Safety, Adherence and Persistence in a Real-World Cohort of German MS Patients Newly Treated With Ocrelizumab: First Insights From the CONFIDENCE Study.

Background: Real-world relapsing multiple sclerosis (RMS) and primary progressive MS (PPMS) populations may be more diverse than in clinical trials. Here, we present a first analysis of safety, adherence and persistence data from a real-world cohort of patients newly treated with ocrelizumab. Methods: CONFIDENCE (ML39632, EUPAS22951) is an ongoing multicenter, non-interventional post authorization safety study assessing patients with RMS or PPMS newly treated with ocrelizumab or other disease-modifying therapies for up to 10 years. For this analysis, patients newly treated with ocrelizumab were analyzed in subgroups by MS phenotype and age over a mean ~1 year of exposure totaling 2,329 patient years [PY]). Results: At data cutoff (14 October 2020), 1,702 patients with RMS and 398 patients with PPMS were treated with ≥1 dose of ocrelizumab. At baseline, the mean ages (SD) of patients with RMS and PPMS were 41.59 (11.24) and 50.95 (9.88) years and the mean EDSS (Expanded Disability Status Scale) was 3.18 (1.87) and 4.41 (1.59), respectively. The most common adverse events (AEs) and serious AEs across both phenotypes were infections and infestations, with infection SAE rates of 2.8 events/100 PY and 1.5 events/100 PY in patients with RMS and PPMS, respectively. Across all phenotypes, ocrelizumab persistence was 92% at 24 months; median time between doses was ~6 months. Conclusions: The ocrelizumab safety profile observed in the CONFIDENCE real-world MS population was consistent to the one observed in pivotal clinical trials. High treatment persistence and adherence were observed. Trial Registration: ML39632, EUPAS22951.

Ocrelizumab Treatment in Patients with Primary Progressive Multiple Sclerosis: Short-term Safety Results from a Compassionate Use Programme in Germany.

OBJECTIVES: In January 2018, the European Union (EU) approved ocrelizumab in relapsing multiple sclerosis (RMS) and as the first disease-modifying therapy (DMT) for patients with primary progressive multiple sclerosis (PPMS) with efficacy proven in a phase 3 randomised controlled trial. Eleven months prior to the European regulatory approval, a compassionate use programme (CUP) made ocrelizumab available to 489 patients with PPMS in Germany, thereby for the first time providing a therapeutic option to patients with PPMS who could not participate in ocrelizumab studies. Here, we report real-world patient characteristics and short-term safety data of patients with PPMS treated with ocrelizumab in this CUP. PATIENTS AND METHODS: This CUP was initiated in February 2017 - shortly before US Food and Drug administration approval in March 2017 - and ended in January 2018, following ocrelizumab approval in the EU. Adult patients (age ≥18 years) with PPMS who had a positive benefit/risk ratio according to the treating physician were eligible for inclusion at German treatment centres. The main exclusion criteria were current/recent treatment with other immune therapies and unresolved/chronic/active infections. Patients received methylprednisolone and an antihistamine before treatment with intravenous ocrelizumab in 6-month cycles. The first ocrelizumab dose was a 300 mg infusion followed by a second 300 mg infusion 2 weeks later; subsequent doses were delivered as a single 600 mg infusion. Adverse events were reported immediately. RESULTS: Of 580 requests received from 104 centres, 525 patients met the eligibility criteria. Thirty-five patients did not participate due to withdrawal by the treating physician, and one due to death prior to treatment. A total of 489 patients received at least one 600 mg dose of ocrelizumab (administered as two 300 mg infusions) and 51 received a second dose. Due to termination of the CUP upon marketing authorisation, the maximum follow-up period was 12 months. Median patient age was 52 years (range: 24-73), and 49% were female. Previous immunomodulatory or immunosuppressive therapies had been received by 41% of patients, with the most commonly used being glucocorticoids, mitoxantrone, interferon-ß and glatiramer acetate. Patients with a previous malignancy, serious disease or infection (42 patients, 9%) had recovered from this prior to the CUP. Nine serious adverse events and 70 non-serious adverse events were reported in 40 patients. Adverse event categories were generally consistent with the known safety profile of ocrelizumab; one patient had carry-over progressive multifocal leukoencephalopathy (PML) due to previous natalizumab treatment. CONCLUSION: This CUP provides first real-world observations of ocrelizumab for the treatment of PPMS in a large patient cohort in Germany, supporting that ocrelizumab is generally well-tolerated in clinical practice. Physicians should be vigilant for early symptoms of PML, as to date, 9 PML cases that were all confounded have been reported in patients treated with ocrelizumab worldwide, with 8 carry-over cases from a prior DMT.

Design of a non-interventional post-marketing study to assess the long-term safety and effectiveness of ocrelizumab in German real world multiple sclerosis cohorts - the CONFIDENCE study protocol.

BACKGROUND: Multiple sclerosis (MS) is a chronic disease that requires lifelong treatment. A highly effective drug not only for relapsing but also for progressive forms of MS with a favorable safety profile is needed to further improve overall patient outcomes. Ocrelizumab, a recombinant humanized monoclonal antibody that selectively targets CD20-expressing B-cells, is the first drug indicated for the treatment of adult patients with relapsing forms of MS (RMS) and primary progressive MS (PPMS). Its safety and effectiveness profile has yet to be studied in a large, real-world setting. CONFIDENCE aims to further characterize the safety profile of ocrelizumab in routine clinical practice. In addition, real-world effectiveness data will be collected to complement the efficacy data documented in the pivotal clinical trials. METHODS: CONFIDENCE is a non-interventional, prospective, multicenter, long-term study collecting primary data from 3000 RMS and PPMS patients newly treated with ocrelizumab and 1500 patients newly treated with other selected MS disease-modifying therapies (DMTs). Treatment must be in accordance with the local label and follow routine practice. Data will be collected at approximately 250 neurological centers and practices across Germany. The recruitment period of 30 months started in April 2018. The observation period per patient is planned 7.5 to 10 years, depending on the date of inclusion, regardless of whether patients discontinue treatment. Visits follow routine practice and will be documented approximately every 6 months. The primary endpoint is the incidence and type of uncommon adverse events and death. Statistical analyses will be mainly descriptive and exploratory. DISCUSSION: CONFIDENCE is a large, non-interventional, post-authorization safety study that assesses long-term safety and effectiveness of ocrelizumab and other DMTs in a real-world setting. Data collected in CONFIDENCE will also be integrated into studies that have been developed to fulfil international regulatory requirements.

Reelin induces EphB activation.

The integration of newborn neurons into functional neuronal networks requires migration of cells to their final position in the developing brain, the growth and arborization of neuronal processes and the formation of synaptic contacts with other neurons. A central player among the signals that coordinate this complex sequence of differentiation events is the secreted glycoprotein Reelin, which also modulates synaptic plasticity, learning and memory formation in the adult brain. Binding of Reelin to ApoER2 and VLDL receptor, two members of the LDL receptor family, initiates a signaling cascade involving tyrosine phosphorylation of the intracellular cytoplasmic adaptor protein Disabled-1, which targets the neuronal cytoskeleton and ultimately controls the positioning of neurons throughout the developing brain. However, it is possible that Reelin signals interact with other receptor-mediated signaling cascades to regulate different aspects of brain development and plasticity. EphB tyrosine kinases regulate cell adhesion and repulsion-dependent processes via bidirectional signaling through ephrin B transmembrane proteins. Here, we demonstrate that Reelin binds to the extracellular domains of EphB transmembrane proteins, inducing receptor clustering and activation of EphB forward signaling in neurons, independently of the 'classical' Reelin receptors, ApoER2 and VLDLR. Accordingly, mice lacking EphB1 and EphB2 display a positioning defect of CA3 hippocampal pyramidal neurons, similar to that in Reelin-deficient mice, and this cell migration defect depends on the kinase activity of EphB proteins. Together, our data provide biochemical and functional evidence for signal integration between Reelin and EphB forward signaling.

Role of GluN2A and GluN2B subunits in the formation of filopodia and secondary dendrites in cultured hippocampal neurons.

GluN receptors are heteromers of obligatory GluN1 subunits and GluN2(A-D) subunits. In the present study, we addressed the question whether GluN2A and GluN2B subunits play distinct roles in the formation of filopodia and dendrites during the early development of hippocampal neurons. In hippocampal neurons brought into culture at embryonic day 17, we studied 2-3 days later the effects of N-methyl-D-aspartic acid (NMDA) on the numbers of filopodia, growth cones, and primary as well as secondary dendrites. Antagonists specific for GluN2A and GluN2B subunits were applied together with NMDA. NMDA only induced the formation of filopodia and secondary dendrites. Whereas filopodia were generated within 15 min by NMDA alone, secondary dendrites were only induced by the joint application of NMDA and the Rho kinase inhibitor Y-27632 for 24 h. The GluN2B antagonists ifenprodil and Ro 25-6981 prevented the NMDA-induced formation of filopodia, whereas the GluN2A antagonists NVP-AAM007 and EAA-090 prevented the formation of secondary dendrites. We conclude that both GluN2 subunits have differential roles in dendritic arborization.

Reelin modulates cytoskeletal organization by regulating Rho GTPases.

The correct positioning of postmitotic neurons in the developing neocortex and other laminated brain structures requires the activation of a Reelin-lipoprotein receptor-Dab1 signaling cascade. The large glycoprotein Reelin is secreted by Cajal-Retzius pioneer neurons and bound by the apolipoprotein E receptor family members Apoer2 and Vldl receptor on responsive neurons and radial glia. This leads to the tyrosine phosphorylation of the cytoplasmic protein Disabled-1 (Dab1) by non-receptor tyrosine kinases of the Src family. Various signaling pathways downstream of Dab1 connect Reelin to the actin and microtubule cytoskeleton. Despite this knowledge, a comprehensive view linking the different cell-biological and biochemical actions of Reelin to its diverse physiological roles not only during neurodevelopment but also in the maintenance and functioning of the adult brain is still lacking. In this review, we discuss our finding that Reelin activates Rho GTPases in neurons in the light of other recent studies, which demonstrate a role of Reelin in Golgi organization, and suggest additional roles of Cdc42 activation by Reelin in radial glial cells of the developing cortex.

Reelin signals through apolipoprotein E receptor 2 and Cdc42 to increase growth cone motility and filopodia formation.

Lipoprotein receptor signaling regulates the positioning and differentiation of postmitotic neurons during development and modulates neuronal plasticity in the mature brain. Depending on the contextual situation, the lipoprotein receptor ligand Reelin can have opposing effects on cortical neurons. We show that Reelin increases growth cone motility and filopodia formation, and identify the underlying signaling cascade. Reelin activates the Rho GTPase Cdc42, known for its role in neuronal morphogenesis and directed migration, in an apolipoprotein E receptor 2-, Disabled-1-, and phosphatidylinositol 3-kinase-dependent manner. We demonstrate that neuronal vesicle trafficking, a Cdc42-controlled process, is increased after Reelin treatment and further provide evidence that the peptidergic VIP/PACAP38 system and Reelin can functionally interact to promote axonal branching. In conclusion, Reelin-induced activation of Cdc42 contributes to the regulation of the cytoskeleton of individual responsive neurons and converges with other signaling cascades to orchestrate Rho GTPase activity and promote neuronal development. Our data link the observation that defects in Rho GTPases and Reelin signaling are responsible for developmental defects leading to neurological and psychiatric disorders.

Sympathetic alpha(2)-adrenoceptors prevent cardiac hypertrophy and fibrosis in mice at baseline but not after chronic pressure overload.

AIMS: alpha(2)-Adrenoceptors modulate cardiovascular function by vasoconstriction or dilatation, by central inhibition of sympathetic activity, or by feedback inhibition of norepinephrine release from sympathetic neurons. Despite detailed knowledge about subtype-specific functions of alpha(2)-receptors, the relative contributions of sympathetic vs. non-sympathetic receptors involved in these cardiovascular effects have not been identified. The aim of this study was to define the physiological and pharmacological role of alpha(2A)-adrenoceptors in adrenergic vs. non-adrenergic cells at baseline and during sympathetic stress. METHODS AND RESULTS: Transgenic mice expressing alpha(2A)-adrenoceptors under control of the dopamine beta-hydroxylase (Dbh) promoter were generated and crossed with mice carrying a constitutive deletion in the alpha(2A)- and alpha(2C)-adrenoceptor genes. alpha(2AC)-deficient mice showed increased norepinephrine plasma levels, cardiac hypertrophy, and fibrosis at baseline. Expression of the Dbh-alpha(2A) transgene in sympathetic neurons prevented these effects. In contrast, Dbh-alpha(2A) receptors mediated only a minor part of the bradycardic and hypotensive effects of the alpha(2)-agonist medetomidine. After chronic pressure overload as induced by transverse aortic constriction in mice, the Dbh-alpha(2A) transgene did not reduce norepinephrine spillover, cardiac dysfunction, hypertrophy, or fibrosis. In isolated wild-type atria, alpha(2)-agonist-induced inhibition of [3H]norepinephrine release was significantly desensitized after pressure overload. In primary sympathetic neurons from Dbh-alpha(2A) transgenic mice, norepinephrine and medetomidine induced endocytosis of alpha(2A)-adrenoceptors into neurite processes. CONCLUSION: alpha(2A)-Adrenoceptors expressed in adrenergic cells are essential feedback inhibitors of sympathetic norepinephrine release to prevent cardiac hypertrophy and fibrosis at baseline. However, these receptors are desensitized by chronic pressure overload which in turn may contribute to the pathogenesis of this condition.

Genetic dissection of alpha2-adrenoceptor functions in adrenergic versus nonadrenergic cells.

Alpha(2)-adrenoceptors mediate diverse functions of the sympathetic system and are targets for the treatment of cardiovascular disease, depression, pain, glaucoma, and sympathetic activation during opioid withdrawal. To determine whether alpha(2)-adrenoceptors on adrenergic neurons or alpha(2)-adrenoceptors on nonadrenergic neurons mediate the physiological and pharmacological responses of alpha(2)-agonists, we used the dopamine beta-hydroxylase (Dbh) promoter to drive expression of alpha(2A)-adrenoceptors exclusively in noradrenergic and adrenergic cells of transgenic mice. Dbh-alpha(2A) transgenic mice were crossed with double knockout mice lacking both alpha(2A)- and alpha(2C)-receptors to generate lines with selective expression of alpha(2A)-autoreceptors in adrenergic cells. These mice were subjected to a comprehensive phenotype analysis and compared with wild-type mice, which express alpha(2A)- and alpha(2C)-receptors in both adrenergic and nonadrenergic cells, and alpha(2A)/alpha(2C) double-knockout mice, which do not express these receptors in any cell type. We were surprised to find that only a few functions previously ascribed to alpha(2)-adrenoceptors were mediated by receptors on adrenergic neurons, including feedback inhibition of norepinephrine release from sympathetic nerves and spontaneous locomotor activity. Other agonist effects, including analgesia, hypothermia, sedation, and anesthetic-sparing, were mediated by alpha(2)-receptors in nonadrenergic cells. In dopamine beta-hydroxylase knockout mice lacking norepinephrine, the alpha(2)-agonist medetomidine still induced a loss of the righting reflex, confirming that the sedative effect of alpha(2)-adrenoceptor stimulation is not mediated via autoreceptor-mediated inhibition of norepinephrine release. The present study paves the way for a revision of the current view of the alpha(2)-adrenergic receptors, and it provides important new considerations for future drug development.

Rho kinase inhibitors Y27632 and H1152 augment neurite extension in the presence of cultured Schwann cells.

BACKGROUND: RhoA and Rho kinase inhibitors overcome the inhibition of axonal regeneration posed by central nervous system (CNS) substrates. METHODS: To investigate if inhibition of the Rho pathway augments the neurite extension that naturally occurs in the peripheral nervous system (PNS) following nerve damage, dorsal root ganglion neurons and Schwann cell co-cultures were incubated with culture medium, C3 fusion toxin, and the Rho kinase (ROCK) inhibitors Y27632 and H1152. The longest neurite per neuron were measured and compared. Incubation with Y27632 and H1152 resulted in significantly longer neurites than controls when the neurons were in contact with Schwann cells. When separated by a porous P.E.T. membrane, only the group incubated with H1152 developed significantly longer neurites. This work demonstrates that Rho kinase inhibition augments neurite elongation in the presence of contact with a PNS-like substrate.

Increased expression of 5-HT(1B) receptors by Herpes simplex virus gene transfer in septal neurons: New in vitro and in vivo models to study 5-HT(1B) receptor function.

Serotonergic modulation of acetylcholine (ACh) release after neuron-specific increase of the expression of 5-HT(1B) receptors by gene transfer was studied in vitro and in vivo. The increased expression of the 5-HT(1B) receptor in vitro was induced by treating rat primary fetal septal cell cultures for 3 days with a viral vector inducing the expression of green fluorescent protein (GFP) vector alone, or, in addition, of 5-HT(1B) receptors (HA1B/GFP vector). The transfection resulted in a high number of GFP-positive cells, part of which being immunopositive for choline acetyltransferase. In HA1B/GFP-cultures (vs. GFP-cultures), electrically evoked ACh release was significantly more sensitive to the inhibitory action of the 5-HT(1B) agonist CP-93,129. Increased expression of the 5-HT(1B) receptor in vivo was induced by stereotaxic injections of the vectors into the rat septal region. Three days later, electrically evoked release of ACh in hippocampal slices of HA1B/GFP-treated rats was lower than in their GFP-treated counterparts, showing a higher inhibitory efficacy of endogenous 5-HT on cholinergic terminals after transfection. Moreover, CP-93,129 had a higher inhibitory potency. In conclusion, the HA1B/GFP vector reveals a useful tool to induce a targeted increase of 5-HT(1B) heteroreceptors on cholinergic neurons in selected CNS regions, which provides interesting perspectives for functional approaches at more integrated levels.

Modulation of electrically evoked serotonin release in cultured rat raphe neurons.

Electrically evoked release of serotonin (5-HT) and its modulation via 5-HT autoreceptors and alpha(2)-heteroreceptors was studied in primary cell cultures prepared from the embryonic (ED 15) rat mesencephalic brain region comprising the raphe nuclei. Cultures were grown for up to 3 weeks on circular glass coverslips. They developed a dense network of non-neuronal and neuronal cells, some of which were positive for tryptophan hydroxylase. To measure 5-HT release, the cultures were pre-incubated with [(3)H]5-HT (in the presence of the selective noradrenaline reuptake inhibitor oxaprotiline [1 micromol/L]), superfused with modified Krebs-Henseleit medium containing 6-nitroqipazine [1 micromol/L] and electrically stimulated using two conditions. Condition A: 360 pulses, 3 Hz, 0.5 ms, 90 mA, or condition B: 4 pulses 100 Hz, 0.5 ms, 90 mA (a condition which diminishes interactions with endogenously released transmitters during ongoing stimulation). After only 1 week in culture, the electrically evoked overflow of [(3)H] was Ca(2+) dependent and tetrodotoxin sensitive, suggesting an action-potential-induced exocytotic release of 5-HT. Using stimulation condition A in cultures grown for 2 weeks, both basal and evoked 5-HT release were strongly enhanced by methiotepine (1 micromol/L) but unaffected by the 5-HT(1B) autoreceptor agonist CP-93, 129 (1 micromol/L) and the alpha(2)-adrenoceptor agonist UK-14, 304 (1 micromol/L). Conversely, using stimulation condition B, not only CP-93, 129 (IC(50) 8.1 +/- 1.4 nmol/L) and UK-14, 304 (IC(50) 14.9 +/- 1.6 nmol/L) had inhibitory effects on cells grown for 2 weeks, but also the 5-HT(1A) agonist 8-hydroxy-2-(di-n-propylamino)tetralin. In conclusion, we describe for the first time electrically evoked release of 5-HT from primary cultures of fetal raphe cells and its modulation via 5-HT(1B) and 5-HT(1A) auto- and alpha(2)-heteroreceptors. Such cultured raphe cells may represent a suitable model to study expression and development of presynaptic receptors on serotonergic neurons in-vitro.

Gabapentin-lactam induces dendritic filopodia and motility in cultured hippocampal neurons.

Gabapentin is currently used as a therapeutic agent against epilepsy as well as neuropathic pain. In contrast to gabapentin, its derivative gabapentin-lactam has a pronounced neuroprotective activity. We have studied in cultured hippocampal neurons whether gabapentin-lactam has also neurotrophic effects. Gabapentin-lactam enhanced the formation of dendritic filopodia, which are necessary for synapse formation. It also induced a network of F-actin-containing neurites. In studies with time lapse microscopy, gabapentin-lactam increased the addition but also the elimination of new branches. Affinity precipitation assays showed that gabapentin-lactam increased the GTP binding of the small GTPases Rac and Cdc42, which facilitate branch addition. Gabapentin-lactam also activated RhoA and phosphatidylinositol 3-kinases. In neurons transfected with dominant-negative RhoA or treated with the RhoA-inactivating C3 toxin, gabapentin-lactam increased the number of dendrites and branches. In the presence of Y-27632, which inhibits Rho kinase, newly added branches induced by gabapentin-lactam were no longer eliminated so that gabapentin-lactam increased the number of branches. Y-27632 [(+)-(R)-trans-4-(1-aminoethyl)-N-(4-pyridyl) cyclohexanecarboxamide] also prevented the gabapentin-lactam induced activation of phosphatidylinositol 3-kinases. The phosphatidylinositol 3-kinase inhibitor LY294002 [2-(4-morpholinyl)-8-phenyl-1(4H)-benzopyran-4-one hydrochloride] reduced the elimination of newly added branches caused by gabapentin-lactam and thus facilitated branch formation. In contrast to gabapentin-lactam, gabapentin had no effect on dendritic filopodia or motility. The effects exerted by gabapentin-lactam on dendritic arborization may be of potential therapeutic interest.

Vasoactive intestinal peptide and PACAP38 control N-methyl-D-aspartic acid-induced dendrite motility by modifying the activities of Rho GTPases and phosphatidylinositol 3-kinases.

Dendrite morphogenesis is highly dynamic and characterized by the addition and elongation of processes and also by their selective maintenance, retraction, and elimination. Glutamate can influence these events via N-methyl-d-aspartic acid (NMDA) receptors. The neuropeptides vasoactive intestinal peptide and pituitary adenylyl cyclase-activating polypeptide-38 (PACAP38) affect neurogenesis and differentiation in the developing nervous system. We report here that the peptides and NMDA acted synergistically on dendrite and branch formation. In stage III hippocampal neurons, NMDA increased not only the addition but also the elimination of new dendrites and branches by activating Rac and Cdc42 and phosphatidylinositol 3-kinases, respectively. When applied alone, the neuropeptides did not influence dendrite or branch formation. However, they reduced the elimination of newly formed dendrites and branches caused by NMDA by preventing the NMDA-induced activation of phosphatidylinositol 3-kinases. This led to the formation of persistent dendrites and branches. Additional timelapse studies on the dynamics of dendrite elongation showed alternating periods of elongation and retraction. Phosphatidylinositol 3-kinases increased the velocities of dendrite elongation and retraction, whereas the neuropeptides prolonged the periods of elongation. By modifying NMDA-induced activation of Rho GTPases and phosphatidylinositol 3-kinases, vasoactive intestinal peptide and PACAP38 could play an important role in the control of dendrite growth and branching during development and in response to neuronal activity.

Metabotropic glutamate receptors modulate the NMDA- and AMPA-induced gene expression in neocortical interneurons.

Group I metabotropic glutamate receptors (mGluRIs) can be colocalized with ionotropic glutamate receptors in postsynaptic membranes. We have investigated whether mGluRIs alter the gene transcription induced by N-methyl-D-aspartate (NMDA) and (S)-alpha-amino-3-hydroxy-5-methyl-4-isoxazolpropionic acid (AMPA) receptors in rat neocortical gamma-aminobutyric acid (GABA) interneurons. In cultures of dissociated interneurons, the mGluRI antagonists LY367385 and MPEP reduced the increase in phosphorylation of the transcription factor CREB induced by NMDA as well as the expression of the proenkephalin (PEnk) gene. In contrast, they enhanced the AMPA-induced CREB phosphorylation and PEnk gene expression. Stimulation of the mGluRIs was due to network activity that caused the release of endogenous glutamate and could be blocked by tetrodotoxin. In organotypic cultures of neocortex, endogenous glutamate enhanced the PEnk gene expression by acting on NMDA and AMPA receptors. These effects were modulated via mGluRIs. In patch-clamp experiments and in biochemical studies on receptor density, stimulation of mGluRIs acutely affected NMDA receptor currents but had no long-term effect on NMDA receptor density at the cell surface. In contrast, stimulation of mGluRIs decreased the density of AMPA receptors located at the cell surface. Our results suggest that mGluRIs regulate the glutamate-induced gene expression in neocortical interneurons in a physiologically relevant manner.

Pituitary adenylyl cyclase-activating polypeptide 38 reduces astroglial proliferation by inhibiting the GTPase RhoA.

Pituitary adenylyl cyclase-activating polypeptide 38 (PACAP38) plays an important role in the proliferation and differentiation of neural cells. In the present study, we have investigated how PACAP38 inhibits the proliferation of cultured neocortical astroglial cells. When applied to synchronized cells during the G(1) phase of the cell cycle, PACAP38 diminished the subsequent nuclear uptake of bromodeoxyuridine. When applied for 2 days, it reduced the cell number. PACAP38 did not exert its antiproliferative effect by activating protein kinase A. It also did not reduce the activity of mitogen-activated protein kinases essential for G(1) phase progression. Instead, PACAP38 acted on a member of the Rho family of small GTPases. It reduced the activity of RhoA as was shown with a Rhotekin pull-down assay. The decrease in endogenous RhoA activity induced by treatment of the cells with C3 exotoxin or by expression of dominant negative RhoA also reduced the nuclear uptake of bromodeoxyuridine. In contrast, expression of constitutively active RhoA prevented the effect of PACAP38. Our data show a novel signal transduction pathway by which the neuropeptide influences cell proliferation.

The Yersinia pseudotuberculosis cytotoxic necrotizing factor (CNFY) selectively activates RhoA.

The cytotoxic necrotizing factors (CNF)1 and CNF2 from pathogenic Escherichia coli strains activate RhoA, Rac1, and Cdc42 by deamidation of Gln63 (RhoA) or Gln61 (Rac and Cdc42). Recently, a novel cytotoxic necrotizing factor termed CNFY was identified in Yersinia pseudotuberculosis strains (Lockman, H. A., Gillespie, R. A., Baker, B. D., and Shakhnovich, E. (2002) Infect. Immun. 70, 2708-2714). We amplified the cnfy gene from genomic DNA of Y. pseudotuberculosis, cloned and expressed the recombinant protein, and studied its activity. Recombinant GST-CNFY induced morphological changes in HeLa cells and caused an upward shift of RhoA in SDS-PAGE, as is known for GST-CNF1 and GST-CNF2. Mass spectrometric analysis of GST-CNFY-treated RhoA confirmed deamidation at Glu63. Treatment of RhoA, Rac1, and Cdc42 with GST-CNFY decreased their GTPase activities, indicating that all of these Rho proteins could serve as substrates for GST-CNFY in vitro. In contrast, RhoA, but not Rac or Cdc42, was the substrate of GST-CNFY in culture cells. GST-CNFY caused marked stress fiber formation in HeLa cells after 2 h. In contrast to GST-CNF1, formation of filopodia or lamellipodia was not induced with GST-CNFY. Accordingly, effector pull-down experiments with lysates of toxin-treated cells revealed strong activation of RhoA but no activation of Rac1 or Cdc42 after 6 h of GST-CNFY-treatment. Moreover, in rat hippocampal neurons, GST-CNFY results in the retraction of neurites, indicating RhoA activation. In contrast, no activation of Rac or Cdc42 was found. Altogether, our data suggest that CNFY from Y. pseudotuberculosis is a strong, selective activator of RhoA, which can be used as a powerful tool for constitutive RhoA activation without concomitant activation of Rac1 or Cdc42.

Rho GTPases and phosphoinositide 3-kinase organize formation of branched dendrites.

Neurons receive information from other neurons via their dendritic tree. Dendrites and their branches result from alternating outgrowth and retraction. The Rho GTPases Rac and Cdc42 (cell division cycle 42) facilitate the outgrowth of branches, whereas Rho attenuates it. The mechanism of neurite retraction is unknown. Because the adenylyl cyclase activator forskolin causes numerous branched extensions in NG108-15 cells, we have investigated the underlying mechanism in this cell line. In additional studies, we used cultured hippocampal neurons in which forskolin induces branched dendrites. In both cell types, forskolin enhanced the activity of Cdc42, but not that of Rac, although both GTPases were necessary for the formation of branched extensions. Time lapse microscopy showed that forskolin did not increase the rate of addition of new extensions or branches, but it reduced the rate of the retraction so that more branched extensions persisted. Inhibition of phosphoinositide 3-kinase activity by wortmannin or LY294002 also reduced the rate of retraction and thus facilitated dendritic arborization. Forskolin diminished the activity of phosphoinositide 3-kinases. Inhibitors of phosphoinositide 3-kinases not only reduced the retraction but also the addition of new dendrites and branches. This reduction was no longer present when Rho kinase was simultaneously inactivated, suggesting an interaction of phosphoinositide 3-kinases and Rho kinase. The present results show a central role of phosphoinositide 3-kinases in dendrite formation. In neuronal cells, increased levels of cAMP can support dendritic arborization by modulating the activity of the lipid kinase.

Cellular uptake of Clostridium botulinum C2 toxin: membrane translocation of a fusion toxin requires unfolding of its dihydrofolate reductase domain.

The Clostridium botulinum C2 toxin is the prototype of the family of binary actin-ADP-ribosylating toxins. C2 toxin is composed of two separated nonlinked proteins. The enzyme component C2I ADP-ribosylates actin in the cytosol of target cells. The binding/translocation component C2II mediates cell binding of the enzyme component and its translocation from acidic endosomes into the cytosol. After proteolytic activation, C2II forms heptameric pores in endosomal membranes, and most likely, C2I translocates through these pores into the cytosol. For this step, the cellular heat shock protein Hsp90 is essential. We analyzed the effect of methotrexate on the cellular uptake of a fusion toxin in which the enzyme dihydrofolate reductase (DHFR) was fused to the C-terminus of C2I. Here, we report that unfolding of C2I-DHFR is required for cellular uptake of the toxin via the C2IIa component. The C2I-DHFR fusion toxin catalyzed ADP-ribosylation of actin in vitro and was able to intoxicate cultured cells when applied together with C2IIa. Binding of the folate analogue methotrexate favors a stable three-dimensional structure of the dihydrofolate reductase domain. Pretreatment of C2I-DHFR with methotrexate prevented cleavage of C2I-DHFR by trypsin. In the presence of methotrexate, intoxication of cells with C2I-DHFR/C2II was inhibited. The presence of methotrexate diminished the translocation of the C2I-DHFR fusion toxin from endosomal compartments into the cytosol and the direct C2IIa-mediated translocation of C2I-DHFR across cell membranes. Methotrexate had no influence on the intoxication of cells with C2I/C2IIa and did not alter the C2IIa-mediated binding of C2I-DHFR to cells. The data indicate that methotrexate prevented unfolding of the C2I-DHFR fusion toxin, and thereby the translocation of methotrexate-bound C2I-DHFR from endosomes into the cytosol of target cells is inhibited.

Cellular uptake of Clostridium difficile toxin B. Translocation of the N-terminal catalytic domain into the cytosol of eukaryotic cells.

Clostridium difficile toxin B (269 kDa) is one of the causative agents of antibiotic-associated diarrhea and pseudomembranous colitis. Toxin B acts in the cytosol of eukaryotic target cells where it inactivates Rho GTPases by monoglucosylation. The catalytic domain of toxin B is located at the N terminus (amino acid residues 1-546). The C-terminal and the middle region of the toxin seem to be involved in receptor binding and translocation. Here we studied whether the full-length toxin or only a part of the holotoxin is translocated into the cytosol. Vero cells were treated with recombinant glutathione S-transferase-toxin B, and thereafter, toxin B fragments were isolated by affinity precipitation of the glutathione S-transferase-tagged protein from the cytosolic fraction of intoxicated cells. The toxin fragment (approximately 65 kDa) was recognized by an antibody against the N terminus of toxin B and was identified by matrix-assisted laser desorption ionization time-of-flight mass spectrometry analysis as the catalytic domain of toxin B. The toxin fragment located in the cytosol possessed glucosyltransferase activity that could modify RhoA in vitro, but it was not able to intoxicate intact cells. After treatment of Vero cells with a radiolabeled fragment of toxin B (amino acid residues 547-2366), radioactivity was identified in the membrane fraction of Vero cells but not in the cytosolic fraction of Vero cells. Furthermore, analysis of cells by fluorescence microscopy revealed that the C terminus of toxin B was located in endosomes, whereas the N terminus was detected in the cytosol. Protease inhibitors, which were added to the cell medium, delayed intoxication of cells by toxin B and pH-dependent translocation of the toxin from the cell surface across the cell membrane. The data indicate that toxin B is proteolytically processed during its cellular uptake process.