MUC1 cell surface mucin is a critical element of the mucosal barrier to infection.
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ABSTRACT:
SUBMITTER: McAuley JL
PROVIDER: S-EPMC1913485 | biostudies-literature |
REPOSITORIES: biostudies-literature
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Project description:Helicobacter pylori infection of the gastric mucosa causes an active-chronic inflammation that is strongly linked to the development of duodenal and gastric ulcers and stomach cancer. However, greater than 80% of individuals infected with H. pylori are asymptomatic beyond histologic inflammation, and it is unknown what factors influence the incidence and character of bacterial-associated gastritis and related disorders. Because previous studies demonstrated that the Muc1 epithelial glycoprotein inhibited inflammation during acute lung infection by Pseudomonas aeruginosa, we asked whether Muc1 might also counter-regulate gastric inflammation in response to H. pylori infection. Muc1(-/-) mice displayed increased bacterial colonization of the stomach and greater TNF-alpha and keratinocyte chemoattractant transcript levels compared with Muc1(+/+) mice after experimental H. pylori infection. Knockdown of Muc1 expression in AGS human gastric epithelial cells by RNA interference was associated with increased phosphorylation of IkappaBalpha, augmented activation and nuclear translocation of NF-kappaB, and enhanced production of interleulin-8 compared with Muc1-expressing cells. Conversely, Muc1 overexpression was correlated with decreased NF-kappaB activation, reduced interleulin-8 production, and diminished IkappaB kinase beta (IKKbeta)/IKKgamma coimmunoprecipitation compared with cells expressing Muc1 endogenously. Cotransfection of AGS cells with Muc1 plus IKKbeta, but not a catalytically inactive IKKbeta mutant, reversed the Muc1 inhibitory effect. Finally, Muc1 formed a coimmunoprecipitation complex with IKKgamma but not with IKKbeta. These results are consistent with the hypothesis that Muc1 binds to IKKgamma, thereby inhibiting formation of the catalytically active IKK complex and blocking the ability of H. pylori to stimulate IkappaBalpha phosphorylation, NF-kappaB activation, and downstream inflammatory responses.
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Project description:The cell surface mucin MUC1 is an important host factor limiting Helicobacter pylori (H. pylori) pathogenesis in both humans and mice by providing a protective barrier and modulating mucosal epithelial and leukocyte responses. The aim of this study was to establish the time-course of molecular events in MUC1-modulated gene expression profiles in response to H. pylori infection in wild type (WT) and MUC1-deficient mice using microarray-determined mRNA expression, gene network analysis and Ingenuity Pathway Analysis (IPA). A time-course over the first 72 h of infection showed significantly higher mucosal loads of bacteria at 8 h of infection in Muc1 -/- mice compared with WT, confirming its importance in the early stages of infection (P = 0.0003). Microarray analysis revealed 266 differentially expressed genes at one or more time-points over 72 h in the gastric mucosa of Muc1 -/- mice compared with WT control using a threshold of 2-fold change. The SPINK1 pancreatic cancer canonical pathway was strongly inhibited in Muc1 -/- mice compared with WT at sham and 8 h infection (P = 6.08E-14 and P = 2.25 E-19, respectively) but potently activated at 24 and 72 h post-infection (P = 1.38E-22 and P = 5.87E-13, respectively). The changes in this pathway are reflective of higher expression of genes mediating digestion and absorption of lipids, carbohydrates, and proteins at sham and 8 h infection in the absence of MUC1, but that this transcriptional signature is highly down regulated as infection progresses in the absence of MUC1. Uninfected Muc1 -/- gastric tissue was highly enriched for expression of factors involved in lipid metabolism and 8 h infection further activated this network compared with WT. As infection progressed, a network of antimicrobial and anti-inflammatory response genes was more highly activated in Muc1 -/- than WT mice. Key target genes identified by time-course microarrays were independently validated using RT-qPCR. These results highlight the dynamic interplay between the host and H. pylori, and the role of MUC1 in host defense, and provide a general picture of changes in cellular gene expression modulated by MUC1 in a time-dependent manner in response to H. pylori infection.
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Project description:MUC1 (or Muc1 in nonhuman species) is a membrane-tethered mucin expressed on the apical surface of mucosal epithelia (including those of the airways) that suppresses Toll-like receptor (TLR) signaling. We sought to determine whether the anti-inflammatory effect of MUC1 is operative during infection with nontypeable Haemophilus influenzae (NTHi), and if so, which TLR pathway was affected. Our results showed that: (1) a lysate of NTHi increased the early release of IL-8 and later production of MUC1 protein by A549 cells in dose-dependent and time-dependent manners, compared with vehicle control; (2) both effects were attenuated after transfection of the cells with a TLR2-targeting small interfering (si) RNA, compared with a control siRNA; (3) the NTHi-induced release of IL-8 was suppressed by an overexpression of MUC1, and was enhanced by the knockdown of MUC1; (4) the TNF-? released after treatment with NTHi was sufficient to up-regulate MUC1, which was completely inhibited by pretreatment with a soluble TNF-? receptor; and (5) primary murine tracheal surface epithelial (MTSE) cells from Muc1 knockout mice exhibited an increased in vitro production of NTHi-stimulated keratinocyte chemoattractant compared with MTSE cells from Muc1-expressing animals. These results suggest a hypothetical feedback loop model whereby NTHi activates TLRs (mainly TLR2) in airway epithelial cells, leading to the increased production of TNF-? and IL-8, which subsequently up-regulate the expression of MUC1, resulting in suppressed TLR signaling and decreased production of IL-8. This report is the first, to the best of our knowledge, demonstrating that the inflammatory response in airway epithelial cells during infection with NTHi is controlled by MUC1 mucin, mainly through the suppression of TLR2 signaling.
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Project description:MUC1 is an integral membrane glycoprotein expressed on epithelial and hematopoietic cells with a COOH-terminus (CT) that mediates intracellular signal transduction. To better understand MUC1-dependent signaling, we searched for proteins binding to its CT using the yeast two-hybrid system with the MUC1 CT as bait and a human epithelial cell cDNA library as prey. Of the six positive clones identified, all encoded calcium-modulating cyclophilin ligand (CAML). The MUC1 CT interacted with CAML in transformed yeast cells as revealed by growth on selective media and in situ X-alpha-galactosidase activity. Binding of the MUC1 CT to CAML in human epithelial cells was confirmed by reciprocal coimmunoprecipitations, confocal microscopy, protein crosslinking, and coupled transcription/translation analyses. By deletion mutagenesis, the NH(2)-terminus of CAML was responsible for binding to the MUC1 CT. Finally, transfection of cells with plasmids encoding MUC1 and CAML increased intracellular calcium levels compared with cells transfected with either plasmid alone, suggesting a possible biological significance of the MUC1-CAML interaction.
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Project description:The gastrointestinal tract is the predicted reservoir for most bloodstream infections (BSIs) after hematopoietic stem cell transplantation (HSCT). Whole-genome sequencing and comparative genomics have the potential to improve our understanding of the dynamics of gut colonization that precede BSI in HSCT recipients. Within a prospective cohort study of children (age <18 years) undergoing HSCT, 9 subjects met criteria for mucosal barrier injury BSI. We performed whole-genome sequencing of the blood culture isolate and weekly fecal samples preceding the BSI to compare the genetic similarity of BSI isolates to fecal strains. We evaluated temporal associations between antibiotic exposures and the abundances of BSI strains in the gut microbiota and correlated the detection of antibiotic resistance genes with the phenotypic antibiotic resistance of these strains. The median patient age was 2.6 years, and 78% were male. BSIs were caused by Escherichia coli (n = 5), Enterococcus faecium (n = 2), Enterobacter cloacae (n = 1), and Rothia mucilaginosa (n = 1). In the 6 BSI episodes with evaluable comparative genomics, the fecal strains were identical to the blood culture isolate (>99.99% genetic similarity). Gut domination by these strains preceded only 4 of 7 E. coli or E. faecium BSIs by a median of 17 days (range, 6 to 21 days). Increasing abundances of the resulting BSI strains in the gut microbiota were frequently associated with specific antibiotic exposures. E. cloacae and R. mucilaginosa were not highly abundant in fecal samples preceding BSIs caused by these species. The detection of antibiotic resistance genes for β-lactam antibiotics and vancomycin predicted phenotypic resistance in BSI strains. Bacterial strains causing mucosal barrier injury BSI in pediatric HSCT recipients were observed in the gut microbiota before BSI onset, and changes in the abundances of these strains within the gut preceded most BSI episodes. However, frequent sampling of the gut microbiota and sampling of other ecological niches is likely necessary to effectively predict BSI in HSCT recipients.
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Project description:BACKGROUND: Gastric carcinoma is the second leading cause of cancer-associated death worldwide. The high mortality associated with this disease is in part due to limited knowledge about gastric carcinogenesis and a lack of available therapeutic and prevention strategies. MUC1 is a high molecular weight transmembrane mucin protein expressed at the apical surface of most glandular epithelial cells and a major component of the mucus layer above gastric mucosa. Overexpression of MUC1 is found in approximately 95% of human adenocarcinomas, where it is associated with oncogenic activity. The role of MUC1 in gastric cancer progression remains to be clarified. METHODOLOGY: We downregulated MUC1 expression in a gastric carcinoma cell line by RNA interference and studied the effects on cellular proliferation (MTT assay), apoptosis (TUNEL assay), migration (migration assay), invasion (invasion assay) and aggregation (aggregation assay). Global gene expression was evaluated by microarray analysis to identify alterations that are regulated by MUC1 expression. In vivo assays were also performed in mice, in order to study the tumorigenicity of cells with and without MUC1 downregulation in MKN45 gastric carcinoma cell line. RESULTS: Downregulation of MUC1 expression increased proliferation and apoptosis as compared to controls, whereas cell-cell aggregation was decreased. No significant differences were found in terms of migration and invasion between the downregulated clones and the controls. Expression of TCN1, KLK6, ADAM29, LGAL4, TSPAN8 and SHPS-1 was found to be significantly different between MUC1 downregulated clones and the control cells. In vivo assays have shown that mice injected with MUC1 downregulated cells develop smaller tumours when compared to mice injected with the control cells. CONCLUSIONS: These results indicate that MUC1 downregulation alters the phenotype and tumorigenicity of MKN45 gastric carcinoma cells and also the expression of several molecules that can be involved in tumorigenic events. Therefore, MUC1 should be further studied to better clarify its potential as a novel therapeutic target for gastric cancer.
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