased FER activity and tyrosine phosphorylation. These effects were abolished by the Src family inhibitor PP2 and strongly mitigated in Fyn-deficient but not in Src-deficient cells. FER overexpression caused cortactin phosphorylation that was further enhanced by hypertonicity. Exchange of tyrosine residues 421, 466, and 482 for phenylalanine prevented cortactin phosphorylation by hypertonicity and strongly decreased it upon FER overexpression, suggesting that FER targets primarily the same osmo-sensitive tyrosines. Because constituents of the cell-cell contacts are substrates of Fyn and FER, we investigated the effect of shrinkage on the adherens junctions. Hypertonicity provoked Fyn-dependent tyrosine phosphorylation in beta-catenin, alpha-catenin, and p120(Cas) and caused the dissociation of beta-catenin from the contacts. This process was delayed in Fyn-deficient or PP2-treated cells. Thus, FER is a volume-sensitive kinase downstream from Fyn, and the Fyn/FER pathway may contribute to the cell size-dependent reorganization of the cytoskeleton and the cell-cell contacts.  (+info)

A role for alpha-and beta-catenins in bacterial uptake. (40/431)

Interaction of internalin with E-cadherin promotes entry of Listeria monocytogenes into human epithelial cells. This process requires actin cytoskeleton rearrangements. Here we show, by using a series of stably transfected cell lines expressing E-cadherin variants, that the ectodomain of E-cadherin is sufficient for bacterial adherence and that the intracytoplasmic domain is required for entry. The critical cytoplasmic region was further mapped to the beta-catenin binding domain. Because beta-catenin is known to interact with alpha-catenin, which binds to actin, we generated a fusion molecule consisting of the ectodomain of E-cadherin and the actin binding site of alpha-catenin. Cells expressing this chimera were as permissive as E-cadherin-expressing cells. In agreement with these data, alpha- and beta-catenins as well as E-cadherin clustered and colocalized at the entry site, where F-actin then accumulated. Taken together, these results reveal that E-cadherin, via beta- and alpha-catenins, can trigger dynamic events of actin polymerization and membrane extensions culminating in bacterial uptake.  (+info)