A Helicobacter pylori Vacuolating Toxin Mutant That Fails To Oligomerize Has a Dominant Negative Phenotype

ABSTRACT Most Helicobacter pylori strains secrete a toxin (VacA) that causes massive vacuolization of target cells and which is a major virulence factor of H. pylori. The VacA amino-terminal region is required for the induction of vacuolization. The aim of the present study was a deeper understanding of the critical role of the N-terminal regions that are protected from proteolysis when VacA interacts with artificial membranes. Using a counterselection system, we constructed an H. pylori strain, SPM 326-Δ49-57, that produces a mutant toxin with a deletion of eight amino acids in one of these protected regions. VacA Δ49-57 was correctly secreted by H. pylori but failed to oligomerize and did not have any detectable vacuolating cytotoxic activity. However, the mutant toxin was internalized normally and stained the perinuclear region of HeLa cells. Moreover, the mutant toxin exhibited a dominant negative effect, completely inhibiting the vacuolating activity of wild-type VacA. This loss of activity was correlated with the disappearance of oligomers in electron microscopy. These findings indicate that the deletion in VacA Δ49-57 disrupts the intermolecular interactions required for the oligomerization of the toxin.

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OX40L/OX40 Signal Promotes IL-9 Production by Mucosal MAIT Cells During Helicobacter pylori Infection

Frontiers in Immunology ◽

10.3389/fimmu.2021.626017 ◽

2021 ◽

Vol 12 ◽

Author(s):

Siqi Ming ◽

Mei Zhang ◽

Zibin Liang ◽

Chunna Li ◽

Jianzhong He ◽

...

Keyword(s):

Helicobacter Pylori ◽

Potential Role ◽

Critical Role ◽

Underlying Mechanism ◽

Mucosal Inflammation ◽

Cross Linking ◽

Mait Cells ◽

H Pylori ◽

Mait Cell

Mucosal associated invariant T (MAIT) cells play a critical role in Helicobacter pylori (H. pylori)-induced gastritis by promoting mucosal inflammation and aggravating mucosal injuries (1, 2). However, the underlying mechanism and key molecules involved are still uncertain. Here we identified OX40, a co-stimulatory molecule mainly expressed on T cells, as a critical regulator to promote proliferation and IL-9 production by MAIT cells and facilitate mucosal inflammation in H. pylori-positive gastritis patients. Serum examination revealed an increased level of IL-9 in gastritis patients. Meanwhile, OX40 expression was increased in mucosal MAIT cells, and its ligand OX40L was also up-regulated in mucosal dendritic cells (DCs) of gastritis patients, compared with healthy controls. Further results demonstrated that activation of the OX40/OX40L pathway promoted IL-9 production by MAIT cells, and MAIT cells displayed a highly-activated phenotype after the cross-linking of OX40 and OX40L. Moreover, the level of IL-9 produced by MAIT cells was positively correlated with inflammatory indexes in the gastric mucosa, suggesting the potential role of IL-9-producing MAIT cells in mucosal inflammation. Taken together, we elucidated that OX40/OX40L axis promoted mucosal MAIT cell proliferation and IL-9 production in H. pylori-induced gastritis, which may provide potential targeting strategies for gastritis treatment.

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Impaired cytoplasmic domain interactions cause co-assembly defect and loss of function in the p.Glu293Lys KNCJ2 variant isolated from an Andersen–Tawil syndrome patient

Cardiovascular Research ◽

10.1093/cvr/cvaa249 ◽

2020 ◽

Author(s):

Szilvia Déri ◽

János Borbás ◽

Teodóra Hartai ◽

Lidia Hategan ◽

Beáta Csányi ◽

...

Keyword(s):

Salt Bridge ◽

Cytoplasmic Domain ◽

Inward Rectifier ◽

Dominant Negative ◽

Dominant Negative Effect ◽

Causative Role ◽

Loss Of Function ◽

Subunit Interactions ◽

Negative Effect

Abstract Aims Subunit interactions at the cytoplasmic domain interface (CD-I) have recently been shown to control gating in inward rectifier potassium channels. Here we report the novel KCNJ2 variant p.Glu293Lys that has been found in a patient with Andersen–Tawil syndrome type 1 (ATS1), causing amino acid substitution at the CD-I of the inward rectifier potassium channel subunit Kir2.1. Neither has the role of Glu293 in gating control been investigated nor has a pathogenic variant been described at this position. This study aimed to assess the involvement of Glu293 in CD-I subunit interactions and to establish the pathogenic role of the p.Glu293Lys variant in ATS1. Methods and results The p.Glu293Lys variant produced no current in homomeric form and showed dominant-negative effect over wild-type (WT) subunits. Immunocytochemical labelling showed the p.Glu293Lys subunits to distribute in the subsarcolemmal space. Salt bridge prediction indicated the presence of an intersubunit salt bridge network at the CD-I of Kir2.1, with the involvement of Glu293. Subunit interactions were studied by the NanoLuc® Binary Technology (NanoBiT) split reporter assay. Reporter constructs carrying NanoBiT tags on the intracellular termini produced no bioluminescent signal above background with the p.Glu293Lys variant in homomeric configuration and significantly reduced signals in cells co-expressing WT and p.Glu293Lys subunits simultaneously. Extracellularly presented reporter tags, however, generated comparable bioluminescent signals with heteromeric WT and p.Glu293Lys subunits and with homomeric WT channels. Conclusions Loss of function and dominant-negative effect confirm the causative role of p.Glu293Lys in ATS1. Co-assembly of Kir2.1 subunits is impaired in homomeric channels consisting of p.Glu293Lys subunits and is partially rescued in heteromeric complexes of WT and p.Glu293Lys Kir2.1 variants. These data point to an important role of Glu293 in mediating subunit assembly, as well as in gating of Kir2.1 channels.

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Colonization and Inflammation Deficiencies in Mongolian Gerbils Infected by Helicobacter pylori Chemotaxis Mutants

Infection and Immunity ◽

10.1128/iai.73.3.1820-1827.2005 ◽

2005 ◽

Vol 73 (3) ◽

pp. 1820-1827 ◽

Cited By ~ 78

Author(s):

David J. McGee ◽

Melanie L. Langford ◽

Emily L. Watson ◽

J. Elliot Carter ◽

Yu-Ting Chen ◽

...

Keyword(s):

Helicobacter Pylori ◽

Immune Cell ◽

Response Regulator ◽

Critical Role ◽

Mongolian Gerbils ◽

Wild Type ◽

In The Wild ◽

H Pylori

ABSTRACT Helicobacter pylori causes disease in the human stomach and in mouse and gerbil stomach models. Previous results have shown that motility is critical for H. pylori to colonize mice, gerbils, and other animal models. The role of chemotaxis, however, in colonization and disease is less well understood. Two genes in the H. pylori chemotaxis pathway, cheY and tlpB, which encode the chemotaxis response regulator and a methyl-accepting chemoreceptor, respectively, were disrupted. The cheY mutation was complemented with a wild-type copy of cheY inserted into the chromosomal rdxA gene. The cheY mutant lost chemotaxis but retained motility, while all other strains were motile and chemotactic in vitro. These strains were inoculated into gerbils either alone or in combination with the wild-type strain, and colonization and inflammation were assessed. While the cheY mutant completely failed to colonize gerbil stomachs, the tlpB mutant colonized at levels similar to those of the wild type. With the tlpB mutant, there was a substantial decrease in inflammation in the gerbil stomach compared to that with the wild type. Furthermore, there were differences in the numbers of each immune cell in the tlpB-mutant-infected stomach: the ratio of lymphocytes to neutrophils was about 8 to 1 in the wild type but only about 1 to 1 in the mutant. These results suggest that the TlpB chemoreceptor plays an important role in the inflammatory response while the CheY chemotaxis regulator plays a critical role in initial colonization. Chemotaxis mutants may provide new insights into the steps involved in H. pylori pathogenesis.

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A 12-Amino-Acid Segment, Present in Type s2 but Not Type s1 Helicobacter pylori VacA Proteins, Abolishes Cytotoxin Activity and Alters Membrane Channel Formation

Journal of Bacteriology ◽

10.1128/jb.183.22.6499-6508.2001 ◽

2001 ◽

Vol 183 (22) ◽

pp. 6499-6508 ◽

Cited By ~ 76

Author(s):

Mark S. McClain ◽

Ping Cao ◽

Hideki Iwamoto ◽

Arlene D. Vinion-Dubiel ◽

Gabor Szabo ◽

...

Keyword(s):

Helicobacter Pylori ◽

Amino Acid ◽

Dominant Negative ◽

Membrane Channels ◽

Wild Type ◽

Amino Terminal ◽

Protein Toxin ◽

H Pylori ◽

Amino Acid Segment ◽

Negative Phenotype

ABSTRACT Helicobacter pylori, a gram-negative bacterium associated with gastritis, peptic ulceration, and gastric adenocarcinoma in humans, secretes a protein toxin, VacA, that causes vacuolar degeneration of epithelial cells. Several different families of H. pylori vacA alleles can be distinguished based on sequence diversity in the “middle” region (i.e., m1 and m2) and in the 5′ end of the gene (i.e., s1 and s2). Type s2 VacA toxins contain a 12-amino-acid amino-terminal hydrophilic segment, which is absent from type s1 toxins. To examine the functional properties of VacA toxins containing this 12-amino-acid segment, we analyzed a wild-type s1/m1 VacA and a chimeric s2/m1 VacA protein. Purified s1/m1 VacA from H. pylori strain 60190 induced vacuolation in HeLa and Vero cells, whereas the chimeric s2/m1 toxin (in which the s1 sequence of VacA from strain 60190 was replaced with the s2 sequence from strain Tx30a) lacked detectable cytotoxic activity. Type s1/m1 VacA from strain 60190 formed membrane channels in a planar lipid bilayer assay at a significantly higher rate than did s2/m1 VacA. However, membrane channels formed by type s1 VacA and type s2 VacA proteins exhibited similar anion selectivities (permeability ratio, PCl/PNa = 5). When an equimolar mixture of the chimeric s2/m1 toxin and the wild-type s1/m1 toxin was added to HeLa cells, the chimeric toxin completely inhibited the activity of the s1/m1 toxin. Thus, the s2/m1 toxin exhibited a dominant-negative phenotype similar to that of a previously described mutant toxin, VacA-(Δ6–27). Immunoprecipitation experiments indicated that both s2/m1 VacA and VacA-(Δ6–27) could physically interact with a c-myc epitope-tagged s1/m1 VacA, which suggests that the dominant-negative phenotype results from the formation of heterooligomeric VacA complexes with defective functional activity. Despite detectable differences in the channel-forming activities and cytotoxic properties of type s1 and type s2 VacA proteins, the conservation of type s2 sequences in many H. pyloriisolates suggests that type s2 VacA proteins retain an important biological activity.

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Entamoeba histolyticaExpressing a Dominant Negative N-Truncated Light Subunit of Its Gal-Lectin Are Less Virulent

Molecular Biology of the Cell ◽

10.1091/mbc.e02-06-0344 ◽

2002 ◽

Vol 13 (12) ◽

pp. 4256-4265 ◽

Cited By ~ 39

Author(s):

Uriel Katz ◽

Serge Ankri ◽

Tamara Stolarsky ◽

Yael Nuchamowitz ◽

David Mirelman

Keyword(s):

Antisense Rna ◽

Mammalian Cells ◽

Dominant Negative ◽

Dominant Negative Effect ◽

Impaired Ability ◽

Reducing Conditions ◽

Negative Effect ◽

Terminal Amino ◽

Heterodimeric Complex

The 260-kDa heterodimeric Gal/GalNAc-specific Lectin (Gal-lectin) of Entamoeba histolytica dissociates under reducing conditions into a heavy (hgl, 170 kDa) and a light subunit (lgl, 35 kDa). We have previously shown that inhibition of expression of the 35-kDa subunit by antisense RNA causes a decrease in virulence. To further understand the role of the light subunit of the Gal-lectin in pathogenesis, amoebae were transfected with plasmids encoding intact, mutated, and truncated forms of the light subunit lgl1 gene. A transfectant in which the 55 N-terminal amino acids of the lgl were removed, overproduced an N-truncated lgl protein (32 kDa), which replaced most of the native 35-kDa lgl in the formation of the Gal-lectin heterodimeric complex and exerted a dominant negative effect. Amoebae transfected with this construct showed a significant decrease in their ability to adhere to and kill mammalian cells as well as in their capacity to form rosettes with and to phagocytose erythrocytes. In addition, immunofluorescence confocal microscopy of this transfectant with anti–Gal-lectin antibodies showed an impaired ability to cap. These results indicate that the light subunit has a role in enabling the clustering of Gal-lectin complexes and that its N-truncation affects this function, which is required for virulence.

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The Role of Subunit Assembly in Peripherin-2 Targeting to Rod Photoreceptor Disk Membranes and Retinitis Pigmentosa

Molecular Biology of the Cell ◽

10.1091/mbc.e03-02-0077 ◽

2003 ◽

Vol 14 (8) ◽

pp. 3400-3413 ◽

Cited By ~ 38

Author(s):

Christopher J.R. Loewen ◽

Orson L. Moritz ◽

Beatrice M. Tam ◽

David S. Papermaster ◽

Robert S. Molday

Keyword(s):

Retinitis Pigmentosa ◽

Critical Role ◽

Dominant Negative ◽

Dominant Negative Effect ◽

Rod Photoreceptor ◽

Wild Type ◽

Photoreceptor Outer Segment ◽

Negative Effect ◽

Retinal Degenerative Diseases ◽

Green Fluorescent

Peripherin-2 is a member of the tetraspanin family of membrane proteins that plays a critical role in photoreceptor outer segment disk morphogenesis. Mutations in peripherin-2 are responsible for various retinal degenerative diseases including autosomal dominant retinitis pigmentosa (ADRP). To identify determinants required for peripherin-2 targeting to disk membranes and elucidate mechanisms underlying ADRP, we have generated transgenic Xenopus tadpoles expressing wild-type and ADRP-linked peripherin-2 mutants as green fluorescent fusion proteins in rod photoreceptors. Wild-type peripherin-2 and P216L and C150S mutants, which assemble as tetramers, targeted to disk membranes as visualized by confocal and electron microscopy. In contrast the C214S and L185P mutants, which form homodimers, but not tetramers, were retained in the rod inner segment. Only the P216L disease mutant induced photoreceptor degeneration. These results indicate that tetramerization is required for peripherin-2 targeting and incorporation into disk membranes. Tetramerization-defective mutants cause ADRP through a deficiency in wild-type peripherin-2, whereas tetramerization-competent P216L peripherin-2 causes ADRP through a dominant negative effect, possibly arising from the introduction of a new oligosaccharide chain that destabilizes disks. Our results further indicate that a checkpoint between the photoreceptor inner and outer segments allows only correctly assembled peripherin-2 tetramers to be incorporated into nascent disk membranes.

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Biallelic and monoallelic variants in PLXNA1 are implicated in a novel neurodevelopmental disorder with variable cerebral and eye anomalies

Genetics in Medicine ◽

10.1038/s41436-021-01196-9 ◽

2021 ◽

Author(s):

Gabriel C. Dworschak ◽

Jaya Punetha ◽

Jeshurun C. Kalanithy ◽

Enrico Mingardo ◽

Haktan B. Erdem ◽

...

Keyword(s):

Developmental Delay ◽

De Novo ◽

Neurodevelopmental Disorder ◽

Structural Modeling ◽

Dominant Negative ◽

Dominant Negative Effect ◽

Global Developmental Delay ◽

Downstream Signaling ◽

Negative Effect

Abstract Purpose To investigate the effect of PLXNA1 variants on the phenotype of patients with autosomal dominant and recessive inheritance patterns and to functionally characterize the zebrafish homologs plxna1a and plxna1b during development. Methods We assembled ten patients from seven families with biallelic or de novo PLXNA1 variants. We describe genotype–phenotype correlations, investigated the variants by structural modeling, and used Morpholino knockdown experiments in zebrafish to characterize the embryonic role of plxna1a and plxna1b. Results Shared phenotypic features among patients include global developmental delay (9/10), brain anomalies (6/10), and eye anomalies (7/10). Notably, seizures were predominantly reported in patients with monoallelic variants. Structural modeling of missense variants in PLXNA1 suggests distortion in the native protein. Our zebrafish studies enforce an embryonic role of plxna1a and plxna1b in the development of the central nervous system and the eye. Conclusion We propose that different biallelic and monoallelic variants in PLXNA1 result in a novel neurodevelopmental syndrome mainly comprising developmental delay, brain, and eye anomalies. We hypothesize that biallelic variants in the extracellular Plexin-A1 domains lead to impaired dimerization or lack of receptor molecules, whereas monoallelic variants in the intracellular Plexin-A1 domains might impair downstream signaling through a dominant-negative effect.

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Identification of a d-glycero-d-manno-Heptosyltransferase Gene from Helicobacter pylori

Journal of Bacteriology ◽

10.1128/jb.187.15.5156-5165.2005 ◽

2005 ◽

Vol 187 (15) ◽

pp. 5156-5165 ◽

Cited By ~ 32

Author(s):

Koji Hiratsuka ◽

Susan M. Logan ◽

J. Wayne Conlan ◽

Vandana Chandan ◽

Annie Aubry ◽

...

Keyword(s):

Helicobacter Pylori ◽

Critical Role ◽

Outer Core ◽

Core Region ◽

Wild Type ◽

Core Oligosaccharide ◽

Detailed Structural Analysis ◽

Insertional Inactivation ◽

H Pylori

ABSTRACT We have identified a Helicobacter pylori d-glycero-d-manno-heptosyltransferase gene, HP0479, which is involved in the biosynthesis of the outer core region of H. pylori lipopolysaccharide (LPS). Insertional inactivation of HP0479 resulted in formation of a truncated LPS molecule lacking an α-1,6-glucan-, dd-heptose-containing outer core region and O-chain polysaccharide. Detailed structural analysis of purified LPS from HP0479 mutants of strains SS1, 26695, O:3, and PJ1 by a combination of chemical and mass spectrometric methods showed that HP0479 likely encodes α-1,2-d-glycero-d-manno-heptosyltransferase, which adds a d-glycero-d-manno-heptose residue (DDHepII) to a distal dd-heptose of the core oligosaccharide backbone of H. pylori LPS. When the wild-type HP0479 gene was reintegrated into the chromosome of strain 26695 by using an “antibiotic cassette swapping” method, the complete LPS structure was restored. Introduction of the HP0479 mutation into the H. pylori mouse-colonizing Sydney (SS1) strain and the clinical isolate PJ1, which expresses dd-heptoglycan, resulted in the loss of colonization in a mouse model. This indicates that H. pylori expressing a deeply truncated LPS is unable to successfully colonize the murine stomach and provides evidence for a critical role of the outer core region of H. pylori LPS in colonization.

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The Role of the PAX8/PPARγFusion Oncogene in Thyroid Cancer

PPAR Research ◽

10.1155/2008/672829 ◽

2008 ◽

Vol 2008 ◽

pp. 1-10 ◽

Cited By ~ 29

Author(s):

Kimberly A. Placzkowski ◽

Honey V. Reddi ◽

Stefan K. G. Grebe ◽

Norman L. Eberhardt ◽

Bryan McIver

Keyword(s):

Thyroid Cancer ◽

Fusion Gene ◽

Molecular Genetic ◽

Dominant Negative ◽

Dominant Negative Effect ◽

Negative Effect ◽

Patients Experience ◽

Made In

Thyroid cancer is uncommon and exhibits relatively low mortality rates. However, a subset of patients experience inexorable growth, metastatic spread, and mortality. Unfortunately, for these patients, there have been few significant advances in treatment during the last 50 years. While substantial advances have been made in recent years about the molecular genetic events underlying papillary thyroid cancer, the more aggressive follicular thyroid cancer remains poorly understood. The recent discovery of the PAX8/PPARγtranslocation in follicular thyroid carcinoma has promoted progress in the role of PPARγas a tumor suppressor and potential therapeutic target. The PAX8/PPARγfusion gene appears to be an oncogene. It is most often expressed in follicular carcinomas and exerts a dominant-negative effect on wild-type PPARγ, and stimulates transcription of PAX8-responsive promoters. PPARγagonists have shown promising results in vitro, although very few studies have been conducted to assess the clinical impact of these agents.

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A role of the (pro)renin receptor in neuronal cell differentiation

AJP Regulatory Integrative and Comparative Physiology ◽

10.1152/ajpregu.90832.2008 ◽

2009 ◽

Vol 297 (2) ◽

pp. R250-R257 ◽

Cited By ~ 61

Author(s):

Aurelie Contrepas ◽

Joy Walker ◽

Annette Koulakoff ◽

Karl J. Franek ◽

Fatimunnisa Qadri ◽

...

Keyword(s):

Neuronal Differentiation ◽

Mouse Brain ◽

Neuronal Cell ◽

Renin Angiotensin System ◽

Experimental Models ◽

Dominant Negative ◽

Dominant Negative Effect ◽

Pc 12 Cells ◽

Negative Effect

The (pro)renin receptor [(P)RR] plays a pivotal role in the renin-angiotensin system. Experimental models emphasize the role of (P)RR in organ damage associated with hypertension and diabetes. However, a mutation of the (P)RR gene, resulting in frame deletion of exon 4 [Δ4-(P)RR] is associated with X-linked mental retardation (XLMR) and epilepsy pointing to a novel role of (P)RR in brain development and cognitive function. We have studied (P)RR expression in mouse brain, as well as the effect of transfection of Δ4-(P)RR on neuronal differentiation of rat neuroendocrine PC-12 cells induced by nerve growth factor (NGF). In situ hybridization showed a wide distribution of (P)RR, including in key regions involved in the regulation of blood pressure and body fluid homeostasis. In mouse neurons, the receptor is on the plasma membrane and in synaptic vesicles, and stimulation by renin provokes ERK1/2 phosphorylation. In PC-12 cells, (P)RR localized mainly in the Golgi and in endoplasmic reticulum and redistributed to neurite projections during NGF-induced differentiation. In contrast, Δ4-(P)RR remained cytosolic and inhibited NGF-induced neuronal differentiation and ERK1/2 activation. Cotransfection of PC-12 cells with (P)RR and Δ4-(P)RR cDNA resulted in altered localization of (P)RR and inhibited (P)RR redistribution to neurite projections upon NGF stimulation. Furthermore, (P)RR dimerized with itself and with Δ4-(P)RR, suggesting that the XLMR and epilepsy phenotype resulted from a dominant-negative effect of Δ4-(P)RR, which coexists with normal transcript in affected males. In conclusion, our results show that (P)RR is expressed in mouse brain and suggest that the XLMR and epilepsy phenotype might result from a dominant-negative effect of the Δ4-(P)RR protein.

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