Lung epithelial barrier function and wound healing are decreased by IL-4 and IL-13 and enhanced by IFN-gamma

To understand the effects of cytokines on epithelial cells in asthma, we have investigated the effects of interleukin (IL)-4, IL-13, and interferon (IFN)-gamma on barrier function and wound healing in Calu-3 human lung epithelial cells. IL-4 and IL-13 treatment of Calu-3 cells grown on Transwell filters resulted in a 70-75% decrease in barrier function as assessed by electrophysiological and [(14)C]mannitol flux measurements. In contrast, IFN-gamma enhanced barrier function threefold using these same parameters. Cells treated concurrently with IFN-gamma and IL-4 or IL-13 showed an initial decline in barrier function that was reversed within 2 days, resulting in barrier levels comparable to control cells. Analysis of the tight junction-associated proteins ZO-1 and occludin showed that IL-4 and IL-13 significantly reduced ZO-1 expression and modestly decreased occludin expression compared with controls. IFN-gamma, quite unexpectedly given its enhancing effect on barrier function, reduced expression of ZO-1 and occludin to almost undetectable levels compared with controls. In wound-healing assays of cells grown on collagen I, IL-4 and IL-13 decreased migration, whereas IFN-gamma treatment enhanced migration, compared with control cells. Addition of IFN-gamma, in combination with IL-4 or IL-13, restored migration of cells to control levels. Migration differences observed between the various cytokine treatments was correlated with expression of the collagen I-binding alpha(2)beta(1)-integrin at the leading edge of cells at the wound front; alpha(2)beta(1)-integrin expression was decreased in IFN-gamma-treated cells compared with controls, whereas it was highest in IL-4- and IL-13-treated cells. These results demonstrate that IL-4 and IL-13 diminish the capacity of Calu-3 cells to maintain barrier function and repair wounds, whereas IFN-gamma promotes epithelial restitution by enhancing barrier function and wound healing.

Interferon-gamma decreases barrier function in T84 cells by reducing ZO-1 levels and disrupting apical actin

The effects of interferon-gamma (IFN-gamma) on tight junctions in T84 human intestinal epithelial cells were investigated. Treatment of T84 cells with IFN-gamma caused a dose- and time-dependent increase in monolayer permeability as assessed by transepithelial electrical resistance measurements. Examination of specific proteins associated with tight junctions by immunoblotting and confocal microscopy revealed changes in the expression levels and localization of some of these proteins after exposure of the cells to IFN-gamma. Specifically, IFN-gamma treatment resulted in an almost total loss of zonula occludens (ZO)-1, whereas the levels of ZO-2 and occludin showed relatively modest decreases compared with untreated cells. Loss of ZO-1 was associated with the altered localization of ZO-2 and occludin. In IFN-gamma-treated cells, ZO-2 and occludin were diffusely distributed, whereas, in control cells, they, along with ZO-1, were predominantly localized to the tight junctions. Analysis of ZO-1 protein and RNA by pulse chase and RT-PCR, respectively, showed an increase in protein turnover, a decrease in protein synthesis, and a reduction in RNA levels following IFN-gamma treatment. In contrast to ZO-1, ZO-2 and occludin did not show any major changes in these parameters. In addition, the organization of actin in the apical and tight junction regions, but not in the mid- or basal regions, of the cells was also perturbed by IFN-gamma treatment of cells. Time-course analysis of IFN-gamma-induced alterations in ZO-1 expression and apical actin perturbation indicated that these two effects were intimately linked and could not be dissociated. These results suggest that IFN-gamma affects barrier function in T84 cells by decreasing the levels of ZO-1 and perturbing apical actin organization, which leads to a disorganization of the tight junction and an increase in paracellular permeability.

Highly polarized HLA class II antigen processing and presentation by human intestinal epithelial cells

The high concentration of foreign antigen in the lumen of the gastrointestinal tract is separated from the underlying lymphocytes by a single cell layer of polarized epithelium. Intestinal epithelial cells can express HLA class II antigens and may function as antigen-presenting cells to CD4(+) T cells within the intestinal mucosa. Using tetanus toxoid specific and HLA-DR-restricted T lymphocytes, we show that polarized intestinal epithelial cells directed to express HLA-DR molecules are able to initiate class II processing only after internalization of antigen from their apical surface. Coexpression of the class II transactivator CIITA in these cells, which stimulates highly efficient class II processing without the characteristic decline in barrier function seen in polarized monolayers treated with the proinflammatory cytokine gamma-IFN, facilitates antigen processing from the basolateral surface. In both cases, peptide presentation to T cells via class II molecules was restricted to the basolateral surface. These data indicate a highly polarized functional architecture for antigen processing and presentation by intestinal epithelial cells, and suggest that the functional outcome of antigen processing by the intestinal epithelium is both dependent on the cellular surface at which the foreign antigen is internalized and by the underlying degree of mucosal inflammation.

Biological consequences of targeting beta 1,4-galactosyltransferase to two different subcellular compartments

beta 1,4-galactosyltransferase is unusual among the glycosyltransferases in that it is found in two subcellular compartments where it performs two distinct functions. In the trans-Golgi complex, galactosyltransferase participates in oligosaccharide biosynthesis, as do the other glycosyltransferases. On the cell surface, however, galactosyltransferase associates with the cytoskeleton and functions as a receptor for extracellular oligosaccharide ligands. Although we now know much regarding galactosyltransferase function in these two compartments, little is known about how it is targeted to these different sites. By cloning the galactosyltransferase gene products, certain features of the protein have been identified that may be critical for its expression on the cell surface or retention within the Golgi complex. This article discusses recent studies which suggest that a cytoplasmic sequence unique to one galactosyltransferase isoform is required for targeting a portion of this protein to the plasma membrane, enabling it to function as a cell adhesion molecule. These findings allow one to manipulate surface galactosyltransferase expression, either positively or negatively, and perturb galactosyltransferase-dependent cellular interactions during fertilization and development.

Alteration of oligosaccharide biosynthesis by genetic manipulation of glycosyltransferases

The alteration of oligosaccharide structures through genetic manipulation of glycosyltransferase activities is now a reality. It is apparent that this technique has greater consequences on oligosaccharide structure when an exogenous enzyme is introduced into cells, and in particular when this enzyme is responsible for a terminal glycosylation step. By contrast, only one study has examined the effects of overexpressing an endogenous glycosyltransferase, in which there was no detectable effect on glycosylation. However, there are still other key regulatory biosynthetic enzymes, such as GlcNAc transferase V and beta 1,3 GlcNAc transferase, whose overexpression may alter glycosylation. Both of these enzymes are required for the biosynthesis of polylactosaminoglycans (polymers of N-acetyllactosamine disaccharides), and their elevation in tumor cells correlates with increased expression of polylactosaminoglycans. Recently, the gene encoding GlcNAc transferase V has been isolated, but its transfection into cells and characterization of the resulting oligosaccharides awaits further study. Alternate strategies for modifying oligosaccharide structures could involve the introduction of more than one glycosyltransferase into cells to ensure the availability of biosynthetic intermediates. Alternatively, the disruption of specific glycosyltransferase genes by homologous recombination could be used to eliminate competing glycosyltransferases that act on a common substrate. Although oligosaccharide biosynthesis is directly dependent upon the presence or absence of specific glycosyltransferases, other factors also contribute to glycosylation. For example, the transport rate of a glycoprotein through the endoplasmic reticulum and Golgi complex, the levels of processing glycosidases, the availability of substrates, the host cell, and ultimately, the peptide backbone of the particular glycoprotein of interest are important contributors to the final outcome of oligosaccharide structure. Despite these complications, further study into the manipulation of glycosyltransferase genes may ultimately allow the controlled and predictable biosynthesis of glycoprotein sugar chains.

Localization of the long form of beta-1,4-galactosyltransferase to the plasma membrane and Golgi complex of 3T3 and F9 cells by immunofluorescence confocal microscopy

beta-1,4-Galactosyltransferase (GalTase) is localized to two subcellular compartments, the Golgi complex, where it participates in cellular glycosylation, and the plasma membrane, where it functions as a receptor for oligosaccharide ligands on opposing cells or in the extracellular matrix. The gene for GalTase encodes two nearly identical proteins that differ only in their N-terminal cytoplasmic domains: both short and long GalTases share an 11-aa cytoplasmic tail, but long GalTase has an additional 13-aa sequence on its cytoplasmic domain. In this study, we investigated the subcellular distribution of endogenous long GalTase in untransfected F9 and 3T3 cells by using confocal microscopy and antibodies specific for the 13-aa sequence unique to long GalTase. Long GalTase was found in the Golgi complex as expected; long GalTase was also found on the plasma membrane in cell-type-specific distributions. In 3T3 cells, long GalTase was evident on the basal surface of cells possessing a migratory phenotype, being concentrated at the leading and trailing edges; nonmigratory cells had little detectable surface immunoreactivity. In F9 cells, long GalTase was localized on the plasma membrane, being concentrated at the apical aspect of intercellular junctions. These results demonstrate that in 3T3 and F9 cells, long GalTase is present on the cell surface in addition to the Golgi complex. The pattern of surface expression shows cell-type specificity that is consistent with GalTase function in cellular interactions.

Overexpressing sperm surface beta 1,4-galactosyltransferase in transgenic mice affects multiple aspects of sperm-egg interactions

Sperm surface beta 1,4-galactosyltransferase (GalTase) mediates fertilization in mice by binding to specific O-linked oligosaccharide ligands on the egg coat glycoprotein ZP3. Before binding the egg, sperm GalTase is masked by epididymally derived glycosides that are shed from the sperm surface during capacitation. After binding the egg, sperm-bound oligosaccharides on ZP3 induce the acrosome reaction by receptor aggregation, presumably involving GalTase. In this study, we asked how increasing the levels of sperm surface GalTase would affect sperm-egg interactions using transgenic mice that overexpress GalTase under the control of a heterologous promoter. GalTase expression was elevated in many tissues in adult transgenic animals, including testis. Sperm from transgenic males had approximately six times the wild-type level of surface GalTase protein, which was localized appropriately on the sperm head as revealed by indirect immunofluorescence. As expected, sperm from transgenic mice bound more radiolabeled ZP3 than did wild-type sperm. However, sperm from transgenic animals were relatively unable to bind eggs, as compared to sperm from wild-type animals. The mechanistic basis for the reduced egg-binding ability of transgenic sperm was attributed to alterations in two GalTase-dependent events. First, transgenic sperm that overexpress surface GalTase bound more epididymal glycoside substrates than did sperm from wild-type mice, thus masking GalTase and preventing it from interacting with its zona pellucida ligand. Second, those sperm from transgenic mice that were able to bind the zona pellucida were hypersensitive to ZP3, such that they underwent precocious acrosome reactions and bound to eggs more tenuously than did wild-type sperm. These results demonstrate that sperm-egg binding requires an optimal, rather than maximal, level of surface GalTase expression, since increasing this level decreases sperm reproductive efficiency both before and after egg binding. Although sperm GalTase is required for fertilization by serving as a receptor for the egg zona pellucida, excess surface GalTase is counterproductive to successful sperm-egg binding.

Effects of overexpression of beta 1,4-galactosyltransferase on glycoprotein biosynthesis in F9 embryonal carcinoma cells

beta 1,4-Galactosyltransferase (GalTase) plays a central role in the biosynthesis of N-acetyllactosamine-containing oligosaccharides. However, despite this seemingly important function, little is known about how changes in the levels of GalTase affect oligosaccharide biosynthesis. We have examined the effects of overexpressing GalTase on the glycosylation of endogenous glycoproteins in F9 mouse embryonal carcinoma cells. Cells transfected with either the short form of the GalTase cDNA (encoding a protein of 386 amino acids) or the long form of the GalTase cDNA (encoding a protein of 399 amino acids) had a 3-fold increase in total GalTase activity, relative to control F9 cells. Analysis of pronase-digested glycopeptides obtained from control and transfected cells after metabolic labelling with [6-3H]galactose revealed no significant qualitative or quantitative differences, as assessed by Bio-Gel P-6 gel filtration chromatography and Tomato lectin affinity chromatography. Furthermore, SDS-PAGE analysis of immunoprecipitated [3H]galactose-labelled lysosomal-associated membrane protein-1 (LAMP-1) glycoprotein showed no difference in amounts or mobility. Pronase digestion and subsequent analysis of the gel-fractionated LAMP-1 glycoproteins also indicated no differences between the various cell lines. The inability of elevated GalTase activity to affect glycosylation was not due to limiting levels of GalTase substrates, since an excess of substrates was detectable in lysed cells using either endogenous or exogenous GalTase and UDP-[3H]galactose. Finally, the subcellular distribution of GalTase, as assessed by sucrose gradient fractionation, was similar between all cell types, thus suggesting that GalTase was appropriately compartmentalized in the transfected cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Evidence for a molecular distinction between Golgi and cell surface forms of beta 1,4-galactosyltransferase

beta 1,4-Galactosyltransferase (GalTase) is present on the plasma membrane of many cell types in addition to its traditional location within the Golgi compartment. Recently, the GalTase gene has been shown to encode two proteins that are identical throughout their length except that one has an additional 13-amino acid extension in its amino-terminal cytoplasmic domain. We present evidence here suggesting that the longer GalTase protein, containing this unique 13-amino acid peptide, is preferentially targeted to the plasma membrane, and the shorter GalTase protein resides primarily within the Golgi compartment. S1 nuclease protection assays of RNA from a variety of cells and tissues show that the relative abundance of the short and long GalTase mRNAs correlates with GalTase-specific activities in the Golgi and plasma membranes, respectively. Furthermore, transfection of cDNAs encoding either the long or short GalTase protein into F9 embryonal carcinoma cells suggests that the long GalTase protein is preferentially expressed on the cell surface. These results propose a molecular distinction between the Golgi and cell surface forms of GalTase as well as a novel mechanism for targeting glycoproteins to the cell surface.

Decrease in polylactosaminoglycans associated with lysosomal membrane glycoproteins during differentiation of CaCo-2 human colonic adenocarcinoma cells

The proportion of labeled polylactosaminoglycans found in glycoproteins decreases during spontaneous differentiation of CaCo-2 human colonic adenocarcinoma cells to enterocytes in culture (A. Youakim and A. Herscovics, Biochem. J., 247: 299-306, 1987). To identify polylactosaminoglycan-containing glycoproteins, CaCo-2 cells were incubated with [3H]glucosamine or [3H]fucose, for 24 h, and membrane glycoproteins solubilized with 0.5% Nonidet P-40 were fractionated by affinity chromatography on Datura stramonium (DSA)-agarose. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis and fluorography showed that a restricted set of glycoproteins with a molecular weight of about 100,000 bound to DSA-agarose. These labeled glycoproteins were shown to contain polylactosaminoglycans by DSA-agarose chromatography and endo-beta-galactosidase digestion of Pronase-derived glycopeptides. Immunoprecipitation of the [3H]glucosamine-labeled Nonidet P-40 extract with polyclonal antibodies to the lysosomal membrane proteins h-lamp-1 and h-lamp-2 followed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and fluorography also revealed a band with a molecular weight of about 100,000. The immunoprecipitates were digested with Pronase, and the resulting glycopeptides were first fractionated on Bio-Gel P-6 into excluded (Fraction I) and included (Fraction II) glycopeptides, and then by DSA-agarose affinity chromatography. A much greater proportion of labeled glycopeptides in undifferentiated cells (3 to 5 days in culture) than in differentiated cells (19 to 27 days in culture) was recovered in Fraction I; these glycopeptides were bound to DSA-agarose and were sensitive to endo-beta-galactosidase. This decrease in polylactosaminoglycans was associated primarily with h-lamp-1. These results indicate that h-lamp-1 of CaCo-2 cells contains polylactosaminoglycans and that it undergoes a change in glycosylation with differentiation.

Differentiation-associated decrease in the proportion of fucosylated polylactosaminoglycans of CaCo-2 human colonic adenocarcinoma cells

CaCo-2 cells are human colonic adenocarcinoma cells which can differentiate spontaneously into enterocytes when maintained confluent for extended periods of time. Cells kept in culture for 4 days (rapidly growing), 7-9 days (early confluence) and 19-22 days (late confluence) were incubated for 24 h with L-[5,6-3H]fucose or D-[6-3H]glucosamine in order to examine the changes in glycoprotein carbohydrate structure that occur during this differentiation. Labelled glycopeptides obtained by exhaustive Pronase digestion of the cell-surface and cell-pellet fractions were fractionated on Bio-Gel P-6. A high-Mr glycopeptide fraction which was excluded from Bio-Gel P-6 was present in all cases. These glycopeptides were then fractionated by affinity chromatography on Datura stramonium agglutinin-agarose. The glycopeptides which were specifically bound to the lectin column were largely degraded by endo-beta-galactosidase, thereby indicating that they consisted of fucosylated polylactosaminoglycans. The proportion of labelled polylactosaminoglycans decreased with increasing time in culture, whereas sucrase activity, which is characteristic of differentiated enterocytes, increased. These results demonstrate that a relatively large decrease in the proportion of fucosylated polylactosaminoglycans occurs with differentiation of CaCo-2 cells.

Cell surface glycopeptides from human intestinal epithelial cell lines derived from normal colon and colon adenocarcinomas

The cell surface glycopeptides from an epithelial cell line (CCL 239) derived from normal human colon were compared with those from three cell lines (HCT-8R, HCT-15, and CaCo-2) derived independently from human colonic adenocarcinomas. Cells were incubated with D-[2-3H]mannose or L-[5,6-3H]fucose for 24 h and treated with trypsin to release cell surface components which were then digested exhaustively with Pronase and fractionated on Bio-Gel P-6 before and after treatment with endo-beta-N-acetylglucosaminidase H. The most noticeable difference between the labeled glycopeptides from the tumor and CCL 239 cells was the presence in the former of an endo-beta-N-acetylglucosaminidase H-resistant high molecular weight glycopeptide fraction which was eluted in the void volume of Bio-Gel P-6. This fraction was obtained with both labeled mannose and fucose as precursors. However, acid hydrolysis of this fraction obtained after incubation with [2-3H]mannose revealed that as much as 60-90% of the radioactivity was recovered as fucose. Analysis of the total glycopeptides (cell surface and cell pellet) obtained after incubation with [2-3H]mannose showed that from 40-45% of the radioactivity in the tumor cells and less than 10% of the radioactivity in the CCL 239 cells was recovered as fucose. After incubation of the HCT-8R cells with D-[1,6-3H]glucosamine and L-[1-14C]fucose, strong acid hydrolysis of the labeled glycopeptide fraction excluded from Bio-Gel P-6 produced 3H-labeled N-acetylglucosamine and N-acetylgalactosamine. This high molecular weight glycopeptide fraction was susceptible to mild alkaline borohydride reduction, yielding a mixture of labeled oligosaccharides which contained N-acetylgalactosaminitol. Thus, the HCT-8R cells are expressing fucosylated mucin-type glycoproteins on their surface.