Pain Reduction in Cervical Dystonia Following Treatment with IncobotulinumtoxinA: A Pooled Analysis.

This analysis pooled pain severity data from four phase 3 and 4 studies of incobotulinumtoxinA (incoBoNT-A) for the treatment of cervical dystonia (CD) in adults. CD-related pain severity was assessed at baseline, each injection visit, and 4 weeks after each injection of incoBoNT-A using the Toronto Western Spasmodic Torticollis Rating Scale pain severity subscale or a pain visual analog scale. Both were analyzed using a score range of 0-10 and pain was categorized as mild, moderate, or severe. Data for 678 patients with pain at baseline were assessed and sensitivity analyses evaluated pain responses in the subgroup not taking concomitant pain medication (n = 384 at baseline). At Week 4 after the first injection, there was a mean change of -1.25 (standard deviation 2.04) points from baseline pain severity (p < 0.0001), with 48.1% showing ≥ 30% pain reduction from baseline, 34.4% showing ≥50% pain reduction from baseline, and 10.3% becoming pain free. Pain responses were sustained over five injection cycles with a trend to incremental improvements with each successive cycle. Pain responses in the subgroup not taking concomitant pain medication demonstrated the lack of confounding effects of pain medications. These results confirmed the pain relief benefits of long-term treatment with incoBoNT-A.

Improvement in Quality-of-Life-Related Outcomes Following Treatment with IncobotulinumtoxinA in Adults with Limb Spasticity: A Pooled Analysis.

A strong correlation has been reported between patient-reported quality of life (QoL) and the investigator-rated Disability Assessment Scale (DAS) in patients with spasticity. The current analysis evaluates the effect of incobotulinumtoxinA on QoL-related outcomes (limb position abnormality, as well as dressing- and hygiene-related disability, measured with the DAS) in adults with upper limb spasticity, using pooled data from six studies. Separate analyses for each DAS domain were performed using data from patients with disabilities for that domain (DAS score ≥1). Results showed that a significantly greater proportion of incobotulinumtoxinA-treated compared with placebo-treated patients achieved a ≥1-point reduction from baseline in each of the DAS domains (improvement) 4 weeks after the first injection. The benefits of incobotulinumtoxinA were observed regardless of the baseline severity of DAS impairment and of the time elapsed since stroke. The effects of incobotulinumtoxinA 4 weeks after injection were maintained or enhanced over multiple injection cycles for all three DAS domains, supporting the use of repeated injection cycles to provide sustained QoL benefit. IncobotulinumtoxinA represents an important treatment option to achieve better QoL-related outcomes for patients with upper limb spasticity, irrespective of the duration of their condition.

Goal analysis in patients with limb spasticity treated with incobotulinumtoxinA in the TOWER study.

PURPOSE: To map spasticity-related goals using the International Classification of Functioning, Disability and Health (ICF) linking rules, and review goal syntax to direct future goal setting. MATERIALS AND METHODS: 1633 treatment goals, set during the TOWER study, were linked to the ICF framework and EQ-5D domains. Goals were mapped independently by two investigators with expertise in ICF linking rules. RESULTS: In total, 1630 (99.8%) goals could be mapped to the ICF (inter-rater agreement on the main ICF category 96.1%). Most goals (80.2%) were mapped to a single ICF category and were related to activities/participation (54.9%). 170 (10.4%) goals were related to general tasks and activities, such as positioning, stretching, and strengthening. In total, 1072 goals (65.6%) mapped to the EQ-5D domains (inter-rater agreement 90.8%). Analysis of the goal syntax highlighted the need to include a verb in patient-centered goals to direct active behavior. CONCLUSIONS: The ICF offers a broad framework for setting patient-centered, easily understandable goals for patients with spasticity, including goals related to (guided) self-management activities. This analysis sheds new light on patient needs and could direct future goal-driven botulinum toxin spasticity treatment focused on enabling patients to better manage activity limitations imposed by their body function impairments.Trial registration: NCT01603459 registered with ClinicalTrials.gov (https://clinicaltrials.gov/ct2/show/NCT01603459).Implications for RehabilitationThe ICF offers a broad framework for setting patient-centered, easily understandable goals for patients with spasticity.ICF domains that include general tasks and demands can be used to establish goals relating to (guided) self-management of spasticity.An ICF-based goal-setting framework may increase the comparability of clinical data across studies.

Pain Reduction in Adults with Limb Spasticity Following Treatment with IncobotulinumtoxinA: A Pooled Analysis.

Some studies have shown that incobotulinumtoxinA reduces spasticity-associated pain, but further evidence is needed. This exploratory analysis pooled pain-relief data from six Phase 2 or 3 studies of incobotulinumtoxinA (four placebo-controlled studies) for treating upper limb spasticity in adults. Spasticity-associated pain was assessed at baseline and 4 weeks post incobotulinumtoxinA injection using the disability assessment scale (DAS) for pain. Only data for patients with pain at baseline were analysed. Overall, 544 (incobotulinumtoxinA, N = 415; placebo, N = 129) of 937 patients (58.1%) experienced pain at baseline. At Week 4, a significantly greater proportion of incobotulinumtoxinA- (52.1%) than placebo-treated patients (28.7%; Chi-square p < 0.0001) showed a response (≥1-point improvement in DAS pain score). In logistic regression analysis, incobotulinumtoxinA-treated patients were 2.6 times more likely to achieve this endpoint than placebo-treated patients. A significant difference between incobotulinumtoxinA and placebo was observed regardless of baseline pain severity. Additionally, 27.1% of incobotulinumtoxinA- versus 12.4% of placebo-treated patients reported complete pain relief at Week 4 (p = 0.0006). Pain relief increased with multiple injection cycles. To achieve patient-centred care, pain relief may be considered a treatment goal in adults with spasticity-associated pain regardless of pain severity. This study contributes to understanding the benefits of incobotulinumtoxinA in treating limb spasticity-associated pain.

Duration and onset of effect of incobotulinumtoxinA for the treatment of blepharospasm in botulinum toxin-naïve subjects.

OBJECTIVE: Blepharospasm is a focal dystonia whereby excessive eyelid muscle contractions cause involuntary eye closure. Botulinum neurotoxin type A (BoNT-A) injections are an approved treatment. This randomized placebo-controlled trial (NCT01896895; EudraCT number 2012-004821-26) assessed the efficacy, safety, and treatment effect duration of incobotulinumtoxinA (Xeomin, Merz Pharmaceuticals GmbH), a BoNT-A formulation without complexing proteins, in BoNT-A-naïve adults with blepharospasm. METHODS: Subjects received incobotulinumtoxinA 50 U, 25 U (total dose) or placebo during a main study period (MP; 6-20 weeks). Patients needing a second injection received incobotulinumtoxinA ≤70 U in an open-label extension period (EP; 6-20 weeks). Treatment effect durations were time from first injection to EP injection or final MP visit and from EP injection to end-of-study visit. Times to effect onset and to waning of effect (MP) were time from injection to first subject-assessed onset effect and time from injection to subject-reported waning of effect, respectively. RESULTS: Of 61 subjects, 39 entered the EP. During the MP, median duration of treatment effect was longer with incobotulinumtoxinA 50 U (20 weeks) versus incobotulinumtoxinA 25 U (11 weeks) or placebo (6 weeks). Median duration of treatment effect was 20 weeks during the EP. Median time to effect onset was 5, 7, and 14 days with 50 U, 25 U, and placebo, respectively (p = .022 for 50 U versus placebo). Median time to waning of treatment effect was comparable between groups. CONCLUSION: Subjects reported an effect onset from 5 days after injection lasting up to 20 weeks (maximum observation period). Data indicate that incobotulinumtoxinA re-treatment of blepharospasm may not be required at fixed 12-week intervals and provide evidence for a patient-tailored approach.

PLAIN LANGUAGE SUMMARYBlepharospasm is a condition in which involuntary contractions of the eyelid muscles cause the eye to close. The condition can be treated with botulinum neurotoxin type A (BoNT-A) injections. This study assessed the duration of effect and time to onset of effect for the BoNT-A formulation incobotulinumtoxinA (Xeomin, Merz Pharmaceuticals GmbH) in adults with blepharospasm. Subjects received a single injection of one of two doses of incobotulinumtoxinA (total dose 25 or 50 U) or placebo and received a second injection of incobotulinumtoxinA only (total dose ≤70 U; the second injection was not compared with placebo) if needed 6­20 weeks after the first injection. After the first injection, the median (mid-point of values from all subjects) duration of treatment effect was longer with the higher incobotulinumtoxinA dose (20 weeks) than with the lower dose (11 weeks) and was longer with both incobotulinumtoxinA doses than with placebo (6 weeks). After the second incobotulinumtoxinA injection, the median duration of treatment effect was 20 weeks. The time to onset of effect was quicker with both incobotulinumtoxinA doses (5 and 7 days for the higher and lower doses, respectively) than with placebo (14 days) and the difference was statistically significant for the higher incobotulinumtoxinA dose compared with placebo. The time to waning of treatment effect was similar for the two incobotulinumtoxinA doses and placebo. This study shows that incobotulinumtoxinA is an effective treatment for blepharospasm, with a fast onset of action. In addition, the effects of one injection can last for up to 20 weeks.

Amantadine: reappraisal of the timeless diamond-target updates and novel therapeutic potentials.

The aim of the current review was to provide a new, in-depth insight into possible pharmacological targets of amantadine to pave the way to extending its therapeutic use to further indications beyond Parkinson's disease symptoms and viral infections. Considering amantadine's affinities in vitro and the expected concentration at targets at therapeutic doses in humans, the following primary targets seem to be most plausible: aromatic amino acids decarboxylase, glial-cell derived neurotrophic factor, sigma-1 receptors, phosphodiesterases, and nicotinic receptors. Further three targets could play a role to a lesser extent: NMDA receptors, 5-HT3 receptors, and potassium channels. Based on published clinical studies, traumatic brain injury, fatigue [e.g., in multiple sclerosis (MS)], and chorea in Huntington's disease should be regarded potential, encouraging indications. Preclinical investigations suggest amantadine's therapeutic potential in several further indications such as: depression, recovery after spinal cord injury, neuroprotection in MS, and cutaneous pain. Query in the database http://www.clinicaltrials.gov reveals research interest in several further indications: cancer, autism, cocaine abuse, MS, diabetes, attention deficit-hyperactivity disorder, obesity, and schizophrenia.

Efficacy of incobotulinumtoxinA for the treatment of adult lower-limb post-stroke spasticity, including pes equinovarus.

BACKGROUND: Lower-limb spasticity can impair ambulation and gait, impacting quality of life. OBJECTIVES: This ancillary analysis of the TOWER study (NCT01603459) assessed the efficacy of incobotulinumtoxinA for lower-limb post-stroke spasticity including pes equinovarus. METHODS: Participants received escalating incobotulinumtoxinA doses (400-800U) across 3 injection cycles. Changes were compared for those treated in the lower limb (with/without upper-limb treatment) or the upper limb only or for participants treated or untreated for pes equinovarus. Outcome measures were those used in the seminal study: resistance to passive movement scale (REPAS), Ashworth Scale (AS), functional ambulation and lower-limb goal attainment. RESULTS: Among 132/155 (85%) participants with post-stroke spasticity, in cycles 1, 2 and 3, 99, 119 and 121 participants received lower-limb treatment with mean (SD) total limb incobotulinumtoxinA doses of 189.2 (99.2), 257.1 (115.0) and 321.3 (129.2) U, respectively. Of these, 80, 105 and 107, respectively, were treated for pes equinovarus. The mean (SD) improvement in REPAS lower-limb score was greater with treatment in the lower limb versus the upper limb only: -1.6 (2.1) versus-0.4 (1.4); -1.9 (1.9) versus -0.6 (1.6); -2.2 (2.2) versus -1.0 (0.0) (P=0.0005, P=0.0133 and P=0.3581; analysis of covariance [ANCOVA], between-group differences) in cycles 1, 2 and 3, respectively. For all cycles, the mean improvement in ankle joint AS score from injection to 4 weeks post-treatment was greater for participants treated versus not treated for pes equinovarus, with a significant between-group difference in cycle 1 (P=0.0099; ANCOVA). At the end of cycle 3, 42% of participants walked independently and 63% achieved 2 of 2 lower-limb treatment goals (baseline 23% and 34%, respectively). CONCLUSIONS: This study supports the efficacy of incobotulinumtoxinA for treatment of pes equinovarus and other patterns of lower-limb post-stroke spasticity.

Quality of life in subjects with upper- and lower-limb spasticity treated with incobotulinumtoxinA.

BACKGROUND: We evaluated quality of life among subjects with upper- and lower-limb spasticity who received escalating doses of incobotulinumtoxinA (total body doses up to 800 U) in the prospective, single-arm, dose-titration TOWER study. METHODS: In this exploratory trial, subjects (N = 155; 18-80 years of age) with upper- and lower-limb spasticity due to cerebral causes who were deemed to require total body doses of up to 800 U incobotulinumtoxinA received three consecutive injection cycles of incobotulinumtoxinA (400, 600, and up to 800 U), each with 12 to 16 weeks' follow-up. QoL was assessed using the EuroQol 5-dimensions questionnaire, three-level (EQ-5D), before and 4 weeks post-injection in each injection cycle and at the end of injection cycle 3. RESULTS: The mean EQ-5D visual analog scale scores of 155 participants continuously improved from study baseline to 4 weeks post-injection in all injection cycles (mean [standard deviation] change 6.7 [14.1], 9.6 [16.3], and 8.6 [17.0] for injection cycles 1, 2, and 3, respectively; p < 0.0001 for all, paired sample t-test). In general, among those with a change in the EQ-5D rating of their condition, the proportion of subjects with 'improvement' was greater than that with 'worsening' for individual EQ-5D dimensions across all injection cycles. At the end of injection cycle 3, the proportion of subjects rating their condition as 'normal' increased from study baseline for all dimensions, and there was a ≥ 46% reduction in the proportion of subjects with a rating of 'severe impairment'. CONCLUSION: These preliminary results suggest that escalating incobotulinumtoxinA doses up to 800 U are associated with improvement in quality of life ratings in subjects with multifocal upper- and lower-limb spasticity, and form a basis for future comparator studies. TRIAL REGISTRATION: ClinicalTrials.gov, NCT01603459. Date of registration: May 22, 2012.

Post hoc analysis of the improvement in shoulder spasticity and safety observed following treatment with incobotulinumtoxinA.

OBJECTIVE: The Titration study in lOWer and uppER-limb spasticity (TOWER) study (NCT01603459), evaluated incobotulinumtoxinA for upper- and lower-limb spasticity. This post hoc analysis assessed shoulder spasticity in patients who received injections into the shoulder. METHODS: Subjects received 3 injection cycles with escalating incobotulinumtoxinA doses on the same side (400, 600, 600-800 U; ≤ 600 U per limb including optional shoulder dose, planned range 100-250 U). Joint function was assessed with the Ashworth Scale shoulder sumscore (AS-SSS) in subjects treated in the shoulder vs those who were not. Safety was assessed in subjects treated in the shoulder, and in those who had upper-limb treatment without shoulder treatment. RESULTS: The proportion of subjects receiving shoulder treatment increased with escalating dose at each cycle (n = 84/140 (60.0%) by cycle 3; mean (standard deviation (SD)) shoulder dose 118.4 U (SD 60.2)). From baseline to 4-weeks post-injection, mean AS-SSS improved by -1.1 (SD 1.9), -1.7 (SD 1.8) and -1.7 (1.8) in cycles 1, 2 and 3, respectively, in subjects treated in the shoulder, and -0.5 (SD 1.3), -0.8 (SD 1.6) and -0.9 (SD 1.4) in subjects who were not. A significant dose effect on AS-SSS was observed in cycle 3 (p = 0.0081). No unexpected safety concerns were reported. CONCLUSION: The results demonstrate an improvement in shoulder spasticity and safety following incobotulinumtoxinA treatment.

Tolerability and Efficacy of Customized IncobotulinumtoxinA Injections for Essential Tremor: A Randomized, Double-Blind, Placebo-Controlled Study.

In this first, double-blind, randomized, placebo-controlled exploratory trial, we evaluate the efficacy and safety of incobotulinumtoxinA and feasibility of using kinematic tremor assessment to aid in the planning of muscle selection in a multicenter setting. Reproducibility of the planning technology to other clinical sites was explored. In this trial (NCT02207946), patients with upper-limb essential tremor (ET) were randomized 2:1 to a single treatment cycle of incobotulinumtoxinA or placebo. A tremor kinematic analytics investigational device was used to define a customized muscle set for injection, related to the pattern of the wrist, forearm, elbow, and shoulder tremor for each patient, and the incobotulinumtoxinA dose per muscle (total ≤ 200 U). Fahn-Tolosa-Marin (FTM) Part B motor performance score, Global Impression of Change Scale (GICS), and kinematic analysis-based efficacy evaluations were assessed. Thirty patients were randomized (incobotulinumtoxinA, n = 19; placebo, n = 11). FTM motor performance scores showed greater improvement with incobotulinumtoxinA versus placebo at Week 4 (p= 0.003) and Week 8 (p= 0.031). The physician-rated GICS score indicated improvement with incobotulinumtoxinA versus placebo at Week 4 (p < 0.05). IncobotulinumtoxinA also decreased accelerometric hand-tremor amplitude versus placebo from baseline to Week 4 (p= 0.004) and Week 8 (p < 0.001), with persistent tremor reduction up to 24 weeks post-injection. IncobotulinumtoxinA produced a slight and transient reduction of maximal grip strength versus placebo; two patients reported localized finger muscle weakness. Customized incobotulinumtoxinA injections decreased tremor severity and improved hand motor function in patients with upper-limb ET after a single injection cycle, with a favorable tolerability profile. The study showed that tremor kinematic analytics technology could be successfully scaled for use in other clinical sites.

Safety and efficacy of incobotulinumtoxinA doses up to 800 U in limb spasticity: The TOWER study.

OBJECTIVE: To evaluate safety (primary objective) and efficacy of increasing doses (400 U up to 800 U) of incobotulinumtoxinA (Xeomin, Merz Pharmaceuticals GmbH) for patients with limb spasticity. METHODS: In this prospective, single-arm, dose-titration study (NCT01603459), patients (18-80 years) with spasticity due to cerebral causes, who were clinically deemed to require total doses of 800 U incobotulinumtoxinA, received 3 consecutive injection cycles (ICs) with 400 U, 600 U, and 600-800 U incobotulinumtoxinA, respectively, each followed by 12-16 weeks' observation. Outcomes included adverse events (AEs), antibody testing, Resistance to Passive Movement Scale (REPAS; based on the Ashworth Scale), and Goal Attainment Scale. RESULTS: In total, 155 patients were enrolled. IncobotulinumtoxinA dose escalation did not lead to an increased incidence of treatment-related AEs (IC1: 4.5%; IC2: 5.3%; IC3: 2.9%). No treatment-related serious AEs occurred. The most frequent AEs overall were falls (7.7%), nasopharyngitis, arthralgia, and diarrhea (6.5% each). Five patients (3.2%) discontinued due to AEs. No patient developed secondary nonresponse due to neutralizing antibodies. Mean (SD) REPAS score improvements from each injection to 4 weeks postinjection increased throughout the study (IC1: -4.6 [3.9]; IC2: -5.9 [4.2]; IC3: -7.1 [4.8]; p < 0.0001 for all). The proportion of patients achieving ≥3 (of 4) treatment goals also increased (IC1: 25.2%; IC2: 50.7%; IC3: 68.6%). CONCLUSION: Escalating incobotulinumtoxinA doses (400 U up to 800 U) did not compromise safety or tolerability, enabled treatment in a greater number of muscles/spasticity patterns, and was associated with increased treatment efficacy, improved muscle tone, and goal attainment. CLINICALTRIALSGOV IDENTIFIER: NCT01603459. CLASSIFICATION OF EVIDENCE: This study provides Class IV evidence that, for patients with limb spasticity, escalating incobotulinumtoxinA doses (400 U up to 800 U) increases treatment efficacy without compromising safety or tolerability.

Metabotropic glutamate receptor 4 interacts with microtubule-associated protein 1B.

The metabotropic glutamate receptor 4 (mGluR4) is a G-protein-coupled receptor that mediates inhibition of neurotransmitter release. Here, we used a proteomic approach to identify novel interaction partners of mGluR4 and report that the cytoplasmic C-terminal tail of mGluR4 interacts with microtubule-associated protein 1B (MAP1B). Binding of MAP1B to mGluR4 is inhibited by Ca(2+)/calmodulin, and MAP1B and mGluR4 colocalize at excitatory synapses in cultured hippocampal neurons. Thus, MAP1B might be implicated in the synaptic trafficking and/or regulation of mGluR4.

Knock-in mice lacking the PDZ-ligand motif of mGluR7a show impaired PKC-dependent autoinhibition of glutamate release, spatial working memory deficits, and increased susceptibility to pentylenetetrazol.

The metabotropic glutamate receptor 7 (mGluR7) is widely expressed throughout the brain and primarily localized at presynaptic active zones, where it is thought to regulate neurotransmitter release. Protein interacting with C kinase 1 (PICK1), a postsynaptic density protein-95/disc-large tumor suppressor protein/zonula occludens-1 (PDZ)-domain protein, binds to the three C-terminal amino acids (-LVI) of the predominant mGluR7 splice variant, mGluR7a, and has been implicated in the synaptic clustering of this receptor. Here, we generated knock-in mice in which the C-terminal LVI coding sequence of exon 10 of the mGluR7 gene was replaced by three alanine codons (-AAA). Immunoprecipitation showed that the PICK1-mGluR7a interaction is disrupted in mGluR7a(AAA/AAA) mice. However, the synaptic localization of mGluR7a was not altered in cultured hippocampal neurons and brain sections prepared from the knock-in animals. In cerebellar granule cell cultures, the group III mGluR agonist l-AP-4 decreased the frequency of spontaneous excitatory currents in neurons derived from wild-type but not mGluR7a(AAA/AAA) mice, consistent with the interaction between mGluR7a and PICK1 being required for protein kinase C-mediated inhibition of glutamate release. At the behavioral level, the mGluR7a(AAA/AAA) mice showed no deficits in motor coordination, pain sensitivity, and anxiety but exhibited significant defects in hippocampus-dependent spatial working memory. In addition, they displayed a high susceptibility to the convulsant drug pentylenetetrazole. Together, these results indicate that PICK1 binding to the C-terminal region of mGluR7a is crucial for agonist-triggered presynaptic signaling in vivo.

PICK1 uncoupling from mGluR7a causes absence-like seizures.

Absence epilepsy is a neurological disorder that causes a recurrent loss of consciousness and generalized spike-and-wave discharges on an electroencephalogram (EEG). The role of metabotropic glutamate receptors (mGluRs) and associated scaffolding proteins in absence epilepsy has been unclear to date. We investigated a possible role for these proteins in absence epilepsy, focusing on the mGluR7a receptor and its PDZ-interacting protein, protein interacting with C kinase 1 (PICK1), in rats and mice. Injection of a cell-permeant dominant-negative peptide or targeted mutation of the mGluR7a C terminus, both of which disrupt the interaction between the receptor and PDZ proteins, caused behavioral symptoms and EEG discharges that are characteristic of absence epilepsy. Inactivation of the Pick1 gene also facilitated pharmacological induction of the absence epilepsy phenotype. The cortex and thalamus, which are known to participate in absence epilepsy, were involved, but the hippocampus was not. Our results indicate that disruption of the mGluR7a-PICK1 complex is sufficient to induce absence epilepsy-like seizures in rats and mice, thus providing, to the best of our knowledge, the first animal model of metabotropic glutamate receptor-PDZ protein interaction in absence epilepsy.

Increases in intracellular calcium triggered by channelrhodopsin-2 potentiate the response of metabotropic glutamate receptor mGluR7.

The metabotropic glutamate receptor 7a (mGluR7a), a heptahelical Galphai/o-coupled protein, has been shown to be important for presynaptic feedback inhibition at central synapses and certain forms of long term potentiation and long term depression. The intracellular C terminus of mGluR7a interacts with calmodulin in a Ca2+-dependent manner, and calmodulin antagonists have been found to abolish presynaptic inhibition of glutamate release in neurons and mGluR7a-induced activation of G-protein-activated inwardly rectifying K+ channel (GIRK) channels in HEK293 cells. Here, we characterized the Ca2+ dependence of mGluR7a signaling in Xenopus oocytes by using channelrhodopsin-2 (ChR2), a Ca2+-permeable, light-activated ion channel for triggering Ca2+ influx, and a GIRK3.1/3.2 concatemer to monitor mGluR7a responses. Application of the agonist (S)-2-amino-4-phosphonobutanoic acid (l-AP4) (1-100 microm) caused a dose-dependent inward current in high K+ solutions due to activation of GIRK channels by G-protein betagamma subunits released from mGluR7a. Elevation of intracellular free Ca2+ by light stimulation of ChR2 markedly increased the amplitude of L-AP4 responses, and this effect was attenuated by the calcium chelator 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid tetrakis (acetoxymethyl ester). l-AP4 responses were potentiated by submembranous [Ca2+] levels within physiological ranges and with a threshold close to resting [Ca2+]i values, as determined by recording the endogenous Xenopus Ca2+-activated chloride conductance. Together, these results show that L-AP4-dependent mGluR7a signaling is potentiated by physiological levels of [Ca2+]i, consistent with a model in which presynaptic mGluR7a acts as a coincidence detector of Ca2+ influx and glutamate release.

Protein interactions in the sumoylation cascade: lessons from X-ray structures.

Sumoylation is a multi-step protein modification reaction in which SUMO (small ubiquitin-like modifier) proteins are covalently attached to lysine residues of substrate proteins. Here, we compare the sequences and structures of modifiers and enzymes involved in sumoylation with those of the related ubiquitination and neddylation cascades. By using available structural data on modifier/enzyme/substrate interactions, we discuss and model sumoylation complexes that include SUMO-1 and the E1 and E2 enzymes Aos1-uba2 and ubc9, or SUMO-1 and E2 together with the E3 ligase RanBP2 and its substrate RanGAP1. Their comparison provides insight into the protein interactions underlying sumoylation, and suggests how SUMO proteins may be translocated between enzymes during the various steps of the protein modification reaction.

Structural determinants of calmodulin binding to the intracellular C-terminal domain of the metabotropic glutamate receptor 7A.

Calmodulin (CaM) binds in a Ca2+-dependent manner to the intracellular C-terminal domains of most group III metabotropic glutamate receptors (mGluRs). Here we combined mutational and biophysical approaches to define the structural basis of CaM binding to mGluR 7A. Ca2+/CaM was found to interact with mGluR 7A primarily via its C-lobe at a 1:1 CaM:C-tail stoichiometry. Pulldown experiments with mutant CaM and mGluR 7A C-tail constructs and high resolution NMR with peptides corresponding to the CaM binding region of mGluR 7A allowed us to define hydrophobic and ionic interactions required for Ca2+/CaM binding and identified a 1-8-14 CaM-binding motif. The Ca2+/CaM.mGluR 7A peptide complex displays a classical wraparound structure that closely resembles that formed by Ca2+/CaM upon binding to smooth muscle myosin light chain kinase. Our data provide insight into how Ca2+/CaM regulates group III mGluR signaling via competition with intracellular proteins for receptor-binding sites.

Sumoylation in neurons: nuclear and synaptic roles?

Sumoylation is a post-translational modification that was originally thought to only target nuclear proteins. Evidence has emerged, however, that the role of sumoylation is much more diverse: three plasma membrane proteins belonging to different protein families (glucose transporters, K(+) channels and metabotropic glutamate receptors) have been shown to be sumoylated. In addition, sumoylation of transcription factors, such as myocyte enhancer factor 2 (MEF2), was found to regulate synapse formation. A major role of sumoylation in other systems is to modify protein-protein interactions, and because protein interactions are particularly elaborate in the nervous system and crucial for synapse formation and function, sumoylation could constitute a major regulatory mechanism in neurons. In this review, we evaluate the available data and discuss possible roles for sumoylation in the regulation of crucial neurobiological processes, such as neuronal development and synaptic transmission.

Pias1 interaction and sumoylation of metabotropic glutamate receptor 8.

Group III presynaptic metabotropic glutamate receptors (mGluRs) play a central role in regulating presynaptic activity through G-protein effects on ion channels and signal transducing enzymes. Like all Class C G-protein-coupled receptors, mGluR8 has an extended intracellular C-terminal domain (CTD) presumed to allow for modulation of downstream signaling. In a yeast two-hybrid screen of an adult rat brain cDNA library with the CTDs of mGluR8a and 8b (mGluR8-C) as baits, we identified sumo1 and four different components of the sumoylation cascade (ube2a, Pias1, Piasgamma, Piasxbeta) as interacting proteins. Binding assays using recombinant GST fusion proteins confirmed that Pias1 interacts not only with mGluR8-C but also with all group III mGluR CTDs. Pias1 binding to mGluR8-C required a region N-terminal to a consensus sumoylation motif and was not affected by arginine substitution of the conserved lysine 882 within this motif. Co-transfection of fluorescently tagged mGluR8a-C, sumo1, and enzymes of the sumoylation cascade into HEK293 cells showed that mGluR8a-C can be sumoylated in vivo. Arginine substitution of lysine 882 within the consensus sumoylation motif, but not other conserved lysines within the CTD, abolished in vivo sumoylation. Our results are consistent with post-translational sumoylation providing a novel mechanism of group III mGluR regulation.