Cellular and molecular action of the mitogenic protein-deamidating toxin from Pasteurella multocida

Oral and intestinal bacterial exotoxins: Potential linked to carcinogenesis

Growing evidence suggests that imbalances in resident microbes (dysbiosis) can promote chronic inflammation, immune-subversion, and production of carcinogenic metabolites, thus leading to neoplasia. Yet, evidence to support a direct link of individual bacteria species to human sporadic cancer is still limited. This chapter focuses on several emerging bacterial toxins that have recently been characterized for their potential oncogenic properties toward human orodigestive cancer and the presence of which in human tissue samples has been documented. These include cytolethal distending toxins produced by various members of gamma and epsilon Proteobacteria, Dentilisin from mammalian oral Treponema, Pasteurella multocida toxin, two Fusobacterial toxins, FadA and Fap2, Bacteroides fragilis toxin, colibactin, cytotoxic necrotizing factors and α-hemolysin from Escherichia coli, and Salmonella enterica AvrA. It was clear that these bacterial toxins have biological activities to induce several hallmarks of cancer. Some toxins directly interact with DNA or chromosomes leading to their breakdowns, causing mutations and genome instability, and others modulate cell proliferation, replication and death and facilitate immune evasion and tumor invasion, prying specific oncogene and tumor suppressor pathways, such as p53 and β-catenin/Wnt. In addition, most bacterial toxins control tumor-promoting inflammation in complex and diverse mechanisms. Despite growing laboratory evidence to support oncogenic potential of selected bacterial toxins, we need more direct evidence from human studies and mechanistic data from physiologically relevant experimental animal models, which can reflect chronic infection in vivo, as well as take bacterial-bacterial interactions among microbiome into consideration.

Pasteurella multocida: Genotypes and Genomics

Pasteurella multocida is a highly versatile pathogen capable of causing infections in a wide range of domestic and wild animals as well as in humans and nonhuman primates. Despite over 135 years of research, the molecular basis for the myriad manifestations of P. multocida pathogenesis and the determinants of P. multocida phylogeny remain poorly defined. The current availability of multiple P. multocida genome sequences now makes it possible to delve into the underlying genetic mechanisms of P. multocida fitness and virulence. Using whole-genome sequences, the genotypes, including the capsular genotypes, lipopolysaccharide (LPS) genotypes, and multilocus sequence types, as well as virulence factor-encoding genes of P. multocida isolates from different clinical presentations can be characterized rapidly and accurately. Putative genetic factors that contribute to virulence, fitness, host specificity, and disease predilection can also be identified through comparative genome analysis of different P. multocida isolates. However, although some knowledge about genotypes, fitness, and pathogenesis has been gained from the recent whole-genome sequencing and comparative analysis studies of P. multocida, there is still a long way to go before we fully understand the pathogenic mechanisms of this important zoonotic pathogen. The quality of several available genome sequences is low, as they are assemblies with relatively low coverage, and genomes of P. multocida isolates from some uncommon host species are still limited or lacking. Here, we review recent advances, as well as continuing knowledge gaps, in our understanding of determinants contributing to virulence, fitness, host specificity, disease predilection, and phylogeny of P. multocida.

Cytosolic Delivery of Multidomain Cargos by the N Terminus of Pasteurella multocida Toxin

The zoonotic pathogen Pasteurella multocida produces a 146-kDa modular toxin (PMT) that enters host cells and manipulates intracellular signaling through action on its Gα protein targets. The N terminus of PMT (PMT-N) mediates cellular uptake through receptor-mediated endocytosis, followed by the delivery of the C-terminal catalytic domain from acidic endosomes into the cytosol. The putative native cargo of PMT consists of a 710-residue polypeptide with three distinct modular subdomains (C1-C2-C3), where C1 contains a membrane localization domain (MLD), C2 has an as-yet-undefined function, and C3 catalyzes the deamidation of a specific active-site glutamine residue in Gα protein targets. However, whether the three cargo subdomains are delivered intact or undergo further proteolytic processing during or after translocation from the late endosome is unclear. Here, we demonstrate that PMT-N mediates the delivery of its native C-terminal cargo as a single polypeptide, corresponding to C1-C2-C3, including the MLD, with no evidence of cleavage between subdomains. We show that PMT-N also delivers nonnative green fluorescent protein (GFP) cargo into the cytosol, further supporting that the receptor-binding and translocation functions reside within PMT-N. Our findings further show that PMT-N can deliver C1-C2 alone but that the presence of C1-C2 is important for the cytosolic delivery of the catalytic C3 subdomain by PMT-N. In addition, we further refine the minimum C3 domain required for intracellular activity as comprising residues 1105 to 1278. These findings reinforce that PMT-N serves as the cytosolic delivery vehicle for C-terminal cargo and demonstrate that its native cargo is delivered intact as C1-C2-C3.

Is submucosal fat injection effective in atrophic rhinitis? An experimental animal study

Atrophic rhinitis (AR) is a disease characterized by the extensive dilatation of the nasal cavity and atrophy of the mucosa, submucosa and bone tissue. Its etiological factors are unknown. There is not a satisfying treatment yet and the treatment of the functional impairment in the atrophic cells is still subject to investigation. The objective of this study is to determine at the histopathological level the possible effects of the submucosal fat injection in an experimental model of AR. 12 albino Wistar-Hannover male rats were included in the study. AR was induced with the Pasteurella multocida toxin, which was diluted with saline. As one of the rats died during the study, it was excluded from the evaluation. The right nasal cavities of all rats (11 nasal cavities) were defined as the control group (Group 1). Fat tissue obtained from the abdominal area was injected in the seven left nasal cavities (Group 2). All injections, which were done to the abdominal regions were also done in the left nasal cavities of the remaining four rats, which constituted the sham group (Group 3). After 14 days, all rats were decapitated and the squamous metaplasia and keratinization in the superficial epithelium, degeneration, vacuolar changes in the basal layer, congestion, inflammatory infiltration, vascular proliferation and glandular atrophy in the submucosa are histopathologically classified. The results were analyzed with statistical methods. Although glandular atrophy was significantly regressed in the fat injection group (Group 2) compared to other groups (p < 0.05), the remaining parameters did not show any significant difference among these three groups. The histopathological effect of the fat injection was modest. We concluded that fat injection treatment has no or at the most a very limited effect in the treatment of atrophic rhinitis.

Detection and genetic characterization of Pasteurella multocida from alpaca (Vicugna pacos) pneumonia cases

Pasteurella multocida is a common constituent of upper respiratory tract microbiota but is frequently isolated of alpaca lung tissues from pulmonary infections. Despite its importance, very little is known about this bacteria at molecular level. In order to characterize P. multocida isolates, 24 isolates recovered from 46 mortal acute cases in young alpacas with suspected pneumonia were analyzed, using biochemical and molecular tests for capsule and LPS typing, virulence factors detection, and ERIC-PCR genetic diversity analysis. All the P. multocida isolates belonged to the capsular type A, LPS genotype L6 (related to serotypes 10, 11, 12, and 15), and possessed virulence factors gene toxA and tbpA. ERIC-PCR analysis revealed two electrophoretic profiles, and the majority of isolates (23/24) shared the same fingerprint, indicating strong evidence that there was a common source of infection for all the affect animals. This study revealed the detection of P. multocida type A, LPS genotype L6, and toxA+ and tbpA+ from dead young alpacas with pneumonia in Peru.

Pasteurella multocida Toxin Triggers RANKL-Independent Osteoclastogenesis

Bone remodeling is a continuous process to retain the structural integrity and function of the skeleton. A tight coupling is maintained between osteoclast-mediated resorption of old or damaged bones and osteoblast-mediated formation of new bones for bone homeostasis. While osteoblasts differentiate from mesenchymal stem cells, osteoclasts are hematopoietic in origin and derived from myeloid precursor cells. Osteoclast differentiation is driven by two cytokines, cytokine receptor activator of NF-κB ligand (RANKL), and macrophage colony-stimulating factor. Imbalances in the activity of osteoblasts and osteoclasts result in the development of bone disorders. Bacterially caused porcine atrophic rhinitis is characterized by a loss of nasal ventral conche bones and a distortion of the snout. While Bordetella bronchiseptica strains cause mild and reversible symptoms, infection of pigs with toxigenic Pasteurella multocida strains causes a severe and irreversible decay. The responsible virulence factor Pasteurella multocida toxin (PMT) contains a deamidase activity in its catalytical domain that constitutively activates specific heterotrimeric G proteins to induce downstream signaling cascades. While osteoblasts are inhibited by the toxin, osteoclasts are activated, thus skewing bone remodeling toward excessive bone degradation. Still, the mechanism by which PMT interferes with bone homeostasis, and the reason for this unusual target tissue is not yet well understood. Here, we show that PMT has the potential to differentiate bone marrow-derived macrophages into functional osteoclasts. This toxin-mediated differentiation process is independent of RANKL, a cytokine believed to be indispensable for triggering osteoclastogenesis, as addition of osteoprotegerin to PMT-treated macrophages does not show any effect on PMT-induced osteoclast formation. Although RANKL is not a prerequisite, toxin-primed macrophages show enhanced responsiveness to low concentrations of RANKL, suggesting that the PMT-generated microenvironment offers conditions where low concentrations of RANKL lead to an increase in the number of osteoclasts resulting in increased resorption. PMT-mediated release of the osteoclastogenic cytokines such as IL-6 and TNF-α, but not IL-1, supports the differentiation process. Although the production of cytokines and the subsequent activation of signaling cascades are necessary for PMT-mediated differentiation into osteoclasts, they are not sufficient and PMT-induced activation of G protein signaling is essential for efficient osteoclastogenesis.

Selective Membrane Redistribution and Depletion of Gαq-Protein by Pasteurella multocida Toxin

Pasteurella multocida toxin (PMT), the major virulence factor responsible for zoonotic atrophic rhinitis, is a protein deamidase that activates the alpha subunit of heterotrimeric G proteins. Initial activation of G alpha-q-coupled phospholipase C-beta-1 signaling by PMT is followed by uncoupling of G alpha-q-dependent signaling, causing downregulation of downstream calcium and mitogenic signaling pathways. Here, we show that PMT decreases endogenous and exogenously expressed G alpha-q protein content in host cell plasma membranes and in detergent resistant membrane (DRM) fractions. This membrane depletion of G alpha-q protein was dependent upon the catalytic activity of PMT. Results indicate that PMT-modified G alpha-q redistributes within the host cell membrane from the DRM fraction into the soluble membrane and cytosolic fractions. In contrast, PMT had no affect on G alpha-s or G beta protein levels, which are not substrate targets of PMT. PMT also had no affect on G alpha-11 levels, even though G alpha-11 can serve as a substrate for deamidation by PMT, suggesting that membrane depletion of PMT-modified G-alpha-q has specificity.

Pasteurella multocida Toxin Manipulates T Cell Differentiation

Pasteurella multocida causes various diseases in a broad range of wild and domestic animals. Toxigenic strains of the serotypes A and D produce an AB protein toxin named Pasteurella multocida toxin (PMT). PMT constitutively activates the heterotrimeric G protein subunits Gαq, Gα13, and Gαi through deamidation of a glutamine residue, which results in cytoskeletal rearrangements as well as increased proliferation and survival of the host cell. In human monocytes, PMT alters the lipopolysaccharide (LPS)-induced activation toward a phenotype that suppresses T cell activation. Here we describe that the toxin also modulates CD4-positive T helper (Th) cells directly. PMT amplifies the expansion of Th cells through enhanced cell cycle progression and suppression of apoptosis and manipulates the differentiation of Th subclasses through activation of Signal Transducers and Activators of Transcription (STAT) family members and induction of subtype-specific master transcription factors. A large population of toxin-treated T cells is double-positive for Foxp3 and RORγt, the transcription factors expressed by Treg and Th17 cells, respectively. This suggests that these cells could have the potential to turn into Th17 cells or suppressive Treg cells. However, in terms of function, the PMT-differentiated cells behave as inflammatory Th17 cells that produce IL-17 and trigger T cell proliferation.

Pasteurella multocida toxin- induced osteoclastogenesis requires mTOR activation

Background

Pasteurella multocida toxin (PMT) is a potent inducer of osteoclast formation. Pigs suffering from an infection with toxigenic Pasteurella multocida strains develop atrophic rhinitis characterised by a loss of turbinate bones and conchae. However, on the molecular level the process of bone loss remains largely uncharacterised.

Results

Recently it was found that PMT activates the serine/threonine kinase mammalian target of rapamycin (mTOR) in fibroblasts. Using RAW264.7 macrophages, we investigated the role of the mTOR complex 1 (mTORC1) in PMT-mediated osteoclast formation. PMT induces the differentiation of RAW264.7 macrophages into multinucleated, tartrate resistant acid phosphatase (TRAP) positive osteoclasts that are capable to resorb bone. In the presence of the mTORC1 inhibitor rapamycin, PMT was significantly less able to induce the formation of TRAP-positive osteoclasts. Accordingly, the resulting resorption of bone was strongly reduced. A major target of mTOR is the 70 kDa ribosomal protein S6 kinase 1 (p70 S6K1). Activated p70 S6K1 decreases the expression of programmed cell death protein 4 (PDCD4), a negative transcriptional regulator of osteoclastogenesis, at the protein and gene level. Ultimately this results in the activation of c-Jun, a component of the activator protein 1 (AP-1) complex, which is a major transcription factor for the induction of osteoclast-specific genes. We now demonstrate that c-Jun and its downstream target, the osteoclast-specific bone degrading protease cathepsin K, are upregulated upon PMT treatment in an mTOR-dependent manner.

Conclusions

Activation of mTOR signalling plays a central role in the formation of osteoclasts through the bacterial toxin PMT. On the molecular level, PMT-induced activation of mTOR leads to down regulation of PDCD4, a known repressor of AP-1 complex, culminating in the activation of c-Jun, an essential transcription factor for triggering osteoclastogenesis.

Electronic supplementary material

The online version of this article (doi:10.1186/s12964-015-0117-7) contains supplementary material, which is available to authorized users.

Backbone and side-chain assignments of an effector membrane localization domain from Vibrio vulnificus MARTX toxin

(1)H, (13)C, and (15)N chemical shift assignments are presented for the isolated four-helical bundle membrane localization domain from the domain of unknown function 5 (DUF5) effector (MLD(VvDUF5)) of the MARTX toxin from Vibrio vulnificus in its solution state. We have assigned 97% of all backbone and side-chain carbon atoms, including 96% of all backbone residues. Secondary chemical shift analysis using TALOS+ demonstrates four helices that align with those predicted by structure homology modeling using the MLDs of Pasteurella multocida toxin (PMT) and the clostridial TcdB and TcsL toxins as templates. Future studies will be towards solving the structure and determining the dynamics in the solution state.

Backbone and side-chain resonance assignments of the membrane localization domain from Pasteurella multocida toxin

(1)H, (13)C, and (15)N chemical shift assignments are presented for the isolated four-helical bundle membrane localization domain (MLD) from Pasteurella multocida toxin (PMT) in its solution state. We have assigned 99% of all backbone and side-chain carbon atoms, including 99% of all backbone residues excluding proline amide nitrogens. Secondary chemical shift analysis using TALOS+ demonstrates four helices, which align with those observed within the MLD in the crystal structure of the C-terminus of PMT (PDB 2EBF) and confirm the use of the available crystal structures as templates for the isolated MLDs.

Determinants of pH-dependent modulation of translocation in dermonecrotic G-protein-deamidating toxins

Cytotoxic necrotizing factors from E. coli (CNF1, CNF2) and Yersinia (CNFy) share N-terminal sequence similarity with Pasteurella multocida toxin (PMT). This common N-terminal region harbors the receptor-binding and translocation domains that mediate uptake and delivery of the C-terminal catalytic cargo domains into the host cytosol. Subtle variations in the N-terminal ~500 amino acids of CNFs and PMT could allow for selective recognition of cellular receptors and thus, selective target cell specificity. Through studies with cellular inhibitors, we have identified an additional novel function for this region in modulating responses of these toxin proteins to changes in pH during intoxication and delivery of the catalytic cargo domain into the cytosol.

Signaling cascades of Pasteurella multocida toxin in immune evasion

Pasteurella multocida toxin (PMT) is a protein toxin found in toxigenic strains of Pasteurella multocida. PMT is the causative agent for atrophic rhinitis in pigs, a disease characterized by loss of nasal turbinate bones due to an inhibition of osteoblast function and an increase in osteoclast activity and numbers. Apart from this, PMT acts as a strong mitogen, protects from apoptosis and has an impact on the differentiation and function of immune cells. Many signaling pathways have been elucidated, however, the effect of these signaling cascades as a means to subvert the host’s immune system are just beginning to unravel.

Pasteurella multocida: from zoonosis to cellular microbiology

In a world where most emerging and reemerging infectious diseases are zoonotic in nature and our contacts with both domestic and wild animals abound, there is growing awareness of the potential for human acquisition of animal diseases. Like other Pasteurellaceae, Pasteurella species are highly prevalent among animal populations, where they are often found as part of the normal microbiota of the oral, nasopharyngeal, and upper respiratory tracts. Many Pasteurella species are opportunistic pathogens that can cause endemic disease and are associated increasingly with epizootic outbreaks. Zoonotic transmission to humans usually occurs through animal bites or contact with nasal secretions, with P. multocida being the most prevalent isolate observed in human infections. Here we review recent comparative genomics and molecular pathogenesis studies that have advanced our understanding of the multiple virulence mechanisms employed by Pasteurella species to establish acute and chronic infections. We also summarize efforts being explored to enhance our ability to rapidly and accurately identify and distinguish among clinical isolates and to control pasteurellosis by improved development of new vaccines and treatment regimens.

Mammalian target of rapamycin complex 1 (mTORC1) plays a role in Pasteurella multocida toxin (PMT)-induced protein synthesis and proliferation in Swiss 3T3 cells

Pasteurella multocida toxin (PMT) is a potent mitogen known to activate several signaling pathways via deamidation of a conserved glutamine residue in the α subunit of heterotrimeric G-proteins. However, the detailed mechanism behind mitogenic properties of PMT is unknown. Herein, we show that PMT induces protein synthesis, cell migration, and proliferation in serum-starved Swiss 3T3 cells. Concomitantly PMT induces phosphorylation of ribosomal S6 kinase (S6K1) and its substrate, ribosomal S6 protein (rpS6), in quiescent 3T3 cells. The extent of the phosphorylation is time and PMT concentration dependent, and is inhibited by rapamycin and Torin1, the two specific inhibitors of the mammalian target of rapamycin complex 1 (mTORC1). Interestingly, PMT-mediated mTOR signaling activation was observed in MEF WT but not in Gα(q/11) knock-out cells. These observations are consistent with the data indicating that PMT-induced mTORC1 activation proceeds via the deamidation of Gα(q/11), which leads to the activation of PLCβ to generate diacylglycerol and inositol trisphosphate, two known activators of the PKC pathway. Exogenously added diacylglycerol or phorbol 12-myristate 13-acetate, known activators of PKC, leads to rpS6 phosphorylation in a rapamycin-dependent manner. Furthermore, PMT-induced rpS6 phosphorylation is inhibited by PKC inhibitor, Gö6976. Although PMT induces epidermal growth factor receptor activation, it exerts no effect on PMT-induced rpS6 phosphorylation. Together, our findings reveal for the first time that PMT activates mTORC1 through the Gα(q/11)/PLCβ/PKC pathway. The fact that PMT-induced protein synthesis and cell migration is partially inhibited by rapamycin indicates that these processes are in part mediated by the mTORC1 pathway.

Structure of the catalytic domain of the Salmonella virulence factor SseI

SseI is secreted into host cells by Salmonella and contributes to the establishment of systemic infections. The crystal structure of the C-terminal domain of SseI has been solved to 1.70 Å resolution, revealing it to be a member of the cysteine protease superfamily with a catalytic triad consisting of Cys178, His216 and Asp231 that is critical to its virulence activities. Structure-based analysis revealed that SseI is likely to possess either acyl hydrolase or acyltransferase activity, placing this virulence factor in the rapidly growing class of enzymes of this family utilized by bacterial pathogens inside eukaryotic cells.

Regulation of Toll-like receptor 4-mediated immune responses through Pasteurella multocida toxin-induced G protein signalling

Background

Lipopolysaccharide (LPS)-triggered Toll-like receptor (TLR) 4-signalling belongs to the key innate defence mechanisms upon infection with Gram-negative bacteria and triggers the subsequent activation of adaptive immunity. There is an active crosstalk between TLR4-mediated and other signalling cascades to secure an effective immune response, but also to prevent excessive inflammation. Many pathogens induce signalling cascades via secreted factors that interfere with TLR signalling to modify and presumably escape the host response. In this context heterotrimeric G proteins and their coupled receptors have been recognized as major cellular targets. Toxigenic strains of Gram-negative Pasteurella multocida produce a toxin (PMT) that constitutively activates the heterotrimeric G proteins Gα_q, Gα₁₃ and Gα_i independently of G protein-coupled receptors through deamidation. PMT is known to induce signalling events involved in cell proliferation, cell survival and cytoskeleton rearrangement.

Results

Here we show that the activation of heterotrimeric G proteins through PMT suppresses LPS-stimulated IL-12p40 production and eventually impairs the T cell-activating ability of LPS-treated monocytes. This inhibition of TLR4-induced IL-12p40 expression is mediated by Gα_i-triggered signalling as well as by Gβγ-dependent activation of PI3kinase and JNK.

Taken together we propose the following model: LPS stimulates TLR4-mediated activation of the NFĸB-pathway and thereby the production of TNF-α, IL-6 and IL-12p40. PMT inhibits the production of IL-12p40 by Gα_i-mediated inhibition of adenylate cyclase and cAMP accumulation and by Gβγ-mediated activation of PI3kinase and JNK activation.

Conclusions

On the basis of the experiments with PMT this study gives an example of a pathogen-induced interaction between G protein-mediated and TLR4-triggered signalling and illustrates how a bacterial toxin is able to interfere with the host’s immune response.

Rho/ROCK-dependent inhibition of 3T3-L1 adipogenesis by G-protein-deamidating dermonecrotic toxins: differential regulation of Notch1, Pref1/Dlk1, and β-catenin signaling

The dermonecrotic toxins from Pasteurella multocida (PMT), Bordetella (DNT), Escherichia coli (CNF1-3), and Yersinia (CNFY) modulate their G-protein targets through deamidation and/or transglutamination of an active site Gln residue, which results in activation of the G protein and its cognate downstream signaling pathways. Whereas DNT and the CNFs act on small Rho GTPases, PMT acts on the α subunit of heterotrimeric G_q, G_i, and G_12/13 proteins. We previously demonstrated that PMT potently blocks adipogenesis and adipocyte differentiation in a calcineurin-independent manner through downregulation of Notch1 and stabilization of β-catenin and Pref1/Dlk1, key proteins in signaling pathways strongly linked to cell fate decisions, including fat and bone development. Here, we report that similar to PMT, DNT, and CNF1 completely block adipogenesis and adipocyte differentiation by preventing upregulation of adipocyte markers, PPARγ and C/EBPα, while stabilizing the expression of Pref1/Dlk1 and β-catenin. We show that the Rho/ROCK inhibitor Y-27632 prevented or reversed these toxin-mediated effects, strongly supporting a role for Rho/ROCK signaling in dermonecrotic toxin-mediated inhibition of adipogenesis and adipocyte differentiation. Toxin treatment was also accompanied by downregulation of Notch1 expression, although this inhibition was independent of Rho/ROCK signaling. We further show that PMT-mediated downregulation of Notch1 expression occurs primarily through G_12/13 signaling. Our results reveal new details of the pathways involved in dermonecrotic toxin action on adipocyte differentiation, and the role of Rho/ROCK signaling in mediating toxin effects on Wnt/β-catenin and Notch1 signaling, and in particular the role of G_q and G_12/13 in mediating PMT effects on Rho/ROCK and Notch1 signaling.

Pasteurella multocida and immune cells

Pasteurella multocida was first discovered by Perroncito in 1878 and named after Louis Pasteur who first isolated and described this Gram-negative bacterium as the cause of fowl disease in 1880. Subsequently, P. multocida was also found to cause atrophic rhinitis in pigs, haemorrhagic septicaemia in cattle and respiratory diseases in many other animals. Among other factors such as lipopolysaccharide, outer membrane proteins and its capsule, the protein toxin (PMT) of P. multocida is an important virulence factor that determines the immunological response of the host's immune system. However, the exact molecular mechanisms taking place in cells of the innate and adaptive immune system are largely unknown for any of these virulence factors. Due to the obvious function of PMT on cells of the porcine skeletal system where it causes bone destruction, PMT was regarded as an osteolytic protein toxin. However, it remained unclear what the actual benefit for the bacteria would be. Recently, more attention was drawn to the osteoimmunological effects of PMT and the interplay between bone and immune cells. This review summarises the knowledge of effects of P. multocida virulence factors on the host's immune system.

Pasteurella multocida toxin interaction with host cells: entry and cellular effects

The mitogenic dermonecrotic toxin from Pasteurella multocida (PMT) is a 1285-residue multipartite protein that belongs to the A-B family of bacterial protein toxins. Through its G-protein-deamidating activity on the α subunits of heterotrimeric G(q)-, G(i)- and G(12/13)-proteins, PMT potently stimulates downstream mitogenic, calcium, and cytoskeletal signaling pathways. These activities lead to pleiotropic effects in different cell types, which ultimately result in cellular proliferation, while inhibiting cellular differentiation, and account for the myriad of physiological outcomes observed during infection with toxinogenic strains of P. multocida.