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Journal of Cancer Research and Clinical Oncology logoLink to Journal of Cancer Research and Clinical Oncology
. 2003 Feb 12;129(1):57–64. doi: 10.1007/s00432-002-0404-8

DC-CLM, a cadherin-like molecule cloned from human dendritic cells, inhibits growth of breast cancer cells

Yingming Jiang 1, Tao Wan 1, Guoyou Chen 1, Fangming Xiu 2, Dajing Xia 2, Weiping Zhang 1, Xiangyang Zhou 1, Xuetao Cao 1,2,✉
PMCID: PMC12161908  PMID: 12618902

Abstract

Purpose

To identify the characteristics and function of a cadherin-like molecule, cloned from a human dendritic cell (DC) cDNA library and designated DC-derived cadherin-like molecule (DC-CLM).

Methods

The mRNA expression of DC-CLM in tissues and cells was analyzed by Northern blot and RT-PCR, respectively. In order to express DC-CLM in target cells, we constructed a pcDNA3.1/DC-CLM expression vector and transfected it into MCF-7 human breast cancer cells. Tumor growth was demonstrated by cell proliferation and colony formation.

Results

DC-CLM cDNA encoded a protein of 260 amino acids and the gene was localized to chromosome 5q31. The predicted protein possessed a definitive cadherin-specific sequence motif and shared homology with classical cadherin. However, no transmembrane segment was observed in DC-CLM. Northern blot revealed the ubiquitous nature of DC-CLM transcripts in human tissues, with high expression in heart, brain, prostate, testis and ovary. RT-PCR demonstrated that DC-CLM was widely expressed in hematopoietic and epithelial tumor cell lines, but was not expressed in MCF-7. Interestingly, DC-CLM expression was upregulated in DC activated by lipopolysaccharides. DC-CLM expression in the stable transfectant (MCF-7/DC-CLM) was confirmed by RT-PCR and Western blot. DC-CLM protein was found to be secreted by MCF-7/DC-CLM but not expressed on the membrane of MCF-7/DC-CLM. DC-CLM transfection resulted in significant inhibition of in vitro growth and colony formation of MCF-7 cells.

Conclusions

A cadherin-like molecule DC-CLM was cloned from human DC and it may be a soluble cadherin-like molecule for tumor suppression. DC-CLM was upregulated in activated DC and may be involved in the effector function of activated DC.

Keywords: Cadherins, Dendritic cells, Molecular cloning, Tumor suppression, Breast cancer

Introduction

Cadherins are a superfamily of transmembrane glycoproteins mediating calcium-dependent homophilic cell-cell adhesion and play a vital role in various morphogenetic events in multicellular organisms (Angst et al. 2001a; Takeichi 1993). The cadherin superfamily includes classical cadherins, protocadherins, desmogleins, desmocollins, truncated-type cadherins (T-cadherins) and other cadherin-related proteins (Angst et al. 2001b). Cadherins are characterized by a tandemly repeated unique domain called the cadherin motif or extracellular domains containing negatively charged DXD, DRE and DXNDNAPXF peptide sequence motifs which engage in Ca2+-dependent homophilic interactions to specify differential cell-cell connections (Nagar et al. 1996; Wu and Maniatis 1999). The characteristic cytoplasmic domain interacts with beta-catenin, which connects with the cytoskeleton through alpha-catenin and determines cell shape and motility. However, the cytoplasmic domain is not a prerequisite for the function of cadherins. T-cadherins, which are devoid of the transmembrane and cytoplasmic domain, are involved in cell-cell contact in epithelial cells and neurons (Ranscht and Dours-Zimmermann 1991; Trusolino et al. 1993).

The potential role of cadherins in cancer development and progression has been widely investigated. It is now clear that cadherin dysfunction is associated with the growth, invasion and metastasis of tumor cells. E-cadherin, which has been studied extensively in breast cancer (Moll et al. 1993), gastric and colon carcinoma (Waki et al. 2002; Salahshor et al. 2001; Mueller et al. 2000), and lung tumors (Bremnes et al. 2002), is related to the phenotype of tumor cells, and has been found to act as a tumor suppressor. H-cadherin/T-cadherin/cadherin-13, which is truncated and lacks both transmembrane and cytoplasmic domains, has also been implicated in tumor suppression (Lee 1996). H-cadherin transfection significantly inhibits the growth and invasion of breast cancer cells in vitro and tumor formation in vivo (Lee et al. 1998). Abnormalities or decreased expression in desmosomal cadherins are correlated with increased invasion and metastasis of squamous cell carcinoma (Jiang et al. 1997). Protocadherin KLC, which is significantly decreased in kidney, liver and colon cancers, suppresses tumor formation in nude mice (Okazaki et al. 2002). However, some cadherins, such as N-cadherin and cadherin-11, promote tumor growth and invasion (Nieman et al. 1999; Pishvaian et al. 1999).

Dendritic cells (DC) are specialized antigen-presenting cells, and play a pivotal role in the induction of antitumor immunity by stimulating tumor-specific T lymphocytes. However, DCs can also produce TNF-α (Verhasselt et al. 1997) and NO (Lu et al. 1996) and express membrane FasL (Lu et al. 1997) and TRAIL (Liu et al. 2001) to inhibit or kill the tumor cells. We have shown that the effector function of DCs can be enhanced after the DCs are activated or stimulated by inflammatory products such as lipopolysaccharide (LPS) or cytokines such as interferon-β (Liu et al. 2001). Exploring the differentially expressed genes in DCs after exposure to stimuli may provide helpful clues to elucidate the mechanism.

Here we report a full-length cDNA, cloned from a human DC cDNA library, that encodes a soluble molecule containing the sequence of the cadherin extracellular domain. We designated it DC-derived cadherin-like molecule (DC-CLM). It was ubiquitous in human tissues and widely expressed in hematopoietic and epithelial tumor cell lines. Upregulation of DC-CLM expression was observed in human DCs activated by LPS. Transfection of MCF-7 human breast cancer cells with DC-CLM cDNA led to growth inhibition of tumor cells. The results suggest that DC-CLM is a soluble cadherin-like molecule and may be related to tumor suppression and the effector function of DCs.

Materials and methods

Cell lines and culture

The isolation of CD14+ human monocytes and generation of peripheral blood monocyte-derived DCs (MoDC) have been described previously by us. Monocytes and DCs with a purity of >90% were used in the following experiments. The cell lines used for RT-PCR analysis of DC-CLM expression were: SMMC 7721 (hepatocellular carcinoma), Jurkat (acute T-cell leukemia), THP-1 (acute monocytic leukemia), Molt4 (acute lymphoblastic leukemia), K562 (chronic myelogenous leukemia), HL60 (promyelocytic leukemia), NB4 (promyelocytic leukemia), U937 (histiocytic lymphoma), Raji (Burkitt's lymphoma), Daudi (Burkitt's lymphoma), Namalwa (mature B-cell neoplasm), Ramos (mature B-cell neoplasm), Hut78 (cutaneous T lymphoma), A549 (lung carcinoma), A172 (breast adenocarcinoma), PC-3 (prostate adenocarcinoma), MCF-7 (breast adenocarcinoma), HeLa (cervix epitheloid carcinoma), CaoV-3 (ovary adenocarcinoma), HT29 (colon adenocarcinoma), LoVo (colon adenocarcinoma), Fib (fibroblast) and WI-38 (human lung fibroblast). The medium used for cell culture was RPMI-1640 supplemented with 10% fetal bovine serum (FBS) (Hyclone, Logan, Utah), 2 mM glutamine, 50 μM mercaptoethanol, 100 U/ml penicillin, and 100 μg/ml streptomycin. For cell activation, DCs and monocytes were treated with 100 ng/ml LPS (Sigma, St. Louis, Mo.) for 30 h.

Cloning of DC-CLM cDNA

Full-length cDNA of DC-CLM was isolated directly from the cDNA library of human DCs by large-scale sequencing, as described previously by us (Cao et al. 2000). Briefly, a DC cDNA library was constructed using the SuperScript Plasmid System for cDNA synthesis and plasmid cloning (Life technologies, Grand Island, N.Y.) according to the manufacturer's manual. By large-scale sequencing of the DC cDNA library, we established an inhouse database of 25,668 expressed sequence tags. A cDNA clone SBBI36 contained an open reading frame (ORF) potentially encoding a protein typical of the cadherin superfamily, which was designated DC-CLM. The nucleotide and amino acid sequences were analyzed using the GCG package.

Northern blot analysis

Northern blot filters containing human poly(A)+ RNA (2 μg/lane) from various tissues were purchased from Clontech Laboratories (Palo Alto, Calif.). The 495-bp cDNA fragment of DC-CLM synthesized by RT-PCR was used as a template for probe synthesis. The filters were hybridized in ExpressHyb hybridization solution (Clontech) according to the manufacturer's instructions with DC-CLM cDNA probe labeled with [32P]dCTP (Amersham Pharmacia). After hybridization, the filters were stringently washed at 50°C for 20 min in 1×SSC and 0.1% SDS, and this was followed by autoradiography.

RT-PCR analysis of DC-CLM expression

Total cellular RNA was extracted with Trizol reagent, and cDNA was synthesized using Superscript II reverse transcriptase (Life Technologies). The specific primers used for DC-CLM amplification were 5′-GAGTTAATTCCGATGGTG -3′ (upstream) and 5′-ATTTCTGGGCTGTTGTCG-3′ (downstream), with the predicted product of 495 bp. The upstream primer of human β-actin is 5′-GCATCGTGATGGACTCCG-3′, and its downstream primer is 5′-TCGGAAGGTGGACAGCGA-3′, with the expected product of 600 bp. The amplification parameters were denaturing for 20 s at 94°C, annealing for 30 s at 54°C, and extension for 30 s at 72°C on a thermocycler PCR9600 (Applied Biosystems, Foster City Calif.). After 30 cycles of amplification, the products were subjected to electrophoresis on 2% agarose gel and ethidium bromide staining.

Recombinant expression of DC-CLM protein in MCF-7 cells

The primers used for constructing the DC-CLM expression vector were 5′-tctagaccgccATGTTTATATCAGGATCCGTG G-3′ (upstream) and 5′-ggggtaccGATGGGGGAAGAAGAAGAATAAATCTTGAATGG-3′ (downstream). The expected product was 799 bp. An XbaI restriction site (underlined) was added before the start codon of DC-CLM, and KpnI was introduced at the C-terminal for in-frame ligation with 6×His. The PCR fragment was inserted with its orientation known into the pcDNA3.1/Myc-His (Invitrogen) expression vector at the sites of XbaI and KpnI under the control of CMV promoter/enhancer. The plasmid of pcDNA3.1/DC-CLM was transfected into MCF-7 cells by lipofectamine (Life Technologies) in the presence of 0.6 mg/ml G418 (Calbiochem, La Jolla, Calif.). After 2 weeks of screening, stable positive clones were obtained and confirmed by RT-PCR and Western blot analysis using anti-His antibody. The clone stably expressing DC-CLM was named MCF-7/DC-CLM and used for functional analysis of DC-CLM. The clone transfected with mock vector pcDNA3.1/Myc-His was named MCF-7/Mock.

Western blot analysis of DC-CLM

To detect the expression of DC-CLM protein, MCF-7/DC-CLM and MCF-7/Mock cells (70% confluence) were collected and sonicated for 5 min (300 W) in cold phosphate buffer. After centrifugation for 30 min (20,000 g, 4°C), the soluble lysate and precipitated cells plus culture supernatant were used for Western blot analysis as previously described (Zhang et al. 2001). Blots were incubated with mouse anti-His monoclonal antibody (Santa Cruz Biotechnology, Santa Cruz, Calif.) for 2 h at 4°C and horseradish peroxidase-coupled anti-mouse second antibody (New England Biolabs, Beverley, Mass.) at a dilution of 1:2000 for 1 h at room temperature. Membrane was visualized via a luminol detection kit (Santa Cruz) and exposed to X-ray film (Kodak XAR film) for 10–45 s.

Assay for MCF-7 cell proliferation

MCF-7/DC-CLM, MCF-7/Mock and parental MCF-7 cells (2×104 cells/100 μl/well) were cultured in 96-well plates (Corning, N.Y.) in RPMI-1640 containing 10% FBS. Plates were incubated in an atmosphere containing 5% CO2 at 37°C for the indicated times. 3H-Thymidine (1 μCi/well) was added to the medium 24 h before the end of culture. The medium was aspirated and the cells were harvested onto glass-fiber strips after trypsin digestion. Incorporated radioactivity (counts per minute) was measured in a liquid scintillation counter. The data are presented as the mean±SD counts per minute of triplicate wells.

Assay for colony formation

The assay was performed according to a previously described method (Perez and Buckwalter 1998; Kogai et al. 2000). Briefly, aliquots of MCF-7/DC-CLM, MCF-7/Mock and parental MCF-7 cells (1×103 cells/well) were plated in triplicate into six-well culture plates (Corning) in RPMI-1640 with 10% FBS. After incubation for 2 weeks, the plates were washed twice with phosphate-buffered saline and immediately fixed and stained with Giemsa solution. The plates were rinsed with distilled water, and colonies containing at least 50 cells were counted.

Results

Identification and sequence analyses of DC-CLM

The full-length cDNA clone of DC-CLM was isolated from the human DC cDNA library and was 1161 bp in length. It contained a 783-nucleotide ORF encoding a peptide of 260 amino acids. The gene was mapped to chromosome 5q31. Many amino acids characteristic of the cadherin ectodomain are conserved in the cadherin-like protein. The sequence of DC-CLM predicted two characteristic cadherin repeat signatures, VXDXNDNXPXF and XIXDXNDNXP, which are common to all classical cadherins (Fig. 1). DC-CLM also contained conserved sequence motifs DXDXGXN and AXDXGXPXR. DXD and LDRE, which are the major conserved features among typical cadherins and putatively form calcium-binding pockets. Moreover, DC-CLM comprised an N-linked glycosylation site, a tyrosine phosphorylation site and three PKC phosphorylation sites with the predicted molecular mass of 28.7 kDa before glycosylation. DC-CLM protein shared moderate homology with the classical cadherin, with 42.7% similarity and 32.0% identity with N-cadherin, and 37.4% similarity and 30.1% identity with E-cadherin (Fig. 2). However, structure analysis of the DC-CLM protein revealed that there was no significant transmembrane segment, suggesting that DC-CLM might belong to the T-cadherin family rather than the classical cadherin family.

Fig. 1.

Fig. 1.

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Nucleotide and deduced amino acid sequences of human DC-CLM. The amino acid sequence is shown as a one-letter code (asterisk stop codon, boxes conserved cadherin motifs, hollow triangle possible N-linked glycosylation site, solid circles protein kinase C phosphorylation sites, solid triangle tyrosine kinase phosphorylation site). The nucleotide sequence of DC-CLM has been deposited in GenBank with the accession number AF135156

Fig. 2.

Fig. 2.

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Alignments of deduced amino acid sequences of DC-CLM and the classical cadherin ectodomain. Amino acids identical to DC-CLM are shown on a black background and those similar to DC-CLM are shown on a stippled background. The cadherin ectodomain repeat signatures are indicated by the single lines. Gaps (...) have been introduced to maximize the homology

Expression pattern of DC-CLM mRNA

Northern blot analysis revealed that an approximately 7.5-kb transcript of DC-CLM was highly expressed in heart, brain, prostate, testis, ovary, small intestine and also in placenta, lung, liver, kidney, pancreas, and colon to a certain extent, but no signals were detected in skeletal muscles, spleen, thymus or peripheral blood lymphocytes (Fig. 3). RT-PCR analysis demonstrated that DC-CLM was widely expressed in a wide spectrum of tumor cell lines and normal cell lines. High expression of DC-CLM was observed in tumor cell lines of hematopoietic origin including K562, NB4, Hut78, Jurkat and Molt-4, and of epithelium origin including Lovo, SMMC 7721 and A549. No expression was detected in THP-1, HL60, Raji or the breast cancer cell line MCF-7 (Fig. 4). We therefore selected the MCF-7 cell line as the model to transfect DC-CLM cDNA and obtained a stable transfectant (MCF-7/DC-CLM).

Fig. 3.

Fig. 3.

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Northern blot analysis of DC-CLM mRNA expression in human tissues. Poly(A)+ RNA (2 μg) from the indicated tissues was hybridized with a 32P-labeled DC-CLM cDNA probe and washed with high stringency. The RNA size markers are indicated on the left. The data are representative of two independent experiments

Fig. 4.

Fig. 4.

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RT-PCR analysis for DC-CLM mRNA expression in various cell lines. The tumor cell lines were subjected to RT-PCR analysis for DC-CLM expression. Human β-actin was also amplified as a positive control. After 30 cycles of amplification, the products were analyzed on 2% agarose gel. The data are representative of two independent experiments

We further analyzed DC-CLM expression in monocytes and DCs. Weak expression of DC-CLM was detected in inactivated monocytes and DCs. Interestingly, upregulation of DC-CLM expression was observed in DCs after stimulation with LPS. After 25 cycles of PCR amplification with specific primers, a specific DC-CLM product was detectable in LPS-stimulated DCs in contrast to their unstimulated counterparts (data not shown). After 30 cycles of PCR amplification, DC-CLM expression was detectable in unstimulated DCs, and more significant expression of DC-CLM was observed in LPS-stimulated DCs, whereas monocytes did not show an increase in DC-CLM expression even if they were activated with LPS for 30 h (Fig. 5). Upregulation of DC-CLM expression in monocyte-derived DCs indicated their potential role in the biological functions of DCs.

Fig. 5.

Fig. 5.

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DC-CLM expression in DCs and monocytes. Freshly isolated monocyte-derived DCs (MoDC) and monocytes with or without stimulation with LPS (100 ng/ml, 30 h) were subjected to RT-PCR analysis for human DC-CLM expression. Human β-actin was also amplified as a positive control. After 30 cycles of amplification, the products were analyzed on 2% agarose gel

Recombinant expression of DC-CLM protein

RT-PCR analysis confirmed the expression of DC-CLM in MCF-7/DC-CLM, and no expression of DC-CLM in controls (Fig. 6A). In order to monitor DC-CLM protein expression, we introduced a 6×His tag into the C-terminal of DC-CLM protein. By Western blot analysis, the His-tagged DC-CLM was found in the culture supernatant and soluble lysate of sonicated MCF-7/DC-CLM cells, and was found to have an apparent molecular mass of about 29 kDa (Fig. 6B), which was almost equal to that predicted from its amino acid sequence, suggesting that no glycosylated DC-CLM was expressed in MCF-7 cells. However, no band was detected in the precipitate of the cell lysate of sonicated MCF-7/DC-CLM cells, indicating that DC-CLM was not expressed on the membrane of MCF-7/DC-CLM. Thus, DC-CLM is a soluble molecule secreted by MCF-7/DC-CLM cells and is not a membrane protein. His-tagged DC-CLM could be efficiently purified by affinity chromatography. Therefore, the MCF-7/DC-CLM transfectants may be useful in functional investigations.

Fig. 6A, B.

Fig. 6A, B.

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DC-CLM expression in MCF-7 cells transfected with full-length DC-CLM cDNA. The stable transfectants of MCF-7 cells with pcDNA3.1 vector (MCF-7/Mock) and pcDNA3.1/DC-CLM (MCF-7/DC-CLM) were established as described in Materials and methods. A RT-PCR confirmation of DC-CLM expression in MCF-7/DC-CLM cells. Human β-actin was amplified as positive control of PCR. After 30 cycles of amplification, the products were analyzed on 2% agarose gel. B Western blot analysis of His-tagged DC-CLM protein. Samples were fractionated by a SDS-PAGE under reducing condition and transferred onto nitrocellulose membrane, incubated with anti-His mAb and HRP-coupled anti-mouse second antibody, and detected with a chemiluminescent substrate LumiGLO. Bands of a protein of about 29 kDa were detected in the culture supernatant (lane 1) and soluble lysate of the sonicated MCF-7/DC-CLM cells (lane 2). No band was found in the precipitate of sonicated MCF-7/DC-CLM cells (lane 3). Lanes 4–6 Corresponding expression in MCF-7/Mock cells

Effect of DC-CLM transfection on the proliferation of MCF-7 cells in vitro

To examine whether the DC-CLM could affect the proliferation of tumor cells, the proliferation of MCF-7/DC-CLM cells was evaluated in terms of 3H-TdR incorporation. After 72 h of culture, proliferation of MCF-7/DC-CLM cells was inhibited significantly as compared with that of MCF-7/Mock and parental MCF-7 cells (P<0.05), indicating that DC-CLM inhibited the in vitro growth of MCF-7 cells (Fig. 7A).

Fig. 7A, B.

Fig. 7A, B.

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Stable DC-CLM expression inhibited the in vitro proliferation and colony formation of transfected MCF-7 cells. A In vitro proliferation of MCF-7 cells was inhibited by DC-CLM transfection. Transfected and untransfected cells were cultured in 96-well flat-bottomed plates with 2×104 cells per well for the indicated times. Before the end of culture, the systems were pulsed with 3H-TdR for 24 h. The results are shown as mean counts per minute of triplicate wells. B The colony formation of MCF-7 cells was inhibited by DC-CLM transfection. The above cells were plated into six-well culture plates at 1×103 cells per well and incubated for 2 weeks. Colonies containing at least 50 cells were counted. The plating efficiency of untransfected cells was about 30%. The results are expressed as cloning efficiency of triplicate wells. *P<0.05 vs control

Effect of DC-CLM transfection on colony formation of MCF-7 cells

The effect of DC-CLM on the colony growth of MCF-7 cells was assessed. As shown in Fig. 7B, a significant reduction in cloning efficiency was observed in MCF-7/DC-CLM cells as compared with that in MCF-7/Mock and parental MCF-7 cells (P<0.05). The result suggested that DC-CLM could inhibit the colony formation of MCF-7 cells.

Discussion

Many molecules classified as cadherin superfamily members have been identified in the past few years (Angst et al. 2001a). However, how many members belong to this family is unknown. It is generally accepted that a typical cadherin comprises five or more cadherin extracellular subdomain repeats, a transmembrane domain and a characteristic cytoplasmic domain, which links to catenins and the cytoskeleton. T-cadherins, which lack the characteristic cytoplasmic domain and transmembrane segment, are found in the nervous system and tumors of different tissue origin and play an important role in cell-cell adhesion (Ranscht and Dours-Zimmermann 1991; Takeuchi et al. 2002; Wyder et al. 2000). The most typical T-cadherin is H-cadherin, which can suppress tumor growth and has been widely investigated in tumor tissues (Sato et al. 1998; Lee et al. 1998; Lee 1996). The soluble fragments of cadherins are a special form of T-cadherin and also play an important role in the maintenance of cell-cell morphology. Soluble fragments of E-cadherin can disrupt cell-cell adhesion in cultured epithelial cells (Ranscht and Dours-Zimmermann 1991). Plasmin produces extracellular E-cadherin fragments which regulate E-cadherin function in cells containing an intact E-cadherin/catenin complex and stimulate tumor growth (Ryniers et al. 2002).

Here we identified a cadherin-like molecule from a human DC cDNA library. The sequence analysis of DC-CLM revealed that, of the known cadherins, DC-CLM showed a close resemblance to the ectodomains of E-cadherin and N-cadherin. However, DC-CLM lacked a transmembrane domain and conserved cytoplasmic domain, which was of great interest because of their potential function, and might be another T-cadherin. Typically, cadherin-like proteins share conserved structural features in their extracellular domain, including VXDXNDNAPXF, DXDXGXN and AXDXGXPXR motifs. DC-CLM shared several conserved cadherin motifs and the calcium-binding pocket, which suggested that DC-CLM might have adhesion capability. Western blot analysis demonstrated that DC-CLM was not a membrane protein and was expressed in the soluble form, which was consistent with the fact that DC-CLM did not have a transmembrane sequence. DC-CLM was expressed in many tissues and cell lines such as heart, brain and ovary, indicating a broad range of functions in the human body.

Cadherin expression in DCs has also been investigated. It is widely recognized that E-cadherin is expressed in Langerhans cells, a type of immature DC (Blauvelt et al. 1995; Borkowski et al. 1994). With maturation of DCs, the expression of E-cadherin is reduced to facilitate the migration of DCs to lymphoid organs (Riedl et al. 2000). In solid tumors, infiltration of DCs is found, and E-cadherin expression in DCs is upregulated by tumor cells, which is thought to inhibit the migration of DCs to present tumor antigens (Padovan et al. 2002). The expression of DC-CLM in DCs enriches the relationship between cadherins and DCs. Interestingly, we found that LPS was able to promote the expression of DC-CLM in DCs.

So the physiological and pathological significance of DC-CLM in DCs remains to be investigated. Recently, the effector function of LPS-activated DCs in inhibiting tumor cell growth has been demonstrated in a wide spectrum of human tumor cell lines in vitro, and this inhibitory effect is independent of TNF-α, FasL and NO (Chapoval et al. 2000). It is suggested that there are other soluble factors secreted by activated DCs that suppress tumor growth. It is noteworthy that, like other members of cadherin family, DC-CLM was able to inhibit the growth and colony formation of human breast cancer cells in the transfection study, suggesting that DC-CLM might be a candidate for such factors. Although the mechanism by which cadherins act on tumor growth is obscure, the alteration of cell-cell adhesion and signal transduction are thought to be important (Peng et al. 2002; Conacci-Sorrell et al. 2002; van de Wetering et al. 2001). Further study should be performed to investigate the direct inhibitory effect of DC-CLM protein on tumor growth and the effect of DC-CLM on cell-cell adhesion and signal transduction.

Acknowledgements

We sincerely thank Mrs. Mei Jin and Mrs. Qunying Shi for their excellent technical assistance.

Footnotes

This work was supported by grants from the National Natural Science Foundation (30100166, 30121002) and the National Key Basic Research Program of China (2001CB510002)

Y.J. and T.W. contributed equally to this work.

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