Integrin receptors play a role in the internalin B-dependent entry of Listeria monocytogenes into host cells

N-Substituted l-Iminosugars for the Treatment of Sanfilippo Type B Syndrome

Sanfilippo syndrome comprises a group of four genetic diseases due to the lack or decreased activity of enzymes involved in heparan sulfate (HS) catabolism. HS accumulation in lysosomes and other cellular compartments results in tissue and organ dysfunctions, leading to a wide range of clinical symptoms including severe neurodegeneration. To date, no approved treatments for Sanfilippo disease exist. Here, we report the ability of N-substituted l-iminosugars to significantly reduce substrate storage and lysosomal dysfunctions in Sanfilippo fibroblasts and in a neuronal cellular model of Sanfilippo B subtype. Particularly, we found that they increase the levels of defective α-N-acetylglucosaminidase and correct its proper sorting toward the lysosomal compartment. Furthermore, l-iminosugars reduce HS accumulation by downregulating protein levels of exostosin glycosyltransferases. These results highlight an interesting pharmacological potential of these glycomimetics in Sanfilippo syndrome, paving the way for the development of novel therapeutic approaches for the treatment of such incurable disease.

Immunoglobulin-fold containing bacterial adhesins: molecular and structural perspectives in host tissue colonization and infection

Immunoglobulin (Ig) domains are one of the most widespread protein domains encoded by the human genome and are present in a large array of proteins with diverse biological functions. These Ig domains possess a central structure, the immunoglobulin-fold, which is a sandwich of two β sheets, each made up of anti-parallel β strands, surrounding a central hydrophobic core. Apart from humans, proteins containing Ig-like domains are also distributed in a vast selection of organisms including vertebrates, invertebrates, plants, viruses and bacteria where they execute a wide array of discrete cellular functions. In this review, we have described the key structural deviations of bacterial Ig-folds when compared to the classical eukaryotic Ig-fold. Further, we have comprehensively grouped all the Ig-domain containing adhesins present in both Gram-negative and Gram-positive bacteria. Additionally, we describe the role of these particular adhesins in host tissue attachment, colonization and subsequent infection by both pathogenic and non-pathogenic Escherichia coli as well as other bacterial species. The structural properties of these Ig-domain containing adhesins, along with their interactions with specific Ig-like and non Ig-like binding partners present on the host cell surface have been discussed in detail.

Listeria monocytogenes: review of pathogenesis and virulence determinants-targeted immunological assays

Listeria monocytogenes is one of the most invasive foodborne pathogens and is responsible for numerous outbreaks worldwide. Most of the methods to detect this bacterium in food require selective enrichment using traditional bacterial culture techniques that can be time-consuming and labour-intensive. Moreover, molecular methods are expensive and need specific technical knowledge. In contrast, immunological approaches are faster, simpler, and user-friendly alternatives and have been developed for the detection of L. monocytogenes in food, environmental, and clinical samples. These techniques are dependent on the constitutive expression of L. monocytogenes antigens and the specificity of the antibodies used. Here, updated knowledge on pathogenesis and the key immunogenic virulence determinants of L. monocytogenes that are used for the generation of monoclonal and polyclonal antibodies for the serological assay development are summarised. In addition, immunological approaches based on enzyme-linked immunosorbent assay, immunofluorescence, lateral flow immunochromatographic assays, and immunosensors with relevant improvements are highlighted. Though the sensitivity and specificity of the assays were improved significantly, methods still face many challenges that require further validation before use.

Targeting Heparan Sulfate Proteoglycans as a Novel Therapeutic Strategy for Mucopolysaccharidoses

Mucopolysaccharidoses (MPSs) are inherited metabolic diseases caused by the deficiency of lysosomal enzymes needed to catabolize glycosaminoglycans (GAGs). Four therapeutic options are currently considered: enzyme replacement therapy, substrate reduction therapy, gene therapy, and hematopoietic stem cell transplantation. However, while some of them exhibit limited clinical efficacy and require high costs, others are still in development. Therefore, alternative treatments for MPSs need to be explored. Here we describe an innovative therapeutic approach based on the use of a recombinant protein that is able to bind the excess of extracellular accumulated heparan sulfate (HS). We demonstrate that this protein is able to reduce lysosomal defects in primary fibroblasts from MPS I and MPS IIIB patients. We also show that, by masking the excess of extracellular accumulated HS in MPS fibroblasts, fibroblast growth factor (FGF) signal transduction can be positively modulated. We, therefore, suggest the use of a competitive binding molecule for HS in MPSs as an alternative strategy to prevent the detrimental extracellular substrate storage.

EGFR activation triggers cellular hypertrophy and lysosomal disease in NAGLU-depleted cardiomyoblasts, mimicking the hallmarks of mucopolysaccharidosis IIIB

Mucopolysaccharidosis (MPS) IIIB is an inherited lysosomal storage disease caused by the deficiency of the enzyme α-N-acetylglucosaminidase (NAGLU) required for heparan sulfate (HS) degradation. The defective lysosomal clearance of undigested HS results in dysfunction of multiple tissues and organs. We recently demonstrated that the murine model of MPS IIIB develops cardiac disease, valvular abnormalities, and ultimately heart failure. To address the molecular mechanisms governing cardiac dysfunctions in MPS IIIB, we generated a model of the disease by silencing NAGLU gene expression in H9C2 rat cardiomyoblasts. NAGLU-depleted H9C2 exhibited accumulation of abnormal lysosomes and a hypertrophic phenotype. Furthermore, we found the specific activation of the epidermal growth factor receptor (EGFR), and increased phosphorylation levels of extracellular signal-regulated kinases (ERKs) in NAGLU-depleted H9C2. The inhibition of either EGFR or ERKs, using the selective inhibitors AG1478 and PD98059, resulted in the reduction of both lysosomal aberration and hypertrophy in NAGLU-depleted H9C2. We also found increased phosphorylation of c-Src and a reduction of the hypertrophic response in NAGLU-depleted H9C2 transfected with a dominant-negative c-Src. However, c-Src phosphorylation remained unaffected by AG1478 treatment, posing c-Src upstream EGFR activation. Finally, heparin-binding EGF-like growth factor (HB-EGF) protein was found overexpressed in our MPS IIIB cellular model, and its silencing reduced the hypertrophic response. These results indicate that both c-Src and HB-EGF contribute to the hypertrophic phenotype of NAGLU-depleted cardiomyoblasts by synergistically activating EGFR and subsequent signaling, thus suggesting that EGFR pathway inhibition could represent an effective therapeutic approach for MPS IIIB cardiac disease.

Genetic variants in the integrin signaling pathway genes predict cutaneous melanoma survival

To identify genetic variants involved in prognosis of cutaneous melanoma (CM), we investigated associations of single nucleotide polymorphisms (SNPs) of genes in the integrin signaling pathway with CM survival by re-analyzing a published genome-wide association study (GWAS) from The University of Texas M.D. Anderson Cancer Center (MDACC) and then validated significant SNPs in another GWAS from Harvard University. In the MDACC study, 1,148 SNPs were significantly associated with CM-specific survival (CMSS) (p ≤ 0.050 and false-positive report probability ≤ 0.20), and nine SNPs were validated in the Harvard study (p ≤ 0.050). Among these, three independent SNPs (i.e., DOCK1 rs11018104 T > A, rs35748949 C > T and PAK2 rs1718404 C > T) showed a predictive role in CMSS, with an effect-allele attributed adjusted hazards ratio [adjHR of 1.50 (95% confidence interval (CI) = 1.18-1.90, p = 7.46E-04), 1.53 (1.18-1.97, 1.18E-03) and 0.58 (0.45-0.76, 5.60E-05), respectively]. Haplotype analysis revealed that a haplotype carrying two risk alleles A-T in DOCK1 was associated with the poorest survival in both MDACC (adjHR = 1.73, 95% CI = 1.19-2.50, p = 0.004) and Harvard (adjHR = 1.95, 95% CI = 1.14-3.33, p = 0.010) studies. In addition, patients with an increasing number of unfavorable genotypes (NUGs) for these three SNPs had a poorer survival. Incorporating NUGs with clinical variables showed a significantly improved ability to classify CMSS (AUC increased from 86.8% to 88.6%, p = 0.031). Genetic variants in the integrin signaling pathway may independently or jointly modulate the survival of CM patients. Further large, prospective studies are needed to validate these findings.

Role of Host Type IA Phosphoinositide 3-Kinase Pathway Components in Invasin-Mediated Internalization of Yersinia enterocolitica

Many bacterial pathogens subvert mammalian type IA phosphoinositide 3-kinase (PI3K) in order to induce their internalization into host cells. How PI3K promotes internalization is not well understood. Also unclear is whether type IA PI3K affects different pathogens through similar or distinct mechanisms. Here, we performed an RNA interference (RNAi)-based screen to identify components of the type IA PI3K pathway involved in invasin-mediated entry of Yersinia enterocolitica, an enteropathogen that causes enteritis and lymphadenitis. The 69 genes targeted encode known upstream regulators or downstream effectors of PI3K. A similar RNAi screen was previously performed with the food-borne bacterium Listeria monocytogenes The results of the screen with Y. enterocolitica indicate that at least nine members of the PI3K pathway are needed for invasin-mediated entry. Several of these proteins, including centaurin-α1, Dock180, focal adhesion kinase (FAK), Grp1, LL5α, LL5β, and PLD2 (phospholipase D2), were recruited to sites of entry. In addition, centaurin-α1, FAK, PLD2, and mTOR were required for remodeling of the actin cytoskeleton during entry. Six of the human proteins affecting invasin-dependent internalization also promote InlB-mediated entry of L. monocytogenes Our results identify several host proteins that mediate invasin-induced effects on the actin cytoskeleton and indicate that a subset of PI3K pathway components promote internalization of both Y. enterocolitica and L. monocytogenes.

Magnetic bead based immuno-detection of Listeria monocytogenes and Listeria ivanovii from infant formula and leafy green vegetables using the Bio-Plex suspension array system

Listeriosis, a disease contracted via the consumption of foods contaminated with pathogenic Listeria species, can produce severe symptoms and high mortality in susceptible people and animals. The development of molecular methods and immuno-based techniques for detection of pathogenic Listeria in foods has been challenging due to the presence of assay inhibiting food components. In this study, we utilize a macrophage cell culture system for the isolation and enrichment of Listeria monocytogenes and Listeria ivanovii from infant formula and leafy green vegetables for subsequent identification using the Luminex xMAP technique. Macrophage monolayers were exposed to infant formula, lettuce and celery contaminated with L. monocytogenes or L. ivanovii. Magnetic microspheres conjugated to Listeria specific antibody were used to capture Listeria from infected macrophages and then analyzed using the Bio-Plex 200 analyzer. As few as 10 CFU/mL or g of L. monocytogenes was detected in all foods tested. The detection limit for L. ivanovii was 10 CFU/mL in infant formula and 100 CFU/g in leafy greens. Microsphere bound Listeria obtained from infected macrophage lysates could also be isolated on selective media for subsequent confirmatory identification. This method presumptively identifies L. monocytogenes and L. ivanovii from infant formula, lettuce and celery in less than 28 h with confirmatory identifications completed in less than 48 h.

Roles for focal adhesion kinase (FAK) in blastomere abscission and vesicle trafficking during cleavage in the sea urchin embryo

Is focal adhesion kinase (FAK) needed for embryonic cleavage? We find that FAK is expressed during early cleavage divisions of sea urchin embryos as determined by polyclonal antibodies to the Lytechinus variegatus protein. FAK is absent in eggs and zygotes and then cycles in abundance during the first cleavages after fertilization. It is maximal at anaphase, similar to the destruction and synthesis of cyclin proteins. To investigate whether FAK is needed during early cleavage, we interfered with its function by microinjecting eggs with anti-FAK antibodies or with FAK antisense morpholino oligonucleotides. Both treatments led to regression of the cleavage furrow. FAK knockdown with antibodies or morpholino oligonucleotides also resulted in an over-accumulation of endocytic vesicles. Thus, FAK could be restricting endocytosis or increasing exocytosis in localized areas important for abscission. FAK appears to be necessary for successful cleavage. These results are the first to document a functional role for FAK during embryonic cleavage.

Analysis of the role of the integrin signaling pathway in hepatocytes during rat liver regeneration

To explore the role of the integrin signaling pathway in hepatocytes during rat liver regeneration, the integrin signaling pathway-related gene expression profile in hepatocytes of regenerative liver was detected using Rat Genome 230 2.0 array. The chip data showed that 265 genes of the integrin signaling pathway were included by Rat Genome 230 2.0 array and 132 genes showed significant expression changes in hepatocytes of regenerative liver. The numbers of up-, down- and up/down-regulated genes were 110, 15 and 7 respectively. In addition, bioinformatics and systems biology methods were used to analyze the role of the integrin signaling pathway in hepatocytes. The analysis of gene synergy value indicated that paths 1, 8, 12, and 15 promoted hepatocyte proliferation at the priming phase of liver regeneration; paths 1, 3, 8, and 12-15 enhanced hepatocyte proliferation at the progressing phase; paths 11 and 14 promoted hepatocyte proliferation, while paths 12 and 13 reduced hepatocyte proliferation at the terminal phase. Additionally, the other 8 paths (2, 4, 5-7, 9-10, and 16) were not found to be related to liver regeneration. In conclusion, 132 genes and 8 cascades of the integrin signaling pathway participated in regulating hepatocyte proliferation during rat liver regeneration.

The regulation of the development and function of dendritic cell subsets by GM-CSF: more than a hematopoietic growth factor

Granulocyte-macrophage colony stimulating factor (GM-CSF) is a cytokine that functions as a hematopoietic growth factor for the generation of white blood cells and is used clinically to stimulate hematopoiesis following chemotherapy. Apart from stimulating production of granulocytes and monocytes/macrophages, GM-CSF has also long been used for in vitro survival/generation of dendritic cells (DCs) from monocytes and bone marrow cells. Evidence has emerged pointing to an additional role for GM-CSF in regulating the function and differential development of several DC subsets. These newly ascribed functions of GM-CSF may underscore its importance in immunity against pathogens as well as initiating/mediating immunopathology in chronic inflammation. Here we summarize recent advances on the role of GM-CSF in regulating the development and function of DC subsets and discuss the biological significance of these new findings.

Identification of components of the host type IA phosphoinositide 3-kinase pathway that promote internalization of Listeria monocytogenes

The bacterial pathogen Listeria monocytogenes causes food-borne illnesses resulting in gastroenteritis, meningitis, or abortion. Listeria promotes its internalization into some human cells through binding of the bacterial surface protein InlB to the host receptor tyrosine kinase Met. The interaction of InlB with the Met receptor stimulates host signaling pathways that promote cell surface changes driving bacterial uptake. One human signaling protein that plays a critical role in Listeria entry is type IA phosphoinositide 3-kinase (PI 3-kinase). The molecular mechanism by which PI 3-kinase promotes bacterial internalization is not understood. Here we perform an RNA interference (RNAi)-based screen to identify components of the type IA PI 3-kinase pathway that control the entry of Listeria into the human cell line HeLa. The 64 genes targeted encode known upstream regulators or downstream effectors of type IA PI 3-kinase. The results of this screen indicate that at least 9 members of the PI 3-kinase pathway play important roles in Listeria uptake. These 9 human proteins include a Rab5 GTPase, several regulators of Arf or Rac1 GTPases, and the serine/threonine kinases phosphoinositide-dependent kinase 1 (PDK1), mammalian target of rapamycin (mTor), and protein kinase C-ζ. These findings represent a key first step toward understanding the mechanism by which type IA PI 3-kinase controls bacterial internalization.

GM-CSF increases cross-presentation and CD103 expression by mouse CD8⁺ spleen dendritic cells

Resident CD8(+) DCs perform several functions, including cross-presenting antigen and rapidly engulfing the Gram-positive intracellular pathogen Listeria monocytogenes. Little is known about how these functions of CD8(+) DCs are modulated. Here, we show that granulocyte-macrophage CSF (GM-CSF), a cytokine that exists at low levels at steady state but is elevated during infection and inflammation, enhances cross-presentation and rapid uptake of L. monocytogenes by resident CD8(+) DCs. This previously unrecognized functional enhancement of CD8(+) DCs by GM-CSF was independent of promoting DC survival in vitro. Enhancement of these functions by GM-CSF was also marked by CD103 expression on CD8(+) DCs that was strongly regulated by GM-CSF. Our findings not only identify GM-CSF as a key molecule regulating CD8(+) DC function, but also as a factor responsible for functional heterogeneity of CD8(+) DCs that is at least substantially demarcated by CD103 expression.

A glance at Listeria and Salmonella cell invasion: different strategies to promote host actin polymerization

The facultative intracellular bacterial pathogens Listeria monocytogenes and Salmonella enterica have evolved multiple strategies to invade a large panel of mammalian cells. These pathogens use the host cell actin system for invasion and became a paradigm for the study of host-pathogen interactions and bacterial adaptation to mammalian hosts. The key signaling component that these pathogens use to orchestrate actin remodeling is the Arp2/3 complex, which is related to polymerization of actin filaments. These bacterial pathogens are able to trigger distinct invasion mechanisms. On the one hand, L. monocytogenes invade a host cell in a way dependent on the specific interactions between bacterial and host cell proteins, which in turn activate the host cell actin polymerizing machinery that culminates with bacterial internalization. Also, Listeria escapes from the newly formed parasitophorous vacuole and moves among adjacent cells by triggering actin polymerization. On the other hand, Salmonella invades a host cell by delivering into the cytoplasm virulence factors which directly interact with host regulators of actin polymerization which leads to bacterial uptake. Moreover, Salmonella avoids vacuole lyses and modulates the early and late endosomal markers presented in the vacuole membrane. This mini-review focuses on the different pathways that L. monocytogenes and S. enterica activate to modulate the actin cytoskeleton in order to invade, to form the parasitophorous vacuole, and to migrate inside host cells.

Structural insights into Met receptor activation

The receptor tyrosine kinase Met plays a pivotal role in vertebrate development and tissue regeneration, its deregulation contributes to cancer. Met is also targeted during the infection by the facultative intracellular bacterium Listeria monocytogenes. The mechanistic basis for Met activation by its natural ligand hepatocyte growth factor/scatter factor (HGF/SF) is only beginning to be understood at a structural level. Crystal structures of Met in complex with L. monocytogenes InlB suggest that Met dimerization by this bacterial invasion protein is mediated by a dimer contact of the ligand. Here, I review the structural basis of Met activation by InlB and highlight parallels and differences to the physiological Met ligand HGF/SF and its splice variant NK1.

Exploitation of the ubiquitin system by invading bacteria

A variety of bacterial intracellular pathogens target the host cell ubiquitin system during invasion, a process that involves transient but fundamental changes in the actin cytoskeleton and plasma membrane. These changes are induced by bacterial proteins, which can be surface associated, secreted or injected directly into the host cell. Here, the invasion strategies of two extensively studied intracellular bacteria, Salmonella enterica serovar Typhimurium and Listeria monocytogenes, are used to illustrate some of the diverse ways by which bacterial pathogens intersect the host cell ubiquitin pathway.