Expression of cadherin-catenin complexes in human leukemia cell lines

Identification of Deregulated Signaling Pathways in Jurkat Cells in Response to a Novel Acylspermidine Analogue-N4-Erucoyl Spermidine

Natural polyamines such as putrescine, spermidine, and spermine are crucial in the cell proliferation and maintenance in all the eukaryotes. However, the requirement of polyamines in tumor cells is stepped up to maintain tumorigenicity. Many synthetic polyamine analogues have been designed recently to target the polyamine metabolism in tumors to induce apoptosis. N⁴-Erucoyl spermidine (designed as N⁴-Eru), a novel acylspermidine derivative, has been shown to exert selective inhibitory effects on both hematological and solid tumors, but its mechanisms of action are unknown. In this study, RNA sequencing was performed to investigate the anticancer mechanisms of N⁴-Eru-treated T-cell acute lymphoblastic leukemia (ALL) cell line (Jurkat cells), and gene expression was examined through different tools. We could show that many key oncogenes including NDRG1, CACNA1G, TGFBR2, NOTCH1,2,3, UHRF1, DNMT1,3, HDAC1,3, KDM3A, KDM4B, KDM4C, FOS, and SATB1 were downregulated, whereas several tumor suppressor genes such as CDKN2AIPNL, KISS1, DDIT3, TP53I13, PPARG, FOXP1 were upregulated. Data obtained through RNA-Seq further showed that N⁴-Eru inhibited the NOTCH/Wnt/JAK-STAT axis. This study also indicated that N⁴-Eru-induced apoptosis could involve several key signaling pathways in cancer. Altogether, our results suggest that N⁴-Eru is a promising drug to treat ALL.

Hydrogen sulfide-releasing aspirin inhibits the growth of leukemic Jurkat cells and modulates β-catenin expression

Hydrogen sulfide-releasing aspirin (HS-ASA) is a novel compound with potential against cancer. It inhibited the growth of Jurkat T-leukemia cells with an IC₅₀ of 1.9 ± 0.2 μM whereas that of ASA was >5000 μM. It dose-dependently inhibited proliferation and induced apoptosis in these cells, causing a G₀/G₁ cell cycle arrest. HS-ASA down-regulated β-catenin protein levels and reduced mRNA and protein expression of β-catenin/TCF downstream target genes cyclinD1 and c-myc. Aspirin up to 5 mM had no effect on β-catenin expression. HS-ASA also increased caspase-3 protein levels and dose-dependently increased its activity. These effects were substantially blocked by z-VAD-fmk, a pan-caspase inhibitor.

Molecular basis for the tissue specificity of β-catenin oncogenesis

Wnt-β-catenin-T-cell factor signaling is causally linked to c-myc-dependent tumorigenesis in mouse and human colon epithelial cells. By contrast, β-catenin is not similarly associated with oncogenic transformation of other tissues, including T cells. The molecular basis for tissue specificity of β-catenin-dependent oncogenesis is unknown. Here, we demonstrate that adenomatous polyposis coli mutant APC(Min/+) mice, which have increased expression of β-catenin in all tissues, develop severe intestinal neoplasia, but fail to develop thymic lymphoma. Whereas β-catenin-dependent signals elicit a proliferative response from intestinal cells, thymocytes experience oncogene-induced senescence (OIS), growth arrest and apoptosis. We demonstrate that the differential cellular response of thymocytes and intestinal epithelial cells is a direct consequence of the gene expression elicited by β-catenin expression in each tissue. We find that whereas intestinal cells induce genes that promote proliferation thymocytes induce expression of genes associated with OIS, growth arrest and p53-dependent apoptosis. We correlate gene expression pattern with the role β-catenin plays in the development of each tissue and suggest that susceptibility of transformation by β-catenin is intimately related to its function during development. We propose that when oncogenes are used as signaling molecules, safety nets in the form of OIS, growth arrest and apoptosis prevent accidental transformation.

Nitric Oxide-Releasing Hybrid Drugs Target Cellular Processes Through S-Nitrosylation

Nitric oxide (NO)-releasing agents such as JS-K and NO-releasing hybrids such as NO- and NONO-nonsteroidal anti-inflammatory drugs are novel agents with great potential for controlling cancer. Although studied extensively, a key question pertaining to their molecular targets and mechanism of action remains unclear: the role of NO in the overall biological effect of these agents. It has been shown that NO can directly modify sulfhydryl residues of proteins through S-nitrosylation and induce apoptosis. We showed that 3 structurally diverse NO-nonsteroidal anti-inflammatory drugs S-nitrosylated nuclear factor-κB p65 in vitro and in vivo and also showed that these agents S-nitrosylated caspase-3 in vivo. JS-K reduced nuclear β-catenin and cyclin D1 protein levels without affecting cytosolic β-catenin expression. On the basis of a time course study, S-nitrsolyation of nuclear β-catenin was determined to precede its degradation. These data provide a mechanistic role for NO and a rationale for the chemopreventive effects of these novel agents.

N-cadherin regulates radial glial fiber-dependent migration of cortical locomoting neurons

During cerebral cortical development, post-mitotic neurons exhibit a multi-step migration. The locomotion mode covers most of the neuronal migration path. Although for many decades, locomoting neurons have been known to migrate along radial glial fibers, how the cortical locomoting neurons attach to and migrate along radial glial fibers was largely unknown. We recently reported that N-cadherin is required for cortical neuronal migration in vivo. Knockdown or dominant negative inhibition of N-cadherin results in severe neuronal migration defects. Furthermore, suppression of Rab5-dependent endocytosis increases cell surface levels of N-cadherin and perturbs neuronal migration. We showed here that N-cadherin overexpression, which would mimic Rab5 suppression, weakly suppressed neuronal migration, suggesting that excess N-cadherin also disturbs neuronal migration. Interestingly, however, N-cadherin knockdown and overexpression in neurons resulted in different morphologies. While N-cadherin-overexpressing cells closely attached to the radial glial fibers similar to control or Rab5-knockdown cells, N-cadherin knockdown weakened the attachment as the average distance between the soma and radial glial fibers was significantly increased. Taken together, these findings suggest that N-cadherin controls the neuronal attachment to radial glial fibers and that N-cadherin-mediated adhesion complexes are reconstituted through Rab GTPases-dependent endocytic pathways to maintain the proper surface N-cadherin level and to promote neuronal migration.

Role for E-cadherin as an inhibitory receptor on epidermal gammadelta T cells

E-cadherin is a homophilic adhesion molecule that maintains homotypic intercellular adhesion between epithelial cells such as epidermal keratinocytes. E-cadherin is also expressed on resident murine epidermal γδ T cells, known as dendritic epidermal T cells (DETCs), but they express another receptor for E-cadherin, α(E)(CD103)β(7) integrin, as well. In this study, we analyzed functional differences between E-cadherin-mediated homophilic binding and heterophilic binding of α(E)β(7) integrin to E-cadherin in heterotypic intercellular adhesion of DETCs to keratinocytes. E-cadherin, but not α(E)β(7) integrin, was downregulated on activation of DETCs in vivo and in vitro. Short-term (1-h) adhesion of DETCs to keratinocytes in vitro was primarily mediated by α(E)β(7) integrin, and blocking of the binding of α(E)β(7) integrin to E-cadherin inhibited the lysis of keratinocytes by DETCs. Stable binding of E-cadherin on DETCs to plate-bound recombinant E-cadherin was observed only after 24-h culture in vitro. Cytokine production and degranulation by DETCs in response to suboptimal TCR cross-linking and mitogen stimulation were augmented by coligation of α(E)β(7) integrin. In contrast, engagement of E-cadherin on DETCs with immobilized anti-E-cadherin Ab, plate-bound recombinant E-cadherin, and E-cadherin on keratinocytes inhibited DETC activation. Therefore, E-cadherin acts as an inhibitory receptor on DETCs, whereas α(E)β(7) integrin acts as a costimulatory receptor. Differential expression of E-cadherin and α(E)β(7) integrin on resting and activated DETCs, as well as their opposite functions in DETC activation, suggests that E-cadherin and α(E)β(7) integrin on DETCs regulate their activation threshold through binding to E-cadherin on keratinocytes.

JS-K, a nitric oxide-releasing prodrug, modulates ß-catenin/TCF signaling in leukemic Jurkat cells: evidence of an S-nitrosylated mechanism

β-Catenin is a central player of the Wnt signaling pathway that regulates cell-cell adhesion and may promote leukemia cell proliferation. We examined whether JS-K, an NO-donating prodrug, modulates the Wnt/β-catenin/TCF-4 signaling pathway in Jurkat T-Acute Lymphoblastic Leukemia cells. JS-K inhibited Jurkat T cell growth in a concentration and time-dependent manner. The IC(50)s for cell growth inhibition were 14±0.7 and 9±1.2μM at 24 and 48h, respectively. Treatment of the cells with JS-K for 24h, caused a dose-dependent increase in apoptosis from 16±3.3% at 10μM to 74.8±2% at 100μM and a decrease in proliferation. This growth inhibition was also due, in part, to alterations in the different phases of the cell cycle. JS-K exhibited a dose-dependent cytotoxicity as measured by LDH release at 24h. However, between 2 and 8h, LDH release was less than 20% for any indicated JS-K concentration. The β-catenin/TCF-4 transcriptional inhibitory activity was reduced by 32±8, 63±5, and 93±2% at 2, 10, and 25μM JS-K, respectively, based on luciferase reporter assays. JS-K reduced nuclear β-catenin and cyclin D1 protein levels, but cytosolic β-catenin expression did not change. Based on a time-course assay of S-nitrosylation of proteins by a biotin switch assay, S-nitrsolyation of nuclear β-catenin was determined to precede its degradation. A comparison of the S-nitrosylated nuclear β-catenin to the total nuclear β-catenin showed that β-catenin protein levels were degraded at 24h, while S-nitrosylation of β-catenin occurred earlier at 0-6h. The NO scavenger PTIO abrogated the JS-K mediated degradation of β-catenin demonstrating the need for NO.

Evidence that Dkk-1 is dysfunctional in ankylosing spondylitis

OBJECTIVE

Dkk-1 is an inhibitory molecule that regulates the Wnt pathway, which controls osteoblastogenesis. This study was undertaken to explore the potential role of Dkk-1 in ankylosing spondylitis (AS), a prototypical bone-forming disease.

METHODS

Serum Dkk-1 levels were measured in 45 patients with AS, 45 patients with rheumatoid arthritis (RA), 15 patients with psoriatic arthritis (PsA), and 50 healthy subjects by sandwich enzyme-linked immunosorbent assay (ELISA). A functional ELISA was used to assess the binding of Dkk-1 to its receptor (low-density lipoprotein receptor-related protein 6). Furthermore, we studied the effect of sera from patients with AS and healthy subjects on the activity of the Wnt pathway in the Jurkat T cell model, with and without a neutralizing anti-Dkk-1 monoclonal antibody, by Western immunoblotting.

RESULTS

Serum Dkk-1 levels were significantly increased in patients with AS (mean +/- SEM 2,730 +/- 135.1 pg/ml) as compared with normal subjects (P = 0.040), patients with RA (P = 0.020), and patients with PsA (P = 0.049). Patients with AS receiving anti-tumor necrosis factor alpha (anti-TNFalpha) treatment had significantly higher serum Dkk-1 levels than patients with AS not receiving such treatment (P = 0.007). Patients with AS studied serially prior to and following anti-TNFalpha administration exhibited a significant increase in serum Dkk-1 levels (P = 0.020), in contrast to patients with RA, who exhibited a dramatic decrease (P < 0.001). Jurkat cells treated with serum from AS patients exhibited increased Wnt signaling compared with cells treated with control serum. In that system, Dkk-1 blockade significantly enhanced Wnt signaling in control serum-treated, but not AS serum-treated, Jurkat T cells.

CONCLUSION

Our findings indicate that in patients with AS, circulating bone formation-promoting factors functionally prevail. This can be at least partially attributed to decreased Dkk-1-mediated inhibition.

Down-regulation of β-catenin nuclear localization by aspirin correlates with growth inhibition of Jurkat cell line

In this study, we examined the effects of aspirin on the growth rates, subcellular distribution of beta-catenin protein, the expression of beta-catenin/TCF signaling pathway target gene cyclin D1 mRNA, and cell cycle of Jurkat cell line (Human T-acute lymphoblastic leukemia). Our results showed that the treatment with aspirin inhibited the growth of Jurkat cell line. Jurkat cells treated with 3 mmol/L of aspirin could significantly decrease nuclear localization of beta-catenin, and at 5 mmol/L of aspirin, the nuclear localization of beta-catenin was undetectable. QRT-PCR showed that the target gene cyclin D1 mRNA expression was gradually decreased with the dosage of aspirin. Aspirin induced G0/G1 cell cycle arrest in Jurkat cells. We are led to conclude that aspirin acts through beta-catenin-independent mechanisms. The effects of aspirin include down-regulation of beta-catenin nuclear localization and G0/G1 cell cycle arrest, which might serve as a means of growth inhibition in aspirin-treated human Jurkat cell line.

Epigenetic silencing of E- and N-cadherins in the stroma of mouse thymic lymphomas

Aberrant expression of some tumour suppressor genes and oncogenes by thymocytes had been involved in the development of primary thymic lymphomas induced by gamma-irradiation, but genetic alterations affecting critical genes expressed by stromal cells have not been yet explored. This paper analyzes a series of such tumours induced in C57BL/6J and in F1 hybrids of BALB/c and C57BL/6J mouse strains. As expected, hystopathological analyses revealed profound disorganizations within the thymus with a poor demarcation of the cortical and medullar areas. Immunological and quantitative on-line RT-PCR analyses confirm that E-cadherin (Cdh1) is essentially expressed by stromal cells of the thymus, while evidencing that the expression of this gene is significantly reduced in all tumours. In addition, and contrary to what one would expect, N-cadherin (Cdh2) that is exclusively expressed by stromal cells is likewise down-regulated in most of the thymic lymphomas. Although hypermethylation of the promoter region appears to be involved in the inactivation of Cdh2 in all tumours, additional epigenetic mechanisms mediated by repressors such as Snai1 may also play a role in Cdh1 silencing. These results represent the first reported case for tumour-associated gene alterations occurring not in the tumour cells per se, but in the stromal cells of primary thymic lymphomas. Additionally, since the expression of both genes is significantly up-regulated after a single high dose of gamma-radiation, but remained unchanged in treated thymic-lymphoma-free-mice, epigenetic down-regulation of E- and N-cadherin appears to occur concomitantly with the progression towards the most advanced stages of gamma-radiation-induced thymic lymphomas.

NO-donating aspirin inhibits the growth of leukemic Jurkat cells and modulates β-catenin expression

beta-Catenin has been implicated in leukemic cell proliferation. We compared the effects of aspirin (ASA) and the ortho, meta, and para positional isomers of NO-donating aspirin (NO-ASA) on cell growth and beta-catenin expression in human Jurkat T leukemic cells. Cell growth inhibition was strong: IC(50) for p-, o-, and m- were 20+/-1.6 (mean+/-SEM), 15+/-1.5, and 200+/-12 microM, respectively, in contrast to that of ASA (3200+/-375 microM). The para isomer of NO-ASA degraded beta-catenin in a dose- and time-dependent manner coinciding with increasing expression of activated caspase-3. The caspase inhibitor ZVAD blocked beta-catenin cleavage by p-NO-ASA and partially reversed cell growth inhibition by p-NO-ASA but not that by ASA. A denitrated analog of p-NO-ASA did not degrade beta-catenin indicating the importance of the NO-donating moiety. Our findings suggest that NO-ASA merits further study as an agent against leukemia.

Accumulation of cytoplasmic beta-catenin and nuclear glycogen synthase kinase 3beta in Epstein-Barr virus-infected cells

Epstein-Barr virus (EBV) causes infectious mononucleosis and is associated with cancers in immunocompromised populations. EBV establishes a latent infection and immortalizes and transforms B lymphocytes. Several latent proteins have profound effects on cellular growth, including activation of NF-kappaB, phosphatidylinositol 3'-OH kinase (PI3K) signaling, and notch signaling. Activation of PI3K can affect the activity of beta-catenin, the target of the wnt signaling pathway. Deregulation of beta-catenin is associated with a number of malignancies. To determine if beta-catenin is regulated by EBV infection, EBV-infected cells were examined for beta-catenin levels and localization. beta-Catenin was increased in EBV-positive tumor cell lines compared to EBV-negative lines, in EBV-infected Burkitt's lymphoma cell lines, and in EBV-transformed lymphoblastoid cell lines (LCL). In contrast to wnt signaling, EBV consistently induced the accumulation of beta-catenin in the cytoplasm but not the nucleus. The beta-catenin regulating kinase, glycogen synthase kinase 3beta (GSK3beta), was shown to be phosphorylated and inactivated in EBV-infected lymphocytes. Inactivated GSK3beta was localized to the nucleus of EBV-infected LCL. Neither the cytoplasmic accumulation of beta-catenin nor the nuclear inactivation of GSK3beta was affected by the inhibition of PI3K signaling. These data indicate that latent infection with EBV has unique effects on beta-catenin signaling that are distinct from activation of wnt and independent of its effects on PI3K.

Frequent beta-catenin overexpression without exon 3 mutation in cutaneous lymphomas

Beta-catenin is a ubiquitously cytoplasmic protein that has a critical role in embryonic development and mature tissue homeostasis through its effects on E-cadherin-mediated cell adhesion and Wnt-dependent signal transduction. Mutations that alter specific beta-catenin residues important for GSK-3beta phosphorylation, or increase the half-life of the protein, were identified in human cancer. However, the role of the Wnt pathway in B- and T-cell oncogenesis has not been extensively investigated. To assess the role of beta-catenin defects in primary cutaneous lymphomas, we examined the expression pattern and the genetic alteration of beta-catenin on 79 samples from 74 patients with primary cutaneous lymphomas from B- and T-cell origin. Immunohistochemical analysis revealed beta-catenin deregulation in five primary cutaneous B-cell lymphomas (21%) and in 21 primary cutaneous T-cell lymphomas (42%) without nuclear accumulation suggesting that activation and accumulation of beta-catenin may play an important role in the development of skin lymphomas. Mutation analysis of beta-catenin exon 3, which included the responsible element for Wnt signaling, was therefore done in 19 samples. However, genetic alterations of beta-catenin exon 3 were not detected in any of these cases suggesting that other regulatory mechanisms may be relevant in activating beta-catenin signaling in cutaneous lymphomas.

Expression of E-cadherin in human mast cell line HMC-1

E-cadherin is one of the cell adhesion molecules normally expressed on epithelial cells. We previously reported that murine bone marrow-derived mast cells express E-cadherin that could be involved in homophilic binding with epithelial cell E-cadherin. In the present study we examined whether E-cadherin is also expressed in human mast cell HMC-1. Gene expression of E-cadherin and beta-catenin was observed in HMC-1 by reverse transcription-polymerase chain reaction (RT-PCR), while N-cadherin expression was undetectable. cDNA sequencing of HMC-1 E-cadherin revealed no deletions or mutations. E-cadherin expression in HMC-1 was confirmed by immunoblotting as well as by flow cytometric analyses. In the presence of E-cadherin blocking antibody or a synthetic E-cadherin decapeptide with HAV sequence in culture medium, adhesion of HMC-1 cells to the A431 epithelial cell monolayer was slightly but significantly suppressed. In contrast, N- or P-cadherin decapeptides did not suppress the binding. These results indicated that human mast cell HMC-1 expresses E-cadherin, and is possibly involved in cellular interactions with epithelial cells, while other functions still remain to be elucidated.

E-cadherin-mediated interactions of thymic epithelial cells with CD103+ thymocytes lead to enhanced thymocyte cell proliferation

Cadherins are a family of cell adhesion molecules that mainly mediate homotypic homophilic interactions, but for E-cadherin, heterophilic interactions with the integrin alpha(E)(CD103)beta(7) have also been reported. In the human thymus, where thymocytes develop in close contact with thymic stromal cells, E-cadherin expression was detected on thymic epithelial cells. By immunofluorescence staining, the strongest expression of E-cadherin was observed on medullary thymic epithelial cells. These cells also express cytosolic catenins, which are necessary to form functional cadherin-catenin complexes. Regardless of their developmental stage, human thymocytes do not express E-cadherin, indicating that homophilic interactions cannot occur. Flow cytometric analysis revealed that the E-cadherin ligand CD103 is expressed on subpopulations of the early CD4(-) CD8(-) double-negative and of the more mature CD8(+) single-positive thymocytes. Using an in vitro cell adhesion assay, double-negative and CD8(+) single-positive thymocytes adhered strongly to isolated thymic epithelial cells. These adhesive interactions could be inhibited by antibodies against E-cadherin or CD103. CD8(+) thymocytes showed a proliferative response when incubated with thymic epithelial cells. This mitogenic effect was inhibited by antibodies against CD103, which strongly indicates a direct involvement of the adhesive ligand pair CD103-E-cadherin in human thymocyte cell proliferation.

Anticancer-drug-induced apoptotic cell death in leukemia cells is associated with proteolysis of beta-catenin

beta-Catenin is a known regulator of cell-cell adhesion and transcriptional regulation. However, the role of beta-catenin and its regulation in non-adherent cells has not been examined. Therefore, we examined the role and fate of beta-catenin during hematopoietic cell apoptosis using Jurkat T-acute lymphoblastic and U937 acute myeloblastic leukemia cells. The results presented here demonstrate that the treatment of Jurkat cells with the apoptosis inducers anti-Fas, TRAIL, staurosporine, and etoposide induces proteolytic fragments of beta-catenin, as did TRAIL and staurosporine in U937 cells. In Jurkat cells, beta-catenin was cleaved at both the N- and C-terminal after anti-Fas addition. Cleavage of intact beta-catenin was completely inhibited by caspase selective protease inhibitors. There was a clear accumulation of the large proteolytic fragment in Jurkat cells treated with lactacystin or N-acetyl-leucyl leucyl-methioninal (ALLM). These results suggest that both the proteasome and calpain may recognize the large beta-catenin fragment as a substrate for further degradation. Densitometric analysis demonstrated that the loss of intact beta-catenin was more rapid in the cell nucleus (beta-catenin T1/2 of approximately 1.5h in cytoplasm and 0.5h in nucleus). Down-regulation of beta-catenin-associated transcription was an early event in response to anti-Fas. These results suggest that beta-catenin plays a role in promoting Jurkat survival.

Regulation of leukemic cell adhesion, proliferation, and survival by beta-catenin

In epithelial cells beta-catenin plays a critical role as a component of the cell-cell adhesion apparatus and as a coactivator of the TCF/LEF (T-cell transcription factor/lymphoid enhancer binding factor) family of transcription factors. Deregulation of beta-catenin has been implicated in the malignant transformation of cells of epithelial origin. However, a function for beta-catenin in hematologic malignancies has not been reported. beta-Catenin is not detectable in normal peripheral blood T cells but is expressed in T-acute lymphoblastic leukemia cells and other tumor lines of hematopoietic origin and in primary lymphoid and myeloid leukemia cells. beta-Catenin function was examined in Jurkat T-acute lymphoblastic leukemia cells. Overexpression of dominant-negative beta-catenin or dominant-negative TCF reduced beta-catenin nuclear signaling and inhibited Jurkat proliferation and clonogenicity. Similarly, these constructs inhibited proliferation of K562 and HUT-102 cells. Reduction of beta-catenin expression with beta-catenin antisense down-regulated adhesion of Jurkat cells in response to phytohemagglutinin. Incubation of Jurkat cells with anti-Fas induced caspase-dependent limited proteolysis of beta-catenin N- and C-terminal regions and rapid redistribution of beta-catenin to the detergent-insoluble cytoskeleton, concomitant with a marked decline in nuclear beta-catenin signaling. Fas-mediated apoptosis was potentiated by inhibition of beta-catenin nuclear signaling. The data suggest that beta-catenin can play a significant role in promoting leukemic cell proliferation, adhesion, and survival.

N-cadherin involvement in the heterotypic adherence of malignant T-cells to epithelia

N-cadherin, a cell adhesion molecule normally found in neural cell tissue, has been found recently to be expressed on the surface of malignant T-cells. The function of N-cadherin on these cells remains unclear. Heterotypic assays between Molt-3 T lymphoblastic leukemia cells and Caco-2 epithelial monolayers were examined under different conditions to assess the functional role of N-cadherin. The results indicate that adherence of Molt-3 cells to Caco-2 monolayers was reduced significantly following pretreatment of Molt-3 cells with 100 microM of an N-cadherin-derived antagonist decapeptide. In contrast, pretreatment of Molt-3 cells with an anti-N-cadherin antibody raised against the first 20 amino acids of N-cadherin sequence led to a surprisingly marked enhancement of Molt-3 cell adherence to Caco-2 monolayers. In addition, the presence of anti-N-cadherin antibody neutralized the inhibitory effect of anti-ICAM-1 on Molt-3 adhesion to Caco-2 monolayers. This novel finding demonstrates that external stimulus through the N-cadherin amino terminus can modulate adhesion of malignant T-cells to epithelia and may promote their ability to invade or metastasize to inflammatory sites.

N-cadherin is developmentally regulated and functionally involved in early hematopoietic cell differentiation

The cadherins, an important family of cell adhesion molecules, are known to play major roles during embryonic development and in the maintenance of solid tissue architecture. In the hematopoietic system, however, little is known of the role of this cell adhesion family. By RT-PCR, western blot analysis and immunofluorescence staining we show that N-cadherin, a classical type I cadherin mainly expressed on neuronal, endothelial and muscle cells, is expressed on the cell surface of resident bone marrow stromal cells. FACS analysis of bone marrow mononuclear cells revealed that N-cadherin is also expressed on a subpopulation of early hematopoietic progenitor cells. Triple-color FACS analysis defined a new CD34(+) CD19(+) N-cadherin(+) progenitor cell population. During further differentiation, however, N-cadherin expression is lost. Treatment of CD34(+) progenitor cells with function-perturbing N-cadherin antibodies drastically diminished colony formation, indicating a direct involvement of N-cadherin in the differentiation program of early hematopoietic progenitors. N-cadherin can also mediate adhesive interactions within the bone marrow as demonstrated by inhibition of homotypic interactions of bone-marrow-derived cells with N-cadherin antibodies. Together, these data strongly suggest that N-cadherin is involved in the development and retention of early hematopoietic progenitors within the bone marrow microenvironment.

Truncated DCC reduces N-cadherin/catenin expression and calcium-dependent cell adhesion in neuroblastoma cells

The deleted in colorectal cancer (DCC) protein is important in the pathway guidance of cells and cell processes during neural development, and DCC has also been implicated in the aberrant cellular migrations of neuroblastoma dissemination. We attempted to further define DCC protein function by the overexpression of full-length and truncated DCC constructs in a human neuroblastoma cell line. Overexpression of the truncated DCC protein resulted in a less epithelioid morphology. This was accompanied by decreases in expression of N-cadherin and alpha- and beta-catenin by immunoblot and Northern blot analysis. Levels of desmoglein were relatively less affected, whereas endogenous DCC protein levels were increased in the truncated transfectants. N-cadherin immunofluorescence was consistent with the immunoblot studies and localized the protein to the cytoplasm and sites of cell-cell contact. Cell aggregation studies demonstrated diminished calcium-dependent aggregation in the truncated transfectants. In conclusion, overexpression of a truncated DCC protein in neuroblastoma cells resulted in the loss of an epithelioid morphology, diminished expression of N-cadherin and alpha- and beta-catenin, and diminished calcium-dependent cell adhesion. These studies provide the first evidence of an apparent functional link between DCC and N-cadherin/catenin-dependent cell adhesion.

E-cadherin and cadherin-associated cytoplasmic proteins are expressed in murine mast cells

Cadherins, calcium-dependent cell adhesion molecules, play crucial roles, not only in the maintenance of tissue integrity, but also in the regulation of many aspects of cell behavior. We investigated the expression of "classic" E-, N- and P-cadherins in bone marrow-derived cultured mast cells (BMMC) and peritoneal mast cells (PMC) from mice. Flow cytometric analysis and immunocytochemical staining indicated that E-cadherin was expressed on the cell surface of BMMC and also at lower levels on PMC. N-cadherin was also expressed on the surface of BMMC, but not of PMC, whereas P-cadherin expression was seen in neither cell type. Significant expression of E- and N-cadherin mRNA was observed in BMMC by reverse transcriptase-polymerase chain reaction (RT-PCR), but PMC expressed only E-cadherin mRNA. Western blotting analysis indicated expression of alpha- and beta-catenins and p120-catenin (or p120 cas) in BMMC, whereas PMC showed less intense expression of alpha- and beta-catenins with high levels of p120 expression. Analyses of beta-catenin or E-cadherin immunoprecipitates from BMMC lysate revealed that alpha-catenin, beta-catenin, and E-cadherin were co-precipitated, suggesting that E-cadherin and catenins form a complex in mast cells. Addition of a blocking antibody of homophilic E-cadherin interactions, or a synthetic E-cadherin-binding decapeptide containing the histidine-alanine-valine (HAV) sequence in methylcellulose cultures of gut intraepithelial mononuclear cells or BMMC, significantly suppressed the clonal growth of mast cells. Furthermore, the blocking antibody or synthetic decapeptide significantly suppressed BMMC adhesion to E-cadherin-expressing F9 cell monolayers. These results indicated that E-cadherin and associated cytoplasmic proteins in mast cells might be involved in the regulation of certain stages of mast cell differentiation and cell-cell interactions.

N-cadherin expressed on malignant T cell lymphoma cells is functional, and promotes heterotypic adhesion between the lymphoma cells and mesenchymal cells expressing N-cadherin

Cadherins are Ca2+-dependent cell-cell adhesion molecules, and are involved in the formation and maintenance of the organocellular architecture. Using a combination of molecular biologic and biochemical methods, we analyzed cadherins expressed on cultured human malignant lymphoma cell lines (adult T cell lymphomas, human T cell leukemia virus type 1-negative T cell lines, and thymus-derived lymphoma cell lines), and obtained evidence that N-cadherin is the major cadherin expressed on these cells. These cells were found to form cell aggregates in a Ca2+-dependent manner, and more importantly to coaggregate and adhere with cells expressing N-cadherin, suggesting that N-cadherin on lymphoma cells is functionally active. Therefore, N-cadherin expressed on lymphoma cells could underlie the frequent invasion of these cells into the mesenchymal tissue in the skin and the central nervous system.

Altered cell adhesion activity by pervanadate due to the dissociation of alpha-catenin from the E-cadherin.catenin complex

Leukemia cells (K562) that grow as non-adhesive single cells and have no endogenous cadherin were transfected with an E-cadherin expression vector, and cell clones stably expressing E-cadherin on their surface were established. The expression of E-cadherin induced the up-regulation of catenins, and E-cadherin became associated with catenins. The transfected cells grew as floating aggregates. Cell aggregation was Ca2+-dependent and was inhibited by E-cadherin antibodies. The aggregates dissociated into single cells on the addition of pervanadate. Pervanadate caused a dramatic augmentation of the phosphorylation of E-cadherin, beta-catenin, and gamma-catenin (plakoglobin), but alpha-catenin was not detectably phosphorylated. After pervanadate treatment, beta-catenin and gamma-catenin migrated more slowly on gel electrophoresis, suggesting changes in their conformations due to eventual changes in their phosphorylation levels. In the treated cells, a significant amount of alpha-catenin was dissociated from the E-cadherin.catenin complex. Aggregates of cells expressing an E-cadherin chimeric molecule covalently linked with alpha-catenin were not dissociated on pervanadate treatment, supporting the idea that the dissociation of alpha-catenin from the complex underlies the observed E-cadherin dysfunction.

Identification of the domain of alpha-catenin involved in its association with beta-catenin and plakoglobin (gamma-catenin)

alpha-Catenin is a 102-kDa protein exhibiting homology to vincuin, and it forms complexes with cadherins or the tumor-suppressor gene product adenomatous polyposis coli through binding to beta-catenin or plakoglobin (gamma-catenin). The incorporation of alpha-catenin into the cadherin-catenin complexes is a prerequisite for expression of the cell-adhesive activity of cadherins. Using an in vitro assay system involving bacterially expressed proteins, we localized a region in alpha-catenin required for molecular interaction with beta-catenin and plakoglobin. Analysis of various truncated alpha-catenin molecules revealed that amino-terminal residues 48-163 are able to bind to beta-catenin and plakoglobin. Consistent with the observation that beta-catenin and plakoglobin bind to the same region of alpha-catenin, beta-catenin competed with the binding of plakoglobin to alpha-catenin and vice versa. Under the conditions used, beta-catenin bound to alpha-catenin with higher affinity than did plakoglobin. Scatchard analysis indicated that the affinity of the interaction between alpha-catenin and beta-catenin or that between alpha-catenin and plakoglobin was moderately strong (Kd = 3. 8 x 10(-8) and 7.7 x 10(-8), respectively). When transfected into L cells expressing E-cadherin, the amino-terminal region of alpha-catenin (from residue 1 to 226) formed complexes with beta-catenin supporting the in vitro binding experiment results.