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Many studies have implicated cell-surface lectins in heterologous cell-cell adhesion, but little is known about the participation of lectins in cellular adhesion in homologous cells. Here, we show the development of a cell model for investigating the direct role of a cell-surface lectin in homologous cell-cell adhesion. Parenchymal cells were isolated from caprine liver using a perfusion buffer, and dispersed in a chemically defined modified Ringer’s solution. These cells undergo autoagglutination in the presence of Ca2+. The autoagglutinated cells can be dissociated specifically with D-galactose (50 mM), which also inhibits the liver cell autoagglutination event. The blood serum protein fetuin has no effect on liver cell autoagglutination, whereas desialylated fetuin (100 μM), with its terminal D-galactose residue, showed a high affinity for blocking the autoagglutination event. The data demonstrates the occurrence of a Ca2+-dependent D-galactose-specific lectin and a lectin receptor on the parenchymal cells. Furthermore, it shows that the observed autoagglutination event is caused by the interaction of the cell-surface lectin with its receptor on the neighbouring homologous cells. The data supports the view that homologous cell-cell contact in mammalian tissues is triggered by such lectin-receptor interaction and that the previously reported cell-surface adhesive proteins serve as a secondary force to strengthen cell adhesion. This cell model could be extremely useful for investigating the direct role of cell-surface lectin and its receptor in homologous cell adhesion in a variety of tissues under normal and pathological conditions.
It was shown that CEACAM5 can mediate cell-cell adhesion through homotypic and heterotypic interactions; however, its role in the expression of the malignant phenotype remains obscure. To study whether the formation of both primary tumors and metastases is directly related to the presence or absence of CEACAM5, we applied the antisense RNA strategy. By transfecting human CX-1.1 colon carcinoma cells with CEACAM5 antisense-expressing vector or with the vector itself, cell variants with a highly decreased expression of CEACAM5 were obtained. Profound differences in proliferative abilities among parental and obtained subclones of CX-1.1 cells were revealed when cells were implanted subcutaneously into nude mice. In contrast to their highly tumorigenic parental CX-1.1 cells (with high expression of membrane-bound and secreted CEACAM5), two subclones (3E and AS6Q) with substantially decreased expression of membrane-bound and secreted CEA showed a considerably diminished growth rate. Even more striking results were obtained with AS8Q cells, producing a residual amount of this glycoprotein. However, 3B cells (producing a large amount of secreted CEACAM5) did not differ significantly in their tumorigenic properties from CX-1.1 cells. Our experiments performed in nu/nu mice suggest that CEACAM5 supports the growth of primary tumors, but is not involved in the formation of metastases by colon cancer cells.
Cell-cell and cell-substrate adhesions are sites of dramatic actin rearrangements and where actin-membrane connections are tightly regulated. Zyxin-VASP complexes localize to sites of cell-cell and cell-substrate adhesion and function to regulate actin dynamics and actin-membrane connections at these sites. To accomplish these functions, zyxin recruits VASP to cellular sites via proline-rich binding sites near zyxin’s amino terminus. While the prevailing thought has been that zyxin simply acts as a scaffold protein for VASP binding, the identification of a LIM domain-VASP interaction could complicate this view. Here we assess how zyxin-VASP binding through both the proline rich motifs and the LIM domains alters specific VASP functions. We find that neither individual interaction alters VASP’s actin regulatory activities. In contrast, however, we find that full-length zyxin dramatically reduces VASPmediated actin bundling and actin assembly. Taken together, these results suggest a model where zyxin-VASP complexes occur in complex organizations with suppressed actin regulatory activity.
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