Biochemical interactions among intercellular adhesion molecules expressed by airway epithelial cells

Interference of mucin 1 inhibits progression of colon carcinoma by repression of Wnt/β-catenin signaling

Mucin 1 (Muc1) is a tumor-associated glycoprotein and has an important role in cancer progression and metastasis. The aim of the study was to explore the effects and mechanism of Muc1 silencing on proliferation and tumor-forming capacity of colon cancer cell lines. In the present study, we first screened the colon cancer cell lines with high expression of Muc1 by western blot analysis. Then, the effective siRNA was selected and used for silencing endogenous Muc1. The results by MTT and vitro scratch assay showed that interference of Muc1 could effectively inhibit HCC2998 proliferation and migration (p<0.01). Also, colony-forming ability in Muc1-siRNA groups was significantly decreased compared with the control group (p<0.01). Cell cycle is detected by flow cytometry that suggested that Muc1-siRNA1 induced cell cycle arrest at S phase in HCC2998. Next, the expression and distribution of β-catenin in cytoplasm and the nucleus was detected by western blot and the results revealed that the expression of β-catenin was redistributed in Muc1-siRNA group. A higher β-catenin level was detected in cytoplasm, while a lower β-catenin level was located in nucleus, compared with controls (p<0.05). The tumorigenicity experiments showed that inhibition of Muc1 could significantly suppress the growth of HCC2998 in nude mice models (p<0.01). This study would effectively provide new clues for colon cancer therapy.

Intercellular adhesion molecule 1: recent findings and new concepts involved in mammalian spermatogenesis

Spermatogenesis, the process of spermatozoa production, is regulated by several endocrine factors, including testosterone, follicle stimulating hormone, luteinizing hormone and estradiol 17β. For spermatogenesis to reach completion, developing germ cells must traverse the seminiferous epithelium while remaining transiently attached to Sertoli cells. If germ cell adhesion were to be compromised for a period of time longer than usual, germ cells would slough from the seminiferous epithelium and infertility would result. Presently, Sertoli-germ cell adhesion is known to be mediated largely by classical and desmosomal cadherins. More recent studies, however, have begun to expand long-standing concepts and to examine the roles of other proteins such as intercellular adhesion molecules. In this review, we focus on the biology of intercellular adhesion molecules in the mammalian testis, hoping that this information is useful in the design of future studies.

Molecular Interactions between MUC1 Epithelial Mucin, β-Catenin, and CagA Proteins

Interleukin (IL)-8-driven neutrophil infiltration of the gastric mucosa is pathognomonic of persistent Helicobacter pylori infection. Our prior study showed that ectopic over-expression of MUC1 in human AGS gastric epithelial cells reduced H. pylori-stimulated IL-8 production compared with cells expressing MUC1 endogenously. Conversely, Muc1 knockout (Muc1(-/-)) mice displayed an increased level of transcripts encoding the keratinocyte chemoattractant (KC), the murine equivalent of human IL-8, in gastric mucosa compared with Muc1(+/+) mice during experimental H. pylori infection. The current study tested the hypothesis that a decreased IL-8 level observed following MUC1 over-expression is mediated through the ability of MUC1 to associate with β-catenin, thereby inhibiting H. pylori-induced β-catenin nuclear translocation. Increased neutrophil infiltration of the gastric mucosa of H. pylori-infected Muc1(-/-) mice was observed compared with Muc1(+/+) wild type littermates, thus defining the functional consequences of increased KC expression in the Muc1-null animals. Protein co-immunoprecipitation (co-IP) studies using lysates of untreated or H. pylori-treated AGS cells demonstrated that (a) MUC1 formed a co-IP complex with β-catenin and CagA, (b) MUC1 over-expression reduced CagA/β-catenin co-IP, and (c) in the absence of MUC1 over-expression, H. pylori infection increased the nuclear level of β-catenin, (d) whereas MUC1 over-expression decreased bacteria-driven β-catenin nuclear localization. These results suggest that manipulation of MUC1 expression in gastric epithelia may be an effective therapeutic strategy to inhibit H. pylori-dependent IL-8 production, neutrophil infiltration, and stomach inflammation.

Site directed processing: role of amino acid sequences and glycosylation of acceptor glycopeptides in the assembly of extended mucin type O-glycan core 2

BACKGROUND

The assembly of Ser/Thr-linked O-glycans of mucins with core 2 structures is initiated by polypeptide GalNAc-transferase (ppGalNAc-T), followed by the action of core 1 beta3-Gal-transferase (C1GalT) and core 2 beta6-GlcNAc-transferase (C2GnT). Beta4-Gal-transferase (beta4GalT) extends core 2 and forms the backbone structure for biologically important epitopes. O-glycan structures are often abnormal in chronic diseases. The goal of this work is to determine if the activity and specificity of these enzymes are directed by the sequences and glycosylation of substrates.

METHODS

We studied the specificities of four enzymes that synthesize extended O-glycan core 2 using as acceptor substrates synthetic mucin derived peptides and glycopeptides, substituted with GalNAc or O-glycan core structures 1, 2, 3, 4 and 6.

RESULTS

Specific Thr residues were found to be preferred sites for the addition of GalNAc, and Pro in the +3 position was found to especially enhance primary glycosylation. An inverse relationship was found between the size of adjacent glycans and the rate of GalNAc addition. All four enzymes could distinguish between substrates having different amino acid sequences and O-glycosylated sites. A short glycopeptide Galbeta1-3GalNAcalpha-TAGV was identified as an efficient C2GnT substrate.

CONCLUSIONS

The activities of four enzymes assembling the extended core 2 structure are affected by the amino acid sequence and presence of carbohydrates on nearby residues in acceptor glycopeptides. In particular, the sequences and O-glycosylation patterns direct the addition of the first and second sugar residues by ppGalNAc-T and C1GalT which act in a site directed fashion.

GENERAL SIGNIFICANCE

Knowledge of site directed processing enhances our understanding of the control of O-glycosylation in normal cells and in disease.

CAR mediates efficient tumor engraftment of mesenchymal type lung cancer cells

The coxsackie-adenovirus receptor (CAR) is a developmentally regulated intercellular adhesion molecule that was previously observed to be required for efficient tumor formation. To confirm that observation, we compared the tumorigenicity of clonally derived test and control cell subsets that were genetically modified for CAR. Silencing CAR in lung cancer cells with high constitutive expression reduced engraftment efficiency. Conversely, overexpressing CAR in lung cancer cells with low constitutive expression did not affect tumor formation or growth kinetics. A blocking antibody to the extracellular domain of CAR inhibited tumor engraftment, implicating that domain as being important to this process. However, differences in adhesion properties attributable to this domain (barrier function and aggregation) could not be distinguished in the test groups in vitro, and the mechanisms underlying CAR's contribution to tumor engraftment remain elusive. Because high CAR cells displayed a spindle-shaped morphology at baseline, we considered whether this expression was an accompaniment of other mesenchymal features in these lung cancer cells. Molecular correlates of CAR were compared in model epithelial and mesenchymal type lung cancer cells. CAR expression is associated with an absence of E-cadherin, diminished expression of alpha- and gamma-catenin, and increased Zeb1, Snail, and vimentin expression in lung cancer cells. In contrast, epithelial type (NCI-H292, Calu3) lung cancer cells show comparatively low CAR expression. These data suggest that if the mesenchymal cell phenotype is an accurate measure of an undifferentiated and invasive state, then CAR expression may be more closely aligned with this phenotype of lung cancer cells.

MUC4 involvement in ErbB2/ErbB3 phosphorylation and signaling in response to airway cell mechanical injury

The receptor tyrosine kinases ErbB2 and ErbB3 are phosphorylated in response to injury of the airway epithelium. Since we have shown that the membrane mucin MUC4 can act as a ligand/modulator for ErbB2, affecting its localization in polarized epithelial cells and its phosphorylation, we questioned whether Muc4 was involved, along with ErbB2 and ErbB3, in the damage response of airway epithelia. To test this hypothesis, we first examined the localization of MUC4 in human airway samples. Both immunocytochemistry and immunofluorescence showed a co-localization of MUC4 and ErbB2 at the airway luminal surface. Sequential immunoprecipitation and immunoblotting from airway cells demonstrated that the MUC4 and ErbB2 are present as a complex in airway epithelial cells. To assess the participation of MUC4 in the damage response, cultures of NCI-H292 or airway cells were scratch-wounded, then analyzed for association of phospho-ErbB2 and -ErbB3 with MUC4 by sequential immunoprecipitation and immunoblotting. Wounded cultures exhibited increased phosphorylation of both receptors in complex with MUC4. Scratch wounding also increased activation of the downstream pathway through Akt, as predicted from our previous studies on Muc4 effects on ErbB2 and ErbB3. The participation of MUC4 in the phosphorylation response was also indicated by siRNA repression of MUC4 expression, which resulted in diminution of the phosphorylation of ErbB2 and ErbB3. These studies provide a new model for the airway epithelial damage response, in which the MUC4-ErbB2 complex is a key element in the sensor mechanism and phosphorylation of the receptors.

Comparison of HeLa-I, HEp-2 and NCI-H292 cell lines for the isolation of human respiratory syncytial virus (HRSV)

Generally, laboratory diagnosis of viral respiratory infections utilizes virus isolation in cell culture and immunofluorescence assays. In this study, three cell lines (HEp-2, NCI-H292 and HeLa-I) were used for HRSV isolation of strains obtained from patients admitted at HU-USP with respiratory tract disease. HRSV was isolated in 46% (37) of 80 specimens inoculated in HeLa-I, 48% (39) in HEp-2, and 36.3% (29) in NCI-H292. Immunofluorescence was considered the gold standard and yielded 53% positive (43). The results from both methods combined had better sensitivity (73.2%) compared to either method alone. Comparing results between the cell lines with HEp-2 cells as the benchmark, the greatest sensitivity (72.2%) was observed in HeLa-I. This data shows that HeLa-I is adequate for HRSV isolation, giving results similar to the HEp-2 cells. The combined use of the HEp-2, HeLa-I and NCI-H292 cells improve the detection of HRSV.