Purification and properties of the cytosolic substrate for botulinum ADP-ribosyltransferase. Identification as an Mr 22,000 guanine nucleotide-binding protein

A comprehensive review of stroke-related signaling pathways and treatment in western medicine and traditional Chinese medicine

This review provides insight into the complex network of signaling pathways and mechanisms involved in stroke pathophysiology. It summarizes the historical progress of stroke-related signaling pathways, identifying potential interactions between them and emphasizing that stroke is a complex network disease. Of particular interest are the Hippo signaling pathway and ferroptosis signaling pathway, which remain understudied areas of research, and are therefore a focus of the review. The involvement of multiple signaling pathways, including Sonic Hedgehog (SHH), nuclear factor erythroid 2-related factor 2 (Nrf2)/antioxidant response element (ARE), hypoxia-inducible factor-1α (HIF-1α), PI3K/AKT, JAK/STAT, and AMPK in pathophysiological mechanisms such as oxidative stress and apoptosis, highlights the complexity of stroke. The review also delves into the details of traditional Chinese medicine (TCM) therapies such as Rehmanniae and Astragalus, providing an analysis of the recent status of western medicine in the treatment of stroke and the advantages and disadvantages of TCM and western medicine in stroke treatment. The review proposes that since stroke is a network disease, TCM has the potential and advantages of a multi-target and multi-pathway mechanism of action in the treatment of stroke. Therefore, it is suggested that future research should explore more treasures of TCM and develop new therapies from the perspective of stroke as a network disease.

Rho signaling research: history, current status and future directions

One of the main research areas in biology from the mid‐1980s through the 1990s was the elucidation of signaling pathways governing cell responses. These studies brought, among other molecules, the small GTPase Rho to the epicenter. Rho signaling research has since expanded to all areas of biology and medicine. Here, we describe how Rho emerged as a key molecule governing cell morphogenesis and movement, how it was linked to actin reorganization, and how the study of Rho signaling has expanded from cultured cells to whole biological systems. We then give an overview of the current research status of Rho signaling in development, brain, cardiovascular system, immunity and cancer, and discuss the future directions of Rho signaling research, with emphasis on one Rho effector, ROCK*.

Physiological roles of Rho and Rho effectors in mammals

Rho GTPase is a master regulator controlling cytoskeleton in multiple contexts such as cell migration, adhesion and cytokinesis. Of several Rho GTPases in mammals, the best characterized is the Rho subfamily including ubiquitously expressed RhoA and its homologs RhoB and RhoC. Upon binding GTP, Rho exerts its functions through downstream Rho effectors, such as ROCK, mDia, Citron, PKN, Rhophilin and Rhotekin. Until recently, our knowledge about functions of Rho and Rho effectors came mostly from in vitro studies utilizing cultured cells, and their physiological roles in vivo were largely unknown. However, gene-targeting studies of Rho and its effectors have now unraveled their tissue- and cell-specific roles and provide deeper insight into the physiological function of Rho signaling in vivo. In this article, we briefly describe previous studies of the function of Rho and its effectors in vitro and then review and discuss recent studies on knockout mice of Rho and its effectors.

Identification and characterization of a mammalian 39-kDa poly(ADP-ribose) glycohydrolase

ADP-ribosylation is a post-translational modification resulting from transfer of the ADP-ribose moiety of NAD to protein. Mammalian cells contain mono-ADP-ribosyltransferases that catalyze the formation of ADP-ribose-(arginine) protein, which can be cleaved by a 39-kDa ADP-ribose-(arginine) protein hydrolase (ARH1), resulting in release of free ADP-ribose and regeneration of unmodified protein. Enzymes involved in poly(ADP-ribosylation) participate in several critical physiological processes, including DNA repair, cellular differentiation, and carcinogenesis. Multiple poly(ADP-ribose) polymerases have been identified in the human genome, but there is only one known poly(ADP-ribose) glycohydrolase (PARG), a 111-kDa protein that degrades the (ADP-ribose) polymer to ADP-ribose. We report here the identification of an ARH1-like protein, termed poly(ADP-ribose) hydrolase or ARH3, which exhibited PARG activity, generating ADP-ribose from poly-(ADP-ribose), but did not hydrolyze ADP-ribose-arginine, -cysteine, -diphthamide, or -asparagine bonds. The 39-kDa ARH3 shares amino acid sequence identity with both ARH1 and the catalytic domain of PARG. ARH3 activity, like that of ARH1, was enhanced by Mg(2+). Critical vicinal acidic amino acids in ARH3, identified by mutagenesis (Asp(77) and Asp(78)), are located in a region similar to that required for activity in ARH1 but different from the location of the critical vicinal glutamates in the PARG catalytic site. All findings are consistent with the conclusion that ARH3 has PARG activity but is structurally unrelated to PARG.

The signaling protein Rho is necessary for vascular smooth muscle migration and survival but not for proliferation

BACKGROUND

The small GTPase Rho has been implicated in a variety of cellular processes. Vascular smooth muscle cell (SMC) migration, proliferation, and apoptosis are important events that contribute to the formation of intimal hyperplasia. To better understand the importance of Rho in intimal hyperplasia, we evaluated the necessity of Rho for these 3 cellular processes.

METHODS

We used for these studies a recombinant C3 exoenzyme (C3), which selectively adenosine diphosphate-ribosylates and, thus, functionally inactivates Rho. SMC migration was determined by scratch and modified Boyden chamber assays, proliferation by tritiated-thymidine incorporation, and apoptosis by terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling.

RESULTS

Pretreatment of human SMC with C3 overnight resulted in adenosine diphosphate-ribosylation and inactivation of Rho. Inactivation of Rho completely eliminated SMC migration in response to platelet-derived growth factor (PDGF)-AB. Furthermore, C3 blocked phosphorylation of focal adhesion kinase, tensin, and paxillin, which are essential for cellular migration. In contrast, C3 did not significantly affect DNA synthesis in response to PDGF-AB or activation of mitogen-activated protein kinase, a signaling mediator of PDGF-stimulated proliferation. However, prolonged inactivation of Rho by C3 induced apoptosis of SMC.

CONCLUSIONS

The small GTPase Rho is necessary for vascular SMC migration and cell survival but not for proliferation. Manipulation of Rho might have therapeutic value in modulating intimal hyperplasia.

Botulinum C3 enzyme changes the lactate dehydrogenase isozyme pattern of primary culture of neurons

Changes in the lactate dehydrogenase (LDH) isozyme pattern of primary culture of neurons treated with botulinum C3 enzyme were examined in order to elucidate the functional changes accompanying the morphological change that follows ADP-ribosylation of Rho protein. Primary neurons were prepared from the cerebrum of ICR mouse embryos on day 15. Neurons were cultured in MEM with 10% fetal calf serum at 37 degrees C. In the neurons treated with C3 enzyme, a typical morphological change was observed after 24 hr, and the LDH isozyme pattern was changed after 72 hr. The ratio of H-subunit to M-subunit in LDH was decreased by C3 treatment, suggesting the induction of a state of lower intracellular oxygen consumption in neurons in the primary cultures.

Ropporin, a sperm-specific binding protein of rhophilin, that is localized in the fibrous sheath of sperm flagella

The small GTPase Rho; functions as a molecular switch that regulates various cellular processes such as cell adhesion, motility, gene expression and cytokinesis. We previously isolated several putative Rho; targets including rhophilin which bound selectively to the GTP-bound form of Rho;. Rhophilin is expressed highly in testis and is localized specifically in sperm flagella. The presence of a PDZ domain at the carboxy terminus of rhophilin suggested that rhophilin works as an adaptor molecule. To test this hypothesis, we employed a yeast two hybrid system using the rhophilin PDZ domain as a bait, and screened a mouse testis cDNA library. We isolated several positive clones containing the same insert. The open reading frame of the cDNA encoded a novel protein of 212 amino acids designated as ropporin from a Japanese word ‘oppo’ (the tail). The amino-terminal 40 amino acid sequence of ropporin showed high homology to that of the regulatory subunit of type II cAMP-dependent protein kinase, which is involved in dimerization and binding to A-kinase anchoring proteins. Consistently, a yeast two hybrid assay and gel filtration of recombinant ropporin indicated that ropporin dimerizes through this domain. Deletion analysis indicated that the carboxy-terminal four amino acids are essential for binding of ropporin to rhophilin, and ropporin and RhoV14 coprecipitated in the presence of rhophilin in vitro. Northern blot analysis showed that ropporin is exclusively expressed in testis, and induced at the late stage of spermatogenesis. This induction paralleled that of rhophilin. Immunocytochemistry using anti-ropporin antibody showed that ropporin is localized in the principal piece and the end piece of sperm flagella. Electronmicroscopy revealed that ropporin is mostly localized in the inner surface of the fibrous sheath while rhophilin is present in the outer surface of the outer dense fiber. These results suggest that rhophilin and ropporin may form a complex in sperm flagella.

Induction of cytokines in a human colon epithelial cell line by Shiga toxin 1 (Stx1) and Stx2 but not by non-toxic mutant Stx1 which lacks N-glycosidase activity

Stx1 and Stx2 produced by Shiga toxin-producing Escherichia coli are cytotoxic due to their N-glycosidase activity on 28S rRNA. In this study, we have shown that proinflammatory cytokine mRNAs, especially IL-8, were induced by Stx1 and Stx2 in Caco-2 cells. A non-toxic mutant of Stxl which lacks N-glycosidase activity did not induce cytokine mRNAs. IL-8 production at the protein level was enhanced by Stx1 and Stx2, but not by the mutant Stx1. These results demonstrate that Shiga toxins induce expression and synthesis of cytokines in Caco-2 cells and their N-glycosidase activity is essential for the induction.

ADP-ribosylation factor proteins mediate agonist-induced activation of phospholipase D

The role of small G proteins of the ADP-ribosylation factor (ARF) and Rho families on the activation of phospholipase D (PLD) by platelet-derived growth factor (PDGF) and phorbol esters (PMA) has been investigated. The activation of PLD by PDGF and PMA was blocked by brefeldin A (BFA), an inhibitor of ARF activation, but not by Clostridium botulinum C3 exotoxin, an inhibitor of the activity of Rho. PDGF and PMA, in the presence of GTPgammaS, promoted the association of ARF and RhoA with cell membranes. Cells depleted of ARF and Rho by digitonin permeabilization showed a significant reduction of the activity of phospholipase D. Recombinant ARF was sufficient to restore agonist-induced PLD activity to digitonin-permeabilized, cytoplasm-depleted cells. In contrast, isoprenylated recombinant RhoA had no effects in this reconstitution assay. HIRcB cells were transiently transfected with wild-type and dominant-negative mutants of ARF1 and ARF6. Neither wt-ARF1 nor wt-ARF6 had any effects on agonist-dependent PLD activity. However, dominant-negative ARF1 and ARF6 mutants blocked the stimulation of PLD by PDGF but only partially inhibited the effects of PMA. These results demonstrate that ARF rather than Rho proteins mediate the activation of PLD by PDGF and phorbol esters in HIRcB fibroblasts.

Crystal structure of human RhoA in a dominantly active form complexed with a GTP analogue

The 2.4-A resolution crystal structure of a dominantly active form of the small guanosine triphosphatase (GTPase) RhoA, RhoAV14, complexed with the nonhydrolyzable GTP analogue, guanosine 5'-3-O-(thio)triphosphate (GTPgammaS), reveals a fold similar to RhoA-GDP, which has been recently reported (Wei, Y., Zhang, Y., Derewenda, U., Liu, X., Minor, W., Nakamoto, R. K., Somlyo, A. V., Somlyo, A. P., and Derewenda, Z. S. (1997) Nat. Struct. Biol. 4, 699-703), but shows large conformational differences localized in switch I and switch II. These changes produce hydrophobic patches on the molecular surface of switch I, which has been suggested to be involved in its effector binding. Compared with H-Ras and other GTPases bound to GTP or GTP analogues, the significant conformational differences are located in regions involving switches I and II and part of the antiparallel beta-sheet between switches I and II. Key residues that produce these conformational differences were identified. In addition to these differences, RhoA contains four insertion or deletion sites with an extra helical subdomain that seems to be characteristic of members of the Rho family, including Rac1, but with several variations in details. These sites also display large displacements from those of H-Ras. The ADP-ribosylation residue, Asn41, by C3-like exoenzymes stacks on the indole ring of Trp58 with a hydrogen bond to the main chain of Glu40. The recognition of the guanosine moiety of GTPgammaS by the GTPase contains water-mediated hydrogen bonds, which seem to be common in the Rho family. These structural differences provide an insight into specific interaction sites with the effectors, as well as with modulators such as guanine nucleotide exchange factor (GEF) and guanine nucleotide dissociation inhibitor (GDI).

Pasteurella multocida toxin and Bordetella bronchiseptica dermonecrotizing toxin elicit similar effects on cultured cells by different mechanisms

We compared the effects of Pasteurella multocida toxin (PMT) with Bordetella bronchiseptica dermonecrotizing toxin (DNT) at a cellular level under same conditions. Both PMT and DNT cause actin stress fiber formation in MC3T3-E1 cells which is known to be regulated by the small GTP-binding protein Rho. DNT induced mobility shifts of Rho on SDS-polyacrylamide gel electrophoresis, indicating direct modification as reported elsewhere. In contrast, no alternations in the electrophoretic mobility of Rho were found in lysates from PMT-treated cells. PMT but not DNT increased the intracellular level of inositol phosphates, indicating the elevation of phospholipase C (PLC) activity in the PMT-treated cells. These results indicate that PMT does not have Rho as a target but activates PLC. The formation of actin stress fiber by PMT seems to be stimulated through the indirect activation of Rho, which resides downstream of PLC, PMT and DNT seem to elicit similar toxic effects, at least in part, through the activation of Rho.

Reconstitution of GTP-gamma-S-dependent phospholipase D activity with ARF, RhoA, and a soluble 36-kDa protein

For activation of kidney membrane phospholipase D (PLD), cytosol is absolutely needed in addition to GTP-gamma-S. The active component of cytosol consists of three protein factors: ADP-ribosylation factor, RhoA, and a soluble 36-kDa protein. Any combination of these two factors synergistically activates PLD to some extent, but the presence of the three factors causes full activation. The 36-kDa protein is stable at 60 degrees C but inactivated at 80 degrees C for 10 min. Tissue distribution of the 36-kDa protein roughly coincides with that of PLD, suggesting physiological relevance of the protein in the regulation of PLD.

Regulation of exocytosis by the small GTP-binding protein Rho in rat basophilic leukemia (RBL-2H3) cells

1. We investigated the effect of Clostridium botulinum C3 ADP-ribosyltransferase upon beta-hexosaminidase release induced by various stimuli from streptolysin-O (0.5-1 U/ml)-permeabilized rat basophilic leukemia (RBL-2H3) cells. 2. The C3 transferase inhibited beta-hexosaminidase release induced by Ca2+ or by guanosine-5'-(3-thiotriphosphate) (GTP gamma S) plus Ca2+. 3. The C3 transferase also inhibited beta-hexosaminidase release induced by stimulating high affinity IgE and m3 muscarinic acetylcholine receptors. 4. The substrate for the C3 transferase was present in cytosol of RBL-2H3 cells, indicating the presence of rho p21. About 60% of the total cellular substrate protein remained within the cells permeabilized by 1 U/ml of streptolysin-O. 5. The protein rho p21 appears to be regulated by several pathways and it may function as an integration point for exocytosis.

Bordetella bronchiseptica dermonecrotizing toxin stimulates assembly of actin stress fibers and focal adhesions by modifying the small GTP-binding protein rho

We studied the biochemical mechanism of morphological changes in cells treated with Bordetella dermonecrotizing toxin (DNT). DNT caused the morphological changes of serum-starved MC3T3-E1 cells from flat shapes to reflactile ones. These changes were accompanied by the assembly of actin stress fibers and focal adhesions, which is known to be regulated by the small GTP-binding protein rho. Clostridium botulinum C3 exoenzyme, which ADP-ribosylates and inactivates rho protein, ‘rounded’ the cells within 2 hours after addition to the extracellular fluid and their rounded shapes were maintained for at least 10 hours. However, when the cells were co-treated with C3 exoenzyme and DNT, they were rounded at 2 hours but recovered an apparently intact morphology after 3–8 hours of incubation. rho proteins in lysates from DNT-treated cells and untreated cells were radiolabeled by [32P]ADP-ribosylation with C3 exoenzyme and analyzed by SDS-polyacrylamide gel electrophoresis. Whereas the lysate from untreated cells showed a single band of [32P]ADP-ribosylated rho protein, the lysate from DNT-treated cells showed an additional two bands as well as the band identical to that of the lysate from untreated cells. Recombinant rhoA protein treated with DNT in vitro also showed a mobility shift in SDS-polyacrylamide gel electrophoresis. These results indicate that DNT causes the assembly of actin stress fibers and focal adhesions by directly modifying rho protein.

Involvement of rho in GTP gamma S-induced enhancement of phosphorylation of 20 kDa myosin light chain in vascular smooth muscle cells: inhibition of phosphatase activity

In beta-escin-permeabilized cultured pig aortic smooth muscle cells GTP gamma S dose-dependently enhances Ca(2+)-induced, wortmannin-sensitive phosphorylation of 20 kDa myosin light chain (MLC20). GTP gamma S does not potentiate thiophosphorylation of MLC20, but does inhibit its dephosphorylation. Pretreatment with C. botulinum exotoxin C3, which specifically ADP-ribosylates and inactivates the rho family of the small molecular weight G proteins, completely abolishes the effects of GTP gamma S. These results indicate that rho is involved in the GTP gamma S-induced enhancement of Ca(2+)-dependent MLC20 phosphorylation in aortic smooth muscle cells, and strongly suggest that this effect of rho is due to inhibition of protein phosphatase activity toward MLC20.

Involvement of botulinum C3-sensitive GTP-binding proteins in alpha 1-adrenoceptor subtypes mediating Ca(2+)-sensitization

The mechanisms of alpha 1-adrenoceptor agonist-mediated sensitization of the contractile apparatus of smooth muscle to Ca2+ were studied in beta-escin-permeabilized thoracic arterial smooth muscle of rabbit. Addition of norepinephrine (10 microM) plus guanosine 5'-triphosphate (GTP, 50 microM) significantly enhanced Ca2+ sensitivity as compared with the addition of 0.3 microM Ca2+ alone (pCa6.5). In beta-escin-skinned smooth muscle of chloroethylclonidine-treated tissues, the enhancement of Ca(2+)-contraction produced by norepinephrine or clonidine was completely inhibited by guanosine 5'-O-(beta-thiodiphosphate) (GDP beta-S, 1 mM). In addition, Clostridium botulinum C3, which inactivates low molecular weight GTP-binding protein families, abolished norepinephrine- or clonidine-induced Ca(2+)-sensitization, but did not affect clonidine-induced translocation of protein kinase C to the membrane. The norepinephrine-enhanced Ca2+ sensitivity was partially reversed by a pretreatment with a selective myosin light chain kinase inhibitor (8R*, 9S*, 11S*)-(-)-9-hydroxy-9-methoxycarbonyl-8-methyl-14-n- propoxy-2,3,9,10-tetrahydro-8,11-epoxy,1H,8H,11H-2,7b,11a- triazadibenzo[a,g]cycloocta[cde]trinden-1-one (KT5926, 500 nM), but those of clonidine and in the chloroethylclonidine-treated tissues norepinephrine were not. These results suggest that Ca(2+)-sensitization produced by the activation of the alpha 1-adrenoceptor subtypes is linked via a low molecular weight GTP-binding protein (Rho), and the regulations of phosphorylation in contractile elements.

Effect of botulinum C3 exoenzyme on cell growth and cytoskeleton organization in transformed human epidermal cells in culture: a possible role for rho protein in epidermal cells

We examined the role of rho gene products (rho proteins) on cell growth and cytoskeleton organization in transformed human epidermal cells in culture (HSC-1), using recombinant botulinum C3 exoenzyme which specifically ADP-ribosylates rho proteins. Incubation of HSC-1 cell lysates with C3 exoenzyme revealed a single [32P]ADP-ribosylated protein with a molecular weight of 23,000. This protein was identified as rhoA protein by isoelectric focusing (pI 6.0). Addition of C3 exoenzyme to the culture medium of HSC-1 cells changed the shape of HSC-1 cells to a round form with beaded processes in a time- and dose-dependent manner. Moreover, C3 treatment reduced the cell growth rate; 72-h treatment with C3 exoenzyme at 1, 3, 10, 30 and 60 micrograms/ml culture medium resulted in 9.0 +/- 1.8%, 20 +/- 2.9%, 26 +/- 2.3%, 50 +/- 1.4% and 40 +/- 2.0% inhibition of the growth rate relative to controls, respectively. Under this condition, actin stress fibers were disassembled, as revealed using fluorescent-labeled phallacidin, whereas keratin intermediate filaments were not affected, visualized by immunofluorescence using anti-keratin antibody. These results suggest that rho proteins are closely related to cell growth and that these proteins regulate, at least in part, the assembly of actin stress fibers in transformed human epidermal cells.

Differentiation-induced increase in Clostridium botulinum C3 exoenzyme-catalyzed ADP-ribosylation of the small GTP-binding protein Rho

The specific [32P]ADP-ribosylation by Clostridium botulinum exoenzyme C3 was used to study differentiation-dependent changes in the regulation of the low-molecular-mass GTP-binding protein Rho. Differentiation of F9 teratocarcinoma cells to neuronal-like cells by treatment with retinoic acid and dibutyryl-adenosine 3',5'-monophosphate [(Bt)2cAMP] increased the C3-catalyzed ADP-ribosylation of RhoA proteins in cytosolic and membrane fractions by about threefold and sixfold, respectively. Phenotypical differentiation of F9 cells was not required for increase in ADP-ribosylation. Increase in ADP-ribosylation after (Bt)2cAMP and retinoic acid treatments was blocked by cycloheximide, indicating the requirement of protein biosynthesis. As deduced from specific rho mRNA amounts and from Western analysis with a monoclonal RhoA antibody, the stimulation in the [32P]ADP-ribosylation of Rho was not caused by an increased de-novo synthesis of Rho proteins. GDP increased the ADP-ribosylation of membrane-associated Rho from non-differentiated, but not from differentiated F9 cells. GTP[S] decreased ADP-ribosylation of membranous Rho from differentiated and much less from non-differentiated F9 cells. Differentiation-dependent increase in ADP-ribosylation of cytosolic Rho was reversed by protein phosphatase type-1. Treatment with SDS (0.01%) which releases Rho from complexation with guanine nucleotide dissociation inhibitor, increased ADP-ribosylation both in differentiated and non-differentiated cells, indicating no differentiation-specific change of such complexes. In total, our data indicate that the induction of the differentiation process in F9 cells is accompanied by changes in the regulation of cytosolic and membrane-associated Rho proteins.

Morphological effects, rate of incorporation, and the enzymatic action of botulinum ADP-ribosyltransferase, known as C3 exoenzyme, on human neuroblastoma GOTO cells

The susceptibility of various lines of cultured cells to botulinum ADP-ribosyltransferase, known as C3 exoenzyme, was examined. Human neuroblastoma GOTO cells were most sensitive. The C3 exoenzyme caused a change in cell shape that involved extension of neurites. The exoenzyme evoked the outgrowth of neurites from chick ganglion as effectively as nerve growth factor, suggesting that C3 exoenzyme possesses neurotropic activity. Experiments with 125I-labeled enzyme revealed that C3 exoenzyme was rapidly incorporated into cells but the number of incorporated enzyme molecules was small. Once C3 exoenzyme had been incorporated, ADP-ribosylation of the substrate (Rho protein) in GOTO cells occurred immediately and rapidly reached a maximum level. However, some of Rho proteins remained unmodified even after induction of the change in morphology. These findings suggest that ADP-ribosylation by C3 exoenzyme is directly associated with the differentiation of GOTO cells but that other events may also participate in this process.

Small GTP-binding proteins of squid photoreceptor. Interaction with photoactivated rhodopsin

Squid photoreceptor membranes contain several small GTP-binding proteins (22-27 kDa) in addition to heterotrimeric G-proteins. In addition, these membranes contain several proteins which can be ADP-ribosylated by exoenzyme C3 from Clostridium botulinum (C3). These proteins are similar but not identical to C3 substrates from bovine rod outer segments. It is shown that substrates of C3 in squid photoreceptor interact with rhodopsin in a light-dependent manner. These data suggest involvement of small GTP-binding proteins in phototransduction processes in invertebrates.

A rho-like protein is involved in the organisation of the contractile ring in dividing sand dollar eggs

Sand dollar eggs were microinjected with botulinum C3 exoenzyme, an ADP-ribosyltransferase from Clostridium botulinum that specifically ADP-ribosylates and inactivates rho proteins. C3 exoenzyme microinjected during nuclear division interfered with subsequent cleavage furrow formation. No actin filaments were detected in the equatorial cortical layer of these eggs by rhodamine-phalloidin staining. When microinjected into furrowing eggs, C3 exoenzyme rapidly disrupted the contractile ring actin filaments and caused regression of the cleavage furrows. C3 exoenzyme had no apparent effect on nuclear division, however, and multinucleated embryos developed from the microinjected eggs. By contrast, C3 exoenzyme did not affect the organisation of cortical actin filaments immediately after fertilisation. Only one protein (molecular weight 22,000) was ADP-ribosylated by C3 exoenzyme in the isolated cleavage furrow. This protein co-migrated with ADP-ribosylated rhoA derived from human platelets when analysed by two-dimensional gel electrophoresis. These results strongly suggest that a rho-like, small GTP-binding protein is selectively involved in the organisation and maintenance of the contractile ring.

MCI-826 is a potent and selective antagonist of peptide leukotrienes (p-LTs) and has characteristics distinctive from those of FPL 55712

Antagonistic effects of a newly synthesized compound, (E)-2,2-diethyl-3'-[2-[2-(4-isopropyl)thiazolyl]ethenyl]succinanilic+ ++ acid sodium salt (MCI-826) on the contraction of the isolated guinea pig trachea and human bronchus induced by various agonists including peptide leukotrienes (p-LTs), histamine, acetylcholine (ACh), prostaglandin (PG) D2 and others were investigated and compared with the effects of a p-LT antagonist, FPL 55712, in some experiments. MCI-826 potently antagonized LTD4- and LTE4-induced contractions at extremely low concentrations in the isolated guinea pig trachea with pA2 values of 8.3 and 8.9, respectively, on a molar basis. These values indicated that MCI-826 is over 100 times stronger than FPL 55712. Similarly, MCI-826 at 10(-8) g/ml (2.4 x 10(-8) M) markedly antagonized LTD4-induced contractions of the isolated human bronchus. Although FPL 55712 fairly inhibited the 10(-9) g/ml LTC4-induced contraction of the isolated guinea pig trachea, MCI-826 had little effect on the contraction at high concentrations like 3 x 10(-6) g/ml (7.1 x 10(-6) M). MCI-826 modestly affected the other agonist-induced contractions and the resting tonus of the isolated guinea pig trachea at 10(-6) g/ml (2.4 x 10(-6) M) or higher concentrations, but FPL 55712 caused fair inhibition of some of those contractions and gradually lowered the resting tonus with time. These results indicate that MCI-826 is a highly potent and selective antagonist of LTD4 and LTE4 and can be a useful tool for biological and pharmacological experiments on p-LTs.

Signal transduction pathways in keratinocytes

Mammalian cells do not live as isolated organisms, but are instead organized into complex, highly specialized tissue organs composed of a homogeneous or a mixed cell population. In order to maintain tissue homeostasis in physiological and pathophysiological conditions, intercellular communication is an absolute requirement. This review will summarize our current knowledge as to how an extracellular signal is transduced via a specific receptor to the interior of the cell and how this signal will induce special cell functions. Attention will be paid to the major signal transduction pathways known to be active in keratinocytes, namely the adenylate cyclase, guanylate cyclase, tyrosine kinase, and phospholipase C systems. Finally, examples will be given of how interactions between these signal transduction pathways can take place and how 'signal cross-talk' might regulate keratinocyte function.

Occurrence and biochemical characterization of GTP-binding proteins in Candida albicans

The activities of GTP-binding and GTPase in Candida albicans were present in the cytosol, KCl- and cholate-extractable fractions. At least two kinds of GTP-binding proteins were found in the cytosolic fraction; the major one with a molecular mass of about 30 kDa and the other about 500 kDa. The former specifically bound guanine nucleotides and was most likely to bind GDP since guanosine 5'-O-(thio) triphosphate (GTP gamma S)-binding was accelerated by addition of (NH4)2SO4. The latter showed no specificity in nucleotide binding and could also bind adenine nucleotides. The proteins were not ADP-ribosylated by either pertussis toxin or cholera toxin. These results indicate that ras-like monomeric, low molecular mass GTP-binding proteins distinct from heterotrimeric G proteins such as Gi, Go and Gs are present in C. albicans.

Clostridium botulinum C3 ADP-ribosyltransferase

C3 and C3-like ADP-ribosyltransferases modify the low-molecular-mass GTP-binding proteins Rho and Rac. ADP-ribosylation occurs in asparagine-41, which is located in the putative effector region of these highly conserved regulatory proteins. First studies indicate that the Rho proteins are somehow involved in the regulation of cytoskeletal proteins, e.g., microfilament proteins. Although the precise mechanism of the interaction of the C3 substrate with cytoskeletal elements is unclear, it appears that the ADP-ribosylation by C3 renders the GTP-binding protein biologically inactive. Thus C3 and/or C3-like ADP-ribosyltransferases may be useful instruments with which to study the physiological functions of its eukaryotic substrates. Moreover, those studies may help to elucidate whether these exoenzymes are of pathophysiological and pathogenetic relevance in diseases caused by clostridia producing these agents.

The 65-kDa protein from pig heart. A new substrate for Clostridium botulinum ADP-ribosyltransferase (exoenzyme C3)

In the pig heart sarcolemma, a 65 kDa protein is found to be ADP-ribosylated by Clostridium botulinum ADP-ribosyltransferase (exoenzyme C3). ADP-ribosylation of this protein is regulated by guanyl nucleotides and cytosol factor in a fashion similar to that for other C3 substrates. The new exoenzyme C3 substrate was partially purified. This protein is supposed to be a GTP-binding one.

Purification and characterization of ADP-ribosyltransferases (exoenzyme C3) of Clostridium botulinum type C and D strains

By cation-exchange column chromatography followed by gel filtration or hydroxylapatite column chromatography, ADP-ribosyltransferases (exoenzyme C3) were isolated from culture supernatants of Clostridium botulinum type C strains Stockholm (CST) and 6813 (C6813) and from type D strains South African (DSA) and 1873 (D1873), and their molecular properties were compared. The purified C3 enzymes were homogeneous in polyacrylamide gel electrophoresis. The C3 enzymes existed as single-chain polypeptides with molecular masses of 25.0 to 25.5 kDa and transferred ADP-riboses to the same substrates in rat brain membrane extract. The C3 enzymes could be roughly classified into two groups with respect to amino acid composition, amino-terminal sequence, and antigenicity. One group contains the C3 enzymes of strains C6813 and DSA, and the other contains those of strains CST and D1873. The specific activity of the C3 enzyme of strain C6813 was about 15 times higher than that of the C3 enzyme of strain CST. These results indicate that the classification of the C3 molecules differs from that of the neurotoxin molecules.

Molecular cloning and sequencing of the epidermal cell differentiation inhibitor gene from Staphylococcus aureus

We recently purified to homogeneity a protein inhibiting differentiation of cultured keratinocytes from extracellular products of Staphylococcus aureus, and named it epidermal cell differentiation inhibitor (EDIN). In the present study, we isolated and sequenced the structural gene coding for EDIN from Staphylococcus aureus E-1 using oligonucleotide probes on the basis of the partial amino acid sequence of the purified EDIN. DNA sequencing of the cloned DNA revealed an open reading frame encoding 247 amino acids as a precursor of EDIN, which included an NH2-terminal signal sequence of 35 amino acid residues. Processing of this precursor produces a mature EDIN protein composed of 212 amino acids with a calculated Mr of 23,782. The EDIN shared 35% amino acid homology with the ADP-ribosyltransferase C3 of Clostridium botulinum. These results with biological properties of EDIN described previously indicate that EDIN is a novel protein.

Reduction of mono(ADP-ribosyl)ation of 20 kDa protein with maturation in rat testis: involvement of guanine nucleotides

When the homogenate prepared from immature rat testes was incubated with [32P]NAD, several proteins (90, 39 and 20 kDa) were ADP-ribosylated in the absence of bacterial toxins. This observation suggested the existence of an endogenous ADP-ribosyltransferase and substrates. The data that the digested product by phosphodiesterase of ADP-ribosylated 20 kDa protein was 5'-AMP suggested that 20 kDa protein was mono(ADP-ribosyl)ated. In addition, the mono(ADP-ribosyl)ation of 20 kDa protein was enhanced by guanine nucleotides such as GTP, GDP and GTP[gamma S], and decreased by the concentrations of 10 mM Mg2+. In contrast, the incorporation of ADP-ribose moiety from NAD to both 90 and 39 kDa proteins was not changed by guanine nucleotides. On the other hand, mono(ADP-ribosyl)ation of 20 kDa protein was not observed in the homogenate prepared from other tissues of the same rats. Furthermore, we found that mono(ADP-ribosyl)ation of 20 kDa protein was decreased with the maturation of the rats and that an endogenous mono(ADP-ribosyl)transferase and 20 kDa protein were located in the nuclei.

Sodium fluoride mimics the effect of prostaglandin E2 on catecholamine release from bovine adrenal chromaffin cells

We have reported recently that prostaglandin E2 (PGE2) stimulated phosphoinositide metabolism in bovine adrenal chromaffin cells and that PGE2 and ouabain, an inhibitor of Na+, K(+)-ATPase, synergistically induced a gradual secretion of catecholamines from the cells. Here we examined the involvement of a GTP-binding protein(s) in PGE receptor-induced responses by using NaF. In the presence of Ca2+ in the medium, NaF stimulated the formation of all three inositol phosphates, i.e., inositol monophosphate, bisphosphate, and trisphosphate, linearly over 30 min in a dose-dependent manner (15-30 mM). This effect on phosphoinositide metabolism was accompanied by an increase in cytosolic free Ca2+. NaF also induced catecholamine release from chromaffin cells, and the dependency of stimulation of the release on NaF concentration was well correlated with those of NaF-enhanced inositol phosphate formation and increase in cytosolic free Ca2+. Although the effect of NaF on PGE2-induced catecholamine release in the presence of ouabain was additive at concentrations below 20 mM, there was no additive effect at 25 mM NaF. Furthermore, the time course of catecholamine release stimulated by 20 mM NaF in the presence of ouabain was quite similar to that by 1 microM PGE2, and both stimulations were markedly inhibited by amiloride, with half-maximal inhibition at 10 microM. Pretreatment of the cells with pertussis toxin did not prevent, but rather enhanced, PGE2-induced catecholamine release over the range of concentrations examined. These results demonstrate that NaF mimics the effect of PGE2 on catecholamine release from chromaffin cells and suggest that PGE2-evoked catecholamine release may be mediated by the stimulation of phosphoinositide metabolism through a putative GTP-binding protein insensitive to pertussis toxin.

Cellular and molecular actions of binary toxins possessing ADP-ribosyltransferase activity

Clostridial organisms produce a number of binary toxins. Thus far, three complete toxins (botulinum, perfringens and spiroforme) and one incomplete toxin (difficile) have been identified. In the case of complete toxins, there is a heavy chain component (Mr approximately 100,000) that binds to target cells and helps create a docking site for the light chain component (Mr approximately 50,000). The latter is an enzyme that possesses mono(ADP-ribosyl)transferase activity. The toxins appear to proceed through a three step sequence to exert their effects, including a binding step, an internalization step and an intracellular poisoning step. The substrate for the toxins is G-actin. By virtue of ADP-ribosylating monomeric actin, the toxins prevent polymerization as well as promoting depolymerization. The most characteristic cellular effect of the toxins is alteration of the cytoskeleton, which leads directly to changes in cellular morphology and indirectly to changes in cell function (e.g. release of chemical mediators). Binary toxins capable of modifying actin are likely to be useful tools in the study of cell biology.

The ram: a novel low molecular weight GTP-binding protein cDNA from a rat megakaryocyte library

A novel low Mr GTP-binding protein cDNA was isolated from a rat megakaryocyte cDNA library with a synthetic oligonucleotide probe corresponding to an 8-amino acid sequence specific for c25KG, a GTP-binding protein previously isolated from human platelet cytosol fraction [(1989) J. Biol. Chem. 264, 17000-17005]. The cDNA has an open reading frame encoding a protein of 221 amino acids with a calculated Mr of 25068. The protein is designated as ram (ras-related gene from megakaryocyte) protein (ram p25). The amino acid sequence deduced from the ram cDNA contains the consensus sequences for GTP-binding and GTPase domains. ram p25 shares about 23%, 39% and 80% amino acid homology with the H-ras, smg25A and c25KG proteins, respectively. The 3.5-kb ram mRNA was detected abundantly in spleen cells.

A GTPase-activating protein for rhoB p20, a ras p21-like GTP-binding protein--partial purification, characterization and subcellular distribution in rat brain

A protein stimulating the GTPase activity of rhoB p20, a ras p21-like GTP-binding protein (G protein), was partially purified from the cytosol fraction of bovine brain. This protein, designated as rhoB p20 GTPase-activating protein (GAP), did not stimulate the GTPase activity of other ras p21/ras p21-like G proteins including c-Ha-ras p21, smg p21 and smg p25A. The activities of c-Ha-ras p21 GAP and smg p21 GAP were also detected in the cytosol fraction of bovine brain and rhoB p20 GAP was separated from these GAPs. The activity of rhoB p20 GAP was eliminated by tryptic digestion or boiling. The Mr value of rhoB p20 GAP was estimated to be 150-200 x 10(3) and 37 x 10(3) by gel filtration and sucrose density gradient ultracentrifugation, respectively. These results indicate that there is rhoB p20 GAP in addition to c-Ha-ras p21 GAP and smg p21 GAP in bovine brain. In rat brain, about 50% of rhoB p20 GAP was found with the highest specific activity in the P2 fraction containing myelin, synaptosomes and mitochondria. In the P2 fraction, about 30% of rhoB p20 GAP was found in the P2C fraction containing mainly synaptosomes. rhoB p20 GAP was detected in the cytosol and particulate fractions of not only rat brain but also other rat tissues.

Effect of botulinum D toxin on human neutrophilic leukocytes and localization of its substrates

Botulinum D toxin has been shown to ADP-ribosylate 22-kD proteins in neutrophilic leukocytes, but the function of these GTP-binding proteins remains unknown. In analogy to small GTP-binding proteins like SEC4 to YPT1, it has been suggested that botulinum D toxin substrates might be involved in secretory process of myeloid cells. Three main findings lead to the opposite conclusion. First of all, in human neutrophils, botulinum D toxin does not modify the release of azurophilic and specific granules induced by a chemoattractant (a formylpeptide) or a phorbol ester. Second, botulinum D toxin ADP-ribosylates 24 to 26-kD proteins that are only present in plasma membranes of human neutrophils. The membrane location of these substrates differs largely from that of the GTP-binding proteins involved in exocytosis and located in granules. Finally, since the same quantity of the toxin substrates is present in neutrophils as in their precursors, HL60 cells (which are devoid of specific granules and characterized by immature azurophilic granules and NADPH oxidase), it is unlikely that endogenous botulinum D toxin substrates are directly involved in the secretory responses of neutrophils.

ADP-ribosylation of the rho/rac proteins induces growth inhibition, neurite outgrowth and acetylcholine esterase in cultured PC-12 cells

Botulinum ADP-ribosyltransferase C3 (C3 exoenzyme) was purified to homogeneity and added to cultured rat pheochromocytoma PC-12 cells. Incubation with this exoenzyme caused inhibition of cell growth and induced neurites as well as acetylcholine esterase in these cells. These changes were dependent on the amount of the enzyme added to the culture, which correlated with the in situ ADP-ribosylation of the rho/rac proteins in the cells. Preincubation with a specific anti-C3 exoenzyme monoclonal antibody inhibited both the ADP-ribosyltransferase activity and the neurite-inducing activity of the enzyme preparation. These results suggest that C3 exoenzyme affected the cellular function of the rho/rac proteins by ADP-ribosylation to induce these changes in the cells.

Evidence for the presence of an endogenous cytosolic protein inhibitor of intestinal fucosyltransferase activities

Soluble endogenous inhibitory activities for glycoprotein: alpha (1-2) and alpha (1-3) fucosyltransferases are demonstrated in rat small intestinal cytosol. These inhibitors are retained on DEAE-cellulose and are eluted as two fractions A and B. Fraction B is non dialyzable, heat stable and pronase-resistant and consists probably of poly-nucleotides. Fraction A is also non-dialyzable, but is thermolabile and pronase-sensitive, suggesting that it contains proteins. The inhibition of fucosyltransferase activity by fraction A is competitive for GDP-fucose and non-competitive for the glycoprotein substrate. Inhibition is not due to interfering enzymatic activities (glycosyl-nucleotide pyrophosphatases, glycosidases or proteases) and is reversible. This protein inhibitor, with a molecular weight of 60,000, is found only in the intestine and the pancreas and appears to be different from the previously reported inhibitors of brain glycolipid glycosyltransferases.