Biochemical interactions among intercellular adhesion molecules expressed by airway epithelial cells

Intercellular adhesion between adjacent airway epithelial cells plays a critical role in maintaining the barrier function of the respiratory mucosa. In the current study, we examined the expression and interaction of cell surface adhesion molecules (E-cadherin, ICAM-1, and MUC1) and their intracellular binding partners (alpha-catenin, beta-catenin, gamma-catenin, and ezrin) in 16HBE14o-, HBE1, 1HAEo-, BEAS-2B, A549, and NCI-H292 human airway epithelial cells. Expression of E-cadherin and MUC1, both in whole cell lysates and biotinylated surface proteins, was observed in 16HBE14o-, HBE1, A549, and NCI-H292 cells, while ICAM-1 was detected only in NCI-H292. In contrast, alpha-, beta-, and gamma-catenin and ezrin were expressed in all of the cells. E-cadherin formed coimmunoprecipitation complexes with beta- and gamma-catenin, whereas MUC1 only associated with beta-catenin. ICAM-1, but not MUC1, coimmunoprecipitated with ezrin in NCI-H292 cells. We conclude that airway epithelial cell-cell adhesion involves a complex network of protein-protein interactions mediated by a diverse array of membrane-bound and cytosolic protein partners.     

Adhesion of lymphocytes to bladder cancer cells: the role of the alpha(E)beta(7) integrin

The alpha(E)beta(7)integrin (defined by CD103) is expressed by most intra-epithelial lymphocytes (IEL) but by fewer than 2% peripheral blood lymphocytes (PBL). An important ligand for this molecule is the epithelial cell adhesion molecule E-cadherin. Loss of E-cadherin is associated with increased invasion and metastasis in bladder cancer. This study examines the role of the alpha(E)beta(7)-E-cadherin interaction in lymphocyte targeting of bladder cancer cells. Lymphocytes were activated in vitro by mixed lymphocyte reaction (MLR) and CD103 was upregulated by treatment with transforming growth factor beta (TGFbeta). The CD103(+) lymphocytes were used in a flow cytometric adhesion assay with bladder cancer cell lines, differing in expression of E-cadherin and intercellular adhesion molecule-1 (ICAM-1). Antibody blockade was used to confirm the relative importance of CD103 and ICAM-1 to intercellular adhesion. Lymphocytes with upregulated CD103 compared to control lymphocytes showed enhanced adhesion to an E-cadherin expressing bladder cancer cell line ( P=0.0003). This increased adhesion could be abrogated by anti-CD103 adhesion blockade. For ICAM-1 expressing bladder cells, adhesion of lymphocytes could be markedly reduced using anti-ICAM-1 blockade. In conclusion, the upregulation of CD103 by lymphocytes increases adhesion to E-cadherin expressing bladder cancer targets. Loss of E-cadherin in bladder cancer progression may provide a mechanism both for increased invasion and effective immune evasion.     

An immunohistochemical study of the expression of cell-cycle-regulated proteins p53, cyclin D1, RB, p27, Ki67 and MSH2 in gallbladder carcinoma and its precursor lesions

Gallbladder carcinomas are rare but highly lethal neoplasms. We examined the expression of five cell-cycle-related molecules (p53, RB, cyclin D1, p27, Ki-67), and MSH2, in 46 carcinomas, 14 adenomas, 15 low-grade dysplasias, 9 intestinal metaplasias and 20 normal gallbladder epithelia. The expression of these molecules was altered in gallbladder carcinomas and adenomas. In gallbladder carcinomas we observed increased expression of p53, cyclin D1, Ki-67, and MSH2 together with decreased expression of RB and p27 protein. Aberrant expression of cyclin D1 and reduced expression of RB were noted in adenomas, and expression of cyclin D1 was elevated in low-grade dysplasias. However, there was no change in the levels of these cell-cycle molecules in metaplasia. Expression of p53, p27, Ki-67, and MSH2 was correlated with clinical stage (P<0.05) and there was also a correlation between the expression of Ki-67 and MSH-2 and patient age (P<0.05). These results suggest that altered expression of cell-cycle molecules p53, cyclin D1, RB, p27, and of MSH-2 is involved in the progression of gallbladder carcinomas.     

Regulation of cellular adhesion molecule expression in murine oocytes,peri-implantation and post-implantation embryos

Expression of the adhesion molecules, ICAM-1, VCAM-1, NCAM, CD44, CD49d (VLA-4, alpha chain), and CD11a (LFA-1, alpha chain) on mouse oocytes, and pre- and peri-implantation stage embryos was examined by quantitative indirect immunofluorescence microscopy. ICAM-1 was most strongly expressed at the oocyte stage, gradually declining almost to undetectable levels by the expanded blastocyst stage. NCAM, also expressed maximally on the oocyte, declined to undetectable levels beyond the morula stage. On the other hand, CD44 declined from highest expression at the oocyte stage to show a second maximum at the compacted 8-cell/morula. This molecule exhibited high expression around contact areas between trophectoderm and zona pellucida during blastocyst hatching. CD49d was highly expressed in the oocyte, remained significantly expressed throughout and after blastocyst hatching was expressed on the polar trophectoderm. Like CD44, CD49d declined to undetectable levels at the blastocyst outgrowth stage. Expression of both VCAM-1 and CD11a was undetectable throughout. The diametrical temporal expression pattern of ICAM-1 and NCAM compared to CD44 and CD49d suggest that dynamic changes in expression of adhesion molecules may be important for interaction of the embryo with the maternal cellular environment as well as for continuing development and survival of the early embryo.     

Synergistic control of keratinocyte adhesion through muscarinic and nicotinic acetylcholine receptor subtypes

The biological mechanisms involved in initiating, coordinating, and ultimately terminating cell-cell adhesion in the stratified epithelium are not well understood at present. This study was designed to elucidate the roles of the muscarinic M3, the nicotinic alpha3, and the mixed muscarinic-nicotinic alpha9 acetylcholine receptors in physiologic control of keratinocyte adhesion. Both muscarinic and nicotinic antagonists caused keratinocyte detachment and reversibly increased the permeability of keratinocyte monolayers, indicative of the involvement of both muscarinic and nicotinic pathways in the cholinergic control of keratinocyte adhesion. Since phosphorylation of adhesion proteins plays an important role in rapid assembly and disassembly of intercellular junctions, we measured muscarinic and nicotinic effects on phosphorylation of keratinocyte adhesion molecules. The phosphorylation levels of E-cadherin, beta-catenin, and gamma-catenin increased following pharmacological blockage of muscarinic receptors. Long-term blocking of alpha3, alpha9, and M3 receptor signaling pathways with antisense oligonucleotides resulted in cell-cell detachment and changes in the expression levels of E-cadherin, beta-catenin, and gamma-catenin in cultured human keratinocytes. Simultaneous inhibition of several receptor subtypes with a mixture of antisense oligonucleotides produced intensified abnormalities with cell adhesion. Moreover, altered cell-cell adhesion was found in the stratified epithelium of alpha3, alpha9, and M3 receptor knockout mice. Keratinocytes from these mice exhibited abnormal expression of adhesion molecules at both the protein and the mRNA levels. Thus, our data indicate that the alpha3, alpha9, and M3 acetylcholine receptors play key roles in regulating in a synergistic mode keratinocyte adhesion, most probably by modulating cadherin and catenin levels and activities. These findings may aid in the development of novel methods useful for the treatment of skin adhesion diseases and tumor metastasis.     

Cholesterol-independent interactions with CD47 enhance alphavbeta3 avidity

Expression in OV10 cells of either wild-type CD47 or its extracellular IgV domain linked to a glycosylphosphatidylinositol anchor-(IgV-GPI) enhanced ligand-induced alpha(v)beta(3) activation as detected by the binding of LIBS1 and LIBS6 mAbs. The amplitude of LIBS binding was greater with both CD47 and IgV-GPI expression, indicating an increase in the population of "activable" integrin molecules. Expression of either CD47 species also increased alpha(v)beta(3)-mediated adhesion to vitronectin, and to surfaces coated with the anti-beta(3) antibody AP3, because of enhanced clustering of alpha(v)beta(3) as confirmed by chemical cross-linking. Cholesterol depletion with methyl-beta-cyclodextrin did not prevent the increase in anti-LIBS binding, but reduced cell adhesion to vitronectin and AP3. However, cells expressing CD47 were partially insulated against this disruption, and IgV-GPI was even more effective. Both CD47 and IgV-GPI were found in cholesterol-rich rafts prepared in the absence of detergent, but only CD47 could recruit alpha(v)beta(3) and its associated signaling molecules to these domains. Thus CD47-alpha(v)beta(3) complexes in cholesterol-rich raft domains appear to engage in G(i)-dependent signaling whereas CD47-alpha(v)beta(3) interactions that lead to integrin clustering are also detergent resistant, but are insensitive to cholesterol depletion and do not require the transmembrane region of CD47.     

Regulation of cellular adhesion molecule expression in murine oocytes, peri-implant ation and post-implantation embryos

Expression of the adhesion molecules, ICAM-1, VCAM-1, NCAM, CD44, CD49d (VLA-4, a chain), and CDlla (LFA-1, a chain) on mouse oocytes, and pre- and peri-implantation stage embryos was examined by quantitative indirect immunofluorescence microscopy. ICAM-1 was most strongly expressed at the oocyte stage, gradually declining almost to undetectable levels by the expanded blastocyst stage. NCAM, also expressed maximally on the oocyte, declined to undetectable levels beyond the morula stage. On the other hand, CD44 declined from highest expression at the oocyte stage to show a second maximum at the compacted 8-cell/morula. This molecule exhibited high expression around contact areas between trophecto-derm and zona pellucida during blastocyst hatching. CD49d was highly expressed in the oocyte, remained significantly expressed throughout and after blastocyst hatching was expressed on the polar trophecto-derm. Like CD44, CD49d declined to undetectable levels at the blastocyst outgrowth stage. Expression of both     

A complex of EpCAM, claudin-7, CD44 variant isoforms, and tetraspanins promotes colorectal cancer progression

High expression of EpCAM and the tetraspanin CO-029 has been associated with colorectal cancer progression. However, opposing results have been reported on CD44 variant isoform v6 (CD44v6) expression. We recently noted in rat gastrointestinal tumors that EpCAM, claudin-7, CO-029, and CD44v6 were frequently coexpressed and could form a complex. This finding suggested the possibly that the complex, rather than the individual molecules, could support tumor progression. The expression of EpCAM, claudin-7, CO-029, and CD44v6 expression was evaluated in colorectal cancer (n = 104), liver metastasis (n = 66), and tumor-free colon and liver tissue. Coexpression and complex formation of the molecules was correlated with clinical variables and apoptosis resistance. EpCAM, claudin-7, CO-029, and CD44v6 expression was up-regulated in colon cancer and liver metastasis. Expression of the four molecules did not correlate with tumor staging and grading. However, coexpression inversely correlated with disease-free survival. Coexpression was accompanied by complex formation and recruitment into tetraspanin-enriched membrane microdomains (TEM). Claudin-7 contributes to complex formation inasmuch as in the absence of claudin-7, EpCAM hardly associates with CO-029 and CD44v6 and is not recruited into TEMs. Notably, colorectal cancer lines that expressed the EpCAM/claudin-7/CO-029/CD44v6 complex displayed a higher degree of apoptosis resistance than lines devoid of any one of the four molecules. Expression of EpCAM, claudin-7, CO-029, and CD44v6 by themselves cannot be considered as prognostic markers in colorectal cancer. However, claudin-7-associated EpCAM is recruited into TEM and forms a complex with CO-029 and CD44v6 that facilitates metastasis formation.     

E-cadherin negatively regulates CD44-hyaluronan interaction and CD44-mediated tumor invasion and branching morphogenesis

CD44 is a principal cell-surface receptor for hyaluronan (HA). Up-regulation of CD44 is often associated with morphogenesis and tumor invasion. On the contrary, reduction of cell-cell adhesion due to down-regulation of E-cadherin is associated with the invasive and metastatic phenotype of carcinomas. In our current study, we investigated the functional relationship between CD44 and E-cadherin. We established an inverse correlation between CD44 and E-cadherin indicating that the cells expressing higher levels of E-cadherin display weaker binding affinity between CD44 and HA. By using TA3 murine mammary carcinoma (TA3) cells, which display CD44-dependent HA binding, branching morphogenesis, and invasion, we demonstrated an inverse functional relationship between CD44 and E-cadherin by transfecting exogenous E-cadherin into the cells. Our results showed that increased expression of E-cadherin in TA3 cells, but not ICAM-1, weakens the binding between CD44 and HA and blocks spreading of the cells on HA substratum and CD44-mediated branching morphogenesis and tumor cell invasion. The results reported here demonstrated for the first time that E-cadherin negatively regulated CD44-HA interaction and CD44 function and suggested that balanced function of CD44 and E-cadherin may be essential for normal epithelial cell functions, and imbalanced up-regulation of CD44 function and/or down-regulation of E-cadherin function likely contributes to tumor progression.     

High levels of ezrin expressed by human pancreatic adenocarcinoma cell lines with high metastatic potential.

Ezrin is a membrane cytoskeleton crosslinker protein that is a member of the ERM (ezrin/radixin/moesin) family. Ezrin binds adhesion molecules such as CD43, CD44, ICAM-1, and ICAM-2, which are implicated in cell migration and metastasis. Ezrin is expressed by many tumor cell lines; however, little is known about the function of ezrin in tumorigenesis and metastasis. Here, we investigated expression of ezrin in pancreatic adenocarcinoma cell lines of different metastatic potential. Among 16 pancreatic adenocarcinoma cell lines, several cell lines showed strong expression of ezrin. Two cell lines with high metastatic potential, S2-CP9 and S2-VP10, showed very high levels of ezrin mRNA and protein, whereas other sublines showed lower levels. There was no relationship between the expression levels of ezrin and the differentiation grades of the cell lines. These results suggest that there is a relationship between high expression of ezrin and metastatic potential of pancreatic carcinomas.     

Modulation of adhesion molecules on human large granular lymphocytes by interleukin-2 in vivo and in vitro.

The modulation of adhesion molecules on human large granular lymphocytes (LGL) by interleukin (IL)-2 was investigated both in vivo and in vitro. Intercellular adhesion molecule-1 (ICAM-1; CD54) expression increased on LGL of cancer patients receiving IL-2 adoptive immunotherapy. ICAM-1 expression on LGL isolated by Percoll gradient centrifugation, LGL purified, and expanded by adherence to plastic surfaces and LGL identified by Leu 19 (CD56) monoclonal antibody were increased significantly in response to IL-2 in vitro. Exposure of LGL to IL-1, interferon (IFN)-gamma, and tumor necrosis factor (TNF) in vitro did not induce ICAM-1. The expression of LFA-1 (CD11a/CD18), a receptor for ICAM-1, and other leukocyte adhesion molecules, including Mac-1 (CD11b/CD18) and p150,95 (CD11c/CD18), was only maintained by IL-2. IL-2 induction of ICAM-1 and the maintenance of CD18 complex expression on small lymphocytes separated by Percoll gradients were similar to that on LGL. We conclude that IL-2 enhances the expression of ICAM-1 on multiple human lymphocyte populations including LGL effectors. Expression of the CD18 complex on LGL does not appear to be highly regulated by IL-2. These findings may have implications relevant to the role of these adhesion molecules in the activities of LGL modulated by IL-2.     

Quantitative immunohistochemical analyses of the expression of E-cadherin, thrombomodulin, CD44H and CD44v6 in primary tumours of pharynx/larynx squamous cell carcinoma and their lymph node metastases.

The quantitative expression of E-cadherin, thrombomodulin, CD44H and CD44v6 in 32 specimens of primary tumours of pharynx/larynx squamous cell carcinoma and their lymph node metastases was studied by immunohistochemistry. With the aim of obtaining comparative and objective data, image acquisition conditions were kept unaltered for all the measurements and the immunostaining intensity was quantified by applying an image processing system. On the one hand, correlations were only observed between CD44H and CD44v6, both in primary tumours and metastases, and between E-cadherin and TM in metastases. On the other hand, statistical analyses of paired data did not show significant differences in the expression of these markers between the two tumour sites. In agreement with previous reports, E-cadherin expression was rather low or negative in primary tumours and metastases of the three poorly differentiated specimens we studied, as well as that of TM, but otherwise some of these samples showed intermediate immunostaining levels of CD44H/CD44v6. It may be concluded from the present study that the quantitative expression of these adhesion molecules in well established lymph node metastases of pharynx/larynx squamous cell carcinoma is essentially unaltered in relation to their primary sites.     

CD31/PECAM-1 is a ligand for alpha v beta 3 integrin involved in adhesion of leukocytes to endothelium

To protect the body efficiently from infectious organisms, leukocytes circulate as nonadherent cells in the blood and lymph, and migrate as adherent cells into tissues. Circulating leukocytes in the blood have first to adhere to and then to cross the endothelial lining. CD31/PECAM- 1 is an adhesion molecule expressed by vascular endothelial cells, platelets, monocytes, neutrophils, and naive T lymphocytes. It is a transmembrane glycoprotein of the immunoglobulin gene superfamily (IgSF), with six Ig-like homology units mediating leukocyte-endothelial interactions. The adhesive interactions mediated by CD31 are complex and include homophilic (CD31-CD31) or heterophilic (CD31-X) contacts. Soluble, recombinant forms of CD31 allowed us to study the heterophilic interactions in leukocyte adhesion assays. We show that the adhesion molecule alpha v beta 3 integrin is a ligand for CD31. The leukocytes revealed adhesion mediated by the second Ig-like domain of CD31, and this binding was inhibited by alpha v beta 3 integrin-specific antibodies. Moreover alpha v beta 3 was precipitated by recombinant CD31 from cell lysates. These data establish a third IgSF-integrin pair of adhesion molecules, CD31-alpha v beta 3 in addition to VCAM-1, MadCAM-1/alpha 4 integrins, and ICAM/beta 2 integrins, which are major components mediating leukocyte-endothelial adhesion. Identification of a further versatile adhesion pair broadens our current understanding of leukocyte-endothelial interactions and may provide the basis for the treatment of inflammatory disorders and metastasis formation.     

Cutting edge: LFA-1 is required for liver NK1.1+TCR alpha beta+ cell development: evidence that liver NK1.1+TCR alpha beta+ cells originate from multiple pathways

Using mice deficient for LFA-1, CD44, and ICAM-1, we examined the role of these adhesion molecules in NK1.1+TCR alpha beta+ (NKT) cell development. Although no defect in NKT cell development was observed in CD44-/- and ICAM-1-/- mice, a dramatic reduction of liver NKT cells was observed in LFA-1-/- mice. Normal numbers of NKT cells were present in other lymphoid organs in LFA-1-/- mice. When LFA-1-/- splenocytes were injected i.v. into wild-type mice, the frequency of NKT cells among donor-derived cells in the recipient liver was normal. In contrast, when LFA-1-/- bone marrow (BM) cells were injected i.v. into irradiated wild-type mice, the frequency of liver NKT cells was significantly lower than that of mice injected with wild-type BM cells. Collectively, these data indicate that LFA-1 is required for the development of liver NKT cells, rather than the migration to and/or subsequent establishment of mature NKT cells in the liver.     

Analysis of cadherin/catenin complexes in transformed thyroid epithelial cells: modulation by beta 1 integrin subunit

We have analysed the expression of cadherin/catenin complex molecules in PC C13 rat thyroid cells transformed in vitro with different oncogenes. No significant downregulation of either E-cadherin, alpha-, beta- and gamma-catenin was detected following the introduction of activated forms of myc, adenovirus E1A, ras, raf, myc + ras, E1A + raf. However, ras- and raf-transformed PC C13 cells showed altered adherens junctions. An altered distribution of cadherin/catenin complexes characterized by radially oriented membrane spikes perpendicular to cell edges was the most prominent feature evidenced by immunofluorescence. No beta1 integrin localization was observed in areas where this altered pattern of E-cadherin expression was detected. However, beta1 integrin subunit expression was detected at areas of cell-cell contact where E-cadherin showed a normal pattern of expression. Furthermore, ras- and raf-transformed PC C13 cells showed the ability to migrate in collagen gels, in contrast to their normal untransformed counterpart. Overexpression of beta1 integrin was found to restore normal E-cadherin localization at cell-cell contacts and to partially inhibit the ability to migrate in collagen gels. Finally, two cell lines obtained by ras transformation in vivo, and derived from a rat primary thyroid carcinoma (TK6) and its lung metastasis (MPTK6), were found to have lost gamma-catenin expression. TK6 lost also E-cadherin expression and membrane localization of alpha-catenin. These results suggest that: i) in vitro thyroid cell transformation is associated to a change in cadherin/catenin complexes distribution rather than to a decrease in expression; ii) in vivo transformation is associated to the loss of expression of some of these molecules likely due to tumor progression; iii) alterations in beta1 integrin subunit expression can result in changes in cadherin/catenin function thus implying that an integrin-cadherin synergy may exist in thyroid cells.     

非小细胞肺癌中E-钙粘素和CD44v6的表达及其意义

为了探讨E-钙粘素(E-cadherin,E-cad)和白细胞分化抗原变异型6(CD44v6)在非小细胞肺癌(NSCLC)中的表达及临床意义,采用免疫组织化学(SP法)对65例NSCLC和20例癌旁组织中E-cad和CD44v6的表达进行研究。结果显示E-cad在肺癌组织中的阳性表达率(32.31%)显著低于癌旁组织(75.00%)(P<0.01),且与NSCLC的TNM分期、淋巴结转移呈负相关(P<0.05),与分化程度呈正相关(P<0.01),而与组织分型无关(P>0.05);CD44v6的阳性表达率与组织分型和分化程度无关(P>0.05),而与TNM分期和淋巴结转移呈正相关(P<0.05,<0.01)。两者在NSCLC中的表达显著相关(P<0.05)。因此检测E-cad和CD44v6的共同表达将是指导临床治疗及估计预后的有意义指标,可应用于临床预后的综合评价。     

Alpha 4 integrin signaling activates phosphatidylinositol 3-kinase and stimulates T cell adhesion to intercellular adhesion molecule-1 to a similar extent as CD3, but induces a distinct rearrangement of the actin cytoskeleton.

Dynamic regulation of beta(2) integrin-dependent adhesion is critical for a wide array of T cell functions. We previously showed that binding of high-affinity alpha(4)beta(1) integrins to VCAM-1 strengthens alpha(L)beta(2) integrin-mediated adhesion to ICAM-1. In this study, we compared beta(2) integrin-mediated adhesion of T cells to ICAM-1 under two different functional contexts: alpha(4) integrin signaling during emigration from blood into tissues and CD3 signaling during adhesion to APCs and target cells. Cross-linking either alpha(4) integrin or CD3 on Jurkat T cells induced adhesion to ICAM-1 of comparable strength. Adhesion was dependent on phosphatidylinositol (PI) 3-kinase but not p44/42 mitogen-activated protein kinase (extracellular regulated kinase 1/2), because it was inhibited by wortmannin and LY294002 but not U0126. These data suggest that PI 3-kinase is a ubiquitous regulator of beta(2) integrin-mediated adhesion. A distinct morphological change consisting of Jurkat cell spreading and extension of filopodia was induced by alpha(4) integrin signaling. In contrast, CD3 induced radial rings of cortical actin polymerization. Inhibitors of PI 3-kinase and extracellular regulated kinase 1/2 did not affect alpha(4) integrin-induced rearrangement of the actin cytoskeleton, but treatment with ionomycin, a Ca(2+) ionophore, modulated cell morphology by reducing filopodia and promoting lamellipodia formation. Qualitatively similar morphological and adhesive changes to those observed with Jurkat cells were observed following alpha(4) integrin or CD3 stimulation of human peripheral blood T cells.     

Carcinoembryonic antigen and CD44 variant isoforms cooperate to mediate colon carcinoma cell adhesion to E- and L-selectin in shear flow

Selectin-mediated adhesion of tumor cells to platelets, leukocytes, and endothelial cells may regulate their hematogenous dissemination in the microvasculature. We recently identified CD44 variant isoforms (CD44v) as functional P-, but not E- or L-, selectin ligands on colon carcinoma cells. Moreover, an approximately 180-kDa sialofucosylated glycoprotein(s) mediated selectin binding in CD44-knockdown cells. Using immunoaffinity chromatography and tandem mass spectrometry, we identify this glycoprotein as the carcinoembryonic antigen (CEA). Blot rolling assays and flow-based adhesion assays using microbeads coated with CEA immunopurified from LS174T colon carcinoma cells and selectins as substrate reveal that CEA possesses E- and L-, but not P-, selectin ligand activity. CEA on CD44-knockdown LS174T cells exhibits higher HECA-452 immunoreactivity than CEA on wild-type cells, suggesting that CEA functions as an alternative acceptor for selectin-binding glycans. The enhanced expression of HECA-452 reactive epitopes on CEA from CD44-knockdown cells correlates with the increased CEA avidity for E- but not L-selectin. Through the generation of stable knockdown cell lines, we demonstrate that CEA serves as an auxiliary L-selectin ligand, which stabilizes L-selectin-dependent cell rolling against fluid shear. Moreover, CEA and CD44v cooperate to mediate colon carcinoma cell adhesion to E- and L-selectin at elevated shear stresses. The novel finding that CEA is an E- and L-selectin ligand may explain the enhanced metastatic potential associated with tumor cell CEA overexpression and the supportive role of selectins in metastasis.     

Galectin-9 suppresses tumor metastasis by blocking adhesion to endothelium and extracellular matrices

We previously described an inverse correlation between galectin-9 (Gal-9) expression and metastasis in patients with malignant melanoma and breast cancer. This study verified the ability of Gal-9 to inhibit lung metastasis in experimental mouse models using highly metastatic B16F10 melanoma and Colon26 colon cancer cells. B16F10 cells transfected with a secreted form of Gal-9 lost their metastatic potential. Intravenous Gal-9 administration reduced the number of metastases of both B16F10 and Colon26 cells in the lung, indicating that secreted Gal-9 suppresses metastasis. Analysis of adhesive molecule expression revealed that B16F10 cells highly express CD44, integrin alpha1, alpha 4, alpha V, and beta1, and that Colon26 cells express CD44, integrin alpha2, alpha 5, alpha V, and beta1, suggesting that Gal-9 may inhibit the adhesion of tumor cells to vascular endothelium and the extracellular matrix (ECM) by binding to such adhesive molecules. Indeed, Gal-9 suppressed the binding of hyaluronic acid to CD44 on both B16F10 and Colon26 cells, and also suppressed the binding of vascular cell adhesion molecule-1 to very late antigen-4 on B16F10 cells. Furthermore, Gal-9 inhibited the binding of tumor cells to ECM components, resulting in the suppression of tumor cell migration. The present results suggest that Gal-9 suppresses both attachment and invasion of tumor cells by inhibiting the binding of adhesive molecules on tumor cells to ligands on vascular endothelium and ECM.