Analysis of dystroglycan regulation and functions in mouse mammary epithelial cells and implications for mammary tumorigenesis

High LARGE1 Expression May Predict Benefit from Adjuvant Chemotherapy in Resected Non-Small-Cell Lung Cancer

Background

LARGE1 plays a pivotal role in glycosylation of alpha-Dystroglycan (α-DG) and is aberrantly downregulated in cell lines originating from epithelium-derived cancers including lung cancer. However, the expression of LARGE1 and its clinical significance in NSCLC are not clear.

Materials and Methods

The data were collected from the TCGA database to investigate LARGE1 expression in stage I–III NSCLC and explore its associations with clinicopathological parameters and overall survival of patients. The prognostic role of LARGE1 was examined in subgroups according to clinical features and treatments. The results were validated in external cohorts from the NCBI GEO database. Gene Set Enrichment Analysis (GSEA) was performed to investigate the potential molecular mechanisms during LARGE1 alteration in NSCLC.

Results

LARGE1 was aberrantly downregulated in NSCLC compared with adjacent tissues and normal lung tissues and in tumors with advanced stage compared with early stage. There was only a trend of association between high LARGE1 with OS in multivariate analysis. Surprisingly, high LARGE1 was significantly associated with improved OS in a subgroup of the patients with adjuvant chemotherapy (ACT) and a significant interaction between LARGE1 expression and ACT was found. Improved OS after ACT was also found in patients with high LARGE1 compared to those with low LARGE1. When combining LARGE1 expression and ACT, compared with patients with non-ACT, HR of low LARGE1/ACT was 0.592 (95% CI=0.432–0.813, P=0.0012), and HR of high LARGE1/ACT was 0.124 (95% CI=0.031–0.505, P=0.0036). The results were verified in two external cohorts from the GEO database. GSEA indicated that LARGE1 might downregulate cell cycle pathway to improve ACT sensitivity and subsequently the prognosis in NSCLC.

Conclusion

High LARGE1 can be used to identify the patients with resected stage I–III NSCLC most likely to benefit from adjuvant chemotherapy.

Dynamic Dystroglycan Complexes Mediate Cell Entry of Lassa Virus

Recognition of cellular receptors allows emerging viruses to break species barriers and is an important determinant for their disease potential. Many virus receptors have complex tissue-specific interactomes, and preexisting protein-protein interactions may influence their function. Combining shotgun proteomics with a biochemical approach, we characterize the molecular composition of the functional receptor complexes used by the highly pathogenic Lassa virus (LASV) to invade susceptible human cells. We show that the specific composition of the receptor complexes affects productive entry of the virus, providing proof-of-concept. In uninfected cells, these functional receptor complexes undergo dynamic turnover involving an endocytic pathway that shares some characteristics with viral entry. However, steady-state receptor uptake and virus endocytosis critically differ in kinetics and underlying signaling, indicating that the pathogen can manipulate the receptor complex according to its needs. Our study highlights a remarkable complexity of LASV-receptor interaction and identifies possible targets for therapeutic antiviral intervention.

Recognition of functional receptors by viruses is a key determinant for their host range, tissue tropism, and disease potential. The highly pathogenic Lassa virus (LASV) currently represents one of the most important emerging pathogens. The major cellular receptor for LASV in human cells is the ubiquitously expressed and evolutionary highly conserved extracellular matrix receptor dystroglycan (DG). In the host, DG interacts with many cellular proteins in a tissue-specific manner. The resulting distinct supramolecular complexes likely represent the functional units for viral entry, and preexisting protein-protein interactions may critically influence DG’s function in productive viral entry. Using an unbiased shotgun proteomic approach, we define the largely unknown molecular composition of DG complexes present in highly susceptible epithelial cells that represent important targets for LASV during viral transmission. We further show that the specific composition of cellular DG complexes can affect DG’s function in receptor-mediated endocytosis of the virus. Under steady-state conditions, epithelial DG complexes underwent rapid turnover via an endocytic pathway that shared some characteristics with DG-mediated LASV entry. However, compared to steady-state uptake of DG, LASV entry via DG occurred faster and critically depended on additional signaling by receptor tyrosine kinases and the downstream effector p21-activating kinase. In sum, we show that the specific molecular composition of DG complexes in susceptible cells is a determinant for productive virus entry and that the pathogen can manipulate the existing DG-linked endocytic pathway. This highlights another level of complexity of virus-receptor interaction and provides possible cellular targets for therapeutic antiviral intervention.

Matrix Metalloproteases-Mediated Cleavage on β-Dystroglycan May Play a Key Role in the Blood-Brain Barrier After Intracerebral Hemorrhage in Rats

BACKGROUND It is well documented that the Blood-Brain barrier (BBB) can be damaged by matrix metalloproteases (MMPs) after intracerebral hemorrhage (ICH), but little is known about the mechanism of this effect. MATERIAL AND METHODS We established an ICH model in rats by injecting collagenase VII into the striatum. Afterwards, intraperitoneal injection of these rats with 40 mg/kg GM6001 (a MMPs inhibitor). The effects of GM6001 on ICH were investigated by neurological severity score, brain water content, Evans blue staining, hematoxylin-eosin staining, immunohistochemical staining, and Western blot assays. RESULTS We demonstrated that the neurological damage caused by ICH was relieved at 5 and 7 days following administration of GM6001. The impaired BBB induced by ICH was improved in response to GM6001 treatment at around 3 days, as evidenced by alleviated cerebral edema, decreased Evans blue extravasation, and a reduction in inflammatory cellular infiltration. Mechanism analysis revealed that ICH induced the generation of β-dystroglycan cleavage, which could be suppressed by GM6001 treatment. Furthermore, we found that recombinant MMP2 and MMP9 triggered the cleavage of β-dystroglycan in vitro, and this action could be inhibited by GM6001 administration. CONCLUSIONS Taken together, our results suggest that MMPs-mediated cleavage on β-dystroglycan may play an important role in BBB after ICH.

Correlation of deregulated like-acetylglucosaminyl transferase and aberrant α-dystroglycan expression with human tongue cancer metastasis

PURPOSE

The present study examined the correlation of α-dystroglycan (α-DG) expression and like-acetylglucosaminyl transferase (LARGE) with metastasis of human tongue cancer.

MATERIALS AND METHODS

Fifty human tongue cancer tissues and 2 tongue squamous cell carcinoma cell lines (CAL27 and SCC4) were involved. Immunohistochemistry was used to detect the expression of α-DG and LARGE. Methylation-specific polymerase chain reaction was performed to assess the methylation status of the LARGE gene promoter. CAL27 and SCC4 cells were transfected with exogenous LARGE and treated with 5-aza-2'-deoxycytidine (Aza-dC), respectively. Glycol sites of α-DG were detected by western blotting. In addition, the laminin overlay assay, cell adhesion assay, and invasion assay were performed.

RESULTS

Immunohistochemical results showed that decreased expression of VIA4-1 and IIH6 (antibodies that recognize the glycol sites of α-DG) were correlated with the lymph node metastasis of tongue cancer (n = 50; P = .016 and .025, respectively). Decreased LARGE expression and hypermethylation of the LARGE gene promoter were correlated with lymph node metastasis and α-DG glycosylation in human tongue cancer (n = 50; P = .043 and .015 respectively). In addition, LARGE overexpression and Aza-dC treatment actively led to restoration of functional α-DG expression, elevation of laminin binding, and decrease of migratory ability in cancer cells.

CONCLUSION

The results suggested that absent α-DG expression and LARGE deregulation were closely associated with nodal metastasis of tongue cancer. Aberrant α-DG expression and glycosylation were attributed at least in part to the abnormal epigenetic modification of LARGE, especially the hypermethylation of its promoter.

Reciprocal expressions between α-dystroglycan and integrin β1, perlecan receptors, in the murine enamel organ development

Signals of perlecan, an extracellular matrix molecule, which accumulates within the intercellular spaces of the stellate reticulum of the enamel organ, are mediated by at least two receptors, dystroglycan (DG) and integrin β1, in a case-dependent manner in various events in embryogenesis and pathogenesis. This study aims to understand the expression profiles of these two perlecan receptors at both protein and gene levels in murine enamel organ development. Before birth, α-DG was immunolocalized in stellate reticulum cells, in which perlecan was colocalized, while integrin β1 was mainly distributed in the peripheral enamel organ cells as well as the dental mesenchymal cells. On and after postnatal Day 1, the expression of α-DG was dramatically decreased in the stellate reticulum, while integrin β1 was enhanced around blood vessels within the enamel organ. Furthermore, biosyntheses of α-DG and integrin β1 by dental epithelial and pulp mesenchymal cells were confirmed in vitro by using immunofluorescence and reverse-transcriptase polymerase chain reaction. The results suggest that DG is a perlecan receptor that specifically functions in the stellate reticulum of the embryonic stage, but that dental epithelial and mesenchymal cells are maturated by capturing perlecan signals differentially through integrin β1.

Dystroglycan function is a novel determinant of tumor growth and behavior in prostate cancer

BACKGROUND

Dystroglycan is a ubiquitously expressed cell adhesion molecule frequently found to be altered or reduced in adenocarcinomas, however the mechanisms or consequences of dystroglycan loss have not been studied extensively.

METHODS

We examined the consequence of overexpression or RNAi depletion of dystroglycan on properties of in vitro growth migration and invasion of LNCaP, PC3, and DU145 prostate cancer cell lines.

RESULTS

Using LNCaP cells we observed cell density-dependent changes in β-dystroglycan with the appearance of several lower molecular weight species ranging in size from 43 to 26 kDa. The bands of 31 and 26 kDa were attributed to proteolysis, whereas bands between 43 and 38 kDa were a consequence of mis-glycosylation. The localization of β-dystroglycan in LNCaP colonies in culture also varied, cells with a mesenchymal appearance at the periphery of the colony had more pronounced membrane localization of dystroglycan. Whereas some cells demonstrated nuclear dystroglycan. Increased dystroglycan levels were inhibitory to growth in soft agar but promoted Matrigel invasion, whereas reduced dystroglycan levels promoted growth in soft agar but inhibited invasion. Similar results were also obtained for PC3 and DU145 cells.

CONCLUSIONS

This study suggests that changes in β-dystroglycan distribution within the cell and/or the loss of dystroglycan during tumorigenesis, through a combination of proteolysis and altered glycosylation, leads to an increased ability to grow in an anchorage independent manner, however dystroglycan may need to be re-expressed for cell invasion and metastasis to occur.

Increased expression of CD133 and reduced dystroglycan expression are strong predictors of poor outcome in colon cancer patients

Background

Expression levels of CD133, a cancer stem cell marker, and of the α-subunit of the dystroglycan (α-DG) complex, have been previously reported to be altered in colorectal cancers.

Methods

Expression levels of CD133 and α-DG were assessed by immunohistochemistry in a series of colon cancers and their prognostic significance was evaluated.

Results

Scattered cells positive for CD133 were rarely detected at the bases of the crypts in normal colonic mucosa while in cancer cells the median percentage of positive cells was 5% (range 0–80). A significant correlation was observed with pT parameter and tumor stage but not with tumor grade and N status. Recurrence and death from disease were significantly more frequent in CD133-high expressing tumors and Kaplan-Meier curves showed a significant separation between high vs low expressor groups for both disease-free (p = 0.002) and overall (p = 0.008) survival.

Expression of α-DG was reduced in a significant fraction of tumors but low α-DG staining did not correlate with any of the classical clinical-pathological parameters. Recurrence and death from the disease were significantly more frequent in α-DG-low expressing tumors and Kaplan-Meier curves showed a significant separation between high vs low expressor tumors for both disease-free (p = 0.02) and overall (p = 0.02) survival. Increased expression of CD133, but not loss of α-DG, confirmed to be an independent prognostic parameters at a multivariate analysis associated with an increased risk of recurrence (RR = 2.4; p = 0.002) and death (RR = 2.3; p = 0.003).

Conclusions

Loss of α-DG and increased CD133 expression are frequent events in human colon cancer and evaluation of CD133 expression could help to identify high-risk colon cancer patients.

Identification of Endothelin-1 and NR4A2 as CD133-regulated genes in colon cancer cells

Several in vitro assays have been proposed to identify cancer stem cells (CSCs), including immunophenotyping, sphere assay and side population (SP) assay. CD133 antigen has been proposed as a CSC marker in colon cancer (CC). However, no functional data are available to date and conflicting results have been reported regarding its role as true CSC marker. Here we set out to identify a molecular signature associated with potential CSC. CD133(+) cells isolated from the CaCo-2 CC cell line were analysed by microarray molecular profiling compared to CD133(-) counterparts. Various differentially expressed genes were identified and the most relevant transcripts found to be over-expressed in CD133(+) cells were evaluated by quantitative RT-PCR in the CD133(+) fractions isolated from several CC cell lines. In the attempt to find a correlation between putative CSCs, isolated by means of CD133 immunophenotyping and the SP approach, we demonstrated a significant enrichment of CD133(+) cells within the SP fraction of CC cells, and comparison of the gene expression profiles revealed that Endothelin-1 (END-1) and nuclear receptor subfamily 4, group A, member 2 (NR4A2) transcripts are highly expressed in both CD133(+) and SP fractions of CC cells. Moreover, depletion of CD133 by siRNA induced a significant attenuation of END-1 and NR4A2 expression levels in CaCo-2 cells, while expression of all three molecules decreased during sodium butyrate-induced differentiation. In conclusion, we have identified a molecular signature associated with potential CSCs and showed for the first time the existence of a functional relationship between CD133, END-1 and NR4A2 expression in colon cancer cells.

Differential expression profiles between α-dystroglycan and integrin β1 in ameloblastoma: two possible perlecan signalling pathways for cellular growth and differentiation

AIMS

Intercellular deposition of perlecan, an extracellular matrix molecule, results in characteristic stellate reticulum-like structures in ameloblastomas. The aims of this study were to elucidate which types of perlecan receptors function within any particular type of tissue architecture of ameloblastoma.

METHODS AND RESULTS

Protein and gene expression profiles for α-dystroglycan and integrin β1 were examined comparatively with those of their ligands in ameloblastoma using surgical specimens and cells in primary culture. In the follicular-type tumour cell foci, α-dystroglycan was localized uniformly over the stellate reticulum-like cells, while integrin β1 was restricted mainly to peripheral cells facing the stroma with the interface of the basement membrane, which was also rich in perlecan. In the plexiform-type, mRNA and protein signals for α-dystroglycan were enhanced in the periphery of tumour cell foci, especially in their invading fronts. Integrin β1 was also immunolocalized in the basal cell zone, which was considered to be the proliferation centre of ameloblastoma cells. Furthermore, biosynthesis of α-dystroglycan and integrin β1 by ameloblastoma cells was confirmed in vitro using immunofluorescence and reverse transcriptase-polymerase chain reaction.

CONCLUSIONS

Ameloblastoma cells proliferate and are differentiated by capturing perlecan differentially with α-dystroglycan and integrin β1, respectively.

Expression of alpha-dystroglycan correlates with tumour grade and predicts survival in oral squamous cell carcinoma

AIMS

Dystroglycan (DG) is a non-integrin adhesion molecule connecting the extracellular matrix to the actin cytoskeleton. Decreased expression of DG has been reported in several human cancers and related to tumour aggressiveness.

METHODS

Expression of the alpha-DG subunit was evaluated by immunostaining in a series of oral squamous cell carcinoma (OSCC) and its relation with traditional prognostic indicators and with the clinical outcome of the patients was evaluated.

RESULTS

Alpha-DG expression was easily detected in normal epithelium with a mean percentage of positive cells >80% but was undetectable in a significant fraction (59%) of OSCC. Loss of alpha-DG staining correlated with higher tumour grade (p = 0.04) and stage (p = 0.01), with nodal involvement (p = 0.001) and with an increased risk of recurrence (p = 0.002) and death (p = 0.004) in a univariate analysis, but it was not confirmed as an independent predictor of clinical outcome in a multivariate analysis.

CONCLUSIONS

Loss of alpha-DG expression, which corresponds to loss of a functional DG complex, is a frequent event in human OSCC. Further studies are warranted on the role of this molecule in the entire multistep process of oral squamous tumorigenesis.

Post-translational modulation of CD133 expression during sodium butyrate-induced differentiation of HT29 human colon cancer cells: implications for its detection

The CD133 molecule has been proposed as a surface marker of cancer stem cells in several human malignancies, including colon cancers. The function and the mechanisms regulating CD133 expression remain unknown. The HT29 human colon cancer cells undergo differentiation following treatment with various agents and represent a useful in vitro model of colon differentiation. This study evaluated the behavior of CD133 during sodium butyrate-induced differentiation of HT29 cells. Treatment with sodium butyrate induced a progressive decrease of CD133 expression, as assessed by flow cytometry using the AC133 monoclonal antibody. Indeed, expression of CD133, which was about 47% in untreated control cells, gradually decreased down to about 3% after 72 h in a time- and dose-dependent manner. No relationship was observed between CD133 protein evaluated by flow cytometry and mRNA expression level, and no changes were detected in the methylation status of the CD133 gene promoter during HT29 differentiation. Moreover, the expression of the CD133 protein, evaluated by Western blot analysis using a specific anti-CD133 antibody directed against the C-terminal intracytoplasmic region of human CD133 protein, did not correlate with flow cytometry results. Different results were also obtained using the two antibodies to analyze the expression of the CD133 molecule in human colon cancers. These findings demonstrate that membrane expression of the CD133 stem cell marker might undergo a complex regulation during differentiation of colon cells and suggest that HT29 cells are a useful in vitro model to study the mechanisms involved in this regulation which likely occurs at a post-transcriptional level.

Mice lacking dystrophin or alpha sarcoglycan spontaneously develop embryonal rhabdomyosarcoma with cancer-associated p53 mutations and alternatively spliced or mutant Mdm2 transcripts

Altered expression of proteins in the dystrophin-associated glycoprotein complex results in muscular dystrophy and has more recently been implicated in a number of forms of cancer. Here we show that loss of either of two members of this complex, dystrophin in mdx mice or alpha sarcoglycan in Sgca(-/-) mice, results in the spontaneous development of muscle-derived embryonal rhabdomyosarcoma (RMS) after 1 year of age. Many mdx and Sgca(-/-) tumors showed increased expression of insulin-like growth factor 2, retinoblastoma protein, and phosphorylated Akt and decreased expression of phosphatase and tensin homolog gene, much as is found in a human RMS. Further, all mdx and Sgca(-/-) RMS analyzed had increased expression of p53 and murine double minute (mdm)2 protein and contained missense p53 mutations previously identified in human cancers. The mdx RMS also contained missense mutations in Mdm2 or alternatively spliced Mdm2 transcripts that lacked an exon encoding a portion of the p53-binding domain. No Pax3:Fkhr or Pax7:Fkhr translocation mRNA products were evident in any tumor. Expression of natively glycosylated alpha dystroglycan and alpha sarcoglycan was reduced in mdx RMS, whereas dystrophin expression was absent in almost all human RMS, both for embryonal and alveolar RMS subtypes. These studies show that absence of members of the dystrophin-associated glycoprotein complex constitutes a permissive environment for spontaneous development of embryonal RMS associated with mutation of p53 and mutation or altered splicing of Mdm2.

Modulation of TRPM6 and Na(+)/Mg(2+) exchange in mammary epithelial cells in response to variations of magnesium availability

Mammary epithelial cells (HC11) chronically adapted to grow in a low-magnesium (0.05 mM vs. 0.5 mM) or in a high-magnesium (40 mM) medium were used to investigate on the mechanisms of cell magnesium transport under conditions of non-physiological magnesium availability. Magnesium influx was higher in low-magnesium cells compared to control or high-magnesium cells, whereas magnesium efflux was higher in high-magnesium cells compared to control and low-magnesium cells. Magnesium efflux was partially inhibited by imipramine, inhibitor of the Na(+)/Mg(2+) exchange. Using a monoclonal antibody detecting a approximately 70 kDa protein associated with Na(+)/Mg(2+) exchange activity, we found that the expression levels of this protein were proportional to magnesium efflux capacity, that is, high-magnesium cells > control cells > low-magnesium cells. As for magnesium influx, this was abolished by Co(III)hexaammine, inhibitor of magnesium channels. Surprisingly, we found that cells grown in low magnesium upregulated mRNA for the magnesium channel TRPM6, but not for other channels like TRPM7 or MagT1. TRPM6 mRNA was also rapidly upregulated or downregulated in HC11 cells deprived of magnesium or in low-magnesium cells re-added with magnesium, respectively. TRPM6 protein levels, as assessed by Western blot and immunofluorescence, underwent similar changes under comparable conditions. We propose that mammary epithelial cells adapt to decreased magnesium availability by upregulating magnesium influx via TRPM6, and counteract increased magnesium availability by increasing magnesium efflux primarily via Na(+)/Mg(2+) exchange. These results show, for the first time, that TRPM6 contributes to regulating magnesium influx in mammary epithelial cells, similar to what is known for intestine and kidney.

Increments of alpha-dystroglycan expression in liver metastasis correlate with poor survival in gastric cancer

BACKGROUND

Dystroglycan (DG) is a recently focused adhesion molecule with possible roles in cancer development and progression. We investigated correlations between alpha-DG expression and prognosis in gastric carcinoma with liver metastasis.

METHODS

For 40 patients with gastric adenocarcinoma and liver-only metastasis, alpha-DG expression was determined by immunohistochemistry in paraffin-embedded surgical specimens of resected stomach tumor, resected liver metastasis, and their normal counterpart tissues. Correlations between alpha-DG expression and prognosis were retrospectively analyzed.

RESULTS

alpha-DG expression was higher in primary gastric cancer (P = 0.006) and lower in liver metastasis (P = 0.002) than in each normal counterpart. In primary stomach cancer, patients who had lower alpha-DG expression in tumors than in normal counterparts showed poor overall survival (OS) (P = 0.028). In contrast, in the liver, patients who had higher alpha-DG expression in tumors than in normal counterparts showed poor OS (P = 0.022). Also, higher alpha-DG expression in liver metastasis than in stomach tumors led to poor recurrence-free survival (P = 0.023) and OS (P = 0.056).

CONCLUSIONS

This approach may be used to further understanding of the pathogenesis of liver metastasis from gastric cancer. Further studies are warranted to reveal the mechanisms of alpha-DG dysregulation in liver metastasis.

Identification of Sp1 and GC-boxes as transcriptional regulators of mouse Dag1 gene promoter

Dystroglycan is a widely expressed adhesion complex that anchors cells to the basement membrane and is involved in embryonic development and differentiation. Dystroglycan expression is frequently reduced in human dystrophies and malignancies, and its molecular functions are not completely understood. Several posttranslational mechanisms have been identified that regulate dystroglycan expression and/or function, while little is known about how expression of the corresponding Dag1 gene is regulated. This study aimed to clone the Dag1 gene promoter and to characterize its regulatory elements. Analysis of the mouse Dag1 gene 5'-flanking region revealed a TATA and CAAT box-lacking promoter including a GC-rich region. Transfection studies with serially deleted promoter constructs allowed us to identify a minimal promoter region containing three Specificity protein 1 (Sp1) sites and an E-box. Sp1 binding was confirmed by chromatin immunoprecipitation assay, and Sp1 downregulation reduced dystroglycan expression in muscle cells. Treatment with 5-aza-2'-deoxycytidine and/or the histone deacetylase inhibitor trichostatin A increased Dag1 mRNA expression levels in myoblasts, and methylation decreased promoter activity in vitro. Furthermore, Dag1 gene promoter methylation was reduced while its expression increased during differentiation of C(2)C(12) myoblast cells in myotubes. In conclusion, for the first time we have characterized the activity of the mouse Dag1 gene promoter, confirming a complex regulation by Sp1 transcription factor, DNA methylation, and histone acetylation, which might be relevant for a better understanding of the physiopathology of the dystroglycan complex.

Differential toxic effects of methyl tertiary butyl ether and tert-butanol on rat fibroblasts in vitro

Methyl tertiary butyl ether (MTBE) is the most widely used motor vehicle fuel oxygenate since it reduces harmful emissions due to gasoline combustion. However, the significant increase in its use in recent years has raised new questions related to its potential toxicity. In fact, although available data are somehow conflicting, there is evidence that MTBE is a toxic substance that may have harmful effects on both animals and humans and an unresolved problem is the role played by MTBE metabolites, especially tertiary butyl alcohol (TBA), in determining toxic effects due to MTBE exposure. In this study, the toxic effects of MTBE have been analyzed on a normal diploid rat fibroblast cell line (Rat-1) and compared to the effects of TBA. The results obtained suggest that both MTBE and TBA inhibit cell growth in vitro but with different mechanisms in terms of effects on the cell cycle progression and on the modulation of cell cycle regulatory proteins. In fact, MTBE caused an accumulation of cells in the S-phase of the cell cycle, whereas TBA caused an accumulation in the G0/G1-phase with different effects on the expression of cyclin D1, p27Kip1, and p53. Moreover, both MTBE and TBA were also shown to induce DNA damage, as assessed in terms of oxidative DNA damage and nuclear DNA fragmentation, that appeared to be susceptible of repair by the cell DNA-repair machinery. In conclusion, these findings suggest that both MTBE and TBA can exert, by acting through different molecular mechanisms, important biological effects on fibroblasts in vitro. Further studies are warranted to shed light on the mechanisms responsible for the observed effects and on their potential significance for the in-vivo exposure.

Expression of beta-dystroglycan is reduced or absent in many human carcinomas

AIMS

Dystroglycan is an important structural and signalling protein that is expressed in most human cells. alpha-Dystroglycan has been investigated and found to be reduced in human cancers, but there is only one published study on the expression of beta-dystroglycan in human cancer and that was only on small numbers of breast and prostatic cancers. The aim was to conduct a comprehensive immunohistochemical survey of the expression of beta-dystroglycan in normal human tissues and common cancers.

METHODS AND RESULTS

Triplicate tissue microarrays of 681 samples of normal human tissues and common cancers were stained using an antibody directed against the cytoplasmic component of beta-dystroglycan. beta-Dystroglycan was strongly expressed at the intercellular junctions and basement membranes of all normal human epithelia. Expression of beta-dystroglycan was absent or markedly reduced in 100% of oesophageal adenocarcinomas, 97% of colonic cancers, 100% of transitional cell carcinomas of the urothelium and 94% of breast cancers. In the breast cancers, the only tumours that showed any retention of beta-dystroglycan expression were small low-grade oestrogen receptor-positive tumours. The only cancers that showed retention of beta-dystroglycan expression were cutaneous basal cell carcinomas.

CONCLUSIONS

There is loss or marked reduction of beta-dystroglycan expression (by immunohistochemistry) in the vast majority of human cancers surveyed. Since beta-dystroglycan is postulated to have a tumour suppressor effect, this loss may have important functional significance.

Targeting of dystroglycan to the cleavage furrow and midbody in cytokinesis

Dystroglycan is a cell adhesion molecule that interacts with ezrin family proteins and also components of the extracellular signal-regulated kinase pathway. Ezrin and extracellular signal-regulated kinase are both involved in aspects of the cell division cycle. We therefore examined the role of dystroglycan during cytokinesis. Endogenous dystroglycan colocalised with ezrin at the cleavage furrow and midbody during cytokinesis in REF52 cells. Live cell imaging of green fluorescent protein-tagged dystroglycan in Swiss 3T3 and Hela cells revealed a similar localisation. Live cell imaging of a dystroglycan lacking its cytoplasmic domain revealed an even membrane localisation but no cleavage furrow or midbody localisation. Deletion of a previously identified ezrin-binding site in the dystroglycan cytoplasmic domain however only resulted in a slight reduction in cleavage furrow localisation but loss of midbody staining. There was no apparent cytokinetic defect in cells depleted for dystroglycan, however apoptosis levels were considerably higher in dystroglycan knockdown cells. Cell cycle analysis showed a delay in G2/M transition, possibly caused by a more than 50% reduction in extracellular signal-regulated kinase levels in the knockdown cells. Dystroglycan may therefore not only have a role in organising the contractile ring through direct or indirect associations with actin, but can also modulate the cell cycle by affecting extracellular signal-regulated kinase levels.

Altered expression of natively glycosylated alpha dystroglycan in pediatric solid tumors

Altered glycosylation and/or expression of dystroglycan have been reported in forms of congenital muscular dystrophy as well as in cancers of the breast, colon, and oral epithelium. To date, however, there has been no study of the expression of dystroglycan in pediatric solid tumors. Using a combination of immunostaining on tissue microarrays and immunoblotting of snap-frozen unfixed tissues, we demonstrate a significant reduction in native alpha dystroglycan expression in pediatric alveolar rhabdomyosarcoma (RMS), embryonal RMS, neuroblastoma (NBL), and medulloblastoma, whereas expression of beta dystroglycan, which is cotranslated with alpha dystroglycan, is largely unchanged. Loss of native alpha dystroglycan expression was significantly more pronounced in stage 4 NBL than in pooled samples of stage 1 and stage 2 NBL, suggesting that loss of native alpha dystroglycan expression increases with advancing tumor stage. Neuroblastoma and RMS samples with reduced expression of native alpha dystroglycan also showed reduced laminin binding in laminin overlay experiments. Expression of natively glycosylated alpha dystroglycan was not altered in several other pediatric tumor types when compared with appropriate normal tissue controls. These data provide the first evidence that alpha dystroglycan glycosylation and laminin binding to alpha dystroglycan are altered in certain pediatric solid tumors and suggest that aberrant dystroglycan glycosylation may contribute to tumor cell biology in patients with RMS, medulloblastoma, and NBL.

Dystroglycan regulates structure, proliferation and differentiation of neuroepithelial cells in the developing vertebrate CNS

In the developing CNS alpha- and beta-dystroglycan are highly concentrated in the endfeet of radial neuroepithelial cells at the contact site to the basal lamina. We show that injection of anti-dystroglycan Fab fragments, knockdown of dystroglycan using RNAi, and overexpression of a dominant-negative dystroglycan protein by microelectroporation in neuroepithelial cells of the chick retina and optic tectum in vivo leads to the loss of their radial morphology, to hyperproliferation, to an increased number of postmitotic neurons, and to an altered distribution of several basally concentrated proteins. Moreover, these treatments also altered the oriented growth of axons from retinal ganglion cells and from tectal projection neurons. In contrast, expression of non-cleavable dystroglycan protein in neuroepithelial cells reduced their proliferation and their differentiation to postmitotic neurons. These results demonstrate that dystroglycan plays a key role in maintaining neuroepithelial cell morphology, and that interfering with dystroglycan function influences proliferation and differentiation of neuroepithelial cells. These data also suggest that an impaired dystroglycan function in neuroepithelial cells might be responsible for some of the severe brain abnormalities observed in certain forms of congenital muscular dystrophy.

Dystroglycan expression is reduced during prostate tumorigenesis and is regulated by androgens in prostate cancer cells

Prostate cancer, the most frequently diagnosed cancer in Western men, can display a high variability in term of clinical aggressiveness and prognosis and none of the available markers is able to accurately predict its clinical course. Dystroglycan (DG), a non-integrin adhesion molecule, is a complex formed by two subunits, alpha- and beta-DG, which bind to extracellular matrix molecules and cytoskeleton, respectively. DG expression is frequently reduced in human cancers and has been related to tumor grade and aggressiveness. This study investigated the role of DG in human prostate tumorigenesis and its suitability as a prognostic marker. The expression level of extracellular alpha-DG subunit was frequently reduced in human prostate cancer cell lines and primary tumors and the percentage of positive tumor cells was significantly further decreased in vivo following androgen ablation therapy (median = 1%) compared to pre-treatment samples (median = 28%). A significant relationship was observed between alpha-DG staining on the post-treatment samples and tumor recurrence. A dose- and time-dependent decrease of DG expression also occurred in human prostate cancer cells following treatment with the anti-androgen flutamide. Stable expression of an exogenous DG cDNA in the LNCaP human prostate carcinoma cell line resulted in a marked inhibition of both anchorage-dependent and independent growth and of the in vivo tumorigenicity. These findings confirm and extend previous evidence that disturbances in the function of the DG complex might contribute to the definition of the malignant behavior of prostate cancer cells and suggest that androgens might regulate DG expression in these cells.

Dystroglycan loss disrupts polarity and beta-casein induction in mammary epithelial cells by perturbing laminin anchoring

Precise contact between epithelial cells and their underlying basement membrane is crucial to the maintenance of tissue architecture and function. To understand the role that the laminin receptor dystroglycan (DG) plays in these processes, we assayed cell responses to laminin-111 following conditional ablation of DG gene (Dag1) expression in cultured mammary epithelial cells. Strikingly, DG loss disrupted laminin-111-induced polarity and beta-casein production, and abolished laminin assembly at the step of laminin binding to the cell surface. Dystroglycan re-expression restored these deficiencies. Investigations of the mechanism revealed that DG cytoplasmic sequences were not necessary for laminin assembly and signaling, and only when the entire mucin domain of extracellular DG was deleted did laminin assembly not occur. These results demonstrate that DG is essential as a laminin-111 co-receptor in mammary epithelial cells that functions by mediating laminin anchoring to the cell surface, a process that allows laminin polymerization, tissue polarity and beta-casein induction. The observed loss of laminin-111 assembly and signaling in Dag1(-/-) mammary epithelial cells provides insights into the signaling changes occurring in breast carcinomas and other cancers, where the binding function of DG to laminin is frequently defective.