Modification of Actin and Rho Proteins by Clostridial ADP-Ribosylating Toxins

The Gram-positive, spore-forming bacterium Paenibacillus larvae is the etiological agent of American Foulbrood, a highly contagious and often fatal honey bee brood disease. The species P. larvae comprises five so-called ERIC-genotypes which differ in virulence and pathogenesis strategies. In the past two decades, the identification and characterization of several P. larvae virulence factors have led to considerable progress in understanding the molecular basis of pathogen-host-interactions during P. larvae infections. Among these virulence factors are three ADP-ribosylating AB-toxins, Plx1, Plx2, and C3larvin. Plx1 is a phage-born toxin highly homologous to the pierisin-like AB-toxins expressed by the whites-and-yellows family Pieridae (Lepidoptera, Insecta) and to scabin expressed by the plant pathogen Streptomyces scabiei. These toxins ADP-ribosylate DNA and thus induce apoptosis. While the presumed cellular target of Plx1 still awaits final experimental proof, the classification of the A subunits of the binary AB-toxins Plx2 and C3larvin as typical C3-like toxins, which ADP-ribosylate Rho-proteins, has been confirmed experimentally. Normally, C3-exoenzymes do not occur together with a B subunit partner, but as single domain toxins. Interestingly, the B subunits of the two P. larvae C3-like toxins are homologous to the B-subunits of C2-like toxins with striking structural similarity to the PA-63 protomer of Bacillus anthracis.

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Rho GTPases as Key Molecular Players within Intestinal Mucosa and GI Diseases

Cells ◽

10.3390/cells10010066 ◽

2021 ◽

Vol 10 (1) ◽

pp. 66

Author(s):

Rashmita Pradhan ◽

Phuong A. Ngo ◽

Luz d. C. Martínez-Sánchez ◽

Markus F. Neurath ◽

Rocío López-Posadas

Keyword(s):

Intestinal Mucosa ◽

Rho Gtpases ◽

Current Knowledge ◽

Cell Types ◽

Effector Proteins ◽

Special Focus ◽

Specific Cell ◽

Rho Proteins

Rho proteins operate as key regulators of the cytoskeleton, cell morphology and trafficking. Acting as molecular switches, the function of Rho GTPases is determined by guanosine triphosphate (GTP)/guanosine diphosphate (GDP) exchange and their lipidation via prenylation, allowing their binding to cellular membranes and the interaction with downstream effector proteins in close proximity to the membrane. A plethora of in vitro studies demonstrate the indispensable function of Rho proteins for cytoskeleton dynamics within different cell types. However, only in the last decades we have got access to genetically modified mouse models to decipher the intricate regulation between members of the Rho family within specific cell types in the complex in vivo situation. Translationally, alterations of the expression and/or function of Rho GTPases have been associated with several pathological conditions, such as inflammation and cancer. In the context of the GI tract, the continuous crosstalk between the host and the intestinal microbiota requires a tight regulation of the complex interaction between cellular components within the intestinal tissue. Recent studies demonstrate that Rho GTPases play important roles for the maintenance of tissue homeostasis in the gut. We will summarize the current knowledge on Rho protein function within individual cell types in the intestinal mucosa in vivo, with special focus on intestinal epithelial cells and T cells.

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Postprenylation CAAX Processing Is Required for Proper Localization of Ras but Not Rho GTPases

Molecular Biology of the Cell ◽

10.1091/mbc.e04-11-0960 ◽

2005 ◽

Vol 16 (4) ◽

pp. 1606-1616 ◽

Cited By ~ 112

Author(s):

David Michaelson ◽

Wasif Ali ◽

Vi K. Chiu ◽

Martin Bergo ◽

Joseph Silletti ◽

...

Keyword(s):

Posttranslational Modifications ◽

Protein Trafficking ◽

Rho Gtpases ◽

Ras Proteins ◽

Rho Proteins ◽

Carboxyl Methylation ◽

C Terminus ◽

Individual Contributions ◽

The Individual ◽

And Function

The CAAX motif at the C terminus of most monomeric GTPases is required for membrane targeting because it signals for a series of three posttranslational modifications that include isoprenylation, endoproteolytic release of the C-terminal– AAX amino acids, and carboxyl methylation of the newly exposed isoprenylcysteine. The individual contributions of these modifications to protein trafficking and function are unknown. To address this issue, we performed a series of experiments with mouse embryonic fibroblasts (MEFs) lacking Rce1 (responsible for removal of the –AAX sequence) or Icmt (responsible for carboxyl methylation of the isoprenylcysteine). In MEFs lacking Rce1 or Icmt, farnesylated Ras proteins were mislocalized. In contrast, the intracellular localizations of geranylgeranylated Rho GTPases were not perturbed. Consistent with the latter finding, RhoGDI binding and actin remodeling were normal in Rce1- and Icmt-deficient cells. Swapping geranylgeranylation for farnesylation on Ras proteins or vice versa on Rho proteins reversed the differential sensitivities to Rce1 and Icmt deficiency. These results suggest that postprenylation CAAX processing is required for proper localization of farnesylated Ras but not geranygeranylated Rho proteins.

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Differential Involvement of the Actin Cytoskeleton in Differentiation and Mitogenesis of Thyroid Cells: Inactivation of Rho Proteins Contributes to Cyclic Adenosine Monophosphate-Dependent Gene Expression but Prevents Mitogenesis

Endocrinology ◽

10.1210/en.2005-0329 ◽

2005 ◽

Vol 146 (12) ◽

pp. 5485-5495 ◽

Cited By ~ 6

Author(s):

Nathalie Fortemaison ◽

Sara Blancquaert ◽

Jacques E. Dumont ◽

Carine Maenhaut ◽

Klaus Aktories ◽

...

Keyword(s):

Actin Cytoskeleton ◽

Dna Synthesis ◽

Primary Cultures ◽

Residual Activity ◽

Cyclin D3 ◽

Actin Stress Fiber ◽

Cyclin Dependent Kinase ◽

Rho Proteins ◽

Thyroid Cells ◽

Toxin B

In thyroid epithelial cells, TSH via cAMP induces a rounding up of the cells associated with actin stress fiber disruption, expression of differentiation genes and cell cycle progression. Here we have evaluated the role of small G proteins of the Rho family and their impact on the actin cytoskeleton in these different processes in primary cultures of canine thyrocytes. TSH and forskolin, but not growth factors, rapidly inactivated RhoA, Rac1, and Cdc42, as assayed by detection of GTP-bound forms. Using toxins that inactivate Rho proteins (toxin B, C3 exoenzyme) or activate them [cytotoxic necrotizing factor 1 (CNF1)], in comparison with disruption of the actin cytoskeleton by dihydrocytochalasin B (DCB) or latrunculin, two unexpected conclusions were reached: 1) inactivation of Rho proteins by cAMP, by disorganizing actin microfilaments and inducing cell retraction, could be necessary and sufficient to mediate at least part of the cAMP-dependent induction of thyroglobulin and thyroid oxidases, but only partly necessary for the induction of Na+/I− symporter and thyroperoxidase; 2) as indicated by the effect of their inhibition by toxin B and C3, some residual activity of Rho proteins could be required for the induction by cAMP-dependent or -independent mitogenic cascades of DNA synthesis and retinoblastoma protein (pRb) phosphorylation, through mechanisms targeting the activity, but not the stimulated assembly, of cyclin D3-cyclin-dependent kinase 4 complexes. However, at variance with current concepts mostly derived from fibroblast models, DNA synthesis induction and cyclin D3-cyclin-dependent kinase 4 activation were resistant to actin depolymerization by dihydrocytochalasin B in canine thyrocytes, which provides a first such example in a normal adherent cell.

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The Crossroads between RAS and RHO Signaling Pathways in Cellular Transformation, Motility and Contraction

Genes ◽

10.3390/genes12060819 ◽

2021 ◽

Vol 12 (6) ◽

pp. 819

Author(s):

Olga Soriano ◽

Marta Alcón-Pérez ◽

Miguel Vicente-Manzanares ◽

Esther Castellano

Keyword(s):

Signaling Pathways ◽

Actin Polymerization ◽

Mapk Pathway ◽

Human Cancer ◽

Cellular Transformation ◽

Dependent Manner ◽

Rho Proteins ◽

Filament Assembly ◽

Multiple Signaling ◽

Mechanical Feedback

Ras and Rho proteins are GTP-regulated molecular switches that control multiple signaling pathways in eukaryotic cells. Ras was among the first identified oncogenes, and it appears mutated in many forms of human cancer. It mainly promotes proliferation and survival through the MAPK pathway and the PI3K/AKT pathways, respectively. However, the myriad proteins close to the plasma membrane that activate or inhibit Ras make it a major regulator of many apparently unrelated pathways. On the other hand, Rho is weakly oncogenic by itself, but it critically regulates microfilament dynamics; that is, actin polymerization, disassembly and contraction. Polymerization is driven mainly by the Arp2/3 complex and formins, whereas contraction depends on myosin mini-filament assembly and activity. These two pathways intersect at numerous points: from Ras-dependent triggering of Rho activators, some of which act through PI3K, to mechanical feedback driven by actomyosin action. Here, we describe the main points of connection between the Ras and Rho pathways as they coordinately drive oncogenic transformation. We emphasize the biochemical crosstalk that drives actomyosin contraction driven by Ras in a Rho-dependent manner. We also describe possible routes of mechanical feedback through which myosin II activation may control Ras/Rho activation.

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Rho-Proteins and Downstream Pathways as Potential Targets in Sepsis and Septic Shock: What Have We Learned from Basic Research

Cells ◽

10.3390/cells10081844 ◽

2021 ◽

Vol 10 (8) ◽

pp. 1844

Author(s):

Maria Luísa da Silveira Hahmeyer ◽

José Eduardo da Silva-Santos

Keyword(s):

Septic Shock ◽

Actin Polymerization ◽

Current Knowledge ◽

Cecal Ligation ◽

Experimental Models ◽

Rho Proteins ◽

Growing Cell ◽

Sepsis And Septic Shock

Sepsis and septic shock are associated with acute and sustained impairment in the function of the cardiovascular system, kidneys, lungs, liver, and brain, among others. Despite the significant advances in prevention and treatment, sepsis and septic shock sepsis remain global health problems with elevated mortality rates. Rho proteins can interact with a considerable number of targets, directly affecting cellular contractility, actin filament assembly and growing, cell motility and migration, cytoskeleton rearrangement, and actin polymerization, physiological functions that are intensively impaired during inflammatory conditions, such as the one that occurs in sepsis. In the last few decades, Rho proteins and their downstream pathways have been investigated in sepsis-associated experimental models. The most frequently used experimental design included the exposure to bacterial lipopolysaccharide (LPS), in both in vitro and in vivo approaches, but experiments using the cecal ligation and puncture (CLP) model of sepsis have also been performed. The findings described in this review indicate that Rho proteins, mainly RhoA and Rac1, are associated with the development of crucial sepsis-associated dysfunction in different systems and cells, including the endothelium, vessels, and heart. Notably, the data found in the literature suggest that either the inhibition or activation of Rho proteins and associated pathways might be desirable in sepsis and septic shock, accordingly with the cellular system evaluated. This review included the main findings, relevance, and limitations of the current knowledge connecting Rho proteins and sepsis-associated experimental models.

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