Deep brain stimulation in Huntington's disease: a literature review

BACKGROUND

Huntington's disease (HD) is a neurodegenerative disorder characterized by involuntary movements, cognitive decline, and behavioral changes. The complex constellation of clinical symptoms still makes the therapeutic management challenging. In the new era of functional neurosurgery, deep brain stimulation (DBS) may represent a promising therapeutic approach in selected HD patients.

METHODS

Articles describing the effect of DBS in patients affected by HD were selected from Medline and PubMed by the association of text words with MeSH terms as follows: "Deep brain stimulation," "DBS," and "HD," "Huntington's disease," and "Huntington." Details on repeat expansion, age at operation, target of operation, duration of follow-up, stimulation parameters, adverse events, and outcome measures were collected.

RESULTS

Twenty eligible studies, assessing 42 patients with HD, were identified. The effect of globus pallidus internus (GPi) DBS on Unified Huntington's Disease Rating Scale (UHDRS) total score revealed in 10 studies an improvement of total score from 5.4 to 34.5%, and in 4 studies, an increase of motor score from 3.8 to 97.8%. Bilateral GPi-DBS was reported to be effective in reducing Chorea subscore in all studies, with a mean percentage reduction from 21.4 to 73.6%.

CONCLUSIONS

HD patients with predominant choreic symptoms may be the best candidates for surgery, but the role of other clinical features and of disease progression should be elucidated. For this reason, there is a need for more reliable criteria that may guide the selection of HD patients suitable for DBS. Accordingly, further studies including functional outcomes as primary endpoints are needed.

Levodopa-carbidopa intrajejunal infusion in Parkinson's disease: untangling the role of age

OBJECTIVES

Levodopa-Carbidopa Intrajejunal gel (LCIG) infusion is an effective intervention for people with advanced Parkinson's disease (PD). Although age may not be a limiting factor for LCIG implant, no data are available on late elderly PD (LE-PD) subjects. In this cross-sectional, we aimed to demonstrate if older age may impact on quality of life (QoL), motor and non-motor symptoms severity, and profile of side effects in PD treated with LCIG.

METHODS

Out of 512 PD subjects treated with LCIG at 9 Italian PD centers, we selected 25 LE-PD defined as age ≥ 80 years at last follow-up who were available to attend the study visit. Twenty-five PD patients (Control-PD, defined as age < 75 years at last follow-up) matched to LE-PD by disease and LCIG duration served as control group. The following motor and non-motor variables were ascertained: quality of life (PDQ-8), time spent in ON, wearing-off Questionnaire, Unified PD Rating Scale, freezing of gait questionnaire, Parkinson's disease sleep scale-2, Non Motor Symptoms Scale (NMSS), and MOCA.

RESULTS

No statistically significant differences were found between LE-PD and Control-PD on PDQ-8 and several motor and non-motor variables. LE-PD had less frequent and milder impulsive-compulsive behaviors and milder dyskinesia. At multivariable regression, worse quality of life was associated with UPDRS-III and NMSS scores but not to age at study visit and age at LICG implant. Rate of adverse effects was similar in both groups. Drop-out rate calculated in the whole PD cohort was comparable between the two groups.

CONCLUSION

Our data provide evidence that valuable LCIG infusion might be achieved in late elderly PD.

EIF2AK2 Missense Variants Associated with Early Onset Generalized Dystonia

Objective

The study was undertaken to identify a monogenic cause of early onset, generalized dystonia.

Methods

Methods consisted of genome‐wide linkage analysis, exome and Sanger sequencing, clinical neurological examination, brain magnetic resonance imaging, and protein expression studies in skin fibroblasts from patients.

Results

We identified a heterozygous variant, c.388G>A, p.Gly130Arg, in the eukaryotic translation initiation factor 2 alpha kinase 2 (EIF2AK2) gene, segregating with early onset isolated generalized dystonia in 5 patients of a Taiwanese family. EIF2AK2 sequencing in 191 unrelated patients with unexplained dystonia yielded 2 unrelated Caucasian patients with an identical heterozygous c.388G>A, p.Gly130Arg variant, occurring de novo in one case, another patient carrying a different heterozygous variant, c.413G>C, p.Gly138Ala, and one last patient, born from consanguineous parents, carrying a third, homozygous variant c.95A>C, p.Asn32Thr. These 3 missense variants are absent from gnomAD, and are located in functional domains of the encoded protein. In 3 patients, additional neurological manifestations were present, including intellectual disability and spasticity. EIF2AK2 encodes a kinase (protein kinase R [PKR]) that phosphorylates eukaryotic translation initiation factor 2 alpha (eIF2α), which orchestrates the cellular stress response. Our expression studies showed abnormally enhanced activation of the cellular stress response, monitored by PKR‐mediated phosphorylation of eIF2α, in fibroblasts from patients with EIF2AK2 variants. Intriguingly, PKR can also be regulated by PRKRA (protein interferon‐inducible double‐stranded RNA‐dependent protein kinase activator A), the product of another gene causing monogenic dystonia.

Interpretation

We identified EIF2AK2 variants implicated in early onset generalized dystonia, which can be dominantly or recessively inherited, or occur de novo. Our findings provide direct evidence for a key role of a dysfunctional eIF2α pathway in the pathogenesis of dystonia. ANN NEUROL 2021;89:485–497

Predictors of COVID-19 outcome in Parkinson's disease

INTRODUCTION

Specific pre-existing medical conditions (e.g. hypertension or obesity), advanced age and male sex appear linked to more severe manifestations of SARS Co-V2 infection, thus raising the question of whether Parkinson's disease (PD) poses an increased risk of morbidity and mortality in COVID-19 patients.

METHODS

In order to describe the outcome of COVID-19 in multi-centre a cohort of PD patients and explore its potential predictors, we gathered the clinical information of 117 community-dwelling patients with COVID-19 followed in 21 tertiary centres in Italy, Iran, Spain, and the UK.

RESULTS

Overall mortality was 19.7%, with a significant effect of co-occurrence of dementia, hypertension, and PD duration.

CONCLUSIONS

The frailty caused by advanced PD poses an increased risk of mortality during COVID-19.

Effects of COVID-19 on Parkinson's Disease Clinical Features: A Community-Based Case-Control Study

The impact of coronavirus disease 2019 (COVID‐19) on clinical features of Parkinson's disease (PD) has been poorly characterized so far. Of 141 PD patients resident in Lombardy, we found 12 COVID‐19 cases (8.5%), whose mean age and disease duration (65.5 and 6.3 years, respectively) were similar to controls. Changes in clinical features in the period January 2020 to April 2020 were compared with those of 36 PD controls matched for sex, age, and disease duration using the clinical impression of severity index for PD, the Movement Disorders Society Unified PD Rating Scale Parts II and IV, and the nonmotor symptoms scale. Motor and nonmotor symptoms significantly worsened in the COVID‐19 group, requiring therapy adjustment in one third of cases. Clinical deterioration was explained by both infection‐related mechanisms and impaired pharmacokinetics of dopaminergic therapy. Urinary issues and fatigue were the most prominent nonmotor issues. Cognitive functions were marginally involved, whereas none experienced autonomic failure. © 2020 International Parkinson and Movement Disorder Society

Concurrent AFG3L2 and SPG7 mutations associated with syndromic parkinsonism and optic atrophy with aberrant OPA1 processing and mitochondrial network fragmentation

Mitochondrial dynamics and quality control are crucial for neuronal survival and their perturbation is a major cause of neurodegeneration. m-AAA complex is an ATP-dependent metalloprotease located in the inner mitochondrial membrane and involved in protein quality control. Mutations in the m-AAA subunits AFG3L2 and paraplegin are associated with autosomal dominant spinocerebellar ataxia (SCA28) and autosomal recessive hereditary spastic paraplegia (SPG7), respectively. We report a novel m-AAA-associated phenotype characterized by early-onset optic atrophy with spastic ataxia and L-dopa-responsive parkinsonism. The proband carried a de novo AFG3L2 heterozygous mutation (p.R468C) along with a heterozygous maternally inherited intragenic deletion of SPG7. Functional analysis in yeast demonstrated the pathogenic role of AFG3L2 p.R468C mutation shedding light on its pathogenic mechanism. Analysis of patient's fibroblasts showed an abnormal processing pattern of OPA1, a dynamin-related protein essential for mitochondrial fusion and responsible for most cases of hereditary optic atrophy. Consistently, assessment of mitochondrial morphology revealed a severe fragmentation of the mitochondrial network, not observed in SCA28 and SPG7 patients' cells. This case suggests that coincidental mutations in both components of the mitochondrial m-AAA protease may result in a complex phenotype and reveals a crucial role for OPA1 processing in the pathogenesis of neurodegenerative disease caused by m-AAA defects.

Quantitative gait analysis in parkin disease: Possible role of dystonia

INTRODUCTION

Parkin disease (PARK2, OMIM 602544) is an autosomal-recessive early-onset parkinsonism characterized by an early occurrence of lower limb dystonia. The aim of this study was to analyze spatiotemporal, kinematic, and kinetic gait parameters in patients with parkin disease in the OFF and ON conditions compared to healthy age-matched controls.

METHODS

Fifteen patients with parkin disease and 15 healthy age-matched controls were studied in a gait analysis laboratory with an integrated optoelectronic system. Spatiotemporal, kinematic, and kinetic gait parameters at a self-selected speed were recorded in the OFF and ON conditions. A jerk index was computed to quantify the possible reduction of smoothness of joint movements.

RESULTS

Compared to controls, parkin patients had, either in the OFF or in the ON conditions, significant reduction of walking velocity, increased step width, and decreased percentage of double support. Kinematic analysis in both conditions showed: increased ankle dorsiflexion and knee flexion at the initial contact; maximal flexion and increased range of motion in mid stance; increased hip flexion and max extension in stance at pelvis; and increased mean tilt antiversion. Kinetics showed increased hip and knee power generation in stance in either condition. The jerk index was increased at all joints both in OFF and ON. There were no correlations between individual gait parameters and clinical ratings.

CONCLUSION

Parkin patients have an abnormal gait pattern that does not vary between the OFF and the ON conditions. Variations recorded with instrumented analysis are more evident for kinematic than kinetic parameters at lower limbs. Severity of dystonia does not correlate with any individual kinematic parameter. © 2016 International Parkinson and Movement Disorder Society.

Tauroursodeoxycholic acid in the treatment of patients with amyotrophic lateral sclerosis

Background and purpose

Tauroursodeoxycholic acid (TUDCA) is a hydrophilic bile acid that is produced in the liver and used for treatment of chronic cholestatic liver diseases. Experimental studies suggest that TUDCA may have cytoprotective and anti‐apoptotic action, with potential neuroprotective activity. A proof of principle approach was adopted to provide preliminary data regarding the efficacy and tolerability of TUDCA in a series of patients with amyotrophic lateral sclerosis (ALS).

Methods

As a proof of principle, using a double‐blind placebo controlled design, 34 ALS patients under treatment with riluzole who were randomized to placebo or TUDCA (1 g twice daily for 54 weeks) were evaluated after a lead‐in period of 3 months. The patients were examined every 6 weeks. The primary outcome was the proportion of responders [those subjects with improvement of at least 15% in the Amyotrophic Lateral Sclerosis Functional Rating Scale Revised (ALSFRS‐R) slope during the treatment period compared to the lead‐in phase]. Secondary outcomes included between‐treatment comparison of ALSFRS‐R at study end, comparison of the linear regression slopes for ALSFFRS‐R mean scores and the occurrence of adverse events.

Results

Tauroursodeoxycholic acid was well tolerated; there were no between‐group differences for adverse events. The proportion of responders was higher under TUDCA (87%) than under placebo (P = 0.021; 43%). At study end baseline‐adjusted ALSFRS‐R was significantly higher (P = 0.007) in TUDCA than in placebo groups. Comparison of the slopes of regression analysis showed slower progression in the TUDCA than in the placebo group (P < 0.01).

Conclusions

This pilot study provides preliminary clinical data indicating that TUDCA is safe and may be effective in ALS.

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Motor features and response to oral levodopa in patients with Parkinson's disease under continuous dopaminergic infusion or deep brain stimulation

BACKGROUND

Subthalamic nucleus deep brain stimulation (STN DBS) and continuous dopaminergic infusions (jejunal levodopa or subcutaneous apomorphine) are indicated in complicated Parkinson's disease (PD), although it remains unsettled how they compare to each other.

METHODS

We investigated the daytime motor condition in patients with advanced PD under monotherapy with jejunal levodopa, subcutaneous apomorphine, or STN DBS and also measured the motor changes produced by an additional standard morning dose of levodopa. Motor performance was assessed with the UPDRS-III, hand taps, the AIMS dyskinesia score and patients' diaries. Outcome measures were time to best motor 'on' after start of morning treatment, daytime variability of motor condition, motor scores.

RESULTS

The time to 'on' was longest in the jejunal levodopa group. DBS and jejunal levodopa treatments produced stable motor conditions without appreciable 'off' episodes. Continuous apomorphine infusion was associated with the worst motor scores (UPDRS-III and taps) and the most frequent off-states. Jejunal levodopa infusion was associated with the highest AIMS scores. Addition of a levodopa dose produced shortening of time to 'on' and a transient motor improvement in the jejunal levodopa group without increase in dyskinesias; in the DBS and apomorphine groups, there was an increase in dyskinesias without changes in UPDRS-III or taps.

CONCLUSIONS

STN DBS provided adequate trade-off between motor improvement and dyskinesia control, although dyskinesias could be elicited by adding oral levodopa. Jejunal levodopa infusion produced adequate motor improvement with slow time to 'on' and moderate dyskinesias. Apomorphine infusion produced insufficient motor control and negligible dyskinesias.

EFNS guidelines on diagnosis and treatment of primary dystonias

OBJECTIVES

to provide a revised version of earlier guidelines published in 2006.

BACKGROUND

primary dystonias are chronic and often disabling conditions with a widespread spectrum mainly in young people.

DIAGNOSIS

primary dystonias are classified as pure dystonia, dystonia plus or paroxysmal dystonia syndromes. Assessment should be performed using a validated rating scale for dystonia. Genetic testing may be performed after establishing the clinical diagnosis. DYT1 testing is recommended for patients with primary dystonia with limb onset before age 30, and in those with an affected relative with early-onset dystonia. DYT6 testing is recommended in early-onset or familial cases with cranio-cervical dystonia or after exclusion of DYT1. Individuals with early-onset myoclonus should be tested for mutations in the DYT11 gene. If direct sequencing of the DYT11 gene is negative, additional gene dosage is required to improve the proportion of mutations detected. A levodopa trial is warranted in every patient with early-onset primary dystonia without an alternative diagnosis. In patients with idiopathic dystonia, neurophysiological tests can help with describing the pathophysiological mechanisms underlying the disorder.

TREATMENT

botulinum toxin (BoNT) type A is the first-line treatment for primary cranial (excluding oromandibular) or cervical dystonia; it is also effective on writing dystonia. BoNT/B is not inferior to BoNT/A in cervical dystonia. Pallidal deep brain stimulation (DBS) is considered a good option, particularly for primary generalized or cervical dystonia, after medication or BoNT have failed. DBS is less effective in secondary dystonia. This treatment requires a specialized expertise and a multidisciplinary team.

In vivo evidence for GABA(A) receptor changes in the sensorimotor system in primary dystonia

BACKGROUND

Preclinical and clinical evidence suggests that impaired gamma-aminobutyric (GABA) control, leading to disinhibition within the sensorimotor system, might play a role in dystonia. Aim of this study is the in vivo assessment of the GABAergic system in dystonia using positron emission tomography (PET) and (11) C-flumazenil, a selective GABA(A) receptor ligand.

METHODS

Fourteen subjects with primary dystonia (9 carriers of the DYT1 mutation and 5 sporadic cases) were compared to 11 controls, using a simplified reference tissue model to measure binding potential.

RESULTS

Voxel-based analyses showed a reduction in GABA(A) receptor expression/affinity both in DYT1 carriers and sporadic patients in primary motor and premotor cortex, primary and secondary somatosensory cortex, and in the motor component of the cingulate gyrus.

CONCLUSIONS

Dysfunction of GABA(A) receptors in sensorimotor systems in primary (genetic and sporadic) dystonia supports the view that lack of GABAergic control may be associated with the generation of dystonic movements.

Low-voltage bilateral pallidal stimulation for severe meige syndrome in a patient with primary segmental dystonia: case report

BACKGROUND AND IMPORTANCE

Meige syndrome (MS) is an adult-onset segmental dystonia characterized by the combination of upper and lower cranial involvement. Its treatment is challenging and the use of oral medication or of botulinum neurotoxin treatment is not decisive. Deep brain stimulation of the globus pallidus internum (GPi DBS) has been used occasionally in severe cases.

CLINICAL PRESENTATION

We report the long-term efficacy of low-voltage chronic bilateral GPi DBS in a patient with segmental dystonia featuring severe MS and cervical brachial involvement. The patient received a bilateral ventroposterolateral GPi implant. Postoperative 3-dimensional reconstruction allowed checking of the definitive position of the electrode and contacts within the targeted nucleus. Following implant, the patient received bilateral low-voltage stimulation, consisting in amplitude of 1.3 V with a pulse width of 90 microseconds and a frequency of 130 Hz, yielding a current of 23 microA. Clinical follow-up for 38 months showed a progressive and sustained improvement of dystonia with unchanged electrical settings throughout the observation period. The patient again undertook normal life activities.

CONCLUSION

Bilateral low-voltage GPi stimulation allowed efficient control of MS symptoms and the associated brachial cervical dystonia.

Emerging parkinsonian phenotypes

There is no unique way to define Parkinson's disease (PD) clinically. "Classical parkinsonian features" can be found not only in sporadic idiopathic PD patients, but also in other parkinsonian disorders, such as genetic forms associated with mutations in PARK or in other genes. The present review will describe the parkinsonian phenotypes emerging from the new Mendelian genes which have been linked to PD (such as PARK9 and PARK14), the associated dystonia-parkinsonism disorders (such as the syndromes of neurodegeneration with brain iron accumulation) and the emerging data on heterozygous variants of genes which could influence the risk to develop PD and the PD phenotypes (like PD associated with glucose cerebrosidase mutations).

PINK1 heterozygous rare variants: prevalence, significance and phenotypic spectrum

Heterozygous rare variants in the PINK1 gene, as well as in other genes causing autosomal recessive parkinsonism, have been reported both in patients and healthy controls. Their pathogenic significance is uncertain, but they have been suggested to represent risk factors to develop Parkinson disease (PD). The few large studies that assessed the frequency of PINK1 heterozygotes in cases and controls yielded controversial results, and the phenotypic spectrum is largely unknown. We retrospectively analyzed the occurrence of PINK1 heterozygous rare variants in over 1100 sporadic and familial patients of all onset ages and in 400 controls. Twenty patients and 6 controls were heterozygous, with frequencies (1.8% vs. 1.5%) not significantly different in the two groups. Clinical features of heterozygotes were indistinguishable to those of wild-type patients, with mean disease onset 10 years later than in carriers of two mutations but worse disease progression. A meta-analysis indicated that, in PINK1 heterozygotes, the PD risk is only slightly increased with a non significant odds ratio of 1.62. These findings suggest that PINK1 heterozygous rare variants play only a minor susceptibility role in the context of a multifactorial model of PD. Hence, their significance should be kept distinct from that of homozygous/compound heterozygous mutations, that cause parkinsonism inherited in a mendelian fashion.

Dystonia gravidarum: A new case with a long follow-up

We report a case of cervical dystonia occurring in a 33-year-old without personal history of movement disorder but with family history of essential tremor, primigravid, primiparous woman at 1 weeks' amenorrhea, resolved completely after delivery in the course of 3 months. Dystonia never recurred in the following 5 years. Several neurological disorders are known to occur or worsen during pregnancy. As far as we know, this is the second reported case of dystonia occurring during pregnancy, thus confirming that dystonia gravidarum represents a new entity and should be considered in women of reproductive age affected by dystonia, especially when presenting with rapid-onset cervical dystonia.

Normal cardiovascular reflex testing in patients withparkin disease

The objective of this study was to investigate cardiovascular autonomic function in patients with parkin disease. Ten patients with a genetically confirmed diagnosis were compared to 11 healthy controls. Symptoms related to autonomic dysfunction were collected by structured interviews. Cardiovascular autonomic reflex function was evaluated using a standard battery of eight tests. Autonomic tests included the study of sympathetic function through the analysis of blood pressure responses to head-up tilt, standing, isometric hand grip, cold pressor, mental arithmetic, Valsalva maneuver (Valsalva overshoot), and the study of parasympathetic function through the analysis of heart rate responses to deep breathing, hyperventilation, and Valsalva ratio. Seven out of 10 patients reported symptoms involving different aspects of autonomic function, while 5 out of 11 controls reported symptoms related exclusively to orthostatic dizziness and constipation. Symptoms related to bladder dysfunction were the most frequent autonomic abnormality occurring in six patients, followed by orthostatic dizziness and dry mouth (in four patients each). Constipation occurred in three patients, sialorrhea in two, and erectile dysfunction, dry eye, and warm intolerance in one each. Cardiovascular reflex testing revealed no difference between patients and controls in quantitative assessment of both sympathetic and parasympathetic functions, except for diastolic blood pressure after isometric hand grip that did not increase normally in parkin patients compared to controls (P = 0.007). These data show that cardiovascular dysautonomia is not associated to the parkin phenotype, whereas urinary complaints are more frequently reported by parkin patients than by controls. Urinary dysautonomia warrants further investigation in patients with parkin disease.

Onset and progression of primary torsion dystonia in sporadic and familial cases

Four hundred and sixty records of patients with primary torsion dystonia (296 women and 164 men) were evaluated. The mean age at disease onset was 48.3 +/- 17.7 years; 13 patients carried the DYT1 CAG deletion. The distribution of age at onset was represented by a bi-modal curve, with a nadir at 21 year separating early onset from late onset cases. In 15.9% of cases there was a positive family history of dystonia. Cranial, cervical or lower limb onset was more common amongst women (M:F ratios were 1:2.7, 1:1.9, and 1:3); by contrast, onset in the upper limb was more common in men (M:F ratio 2.2:1). As expected, disease progression was more pronounced in cases with early onset; it was reckoned that onset at or above 32 years was associated with a negligible likelihood to progress to a generalized form. The mean age at onset of familial cases was 44.8 +/- 11.2 years, significantly lower than the mean age at onset of sporadic cases (53.5 +/- 13.4 years). Familial cases were characterized by more sites involved throughout disease course. Familial cases had a higher tendency to progress to a segmental or generalized form than sporadic cases.

Punding and computer addiction in Parkinson's disease

Punding is a stereotypical behavior in which there is an intense fascination with repetitive handling and examining of mechanical objects, such as taking apart watches and radios or arranging common objects (lining up pebbles, rocks, or other small objects). This disabling condition, different from both obsessive-compulsive disorder and mania, is probably underreported. Punding is thought to be related to dopaminergic stimulation, although only a few observations of this condition in patients with Parkinson's disease (PD) under therapy has been reported. We report a man with PD who developed an unusual, severe, repetitive behavior characterized by spending most of his time on his computer; this abnormal behavior was concomitant with the introduction of L-dopa (400 mg per day) and was not associated to a pattern of chronic inappropriate overuse of dopaminergic medication or other psychiatric symptoms. The patient had the feeling he was forced into a disruptive and unproductive behavior, and he made several attempts to quit without succeeding.

The PINK1 phenotype can be indistinguishable from idiopathic Parkinson disease

Mutations in the PINK1 gene cause autosomal recessive parkinsonism characterized by early onset and a variable phenotypic presentation. A patient homozygous for the Ala168Pro mutation has been fully characterized clinically. Apart from onset at age 39 years and the excellent and sustained response to levodopa, all clinical and laboratory features, including SPECT and assessment of autonomic function, were indistinguishable from typical idiopathic Parkinson disease.

Phosphoserine/threonine-binding domains

Phosphorylation of proteins on serine and threonine residues has traditionally been viewed as a means to allosterically regulate catalytic activity. Research within the past five years, however, has revealed that serine/threonine phosphorylation can also directly result in the formation of multimolecular signaling complexes through specific interactions between phosphoserine/threonine (pSer/Thr)-binding modules and phosphorylated sequence motifs. pSer/Thr-binding proteins and domains currently include 14-3-3, WW domains, forkhead-associated domains, and, tentatively, WD40 repeats and leucine-rich regions. It seems likely that additional modules will be found in the future. The amino acid sequences recognized by these pSer/Thr-binding modules show partial overlap with the optimal phosphorylation motifs for different protein kinase subfamilies, allowing the formation of specific signaling complexes to be controlled through combinatorial interactions between particular upstream kinases and a particular binding module. The structural basis for pSer/Thr binding differs dramatically between 14-3-3 proteins, WW domains and forkhead-associated domains, suggesting that their pSer/Thr binding function was acquired through convergent evolution.

A novel ability of Smad3 to regulate proteasomal degradation of a Cas family member HEF1

Smad3 is a key signal transducer of transforming growth factor-ss (TGF-ss) and activin, and is known to be a DNA-binding transcriptional regulator. Here we report a novel property of Smad3 in regulating the proteasomal degradation of the human enhancer of filamentation 1 (HEF1), which is a member of the Cas family of cytoplasmic docking proteins. Our studies revealed that Smad3 interacts with HEF1 and triggers the proteasomal degradation of HEF1 in overexpression systems. In addition, TGF-ss stimulation induces rapid proteasomal degradation of endogenous HEF1 in different TGF-ss-responsive cell lines. Interestingly, the degradation of HEF1 protein in epithelial cells is followed closely by an increase in HEF1 mRNA, resulting in a time-dependent increase in HEF1 protein level in TGF-ss-treated cells. Furthermore, we observed that an elevated HEF1 protein level inhibits TGF-ss-induced Smad3-mediated gene responses. These data provide the first evidence for a novel cytoplasmic activity of Smad3 in regulating proteasomal degradation of HEF1 and also suggest a role for HEF1 in a negative feedback mechanism of the TGF-ss signaling pathway.