Role of temperature in de-mixing absorbance spectra composed of compound electrolyte solutions.

This work is focused on the role of temperature in the de-mixing of absorbance spectra measured in mixed aqueous Na2SO4 and NaNO3 solutions. First, the influence of temperature on the absorbance spectrum of demineralized water was determined. Second, the absorbance spectra of five separate electrolytes (NaNO2, NaNO3, CaCl2, K2CO3, and NaOH) at three temperatures (4°C, 25°C, and 50°C) for concentrations ranging from 0.0625 M to 0.5 M were examined. These five electrolytes show similar temperature dependencies. Finally, absorbance spectra of mixed solutions were investigated at temperatures of 5°C, 15°C, 25°C, 35°C, and 45°C for concentrations ranging from 0.0625 M to 0.5 M per electrolyte in the mixture. The spectral window from 650 to 1100 nm was utilized to observe the ionic and temperature influences on the vibrational modes of the OH bond in the solvent molecules. The effects of dissolving Na2SO4 and NaNO3 are nonlinearly cumulative at lower temperatures indicating extended alteration of the water structure beyond the first hydration shell. A similar trend was observed for a mixture of Na2CO3 and NaCl. Furthermore, it was found that higher temperatures are better for recovering the separate component absorption signatures of an electrolyte mixture. The near-infrared spectral regime is well suited for integrated sensing, and therefore these results can help in designing an integrated sensor to identify inorganic species in water.

Epidermal growth factor-like repeats mediate lateral and reciprocal interactions of Ep-CAM molecules in homophilic adhesions.

Ep-CAM is a new type of cell adhesion molecule (CAM) which does not structurally resemble the members of the four major families (cadherins, integrins, selectins, and CAMs of the immunoglobulin superfamily) and mediates Ca(2+)-independent, homophilic adhesions. The extracellular domain of Ep-CAM consists of a cysteine-rich region, containing two type II epidermal growth factor (EGF)-like repeats, followed by a cysteine-poor region. We generated mutated Ep-CAM forms with various deletions in the extracellular domain. These deletion mutants, together with monoclonal antibodies recognizing different epitopes in the extracellular domain, were used to investigate the role of the EGF-like repeats in the formation of intercellular contacts mediated by Ep-CAM molecules. We established that both EGF-like repeats are required for the formation of Ep-CAM-mediated homophilic adhesions, including the accumulation of Ep-CAM molecules at the cell-cell boundaries, and the anchorage of the Ep-CAM adhesion complex to F-actin via alpha-actinin. Deletion of either EGF-like repeat was sufficient to inhibit the adhesion properties of the molecule. The first EGF-like repeat of Ep-CAM is required for reciprocal interactions between Ep-CAM molecules on adjacent cells, as was demonstrated with blocking antibodies. The second EGF-like repeat was mainly required for lateral interactions between Ep-CAM molecules. Lateral interactions between Ep-CAM molecules result in the formation of tetramers, which might be the first and necessary step in the formation of Ep-CAM-mediated intercellular contacts.

Effect of climate conditions and plant developmental stage on the stability of antibodies expressed in transgenic tobacco.

Plants are regarded as a promising system for the production of heterologous proteins. However, little is known about the influence of plant physiology and plant development on the yield and quality of the heterologous proteins produced in plants. To investigate this, tobacco (Nicotiana tabacum cv Samsun NN) was transformed with a single construct that contained behind constitutive promotors the light- and heavy-chain genes of a mouse antibody. The in planta stability of the antibody was analyzed in transgenic plants that were grown under high and low irradiation at 15 degrees C and 25 degrees C. High-light conditions favored the production of biomass, of total soluble protein, and of antibody. The plants grown at 25 degrees C developed faster and contained less antibody per amount of leaf tissue than the plants grown at 15 degrees C. Both endogenous protein and antibody content showed a strong decline during leaf development. The heavy chains of the antibody underwent in planta degradation via relatively stable fragments. In vitro incubations of purified plantibody with leaf extracts of wild-type tobacco indicated the involvement of acidic proteases. It is interesting that the same antibody produced by mouse hybridoma cells exhibited higher stability in this in vitro assay. This may be explained by the assumption that the plant type of N-glycosylation contributes less to the stability of the antibody than the mouse-type of N-glycosylation. The results of this study indicate that proteolytic degradation during plant development can be an important factor affecting yield and homogeneity of heterologous protein produced by transgenic plants.

The structural analysis of adhesions mediated by Ep-CAM.

The epithelial cell adhesion molecule Ep-CAM is capable of mediating Ca2+-independent homotypic cell-cell adhesion when introduced into cells lacking their own means of cell-cell interactions. We used (confocal) immunofluorescent and (immuno-) electron microscopy to investigate the structural organization of Ep-CAM-mediated adhesions and their relation to other types of intercellular adhesions. Ep-CAM-transfected cell lines, cells of epithelial origin, and epithelial tissues were analyzed. In transfected L cells Ep-CAM brings the opposing intercellular membranes into a close proximity (approximately 10-14 nm) at sporadic contacts; however, no structures resembling junctional complexes were observed. In L cells cotransfected with Ep-CAM and E-cadherin, both molecules localize at the sites of cell-cell contact, forming independent adhesion sites with no Ep-CAM detectable within the structurally distinguishable cadherin-mediated adherens junctions. In well-differentiated carcinoma cell lines Ep-CAM colocalized with E-cadherin practically along the whole lateral domain; however, no colocalization was observed between Ep-CAM and the components of the tight junction complex (occludin and ZO-1), desmosomes (desmoplakins I/II), or cell-substrate adhesions (beta1 integrins). This was confirmed by analysis of polarized epithelium of normal colon where Ep-CAM was present at the lateral membrane including the adherens junction areas, but was fully excluded from the apical cell membrane (microvilli), tight junctions, and desmosomes. We conclude that (1) Ep-CAM does not form junctional complexes in L cells, (2) in epithelial cells, cell surface Ep-CAM is present at the lateral cell membrane, but is excluded from tight junctions and desmosomes, and (3) in epithelial cells, Ep-CAM is present within adhesions mediated by the classic cadherins (especially E-cadherin) with both types of molecules remaining as independent clusters. The colocalization with cadherins might be important for the modulating effect of Ep-CAM on cadherin-mediated adhesions.

Cytoplasmic tail regulates the intercellular adhesion function of the epithelial cell adhesion molecule.

Ep-CAM, an epithelium-specific cell-cell adhesion molecule (CAM) not structurally related to the major families of CAMs, contains a cytoplasmic domain of 26 amino acids. The chemical disruption of the actin microfilaments, but not of the microtubuli or intermediate filaments, affected the localization of Ep-CAM at the cell-cell boundaries, suggesting that the molecule interacts with the actin-based cytoskeleton. Mutated forms of Ep-CAM were generated with the cytoplasmic domain truncated at various lengths. All of the mutants were transported to the cell surface in the transfectants; however, the mutant lacking the complete cytoplasmic domain was not able to localize to the cell-cell boundaries, in contrast to mutants with partial deletions. Both the disruption of the actin microfilaments and a complete truncation of the cytoplasmic tail strongly affected the ability of Ep-CAM to mediate aggregation of L cells. The capability of direct aggregation was reduced for the partially truncated mutants but remained cytochalasin D sensitive. The tail truncation did not affect the ability of the transfectants to adhere to solid-phase-adsorbed Ep-CAM, suggesting that the ability to form stable adhesions and not the ligand specificity of the molecule was affected by the truncation. The formation of intercellular adhesions mediated by Ep-CAM induced a redistribution to the cell-cell boundaries of alpha-actinin, but not of vinculin, talin, filamin, spectrin, or catenins. Coprecipitation demonstrated direct association of Ep-CAM with alpha-actinin. Binding of alpha-actinin to purified mutated and wild-type Ep-CAMs and to peptides representing different domains of the cytoplasmic tail of Ep-CAM demonstrates two binding sites for alpha-actinin at positions 289 to 296 and 304 to 314 of the amino acid sequence. The results demonstrate that the cytoplasmic domain of Ep-CAM regulates the adhesion function of the molecule through interaction with the actin cytoskeleton via alpha-actinin.

Epithelial cell adhesion molecule (Ep-CAM) modulates cell-cell interactions mediated by classic cadherins.

The contribution of noncadherin-type, Ca2+-independent cell-cell adhesion molecules to the organization of epithelial tissues is, as yet, unclear. A homophilic, epithelial Ca2+-independent adhesion molecule (Ep-CAM) is expressed in most epithelia, benign or malignant proliferative lesions, or during embryogenesis. Here we demonstrate that ectopic Ep-CAM, when expressed in cells interconnected by classic cadherins (E- or N-cadherin), induces segregation of the transfectants from the parental cell type in coaggregation assays and in cultured mixed aggregates, respectively. In the latter assay, Ep-CAM-positive transfectants behave like cells with a decreased strength of cell-cell adhesion as compared to the parental cells. Using transfectants with an inducible Ep-CAM-cDNA construct, we demonstrate that increasing expression of Ep-CAM in cadherin-positive cells leads to the gradual abrogation of adherens junctions. Overexpression of Ep-CAM has no influence on the total amount of cellular cadherin, but affects the interaction of cadherins with the cytoskeleton since a substantial decrease in the detergent-insoluble fraction of cadherin molecules was observed. Similarly, the detergent-insoluble fractions of alpha- and beta-catenins decreased in cells overexpressing Ep-CAM. While the total beta-catenin content remains unchanged, a reduction in total cellular alpha-catenin is observed as Ep-CAM expression increases. As the cadherin-mediated cell-cell adhesions diminish, Ep-CAM-mediated intercellular connections become predominant. An adhesion-defective mutant of Ep-CAM lacking the cytoplasmic domain has no effect on the cadherin-mediated cell-cell adhesions. The ability of Ep-CAM to modulate the cadherin-mediated cell-cell interactions, as demonstrated in the present study, suggests a role for this molecule in development of the proliferative, and probably malignant, phenotype of epithelial cells, since an increase of Ep-CAM expression was observed in vivo in association with hyperplastic and malignant proliferation of epithelial cells.

Expression of Ep-CAM in cervical squamous epithelia correlates with an increased proliferation and the disappearance of markers for terminal differentiation.

Ep-CAM, an epithelial adhesion molecule, is absent in normal squamous epithelia but can be detected in some squamous carcinomas. Using a panel of monoclonal antibodies to keratinocyte differentiation and proliferation markers, we investigated the association of EP-CAM expression with differentiation-related and/or neoplastic changes in cervical epithelium. Normal endocervical glandular epithelium (Both columnar and reserve cells) appeared strongly positive for EP-CAM, whereas ectocervical squamous epithelial cells did not express this molecule. Expression of Ep-CAM (in basal cells) was sometimes observed in morphologically normal ectocervical tissue but only in areas bordering cervical intraepithelial neoplasia (CIN) lesions. At the early stages of neoplasia the expression of Ep-CAM was regularly present in squamous epithelium, in general consistent with the areas of atypical, undifferentiated cells. Thus, in CIN grades I and II, the basal/suprabasal layers of the epithelia were positive, whereas in CIN grade III lesions, up to 100% of the cells over the whole thickness of the epithelium sometimes excluding the very upper layers, expressed Ep-CAM. A clear increase, not only in number of positive cells but also in levels of Ep-CAM expression (intensity) was observed during progression from CIN I to CIN III. Expression of Ep-CAM in ectocervical lesions did not coincide with a reappearance of the simple epithelium cytokeratins (CK8 and CK18). On the other hand, expression of Ep-CAM in atypical cells of CIN lesions correlated with the disappearance of CK13, which normally marks cells undergoing squamous differentiation. As was shown with Ki-67, a marker for proliferating cell populations, the areas of Ep-CAM expression were also the areas of enhanced proliferation. Cells expressing Ep-CAM did not express involucrin, a marker for cells committed to terminal differentiation. In the majority of both squamous and adenocarcinomas of the cervix a strong expression of Ep-CAM was observed, although some decrease in the expression (both the intensity and the number of positive cells), as compared with CIN III lesions, was observed in the areas of squamous differentiation. This study demonstrates that the expression of Ep-CAM in cervical squamous epithelium is associated with abnormal proliferation of cell populations that are not committed to terminal differentiation.

Evidence for a role of the epithelial glycoprotein 40 (Ep-CAM) in epithelial cell-cell adhesion.

Recently we have demonstrated that a 40kD human epithelium-specific glycoprotein exhibit the features of a homophilic cell-cell adhesion molecule, when expressed in transfected murine cells. We suggested the name Ep-CAM for this molecule (Litvinov et al., J. Cell Biol., 125: 437-446). Here we investigate the possible biological function of Ep-CAM in its natural environment--cells of epithelial origin. Immunolocalization of Ep-CAM in tissues and in cultures of epithelial/carcinoma cells showed that the majority of the Ep-CAM molecules are localized at cell-cell boundaries, predominantly along the whole lateral domain of polarized cells. In vitro, on single cells in suspension, the Ep-CAM molecules are present on the entire cell surface, and when the single cells grow attached, Ep-CAM is present at their pseudo-apical domain. During formation of intercellular contacts by such single cells, the majority of the Ep-CAM molecules are redistributed from the pseudoapical to the lateral domain of the cell membrane. Attachment of cells to the substrate does not cause redistribution of the molecules to the site of substrate attachment irrespective of the adhesive substrate (fibronectin, collagens, laminin, EHS-matrigel were tested). The monoclonal antibody 323/A3, reactive with the extracellular domain of the Ep-CAM molecule, has a strong negative effect on the aggregating behavior of COV362 ovarian carcinoma cells and RC-6 immortalized mammary epithelial cells. The mAb affected cell aggregation in both cell lines in the presence of Ca++, but with RC-6 cells the effect was more pronounced in low-calcium medium. The effects of the 323/A3 mAb on the already established intercellular contacts was not significant. The data presented demonstrate that the Ep-CAM molecules are functionally active in the epithelial and carcinoma cells tested, are capable of mediating Ca(++)-independent intercellular adhesions, and are not likely to be involved in cell-substrate adhesion.

Ep-CAM: a human epithelial antigen is a homophilic cell-cell adhesion molecule.

The epithelial glycoprotein 40 (EGP40, also known as GA733-2, ESA, KSA, and the 17-1A antigen), encoded by the GA-733-2 gene, is expressed on the baso-lateral cell surface in most human simple epithelia. The protein is also expressed in the vast majority of carcinomas and has attracted attention as a tumor marker. The function of the protein is unknown. We demonstrate here that EGP40 is an epithelium-specific intercellular adhesion molecule. The molecule mediates, in a Ca(2+)-independent manner, a homophilic cell-cell adhesion of murine cells transfected with the complete EGP40 cDNA. Two murine cell lines were tested for the effects of EGP40 expression: fibroblastic L cells and dedifferentiated mammary carcinoma L153S cells. The expression of the EGP40 protein causes morphological changes in cultures of transfected cells--increasing intercellular adhesion of the transfectants--and has a clear effect on cell aggregating behavior in suspension aggregation assays. EGP40 directs sorting in mixed cell populations, in particular, causes segregation of the transfectants from the corresponding parental cells. EGP40 expression suppresses invasive colony growth of L cells in EHS-matrigel providing tight adhesions between cells in growing colonies. EGP40 can thus be considered a new member of the intercellular adhesion molecules. In its biological behavior EGP40 resembles to some extent the molecules of the immunoglobulin superfamily of cell adhesion molecules (CAMs), although no immunoglobulin-like repeats are present in the EGP40 molecule. Certain structural similarities in general organization of the molecule exist between EGP40 and the lin-12/Notch proteins. A possible role of this adhesion molecule in formation of architecture of epithelial tissues is discussed. To reflect the function of the molecule the name Ep-CAM for EGP40 seems appropriate.