Galpha(12/13) mediates alpha(1)-adrenergic receptor-induced cardiac hypertrophy

In neonatal cardiomyocytes, activation of the G(q)-coupled alpha(1)-adrenergic receptor (alpha(1)AR) induces hypertrophy by activating mitogen-activated protein kinases, including c-Jun NH(2)-terminal kinase (JNK). Here, we show that JNK activation is essential for alpha(1)AR-induced hypertrophy, in that alpha(1)AR-induced hypertrophic responses, such as reorganization of the actin cytoskeleton and increased protein synthesis, could be blocked by expressing the JNK-binding domain of JNK-interacting protein-1, a specific inhibitor of JNK. We also identified the classes and subunits of G proteins that mediate alpha(1)AR-induced JNK activation and hypertrophic responses by generating several recombinant adenoviruses that express polypeptides capable of inhibiting the function of specific G-protein subunits. alpha(1)AR-induced JNK activation was inhibited by the expression of carboxyl terminal regions of Galpha(q), Galpha(12), and Galpha(13). JNK activation was also inhibited by the Galpha(q/11)- or Galpha(12/13)-specific regulator of G-protein signaling (RGS) domains and by C3 toxin but was not affected by treatment with pertussis toxin or by expression of the carboxyl terminal region of G protein-coupled receptor kinase 2, a polypeptide that sequesters Gbetagamma. alpha(1)AR-induced hypertrophic responses were inhibited by Galpha(q/11)- and Galpha(12/13)-specific RGS domains, C3 toxin, and the carboxyl terminal region of G protein-coupled receptor kinase 2 but not by pertussis toxin. Activation of Rho was inhibited by carboxyl terminal regions of Galpha(12) and Galpha(13) but not by Galpha(q). Our findings suggest that alpha(1)AR-induced hypertrophic responses are mediated in part by a Galpha(12/13)-Rho-JNK pathway, in part by a G(q/11)-JNK pathway that is Rho independent, and in part by a Gbetagamma pathway that is JNK independent.

Clostridium perfringens iota toxin: characterization of the cell-associated iota b complex

Clostridium perfringens type E iota toxin consists of two unlinked proteins designated as iota a (Ia; molecular mass approximately 47 kDa), an ADP-ribosyltransferase and iota b (Ib; molecular mass approximately 81 kDa) which binds to the cell surface and facilitates Ia entry into the cytosol. By Western-blot analysis, Ib incubated with Vero cells at 37 degrees C generated a cell-associated, SDS-insoluble oligomer of Ib (molecular mass>220 kDa) within 15 s, which was still evident 110 min after washing cells. Ib oligomerization was temperature, but not pH, dependent and was facilitated by a cell-surface protein(s). Within 5 min at 37 degrees C, cell-bound Ib generated Na(+)/K(+) permeable channels that were blocked by Ia. However, Ib-induced channels or oligomers were not formed at 4 degrees C. Two monoclonal antibodies raised against Ib that recognize unique, neutralizing epitopes within residues 632-655 either inhibited Ib binding to cells and/or oligomerization, unlike a non-neutralizing monoclonal antibody that binds within Ib residues 28-66. The Ib protoxin (molecular mass approximately 98 kDa), which does not facilitate iota cytotoxicity but binds to Vero cells, did not oligomerize or form ion-permeable channels on cells, and neither trypsin nor chymotrypsin treatment of cell-bound Ib protoxin induced large complex formation. The link between Ib oligomers and iota toxicity was also apparent with a resistant cell line (MRC-5), which bound to Ib with no evidence of oligomerization. Overall, these studies revealed that the biological activity of iota toxin is dependent on a long-lived, cell-associated Ib complex that rapidly forms ion-permeable channels in cell membranes. These results further reveal the similarities of C. perfringens iota toxin with other bacterial binary toxins produced by Bacillus anthracis and C. botulinum.

Cerivastatin, a hydroxymethylglutaryl coenzyme A reductase inhibitor, inhibits cardiac myocyte hypertrophy induced by endothelin

We investigated the direct effects of cerivastatin on hypertrophy of cultured rat neonatal myocytes induced by endothelin and the mechanism by which cerivastatin exerts its effects. Endothelin significantly increased [14C]phenylalanine ([14C]Phe) incorporation, atrial natriuretic peptide (ANP) release, ANP mRNA expression and cell size. Cerivastatin significantly reduced the increase in [14C]phenylalanine incorporation, ANP peptide release, ANP mRNA expression and cell size induced by endothelin, but pravastatin did not. Exogenous mevalonate completely prevented the inhibitory effect of cerivastatin on [14C]phenylalanine incorporation, ANP release and cell size. Cotreatment with geranylgeranyl pyrophosphate also attenuated the effect of cerivastatin on [14C]phenylalanine incorporation, but cotreatment with farnesyl pyrophosphate or squalene did not. Furthermore, both Rho inhibitor C3 exoenzyme and Rho-dependent kinase inhibitor, (R)-(+)-trans-N-(4-pyridyl)-4-(1-aminoethyl)-cyclohexanecarboxamide.2HCl (Y27632) significantly decreased [14C]phenylalanine incorporation, ANP secretion, ANP mRNA expression and cell size. Cerivastatin decreased endothelin-induced Rho protein expression, and mevalonate and geranylgeranyl pyrophosphate reversed this effect. These results suggest that cerivastatin directly attenuates cardiac hypertrophy induced by endothelin in cultured rat myocytes partly by inhibition of the Rho pathway.

Involvement of Rho and p38 MAPK in endothelin-1-induced expression of PGHS-2 mRNA in osteoblast-like cells

Prostaglandins (PGs) play an important role in bone remodeling because eicosanoids are local mediators of bone metabolism, which can induce physiological and pathological responses of bone tissue. Biosynthesis of PGs is catalyzed by constitutively expressed PG endoperoxide G/H synthase (PGHS) 1 and by the inducible isoform PGHS-2. In MC3T3-E1 osteoblast-like cells, expression of PGHS-2 was shown by mechanical forces, cytokines, growth factors, and hormones. Recently, endothelin (ET) 1-stimulated PGHS-2 mRNA expression was described, leading to a burst in prostaglandin E2 (PGE2) production. In this study, we investigated ET-1-induced signal transduction pathway(s) involved in the PGHS-2 mRNA production. Time course of PGHS-2 mRNA expression reaching the maximum within 45 minutes is in good agreement with the concept of an immediate early gene product. Inhibition of phospholipase C (PLC), phospholipase D (PLD), phosphatidylinositol-3 kinase (PI-3-kinase), and protein kinase C (PKC) had no influence on PGHS-2 synthesis. Using specific blockers of tyrosine kinases indicated involvement of p38 MAPK but not p42/44 MAPK. By preloading cells with exoenzyme C3, we were able to show requirement of the Rho family of G proteins for p38 MAPK phosphorylation and PGHS-2 mRNA synthesis, whereas pertussis toxin (PTX) and cholera toxin (CTX) had no remarkable effect.

Tenascin-C modulates matrix contraction via focal adhesion kinase- and Rho-mediated signaling pathways

A provisional matrix consisting of fibrin and fibronectin (FN) is deposited at sites of tissue damage and repair. This matrix serves as a scaffold for fibroblast migration into the wound where these cells deposit new matrix to replace lost or damaged tissue and eventually contract the matrix to bring the margins of the wound together. Tenascin-C is expressed transiently during wound repair in tissue adjacent to areas of injury and contacts the provisional matrix in vivo. Using a synthetic model of the provisional matrix, we have found that tenascin-C regulates cell responses to a fibrin-FN matrix through modulation of focal adhesion kinase (FAK) and RhoA activation. Cells on fibrin-FN+tenascin-C redistribute their actin to the cell cortex, downregulate focal adhesion formation, and do not assemble a FN matrix. Cells surrounded by a fibrin-FN+tenascin-C matrix are unable to induce matrix contraction. The inhibitory effect of tenascin-C is circumvented by downstream activation of RhoA. FAK is also required for matrix contraction and the absence of FAK cannot be overcome by activation of RhoA. These observations show dual requirements for both FAK and RhoA activities during contraction of a fibrin-FN matrix. The effects of tenascin-C combined with its location around the wound bed suggest that this protein regulates fundamental processes of tissue repair by limiting the extent of matrix deposition and contraction to fibrin-FN-rich matrix in the primary wound area.

Requirement for RhoA kinase activation in leukocyte de-adhesion

Leukocyte migration from bloodstream to tissue requires rapid coordinated regulation of integrin-dependent adhesion and de-adhesion. Whether de-adhesion is an active process mediated by a distinct signaling pathway(s) or a passive decay of initial adhesion remains undetermined. We found that blockade of RhoA with C3 exoenzyme or inhibition of RhoA kinase by the specific inhibitor Y-27632 enhanced phorbol ester-stimulated alpha(4)beta(1)-dependent adhesion of Jurkat cells at 30 min. Similarly, Y-27632 treatment increased stimulated beta(2) integrin-dependent neutrophil adhesion at 30 min but not at 5 min. Because reduced de-adhesion could mimic augmentation of adhesion at later time points, we developed an assay to measure de-adhesion specifically. Treatment of phorbol ester-or bacterial chemoattractant peptide-but not Mn(2+)-stimulated neutrophils adherent to serum-coated plastic or endothelial cells with Y-27632 or C3 exoenzyme markedly reduced the rate of de-adhesion, while markedly increasing their spreading. RhoA kinase inhibitor effects on de-adhesion and spreading were reversed by treatment with the cytoskeletal-disrupting agent cytochalasin D. Treatment with Y-27632 influenced neither integrin activation epitope nor integrin clustering. We conclude that activation of RhoA kinase promotes leukocyte de-adhesion by inhibiting cytoskeletal-dependent spreading, and that these effects of RhoA kinase constitute a new mechanism for regulation of integrin receptor avidity.

Inhibitory effect of fluvastatin on lysophosphatidylcholine-induced nonselective cation current in Guinea pig ventricular myocytes

Using the whole-cell voltage-clamp method, we investigated the effect of fluvastatin, a 3-hydroxy-3-methylglutaryl-CoA reductase inhibitor, on lysophosphatidylcholine (LPC)-induced nonselective cation current (I(NSC)) in guinea pig cardiac ventricular myocytes. External LPC (3 to approximately 50 microM) induced I(NSC) in a dose-dependent manner with a lag. With fluvastatin (5 microM) in the external solution, LPC induced I(NSC), which was significantly smaller and with a longer lag compared with that in the absence of fluvastatin. With mevalonic acid (MVA) (100 microM) in the external solution, fluvastatin did not diminish LPC-induced I(NSC). Geranylgeranylpyrophosphate, an MVA metabolite, in the pipette solution prevented fluvastatin from diminishing LPC-induced I(NSC), suggesting that isoprenylated signaling molecules, such as the small G-protein Rho, might be involved in the LPC effect. Botulinum toxin C3, Rho-kinase inhibitor (R)-(+)-trans-N-(4-pyridyl)-4-(1-aminoethyl)-cyclohexanecarboxamide, 2 HCl (Y-27632), or pertussis toxin in the pipette solution suppressed LPC-induced I(NSC). We conclude that LPC induces I(NSC) via a Gi/Go-coupled receptor and Rho-mediated pathway. The inhibitory effect of fluvastatin on LPC-induced I(NSC) provides a new insight into the signal transduction mechanism and may have important clinical implications.

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.

Spatiotemporal regulation of moesin phosphorylation and rear release by Rho and serine/threonine phosphatase during neutrophil migration

Neutrophil motility is crucial to effective host defenses against microorganisms. While uropod retraction is a critical step in the migration of neutrophils, the underlying molecular mechanism is not well understood. Here, we show that inhibition of the Rho small GTPase with C3 exoenzyme prevented the retraction of trailing uropods, indicating that the process of rear release is mediated by a Rho signaling pathway. C3 exoenzyme caused marked elongation of directionally migrating neutrophils, suggesting an additional role for Rho in the maintenance of functional polarized cell shape. We also show that phosphorylation and dephosphorylation of the plasma membrane-actin filament cross-linker moesin are spatiotemporally controlled in migrating neutrophils. In particular, phosphorylation of moesin at threonine 558 depended on Rho activity. Videomicroscopy showed that dephosphorylation of this carboxy-terminal threonine preceded uropod retraction. Calyculin A, an inhibitor of type 1 and type 2A serine/threonine phosphatases, suppressed the moesin dephosphorylation and impaired uropod retraction in a dose-dependent manner. Cypermethrin, an inhibitor of type 2B serine/threonine phosphatase, had no such effects. The finding that Rho small GTPase and type 1/type 2A phosphatases are involved in rear release yields novel insights into the biochemical mechanisms of neutrophil migration.

Activation of small GTPase Rho is required for autocrine motility factor signaling

The hallmark of tumor metastasis is the dissemination of cells from the primary growth site to distant organs. Autocrine motility factor (AMF), a tumor-associated C-X-X-C cytokine, the ligand for a unique 78 kDa seven transmembrane receptor, is a potent simulator of cell motility, a process that is a prerequisite for tumor progression and metastasis. Because little is known about AMF-dependent signaling, we sought to study whether AMF signaling involves family members of the Rho-like GTPases. AMF stimulation of human melanoma cells resulted in stress-fiber formation, concomitant with up-regulation and activation of both RhoA and Rac1 expression with no apparent changes in the expression level or activation state of Cdc42. Treatment of the cells with C3 exoenzyme before AMF stimulation inhibited both the formation of stress-fiber-like structures and the activation of RhoA. In addition, both c-Jun NH(2)-terminal kinase 1 and c-Jun NH(2)-terminal kinase 2 were simultaneously activated by AMF, supporting the notion that they are involved in the signaling pathway of RhoA. We thus conclude that AMF signaling shares a similar pathway to previously established paracrine factors signaling involving cytoskeletal rearrangement and morphological alterations mediated by the small RhoA-like GTPases.

Improved anti-tumor activity and safety of interleukin-13 receptor targeted cytotoxin by systemic continuous administration in head and neck cancer xenograft model

BACKGROUND

IL-13 receptor (IL-13R) targeted cytotoxin, IL13-PE38QQR, has been shown to have very potent anti-tumor activity to IL-13R-expressing head and neck tumor cells in vitro and in vivo. However, its effect is limited in aggressive tumors. To further improve the anti-tumor activity and safety of IL-13 cytotoxin, we employed continuous infusion technique in animal model of head and neck cancer.

MATERIALS AND METHODS

We surgically implanted continuous infusion (CI) pump intraperitoneally that released drug for 7 days, and its anti-tumor effect was evaluated. A comparison was made for antitumor activity and safety with intravenously (IV) administered IL-13 cytotoxin in a head and neck (KCCT873 and HN12) subcutaneous (SC) xenograft tumor models in nude mice. Vital organ toxicities were assessed by histologic examinations and blood serum chemistry analyses.

RESULTS

The 50 or 75 micro g/kg/day for 7 days of IL-13 cytotoxin either by IV or CI administration did not show any difference in safety or anti-tumor activity. IV administration of 150 or 200 micro g/kg/day of IL-13 cytotoxin for 7 days was lethal to nude mice, whereas 200 micro g/kg/day X 7 days of CI administration was highly effective in the regression of established tumors without any toxicities. Additionally, CI administration of IL-13 cytotoxin (200 micro g/kg/day) showed growth inhibition of larger HN12 tumors in nude mice.

CONCLUSION

With a CI schedule, IL-13 cytotoxin can be systemically administrated at approximately twice the dose otherwise given by daily IV bolus administration.

Mitogen activated protein kinase pathway is involved in RhoC GTPase induced motility, invasion and angiogenesis in inflammatory breast cancer

Inflammatory breast cancer (IBC) is the most lethal form of locally advanced breast cancer known. IBC carries a guarded prognosis primarily due to rapid onset of disease, typically within six months, and the propensity of tumor emboli to invade the dermal lymphatics and spread systemically. Although the clinical manifestations of IBC have been well documented, until recently little was known about the genetic mechanisms underlying the disease. In a comprehensive study aimed at identifying the molecular mechanisms responsible for the unique IBC phenotype, our laboratory identified overexpression of RhoC GTPase in over 90% of IBC tumors in contrast to 36% of stage-matched non-IBC tumors. We also demonstrated that overexpression of RhoC GTPase in human mammary epithelial (HME) cells nearly recapitulated the IBC phenotype with regards to invasion, motility and angiogenesis. In the current study we sought to delineate which signaling pathways were responsible for each aspect of the IBC phenotype. Using well-established inhibitors to the mitogen activated protein kinase (MAPK) and phosphatidylinositol-3 kinase (PI3K) pathways. We found that activation of the MAPK pathway was responsible for motility, invasion and production of angiogenic factors. In contrast, growth under anchorage independent conditions was dependent on the PI3K pathway.

Novel anti-CD30 recombinant immunotoxins containing disulfide-stabilized Fv fragments

PURPOSE

To develop a novel targeting reagent to CD30 expressed on Hodgkin'sdisease and anaplastic large cell lymphoma, we made a panel of recombinant immunotoxins specific for CD30 using Fvs of newly produced anti-CD30 monoclonal antibodies (MAbs) and a M(r) 38,000 truncated mutant of Pseudomonas exotoxin.

EXPERIMENTAL DESIGN

A group of MAbs against CD30 was produced and characterized for their reactivity and epitopes. Recombinant immunotoxins were made using the Fv genes cloned from the hybridomas. Their cytotoxic activities were examined on various CD30-positive cell lines.

RESULTS

Six MAbs were produced. All reacted with recombinant soluble CD30 and to a CD30-Fc fusion protein, and bound to native CD30 expressed on Hodgkin's lymphoma-derived cell lines. The epitopes of the six MAbs were classified into two groups by a mutual competition assay for the binding to CD30 on cells. Sequencing the cDNAs revealed that all of the variable chains are unique except one valiable light that is shared by two MAbs. We made four disulfide stabilized Fv-based recombinant immunotoxins, in which the valiable heavy, which is genetically fused with truncated mutant of Pseudomonas exotoxin, forms a disulfide bond with the valiable light. The purified immunotoxins bound to recombinant soluble CD30 immobilized on a biosensor chip with K(d)s of 4-400 nM. Fluorescence-activated cell sorter analysis confirmed their specific binding. In vitro cytotoxicity tests showed that the immunotoxins specifically kill a variety of CD30-positive lymphoma cell lines as well as CD30-transfected A431 cells. The IC(50) ranged from 0.3 to 100 ng/ml.

CONCLUSIONS

Four anti-CD30 disulfide stabilized Fv immunotoxins were successfully produced. Two of these showed good cytotoxic activity to various CD30-positive cell lines. These newly produced immunotoxins should be additionally evaluated for the treatment of CD30-positive lymphomas.

Inhibition of Rho-kinase induces alphaB-crystallin expression in lens epithelial cells

The small heat shock protein, alphaB-crystallin, has been shown to interact with actin and intermediate filament proteins. However, little is known regarding the cellular mechanisms regulating such interactions. In this study, we explored the role of the Rho/Rho-kinase pathway in alphaB-crystallin distribution and expression in porcine lens epithelial cells. alphaB-crystallin was distributed uniformly throughout the cytoplasm and did not exhibit any unique redistribution in response to actin depolymerization induced by Rho/Rho-kinase inhibitors (C3-exoenzyme or Y-27632) or by overexpression of the dominant negative mutant of Rho-kinase (DNRK) in porcine lens epithelial cells. Interestingly, alphaB-crystallin levels markedly increased in lens epithelial cells treated with the inhibitors of Rho/Rho-kinase proteins (lovastatin, Y-27632 or DNRK) while a protein kinase C inhibitor (GF109203x) was found to have no effect. Further, Y-27632 showed a dose (2-50 microM) response effect on alphaB-crystallin induction. Nocodazole, a microtubule-depolymerizing agent, elicited an increase in alphaB-crystallin levels but latrunculin, an actin depolymerizing agent, did not show any significant effect. Pretreatment with cycloheximide or genistein blocked the Rho-kinase inhibitor-induced increase in alphaB-crystallin protein levels. Rho-kinase inhibitor-induced increases in alphaB-crystallin levels were found to be associated with activation of P38 mitogen-activated protein kinase (MAPK). These results suggest that Rho/Rho-kinase negatively regulates alphaB-crystallin expression, and this response appears to be dependent on tyrosine-protein kinase and P38 MAPK function. Finally, alphaB-crystallin induction appears to be better correlated with the direct inhibition of Rho/Rho-kinase than with actin depolymerization per se.

Rho-dependent and -independent activation mechanisms of ezrin/radixin/moesin proteins: an essential role for polyphosphoinositides in vivo

Ezrin/radixin/moesin (ERM) proteins crosslink actin filaments to plasma membranes and are involved in the organization of the cortical cytoskeleton, especially in the formation of microvilli. ERM proteins are reported to be activated as crosslinkers in a Rho-dependent manner and are stabilized when phosphorylated at their C-terminal threonine residue to create C-terminal threonine-phosphorylated ERM proteins (CPERMs). Using a CPERM-specific mAb, we have shown, in vivo, that treatment with C3 transferase (a Rho inactivator) or staurosporine (a protein kinase inhibitor) leads to the dephosphorylation of CPERMs, the translocation of ERM proteins from plasma membranes to the cytoplasm and microvillar breakdown. We further elucidated that ERM protein activation does not require C-terminal phosphorylation in A431 cells stimulated with epidermal growth factor. In certain types of kidney-derived cells such as MDCK cells, however, ERM proteins appear to be activated in the absence of Rho activation and remain active without C-terminal phosphorylation. Interestingly, microinjection of an aminoglycoside antibiotic, neomycin, which binds to polyphosphoinositides, such as phosphatidylinositol (4,5)-bisphosphate [PtdIns(4,5)P(2)], affected the activation of ERM proteins regardless of cell type. These findings not only indicate the existence of a Rho-independent activation mechanism of ERM proteins but also suggest that both Rho-dependent and -independent activation of ERM proteins require a local elevation of PtdIns(4,5)P(2) concentration in vivo.

Inhibition of Rho/Rho-kinase signaling downregulates plasminogen activator inhibitor-1 synthesis in cultured human monocytes

Increased production of plasminogen activator inhibitor-1 (PAI-1) in plaques plays a role in the pathogenesis of atherosclerosis. This study was conducted to investigate the effect of blockade of Rho/Rho-kinase signaling on the synthesis of PAI-1 in cultured human peripheral blood monocytes. HMG-CoA reductase inhibitors (statins) and inhibitors of Rho and Rho-kinase were added to monocyte cultures. The levels of PAI antigen and mRNA were determined by Western blotting and RT-PCR, respectively, and PAI-1 expression was assessed by immunohistochemistry. We performed pull-down assays to determine the activity of Rho by measuring the GTP-bound form of Rho A. In unstimulated and lipopolysaccharide (LPS)-stimulated cultured monocytes, statins reduced the levels of PAI-1 antigen and mRNA. The suppressive effects of statins on PAI-1 synthesis were reversed by geranylgeranylpyrophosphate (GGPP) and were mimicked by C3 exoenzyme. Immunohistochemistry confirmed the role of lipid modification by GGPP in suppressive effect of statins in PAI-1 synthesis. Pull-down assays demonstrated that statins decreased the levels of the GTP-bound form of Rho A. Our findings suggest that statins decrease the activity of Rho by inhibiting geranylgeranylation. Moreover, Rho-kinase inhibitors, Y-27632 and fasudil, suppressed the synthesis of PAI-1 in this culture system. We show that inhibition of Rho/Rho-kinase signaling downregulates the synthesis of PAI-1 in human monocytes.

ADP ribosylation of human neutrophil peptide-1 regulates its biological properties

In human airways, epithelial cells lining the lumen and intraluminal cells (e.g., polymorphonuclear cells) participate in the innate immune response. These cells secrete or express on their surfaces arginine-specific ADP ribosyltransferases. Defensins, antimicrobial proteins secreted by immune cells, are arginine-rich, leading us to hypothesize that ADP ribosylation could modify their biological activities. We found that an arginine-specific ADP ribosyltransferase-1 present on airway epithelial cells modifies Arg-14 of alpha defensin-1. ADP-ribosylated defensin-1 had decreased antimicrobial and cytotoxic activities but still stimulated T cell chemotaxis and IL-8 release from A549 cells. Further, ADP-ribosylated defensin-1 inhibited cytotoxic and antimicrobial activities of unmodified defensin-1. We identified ADP-ribosylated defensin-1 in bronchoalveolar lavage fluid from smokers but not from nonsmokers, confirming its existence in vivo. Thus, airway mono-ADP-ribosyltransferases could have an important regulatory role in the innate immune response through modification of alpha defensin-1 and perhaps other basic molecules, with alteration of their biological properties.

Microtubule dynamics differentially regulates Rho and Rac activity and triggers Rho-independent stress fiber formation in macrophage polykaryons

Multinucleated giant cells (MNGC) derived from avian peripheral blood monocytes present a dense microtubular network emanating from peripherally located centrosomes. We were interested to study how microtubule and F-actin cytoskeletons cooperate in MNGC to maintain cell shape. Microtubule depolymerization by nocodazole triggered the reorganization of the F-actin cytoskeleton in MNGC that is normally organized into podosomes, cortical actin filaments and membrane ruffles. After nocodazole treatment, F-actin was redistributed into unusual transverse fibers associated with focal adhesion plaques. When microtubules were allowed to repolymerize after nocodazole removal, F-actin appeared transiently, together with the small GTPase Rac, in large membrane ruffles. Using affinity precipitation assays, we show that microtubule depolymerization leads to activation of Rho and inhibition of Rac, whereas microtubule repolymerization induces Rac activation and Rho inhibition. Thus, the level of microtubule polymerization inversely regulates Rho and Rac activity in MNGC. Moreover, using C3 exoenzyme, a known inhibitor of Rho, we demonstrate that both the F-actin fiber formation in response to microtubule depolymerization and the formation of membrane ruffles after microtubule repolymerization occur in C3-treated MNGC, indicating that Rho is not required for these events.

ROCK and mDia1 antagonize in Rho-dependent Rac activation in Swiss 3T3 fibroblasts

The small GTPase Rho acts on two effectors, ROCK and mDia1, and induces stress fibers and focal adhesions. However, how ROCK and mDia1 individually regulate signals and dynamics of these structures remains unknown. We stimulated serum-starved Swiss 3T3 fibroblasts with LPA and compared the effects of C3 exoenzyme, a Rho inhibitor, with those of Y-27632, a ROCK inhibitor. Y-27632 treatment suppressed LPA-induced formation of stress fibers and focal adhesions as did C3 exoenzyme but induced membrane ruffles and focal complexes, which were absent in the C3 exoenzyme-treated cells. This phenotype was suppressed by expression of N17Rac. Consistently, the amount of GTP-Rac increased significantly by Y-27632 in LPA-stimulated cells. Biochemically, Y-27632 suppressed tyrosine phosphorylation of paxillin and focal adhesion kinase and not that of Cas. Inhibition of Cas phosphorylation with PP1 or expression of a dominant negative Cas mutant inhibited Y-27632-induced membrane ruffle formation. Moreover, Crk-II mutants lacking in binding to either phosphorylated Cas or DOCK180 suppressed the Y-27632-induced membrane ruffle formation. Finally, expression of a dominant negative mDia1 mutant also inhibited the membrane ruffle formation by Y-27632. Thus, these results have revealed the Rho-dependent Rac activation signaling that is mediated by mDia1 through Cas phosphorylation and antagonized by the action of ROCK.

A recombinant CD7-specific single-chain immunotoxin is a potent inducer of apoptosis in acute leukemic T cells

A recombinant immunotoxin was constructed from the hybridoma antibody TH-69 directed against human CD7, a surface antigen of leukemic T cells. The antibody was subcloned as a single chain Fv (scFv) fragment and genetically linked to a truncated Pseudomonas exotoxin A fragment containing the catalytic domains II and III but lacking the receptor binding domain I. Domain I was replaced by the scFv, thus conferring restricted specificity for CD7-positive cells. The bacterially expressed and purified toxin retained binding specificity for CD7-positive cells. It promoted apoptosis in two CD7-positive cell lines derived from T-lineage acute lymphoblastic leukemias, CEM and Jurkat, but not in the CD7-negative B-lymphoid lines REH, Nalm-6, and SEM. Maximum killing in excess of 95% was reached after 96 h in CEM and Jurkat cells with a single dose of 100 ng/ml. Cells treated with a similarly constructed scFv-exotoxin A immunotoxin against melanoma-associated chondroitin sulfate proteoglycan, an antigen absent from leukemic T cells, remained unaffected. Lysis of target cells occurred via apoptosis as evidenced by staining with Annexin V and specific cleavage of poly(ADP-ribose) polymerase. Approximately 20% of leukemic cells from a patient with CD7-positive acute T-cell leukemia kept in long-term primary culture for 30 cell generations were killed within 96 h after treatment with the toxin. These findings justify further evaluation of the agent in view of potential therapeutic applications.

Rho activity can alter the translation of p27 mRNA and is important for RasV12-induced transformation in a manner dependent on p27 status

The amount of p27(Kip1) establishes a threshold to which G(1) cyclin-cyclin-dependent kinase complexes must surpass prior to cells progressing into S-phase. The amount of p27 is greatest in G(0) cells, intermediate in G(1) cells, and lowest in S-phase cells. However, there is little known regarding the pathways and mechanisms controlling p27 accumulation in G(0) cells. We report that inhibition of Rho, by either lovastatin or C3 exoenzyme, can increase the translational efficiency of p27 mRNA. Similar pharmacologic inhibition of the phosphatidylinositol 3-kinase, the S6 kinase, and the Mek1 kinase pathways all fail to increase translational efficiency in MDA468 cells. This Rho-responsive element lies within a 300-nucleotide region at the 3'-end of the mRNA. By supporting the significance of this signaling pathway to Rho function, we showed that the suppression of Ras(V12) transformation by RhoA(N19) is blocked in p27-/- cells. In contrast this activity is not blocked in Rb-/- or p16-/- cells. The resistance of p27-/- cells to RhoA(N19) is not associated with a failure of RhoA(N19) to accumulate to amounts sufficient to block Rho activity as measured by the organization of actin stress fibers. Together these results indicate a link between Rho and p27.

NGF enhances sensory axon growth induced by laminin but not by the L1 cell adhesion molecule

Neurotrophins and cell adhesion molecules regulate axon guidance, but their potential coordinate interactions are not well defined. In particular, it has been difficult to define the role of signaling from different surface molecules in neurotrophin-induced axon growth because of the strong dependence of embryonic neurons on this class of molecules for survival. We have addressed this issue using Bax deficient neurons, which do not require neurotrophins for survival. The L1 neural cell adhesion molecule and laminin each supported NGF-independent axon growth of cultured sensory neurons from dorsal root ganglia of embryonic Bax(-/-) mice. However, nerve growth factor (NGF) stimulated additional axon growth of sensory neurons on laminin but not on L1 substrates. Inhibition of the small GTPase RhoA by the dominant-negative mutant RhoA(T19N) restored NGF responsiveness of axon growth on L1 to Bax(-/-) neurons. Constitutively activated RhoA(Q63L) did not affect axon growth on L1 but inhibited NGF-stimulated axon growth on laminin. Consistent with the concept that RhoA was downregulated by NGF in neurons on laminin but not L1, the RhoA inhibitor C2IN-C3 toxin stimulated axon growth on L1 in wild-type DRG neurons in NGF. These results demonstrate a novel substrate-dependent regulation of NGF-induced growth of embryonic sensory axons mediated by RhoA GTPase.

Endothelial Rho signaling is required for monocyte transendothelial migration

Bacterial toxins affecting Rho activity in microvascular endothelial cells were employed to elucidate whether endothelial Rho participates in regulating the migration of monocytes across monolayers of cultured endothelial cells. Inactivation of Rho by the Clostridium C3 exoenzyme resulted in an increased adhesion of peripheral blood monocytes to the endothelium and a decreased rate of transendothelial monocyte migration. Cytotoxic necrotizing factor 1-mediated activation of endothelial Rho also reduced the rate of monocyte transmigration, but did not affect monocyte-endothelium adhesion. Thus, efficient leukocyte extravasation requires Rho signaling not only within the migrating leukocytes but also within the endothelial lining of the vessel wall.

Binding component of Clostridium perfringens iota-toxin induces endocytosis in Vero cells

Clostridium perfringens iota-toxin is a binary toxin consisting of two individual proteins, the binding component (Ib) and the enzyme component (Ia). Wild-type Ib bound to Vero cells at 4 and 37 degrees C and formed oligomers at 37 degrees C but not at 4 degrees C. The Ib-induced K(+) release from the cells was dependent on the oligomer formation of Ib in the cells, but the oligomer formation did not induce rounding activity or cytotoxicity. After incubation of the cells with recombinant Ib (rIb) at 37 degrees C, the Ib oligomer in the cell became resistant to pronase treatment with time, but the Ib monomer was sensitive to the treatment. Furthermore, treatment of Vero cells with rIb in the presence of bafilomycin, methylamine, or ethylamine resulted in accumulation of the oligomer in the cells but had no effect on K(+) release. Moreover, incubation with Ib plus Ia in the presence of these agents caused no rounding in the cells. These observations suggest that Ib binds to Vero cells, itself oligomerizing to form ion-permeable channels and that the formation of oligomer then induces endocytosis.

RhoA- and RhoD-dependent regulatory switch of Galpha subunit signaling by PAR-1 receptors in cellular invasion

Thrombin and proteinase-activated receptors (PAR) specifically regulate several functions that markedly enhance the transformation phenotype such as inflammation, cell proliferation, tumor growth, and metastasis. We recently reported that thrombin inhibits cellular invasion induced by src, hepatocyte growth factor (HGF), and leptin in kidney and colonic epithelial cells via predominant activation of the pertussis toxin (PTx) -sensitive G-proteins Galphao/Galphai. We provide pharmacological and biochemical evidence that in the presence of PTx, PAR-1 induced cellular invasion through Galpha12/Galpha13- and RhoA/Rho kinase (ROCK) -dependent signaling. However, inhibition of the endogenous small GTPase RhoA by the C3 exoenzyme, dominant-negative N19-RhoA, activated G26V-RhoD, and activators of the nitric oxide/cGMP pathways conferred invasive activity to PAR-1 via a signaling cascade using Galphaq, phospholipase C (PLC), Ca(2+)/calmodulin myosin light chain kinase (CaM-MLCK), and phosphorylation of MLC. We found that cellular invasion induced by the src oncogene is abrogated by inhibitors of the RhoA/ROCK pathway and is independent of PLC/CaM-MLCK signaling. Our data demonstrate that the RhoA and RhoD small GTPases are acting as a molecular switch of cellular invasion and reveal a novel critical mechanism by which PAR-1 bypass Galphao/i and RhoA inhibition via differential coupling to heterotrimeric G-proteins linked to divergent or convergent biological responses. Our data also indicate that Rho GTPases and ROCK mediate a src-dependent invasion signal in kidney and colonic cancer cells. We conclude that dynamic regulation of Rho GTPases activation and inactivation by oncogenes, growth factors, cGMP-inducing agents, and adhesion molecules can initiate convergent invasion signals controlled by the thrombin PAR-1 in cancer cells.-Nguyen, Q.-D., Faivre, S., Bruyneel, E., Rivat, C., Seto, M., Endo, T., Mareel, M., Emami, S., Gespach, C. RhoA- and RhoD-dependent regulatory switch of Galpha subunit signaling by PAR-1 receptors in cellular invasion.